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

Abstract

The invention discloses an MEMS scanning mirror and a processing method thereof. The scanning mirror comprises outer frame body silicon, a mass block, a metal mirror surface, four groups of silicon torsion beams, a metal lower electrode, a PZT piezoelectric film and a metal upper electrode, according to the piezoelectric driving MEMS two-dimensional scanning mirror, after voltage is applied to the metal upper electrode and the metal lower electrode, the PZT piezoelectric film is deformed and warped, so that the silicon torsion beam is driven to be twisted, the middle mass block and the metal mirror surface are driven to deflect, voltage is applied to the four groups of different scanning structures, and the piezoelectric driving MEMS two-dimensional scanning mirror is obtained. And two-dimensional scanning can be realized. Voltage is applied to the piezoelectric driving arm to drive the reflecting mirror surface to deflect, the size of the whole scanning system can be reduced while a large deflection angle is achieved, PZT is used as an angle sensor, the technological process is reduced, the tape-out yield and the integration level of the system are improved, and an integrated MEMS scanning device with a high quality factor is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-electromechanical machining, and in particular to a piezoelectrically driven MEMS two-dimensional scanning mirror and a machining method thereof. Background Art

[0002] Optical scanning mirrors based on MEMS technology are one of the core components of many optical systems, and play an important role in optical imaging, laser scanning, projection display, laser radar, free space optical communication, etc. Compared with traditional optical scanning mirrors, the use of MEMS technology to integrate compact micro-mirrors on silicon-based chips greatly reduces the mass of movable parts, reduces the rotational inertia of the system, and effectively improves the reliability and mechanical shock resistance of the system.

[0003] At present, the driving modes of MEMS scanning mirrors mainly include electrostatic drive, electromagnetic drive, piezoelectric drive, electrothermal drive and pneumatic drive. Among them, the response speed of electrothermal and pneumatic drive is too slow and the power consumption is high. Electromagnetic drive requires external magnets and is subject to electromagnetic interference. They are not suitable for the current development trend of high speed and miniaturization. Most MEMS scanning mirrors on the market use electrostatic drive, but the driving voltage required for electrostatically driven micro-scanning mirrors is relatively high and there is a "pull-down effect" between the electrode plates of the flat capacitor, which limits the scanning angle of the micro-scanning mirror. Piezoelectric driven micro-scanning mirrors have relatively good stability, and have a large scanning angle and resonant frequency. However, due to the limited elongation of the piezoelectric film, it is easy to break down the piezoelectric film when a large driving voltage is applied to obtain displacement. Therefore, the quality requirements of the piezoelectric film are high, which also puts forward requirements for the processing technology.

[0004] MEMS scanning mirrors can be divided into one-dimensional scanning mirrors and two-dimensional scanning mirrors according to the dimension of the scanning direction. Among them, the structure of the one-dimensional scanning mirror is relatively simple, and there is no coupling effect in two directions, which can achieve a relatively higher scanning frequency and maximum scanning angle. The one-dimensional MEMS scanning mirror cooperates with a laser beam expansion lens or a single-axis rotary motor to realize two-dimensional beam scanning. In general, although the one-dimensional scanning mirror can achieve a higher scanning angle and scanning frequency, the overall system is not compact enough, which greatly weakens the advantages of MEMS devices over traditional devices. The two-dimensional scanning mirror can realize beam scanning in two directions, which can give full play to the advantages of high integration and small space occupation. The two-dimensional MEMS scanning mirror has a combination of three scanning modes, namely: dual-axis resonant type, one-axis resonant type and one-axis quasi-static type, and dual-axis quasi-static type. Among them, the dual-axis quasi-static type can realize flexible pattern control, but the scanning range is small and the scanning frequency is low. The one-axis resonant type and one-axis quasi-static type can realize the grating scanning mode, and its resonant axis can achieve a larger scanning angle and a relatively uniform point cloud distribution. The dual-axis resonant scanning can give full play to the advantages of resonance and achieve the maximum scanning range and frequency. The common two-dimensional scanning mirror is small, usually about 1 mm in size. This is because the suspended cantilever beam is unstable due to the stress of the material. If the mirror size is too large, it will break under the torsion during operation, and then the device will fail. 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 processing a piezoelectrically driven MEMS two-dimensional scanning mirror, and the method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror 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, a bulk silicon, 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 film on the surface of the metal film by a sol-gel method;

[0011] Step S4, completing the patterning of 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, completing the metal film deposition preparation of the upper electrode and the mirror of the device by photolithography and electron beam evaporation;

[0014] 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;

[0015] Step S8, etching the back-sealed SiO2 on the back of the device by coating and wet etching;

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

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

[0018] 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.

