CN119758585A - Piezoelectric driving MEMS two-dimensional scanning mirror and processing method thereof - Google Patents

Abstract

The invention discloses an MEMS scanning mirror and a processing method thereof, wherein the scanning mirror comprises an outer frame body silicon, a mass block, a metal mirror surface, 4 groups of silicon torsion beams, a metal lower electrode, a PZT piezoelectric film and a metal upper electrode, wherein the piezoelectric driving MEMS two-dimensional scanning mirror can deform the PZT piezoelectric film to generate warping after voltage is applied to the metal upper electrode and the metal lower electrode, so that the silicon torsion beams are driven to warp, the middle mass block and the metal mirror surface are driven to deflect, and two-dimensional scanning can be realized by applying voltage to 4 groups of different scanning structures. According to the invention, the piezoelectric driving arm is applied with voltage to drive the reflecting mirror surface to deflect, so that the volume of the whole scanning system can be reduced while a large deflection angle is realized, the PZT is used as an angle sensor, the process flow is reduced, the flow sheet yield and the system integration level are improved, and an integrated MEMS scanning device with high quality factor is formed.

Description

Piezoelectric driving MEMS two-dimensional scanning mirror and processing method thereof

Technical Field

The invention relates to the technical field of micro-electromechanical processing, in particular to a piezoelectric driving MEMS two-dimensional scanning mirror and a processing method thereof.

Background

The optical scanning mirror realized based on MEMS technology is one of the core components of many optical systems, and has important roles in the aspects of optical imaging, laser scanning, projection display, laser radar, free space optical communication and the like. Compared with the traditional optical scanning mirror, the micro-reflecting mirror with exquisite volume is integrated on the silicon-based chip by utilizing the MEMS technology, so that the mass of a movable part is greatly reduced, the rotation inertia of the system is lightened, and the reliability and the mechanical shock resistance of the system are also effectively improved.

At present, the driving modes of the MEMS scanning mirror mainly comprise electrostatic driving, electromagnetic driving, piezoelectric driving, electrothermal driving, pneumatic driving and other driving modes. In this case, the response speed of the electrothermal and pneumatic driving is too slow, the power consumption is high, the electromagnetic driving needs an additional magnet and is subject to electromagnetic interference, and the electromagnetic driving is not suitable for the current development trend of high speed and miniaturization. Most MEMS scanning mirrors in the market adopt an electrostatic driving mode, but the driving voltage required by the electrostatic driving type micro scanning mirror is higher, and the scanning angle of the micro scanning mirror is limited due to the 'pull-down effect' existing between the plate capacitance electrode plates. The piezoelectric driving type micro scanning mirror has relatively good stability, and has larger scanning angle and resonant frequency, but because the elongation of the piezoelectric film is limited, the piezoelectric film is easy to break down when larger driving voltage is applied to obtain displacement, so the quality requirement on the piezoelectric film is higher, and the requirement on the processing technology is also provided.

MEMS scanning mirrors can be classified into one-dimensional scanning mirrors and two-dimensional scanning mirrors according to the dimension of the scanning direction. The one-dimensional scanning mirror has a simple structure, has no coupling influence in two directions, and can realize relatively higher scanning frequency and maximum scanning angle. The one-dimensional MEMS scanning mirror is matched with a laser beam expanding lens or a single-shaft rotating motor and the like, so that two-dimensional light beam scanning can be realized. In general, while one-dimensional scanning mirrors can achieve higher scan angles and scan frequencies, the overall system is not compact enough, greatly diminishing the advantages of MEMS devices over conventional devices. The two-dimensional scanning mirror can realize the scanning of light beams in two directions, and can fully exert the advantages of high integration level, small occupied space and the like. The two-dimensional MEMS scanning mirror has three scanning modes, namely a biaxial resonance type, a one-axis quasi-static type and a biaxial quasi-static type. The biaxial quasi-static pattern control can be realized, but the scanning range is small, and the scanning frequency is low. The one-axis resonance type one-axis quasi-static type can realize a raster scanning mode, the resonance axis can realize a larger scanning angle, and meanwhile, the uniform point cloud distribution can be realized. And the biaxial resonance scanning can fully play the resonance advantage, and realize the maximum scanning range and frequency. The mirror surface of a common two-dimensional scanning mirror is smaller and is generally 1mm in size, because a suspended cantilever beam is unstable due to the stress influence of materials, if the mirror surface is oversized, the mirror surface can break under the torsion action during operation, and then the device fails.

