JP2004195599A - On-substrate structure and method for forming protrusions used for the structure - Google Patents

Abstract

The present invention provides a structure on a substrate that can effectively prevent attraction between a beam portion and a substrate, and a simple method of forming projections used for the structure.
A plate beam A1 having a fixed portion 13a fixed to the substrate and a movable end 13b capable of changing a distance between the substrate is provided on the substrate 10, and the plate beam is provided on the substrate. Is formed on the substrate by removing the sacrifice layer after the sacrifice layer 11 is interposed therebetween, and the structure other than the fixed portion is separated from the substrate. An adsorption prevention structure including a plurality of conical projections P1 or an adsorption prevention structure including a plurality of projections having random heights is provided on one main surface of the plate-shaped beam portion facing the substrate.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an on-substrate structure such as an electrostatic actuator used for an optical switch and the like, and a method for forming a projection used for the structure.
[0002]
[Prior art]
As a drive mechanism using electrostatic force used in MEMS (Micro-Electro Mechanical System), a fixed electrode formed on a silicon substrate, an insulating protective film formed on the upper surface, 2. Description of the Related Art There is an electrostatic actuator including a movable electrode that faces a certain space and a support member that holds the electrode at a predetermined position.
[0003]
However, for example, when forming a cantilever structure on a silicon substrate, there are the following problems. (1) Adsorption in the sacrificial layer removing step for forming the hollow structure, and (2) Adsorption caused by contact when operated by external force.
Hereinafter, these two problems will be described.
[0004]
The problem of (1) is to remove the sacrificial layer by a wet process to form a hollow structure and then to dry the sacrificial layer. At this time, the upper member is pulled down by the surface tension of the liquid / gas interface, and the rigidity of the constituent members is reduced. Is low, this is caused by contact with the lower member without being able to withstand the pulling force. On the other hand, the problem (2) is caused by the fact that when two objects having a hollow portion come into contact with each other by external force, if the surfaces are both smooth, they are adsorbed by the coagulated moisture at the contact interface.
As described above, when a structure having a minute space is formed, there is a problem that the structure is adsorbed in both the manufacturing process and the driving.
[0005]
In order to solve these problems, for example, as shown in FIG. 6 on page 20 of Non-Patent Document 1, a protrusion is provided on the movable side structure, or as shown in FIG. In addition, a spring structure is arranged between the electrodes, and the structure is peeled off with a force greater than the adsorption force, or a chemical surface treatment is applied using perfluorodisiltrichlorosilane (FDTS) to remove the water. A method for reducing the attraction force has been proposed.
[0006]
Non-Patent Documents 3 and 4 report that fine projections can be formed by using an EB exposure system or stereolithography, but such a surface cannot be obtained without using a very special manufacturing apparatus. Cannot be processed.
[0007]
[Non-patent document 1]
Kazuhiro Hane, "MEMS Technology and Optical Technology (Optical Communication)", Materials of the 28th Winter Seminar of the Optical Society of Japan, Optical Society of Japan, January 21, 2002, p20.
[Non-patent document 2]
Li Fan, et al. “Digital MEMS switch for planar photonic crossconnects” OFC2002, p93-94, Tu04
[Non-Patent Document 3]
Hiroshi Toyota et al. “Fabrication of Microcone Array for Antireflection Structred Surface” Jpn. J. Appl. Phys. Vol.40 (2001) pp.L747-L749,
[Non-patent document 4]
Shoji Maruo and Koji Ikuta, “Three-dimensional microfabrication by use of single-photon-absorbed polymerization” Appl. Phys. Lett.Vol.76 (2000) No.19 pp.2656-2685,
[0008]
[Problems to be solved by the invention]
In view of the above, the present invention provides a structure on a substrate that can effectively prevent attraction between the beam portion and the substrate, and a method for easily forming a projection used for the structure (can be manufactured without using a special manufacturing apparatus). The purpose is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an on-substrate structure according to the present invention includes a plate having a fixed portion fixed to the substrate and a movable end capable of changing a distance between the substrate and the fixed portion. An on-substrate structure comprising a beam-like portion, wherein the plate-like beam portion is formed on the substrate via a sacrificial layer, and then the sacrificial layer is removed to remove the fixing portion and separate from the substrate. And
In the portion of the upper surface of the substrate facing the plate-like beam portion, a suction prevention structure composed of a plurality of conical projections, or on one main surface of the plate-like beam portion facing the substrate, a random height And a suction prevention structure comprising a plurality of protrusions having the following.
