MEMS galvanometer preparation method

Abstract

The invention provides an MEMS (Micro Electro Mechanical System) galvanometer and a preparation method thereof, and the MEMS galvanometer comprises a first mirror surface and a galvanometer driving structure which are arranged on top silicon of silicon-on-insulator; and the second mirror surface is arranged in a back cavity formed by etching the wafer bottom silicon of the silicon-on-insulator and corresponds to the first mirror surface in position. According to the galvanometer, the number of the galvanometer surfaces is doubled while the structural complexity of a device is not increased, the field angle and the scanning efficiency of a laser radar manufactured based on the galvanometer are doubled, and the problem that the scanning efficiency of a scanning galvanometer is insufficient in a large-range scanning application scene can be well solved.

Description

Technical Field

[0001] This application relates to the field of microelectromechanical system technology, and particularly to a method for fabricating a MEMS galvanometer mirror. Background Art

[0002] MEMS (Microelectro Mechanical System) galvanometer mirrors play a crucial role in the field of laser applications. Currently, MEMS galvanometer mirrors are widely used in fields such as consumer electronics, medical, military defense, and communication. Their main application directions are in three aspects: laser scanning, optical communication, and digital display. Among them, the applications of MEMS galvanometer mirrors in laser scanning include lidar, 3D cameras, barcode scanners, laser printers, medical imaging, etc.; in optical communication, they are used in optical add-drop multiplexers, optical attenuators, optical switches, and gratings; in digital display, they are used in laser microprojection, digital cinemas, automotive head-up displays (HUDs), laser keyboards, augmented reality (AR), etc.

[0003] Currently, due to the influence of its own structure, the mechanical rotation angle of MEMS galvanometer mirrors is generally 10° - 30°, and some are even only a few degrees. Due to the limited rotation angle of MEMS galvanometer mirrors, the field of view angle of lidar is restricted. Lidar manufacturers need to adopt special structures such as light source beam expansion, splicing of multiple lasers, or even using multiple MEMS galvanometer mirrors to expand the field of view angle. However, these methods have problems such as complex structure, low efficiency, and high fabrication difficulty. Summary of the Invention

[0004] The purpose of this application aims to at least solve one of the above technical defects, especially the problem that the structure of MEMS galvanometer mirrors with a large field of view angle in the prior art is complex and difficult to fabricate.

[0005] In a first aspect, an embodiment of this application provides a MEMS galvanometer mirror, including: a first mirror surface and a galvanometer mirror driving structure, disposed on the top silicon of silicon-on-insulator; a second mirror surface, disposed in a back cavity etched in the bottom silicon of silicon-on-insulator, corresponding to the position of the first mirror surface.

[0006] In a second aspect, an embodiment of this application provides a method for fabricating a MEMS galvanometer mirror, including:

[0007] Fabricating a first mirror surface and a galvanometer mirror driving structure on the top silicon of silicon-on-insulator;

[0008] Fabricating a protection structure for protecting the first mirror surface and the galvanometer mirror driving structure;

[0009] Etching the bottom silicon of silicon-on-insulator to form a back cavity;

[0010] Fabricating a second mirror surface at a position corresponding to the first mirror surface in the back cavity;

[0011] Remove the protection structure and perform a release process on the buried oxide layer of silicon-on-insulator to release the first mirror, the galvanometer driving structure, and the second mirror.

[0012] In one embodiment, the galvanometer driving structure is a piezoelectric driving structure. The first mirror and the galvanometer driving structure are fabricated on top of the top silicon of silicon-on-insulator, including:

[0013] Perform thermal oxidation on the silicon-on-insulator to form a first oxide layer on the surface of the top silicon and a second oxide layer on the surface of the bottom silicon;

[0014] Deposit a bottom electrode layer, a piezoelectric layer, and a top electrode layer in sequence on the first oxide layer;

[0015] According to the pattern of the cantilever beam, etch the top electrode layer and the piezoelectric layer to obtain the top electrode region and the piezoelectric driving region of the piezoelectric driving structure;

[0016] According to the patterns of the first mirror and the cantilever beam, etch the bottom electrode layer to obtain the bottom electrode region of the piezoelectric driving structure and the first mirror;

[0017] According to the patterns of the first mirror and the cantilever beam, etch the first oxide layer and the top silicon to obtain a frame region, a first support region corresponding to the piezoelectric driving structure, and a second support region corresponding to the first mirror.

[0018] In one embodiment, the top electrode layer, the piezoelectric layer, and the bottom electrode layer are etched using an ion beam etching process or a reactive ion etching process.

[0019] In one embodiment, the first oxide layer is etched using an inductively coupled plasma enhanced etching process or a reactive ion etching process; the top silicon is etched using a deep reactive ion etching process.