Disclosure of Invention

The invention discloses a MEMS scanning mirror design and a process design, which aims at least solving the problems existing in the prior art, the MEMS scanning mirror optimizes the design structure and the process flow, can improve the stability of devices, and has good process repeatability.

Specifically, the invention discloses a piezoelectric driving MEMS two-dimensional scanning mirror processing method, which comprises the following steps:

Step S1, preparing an insulating layer SiO ₂ on an SOI substrate by plasma vapor deposition;

The SOI substrate comprises a multilayer structure, and comprises a back seal SiO ₂, bulk silicon, an oxygen-buried layer and a device layer Si from bottom to top;

Step S2, preparing metallic titanium and metallic platinum on the upper layer of the insulating layer SiO ₂ through magnetron sputtering;

S3, preparing a PZT piezoelectric film on the surface of the metal film by a sol-gel method;

step S4, patterning the PZT piezoelectric film is completed through photoetching and wet etching;

step S5, patterning the lower electrode metal film is completed through photoetching and RIE (reactive ion etching);

step S6, completing metal film deposition preparation of an upper electrode and a mirror surface of the device through photoetching and electron beam evaporation;

Step S7, patterning the Si torsion beam of the device layer by photoetching, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance;

S8, etching the back seal SiO ₂ of the back surface of the device through spin coating and wet etching;

and S9, etching the device body silicon by spin coating and deep reactive ion beam etching, and releasing stress.

Further, in the step 2, the thickness of the metallic titanium is 20nm, and the thickness of the metallic platinum is 200nm;

Titanium metal is connected with the insulating layer SiO ₂ and serves as an adhesion layer between platinum metal and the insulating layer SiO ₂.

Further, in step 3, the PZT thin film is lead acetate trihydrate, zirconium tetra-n-butoxide and tetrabutyl titanate, and is dissolved into PZT sol through ethylene glycol methyl ether after being decocted into PZT xerogel, and the PZT sol is spin-coated on the surface of a substrate and is subjected to rapid annealing at 700 ℃, and finally the PZT thin film with the thickness of 2um is prepared after repeated operation for many times.

Further, in step 4, the HMDS tackifier is baked on the PZT surface film to improve the adhesion capability of the photoresist and the substrate surface, and the baking temperature is 135 ℃;

Spin-coating positive photoresist to form a film and baking at 95 ℃ for 90 seconds to remove redundant moisture in the photoresist, and performing proper exposure on the substrate under the mask by using a photoetching machine;

Immersing a sample substrate into ZX-238 developing solution to react photoresist of the exposed part, taking out, flushing the surface of the substrate by deionized water to remove residual developing solution, drying the substrate by nitrogen, placing the substrate on a 110 ℃ hot plate for 5min to heat, curing the photoresist and improving the acid etching resistance of the photoresist;

then, preparing etching solution for wet etching PZT, and continuously and alternately carrying out the substrate in etching solution, rinsing solution and deionized water, so that the reaction product is effectively prevented from adhering to the surface to influence the reaction;

finally, the patterned PZT is obtained after the patterning PZT is cleaned in organic solution such as acetone.

Further, in step 5, the metal titanium and metal platinum layers are etched by high power Ar ion bombardment with ion beam etching, and after etching, the metal titanium and metal platinum layers are washed by using an organic solvent such as acetone.

Further, in step 6, a mask pattern required for depositing the metal film is prepared by using the photoresist exposure process described in step 4, and the photoresist required to be used in step 6 is a photoresist to facilitate the stripping process after depositing the metal film;

Forming a mask pattern with an electrode and a mirror window on the surface of the sample after exposure and development, and then depositing a metal layer on the surface of the sample by using an electron beam evaporation device, wherein the metal layer is deposited to be Ti-20nm and Au-200nm;

after deposition, soaking the sample substrate into acetone, dissolving photoresist, removing redundant metal layers, sequentially putting into isopropanol and absolute ethyl alcohol for ultrasonic cleaning after stripping, taking out the sample, flushing with deionized water, and drying with N2.