The on-substrate structure according to the present invention having the above-described structure is characterized in that, in the process of forming the plate-like beam portion and removing the sacrificial layer via the sacrificial layer on the substrate, Since the suction preventing structure can be formed, the suction between the beam portion and the substrate can be effectively prevented, and the suction preventing structure can be formed by a simple method without using a special manufacturing apparatus.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
The on-substrate structure of the first embodiment is an electrostatic actuator in which a plate-like beam portion A1 is formed on a substrate 10, and is configured as follows.
In the first embodiment, the substrate 10 serving as the base of the on-substrate structure uses a low-resistance silicon substrate to form one electrode of the electrostatic actuator by itself.
Further, the plate-like beam portion A1 includes an actuator base 13 and an electrode film 14 formed on the base 13, and the electrode film 14 constitutes the other electrode of the electrostatic actuator.
[0011]
The plate-like beam portion A1 is apart from the substrate 10 except that it is fixed to the upper surface of the substrate 10 at the fixing portion 13a, which is one end thereof, and is a voltage applied between the substrate 10 and the electrode film 14. The position of the moving end 13b, which is the other end of the plate-like beam portion A1, changes according to the value.
[0012]
Here, in particular, in the on-substrate structure according to the first embodiment, a plurality of conical protrusions P1 are formed on a portion of the upper surface of the substrate 10 facing the plate-like beam portion A1, and the plurality of protrusions P1 form the substrate. A suction prevention structure for preventing suction between the plate 10 and the plate-like beam portion A1 is configured.
More specifically, in the first embodiment, each of the plurality of conical-shaped protrusions P1 is more preferably formed as a sharp shape formed such that the gradient toward the upper surface of the substrate 10 becomes steeper toward the tip. It has a tip portion having a peak, and the contactable area between the substrate 10 (tip of the protrusion) and the plate-like beam portion A1 can be extremely small, so that the suction between the substrate 10 and the plate-like beam portion A1 can be effectively prevented. .
[0013]
In other words, between two objects facing each other via a minute gap (for example, several μm) like a substrate and a plate-like beam in an electrostatic actuator, moisture in the atmosphere agglomerates in the minute gap, and the two objects are separated by the moisture. Adsorb. In the present invention, by providing a plurality of protrusions P1 having the above-described shape between the two objects, the area where moisture is agglomerated is suppressed to be small and adsorption is prevented. Further, in the first embodiment, in order to minimize the area where the water aggregates as much as possible, the tip of the projection P1 is set closer to the tip so that the increment of the inclination is increased to prevent the adsorption more effectively. ing.
Hereinafter, a method for manufacturing the electrostatic actuator that is the on-substrate structure according to the first embodiment will be described.
[0014]
(Manufacturing Method of First Embodiment)
In the present manufacturing method, an electrostatic actuator is manufactured through the following steps using a low-resistance silicon substrate that can also serve as a fixed electrode as the base substrate 10.
<Formation of sacrificial layer 11>
In this manufacturing method, first, a sacrifice layer 11 is formed on the upper surface of the substrate 10 by using a material that can be selectively removed to make the plate-like beam portion A1 have a hollow structure.
More specifically, as shown in FIG. 2A, a first sacrificial layer 11a made of a thermal oxide film is formed to a thickness of, for example, 1.5 μm, and has a different etching rate from the first sacrificial layer 11a. The second sacrificial layer 11b made of a different TEOS silicon oxide film is formed to a thickness of, for example, 1.0 μm.
As a result, a sacrifice layer 11 having a multilayer structure composed of the first sacrifice layer 11a and the second sacrifice layer 11b having different etching rates is formed (FIG. 2B).
Here, the TEOS silicon oxide film is a silicon oxide film formed by a plasma CVD method or the like using a reaction between tetraethyloxysilane and ozone, and has an order of magnitude higher etching rate with respect to an HF aqueous solution than a thermal oxide film ( About 10 times).
