RU2353998C1 - Method for manufacture of gas and liquid flow velocity sensor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: in method for manufacture of gas and liquid flow velocity sensor, on planar surface of semiconducting substrate multilayer film structure is arranged, which contains mechanically stressed layers in the following sequence: compressed, stretched and also conducting. Pattern of heat loss anemometer is set lithographically, which includes section separated from substrate for formation of tubular sensitive element under action of mechanical stresses and section of current carriers to ends of tubular sensitive element. Then on remaining part of multilayer film structure through windows are formed down to substrate for further etching of substrate. Low-ohm current carriers are created on sections of current carriers, which are also mechanical supports, or mechanical support is additionally formed for tubular sensitive element. Substrate material is etched under section intended for formation of tubular sensitive element, which transforms it into tubular sensitive element. In conclusion substrate material is removed to form both chip and holders of tubular sensitive element, on which current carriers are located.

EFFECT: increased mechanical strength of finished products and increased accuracy of measurements.

15 cl, 9 dwg

Description

The invention relates to measuring technique and can be used to measure flow characteristics in such areas of human activity as aerodynamics, chemistry, biology and medicine, in which ultra-sensitive and ultra-fast sensors that record the gas or liquid flow rate, as well as their composition, are urgently needed.

Currently, the most widely used sensors are those that operate on the laws of heat transfer between a heated body and a test gas or liquid. The traditionally sensitive element of such sensors is a metal wire with a diameter of 2 to 10 microns and a length of 100 to 2000 microns or a conductive film that heats up when an electric current is passed through them.

In the first case, structurally, the hot-wire anemometer sensor is a rod, in the end of which, in the form of a nozzle, legs are made with a wire fixed to them, for example, platinum. In the second case, the sensor is a quartz rod with a conical end-substrate, with a platinum film concentrically located at its apex, for example, with contacts diametrically diverging from it, for example, of gold. The sensors of the above structures introduce small perturbations into the flow, and local measurements of speed at any point are possible with them.

When electric current flows, the wire or film is heated to temperatures higher than the temperature of the gas or liquid flow. The flow of gas or liquid cools the sensitive element, causing a drop in its temperature to change the electrical resistance. Resistance changes due to convection heat loss due to flow.

A change in the temperature of the sensitive element can also be caused by a change in the composition of the gas mixture due to a change in its thermal conductivity, which is used in gas analyzers.

An insurmountable negative feature of these traditional sensors is their low speed, the time constant is in the range from 0.2 to 1 ms and is limited in the case of wire sensors by the heat capacity of the sensing element, and in the case of film sensors, by heat exchange with the substrate (JOHinze, Turbulence an Introduction to its Mechanism and Theory, McGraw-Hill Book Company, INC., New York, 1959, 680 p .; W. Goopel, J. Hesse, JNZemel, Sensors, A Comprehensive Survey, Vol.7, “Mechanical sensors”, edited by HHBau, NF de Rooij, and B. Kloeck, VCH Publishers Inc., New York (USA) 1994, 574 pp .; W. Gopel, J. Hesse, JNZemel, Sensors, A Comprehensive Survey, Vol.8, " Micro-and nanosensor technology / trends in sensor markets ", edited by H. Meixner and R. Jones, VCH Publishers Inc., New York (USA), 1995, 565 pp .; F.Mailly, A. Giani, R. Bonnot, P. Temple-Boyer, F. Pascal-Delannoy , A.Foucaran, A. Boyer, “Anemometer with hot platinum thin film”, Sensors and Actuators A 94 (2001) pp. 32-38; S. Hung, S. Wong, W. Fang, “The development and application of microthermal sensors with a mesh-membrane supporting structure ”, Sensors and Actuators A 84 (2000) pp. 70-75). As a result, for example, the sensitivity of traditional hot-wire anemometer sensors rapidly decreases at frequencies greater than 1 kHz and becomes insufficient for recording at high-frequency pulsations (more than 100 kHz), characteristic of high-speed flows and the occurrence of turbulence.

Only inertial wire and film sensors of hot-wire anemometers manufactured by foreign companies (mainly the USA) are commercially available. The world is actively searching for methods of mass production of hot-wire anemometric sensors through the use of integrated circuit technology. Attempts are also being made to increase sensitivity and speed by fabricating from suspended bridges and membranes (W. Gopel, J. Hesse, JN Zemel, Sensors, A Comprehensive Survey, Vol. 7, “Mechanical sensors”, edited by HHBau, NF de Rooij and B. Kloeck, VCH Publishers Inc., New York (USA) 1994, 574 pp .; W. Goel, J. Hesse, JN Zemel, Sensors, A Comprehensive Survey, Vol. 8, “Micro-and nanosensor technology / trends in sensor markets ”, edited by H. Meixner and R. Jones, VCH Publishers Inc., New York (USA), 1995, 565 pp. F.Mailly, A. Giani, R. Bonnot, P. Temple-Boyer, F .Pascal-Delannoy, A.Foucaran, A. Boyer, “Anemometer with hot platinum thin film”, Sensors and Actuators A 94 (2001) pp. 32-38; S. Hung, S. Wong, W. Fang, “The development and application of microthermal sensors with a mesh-membrane supporting structure ”, Sensors and Actuators A 84 (2000) pp. 70-75).

An important point in the design of individual sensors of hot-wire anemometers, for example, in sensors with a sensitive element lying in the plane of the chip substrate, is the solution to the problem of the removal of the sensitive element outside the holder or chip. Since if the sensitive element is located in the plane of the substrate, then measurements can be carried out only in the boundary layer on the surface under study due to the significant input of disturbances by the holder or substrate into the incident flow, which limits the possibility of measurement at any given point of the stream above the surface under study.

In the case of a sensor with a sensitive element lying in the plane of the chip substrate, a true measurement of the flow velocity is possible only when it is embedded in the test surface. In other cases, the location of the sensor, the substrate-chip introduces disturbances into the flow before it reaches the sensing element. In the case of solving the problem of the removal of the sensitive element beyond the substrate, it is possible to measure the flow velocity at any point above the surface under study.

Attempts to solve this problem were made using planar technology methods (J. Chen and C. Liu, “Development and Characterization of Surface Micromachined, Out-of-Plane Hot-Wire Anemometer”, Journal of microelectromechanical systems, vol. 12, no. 6, (2003) pp. 979-988; C. Liu, J. Chen, “Microscale out-of-plane anemometer.” United States Patent, Patent No .: US 2005/0109102 A1, Date of Patent May 26, 2005) . The next step was the successful integration of this type of sensor with a control circuit (J. Chen, J. Engel, M. Chang, C. Liu, “3D Out-of-Plane Flow Sensor Array with Integrated Circuits”, in Proceedings of the 18th European Conference on Solid-State Transducers (Eurosensors XVI), Rome, Italy, September 2004) and measuring flow characteristics using an array of sensors integrated with an integrated control circuit (J. Chen, J. Engel, M.Chang, C. Liu, “ A Monolithic Integrated Array of Out-of-Plane Hot-Wire Flow Sensors and Demonstration of Boundary-Layer Flow Imaging ", in Proceedings of the 18th IEEE International Conference on Micro Electro Mechanical Systems (MEMS '05), pp. 299-302, Miami Beach, Fla, USA, January-February 2005). The use of planar technologies made it possible to fabricate coplanar sensors (T. Ebefors, E. Kalvesten, G. Stemme, “Three dimensional silicon triple-hot-wire anemometer based on polyimide joints” IEEE Int. Workshop on Micro Electro Mechanical System (MEMS '98), Heidelberg, Germany, January 25-29, 1998; F. Carlsson, M. Thunblom, P. Johansson, A. Bakchinov, L. Löfdah, T. Ebefors and G. Stemme, “Using Silicon Based Hot-Wires for Turbulence Measurements” , http://www.s3.kth.se/mst/research/publications/pdf/2000/teexpfluidmanuscript.pdf, 1999), which allow measuring the flow in three directions, for this purpose two filaments of polysilicon were formed in the substrate plane, and the third was raised perpendicular to the method based on shrinkage by annealing liimida filling the V-shaped grooves. One of the significant drawbacks of all the last listed sensor designs with a hot-wire anemometer is their low mechanical strength.