Further, in step 7, a mask pattern required for etching the device layer is prepared using the photoresist exposure process described in step 4;

using AZ 4620 thick photoresist as a mask, and etching 3 layers of films, namely an insulating layer SiO ₂, a device layer Si and an oxygen-buried layer SiO ₂;

Etching the insulating layer SiO ₂ and the buried oxide layer by adopting a reactive ion beam;

for the piece layer Si, deep reactive ion beam etching for Si is employed;

after the etching operation is completed, an organic solution such as acetone is used for ultrasonic cleaning.

In step 8, the front surface of the substrate is uniformly coated with AZ 5214 photoresist for protection, and then an acid-etching-resistant blue film is attached to the front surface;

after the protection of the substrate is finished, immersing the protected substrate in a hydrofluoric acid buffer solution for etching for 1h, then taking out a sample, flushing the surface of the substrate with deionized water to remove residual hydrofluoric acid on the surface, immersing the substrate in acetone, and standing for 5min;

And then immersing the substrate into acetone again, performing ultrasonic cleaning under low power by using an ultrasonic cleaner to completely remove residues such as photoresist, sequentially performing ultrasonic cleaning on the substrate by using isopropanol and absolute ethyl alcohol to remove organic residues, and finally washing the substrate by using deionized water and then drying by using nitrogen.

In step 9, spin-coating photoresist after baking HMDS on the front surface to protect the structure of the front surface and reduce the permeation influence of vacuum oil;

Baking the photoresist on the front surface at 110 ℃, and then baking and coating HMDS on the back surface and spin-coating the photoresist;

Pre-baking at 100 ℃, exposing, patterning, developing, post-baking and removing residual glue by using a Plasma cleaning instrument;

Slightly coating a layer of vacuum oil on the front surface of the substrate after the spin coating of the substrate is completed, and laminating the vacuum oil on the silicon oxide gasket;

and (3) performing bulk silicon etching by using deep reactive ion beam etching equipment, wherein after the etching is finished, the cyan of the whole silicon oxide is represented as the end of the bulk silicon etching of the device layer, and then, cleaning by using organic solution such as acetone and the like to obtain the final MEMS micro-scanning mirror.

The piezoelectric driving MEMS two-dimensional scanning mirror comprises an outer frame body silicon, a mass block, a metal mirror surface, 4 groups of silicon torsion beams, a metal lower electrode, a PZT piezoelectric film and a metal upper electrode;

the silicon of the outer frame body is hollowed out as a center the structure is made by etching bulk silicon;

The mass block is arranged at the hollow part of the silicon center of the outer frame body and is made by etching an oxygen-buried layer, a device layer Si and an insulating layer SiO ₂;

the metal mirror surface is formed by depositing a metal layer on the top of the mass block;

The metal lower electrodes are respectively arranged at 4 corners of the outer frame body silicon in an L shape and extend towards the center of the outer frame body silicon, are arranged at the top of the outer frame body silicon through the oxygen burying layer, the device layer Si and the insulating layer and are metal platinum at the top of the insulating layer;

the PZT piezoelectric thin films are respectively arranged at the tops of the corresponding metal lower electrodes;

The metal upper electrodes are respectively metal layers deposited on the tops of the corresponding PZT piezoelectric films;

The silicon torsion beam is of a serpentine structure formed by etching the device layer Si, one end of the silicon torsion beam is connected with the device layer Si below the corresponding metal lower electrode, and the other end of the silicon torsion beam is connected with the device layer Si in the mass block;

The piezoelectric driving MEMS two-dimensional scanning mirror can deform the PZT piezoelectric film and warp after voltage is applied to the metal upper electrode and the metal lower electrode, so that the silicon torsion beam is driven to twist, the middle mass block and the metal mirror face are driven to deflect, and two-dimensional scanning can be realized by applying voltage to 4 groups of different scanning structures.

The beneficial effects achieved by the invention are as follows:

The invention avoids the defect that the one-dimensional MEMS scanning mirror is not compact enough, and the two-dimensional MEMS scanning mirror is used for designing and playing the advantages of high integration level, small space and the like of the MEMS device compared with the traditional device.

The present invention uses a biaxial resonant design to achieve maximum scan range and frequency.

The invention reduces and improves the micro-nano processing technological process and reduces the attenuation to the device performance caused by the wet etching process of the device.