[0015]
<Plate beam part A1 film formation process>
Next, an insulating film 13 for an actuator base is formed on the sacrificial layer 11 by forming a low-stress silicon nitride film to a thickness of, for example, 0.7 μm using LP (low pressure) -CVD. An electrode film 14 is formed on the insulating film 13 by forming a Cr film to a thickness of 5 nm by an evaporation method and then forming an Au film to a thickness of 100 nm (FIG. 2C).
[0016]
<Etching hole forming step>
Next, as shown in FIG. 2D, an etching hole 12 (for example, a diameter of 4 μm) penetrating the electrode film 14 and the insulating film 13 is formed at a pitch of, for example, 20 μm using a metal mask or the like.
[0017]
<Pattern beam A1 patterning process>
In the patterning step, first, the insulating film 13 is patterned into the shape of the plate-like beam portion A1 (FIG. 3A), and thereafter, the electrode film 14 is patterned into a predetermined shape (FIG. 3B). .
[0018]
<Removal of sacrificial layer 11 and formation of protrusion P1>
Next, the sacrificial layer 11 is removed by etching with a 50% HF aqueous solution (FIG. 3C).
At this time, in the sacrificial layer 11 immediately below the patterned plate-shaped beam portion A1, isotropic etching proceeds from each of the etching holes 12 via the etching holes 12.
As a result, in the sacrificial layer 11 immediately below the plate-shaped beam portion A1, as shown in FIG. 4, the substantially spherical iso-etched surface EL1 moves in the direction in which the diameter increases with the etching hole 12 as the center with time. . Such isotropic etching proceeds until four pyramid-shaped projections P1 are formed at the center of the four etching holes 12 by the four equally etched surfaces. The projection P1 thus formed has four peaks corresponding to the four equally etched surfaces, and has a sharp peak (tip).
That is, in the projections P1 produced by the present method, the four side surfaces formed respectively corresponding to the four equally etched surfaces have a steeper gradient with respect to the upper surface of the substrate 10 as being closer to the front end, and the area of the front end portion is extremely large. Can be smaller.
[0019]
In the present embodiment, four etching holes are formed equidistantly from one conical projection P1, but the present invention is not limited to this. The number of etching holes provided may be three or more. At this time, the projection formed by the three etching holes has a substantially triangular pyramid shape, and the projection formed by n (3 or more integer) etching holes generally has an n-pyramid shape, but n is large. Then, it actually becomes closer to a conical shape.
Further, in the first embodiment, since the sacrificial layer 11 is formed of two layers having different etching rates (a layer having a high etching rate is formed thereon), it is easy to control the height of the protrusion.
[0020]
As described above, the on-substrate structure that can effectively prevent the adsorption between the plate-shaped beam portion A1 and the substrate 10 can be manufactured.
The material and film thickness exemplified in the above description of the manufacturing method, that is, the first sacrificial layer 11a made of a thermal oxide film is formed to a thickness of 1.5 μm, and the second sacrificial layer 11b made of a TEOS silicon oxide film is formed. An insulating film 13 made of a low stress silicon nitride film was formed to a thickness of 1.0 μm, an insulating film 13 made of a low stress silicon nitride film was formed to a thickness of 0.7 μm, and an electrode film 14 made of a Cr film (5 nm) / Au film (100 nm) was formed. When the etching holes 12 having a diameter of 4 μm were formed at a pitch of, for example, 20 μm, and the etching was performed, the protrusions P1 having a sharp peak with a height h of 0.9 μm or less could be formed.
Here, the height of the projection P1 can be set to an arbitrary height, for example, 0.5 μm, by stopping the etching when the projection P1 having a desired height is formed.
[0021]
The present inventors manufactured an electrostatic actuator provided with protrusions having different pitches by the method described above, and confirmed the adsorption preventing effect.
The manufactured actuator has the structure shown in FIG. 1, and the shape of the plate-like beam A1 is 300 μm in width × 1200 μm in length and 0.7 μm in thickness, and the gap between the substrate 10 and the plate-like beam A1 is 3 μm. It was set to 0.5 μm. In addition, the area of the electrode 14 of the plate-shaped beam part A1 was 280 μm × 900 μm.
