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

Abstract

The application discloses a MEMS scanning mirror and a processing method thereof. The scanning mirror comprises an outer frame body silicon, a mass block, a metal mirror surface and four groups of silicon torsion beams, a metal lower electrode, a PZT piezoelectric film and a metal upper electrode. The piezoelectric driving MEMS two-dimensional scanning mirror is deformed by applying voltage to the metal upper electrode and the metal lower electrode, so that the PZT piezoelectric film is warped, the silicon torsion beams are twisted, the mass block and the metal mirror surface in the middle are deflected, and two-dimensional scanning can be realized by applying voltage to four groups of different scanning structures. The application drives the reflecting mirror 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, so that the process flow is reduced, the yield of the chip is improved, the integration of the system is improved, and an integrated and high-quality MEMS scanning device is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-electro-mechanical processing, and particularly relates to a piezoelectric driving MEMS two-dimensional scanning mirror and a processing method thereof. BACKGROUND

[0002] The optical scanning mirror realized based on the MEMS technology is one of core components of many optical systems, and plays an important role in optical imaging, laser scanning, projection display, laser radar, free space optical communication and the like. Compared with the traditional optical scanning mirror, the micro mirror with a small volume is integrated on a silicon chip by using the MEMS technology, so that the mass of the movable component is greatly reduced, the rotational inertia of the system is reduced, and the reliability and the mechanical impact resistance of the system are effectively improved.

[0003] At present, the driving modes of the MEMS scanning mirror mainly include electrostatic driving, electromagnetic driving, piezoelectric driving, electrothermal driving and pneumatic driving. Among them, the electrothermal and pneumatic driving has a slow response speed and high power consumption, and the electromagnetic driving needs an external magnet and is affected by electromagnetic interference, which are not suitable for the current development trend of high speed and miniaturization. Most of the MEMS scanning mirrors on the market adopt the electrostatic driving mode, but the required driving voltage of the electrostatic driving type micro scanning mirror is high, and the "pull-down effect" between the plate capacitor electrode plates limits the scanning angle of the micro scanning mirror. The piezoelectric driving type micro scanning mirror has a relatively good stability, and has a large scanning angle and a resonant frequency, but since the elongation of the piezoelectric film is limited, the piezoelectric film is easily broken down when a large driving voltage is applied to obtain displacement, so the quality of the piezoelectric film is required to be high, which also requires a processing technology.

[0004] MEMS scanning mirrors can be categorized as one-dimensional or two-dimensional based on the scanning direction. One-dimensional scanning mirrors have a simpler structure and avoid coupling effects in two directions, enabling relatively higher scanning frequencies and maximum scanning angles. One-dimensional MEMS scanning mirrors, when combined with laser beam expanders or single-axis rotary motors, can achieve two-dimensional beam scanning. Generally speaking, while one-dimensional scanning mirrors can achieve higher scanning angles and frequencies, the overall system is less compact, significantly reducing the advantages of MEMS devices over traditional devices. Two-dimensional scanning mirrors can achieve beam scanning in two directions, leveraging their advantages of high integration and compact footprint. Two-dimensional MEMS scanning mirrors offer three scanning mode combinations: dual-axis resonant, single-axis resonant / single-axis quasi-static, and dual-axis quasi-static. The dual-axis quasi-static mode offers flexible pattern control but has a limited scanning range and lower scanning frequency. The single-axis resonant / single-axis quasi-static mode enables raster scanning, with its resonant axis enabling a larger scanning angle and a more uniform point cloud distribution. Dual-axis resonant scanning can fully exploit the advantages of resonance to achieve the maximum scanning range and frequency. Common two-dimensional scanning mirrors have relatively small surfaces, typically around 1mm. This is because the suspended cantilever beam is unstable due to material stress. If the mirror surface is too large, it can break under torsion during operation, leading to device failure. Summary of the Invention

[0005] The present invention discloses a MEMS scanning mirror design and process design, aiming to at least solve the problems existing in the prior art. The MEMS scanning mirror optimizes the design structure and process flow, can improve the stability of the device, and has good process repeatability.