A known method of manufacturing a gas and liquid flow velocity sensor (US patent for invention No. 6923054, IPC 7 G01F 1/68), which consists in the fact that a multilayer film structure is made on the planar surface of the substrate using the methods of planar semiconductor technology to form the structural elements of the anemometer and the final stage through the magnetic field carry out the removal of the sensitive element from the surface of the substrate. Thus, a sacrificial layer is first applied to the substrate, including successively deposited layers: chromium about 10 nm thick to ensure good adhesion, copper 250 nm thick and titanium 25 nm thick to prevent copper oxidation processes. Then a photoresist is applied and photolithography is carried out, at the same time forming the holders of the holders in the windows of the mounting pad, and on the sacrificial layer - the base of the holders in the form of two strips. Then, by spraying a four-layer Cr / Pt / Ni / Pt film, with layer thicknesses of 20 nm, 20 nm, 80 nm, and 20 nm, respectively, and lithography, a sensitive element is made in the form of a strip located between the ends of the base of the holders from photoresist. Then a two-layer Cr / Au film 500 nm thick is sprayed and lithography is carried out, forming current leads to the sensitive element located on the basis of the holders, and articulation elements of the holders and mounting sites of the holders. After the electrochemical deposition of ferromagnetic material on the current leads and partially on the connecting elements at the places of their connection with the holders and mountings, the sacrificial layer is removed by using liquid etching in a mixture of acetic acid and hydrogen peroxide. In conclusion, using a permanent magnet, a magnetic field of 800 G is applied to the base of the substrate, under the action of which the holders are lifted above the substrate together with the sensing element as a result of rotational movement made by the holders relative to the articulating elements. As the substrate using a plate of silicon, or glass, or polymer. The photoresist is a 2.7 μm thick polyimide layer obtained by centrifugation.

The disadvantages of the known technical solutions include, firstly, the low mechanical strength of the manufactured products, and secondly, insufficiently high measurement accuracy. The above disadvantages are due to the design features of the manufacture of the sensing element in the form of a wire representing a thin layer strip. Such an element does not have sufficient mechanical strength. In addition, for this design of the sensing element, there is a dependence of the output voltage on the angle of blowing of the wire, leading to distortion of characteristics, due to the quadrangular cross-sectional shape of the wire.

The closest technical solution to the claimed invention is a method of manufacturing a gas and liquid flow velocity sensor (US patent for the invention No. 5883310, IPC 6 G01B 7/16), which consists in the fact that on the planar surface of the substrate a multilayer film structure is made and using techniques of planar semiconductor technology form an anemometer. In this case, a stop layer of silicon heavily doped with boron is first formed on the substrate, then an epitaxial silicon layer doped with boron 10 μm thick is grown on it, onto which a 0.5 μm thick silicon dioxide layer is applied. A thick layer of silicon dioxide is formed on the non-planar side of the substrate. Then, a layer of amorphous silicon with a thickness of 600 nm is deposited at 560 ° C on the planar side and a plasma anemometer is lithographically created by etching in the plasma, specifying portions of the holders and the sensing element; an amorphous silicon layer is also formed on the nonplanar side. To obtain on the planar side of the structural polysilicon elements of the anemometer, boron ions are implanted with an energy of 80 keV with a dose of 10 ¹⁶ cm ^-2 followed by annealing at 1100 ° C for 30 minutes. After annealing, metallization with aluminum is carried out, followed by photolithographic creation of a pattern in the areas of polysilicon and silicon dioxide from the holders. Then, on the planar side, a low-temperature layer of silicon dioxide (at 450 ° C) with a thickness of 3 μm is deposited. Windows are formed on the planar and non-planar sides, respectively, to the epitaxial layer of silicon through a low-temperature layer of silicon dioxide and a layer of silicon dioxide with a thickness of 0.5 μm and to the substrate through an amorphous layer of silicon and a thick layer of silicon dioxide by wet and dry etching. The window size on the non-planar side significantly exceeds the window size on the planar side. On the non-planar side, by etching for 95 hours at 95 ° C, the substrate material is removed, forming a cavity under the stop layer, lying in the lateral direction under the window on the planar side and the main part of the anemometer, to the aluminum metallization sites. From the planar side, through the window under the main part of the anemometer, in the lateral direction to the aluminum metallization sites, the material of the epitaxial silicon layer is removed, creating a cavity above the stop layer, divided with a cavity under the stop layer by means of the stop layer. Then, the stop layer separating the two cavities is removed, and the low temperature layer of silicon dioxide is removed.

The disadvantages of the known technical solutions include, firstly, the low mechanical strength of the manufactured products, and secondly, insufficiently high measurement accuracy. The above disadvantages are due to the design features of the manufacture of the sensing element in the form of a wire representing a thin layer strip. Such an element does not have sufficient mechanical strength. In addition, for this design of the sensing element, there is a dependence of the output voltage on the angle of blowing of the wire, leading to distortion of characteristics, due to the quadrangular (trapezoidal) cross-sectional shape of the wire.

The technical result of the invention is to increase the mechanical strength of the finished product and increase the accuracy of measurements.

The technical result is achieved by the fact that in the method of manufacturing the gas and liquid flow velocity sensor, which consists in the fact that a multilayer film structure is made on the planar surface of the substrate, the anemometer is set lithographically, the multilayer film structure is made containing mechanically stressed layers, and the anemometer is set to include a detachable from the substrate, a section intended for the formation of a tubular sensitive element under the action of mechanical stresses, and a section then gadgets to the ends of the tubular sensing element, after which through the rest of the multilayer film structure through holes are formed to the surface of the substrate, providing subsequent etching of the substrate, or the formation of these through windows is carried out in the process of lithographic job drawing anemometer, then etching the substrate material under the multilayer film structures intended for the formation of a tubular sensitive element, the specified area under the action of internal The early mechanical stresses are transformed into a tubular sensitive element; finally, by removing the substrate material, holders of the tubular sensitive element are formed on which the current conductors are located, and they also form a chip as a whole.

In the method, a semiconductor wafer is used as a substrate.

In the method, a Si plate, or InP, or GaAs is used as a substrate.

In the method, a multilayer film structure is made containing mechanically stressed layers sequentially on a substrate: a compressed layer, a stretched layer, which are forming for the tubular sensing element, a conductive layer; or a compressed layer, an extended layer, which are forming for the tubular sensing element, moreover, one of them or both create with the possibility of performing the function of a conductive layer.

In the method, layers of a multilayer film structure are made of metals, or dielectrics, or semiconductors, or layers of the above materials are combined.

In the method for creating a compressed layer of used SiO _2, for creating a stretched layer - Si ₃ N _4, a conductive layer is formed from a Au with sublayer Ti, or to create a compressed layer using In _x Ga _1-x As, to create a stretched layer - In _y Ga _1-y As, a conductive layer is made of Au with a Ti sublayer, or In _x Ga _1-x As is used to create a compressed layer, In _y Ga _1-y As is used to create a stretched layer, the layers being doped, acting as a conductive layer layer, or to create a compressed layer using Ta ₂ O _5, to create a stretched layer - Ta, being layers create performing and the function of the conductive layer, or to create a compressed layer using SiGe, for creating a stretched layer - Si, the layers being created fulfilling the function of the conductive layer, or to create a compressed layer using SiO _2, for creating a stretched layer - Au with sublayer Ti, wherein the layer is produced performing the function of a conductive layer.

In the method, the total thickness of the multilayer film structure is 5 ÷ 200 nm.

In the method, the final stage of manufacturing a multilayer film structure with mechanically strained layers, which consists in creating a conductive layer, is carried out simultaneously with the initial stage of setting the pattern of the anemometer, which consists in applying a resist, the subsequent formation of a through window in it with a geometry that determines the pattern of the anemometer in which the application conductive layer.

Through the method, through-holes are formed to the surface of the substrate, providing subsequent etching of the substrate by applying a protective mask from the photoresist to the areas of the anemometer pattern and then etching the unprotected sections of the multilayer film structure to the substrate or partially with the substrate material.