[0020] In one embodiment, the bottom silicon of the silicon-on-insulator is etched to form a back cavity, including:

[0021] Etch the second oxide layer and the bottom silicon in sequence to form a back cavity.

[0022] In one embodiment, the galvanometer driving structure is an electrostatic driving structure. The first mirror and the galvanometer driving structure are fabricated on top of the top silicon of silicon-on-insulator; including:

[0023] Deposit a metal layer on the top silicon;

[0024] According to the patterns of the electrodes and the first mirror, etch the metal layer to obtain the electrode region of the electrostatic driving structure and the first mirror;

[0025] According to the corresponding graphics of the outer frame, anchor points, comb teeth, and the support base of the first mirror, etch the top silicon of the chip to obtain the frame area, anchor point area, comb tooth area of the electrostatic drive structure, and the third support area corresponding to the first mirror.

[0026] In one embodiment, the ion beam etching process is used to etch the metal layer.

[0027] In one embodiment, the materials of the protection structure include polymethyl methacrylate, polydimethylsiloxane, or polyurethane.

[0028] In one embodiment, a second mirror is prepared at a position corresponding to the first mirror in the back cavity, including:

[0029] Determine the target position according to the projection of the first mirror in the back cavity;

[0030] Perform pattern transfer at the target position according to the pattern of the first mirror to prepare the second mirror.

[0031] In one embodiment, the process of the release treatment is a wet process or a hydrogen fluoride gas release process.

[0032] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0033] Based on the MEMS galvanometer in the above embodiments, it includes a first mirror, a galvanometer drive structure, and a second mirror. The first mirror and the galvanometer drive structure are disposed on the top silicon of the silicon-on-insulator. The second mirror is disposed in the back cavity etched from the bottom silicon of the silicon-on-insulator and corresponds to the position of the first mirror. The second mirror shares the galvanometer drive structure of the first mirror. Without increasing the complexity of the device structure, the number of galvanometer mirrors is doubled. The lidar made based on this galvanometer will also double the field of view angle and scanning efficiency, and can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-range scanning. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 It is a schematic flowchart of the method for preparing a MEMS galvanometer provided by an embodiment of the present application;

[0036] Figure 2 For using Figure 1Schematic cross-section of the first mirror surface and the galvanometer driving structure prepared by the preparation method in;

[0037] Figure 3 For Figure 2 Schematic cross-section of the protection structure prepared for the structure in;

[0038] Figure 4 For Figure 3 Schematic cross-section of the structure in after etching the back cavity;

[0039] Figure 5 For Figure 4 Schematic cross-section of the second mirror surface prepared for the structure in;

[0040] Figure 6 For Figure 5 Schematic cross-section of the structure in after removing the protection structure and performing the release treatment;

[0041] Figure 7 For the use of Figure 1 Schematic cross-section of the wafer used for preparing the MEMS galvanometer of the piezoelectric driving structure by the preparation method in;

[0042] Figure 8 For Figure 7 Schematic cross-section of the structure in after thermal oxidation treatment;

[0043] Figure 9 For Figure 8 Schematic cross-section of the structure in after depositing the bottom electrode layer, the piezoelectric layer and the top electrode layer;

[0044] Figure 10 For Figure 9 Schematic cross-section of the structure in after etching;

[0045] Figure 11 For Figure 10 Schematic cross-section of the structure in after etching;

[0046] Figure 12 For Figure 11 Schematic cross-section of the structure in after etching;

[0047] Figure 13 For Figure 12 Schematic cross-section of the structure in after etching;

[0048] Figure 14 For Figure 13 Schematic cross-section of the structure in after growing the second mirror surface;

[0049] Figure 15 For Figure 14 Schematic cross-section of the structure in after the release treatment;

[0050] Figure 16 is Figure 15 a top view of a MEMS galvanometer of a piezoelectric drive structure formed;

[0051] Figure 17 is to use Figure 1 a schematic cross-sectional view of a wafer used to prepare a MEMS galvanometer of an electrostatic drive structure by the preparation method in;

[0052] Figure 18 is Figure 17 a schematic cross-sectional view of the structure in after depositing a metal layer;

[0053] Figure 19 is Figure 18 a schematic cross-sectional view of the structure in after etching;

[0054] Figure 20 is Figure 19 a schematic cross-sectional view of the structure in after etching;

[0055] Figure 21 is Figure 20 a schematic cross-sectional view of the structure in after etching and growing a second mirror surface;

[0056] Figure 22 is Figure 21 a schematic cross-sectional view of the structure in after release treatment;

[0057] Figure 23 is Figure 22 a top view of a MEMS galvanometer of an electrostatic drive structure formed. Detailed implementation manners

[0058] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without making creative efforts belong to the scope of protection of the present application.

[0059] The present application provides a method for preparing a MEMS galvanometer. Please refer to Figure 1 , which includes steps S102 to step S110.