Then, four types of electrostatic actuators in which protrusions having a height of about 0.5 μm are formed at a pitch of 10 μm, 40 μm, 60 μm, and 80 μm μm on the surface of the substrate 10 (the surface of the fixed electrode) are manufactured. The operation status when the ON / OFF of the voltage applied between both electrodes was repeatedly driven was confirmed. FIG. 5 shows the state of adsorption when a DC voltage is applied to repeatedly drive, by the ratio of non-adsorption to 20 samples. The environment for the adsorption confirmation test was an atmosphere of 25 ° C. and 65% RH. As is clear from FIG. 5, it can be seen that the denser the protrusions, the more difficult it is to adsorb.
[0022]
In the above-described method for manufacturing an on-substrate structure according to the first embodiment, since the projection P1 is formed by forming the etching hole 12 in the plate-shaped beam portion, the shape and the arrangement of the etching hole 12 can be adjusted. Thus, the shape and arrangement of the protrusions P1 can be set, and the protrusions P1 having a desired shape and arranged at a desired position can be easily formed.
This makes it possible to realize an adsorption prevention structure that can more effectively prevent adsorption in the on-substrate structure.
[0023]
In addition, the protrusion P1 manufactured by the method of the present embodiment has a steep gradient with respect to the upper surface of the substrate 10 as it is closer to the tip, and the area of the tip can be extremely small. It is possible to reduce the size, and it is possible to more effectively prevent the plate-like beam portion from adsorbing to the substrate.
Further, in the first embodiment, since the etching hole is formed in the plate-like beam portion and the projection P1 is formed using the sacrificial layer, the projection can be easily formed.
[0024]
Embodiment 2 FIG.
The on-substrate structure according to the second embodiment has protrusions P21 formed by a method different from that of the first embodiment, and is manufactured as follows.
<Deposition of insulating film 21>
In the manufacturing method according to the second embodiment, a low-resistance silicon substrate is used as the substrate 20 and a projection is first formed on the base substrate 20 as in the first embodiment, in order to form a fixed electrode using the base substrate 20. An insulating film 21 made of SiOx is formed (FIG. 6A).
[0025]
<Metal mask formation and etching hole formation>
Next, a metal mask film made of, for example, Cr is formed on the insulating film 21, and an etching hole Eh for forming the projection P20 is formed, thereby manufacturing an etching mask M1 having an etching hole (FIG. 7 (a)).
Here, in the second embodiment, as shown in FIG. 7 (a), the center of the position where the projection P20 is to be formed is equidistant from the center, and two adjacent intervals are equal to each other. Thus, three etching holes Eh are formed. That is, in the second embodiment, three etching holes are arranged for one projection P20 so that an equilateral triangle is formed by their centers, and the projection P20 is formed at the center of gravity.
The present invention is not particularly limited by the material constituting the metal mask, and any material having resistance to an etchant used for etching the insulating film 21 can be used. Is formed of SiO2 and a material such as Cr, Mo, W, Ni, Au or the like can be used when an HF aqueous solution is used as an etching solution.
[0026]
<Etching process: projection formation>
Next, the insulating film 21 is isotropically etched through the etching hole Eh using the metal mask M1 having the etching hole Eh.
At the time of this etching, the spherical equal etching surface EL1 advances in the direction in which the diameter increases with the etching hole Eh as the center, and the conical projection P20 is formed by the three equal etching surfaces EL2 immediately below the center of gravity of the three etching holes Eh. It is formed.
In this manner, a projection P21 having three side surfaces P2a respectively corresponding to the three equal etching surfaces EL2 and having sharp peaks (tips) is formed.
That is, in the projections P21 produced by the present method, the three side surfaces formed respectively corresponding to the three equally etched surfaces have a steeper gradient with respect to the upper surface of the substrate 20 as being closer to the front end, and the area of the front end portion is extremely large. Can be smaller.
In FIG. 7 (b), what is denoted by reference numeral P2b is a ridge line where two side surfaces P2a intersect.
The insulating film 21 located in a region other than the region where the protrusion P21 is formed is covered with a metal mask M1 having no etching hole, and remains without being removed in this etching step, but is finally removed as a sacrificial layer. You.
[0027]
<Protrusion protection film formation>
In order to protect the projections P21a (made of SiOx) on the surface of the projections P21a formed as described above when removing a sacrificial layer made of SiOx described later, protection that is resistant to the etching solution of the sacrificial layer. A film P21b (in the case where the sacrificial layer and the protrusion P21a are formed of SiOx, for example, a SiNx film by LP-CVD) is formed.