In the method, low-resistance current conductors are formed at the current lead sections, which are also mechanical stops for the tubular sensing element by applying a protective mask made of photoresist, chemical deposition through the mask onto the current lead sections of a nickel layer 5 ÷ 10 μm thick, removing the protective mask and conducting annealing for relaxation stresses in the deposited material and increase the strength of current leads.

The additional formation of mechanical stops for the tubular sensing element is carried out by means of a SU-8 photoresist with a thickness of up to 50 μm.

In the method, the etching of the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element for transforming the indicated portion under the action of mechanical stresses into the tubular sensing element is carried out by selective anisotropic etching or by selective etching with preliminary protection of the planar side by resist and etching of the substrate material from the non-planar side to a thickness comparable to the size of the side of the plot in ide strips, transformed into a tubular sensing element by folding in a direction along the specified side.

In the method, the holders of the tubular sensitive element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate simultaneously with the formation of the tubular sensitive element or after the formation of the tubular sensitive element and formed by selective etching of the substrate material.

In sections of current leads, low-resistance current conductors are formed.

On current leads additionally form a mechanical stop for the tubular sensing element.

The invention is illustrated by the following description and the accompanying drawings. Figure 1 schematically shows a gas and liquid flow velocity sensor, its main structural elements: a) a model with current conductors acting as an abutment for a tubular sensing element, b) a model with an additional covering function of an abutment coating of current leads, where 1 is a tubular sensitive element, 2 - holders or legs-current leads of the tubular sensing element, 3 - housing required for integration. Figure 2 schematically shows a detailed image of a model of a gas and liquid flow velocity sensor with an additional coating of conductors serving as an abutment for a tubular sensitive element, where 3 is a housing necessary for integration, 4 is a forming compression layer, 5 is a forming forming layer, 6 is a conductive layer, 7 is an additional layer that reduces resistance, 8 is a layer that performs the function of a mechanical stop for a tubular sensing element. Figure 3 schematically shows a detailed image of a model of a gas and liquid flow velocity sensor with current conductors acting as an abutment for a tubular sensing element, where 3 is a housing necessary for integration, 4 is a forming compression layer, 5 is a forming forming layer, 6 is a conducting layer, 9 - a layer that performs the function of low-resistance current leads and mechanical stops for a tubular sensing element. Figure 4 schematically shows the technological route for manufacturing a chip of a tubular anemometer with conductors serving as an abutment for a tubular sensing element, where 1 is a tubular sensing element, 2 are holders or legs-current leads of a tubular sensing element, 4 is a shaping compressed layer, 5 is a shaping a stretched layer, 6 - a conductive layer, 9 - a layer that performs the function of low-resistance current leads and mechanical stops for a tubular sensing element, 10 - a substrate, 11 - a layer that improves adhesion, 12 - photoresis . Figure 5 schematically shows the technological route for manufacturing a chip of a tubular anemometer with an additional coating of conductors serving as an abutment for a tubular sensitive element, where 4 is a forming compression layer, 5 is a forming forming layer, 6 is a conductive layer, 7 is an additional layer that reduces resistance, 8 - a layer that performs the function of a mechanical stop for a tubular sensitive element, 10 - a substrate, 11 - a layer that improves adhesion, 12 - photoresist, 13 - a protective layer. 6 schematically shows the technological route of manufacturing a tube anemometer chip with mechanically stressed layers that simultaneously perform the functions of forming and conducting layers, where 7 is an additional layer that reduces resistance, 8 is a layer that performs the function of a mechanical stop for a tubular sensitive element, 10 is a substrate 13 - a protective layer, 14 - forming a compressed layer that simultaneously performs the function of a conductive layer, 15 - forming a stretched layer that simultaneously performs a function of conductive on the layer. Figure 7 shows the images obtained by electron microscopy mounted on a substrate of sensors with a suspended tubular sensing element: a) a top view, b) a view in an inclined position. Figure 8 is a photograph of a hot-wire anemometer chip. Figure 9 shows a photograph of a chip tubular anemometer integrated with a sapphire holder.

The proposed method of manufacturing a gas and liquid flow velocity sensor is used in the manufacture of sensors containing a tubular sensing element 1, mounted on holders 2 (or current legs), made in a housing for further integration 3 (see figa) and b) ) The tubular conductive sensing element is placed outside the chip due to the legs-current leads made of the substrate material 10 (see Fig. 4-6). All structural elements of the sensor of the hot-wire anemometer (see Fig.1-6) are made in a single technological process. The manufacturing method used: a) technology of semiconductor and hybrid metal-semiconductor micro- and nanotubes (V.Ya.Prinz, VASeleznev, AKGutakovsky, AVChehovskiy, VVPreobrazenskii, MAPutyato, TAGavrilova. Free-standing and overgrown InGaAs / GaAs nanotubes, nanohelices and their arrays. Physica E, 2000, v. 6, No. 1-4, pp. 828-831); b) traditional methods of optical lithography; c) metal spraying methods widely used in planar technology; d) selective and anisotropic etching of substrates.

The method allows the manufacture of sensors of various modifications (see Figure 1-3), characterized by the materials used to create a multilayer film structure, layer thicknesses, substrate materials, current leads and mechanical stops for a tubular sensing element. Figure 2 shows in detail the design of the sensor depicted in Figure 1b), Figure 3 shows the design of the sensor depicted in Figure 1a). In both versions, the tubular sensing element comprises a shaping compressed layer 4, a shaping stretched layer 5 and a conductive layer 6.

To obtain a tubular sensing element, a multilayer film structure, which is the basis, is made containing mechanically stressed layers that are formative. A compressed layer 4, an extended layer 5 (see Fig. 4a) and 5a)) and a conductive layer 6 (see Fig. 4b) -5b)) are successively formed on the substrate 10. Between the forming stretched layer 5 and the conductive layer 6, an adhesion improving layer 11 may be additionally formed. The forming layers 4 and 5 provide for folding of the applied conductive layer 6 into the tube when the substrate is removed underneath. Layers 4-6, as well as 11 multilayer film structures are made of amorphous, or polycrystalline, or single crystal metals, or dielectrics, or semiconductors, or their compositions. These layers are formed by epitaxy of crystalline substances with different constant lattices under the conditions of pseudomorphic growth, or they are made by vacuum spraying from materials characterized by different deformations relative to the substrate and each other, or using the first and second. Other formation methods can also be used, for example, thermal oxidation, low-temperature plasma-chemical deposition, and deposition by ion beam sputtering of a target.

The substrate 10, on which a multilayer film structure with mechanically strained layers is formed, can be an amorphous, or polycrystalline, or single crystal metal plate, or semiconductor, or dielectric. In the case of using a conductive material for the substrate 10, it is necessary to provide electrical insulation using a dielectric as the material of the forming compression layer 4.

In addition to the above cases, it is possible to modify the sensor in which a multilayer film structure is made containing compressed and stretched layers that form on the substrate for the tubular sensing element, of which one or both are designed to perform the function of a conductive layer (see Fig. 6a)). In this case, there is no need to specifically form the conductive layer 6, as well as an additional layer 11. The combination of functions can be carried out, for example, by the fact that the said forming compression layer 14, which simultaneously performs the function of the conductive layer, and the shape-forming stretched layer 15, that simultaneously performs the function of the conductive layer are made of semiconductor material heavily alloyed.

After the formation of the multilayer film structure, which ends with the creation of the conductive layer 6, lithographically set the pattern of the anemometer, for example by explosive lithography. The initial stage of the operation of forming a pattern in some cases (Figure 4-5) is carried out simultaneously with the creation of a conductive layer 6, which is the final stage of manufacturing a multilayer film structure with mechanically stressed layers. At the initial stage of creating an anemometer pattern, a resist is applied to the created pair of forming layers 4 and 5 and a through window is formed in it. Then carry out the application of the conductive layer, including in the formed through window. The geometry of the through window determines the pattern of the anemometer. The figure of the anemometer contains details: a portion of the multilayer film structure detachable from the substrate for forming a tubular sensitive element under the action of mechanical stresses, and a portion of current leads to the ends of the tubular sensitive element, which subsequently remains connected to the substrate (see Fig. 4b) -5b)) .