[0019] Furthermore, in step 3, the PZT film is lead acetate trihydrate, tetra-n-butoxyzirconium 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 um is finally obtained.

[0020] Furthermore, in step 4, a HMDS adhesion promoter is thinly coated on the PZT surface to improve the adhesion between the photoresist and the substrate surface, and the baking temperature is 135° C.;

[0021] 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, and a photolithography machine is used to properly expose the substrate under the mask;

[0022] Then, the sample substrate was immersed in ZX-238 developer to react the exposed part of the photoresist, and after being taken out, the substrate surface was rinsed with deionized water to remove the residual developer and dried with nitrogen, and then placed on a 110°C hot plate for 5 minutes to cure the photoresist and improve the acid corrosion resistance of the photoresist;

[0023] Then, an etching solution for wet etching of PZT is prepared and the substrate is continuously rotated in the etching solution-rinsing solution-deionized water to effectively prevent the reaction products from adhering to the surface and affecting the reaction;

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

[0025] Furthermore, in step 5, 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, organic solvents such as acetone are used for cleaning.

[0026] Furthermore, in step 6, the mask pattern required for depositing the metal film is prepared using the photoresist exposure process described in step 4. The photoresist required to be used in step 6 is a reverse photoresist to facilitate the stripping process after the metal film is deposited.

[0027] 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 as Ti-20nm and Au-200nm.

[0028] After deposition, the sample substrate was immersed in acetone to dissolve the photoresist and remove the excess metal layer. After stripping, it was ultrasonically cleaned in isopropanol and anhydrous ethanol in turn. The sample was then taken out, rinsed with deionized water and dried with N2.

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

[0030] Using AZ 4620 thick photoresist as a mask, this time we need to etch three layers of thin films, namely: insulating layer SiO2, device layer Si and buried oxide layer SiO2;

[0031] Reactive ion beam etching is used for the insulating layer SiO2 and buried oxide layer;

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

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

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

[0035] After the protection of the substrate is completed, the protected substrate is immersed in a hydrofluoric acid buffer solution and etched for 1 hour. Then the sample is taken out and the substrate surface is rinsed with deionized water to remove the residual hydrofluoric acid on the surface. The substrate is immersed in acetone and allowed to stand for 5 minutes.

[0036] The substrate was then immersed in acetone again and ultrasonically cleaned at low power using an ultrasonic cleaner to completely remove photoresist and other residues. The substrate was then ultrasonically cleaned using isopropyl alcohol and anhydrous ethanol in turn to remove organic residues. Finally, the substrate was rinsed with deionized water and blown dry with nitrogen.

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

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

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

[0040] After the substrate is coated with the glue, 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 cyan in color as silicon oxide, indicating that the etching of the bulk silicon of the device layer 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, the piezoelectrically driven MEMS two-dimensional scanning mirror comprising an outer frame body silicon, a mass block, a metal mirror surface, four groups of silicon torsion beams, a metal lower electrode, a PZT piezoelectric film and a metal upper electrode;

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

[0044] The mass block is arranged at the hollowed-out center of the silicon of the outer frame body 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 arranged at the four corners of the outer frame silicon and extends to the center of the outer frame silicon, and 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 the top of the 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-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 the metal mirror to deflect. Two-dimensional scanning can be achieved by applying voltage to four groups of different scanning structures.

[0051] The beneficial effects achieved by the present invention are:

[0052] The present invention avoids the disadvantage that the one-dimensional MEMS scanning mirror is not compact enough, and uses a two-dimensional MEMS scanning mirror design to give full play to the advantages of high integration and small space brought by MEMS devices to the system compared with traditional devices.

[0053] The present invention uses a dual-axis resonant design to achieve maximum scanning range and frequency.

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

[0055] The piezoelectric two-dimensional resonant MEMS micro-scanning mirror proposed in the present invention drives the reflective mirror surface to deflect by applying voltage to the piezoelectric drive arm, thereby achieving a large deflection angle while reducing the volume of the entire scanning system. PZT is used as an angle sensor, which reduces the process flow, improves the wafer yield and system integration, and specifically optimizes the device execution structure, sensor material structure, fixed support structure and other structures to form an integrated, high-quality factor MEMS scanning device. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0057] Figure 2 The overall flow chart of the micro-scanning mirror process proposed by the present invention.

[0058] Figure 3 Schematic diagram of the cross-section of the micro-scanning mirror process proposed by the present invention.