[0028]
<Planarization process>
Next, the surface irregularities formed by the plurality of projections P21 are flattened by forming the SOG film 22 (FIG. 8A). Here, the SOG film is a film formed by spin-coating a material obtained by dissolving silanol (Si (OH) 4) in alcohol and baking at a temperature of about 400 ° C.
The SOG film 22 is finally removed as a sacrificial layer.
[0029]
<Plate beam forming process>
Next, an SiNx film 23 for forming the plate-like beam portion is formed and patterned into the shape of the plate-like beam portion (FIG. 8B), and an electrode film is formed on the patterned SiNx film 23. 24 are formed and patterned into a predetermined shape (FIG. 8C).
Then, the insulating layer 21 and the SOG film 22 remaining as the sacrificial layer are removed by etching with a hydrofluoric acid solution or the like (FIG. 8D).
[0030]
In the above-described second embodiment, an on-substrate structure that can effectively prevent adsorption of the plate-like beam portion A2 and the substrate 20 can be manufactured.
[0031]
Further, according to the manufacturing method of the second embodiment, since the projections are formed by forming the masks for forming the projections separately from the plate-shaped beam portions, the predetermined projections (shape and arrangement) can be formed. A desired projection can be formed using a mask suitable for formation (a material and a film thickness can be set as a preferable mask), and a more appropriate suction prevention structure can be realized.
[0032]
In the above description of Embodiments 1 and 2, preferred materials that can be used in the present invention and specific shapes (thicknesses and the like) have been described, but the present invention is not limited to these specific materials. The shape and shape are not limited.
For example, when an SiOx film is used as a sacrificial layer film that can be selectively removed and an etching solution for selective removal is HF, a selective insulating film for forming the plate-like beam portion A1 is replaced with SiNx. Alternatively, polysilicon may be used.
In addition, aluminum, gold, platinum, or the like can be used as an electrode material.
[0033]
Further, instead of SiOx, an organic material such as polyimide or resist can be used as the sacrificial layer film 11 which can be selectively removed. When an organic substance such as polyimide or resist is used as the sacrificial layer film 11, dry etching of oxygen plasma can be used for selective removal, and a selective insulating film for forming the plate-like beam portion A1 is formed of SiOx or polysilicon. Alternatively, SiNx can be used, and aluminum, gold, platinum, or the like can be used as an electrode material.
[0034]
Although a Cr underlayer is provided to enhance the adhesion between Au and SiNx, a film of NiCr, Ti, Ti / Pt or the like may be used.
[0035]
In the first and second embodiments, an electrostatic actuator in which two electrode films are horizontally opposed to each other has been described as an example. However, the direction of the electrodes is not limited to this, and the electrode surface is in a vertical direction. May be. In this case, the protrusion may be provided on the electrode surface side that is perpendicular to and opposed to the vertical electrode surface. Furthermore, although the electrostatic actuator has been described here, the present invention is not limited to this, and is not limited to electrostatic force. It may be provided on the surface side. Further, although the silicon substrate is formed so as to also serve as the fixed electrode, a metal wiring may be separately formed, an insulating film may be formed thereon, and then a protrusion may be provided thereon.
[0036]
Embodiment 3 FIG.
The on-substrate structure according to the third embodiment of the present invention is different from the first and second embodiments in that a plurality of protrusions having random heights are formed on the main surface of the plate-shaped beam portion facing the substrate. Is different and is easily produced as follows.
[0037]
In this manufacturing method, first, a thermal oxide film 31 made of SiOx is formed on a silicon substrate 30 (FIG. 9A).
Next, an etching mask M3 made of Cr for forming a minute dent in the thermal oxide film 31 is formed, excluding a region for forming a minute dent (projection) (a region for forming a plate-like beam portion). A resist film R3 is formed. Then, using the etching mask M3 made of chromium, the thermal oxide film 31 is etched for about several seconds with buffered hydrofluoric acid (BHF) (16%), which is a mixed solution of hydrofluoric acid and ammonium fluoride.
In the third embodiment, chromium is selected as a material for forming the etching mask, and a film is formed for about 10 seconds at 100 W DC while rotating the substrate using a parallel-plate magnetron sputtering apparatus. Then, an etching mask M3 made of chromium is formed so as to have a short thickness.