In the case when the forming layers themselves perform the function of conductive layers (Fig.6), the lithographic task of the hot-wire anemometer drawing follows immediately after the operation of creating a multilayer film structure with mechanically stressed layers, without combining the initial and final stages of these operations in time. Creating a hot-wire anemometer pattern is carried out by conducting lithography on mechanically stressed layers 4 and 5, for example, by the method of optical lithography (see Fig.6b)).

Then, through the field of the created figure of the anemometer, through windows are formed to the surface of the substrate (see Fig. 4c) -5c)). They are designed to ensure the subsequent etching of the substrate material. A protective mask of photoresist is applied to the areas of the anemometer pattern and then etched unprotected sections of the multilayer film structure are carried out to the substrate or partially with the substrate material. In the case of forming stress layers that perform the function of conductive layers (see Fig.6), the operation of creating a hot-wire anemometer pattern also ensures the formation of through windows to the substrate (see Fig.6b)), which are intended for subsequent etching of the substrate material.

In sections of the current leads of the created figure of the anemometer, low-resistance current conductors are formed, which are also mechanical stops (see Fig. 4d), layer 9, which performs the function of low-resistance current leads and mechanical stops for a tubular sensitive element), or an additional mechanical stop is made for a tubular sensitive element ( see Fig. 5d) and e), Fig. 6c) and d)). In the first case, a protective mask is formed from the photoresist and, by chemical deposition through the mask, a thick metal layer is applied to the current lead sections, for example, nickel with a thickness of 5-10 μm, then the protective mask is removed and annealed to relax the stresses in the deposited material and increase the strength of the current leads. In the second case, first a relatively thin metal layer is deposited (additional layer 7, which reduces resistance), for example, 300 nm thick gold, and then mechanical stops are formed for the tubular sensitive element from a dielectric material, for example, SU-8 photoresist up to 50 μm thick (layer 8 acting as a mechanical stop for a tubular sensing element).

Thus, before the final stage of manufacturing the sensor, all parts of the hot-wire anemometer, which are parts of a multilayer film structure with strained layers, are in a flat state due to communication with the substrate.

If the anisotropy of the etching of the substrate is not used to form the tubular sensor 1 (as is the case in Fig. 4e)), then the surface of the substrate 10 with the hot-wire anemometer parts made on it is protected with a resist 13 or wax before the final stage (see Fig. .5e) and Fig. 6d)).

At the final stage of the manufacture of the sensor, the tubular sensing element is formed by etching the substrate material under the portion of the multilayer film structure designed to form the tubular sensitive element. When the substrate material 10 is removed by etching, the indicated section is freed from communication with the substrate 10 and, under the action of internal mechanical stresses, is transformed into a tubular sensitive element 1 (see Fig. 4e), e). Fig.5e), Fig.6e)), located above the surface of the substrate 10. A portion of the current leads to the ends of the tubular sensing element remains connected with the substrate.

This operation is carried out, for example, by selective anisotropic etching of the substrate (see Fig. 4d)), while forming a tubular sensing element 1 and the outline of the future chip.

Also, this operation can be carried out by selective etching. Before that, having previously protected the planar side of the substrate 10, on which the sensor parts were made, by resist 13 or wax, the substrate material 10 is etched from the non-planar side to a thickness comparable to the size of the side of the section in the form of a strip that can be transformed into a tubular sensitive element by folding in the direction along specified side. During this operation, the formation of individual chips with legs-conductors (holders 2), on which a tubular sensing element 1 is fixed (see Fig. 1a), is simultaneously carried out.

In the previous case, the formation of individual chips is carried out by further selective etching of the substrate 10 (see Fig. 4e)). To protect future chips from pickling, surface melting with melted wax is used. The formation of individual chips is completed by the removal of wax in toluene. The formation of individual chips is also possible at the previous stage (see Fig. 4e)) provided that the substrate is preliminarily thinned to a thickness comparable to the size of the side of the strip-like section that can be transformed into a tubular sensitive element by folding in the direction along this side. In this case, the tubular sensitive element and the chip as a whole are formed simultaneously with the legs-conductors (holders 2) on which the tubular sensitive element 1 is fixed (see Fig. 1b).

In the case of additional formation of mechanical stops for the tubular sensing element (see Fig. 5g) and e), Fig. 6c) and d)) in the layer 8, which serves as a mechanical stop for the tubular sensitive element, open the windows to a depth of additional layer 7, reducing resistance (see Fig.1b), Fig.2), in order to ensure electrical connection when the sensor measures.

The legs-current leads (holders 2) of the sensor may contain, in addition to the above layers, also other elements that make it possible to strengthen the fastening areas of the tubular sensitive element to the legs-current leads.

Finished products are presented in Fig.7-9.

The achievement of the technical result in the present invention is based on the manufacture of the sensing element tubular based on a multilayer film structure containing mechanically stressed layers. Firstly, the presence of mechanically stressed layers, rolled up as a result of mechanical stresses into the tube, provides strength to the finished products. Secondly, the shape of the sensor element, tubular, with a transverse circular cross section, eliminates the dependence of the output voltage on the angle of blowing of the wire, leading to distortion of characteristics. In contrast to the known technical solutions with sensitive elements characterized by quadrangular cross-sectional shapes, for a tubular sensitive element with a cross-section in the form of a circle, whatever the angle of blowing, the measurement result will be the same.

Also, in the products made by the proposed method, it is possible to reduce the cross section of the sensing element. By reducing the cross section, heat transfer proportionally decreases along the sensing element. Therefore, its length can be chosen much less than that of a traditional wire sensor. This circumstance additionally contributes to increasing the strength of the product as a whole, as well as increasing the spatial resolution of the sensor.

In addition, the frequency response of the sensors manufactured by the proposed method will not deteriorate compared to traditional sensors, but the time constant at the same cross-sectional dimensions will decrease in proportion to the decrease in the cross-sectional area, i.e. approximately 25 times.

A significant advantage of the developed technology for manufacturing sensors of hot-wire anemometers is the possibility of their mass production in a single technological process, which reduces their cost by tens and hundreds of times in comparison with the methods used in the world for the manufacture of traditional wire anemometers. The use of optical masks makes it possible to produce hundreds of anemometers in one technological route.

The most important parameters of the sensors are: a) sensitivity - a characteristic that determines how small changes in the flow rate can be measured; b) time constant - a characteristic that determines the speed; c) strength.

It is well known that replacing solid cylindrical rods with tubes allows you to create lighter structures that are practically inferior in strength to the original ones. In our case, the wire is replaced with a thin-walled tube. And it is very important to know how much the mechanical strength of the structure decreases. In the flow, the load is affected by the load created by the movement of the flow, therefore, as a first approximation, this problem can be reduced to the problem of a rod with rigidly fixed ends with a uniformly distributed load.

Assume that a uniformly distributed load q acts on a rod of length L fixed along the edges. It was shown (Timoshenko S.P., Hera J. Material Mechanics. Moscow, Mir, 1976) that for this problem, the bending moment M is described by the formula:

where q is the uniformly distributed load;

L is the length of the rod;

x is the coordinate along the axis of the rod.

At x = L / 2, the maximum bending moment arises equal to

The thickness of the rod stresses are distributed according to the expression

where σ is the longitudinal mechanical stress;

y is the coordinate in the transverse direction;

J _z is the moment of inertia of the cross section relative to the z axis.

And at the surface of the rod voltage reaches its maximum value:

For a cylindrical incomplete rod with a diameter of d _{out, the} moment of inertia J _z is

For tube:

where d _in is the inner diameter of the tube;

d _out is the outer diameter of the tube.

In the case d _in = 0, expression (6) goes over into (5). Thus, to compare the strength of the tube with the strength of a solid rod with their same length, it is sufficient to compare the moments of inertia of the cross sections.