[0060] S102, prepare a first mirror surface and a galvanometer drive structure on the top silicon of silicon on insulator.

[0061] It can be understood that silicon on insulator (SOI, Silicon On Insulator) is a substrate technology that replaces the traditional substrate silicon with an engineered substrate. Please refer to Figure 2, from top to bottom, the substrate includes a top silicon layer 11, a buried oxide layer 12, and a bottom silicon layer 13. In microelectromechanical systems, circuits are often fabricated on the top silicon layer 11. The buried oxide layer 12 can act as an insulator, while the bottom silicon layer 13, being thicker than the other two layers, mainly provides mechanical support for the upper two layers. The main structure of the MEMS galvanometer mirror includes a mirror surface and a driving structure. The driving structure is used to drive the mirror surface to rotate controllably within a certain range, so that when a laser beam hits the mirror surface, the reflected laser beam can be scanned within a certain range as the galvanometer mirror rotates. In this step, the first mirror surface 14 and the galvanometer mirror driving structure 15 that plays a driving role are fabricated on the top silicon layer 11 of silicon-on-insulator. The galvanometer mirror driving structure 15 can be a driving structure based on principles such as electrostatic driving, piezoelectric driving, electrothermal driving, and electromagnetic driving. When fabricating the first mirror surface 14 and the galvanometer mirror driving structure 15, the corresponding parts on the top silicon layer 13 will be retained, and the remaining parts of the top silicon layer 13 will be etched to facilitate the subsequent release of the first mirror surface 14 and the galvanometer mirror driving structure 15.

[0062] S104, fabricate a protection structure for protecting the first mirror surface and the galvanometer mirror driving structure.

[0063] The side of the silicon-on-insulator close to the top silicon layer 11 is called the front side, and the side close to the bottom silicon layer 13 is called the back side. In traditional MEMS galvanometer mirrors, only the front side has a reflection effect. The idea of this embodiment is to add a second mirror surface on the back side of the first mirror surface 14, so that both the front and back sides of the entire structure can participate in laser scanning. However, the process of fabricating the second mirror surface may damage the already fabricated first mirror surface 14 and the galvanometer mirror driving structure 15. Therefore, please refer to Figure 3 , in this step, a protection structure 16 for protecting the first mirror surface 14 and the galvanometer mirror driving structure 15 is formed. The protection structure 16 can accommodate the first mirror surface 14 and the galvanometer mirror driving structure 15, and the material of the protection structure 16 can resist corrosion during the fabrication process of the second mirror surface, thereby keeping the first mirror surface 14 and the galvanometer mirror driving structure 15 intact.

[0064] S106, etch the bottom silicon layer of the silicon-on-insulator to form a back cavity.

[0065] It can be understood that, please refer to Figure 5 , that is, from the back of the structure obtained in step S104, the bottom silicon layer 13 in the central region is etched away, and the space surrounded by the remaining bottom silicon layer 13 will form a back cavity 17. This back cavity 17 provides space for the rotation of the galvanometer mirror. During the fabrication process of S106, the protection structure 16 can also resist corrosion in this process, thereby protecting the integrity of the first mirror surface 14 and the galvanometer mirror driving structure 15.

[0066] S108, fabricate a second mirror surface at a position corresponding to the first mirror surface in the back cavity.

[0067] It can be understood that the position corresponding to the first mirror 14 here means that the first mirror 14 and the second mirror 18 are arranged opposite to each other, one is located on the front of the whole structure, and the other is located on the back of the whole structure, scanning in two opposite directions respectively. When the mirror driving structure 15 drives the first mirror 14 to rotate, the second mirror 18 will also be driven to rotate together. Different from step S102, since the second mirror 18 shares the mirror driving structure 15 with the first mirror 14, there is no need to additionally set up a separate driving structure. In this step, only the second mirror 18 itself needs to be prepared. The sizes and shapes of the first mirror 14 and the second mirror 18 can be selected differently, and the two do not need to be coaxial, that is, the centers of the two mirrors do not need to be on the same straight line. Just adding the second mirror 18 on the back of the first mirror 14 can achieve the purpose of improving the scanning efficiency. However, in order for the second mirror 18 to maximize the scanning efficiency, the position where it is set can be arranged coaxially with the first mirror 14, that is, the centers of the two mirrors are on the same straight line, and the sizes and shapes of the two are also selected to be the same.

[0068] S110, Remove the protection structure and perform a release process on the buried oxide layer of silicon on insulator to release the first mirror, the galvanometer driving structure and the second mirror.