[0038]
As described above, in the etching mask M3 formed as an extremely thin mask, a large number of extremely small pinholes are uniformly present throughout the mask. The present invention utilizes the pinholes. By etching the thermal oxide film 31 through the etching mask M3 having the large number of pinholes, minute recesses are formed corresponding to the respective pinholes. (FIG. 9 (b)). The details of the formation of the minute recess using the pinhole of the mask will be described later.
[0039]
Then, after a minute concave portion is formed in the thermal oxide film 31 by etching, the resist R3 and the etching mask M3 are removed, and an SiNx film 33 for forming the plate-like beam portion is formed to form a desired plate-like beam portion. It is patterned into a shape (FIG. 9C). The SiNx film 33 is formed as a low stress film using an LP (low pressure) -CVD apparatus.
[0040]
Next, Cr / Au, which is an electrode film, is formed and patterned into a predetermined shape (FIG. 10A).
Then, a hollow structure is formed by removing the thermal oxide film 31, which is also a sacrificial layer, with HF or the like except for a portion immediately below the fixed end 33a.
In this way, it is possible to manufacture a structure that has a large number of protrusions on the main surface of the plate-shaped beam portion facing the substrate and is hard to be attracted.
At this time, it is preferable to control the film stress of each constituent thin film so that the plate-shaped beam portion as the upper movable member does not warp. However, the above-described method can be applied to a warped member.
[0041]
Hereinafter, the formation of the minute recess using the pinhole of the etching mask will be described in detail.
In the manufacturing method according to the third embodiment, when forming an etching mask, the film forming conditions and the thickness of the etching mask are set so as to form a pinhole through which an etching solution can penetrate, and the pinhole is used. To form minute concave portions in a layer below the mask.
Accordingly, the shape (depth (depth as an absolute dimension), depth relative to the opening diameter, etc.) of the minute concave portion is mainly determined by the thickness of the etching mask and the etching time, and the film thickness of the etching mask and the etching There is an optimal solution between time.
In addition, as for the protrusion for preventing adsorption, it is preferable that a relatively large number of protrusions are almost uniformly distributed in a region where the protrusion is formed, so that as many pinholes as possible are uniformly distributed as an etching mask. It is preferable to form a thin film.
[0042]
According to the study by the present inventors, if the thickness of the etching mask is 1 nm or less, the setting of etching conditions (especially etching time) for forming a desired minute concave portion is relatively easy, and the desired protrusion ( It has been confirmed that a minute concave portion corresponding to the shape of the protrusion and the distribution of the protrusion can be easily formed.
When the thickness of the etching mask is 1 nm or more, as the thickness increases, it becomes more difficult to set etching conditions for forming a desired minute concave portion.
Further, when the etching mask becomes thicker, the pinhole does not uniformly exist in the entire required region, and from that point, it is preferable to set the thickness of the etching mask to 1 nm or less.
[0043]
As an example, a chromium film having a thickness of 0.7 nm is used as an etching mask, and a SiO2 film as a base film is formed by four types of etching times (2.25 minutes, 3.0 minutes, 3.75 minutes, 5.25). FIGS. 11 to 14 show the results of measurement of the respective surface shapes obtained by etching using the atomic force microscope (AFM).
In this example, a chromium film as an etching mask was produced using a sputtering apparatus under the following conditions.
(1) Ultimate vacuum: 1 × 10 ^-6 Torr or less,
(2) Argon gas pressure: 2-3 Torr,
(Set as small as possible as long as stable discharge is possible)
(3) Substrate temperature: 20 ° C.
(Set so that the movement of sputter particles attached to the substrate is minimized)
(4) DC magnetron sputtering power: 100 W to 300 W
(Set so that film thickness can be controlled accurately)
(5) Distance between sample and target: 15 cm,
(Setting to reduce the influence of plasma)
(6) Film formation time: 4 sec / 100 W,
(Set to be 0.7nm thick)
[0044]
In the above example, an etching time of 4.5 minutes was further added, and the etching depth with respect to the etching time is shown in FIG. 15, and the surface roughness with respect to the etching time is shown in FIG.