The piezoelectric two-dimensional resonant MEMS micro-scanning mirror provided by the invention drives the reflecting mirror surface to deflect by applying voltage to the piezoelectric driving arm, so that the volume of the whole scanning system can be reduced while a large deflection angle is realized, the PZT is used as an angle sensor, the process flow is reduced, the flow sheet yield and the system integration level are improved, and the structures such as a device executing structure, a sensing material structure, a supporting structure and the like are optimized in a targeted manner, so that an integrated MEMS scanning device with high quality factor is formed.

Drawings

FIG. 1 is a schematic diagram of a front structure of a piezoelectric two-dimensional resonant MEMS micro-scanning mirror.

FIG. 2 is a flow chart of the overall process of the micro-scanning mirror according to the present invention.

FIG. 3 is a schematic cross-sectional view of a micro-mirror process according to the present invention.

Wherein, the piezoelectric ceramic comprises a metal mirror surface, upper electrodes of B1, B2, B3 and B4. metals, piezoelectric films of C1, C2, C3 and C4.PZT, lower electrodes of D1, D2, D3 and D4. metals, torsion beams of E1, E2, E3 and E4. silicon, a mass block and outer frame body silicon;

1. Back sealing SiO2, bulk silicon, buried oxide layer silicon, device layer silicon, insulating layer silicon oxide, lower electrode metal film, piezoelectric film, upper electrode metal film and metal mirror surface.

Detailed Description

The invention will be further described with reference to specific embodiments, and advantages and features of the invention will become apparent from the description. These examples are merely exemplary and do not limit the scope of the invention in any way. It will be understood by those skilled in the art that various changes and substitutions of details and forms of the technical solution of the present invention may be made without departing from the spirit and scope of the present invention, but these changes and substitutions fall within the scope of the present invention.

As shown in FIG. 1, the invention provides a design and processing method of a piezoelectric two-dimensional resonant MEMS micro-scanning mirror, which improves the mirror surface size through a topology optimization method, solves the problem of smaller mirror surface size (typically 1-2 mm) of a traditional MEMS scanning device, has high resonant frequency, is integrated into a laser radar and other systems, does not increase the complexity of an optical system and does not lose energy to reduce the measuring range, and can provide more scanning modes. And the MEMS scanning device with large mirror surface size (3-10 mm), high resonant frequency (> 2 KHz) and high stability (quality factor > 200) is developed by comprehensive structural design, topological optimization, material optimization and the like, so that the integration level of the MEMS micro scanning mirror in an optical system is further improved.

The scanning mirror mainly comprises a driving main body (BCD in fig. 1), a silicon torsion beam (E in fig. 1), a scanning mirror (A in fig. 1) and a substrate (G in fig. 1), wherein the principle is that a piezoelectric functional layer C is deformed and warped after voltage is applied to an upper electrode B and a lower electrode D in the driving main body, so that the driving snake beam E is driven to twist, the middle mirror surface is driven to deflect, and two-dimensional scanning can be realized by applying voltage to 4 groups of different scanning structures.

As shown in fig. 2, the method for manufacturing the MEMS micro-scanning mirror specifically includes the following steps:

S1, preparing an insulating layer SiO2 on an SOI substrate by plasma vapor deposition;

S2, preparing metallic titanium and metallic platinum on the upper layer of the insulating layer SiO2 through magnetron sputtering;

S3, preparing a PZT piezoelectric film on the surface of the metal film by a sol-gel method;

s4, patterning the PZT piezoelectric film by photoetching and wet etching

S5, patterning the lower electrode metal film by photoetching and RIE (reactive ion etching) reactive ion beam etching

S6, completing metal film deposition preparation of the upper electrode and the mirror surface of the device through photoetching and electron beam evaporation

And S7, patterning the Si torsion beam of the device layer by photoetching, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance.

S8, etching back seal SiO2 on the back of the device is completed through spin coating and wet etching

S9, etching the device body silicon by spin coating and deep reactive ion beam etching, and releasing stress.

The method for manufacturing the MEMS micro-scanning mirror is described in detail below with reference to the specific drawings.

Firstly, step S1 is performed, and for the customized SOI wafer, the main structure is shown in fig. 3 (a), wherein 1 is back-sealed SiO2, which is used for protecting 2-body silicon, so that the bottom of the substrate is not stained by instruments and equipment in the process, 3 is an oxygen-buried layer, and 4 is a device layer Si. After standard chemical cleaning of the substrate, a 200um layer of SiO2 was deposited as an insulating layer on the substrate using plasma chemical vapor deposition, as shown at 5 in fig. 3 (b).