[0006] Specifically, the present invention discloses a method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror, which comprises the following steps:

[0007] Step S1, preparing an insulating layer SiO2 on an SOI substrate by plasma vapor deposition;

[0008] The SOI substrate comprises a multi-layer structure, which comprises, from bottom to top, a back-sealing SiO2 layer, a bulk silicon layer, a buried oxide layer and a device layer Si;

[0009] Step S2, preparing metal titanium and metal platinum on the upper layer of the insulating layer SiO2 by magnetron sputtering;

[0010] Step S3, preparing a PZT piezoelectric thin film on the surface of the metal film by a sol-gel method;

[0011] Step S4, patterning the PZT piezoelectric film by photolithography and wet etching;

[0012] Step S5, patterning the lower electrode metal film by photolithography and RIE reactive ion beam etching;

[0013] Step S6, depositing the metal film of the device upper electrode and mirror surface by photolithography and electron beam evaporation;

[0014] Step S7, patterning the device layer Si torsional beam by photolithography, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance;

[0015] Step S8, completing the etching of the device back surface back sealing SiO2 by uniform coating and wet etching;

[0016] Step S9, completing the etching of the device bulk silicon by uniform coating and deep reactive ion beam etching, and releasing the stress.

[0017] Further, in step 2, the thickness of the metal titanium is 20 nm, and the thickness of the metal platinum is 200 nm.

[0018] The metal titanium is connected with the insulating layer SiO2, and serves as an adhesion layer between the metal platinum and the insulating layer SiO2.

[0019] Further, in step 3, the PZT film is lead acetate trihydrate, tetra-n-butoxyzirconium and tetrabutyl titanate, which is dissolved into PZT sol by ethylene glycol methyl ether after being synthesized into PZT dry gel, is spin-coated onto the surface of the substrate, and is finally obtained after repeated operations for multiple times under rapid annealing at 700°C, and the thickness of the PZT film is 2 um.

[0020] Further, in step 4, the HMDS adhesion promoter is baked on the surface of the PZT film, which is used to improve the adhesion of the photoresist to the surface of the substrate, and the baking temperature is 135°C.

[0021] Then, the positive photoresist is spin-coated into a film and is baked at 95°C for 90s to remove the excess water in the photoresist, and the substrate under the mask is properly exposed by using a photoetching machine;

[0022] Then, the sample substrate is immersed into the ZX-238 developing solution to react the photoresist in the exposed part, and after being taken out, the surface of the substrate is washed by using deionized water to remove the residual developing solution and is blown dry by using nitrogen, and is placed on a 110°C hot plate for 5 min heating to solidify the photoresist and improve the acid-etching resistance of the photoresist;

[0023] Then, the etching solution for wet etching PZT is configured, and the substrate is continuously alternated in the etching solution-rinsing solution-deionized water to effectively prevent the reaction product from adhering to the surface and affecting the reaction;

[0024] Finally, after being cleaned in an organic solution such as acetone, the patterned PZT is obtained.

[0025] Further, in step 5, the metal titanium and platinum layers are etched by using high-power Ar ion beam bombardment, and after the etching is completed, the sample is cleaned by using an organic solvent such as acetone.

[0026] Further, in step 6, a mask pattern required for depositing a metal thin film is prepared by using the photoresist exposure process described in step 4, and in step 6, a photoresist that is a reverse photoresist is used so as to facilitate the stripping process after the metal thin film is deposited;

[0027] After the exposure and development, a mask pattern with an electrode and a mirror window is formed on the surface of the sample, and then a metal layer is deposited on the surface of the sample by using an electron beam evaporation device, and the metal layer is deposited as Ti-20 nm and Au-200 nm;

[0028] After the deposition, the sample substrate is soaked in acetone to dissolve the photoresist and remove the excess metal layer, and after the stripping is completed, the sample is sequentially placed in isopropanol and anhydrous ethanol for ultrasonic cleaning, and then the sample is taken out and washed with deionized water and dried with N2.