From FIGS. 15 and 16, it can be seen that as the etching time becomes longer, the etched surface generally recedes, and the surface roughness of the etched surface decreases accordingly. On the other hand, in the structure shown in FIG. 1, the size of the plate-shaped beam portion is 0.3 mm width × 0.9 mm length, the thickness of the plate-shaped beam portion (SiNx) is 0.7 μm, Is set to 2.5 μm, it has been experimentally confirmed that if the surface roughness Ra becomes about 10 nm (the initial surface roughness Ra of the SiOx film before etching: Ra: 3 nm), no adsorption occurs. .
Therefore, when the thickness of a chromium film formed by sputtering as an etching mask is 0.7 nm (film formation time: 4 sec), the etching time for forming a surface effective for forming a projection effective for adsorption is 3.0. It turns out that it is between 3.75 minutes.
[0045]
However, whether or not it is adsorbed is greatly affected by the size of the hollow structure (the distance between the plate-like beam and the substrate), the external force that can be applied during manufacturing and use, and the temperature and humidity environment. On the other hand, the optimum protrusion shape and the corresponding optimum surface roughness are different. Therefore, when applying the present invention, it is necessary to separately optimize according to the device structure to be applied.
[0046]
In the above-described third embodiment, since extremely small concave portions can be formed on the surface of the sacrificial layer, projections of sub-μm or less can be formed at an extremely narrow pitch (for example, pitch of sub-μm or less). An adsorption preventing structure capable of effectively preventing adsorption can be formed on the lower surface of the plate-shaped beam portion (the surface facing the substrate).
[0047]
Further, since the anti-suction structures described in the first to third embodiments are configured by extremely small projections formed by the respective unique manufacturing methods, the electrostatic actuators having the anti-suction structures are: The electrostatic field distribution for operating the actuator is hardly disturbed by the protrusion.
Therefore, the electrostatic actuators according to the first to third embodiments can prevent the substrate and the plate-shaped beam from being attracted to each other without deteriorating the stable operation of the actuator. it can.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, an on-substrate structure capable of effectively preventing adsorption of a plate-shaped beam portion and a substrate, and a projection forming method capable of easily forming the adsorption prevention structure are provided. it can.
[Brief description of the drawings]
FIG. 1 is a perspective view of an on-substrate structure according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the first half of a step in the method of manufacturing the on-substrate structure according to the first embodiment;
FIG. 3 is a cross-sectional view showing the latter half of the method of manufacturing the on-substrate structure according to the first embodiment;
FIGS. 4A and 4B are a plan view and a cross-sectional view illustrating a state in which protrusions are formed in the method of manufacturing the on-substrate structure according to the first embodiment; FIGS.
FIG. 5 is a graph showing a non-adsorption ratio with respect to a protrusion interval in the on-substrate structure according to the first embodiment;
FIG. 6 is a cross-sectional view showing the first half of a method of manufacturing the on-substrate structure according to the second embodiment;
FIGS. 7A and 7B are a plan view and a cross-sectional view illustrating a state in which projections are formed in the method of manufacturing the on-substrate structure according to the second embodiment; FIGS.
FIG. 8 is a cross-sectional view showing a latter half of a step in the method for manufacturing a structure on a substrate according to the second embodiment.
FIG. 9 is a cross-sectional view showing a first-half step in the method of manufacturing the on-substrate structure according to the third embodiment.
FIG. 10 is a cross-sectional view showing a latter half of a step in the method for manufacturing an on-substrate structure according to the third embodiment.
FIG. 11 is a photograph of the surface when the SiO2 film as the base film is etched for 2.25 minutes using an etching metal mask having a pinhole (a chrome film of 0.7 nm) in the manufacturing method of the third embodiment. a) and the cross-sectional shape (b).
FIG. 12 is a photograph of the surface when the SiO2 film as the base film is etched for 3.0 minutes using an etching metal mask having a pinhole (a chrome film of 0.7 nm) in the manufacturing method of the third embodiment. a) and the cross-sectional shape (b).
FIG. 13 is a cross-sectional view showing a case where an underlayer SiO 2 film is etched for 3.75 minutes using an etching metal mask having a pinhole (a 0.7-nm chromium film) in the manufacturing method of the third embodiment. .
FIG. 14 is a cross-sectional view showing a case where an SiO2 film as a base film is etched for 5.25 minutes using an etching metal mask having a pinhole (a 0.7-nm chromium film) in the manufacturing method of the third embodiment; .