Next, step S2 is performed, in which a thin metal film is deposited on the surface of the sample by electron beam evaporation, as shown in fig. 3 (c) 6, and Ti-20nm-Pt-200nm is deposited in the present invention, wherein Ti is used as an adhesion layer between the metal Pt and the insulating layer SiO2, and the structure of the deposited substrate is shown in fig. 3 (c).

Next, step S3 is performed to synthesize lead zirconate titanate (PZT) on the surface of the metal thin film using a sol-gel method, as shown by 7 in fig. 3 (d), in which the previously deposited Pt has good thermal stability, both as a good electrode layer and as a barrier layer for interdiffusion of the substrate and ferroelectric material. Preparing a PZT film by a sol-gel method, wherein experimental raw materials are lead acetate trihydrate, zirconium tetra-n-butoxide and tetrabutyl titanate, dissolving into PZT sol by ethylene glycol methyl ether after decocting into PZT xerogel, spin-coating the PZT sol onto the surface of a substrate, performing rapid annealing at 700 ℃, and finally preparing the PZT film with the thickness of about 2um after repeated operation.

And then, executing a step S4, as shown in fig. 3 (e), baking and coating an HMDS tackifier on the surface of a substrate PZT for improving the adhesion capability of photoresist and the surface of the substrate, baking at the temperature of 135 ℃, then spin-coating positive photoresist (AZ 5214 is optional) for forming a film and baking at the temperature of 95 ℃ for 90 seconds, removing redundant moisture in the photoresist, using a photoetching machine to properly expose the substrate under a mask, immersing a sample substrate into ZX-238 developing solution for reacting the photoresist of the exposed part, taking out, washing the surface of the substrate by deionized water for removing residual developing solution, drying the substrate by nitrogen, placing on a 110 ℃ hot plate for heating for 5 minutes, curing the photoresist and improving the acid etching resistance of the photoresist. An etching solution for wet etching PZT is then provided. In this example, a mixed solution of HCl for reacting Pb and Ti and HF for removing Ti and Cr was used as the PZT thin film etching solution. Because of the relatively high Pb content of PZT thin films, HCl in etching solutions is generally much higher than HF. In the experiment, etching liquid is prepared according to the water-hydrochloric acid-hydrofluoric acid=70:30:0.5, meanwhile, the dilute hydrochloric acid with the water-hydrochloric acid=40:10 is used as a rinsing liquid, pb is conveniently further etched, the substrate is continuously and alternately carried out in the etching liquid-rinsing liquid-deionized water, and the reaction products are effectively prevented from being attached to the surface to influence the reaction. And finally, cleaning in organic solution such as acetone to obtain patterned PZT, wherein the patterns are shown in figure 1, the corresponding areas of C1, C2, C3 and C4 are PZT piezoelectric films, and the PZT films in the other areas are corroded.

And then, executing step S5, preparing a mask pattern required for etching the metal film by using the photoresist exposure process described in S4, and finally forming a PZT piezoelectric film with corresponding areas of D1, D2, D3 and D4 as metal lower electrodes in the figure 1, wherein Pt in the other areas is etched away, so as to prevent the lower electrodes from being tested and connected and prevent the upper electrode and the lower electrode from being conducted, and the D area is designed as an L shape and the long end of the D area is slightly larger than that of the C area. As shown in fig. 3 (f), the etched metal is mainly Pt/Ti, and since Pt is an inert metal and does not react with most of the reaction gases, the metal is etched by high-power Ar ion bombardment by ion beam etching, ti as an adhesion layer has high activity and is easy to remove, and the thickness is only about 20nm, and can be removed in ion beam etching, and after etching, an organic solvent such as acetone is used for cleaning.

Next, step S6 is performed, as shown in fig. 3 (g), to prepare a mask pattern required for depositing the metal film by using the photoresist exposure process described in S4, and it should be noted that the photoresist required in this step is a photoresist (optionally AZ 2070), which is more advantageous for the stripping process after depositing the metal film. After exposure and development, a mask pattern with an electrode and a mirror window is formed on the surface of a sample, then an electron beam evaporation device is used for depositing a metal layer on the surface of the sample, ti-20nm-Au-200nm is deposited on the surface of the sample, as shown in figure 1, deposition areas are B1-B4 and A respectively, wherein B1-B4 are upper electrodes of a device, the B area is slightly smaller than the C area for preventing the upper electrode and the lower electrode from being conducted, and the A area is the mirror surface of the device. After deposition, soaking the sample substrate into acetone, dissolving photoresist, removing redundant metal layers, sequentially putting into isopropanol and absolute ethyl alcohol for ultrasonic cleaning after stripping, taking out the sample, flushing with deionized water, and drying with N2.