[0029] Further, in step 7, a mask pattern required for etching a device layer is prepared by using the photoresist exposure process described in step 4;

[0030] AZ 4620 thick photoresist is used as a mask, and this time, 3 layers of thin films need to be etched, which are: an insulating layer SiO2, a device layer Si, and a buried oxide layer SiO2;

[0031] For the insulating layer SiO2 and the buried oxide layer, a reactive ion beam etching is used;

[0032] For the device layer Si, a deep reactive ion beam etching for Si is used;

[0033] After the etching operation is completed, an organic solution such as acetone is used for ultrasonic cleaning.

[0034] Further, in step 8, AZ 5214 photoresist is used to uniformly coat the front surface of the substrate for protection, and then an acid-resistant blue film is attached to the front surface;

[0035] After the protection of the substrate is completed, the protected substrate is immersed in a hydrofluoric acid buffer solution for etching for 1 h, and then the sample is taken out and the surface of the substrate is washed with deionized water to remove the residual hydrofluoric acid on the surface, and the substrate is immersed in acetone and left for 5 min;

[0036] Then the substrate is again immersed in acetone and ultrasonic cleaned at a low power by using an ultrasonic cleaning machine, and the photoresist and other residues are completely removed, and then the substrate is sequentially cleaned by using isopropanol and anhydrous ethanol, and the organic residues are removed, and finally the substrate is washed with deionized water and dried with nitrogen.

[0037] Furthermore, in step 9, after HMDS is baked on the front side, photoresist is spin-coated to protect the front side structure and reduce the penetration effect of vacuum oil.

[0038] Bake the front photoresist at 110°C, then bake HMDS on the back and spin-coat photoresist;

[0039] Pre-bake at 100°C, expose the pattern and develop, then post-bake and use a plasma cleaner to remove residual glue;

[0040] After the substrate is coated, a layer of vacuum oil is lightly applied on the front of the substrate, and the substrate is laminated on the silicon oxide gasket through the vacuum oil;

[0041] Use deep reactive ion beam etching equipment to etch the bulk silicon. After the etching is completed, the entire layer will appear blue in color as silicon oxide, indicating that the device layer bulk silicon etching is complete. Then use acetone or other organic solutions to clean it to obtain the final MEMS micro-scanning mirror.

[0042] A piezoelectrically driven MEMS two-dimensional scanning mirror is also provided, comprising an outer silicon frame, a mass block, a metal mirror, four groups of silicon torsion beams, a metal bottom electrode, a PZT piezoelectric film, and a metal top electrode;

[0043] The outer frame body silicon has a central hollow structure and is made by etching the body silicon;

[0044] The mass block is arranged at the hollowed-out center of the outer frame silicon and is made by etching the buried oxide layer, the device layer Si and the insulating layer SiO2;

[0045] The metal mirror is made by depositing a metal layer on top of the mass block;

[0046] The metal bottom electrode is L-shaped and is respectively arranged at the four corners of the outer frame silicon and extends to the center of the outer frame silicon. It is arranged on the top of the outer frame silicon through the buried oxide layer, the device layer Si and the insulating layer, and is the metal platinum on the top of the insulating layer;

[0047] The PZT piezoelectric films are respectively arranged on top of the corresponding metal lower electrodes;

[0048] The metal upper electrodes are respectively metal layers deposited on top of corresponding PZT piezoelectric films;

[0049] The silicon torsion beam is a serpentine structure formed by etching the device layer Si, one end of which is connected to the device layer Si below the corresponding metal bottom electrode, and the other end is connected to the device layer Si in the mass block;

[0050] The piezoelectric drive MEMS two-dimensional scanning mirror is deformed by applying voltage to the metal upper electrode and the metal lower electrode, warping occurs, the silicon torsional beam is twisted, and the middle mass and the metal mirror surface are deflected, and two-dimensional scanning can be realized by applying voltage to four groups of different scanning structures.

[0051] The present application has the following advantages:

[0052] The present application avoids the shortcomings of one-dimensional MEMS scanning mirrors, and uses two-dimensional MEMS scanning mirror design to exert the advantages of high integration and small space of MEMS devices compared with traditional devices.

[0053] The present application uses a biaxial resonant design to achieve the maximum scanning range and frequency.

[0054] The present application reduces and improves the micro-nano processing flow, and reduces the attenuation of the device performance caused by the wet etching process of the device.