FIG. 15 is a graph showing a depth with respect to an etching time in the manufacturing method according to the third embodiment.
FIG. 16 is a graph showing surface roughness versus etching time in the manufacturing method of the third embodiment.
[Explanation of symbols]
Reference numerals 10, 20, 30 Substrate, 11 sacrificial layer, 11a first sacrificial layer, 11b second sacrificial layer, 12, Eh etching hole, 13 actuator base, 13a, 33a fixing portion, 13b moving end, 14, 24 electrode film, 22 SOG film, 23SiNx film, 31 thermal oxide film, A1, A2 plate beam, P1, P21, P21a projection, EL1, EL2 etching surface, M1, M3 etching mask, P2a projection side surface, P21b protective film, R3 resist film.

Claims (13)

On the substrate, a plate-shaped beam portion having a fixed portion fixed to the substrate and a movable end capable of changing the distance between the substrate, the plate-shaped beam portion has a sacrifice layer on the substrate. An on-substrate structure that is separated from the substrate except for the fixing portion by removing the sacrificial layer after being formed through,
An on-substrate structure including a suction prevention structure including a plurality of conical projections at a portion of the upper surface of the substrate facing the plate-like beam portion. The on-substrate structure according to claim 1, wherein each of the plurality of protrusions is formed such that a portion closer to the tip has a steeper gradient with respect to the upper surface of the substrate. The on-substrate structure according to claim 1, wherein each of the protrusions is constituted by a plurality of side surfaces formed such that a slope closer to the top surface of the protrusion is steeper as the portion is closer to the tip. The on-substrate structure according to any one of claims 1 to 3, wherein a plurality of through holes are formed in the beam portion at positions equidistant from a tip of the projection, respectively, corresponding to the projection. . The on-substrate structure according to any one of claims 1 to 3, wherein the protrusion includes two different layers. On the substrate, a plate-shaped beam portion having a fixed portion fixed to the substrate and a movable end capable of changing the distance between the substrate, the plate-shaped beam portion has a sacrifice layer on the substrate. An on-substrate structure that is separated from the substrate except for the fixing portion by removing the sacrificial layer after being formed through,
An on-substrate structure comprising a plate-shaped beam portion, on one main surface facing the substrate, having an adsorption prevention structure including a plurality of protrusions having random heights. The substrate has conductivity, and the plate-shaped beam portion has an electrode film facing the substrate, and the position of the moving end is changed by a voltage applied between the substrate and the electrode film. The structure on a substrate according to any one of claims 1 to 6. A first electrode film is formed on the substrate, and the plate-like beam portion has a second electrode film facing the substrate, and a voltage is applied between the first and second electrode films. The on-substrate structure according to any one of claims 1 to 6, wherein the position of the moving end varies depending on the applied voltage. A method of forming protrusions on a substrate, comprising:
A first layer forming step of forming a first layer made of a first material on a substrate;
A second layer forming step of forming a second layer on the first layer with a second material different from the first layer;
A through-hole forming step of forming at least three through-holes in the second layer so as to be equidistant from the center of the point where the projection is to be formed;
An etching step of isotropically etching the first layer from each of the through holes using the second layer as a mask,
A method for forming projections, wherein the projections are formed on an etched surface by etching from the through holes. 10. The projection forming method according to claim 9, wherein the first layer forming step includes laminating and forming two layers having different etching rates in the etching step. A method of forming a plurality of protrusions on a surface of a plate-like beam portion fixed on the substrate facing the substrate in part on the substrate,
A sacrificial layer forming step of forming a sacrificial layer on the substrate,
A mask forming step of forming an etching mask on the sacrificial layer so that a large number of pinholes capable of penetrating an etching solution are formed;
A hole forming step of forming a plurality of holes corresponding to the respective pin holes in the sacrificial layer by etching the sacrificial layer from the pin holes using the etching mask as a mask;
Forming a film for forming the plate-like beam portion so as to fill the plurality of holes on the sacrificial layer having the plurality of holes, and a beam portion forming step of patterning into a shape of the plate-like beam portion; ,
A sacrificial layer removing step of removing the sacrificial layer except for the fixing portion by etching. The method according to claim 11, wherein the etching mask is made of Cr. 13. The projection forming method according to claim 12, wherein the etching mask made of Cr is formed to a thickness of 1 nm or less.

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