Next, step S7 is performed, as shown in fig. 3 (h), and a mask pattern required for etching the device layer is prepared by using the photoresist exposure process described in S4, where the area to be etched is a white blank area in fig. 1, and the main purpose of the mask pattern is to etch away the white blank area in the middle of the silicon torsion beams E1 to E4 to form a suspended silicon torsion beam, and simultaneously, also to etch the BCD part and the middle mass block F part, so that the middle mirror part is connected with the BCD device functional layer only through the E silicon torsion beams E1 to E4. The three layers of the buried oxide layer, the device layer Si and the insulating layer SiO ₂ below the projection area of the metal lower electrode are reserved as supporting structures, and the silicon torsion beams E1-E4 only comprise the device layer Si correspondingly, and the buried oxide layer and the insulating layer SiO ₂ on the upper side and the lower side of the silicon torsion beams are removed through etching. The mass block F is composed of three layers of an oxygen buried layer, a device layer Si and an insulating layer SiO ₂ below the projection area of the metal mirror surface.

Because the etching depth is deeper (> 20 um), AZ 5214 is difficult to play a good role of a mask, the AZ 4620 thick photoresist is used as the mask, and 3 layers of films are required to be etched at the present time, namely an insulating layer SiO2 (200 nm), a device layer Si (20 um) and an oxygen buried layer SiO2 (2 um), reactive ion beam etching is adopted for SiO2, deep reactive ion beam etching aiming at Si is adopted for Si, and the deep reactive ion beam etching mainly uses SF6 and other gases to react and passivate the Si, so that the etching selectivity and the depth-width ratio are good. After the etching operation is completed, an organic solution such as acetone is used for ultrasonic cleaning.

Next, step S8 is performed, as shown in fig. 3 (i), where AZ 5214 photoresist is used to perform photoresist protection on the front surface of the substrate, and then an acid-etching-resistant blue film is attached to the front surface, where the photoresist protection has two main purposes, firstly, to prevent the contact between the substrate surface and the BOE hydrofluoric acid buffer solution, because hydrofluoric acid will react to damage the PZT structure and the oxygen buried layer, and secondly, the blue film may not directly contact the device surface, so as to prevent the possible influence of the blue film residual photoresist on the substrate. After the protection of the substrate is finished, preparing a hydrofluoric acid buffer solution, etching back-sealed SiO2 by using the HF= 4;1 hydrofluoric acid buffer solution, immersing the protected substrate in the hydrofluoric acid buffer solution for etching for 1h, taking out a sample, washing the surface of the substrate by using deionized water to remove residual hydrofluoric acid on the surface, immersing the substrate in acetone for standing for 5min, naturally separating a blue film from the substrate due to gradual reaction and dissolution of the photoresist, immersing the substrate in acetone again, performing ultrasonic cleaning under low power by using an ultrasonic cleaner, completely removing residues such as the photoresist, sequentially using isopropanol and absolute ethyl alcohol to ultrasonically clean the substrate, removing organic residues, and finally using nitrogen to blow-dry after washing the substrate by using deionized water.

Finally, step S9 is performed, as shown in fig. 3 (j), considering that the back deep silicon etching needs to be changed for front protection and lamination, overall spin coating, and other processes. After the substrate is cleaned, the front surface is firstly baked and coated with HMDS and then is spin-coated with AZ 5214 photoresist, so that the structure of the front surface is protected, and meanwhile, the permeation influence of vacuum oil can be reduced. The front side photoresist was baked at 110 ℃, followed by HMDS and AZ 4620 photoresist spin-on the back side (i.e., the side to be etched). Pre-baking at 100 ℃, exposing, patterning and developing, and then post-baking and removing residual glue by using a Plasma cleaner. After the spin coating of the substrate is completed, a layer of vacuum oil is slightly coated on the front surface of the substrate, and the silicon oxide gasket is laminated by the vacuum oil. And then, carrying out bulk silicon etching by using deep reactive ion beam etching equipment, wherein the difference from the step S7 is that the etching depth is deeper (400 um) and the area is larger, the cyan which integrally presents silicon oxide after the etching is finished, namely, the etching of the bulk silicon of the Si layer is finished, and then, washing by using organic solution such as acetone and the like to obtain the final MEMS micro-scanning mirror.