The moment of inertia of the cross section of a tube with a diameter of 10 μm and a wall thickness of 100 nm is almost 13 times less than the moment of inertia of the cross section of an incomplete rod with a diameter of 10 μm. Accordingly, the strength of the tube is 13 times less, which corresponds to the strength of a solid rod with a diameter of about 5.3 microns.

The cross-sectional area of a wire with a diameter of 5.3 μm is

S≈22 · 10 ^-12 m ² .

The cross-sectional area of the tube with a diameter of 10 μm and a wall thickness of 100 nm is

S≈3.11 · 10 ^-12 m ² .

The cross-sectional area (respectively, and mass) of the tube is almost seven times smaller than the wire (solid rod). Accordingly, with the same strength characteristics, the tube has seven times less inertia. In addition, the heat exchange surface area of the tube is almost two times larger than the wire, which further reduces its inertia. From published data (J.O. Hinze, Turbulence an Introduction to its Mechanism and Theory, McGraw-Hill Book Company, INC., New York, 1959, 680 p.) It follows that the time constant τ of the thread is proportional to its total heat capacity:

where c is the specific heat of the thread;

m is the mass of the thread.

Thus, the strength of the sensitive element of the closest prototype (US patent for invention No. 5883310, IPC 6 G01B 7/16) is at least 20 times less than the proposed tubular element, with the same mass, and accordingly the cross-sectional area.

The gas and liquid flow rate sensor is used as follows.

To measure the flow rate of, for example, gas, a tubular sensing element is connected via current leads through a bridge measuring circuit to a recording device and heated by passing an electric current. The sensor is installed in the stream so that the tubular sensing element is perpendicular to the direction of flow. The tubular sensing element is cooled by a gas stream, causing a drop in its temperature and, consequently, a decrease in electrical resistance. According to the testimony of the recording device using the previously obtained individual calibration characteristics of the sensor determine the flow rate.

As information confirming the possibility of achieving a technical result with the implementation of the purpose of the invention, we give the following examples of the method.

Example 1

A multilayer film structure with mechanically strained layers 4-6 is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 ( see Figure 4).

As the substrate 10, a single crystal Si semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: the compressed layer 4, the stretched layer 5, which are forming for the tubular sensing element 1 (see Fig. 4a)), and the conductive layer 6 (see Fig. 4b)). These layers are made of dielectrics and metals. To create a compressed layer 4, SiO _{2 is used} , to create a stretched layer 5, Si ₃ N ₄ , and a conductive layer 6 is created from Au with a Ti sublayer that acts as an adhesion-improving layer 11. The compressed layer 4 of thermal SiO _{2 is} formed with a thickness of 20 nm, and the stretched layer 5 Si ₃ N _{4 is} formed by low-temperature plasma-chemical deposition with a thickness of 20 nm. The conductive layer 6 Au with a Ti sublayer, which is an adhesion-improving layer 11, is applied by vacuum deposition, respectively, with thicknesses of 50 and 5 nm (see Fig. 4b).

In this case, the final stage of manufacturing a multilayer film structure with mechanically strained layers, which consists in creating a conductive layer, is carried out simultaneously with the initial stage of setting the pattern of the anemometer, which consists in applying a resist, the subsequent formation of a through window with a geometry that determines the pattern of the anemometer in which the application conductive layer (see Fig.4b)). Partially time-aligned operations are performed using explosive lithography. Before the formation of the conductive layer 6 with an additional layer 11 that improves adhesion, a resist is applied, a through window is formed through it to the stretched stress layer 6, and then an additional layer 11, which improves adhesion, is sprayed first, and then the conductive layer 6, including and out the window, after which the resist is removed.

Then, through windows to the surface of the substrate 10 are formed on the remaining part of the multilayer film structure, which ensures subsequent etching of the substrate (see Fig. 4c). A protective mask of photoresist 12 is applied to the sections of the anemometer pattern, and then the unprotected sections of the multilayer film structure are etched partially with the substrate material 10. Plasma-chemical etching of SiO ₂ / Si ₃ N _{4 is} carried out in CF ₄ plasma.

Further, on the sections of the current leads of the anemometer drawing, low-resistance current conductors are formed, which are also mechanical stops for the tubular sensitive element (see Fig. 4d). For this, a protective mask made of photoresist is first applied, then a nickel layer of 10 μm thick is chemically deposited onto the current guide sections, after which the protective mask is removed and annealed to relax the stresses in the deposited material and increase the strength of the current leads. Chemical precipitation of nickel is carried out from a solution: nickel sulfate (20 ÷ 30 g / l), sodium acetic acid (10 ÷ 20 g / l), sodium phosphoric acid (25 ÷ 30 g / l), acetic acid (5 ÷ 6 g / l) . The deposition temperature is 80 ° C, the time is 1 hour. The protective mask is removed in acetone and annealed at a temperature of 400 ° C in an inert atmosphere for 1 hour.

Next, the substrate material 10 is etched under the portion of the multilayer film structure for forming the tubular sensing element 1, and this portion is transformed into the tubular sensing element 1 by the action of internal mechanical stresses (see Fig. 4e)). This operation is carried out by selective anisotropic etching of a silicon substrate in an aqueous solution of ammonia NH ₄ OH: H ₂ O (1: 5.3).

In conclusion, by removing the substrate material 10, holders 2 of the tubular sensing element are formed on which the current conductors are located, and also a chip is formed as a whole (see Fig. 4e)). This operation is carried out after the formation of the tubular sensing element by selective etching of the substrate material in the etchant HNO ₃ : HF: CH ₃ UN in a ratio of 1: 1: 1. In order to protect future chips from pickling, the surface is poured with melted wax. After completion of chip etching, the wax is removed in toluene.

Note that after the formation of the tubular sensing element, the dielectric layers are located outside the tube, and heating is carried out by passing an electric current through the gold film inside. Since dielectrics have a thermal conductivity that is 10 times less than that of metals, it would seem that this is a negative factor during heat transfer between the gas stream and the tube surface. However, in our case, the thickness of the dielectric is only 40 nm and, therefore, their low thermal conductivity can be neglected. In addition, it is known that in traditional wire sensors in order to stabilize their characteristics during operation (contamination of the surface of the sensitive element by particles of the flow causes a change in the characteristics of the sensors), the sensitive element is specially coated with SiO ₂ . Therefore, in our case, the problem of a protective coating is solved automatically.

Example 2

A multilayer film structure with mechanically strained layers 4-6 is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 ( see Figure 5).

As the substrate 10, a single-crystal semi-insulating InP semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compressed layer 4, an extended layer 5, which are forming for the tubular sensing element 1 (see Fig. 5a)), and a conductive layer 6 (see Fig. 5b)). These layers are made of semiconductors and metals. In _x Ga _1-x As (x = 0.62) is used to create the compressed layer 4, In _y Ga _1-y As (y = 0.45) is used to create the stretched layer 5, and the conductive layer 6 is created from Au with the Ti sublayer, which acts as an adhesion improving layer 11. The compressed layer 4 is formed with a thickness of 20 nm, the stretched layer 5 is formed with a thickness of 20 nm. Forming layers 4 and 5 are obtained by epitaxy of crystalline substances with different constant lattices in compliance with the conditions of pseudomorphic growth. The conductive layer 6 Au with a Ti sublayer, which is an adhesion-improving layer 11, is applied by vacuum deposition, respectively, with thicknesses of 50 and 5 nm (see Fig. 5b)).

In this case, the final stage of the operation of manufacturing a multilayer film structure with mechanically strained layers, which consists in creating a conductive layer, is carried out simultaneously with the initial stage of the operation of setting the pattern of the anemometer, which consists in applying a resist, the subsequent formation of a through window in it with a geometry that defines the pattern of the anemometer, in which carry out the application of the conductive layer (see Fig.5b)). Partially time-aligned operations are performed using explosive lithography. In explosive lithography, before forming a conductive layer 6 with an additional layer 11 that improves adhesion, a resist is applied, a window is formed through it, to the stretched stress layer 6, and then an additional layer 11, which improves adhesion, is sprayed first, and then the conductive layer 6, including through the window, after which the resist is removed.