[0055] The piezoelectric two-dimensional resonant MEMS micro scanning mirror proposed by the present application deflects the mirror surface by applying voltage to the piezoelectric driving arm, while realizing large deflection angle, the volume of the whole scanning system can be reduced, PZT is used as an angle sensor, the process flow is reduced, the yield of the wafer is improved, and the integration of the system is improved, the device structure, sensing material structure, fixed structure and other structures are optimized, and an integrated MEMS scanning device with high quality factor is formed. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 Front structure diagram of the piezoelectric two-dimensional resonant MEMS micro scanning mirror.

[0057] Figure 2 The whole process flow chart of the micro scanning mirror proposed by the present application.

[0058] Figure 3 The process section view diagram of the micro scanning mirror proposed by the present application.

[0059] Wherein: A. Metal mirror; B1, B2, B3, B4. Metal upper electrode; C1, C2, C3, C4. PZT piezoelectric film; D1, D2, D3, D4. Metal lower electrode; E1, E2, E3, E4. Silicon torsional beam; F. Mass; G. Outer frame silicon;

[0060] 1. Back sealing SiO2; 2. Bulk silicon; 3. Buried oxygen layer silicon oxide; 4. Device layer silicon; 5. Insulating layer silicon oxide; 6. Lower electrode metal film; 7. Piezoelectric film; 8-1. Upper electrode metal film; 8-2. Metal mirror. DETAILED DESCRIPTION

[0061] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are merely exemplary and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solutions of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, and such modifications and replacements fall within the scope of protection of the present invention.

[0062] Figure 1 As shown, the present invention proposes a design and fabrication method for a piezoelectric two-dimensional resonant MEMS micro-scanning mirror that increases mirror size through topology optimization. This solves the problem of small mirror size (typically 1-2mm) in traditional MEMS scanning devices while also achieving a high resonant frequency. Integration into systems such as lidar does not increase the complexity of the optical system, nor does it reduce energy loss and range, and can provide more scanning modes. By integrating structural design, topology optimization, and material optimization, a MEMS scanning device with a large mirror size (3-10mm), high resonant frequency (>2kHz), and high stability (quality factor >200) was developed, further improving the integration of MEMS micro-scanning mirrors into optical systems.

[0063] The scanning mirror is mainly composed of a driving body ( Figure 1 BCD), silicon torsion beam ( Figure 1 Middle E), scanning mirror ( Figure 1 Middle A) and base ( Figure 1 G) structure, the principle of which is that after applying voltage to the upper electrode B and the lower electrode D in the driving body, the piezoelectric functional layer C will be deformed and warped, thereby driving the driving serpentine beam E to twist, and then driving the middle mirror to deflect. By applying voltage to 4 groups of different scanning structures, two-dimensional scanning can be achieved.

[0064] like Figure 2 As shown, specifically, the method for manufacturing the MEMS micro scanning mirror includes the following steps:

[0065] S1, preparing an insulating layer SiO2 on the SOI substrate by plasma vapor deposition;

[0066] S2, preparing metal titanium and metal platinum on the upper layer of the insulating layer SiO2 by magnetron sputtering;

[0067] S3, preparing PZT piezoelectric thin film on the surface of metal film by sol-gel method;

[0068] S4, patterning of PZT piezoelectric film by photolithography and wet etching

[0069] S5, complete the patterning of the lower electrode metal film through photolithography and RIE reactive ion beam etching

[0070] S6, complete the metal film deposition preparation of the device electrode and mirror through photolithography and electron beam evaporation

[0071] S7, completing the patterning of the device layer Si torsion beam by photolithography, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance.

[0072] S8, complete the SiO2 etching on the back of the device by coating and wet etching

[0073] S9, complete the device body silicon etching through coating and deep reactive ion beam etching, and release the stress.

[0074] The following is a detailed introduction to the method for manufacturing the MEMS micro scanning mirror of the present invention with reference to the accompanying drawings.