The above is only a specific step of the present invention, and the protection scope of the present invention is not limited in any way, and all the technical solutions formed by equivalent transformation or equivalent substitution fall within the protection scope of the present invention, and the present invention does not detail the part of the known technology of the person skilled in the art.

Claims (10)

1. The piezoelectric driving MEMS two-dimensional scanning mirror processing method is characterized by comprising the following steps of:

Step S1, preparing an insulating layer SiO ₂ on an SOI substrate by plasma vapor deposition;

The SOI substrate comprises a multilayer structure, and comprises a back seal SiO ₂, bulk silicon, an oxygen-buried layer and a device layer Si from bottom to top;

Step S2, preparing metallic titanium and metallic platinum on the upper layer of the insulating layer SiO ₂ through magnetron sputtering;

S3, preparing a PZT piezoelectric film on the surface of the metal film by a sol-gel method;

step S4, patterning the PZT piezoelectric film is completed through photoetching and wet etching;

step S5, patterning the lower electrode metal film is completed through photoetching and RIE (reactive ion etching);

step S6, completing metal film deposition preparation of an upper electrode and a mirror surface of the device through photoetching and electron beam evaporation;

Step S7, patterning the Si torsion beam of the device layer by photoetching, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance;

S8, etching the back seal SiO ₂ of the back surface of the device through spin coating and wet etching;

and S9, etching the device body silicon by spin coating and deep reactive ion beam etching, and releasing stress.

2. The method of claim 1, wherein in step 2, the metallic titanium has a thickness of 20nm and the metallic platinum has a thickness of 200nm;

Titanium metal is connected with the insulating layer SiO ₂ and serves as an adhesion layer between platinum metal and the insulating layer SiO ₂.

3. The method of fabricating a piezoelectric driven MEMS two-dimensional scanning mirror according to claim 1, wherein in step 3, the PZT thin film is composed of lead acetate trihydrate, zirconium tetra-n-butoxide and tetrabutyl titanate, and is dissolved into PZT sol by ethylene glycol methyl ether after being decocted into PZT xerogel, spin-coated on the substrate surface and rapidly annealed at 700 ℃, and finally the PZT thin film having a thickness of 2um is fabricated after repeated operations.

4. The method of claim 1, wherein in step 4, HMDS adhesion promoter is baked on the PZT surface film to improve the adhesion between the photoresist and the substrate surface, and the baking temperature is 135 ℃;

Spin-coating positive photoresist to form a film and baking at 95 ℃ for 90 seconds to remove redundant moisture in the photoresist, and performing proper exposure on the substrate under the mask by using a photoetching machine;

Immersing a sample substrate into ZX-238 developing solution to react photoresist of the exposed part, taking out, flushing the surface of the substrate by deionized water to remove residual developing solution, drying the substrate by nitrogen, placing the substrate on a 110 ℃ hot plate for 5min to heat, curing the photoresist and improving the acid etching resistance of the photoresist;

then, preparing etching solution for wet etching PZT, and continuously and alternately carrying out the substrate in etching solution, rinsing solution and deionized water, so that the reaction product is effectively prevented from adhering to the surface to influence the reaction;

finally, the patterned PZT is obtained after the patterning PZT is cleaned in organic solution such as acetone.

5. The method according to claim 4, wherein in step 5, the metal titanium and the metal platinum layer are bombarded with high-power Ar ions by ion beam etching, and the metal titanium and the metal platinum layer are washed with an organic solvent such as acetone after the etching is completed.

6. The method according to claim 4, wherein in step 6, a mask pattern required for depositing the metal film is prepared by using the photoresist exposure process described in step 4, and the photoresist required in step 6 is a resist to facilitate the lift-off process after depositing the metal film;

Forming a mask pattern with an electrode and a mirror window on the surface of the sample after exposure and development, and then depositing a metal layer on the surface of the sample by using an electron beam evaporation device, wherein the metal layer is deposited to be Ti-20nm and Au-200nm;

after deposition, soaking the sample substrate into acetone, dissolving photoresist, removing redundant metal layers, sequentially putting into isopropanol and absolute ethyl alcohol for ultrasonic cleaning after stripping, taking out the sample, flushing with deionized water, and drying with N2.