Then, through windows to the surface of the substrate 10 are formed on the remaining part of the multilayer film structure, which ensures subsequent etching of the substrate (see Fig. 5c). A protective mask of photoresist 12 is applied to the areas of the anemometer pattern and then the unprotected sections of the multilayer film structure are etched to the substrate 10. In _x Ga _1-x As / In _y Ga _1-y As is etched in a solution of H ₃ PO ₄ : H ₂ O ₂ : H ₂ O with a ratio of 3: 1: 50.

Further, at the sections of the current leads of the anemometer drawing, the formation of low-resistance current leads (see Fig. 5d)). To do this, a layer of gold with a thickness of 300 nm is sprayed through the mask (additional layer 7, which reduces resistance).

Additionally form a mechanical stop for the tubular sensing element (see Fig.5d)). For the manufacture of mechanical stops for a tubular sensing element, a dielectric material, a SU-8 photoresist, up to 50 μm thick (layer 8, acting as a mechanical stop for a tubular sensitive element) is used.

Before the final stage, the surface of the substrate 10 with the parts of the hot-wire anemometer made on it is protected by a resist 13 (see Fig. 5e)).

At the final stage, the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element is etched. The specified area under the influence of internal mechanical stress is transformed into a tubular sensing element. In conclusion, by removing the substrate material, holders of the tubular sensitive element are formed on which the current conductors are located, and they also form a chip as a whole (see Fig. 5e)).

The operation is carried out by selective etching. Having previously protected the planar side with resist 13, etch the substrate material 10 from the non-planar side to a thickness comparable to the size of the side of the strip-like section that can be transformed into a tubular sensitive element by folding in the direction along this side. The holders of the tubular sensing element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate 10 simultaneously with the formation of the tubular sensing element. As an etchant, HCl: H ₃ PO ₄ with a ratio of 1: 3 was used (it was found that this etchant does not poison In _x Ga _1-x As (x = 0.62)).

Example 3

A multilayer film structure with mechanically strained layers is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 (see Fig. .6).

As the substrate 10, a single-crystal semi-insulating InP semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compression forming layer 14, which simultaneously performs the function of the conductive layer, and a shape-forming stretched layer 15, which simultaneously performs the function of the conductive layer. These layers are made of semiconductor material heavily doped, up to n-type conductivity (see Fig. 6a)). In _x Ga _1-x As (x = 0.62) is used to create the compressed layer 14, In _y Ga _1-y As (y = 0.45) is used to create the stretched layer 15. The compressed layer 14 is formed with a thickness of 25 nm, and the stretched layer 15 is formed with a thickness of 25 nm. Forming layers 14 and 15, which simultaneously perform the function of a conductive layer, are obtained by epitaxy of crystalline substances with various constant lattices, subject to the conditions of pseudomorphic growth.

The formation of through windows, ensuring the implementation of subsequent operations of etching the substrate, is carried out in the process of lithographic job drawing anemometer. For lithographic job drawing anemometer and the simultaneous formation of through windows (see Fig.6b)) use the method of optical lithography. The In _x Ga _1-x As / In _y Ga _1-y As heterofilm is etched through a mask in a H ₃ PO ₄ : H ₂ O ₂ : H ₂ O solution with a ratio of 3: 1: 50 to a substrate of 10.

Further, at the sections of the current leads of the anemometer drawing, the formation of low-resistance current leads (see Fig.6c)). To do this, a layer of gold with a thickness of 300 nm is sprayed through the mask (additional layer 7, which reduces resistance).

Additionally form a mechanical stop for the tubular sensing element (see Fig.6d). For the manufacture of mechanical stops for a tubular sensing element, a dielectric material, a SU-8 photoresist, up to 50 μm thick (layer 8, acting as a mechanical stop for a tubular sensitive element) is used.

Before the final stage, the surface of the substrate 10 with the parts of the hot-wire anemometer made on it is protected by a resist 13 (see Fig.6d)).

At the final stage, the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element is etched. The specified area under the influence of internal mechanical stress is transformed into a tubular sensing element. In conclusion, by removing the substrate material, holders of the tubular sensing element are formed on which the current conductors are located, and also a chip is formed as a whole (see Fig. 6e)).

The operation is carried out by selective etching. Having previously protected the planar side with resist 13, etch the substrate material 10 from the non-planar side to a thickness comparable to the size of the side of the strip-like section that can be transformed into a tubular sensitive element by folding in the direction along this side. The holders of the tubular sensing element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate 10 simultaneously with the formation of the tubular sensing element. As an etchant, HCl: H ₂ PO ₄ with a ratio of 1: 3 was used (it was found that this etchant does not poison In _x Ga _1-x As (x = 0.62)).

Example 4

A multilayer film structure with mechanically strained layers is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 (see Fig. .6).

As the substrate 10, a single-crystal semi-insulating GaAs semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compression forming layer 4, which simultaneously performs the function of an insulating layer, and a shape-forming stretched layer 15, which simultaneously performs the function of a conductive layer. These layers are made respectively from Ta ₂ O ₅ and Ta (see Figa)). The compressed layer 4 is formed with a thickness of 20 nm, and the stretched layer 15 is formed with a thickness of 20 nm. Forming layers 4 and 15 are obtained by ion beam sputtering of the target.

The formation of through windows, ensuring the implementation of subsequent operations of etching the substrate, is carried out in the process of lithographic job drawing anemometer. For lithographic job drawing of the anemometer and the simultaneous formation of through windows (see Fig.6b)) use ion etching to the substrate 10.

Further, at the sections of the current leads of the anemometer drawing, the formation of low-resistance current leads (see Fig.6c)). To do this, a layer of gold with a thickness of 300 nm is sprayed through the mask (additional layer 7, which reduces resistance).

Additionally form a mechanical stop for the tubular sensing element (see Fig.6d). For the manufacture of mechanical stops of the tubular sensing element, a dielectric material, a SU-8 photoresist with a thickness of up to 50 μm (layer 8, acting as a mechanical stop for the tubular sensing element) is used.

Before the final stage, the surface of the substrate 10 with the parts of the hot-wire anemometer made on it is protected by a resist 13 (see Fig.6d)).

At the final stage, the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element is etched. The specified area under the influence of internal mechanical stress is transformed into a tubular sensing element. In conclusion, by removing the substrate material, holders of the tubular sensing element are formed on which the current conductors are located, and also a chip is formed as a whole (see Fig. 6e)).

The operation is carried out by selective etching. Having previously protected the planar side with resist 13, etch the substrate material 10 from the non-planar side to a thickness comparable to the size of the side of the strip-like section that can be transformed into a tubular sensitive element by folding in the direction along this side. The holders of the tubular sensing element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate 10 simultaneously with the formation of the tubular sensing element. As an etchant, H ₃ PO ₄ : H ₂ O ₂ : H ₂ O with a ratio of 7: 3: 3 is used.

Example 5

A multilayer film structure with mechanically strained layers is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 (see Fig. .6).

As the substrate 10, a single crystal Si semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compression forming layer 14, which simultaneously performs the function of the conductive layer, and a shape-forming stretched layer 15, which simultaneously performs the function of the conductive layer. These layers are made respectively of SiGe and Si (see Fig. 6a)). The compressed SiGe layer 14 is formed with a thickness of 20 nm, and the stretched Si layer 15 is also formed with a thickness of 20 nm. Forming layers 14 and 15, which simultaneously perform the function of a conductive layer, are obtained by molecular beam epitaxy from crystalline substances with different lattice constants, observing the conditions of pseudomorphic growth. In this case, the forming layer 14, which simultaneously performs the function of the conductive layer, is heavily doped with boron (10 ²⁰ cm ^-3 ).

The formation of through windows, ensuring the implementation of subsequent operations of etching the substrate, is carried out in the process of lithographic job drawing anemometer. For lithographic job drawing anemometer and the simultaneous formation of through windows (see Fig.6b)) use reactive ion etching to the substrate 10 in plasma SF ₆ .