[0075] First, step S1 is executed. For a customized SOI wafer, its main structure is as follows: Figure 3 As shown in (a), 1 is the back-sealing SiO2, which is used to protect the bulk silicon 2 so that the bottom of the substrate will not be contaminated by the instruments and equipment during the process, 3 is the buried oxide layer, and 4 is the device layer Si. After the substrate is cleaned with standard chemical cleaning, a 200μm SiO2 layer is deposited on the substrate using plasma chemical vapor deposition as an insulating layer, as shown in the figure. Figure 3 As shown in 5 in (b).

[0076] Then, step S2 is performed to deposit a metal thin film on the sample surface using electron beam evaporation. Figure 3 As shown in 6 in (c), in the present invention, Ti-20nm-Pt-200nm is deposited, wherein Ti serves as an adhesion layer between the metal Pt and the insulating layer SiO2. The substrate structure after deposition is as follows Figure 3 (c) shown.

[0077] Then, step S3 is performed to synthesize lead zirconate titanate (PZT) on the surface of the metal film using a sol-gel method. Figure 3 As shown in Figure 7 (d), the previously deposited Pt has excellent thermal stability, serving as both a good electrode layer and a barrier to interdiffusion between the substrate and the ferroelectric material. PZT thin films were prepared using a sol-gel method. Lead acetate trihydrate, tetra-n-butoxyzirconium, and tetrabutyl titanate were used as the raw materials. After boiling to form a PZT xerogel, the mixture was dissolved in ethylene glycol methyl ether to form a PZT sol. This was then spin-coated onto the substrate surface and rapidly annealed at 700°C. This process was repeated multiple times to produce a PZT thin film approximately 2 μm thick.

[0078] Then execute step S4, as Figure 3(e) As shown, HMDS adhesion promoter is baked on the surface of the PZT substrate to improve the adhesion of the photoresist to the substrate surface. The baking temperature is 135°C. Then, a positive photoresist (optionally AZ 5214) is spin-coated to form a film and baked at 95°C for 90s to remove excess water in the photoresist. The substrate under the mask is exposed to light using a photolithography machine. Then, the sample substrate is immersed in ZX-238 developer to react away the exposed part of the photoresist. After removal, the substrate surface is rinsed with deionized water to remove residual developer and dried with nitrogen. The substrate is placed on a hot plate at 110°C for 5 min to cure the photoresist and improve the acid-etching resistance of the photoresist. Then, an etching solution for wet etching PZT is prepared. In this example, a mixture of HCl and HF is used as the PZT etching solution, in which HCl is used to react with Pb and Ti, and HF is used to remove Ti and Cr. Since the content of Pb in the PZT film is usually high, the proportion of HCl in the etching solution is usually much higher than that of HF. In the experiment, the etching solution is prepared according to water: hydrochloric acid: hydrofluoric acid = 70:30:0.5, and dilute hydrochloric acid is used as a rinsing solution according to water: hydrochloric acid = 40:10, which facilitates further etching of Pb. The substrate is continuously rotated among the etching solution, the rinsing solution, and deionized water to effectively prevent the reaction products from adhering to the surface and affecting the reaction. After cleaning in an organic solvent such as acetone, a patterned PZT is finally obtained, and the pattern can be seen as Figure 1 In which C1, C2, C3, C4 correspond to the PZT piezoelectric film, and the PZT film in the remaining areas is etched.

[0079] Then step S5 is performed, and the mask pattern required for etching the metal film is prepared using the photoresist exposure process described in S4, and finally a structure as shown in Figure 1 In which D1, D2, D3, D4 correspond to the lower metal electrode, and the Pt in the remaining areas is etched. In order to give the position of the lower electrode test and connection and prevent the upper and lower electrodes from being conductive, the D area is designed as an "L" shape, and the long end is slightly larger than the C area which is the PZT piezoelectric film. The shape after etching is as shown in Figure 3 (f) As shown, the main metal to be etched is Pt / Ti. Since Pt is an inert metal and does not react with most reaction gases, it is etched using high-power Ar ion bombardment in ion beam etching. Ti, as an adhesion layer, is highly active and easy to remove, and its thickness is only about 20 nm, so it can be removed together in ion beam etching. After etching, organic solvents such as acetone are used for cleaning.