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

[0060] 1. Back seal SiO2; 2. Bulk silicon; 3. Buried oxide 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 in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only 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 solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0062] Figure 1 As shown, the present invention proposes a design and processing method for a piezoelectric two-dimensional resonant MEMS micro-scanning mirror that increases the mirror size by a topology optimization method, which solves the problem of small mirror size (typically 1-2mm) of traditional MEMS scanning devices, and at the same time has a high resonant frequency. When integrated into systems such as laser radar, it will not increase the complexity of the optical system and will not lose energy and reduce the range, and can provide more scanning modes. A MEMS scanning device with a large mirror size (3-10mm), a high resonant frequency (>2KHz), and high stability (quality factor>200) is developed by comprehensive structural design, topology optimization, and material optimization, further improving the integration of MEMS micro-scanning mirrors in 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 a 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 a PZT piezoelectric film on the surface of the metal film by a sol-gel method;

[0068] S4, PZT piezoelectric film patterning is completed 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 upper 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, completing the device body silicon etching by coating and deep reactive ion beam etching, and releasing the stress.

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

[0075] First, step S1 is performed. 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 2 bulk silicon so that the bottom of the substrate will not be contaminated by instruments and equipment during the process, 3 is the buried oxide layer, and 4 is the device layer Si. After the substrate is subjected to standard chemical cleaning, a 200um SiO2 layer is deposited on the substrate using plasma chemical vapor deposition as an insulating layer, as shown in FIG. Figure 3 As shown in (b) 5.

[0076] Then, step S2 is performed to deposit a metal film on the sample surface using electron beam evaporation. Figure 3 (c) As shown in 6, 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, and the substrate structure after deposition is as follows Figure 3 (c) as 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 (d) 7, the previously deposited Pt has good thermal stability and is not only a good electrode layer, but also a barrier layer for the mutual diffusion of the substrate and the ferroelectric material. The PZT film was prepared by the sol-gel method. The experimental raw materials selected were lead acetate trihydrate, tetra-n-butoxy zirconium and tetrabutyl titanate. After being boiled into PZT dry gel, it was dissolved into PZT sol by ethylene glycol methyl ether, spin-coated onto the substrate surface and rapidly annealed at 700°C. After repeated operations for many times, a PZT film with a thickness of about 2um was finally obtained.

[0078] Then execute step S4, such as Figure 3As shown in (e), HMDS adhesion promoter is baked on the surface of substrate PZT to improve the adhesion between photoresist and substrate surface, and the baking temperature is 135°C. Then, positive photoresist (AZ 5214 is optional) 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 properly exposed using a photolithography machine. Then, the sample substrate is immersed in ZX-238 developer to react the exposed part of the photoresist. After taking it out, the substrate surface is rinsed with deionized water to remove the residual developer and the substrate is blown dry with nitrogen. It is placed on a hot plate at 110°C for 5 minutes to heat to cure the photoresist and improve the acid corrosion resistance of the photoresist. Then, an etching solution for wet etching of PZT is prepared. In this example, a mixture of HCl and HF is used as the PZT thin film etching solution, in which HCl is used to react with Pb and Ti, and HF is used to remove Ti and Cr. Since PZT thin films often contain a high content of Pb, the proportion of HCl in the etching solution is generally much higher than that of HF. In the experiment, the etching solution was prepared according to water: hydrochloric acid: hydrofluoric acid = 70:30:0.5, and dilute hydrochloric acid was used as a rinse solution according to water: hydrochloric acid = 40:10 to facilitate further etching of Pb. The substrate was continuously rotated in the etching solution-rinsing solution-deionized water to effectively prevent the reaction products from adhering to the surface and affecting the reaction. After cleaning in organic solutions such as acetone, a patterned PZT was finally obtained, as shown in the figure. Figure 1 In the figure, the areas corresponding to C1, C2, C3, and C4 are PZT piezoelectric films, and the PZT films in the remaining areas are all corroded.

[0079] Then, step S5 is performed to prepare a mask pattern required for etching the metal film using the photoresist exposure process described in S4, and finally form a Figure 1 The corresponding areas of D1, D2, D3, and D4 are metal lower electrodes, and the Pt in the rest of the areas are etched away. To prevent the location of the lower electrode test and connection and to prevent the upper and lower electrodes from conducting, the D area is designed to be "L" shaped and its long end is slightly larger than that of the C area, which is the PZT piezoelectric film. The shape after etching is as follows Figure 3 As shown in (f), the metal that needs to be etched is Pt / Ti. Since metal Pt is an inert metal and does not react with most reactive gases, ion beam etching is used to bombard it with high-power Ar ions. Ti as an adhesion layer is highly active and easy to remove. At the same time, its thickness is only about 20nm, so it can be removed together with the ion beam etching. After etching, it is cleaned with organic solvents such as acetone.