Further, in the sections of the current leads of the anemometer drawing, low-resistance current conductors are formed, which are also mechanical stops for the tubular sensing element (the operation is not shown in Fig.6). For this, a protective mask from a photoresist is first applied, then a nickel layer 9 of 8 μm thickness is chemically precipitated through the mask onto the current guide sections, after which the protective mask is removed and annealed to relax the stresses in the deposited material and increase the strength of the current leads. Chemical precipitation of nickel is carried out from a solution: nickel sulfate (20 ÷ 30 g / l), sodium acetic acid (10 ÷ 20 g / l), sodium phosphoric acid (25 ÷ 30 g / l), acetic acid (5 ÷ 6 g / l) . The deposition temperature is 80 ° C, the time is 1 hour. The protective mask is removed in acetone and annealed at a temperature of 400 ° C in an inert atmosphere for 1 hour.

The substrate material 10 is etched under a portion of the multilayer film structure for forming the tubular sensing element 1, and this portion is transformed into a tubular sensing element 1 by the action of internal mechanical stresses (see Fig. 4e)). This operation is carried out by selective anisotropic etching of a silicon substrate in an aqueous solution of ammonia NH ₄ OH: H ₂ O (1: 5.3).

In conclusion, by removing the substrate material 10, holders 2 of the tubular sensing element are formed on which the current conductors are located, and also a chip is formed as a whole (see Fig. 4e)). This operation is carried out after the formation of the tubular sensing element by selective etching of the substrate material in the etchant HNO ₃ : HF: CH ₃ UN in a ratio of 1: 1: 1. In order to protect future chips from pickling, the surface is poured with melted wax. After the formation is complete by etching the chip, the wax is removed in toluene.

Example 6

A multilayer film structure with mechanically strained layers is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensitive element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensitive element 1.

As the substrate 10, a single crystal Si semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compression forming layer 4 and a forming tension layer 15, which simultaneously performs the function of a conductive layer. These layers are made respectively of SiO ₂ and Au with a Ti sublayer. The compressed layer 4 of SiO _{2 is} formed with a thickness of 20 nm, and the stretched layer of 15 Au with the Ti sublayer is 50 nm thick for Au, 5 nm thick for the Ti sublayer. The forming layer 4 and 15, which simultaneously performs the function of a conductive layer, is obtained, respectively, by thermal oxidation of silicon and electron beam spraying in vacuum.

The formation of through windows, ensuring the implementation of subsequent operations of etching the substrate, is carried out in the process of lithographic job drawing anemometer. For lithographic assignment of the anemometer pattern and the simultaneous formation of through windows, explosive lithography is used in relation to the upper layer of gold with a titanium sublayer. Before forming the stretched layer 15, which simultaneously performs the function of the conductive layer, a resist is applied, a window is formed through it, until the compressed stress layer 4 is compressed, and then the mold-forming layer 15, which simultaneously performs the function of the conductive layer, is sprayed, first, the Ti sublayer, which improves adhesion, and then the Au layer, including through the window, after which the resist is removed, which creates an anemometer pattern in relation to the upper layer. Next, using the pattern of the upper layer as a mask, etching the forming layer 4 to the substrate 10 is carried out by the liquid method.

Further, on the sections of the current leads of the anemometer drawing, low-resistance current conductors are formed, which are also mechanical stops for the tubular sensitive element. For this, a protective mask from a photoresist is first applied, then a nickel layer 9 of 5 μm thickness is chemically precipitated through the mask onto the current guide sections, after which the protective mask is removed and annealed to relax the stresses in the deposited material and increase the strength of the current leads. Chemical precipitation of nickel is carried out from a solution: nickel sulfate (20 ÷ 30 g / l), sodium acetic acid (10 ÷ 20 g / l), sodium phosphoric acid (25 ÷ 30 g / l), acetic acid (5 ÷ 6 g / l) . The deposition temperature is 80 ° C, the time is 1 hour. The protective mask is removed in acetone and annealed at a temperature of 400 ° C in an inert atmosphere for 1 hour.

The substrate material 10 is etched under a portion of the multilayer film structure for forming the tubular sensing element 1, and this portion is transformed into a tubular sensing element under the action of internal mechanical stresses 1. This operation is carried out by selective anisotropic etching of the silicon substrate in an aqueous solution of ammonia NH ₄ OH: H ₂ O (1: 5.3).

In conclusion, by removing the substrate material 10, holders 2 of the tubular sensing element are formed on which the current leads are located, and a chip is formed on the whole. This operation is carried out after the formation of the tubular sensing element by selective etching of the substrate material in the etchant HNO ₃ : HF: CH ₃ UN in a ratio of 1: 1: 1. In order to protect future chips from pickling, the surface is poured with melted wax. After completion of chip etching, the wax is removed in toluene.

Example 7

A multilayer film structure with mechanically strained layers is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 (see Fig. .6).

As the substrate 10, a single-crystal semi-insulating InP semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: a compression forming layer 14, which simultaneously performs the function of the conductive layer, and a shape-forming stretched layer 15, which simultaneously performs the function of the conductive layer. These layers are made of semiconductor material heavily doped, up to n-type conductivity (see Fig. 6a)). In _x Ga _1-x As (x = 0.62) is used to create the compressed layer 14, In _y Ga _1-y As (y = 0.45) is used to create the stretched layer 55. The compressed layer 14 is formed with a thickness equal to about ten monolayers, and the stretched layer is the same. The total thickness of the layers 14 and 15 is about 5 nm. Forming layers 14 and 15, which simultaneously perform the function of a conductive layer, are obtained by epitaxy of crystalline substances with various constant lattices, subject to the conditions of pseudomorphic growth.

The formation of through windows, ensuring the implementation of subsequent operations of etching the substrate, is carried out in the process of lithographic job drawing anemometer. For lithographic job drawing anemometer and the simultaneous formation of through windows (see Fig.6b)) use the method of optical lithography. The In _x Ga _1-x As / In _y Ga _1-y As heterofilm is etched through a mask in a solution of H ₃ PO ₄ : H ₂ O ₂ : H ₂ O with a ratio of 3: 1: 50 to a substrate of 10.

Further, at the sections of the current leads of the anemometer drawing, the formation of low-resistance current leads (see Fig.6c)). To do this, a layer of gold with a thickness of 300 nm is sprayed through the mask (additional layer 7, which reduces resistance).

Additionally form a mechanical stop for the tubular sensing element (see Fig.6d). For the manufacture of mechanical stops for a tubular sensing element, a dielectric material, a SU-8 photoresist, up to 50 μm thick (layer 8, acting as a mechanical stop for a tubular sensitive element) is used.

Before the final stage, the surface of the substrate 10 with the parts of the hot-wire anemometer made on it is protected by a resist 13 (see Fig.6d)).

At the final stage, the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element is etched. The specified area under the influence of internal mechanical stress is transformed into a tubular sensing element. In conclusion, by removing the substrate material, holders of the tubular sensing element are formed on which the current conductors are located, and also a chip is formed as a whole (see Fig. 6e)).

The operation is carried out by selective etching. Having previously protected the planar side with resist 13, etch the substrate material 10 from the non-planar side to a thickness comparable to the size of the side of the strip-like section that can be transformed into a tubular sensitive element by folding in the direction along this side. The holders of the tubular sensing element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate 10 simultaneously with the formation of the tubular sensing element. As an etchant, HCl: H ₃ PO ₄ with a ratio of 1: 3 was used (it was found that this etchant does not poison In _x Ga _1-x As (x = 0.62)).

Example 8

A multilayer film structure with mechanically strained layers 4-6 is made on the planar surface of the substrate 10, and an anemometer pattern is lithographically set, including a section detachable from the substrate for forming the tubular sensing element 1 under the action of mechanical stresses, and a portion of the current leads to the ends of the tubular sensing element 1 ( see Figure 4).

As the substrate 10, a single crystal Si semiconductor wafer with an orientation of (100) is used.