[0080] Then step S6 is performed, and Figure 3(g) The mask pattern required for depositing the metal film is prepared using the photoresist exposure process described in S4, and it should be noted that the photoresist used in this step is the reverse photoresist (optional AZ 2070), which is more conducive to the stripping process after the metal film is deposited. After exposure and development, a mask pattern with electrodes and mirror windows is formed on the sample surface, and then a metal layer is deposited on the sample surface using an electron beam evaporation device. This time, Ti-20 nm-Au-200 nm is deposited, as shown in Figure 1 The deposition area is B1-B4 and A, as shown in

[0081] Then step S7 is performed, as shown in Figure 3 (h) The mask pattern required for etching the device layer is prepared using the photoresist exposure process described in S4, and the area to be etched is Figure 1 The main purpose of etching the white space in the middle of the silicon torsional beam E1-E4 is to form a suspended silicon torsional beam, and also to etch the BCD part and the mass F part in the middle, so that the middle mirror part is connected only through the E silicon torsional beam E1-E4 and the BCD device functional layer. The buried oxide layer, device layer Si, and insulating layer SiO2 under the projection area of the metal lower electrode are all retained as support structures. The silicon torsional beam E1-E4 only includes the device layer Si, and the buried oxide layer and insulating layer SiO2 on both sides are removed by etching. The mass F is composed of the buried oxide layer, device layer Si, and insulating layer SiO2 under the projection area of the metal mirror.

[0082] Since the etching depth this time is deep (>20um), AZ 5214 cannot play a good role as a mask, so AZ4620 thick photoresist is used as a mask. This time, 3 layers of film need to be etched: insulating layer SiO2 (200nm), device layer Si (20um), and buried oxide layer SiO2 (2um). For SiO2, reactive ion beam etching is used, and for Si, deep reactive ion beam etching for Si is used. Deep reactive ion beam etching mainly uses gases such as SF6 to react with Si and perform passivation and other operations, with good etching selectivity and aspect ratio. After etching, ultrasonic cleaning with organic solvents such as acetone is performed.

[0083] Then step S8 is performed, as shown in Figure 3(i) as shown, using AZ 5214 photoresist to coat the front surface of the substrate for protection, and then attaching an acid-etch-resistant blue film to the front surface. The main purposes of coating for protection are: first, to prevent the substrate surface from contacting the BOE hydrofluoric acid buffer, because the hydrofluoric acid will react to cause damage to the PZT structure and the buried oxygen layer; second, to prevent the blue film from directly contacting the device surface, so as to prevent possible effects of blue film residues on the substrate. After completing the protection of the substrate, the hydrofluoric acid buffer is configured, and in this experiment, the NH4F:HF = 4; 1 hydrofluoric acid buffer is used to etch the back-sealed SiO2. The protected substrate is immersed in the hydrofluoric acid buffer for etching for 1 h, and then the sample is taken out to wash the surface of the substrate with deionized water to remove the surface residual hydrofluoric acid. The substrate is immersed in acetone and left to stand for 5 min. Since the photoresist is gradually dissolved by the reaction, the blue film will naturally separate from the substrate. Then the substrate is immersed in acetone again and cleaned with an ultrasonic cleaner at low power, so as to completely remove the photoresist and other residues. Then the substrate is sequentially cleaned with isopropyl alcohol and anhydrous ethanol to remove organic residues. Finally, the substrate is washed with deionized water and dried with nitrogen.

[0084] Finally, step S9 is executed, as shown in Figure 3 (j) as shown, considering that the back surface deep silicon etching needs to be protected and laminated on the front surface, and the overall coating process needs to be changed. After cleaning the substrate, HMDS is baked on the front surface, and then AZ 5214 photoresist is spin-coated to protect the structure on the front surface, which can also reduce the influence of vacuum oil penetration. The photoresist on the front surface is dried at 110°C, and then HMDS is baked on the back surface (i.e. the surface to be etched) and AZ 4620 photoresist is spin-coated. Pre-baking is performed at 100°C, and then the pattern is exposed, developed, post-baked, and cleaned with a Plasma plasma cleaner to remove residues. After completing the coating of the substrate, a layer of vacuum oil is lightly coated on the front surface of the substrate, and the laminated substrate is laminated on the silicon pad through the vacuum oil. Then, the deep reactive ion beam etching equipment is used for bulk silicon etching. Different from S7, the etching depth is deeper (400 um) and the area is larger. After etching is completed, the substrate presents a blue color of silicon oxide, which means that the bulk silicon etching of the Si layer is completed. Then, the final MEMS micro scanning mirror can be obtained by cleaning with an organic solvent such as acetone.