7. The method of fabricating a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 4, wherein in step 7, a mask pattern required for etching the device layer is prepared using the photoresist exposure process described in step 4;

using AZ 4620 thick photoresist as a mask, and etching 3 layers of films, namely an insulating layer SiO ₂, a device layer Si and an oxygen-buried layer SiO ₂;

Etching the insulating layer SiO ₂ and the buried oxide layer by adopting a reactive ion beam;

for the piece layer Si, deep reactive ion beam etching for Si is employed;

after the etching operation is completed, an organic solution such as acetone is used for ultrasonic cleaning.

8. The method of claim 1, wherein in step 8, AZ 5214 photoresist is used to uniformly coat the front surface of the substrate for protection, and then an acid-etch-resistant blue film is applied to the front surface;

after the protection of the substrate is finished, immersing the protected substrate in a hydrofluoric acid buffer solution for etching for 1h, then taking out a sample, flushing the surface of the substrate with deionized water to remove residual hydrofluoric acid on the surface, immersing the substrate in acetone, and standing for 5min;

And then immersing the substrate into acetone again, performing ultrasonic cleaning under low power by using an ultrasonic cleaner to completely remove residues such as photoresist, sequentially performing ultrasonic cleaning on the substrate by using isopropanol and absolute ethyl alcohol to remove organic residues, and finally washing the substrate by using deionized water and then drying by using nitrogen.

9. The method according to claim 1, wherein in step 9, the HMDS is baked on the front surface and then spin-coated with photoresist to protect the front surface structure and reduce the permeation effect of vacuum oil;

Baking the photoresist on the front surface at 110 ℃, and then baking and coating HMDS on the back surface and spin-coating the photoresist;

Pre-baking at 100 ℃, exposing, patterning, developing, post-baking and removing residual glue by using a Plasma cleaning instrument;

Slightly coating a layer of vacuum oil on the front surface of the substrate after the spin coating of the substrate is completed, and laminating the vacuum oil on the silicon oxide gasket;

and (3) performing bulk silicon etching by using deep reactive ion beam etching equipment, wherein after the etching is finished, the cyan of the whole silicon oxide is represented as the end of the bulk silicon etching of the device layer, and then, cleaning by using organic solution such as acetone and the like to obtain the final MEMS micro-scanning mirror.

10. A piezoelectric MEMS two-dimensional scanning mirror produced by the method of producing a piezoelectric MEMS two-dimensional scanning mirror according to any one of claims 1 to 9, characterized in that the piezoelectric MEMS two-dimensional scanning mirror comprises an outer frame body of silicon, a mass block, a metal mirror surface, and 4 sets of silicon torsion beams, a metal bottom electrode, a PZT piezoelectric film, and a metal top electrode;

the silicon of the outer frame body is hollowed out as a center the structure is made by etching bulk silicon;

The mass block is arranged at the hollow part of the silicon center of the outer frame body and is made by etching an oxygen-buried layer, a device layer Si and an insulating layer SiO ₂;

the metal mirror surface is formed by depositing a metal layer on the top of the mass block;

The metal lower electrodes are respectively arranged at 4 corners of the outer frame body silicon in an L shape and extend towards the center of the outer frame body silicon, are arranged at the top of the outer frame body silicon through the oxygen burying layer, the device layer Si and the insulating layer and are metal platinum at the top of the insulating layer;

the PZT piezoelectric thin films are respectively arranged at the tops of the corresponding metal lower electrodes;

The metal upper electrodes are respectively metal layers deposited on the tops of the corresponding PZT piezoelectric films;

The silicon torsion beam is of a serpentine structure formed by etching the device layer Si, one end of the silicon torsion beam is connected with the device layer Si below the corresponding metal lower electrode, and the other end of the silicon torsion beam is connected with the device layer Si in the mass block;

The piezoelectric driving MEMS two-dimensional scanning mirror can deform the PZT piezoelectric film and warp after voltage is applied to the metal upper electrode and the metal lower electrode, so that the silicon torsion beam is driven to twist, the middle mass block and the metal mirror face are driven to deflect, and two-dimensional scanning can be realized by applying voltage to 4 groups of different scanning structures.