[0080] Then execute step S6, such as Figure 3As shown in (g), the photoresist exposure process described in S4 is used to prepare the mask pattern required for depositing the metal film. It should be noted that the photoresist required to be used in this step is a reverse photoresist (optionally AZ 2070), which is more conducive to the stripping process after the deposition of the metal film. After exposure and development, a mask pattern with electrodes and mirror windows is formed on the sample surface. Then, an electron beam evaporation device is used to deposit a metal layer on the sample surface. This time, Ti-20nm-Au-200nm is deposited, as shown in FIG. Figure 1 As shown, the deposition areas are B1~B4 and A, where B1~B4 are used as the upper electrodes of the device. To prevent the upper and lower electrodes from being conductive, the B area is slightly smaller than the C area; the A area is the mirror surface of the device. After deposition, the sample substrate is soaked in acetone to dissolve the photoresist and remove the excess metal layer. After stripping, it is placed in isopropanol and anhydrous ethanol for ultrasonic cleaning in turn. Then the sample is taken out, rinsed with deionized water and blown dry with N2.

[0081] Then execute step S7, such as Figure 3 As shown in (h), the mask pattern required for etching the device layer is prepared using the photoresist exposure process described in S4, where the area to be etched is Figure 1 The white blank area in the middle is mainly used 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. At the same time, the BCD part and the middle mass block F are also etched, so that the middle mirror part is only connected to the BCD device functional layer through the E silicon torsion beams E1 to E4. The three layers of buried oxide layer, device layer Si and insulating layer SiO2 below the metal lower electrode projection area are retained as support structures. The silicon torsion beams E1 to E4 only include the device layer Si, and the buried oxide layer and insulating layer SiO2 on the upper and lower sides are removed by etching. The mass block F is composed of three layers of buried oxide layer, device layer Si and insulating layer SiO2 below the metal mirror projection area.

[0082] Since the etching depth is deep (>20um), AZ 5214 can hardly play a good role as a mask, so AZ4620 thick photoresist is used as a mask. Three layers of thin films need to be etched this time, namely: insulating layer SiO2 (200nm), device layer Si (20um) and buried oxide layer SiO2 (2um). Reactive ion beam etching is used for SiO2, and deep reactive ion beam etching for Si is used for Si. Deep reactive ion beam etching mainly uses SF6 and other gases to react and passivate Si, and has a good etching selectivity and aspect ratio. After the etching operation is completed, use acetone and other organic solutions for ultrasonic cleaning.

[0083] Then execute step S8, as Figure 3As shown in (i), AZ 5214 photoresist is used to coat the front side of the substrate for protection, and then an acid-resistant blue film is attached to the front side. The coating protection has two main purposes. First, it is to prevent the substrate surface from contacting with the BOE hydrofluoric acid buffer, because hydrofluoric acid will react and destroy the PZT structure and buried oxide layer. Second, it can prevent the blue film from directly contacting the device surface to prevent possible blue film residue from affecting the substrate. After completing the protection of the substrate, prepare hydrofluoric acid buffer. In this experiment, 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 hour. Then the sample is taken out and the surface of the substrate is rinsed with deionized water to remove the residual hydrofluoric acid on the surface. The substrate is immersed in acetone and allowed to stand for 5 minutes. As 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 an ultrasonic cleaner is used to perform ultrasonic cleaning at low power to completely remove the photoresist and other residues. Then, isopropanol and anhydrous ethanol are used to ultrasonically clean the substrate in turn to remove organic residues. Finally, the substrate is rinsed with deionized water and blown dry with nitrogen.

[0084] Finally, step S9 is executed. Figure 3 As shown in (j), considering that the deep silicon etching on the back side requires protection of the front side and lamination, the overall process of photoresist coating needs to be changed. After the substrate is cleaned, HMDS is first baked on the front side and then AZ 5214 photoresist is spin-coated to protect the structure on the front side and reduce the penetration effect of vacuum oil. The photoresist on the front side is dried at 110°C, and then HMDS is baked on the back side (i.e. the side to be etched) and AZ 4620 photoresist is spin-coated. Pre-bake at 100°C, expose the pattern and develop, then post-bake and use a Plasma plasma cleaner to remove the residual glue. After the substrate is coated with photoresist, a layer of vacuum oil is lightly applied on the front side of the substrate, and the wafer is laminated on the silicon oxide gasket through the vacuum oil. Then, a deep reactive ion beam etching device is used to etch the bulk silicon. The difference from S7 is that this time the etching depth is deeper (400um) and the area is larger. After the etching is completed, the entire surface appears cyan in color as silicon oxide, indicating that the Si layer bulk silicon etching is complete. Then, it is cleaned with organic solutions such as acetone to obtain the final MEMS micro-scanning mirror.