[0085] The above is only a specific step of the present application, and does not constitute any limitation on the protection scope of the present application; any technical solution formed by equivalent transformation or equivalent replacement falls within the protection scope of the present application; and the part not described in detail in the present application belongs to the known technology of those skilled in the art.

Claims

1. A method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror, characterized in that: The piezoelectric driven MEMS two-dimensional scanning mirror processing method comprises the following steps: Step S1, preparing an insulating layer SiO2 on an SOI substrate by plasma vapor deposition; The SOI substrate comprises a multi-layer structure, which comprises, from bottom to top, a back-sealing SiO2 layer, a bulk silicon layer, a buried oxide layer and a device layer Si; Step S2, preparing metal titanium and metal platinum on the upper layer of the insulating layer SiO2 by magnetron sputtering; Step S3, preparing a PZT piezoelectric thin film on the surface of the metal film by a sol-gel method; Step S4, patterning the PZT piezoelectric film by photolithography and wet etching; Step S5, patterning the lower electrode metal film by photolithography and RIE reactive ion beam etching; Step S6, completing the metal film deposition preparation of the device upper electrode and mirror by photolithography and electron beam evaporation; Step S7, completing the patterning of the device layer Si torsion beam by photolithography, deep reactive ion beam etching and reactive ion beam etching to release the buried oxide layer in advance; Step S8, etching the back-sealed SiO2 on the back of the device by coating and wet etching; Step S9, completing the etching of the device body silicon by coating and deep reactive ion beam etching, and releasing the stress; In step S4, a thin film of HMDS adhesion promoter is baked on the PZT surface to improve the adhesion between the photoresist and the substrate surface. The baking temperature is 135°C. Then, a positive photoresist is spin-coated to form a film and baked at 95°C for 90 seconds to remove excess moisture in the photoresist. The substrate under the mask is properly exposed using a photolithography machine. The sample substrate was then immersed in ZX-238 developer to react with the exposed portion of the photoresist. After removal, the substrate surface was rinsed with deionized water to remove the residual developer and dried with nitrogen. The substrate was then placed on a hot plate at 110°C for 5 minutes to cure the photoresist and improve its acid resistance. Then, an etching solution for wet etching of PZT is prepared and the substrate is rotated in the etching solution, the rinsing solution and the deionized water to effectively prevent the reaction products from adhering to the surface and affecting the reaction. Finally, the patterned PZT was obtained after cleaning in an acetone organic solution.

2. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S2, the thickness of the titanium metal is 20 nm, and the thickness of the platinum metal is 200 nm; The metallic titanium is connected to the insulating layer SiO2 and serves as an adhesion layer between the metallic platinum and the insulating layer SiO2.

3. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S3, the PZT piezoelectric film is lead acetate trihydrate, tetra-n-butoxy zirconium and tetrabutyl titanate, which are boiled into PZT dry gel and then dissolved into PZT sol by ethylene glycol methyl ether, spin-coated onto the substrate surface and rapidly annealed at 700°C. After repeated operations, a PZT film with a thickness of 2 μm is finally obtained.

4. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S5, ion beam etching is used to bombard the metal titanium and metal platinum layers with high-power Ar ions for etching, and after the etching is completed, the layers are cleaned with acetone organic solvent.

5. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S6, the mask pattern required for depositing the metal film is prepared using the photoresist exposure process described in step S4. The photoresist required to be used in step S6 is a reverse photoresist to facilitate the stripping process after the metal film is deposited. After exposure and development, a mask pattern with electrodes and mirror windows was formed on the sample surface. Then, an electron beam evaporation device was used to deposit a metal layer on the sample surface. The metal layer was deposited with Ti-20nm and Au-200nm. After deposition, the sample substrate was immersed in acetone to dissolve the photoresist and remove the excess metal layer. After stripping, it was placed in isopropyl alcohol and anhydrous ethanol for ultrasonic cleaning. The sample was then taken out, rinsed with deionized water, and blown dry with N2.

6. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S7, the photoresist exposure process described in step S4 is used to prepare a mask pattern required for etching the device layer; Using AZ 4620 thick photoresist as a mask, this time we need to etch three thin films: the insulating layer SiO2, the device layer Si, and the buried oxide layer SiO2; Reactive ion beam etching is used for the insulating layer SiO2 and buried oxide layer; For the Si layer, deep reactive ion beam etching for Si is used; After the etching operation is completed, ultrasonic cleaning is performed using an acetone organic solution.

7. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step S8, AZ 5214 photoresist is used to coat the front surface of the substrate for protection, and then an acid-resistant blue film is applied to the front surface; After the substrate is protected, the protected substrate is immersed in hydrofluoric acid buffer and etched for 1 hour. The sample is then taken out and the substrate surface is rinsed with deionized water to remove residual hydrofluoric acid on the surface. The substrate is then immersed in acetone and allowed to stand for 5 minutes. The substrate was then immersed in acetone again and ultrasonically cleaned at low power using an ultrasonic cleaner to completely remove the photoresist residue. The substrate was then ultrasonically cleaned using isopropyl alcohol and anhydrous ethanol in sequence to remove organic residues. Finally, the substrate was rinsed with deionized water and blown dry with nitrogen.

8. The method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, wherein: In step S9, after HMDS is baked on the front surface, photoresist is spin-coated to protect the front surface structure and reduce the penetration effect of vacuum oil; Bake the front photoresist at 110°C, then bake HMDS on the back and spin-coat photoresist; Pre-bake at 100°C, expose the pattern and develop, then bake and use a plasma cleaner to remove residual glue; After the substrate is coated, a layer of vacuum oil is lightly applied on the front of the substrate, and the substrate is laminated on the silicon oxide gasket through the vacuum oil; Use deep reactive ion beam etching equipment to etch the bulk silicon. After the etching is completed, the entire layer appears cyan with silicon oxide, indicating that the device layer bulk silicon etching is complete. Then use acetone organic solution to clean it to obtain the final MEMS micro-scanning mirror.

9. A piezoelectrically driven MEMS two-dimensional scanning mirror manufactured according to the method for manufacturing a piezoelectrically driven MEMS two-dimensional scanning mirror according to any one of claims 1 to 8, characterized in that: The piezoelectrically driven MEMS two-dimensional scanning mirror comprises an outer silicon frame, a mass block, a metal mirror, four groups of silicon torsion beams, a metal bottom electrode, a PZT piezoelectric film and a metal top electrode; The outer frame body silicon has a central hollow structure and is made by etching the body silicon; The mass block is arranged at the hollowed-out center of the outer frame silicon and is made by etching the buried oxide layer, the device layer Si and the insulating layer SiO2; The metal mirror is made by depositing a metal layer on top of the mass block; The metal bottom electrode is L-shaped and is respectively arranged at the four corners of the outer frame silicon and extends to the center of the outer frame silicon. It is arranged on the top of the outer frame silicon through the buried oxide layer, the device layer Si and the insulating layer, and is the metal platinum on the top of the insulating layer; The PZT piezoelectric films are respectively arranged on top of the corresponding metal lower electrodes; The metal upper electrodes are respectively metal layers deposited on top of corresponding PZT piezoelectric films; The silicon torsion beam is a serpentine structure formed by etching the device layer Si, one end of which is connected to the device layer Si below the corresponding metal bottom electrode, and the other end is connected to the device layer Si in the mass block; The piezoelectric-driven MEMS two-dimensional scanning mirror causes the PZT piezoelectric film to deform and warp after applying voltage to the metal upper electrode and the metal lower electrode, thereby causing the silicon torsion beam to twist, and then causing the middle mass block and metal mirror to deflect. By applying voltage to four groups of different scanning structures, two-dimensional scanning is achieved.

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