In the multilayer film structure, the layers are formed sequentially on the substrate 10: the compressed layer 4, the stretched layer 5, which are forming for the tubular sensing element 1 (see Fig. 4a)), and the conductive layer 6 (see Fig. 4b)). These layers are made of dielectrics and metals. To create a compressed layer 4, SiO _{2 is used} , to create a stretched layer 5, Si ₃ N ₄ , and a conductive layer 6 is created from Au with a Ti sublayer, which acts as an adhesion-improving layer 11. The compressed layer 4 of thermal SiO _{2 is} formed with a thickness of 75 nm, and the stretched layer 5 Si ₃ N _{4 is} formed by low-temperature plasma-chemical deposition with a thickness of 75 nm. The conductive layer 6 Au with a Ti sublayer, which is an adhesion-improving layer 11, is applied by vacuum deposition, respectively, with thicknesses of 50 and 5 nm (see Fig. 4b).

In this case, the final stage of manufacturing a multilayer film structure with mechanically strained layers, which consists in creating a conductive layer, is carried out simultaneously with the initial stage of setting the pattern of the anemometer, which consists in applying a resist, the subsequent formation of a through window with a geometry that determines the pattern of the anemometer in which the application conductive layer (see Fig.4b)). Partially time-aligned operations are performed using explosive lithography. Before the formation of the conductive layer 6 with an additional layer 11 that improves adhesion, a resist is applied, a through window is formed through it to the stretched stress layer 6, and then an additional layer 11, which improves adhesion, is sprayed first, and then the conductive layer 6, including and out the window, after which the resist is removed.

Then, through windows to the surface of the substrate 10 are formed on the remaining part of the multilayer film structure, which ensures subsequent etching of the substrate (see Fig. 4c). A protective mask of photoresist 12 is applied to the sections of the anemometer pattern, and then the unprotected sections of the multilayer film structure are etched partially with the substrate material 10. Plasma-chemical etching of SiO ₂ / Si ₃ N _{4 is} carried out in CF ₄ plasma.

Further, on the sections of the current leads of the anemometer drawing, low-resistance current conductors are formed, which are also mechanical stops for the tubular sensitive element (see Fig. 4d). For this, a protective mask made of photoresist is first applied, then a nickel layer of 10 μm thick is chemically deposited onto the current guide sections, after which the protective mask is removed and annealed to relax the stresses in the deposited material and increase the strength of the current leads. Chemical precipitation of nickel is carried out from a solution: nickel sulfate (20 ÷ 30 g / l), sodium acetic acid (10 ÷ 20 g / l), sodium phosphoric acid (25 ÷ 30 g / l), acetic acid (5 ÷ 6 g / l) . The deposition temperature is 80 ° C, the time is 1 hour. The protective mask is removed in acetone and annealed at a temperature of 400 ° C in an inert atmosphere for 1 hour.

The substrate is preliminarily thinned to a thickness comparable to the size of the side of the strip-shaped section that can be transformed into a tubular sensing element by folding in the direction along this side. In this case, selective etching of the substrate material in the etchant HNO ₃ : HF: CH ₃ UN in a ratio of 1: 1: 1 is used. In order to protect against pickling of manufactured elements, the surface is poured with melted wax. After the preliminary thinning operation is completed, the wax is removed in toluene.

The substrate material 10 is etched under the portion of the multilayer film structure for forming the tubular sensing element 1, this portion is transformed into tubular sensing element 1 by the action of internal mechanical stresses, simultaneously the holders 2 of the tubular sensing element on which the current conductors are located, and also form a whole chip. This operation is carried out by selective anisotropic etching of a silicon substrate in an aqueous solution of ammonia NH ₄ OH: H ₂ O (1: 5.3).

Claims (15)

1. A method of manufacturing a gas and liquid flow velocity sensor, which consists in the fact that a multilayer film structure is made on the planar surface of the substrate, an anemometer pattern is lithographically characterized, wherein the multilayer film structure is made containing mechanically stressed layers, and the anemometer pattern is set to include detachable from substrate section, designed to form a tubular sensitive element under the action of mechanical stresses, and a section of current leads to the ends of the pipes a sensing element, after which through the rest of the multilayer film structure are formed through windows to the substrate surface, which provide subsequent etching of the substrate, or the formation of these through windows is carried out in the process of lithographic job drawing anemometer, then etching the substrate material under the multilayer film structure intended for the formation of a tubular sensing element, the specified area under the action of internal mechanical voltages are transformed into a tubular sensing element; finally, by removing the substrate material, holders of the tubular sensitive element are formed on which the current conductors are located, and also form a chip as a whole. 2. The method according to claim 1, characterized in that a semiconductor wafer is used as a substrate. 3. The method according to claim 2, characterized in that as the substrate using a plate of Si, or InP, or GaAs. 4. The method according to claim 1, characterized in that the multilayer film structure is made containing mechanically stressed layers sequentially on a substrate: a compressed layer, a stretched layer, which are forming for the tubular sensing element, a conductive layer; or a compressed layer, an extended layer, which are forming for the tubular sensing element, moreover, one of them or both create with the possibility of performing the function of a conductive layer. 5. The method according to claim 4, characterized in that the layers of the multilayer film structure are made of metals, or dielectrics, or semiconductors, or combine layers of these materials. 6. The method according to claim 4, characterized in that SiO _{2 is} used to create a compressed layer, Si ₃ N _{4 is} used to create a stretched layer, a conductive layer is created from Au with a Ti sublayer, or In _x Ga _{1- is} used to create a compressed layer _x As, to create a stretched layer - In _y Ga _1-y As, a conductive layer is created from Au with a Ti sublayer, or In _x Ga _1-x As is used to create a compressed layer, To create a stretched layer - In _y Ga _1-y As, moreover, the layers are created by doping, performing the function of a conductive layer, or Ta ₂ O _{5 is} used to create a compressed layer, Ta is used to create a stretched layer, and m layers are created to act as a conductive layer, or SiGe is used to create a compressed layer, Si is used to create a stretched layer, and layers are used to create a conductive layer, or SiO _{2 is} used to create a compressed layer, Au with an Ti sublayer is created, moreover, the layer is created to perform the function of a conductive layer. 7. The method according to any one of claims 4 to 7, characterized in that the total thickness of the multilayer film structure is 5 ÷ 200 nm. 8. The method according to claim 1 or 4, characterized in that the final stage of manufacturing a multilayer film structure with mechanically stressed layers, which consists in creating a conductive layer, is carried out simultaneously with the initial stage of setting the pattern of the anemometer, which consists in applying a resist, and then forming a through windows with geometry defining the anemometer pattern in which the conductive layer is applied. 9. The method according to claim 1, characterized in that through windows are formed to the surface of the substrate, providing subsequent etching of the substrate, by applying a protective mask of photoresist to the areas of the anemometer pattern and subsequent etching of the unprotected sections of the multilayer film structure to the substrate or partially with the material the substrate. 10. The method according to claim 1, characterized in that in the sections of the current conductors, low-resistance current conductors are formed, which are also mechanical stops for the tubular sensing element, by applying a protective mask of photoresist, chemical deposition through the mask on the sections of the current leads of a nickel layer with a thickness of 5 ÷ 10 microns, removing the protective mask and conducting annealing to relax stresses in the deposited material and increase the strength of current leads. 11. The method according to claim 1, characterized in that the additional formation of mechanical stops for the tubular sensing element is carried out by means of a SU-8 photoresist with a thickness of up to 50 μm. 12. The method according to claim 1, characterized in that the etching of the substrate material under the portion of the multilayer film structure designed to form the tubular sensing element, for transforming the specified section under the action of mechanical stresses into the tubular sensing element, is carried out by selective anisotropic etching or by selective etching with preliminary protection of the planar side by resist and etching the substrate material from the non-planar side to a thickness comparable to p By measuring the sides of a strip-shaped section, which can be transformed into a tubular sensing element by folding in a direction along this side. 13. The method according to claim 1, characterized in that the holders of the tubular sensitive element on which the current conductors are located, and in general the chip is formed by selective etching of the substrate simultaneously with the formation of the tubular sensitive element or after the formation of the tubular sensitive element and formed by selective etching of the substrate material. 14. The method according to claim 1, characterized in that after the formation of the through windows in the sections of the current leads, the formation of low-resistance current leads. 15. The method according to 14, characterized in that on the conductors additionally form a mechanical stop for the tubular sensing element.

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