[0085] The above are only specific steps of the present invention and do not constitute any limitation to the protection scope of the present invention; any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention; some parts not elaborated in detail in the present invention belong to the known technologies 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, a bulk silicon, 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 film on the surface of the metal film by a sol-gel method; Step S4, completing the patterning of 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 upper electrode and the mirror of the device 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.

2. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step 2, 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 processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step 3, the PZT film is lead acetate trihydrate, tetra-n-butoxyzirconium 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 um is finally obtained.

4. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step 4, a HMDS adhesion promoter is thinly coated on the PZT surface to improve the adhesion between the photoresist and the substrate surface, and 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, and a photolithography machine is used to properly expose the substrate under the mask; Then, the sample substrate was immersed in ZX-238 developer to react the exposed part of the photoresist, and after being taken out, the substrate surface was rinsed with deionized water to remove the residual developer and dried with nitrogen, and then placed on a 110°C hot plate for 5 minutes to cure the photoresist and improve the acid corrosion resistance of the photoresist; Then, an etching solution for wet etching of PZT is prepared and the substrate is continuously rotated in the etching solution-rinsing solution-deionized water to effectively prevent the reaction products from adhering to the surface and affecting the reaction; Finally, after cleaning in an organic solution such as acetone, the patterned PZT is finally obtained.

5. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 4, characterized in that: In step 5, 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, organic solvents such as acetone are used for cleaning.

6. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 4, characterized in that: In step 6, the mask pattern required for depositing the metal film is prepared using the photoresist exposure process described in step 4. The photoresist required to be used in step 6 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 as 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 ultrasonically cleaned in isopropanol and anhydrous ethanol in turn. The sample was then taken out, rinsed with deionized water and dried with N2.

7. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 4, characterized in that: 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, this time we need to etch three layers of thin films, namely: insulating layer SiO2, device layer Si and 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 organic solution such as acetone.

8. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step 8, AZ 5214 photoresist is used to coat the front side of the substrate for protection, and then an acid-resistant blue film is attached to the front side; After the protection of the substrate is completed, the protected substrate is immersed in a hydrofluoric acid buffer solution and etched for 1 hour, then the sample is taken out and the substrate surface is rinsed with deionized water to remove the residual hydrofluoric acid on the surface, and the substrate is 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 photoresist and other residues. The substrate was then ultrasonically cleaned using isopropyl alcohol and anhydrous ethanol in turn to remove organic residues. Finally, the substrate was rinsed with deionized water and blown dry with nitrogen.

9. The method for processing a piezoelectrically driven MEMS two-dimensional scanning mirror according to claim 1, characterized in that: In step 9, after HMDS is baked on the front side, photoresist is spin-coated to protect the structure on the front side and reduce the penetration effect of vacuum oil; Bake the photoresist on the front side at 110°C, then bake HMDS and spin-coat photoresist on the back side; Pre-bake at 100°C, expose patterning and develop, then post-bake and use a plasma cleaning machine to remove residual glue; After the substrate is coated with the glue, 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 will appear cyan in color as silicon oxide, indicating that the etching of the bulk silicon of the device layer is complete. Then use acetone or other organic solutions to clean it to obtain the final MEMS micro-scanning mirror.

10. A piezoelectrically driven MEMS two-dimensional scanning mirror manufactured according to any one of claims 1 to 9, characterized in that: The piezoelectrically driven MEMS two-dimensional scanning mirror comprises an outer frame silicon, a mass block, a metal mirror surface, four groups of silicon torsion beams, a metal bottom electrode, a PZT piezoelectric film and a metal top electrode; The outer frame body silicon is a central hollow structure made by etching body silicon; The mass block is arranged at the hollowed-out center of the silicon of the outer frame body 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 arranged at the four corners of the outer frame silicon and extends to the center of the outer frame silicon, and 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 the top of the 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 the metal mirror to deflect. Two-dimensional scanning can be achieved by applying voltage to four groups of different scanning structures.

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