[0069] It can be understood that currently, the first mirror 14, the galvanometer driving structure 15 and the second mirror 18 are still inseparable from the external frame through the buried oxide layer 12. Therefore, it is necessary to remove the buried oxide layer in a specific area, so that the first mirror 14, the galvanometer driving structure 15 and the second mirror 18 are in a suspended state. This process of removing the buried oxide 12 layer is the release process. And the protection structure 16 is also irrelevant to the function of the galvanometer itself and needs to be removed. The sequence of removing the protection structure 16 and releasing the buried oxide layer 12 is mainly determined by the process of the release process. If the release process has no corrosive effect on the first mirror 14 and the galvanometer driving structure 15, the protection structure can be removed first. Otherwise, the protection structure 16 should be retained. If the second mirror 18 is also corroded by the release process, certain means should also be used to protect it. Please refer to Figure 6 , Figure 6 The area released by the buried oxide layer 12 in is only schematically drawn and may be different in galvanometers of different structures. It is worth mentioning that Figures 2 to 6 The first mirror 14, the galvanometer driving structure 15 and the second mirror 18 in are only schematically drawn, only showing the relative positional relationship with the silicon on insulator on the top, and do not represent the specific materials, structures, etc. of the first mirror 14, the galvanometer driving structure 15 and the second mirror 18.

[0070] Based on the MEMS galvanometer preparation method in this embodiment, after the original first mirror surface and the mirror surface driving structure are prepared, they are covered and protected by certain means to ensure that subsequent processes do not cause pollution and damage to the first mirror surface. The wafer is inverted to the back side to prepare the second mirror surface. After the second mirror surface is prepared, the overall movable structure is released. This solution doubles the number of galvanometer mirror surfaces without increasing the complexity of the device structure. The lidar made based on this galvanometer will also double the field of view angle and scanning efficiency, and can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-range scanning. Moreover, the structure and preparation process of this galvanometer are simple, which can greatly improve the preparation efficiency.

[0071] In one of the embodiments, the galvanometer driving structure is a piezoelectric driving structure. Preparing the first mirror surface and the galvanometer driving structure on the first surface of silicon-on-insulator includes:

[0072] (1) Perform thermal oxidation treatment on the silicon-on-insulator to form a first oxide layer on the surface of the top silicon wafer and a second oxide layer on the surface of the bottom silicon wafer.

[0073] Please refer to Figure 7 , the silicon-on-insulator from top to bottom is the top silicon wafer 101, the buried oxide layer 102, and the bottom silicon wafer 103. Please refer to Figure 8 , after the thermal oxidation treatment, both the top silicon wafer 101 and the bottom silicon wafer 103 will contact oxygen and react, thereby generating the first oxide layer 104 and the second oxide layer 105 respectively.

[0074] (2) Deposit a bottom electrode layer, a piezoelectric layer, and a top electrode layer in sequence on the first oxide layer.

[0075] It can be understood that in the piezoelectric driving structure, the inverse piezoelectric effect that occurs on the piezoelectric material is utilized, that is, the piezoelectric material will generate deformation when a voltage is applied. Therefore, the size, frequency, etc. of the deformation can be controlled by controlling the electrical signal applied to it. To utilize this effect, please refer to Figure 9, it is necessary to sequentially deposit and grow a bottom electrode layer 106, a piezoelectric layer 107, and a top electrode layer 108 on the first oxide layer 104. Among them, the bottom electrode layer 106 and the top electrode layer 108 will serve as the medium for applying an electric field to the piezoelectric layer 107 and have good electrical conductivity. And the bottom electrode layer 106 will serve as the basis of the first mirror in subsequent processes. Therefore, the material selection should also consider the laser reflection ability. Therefore, the materials of the bottom electrode layer 106 and the top electrode layer 108 include, but are not limited to, metal materials with strong laser reflection ability such as gold, silver, titanium, platinum, aluminum, copper, and molybdenum. The piezoelectric layer 107 should be made of piezoelectric materials, including, but not limited to, aluminum nitride, barium titanate, lead zirconate titanate, modified lead zirconate titanate, lead metaniobate, lead barium lithium niobate, modified lead titanate, zinc oxide, lithium gallate, lithium germanate, titanium germanate, lithium niobate, and lithium tantalate. The deposition process here can be physical vapor deposition.

[0076] (3) According to the pattern of the cantilever beam, etch the top electrode layer and the piezoelectric layer to obtain the top electrode region and the piezoelectric drive region of the piezoelectric drive structure.

[0077] It can be understood that one end of the cantilever beam is fixed to the outer frame of the entire galvanometer, and the other end is connected to the first mirror. Its function is to suspend the mirror and drive the mirror to twist and rotate through elastic deformation. The piezoelectric drive structure includes this cantilever beam. According to the principle of the inverse piezoelectric effect, the piezoelectric drive structure should include a top electrode region, a piezoelectric drive region, and a bottom electrode region. The elastic deformation is generated by applying an electric current to the top electrode region and the bottom electrode region to apply an electric field to the piezoelectric drive region. The shape of the cantilever beam will affect the rotation angle, frequency, etc. of the mirror. Therefore, the shape of the cantilever beam will be designed according to the functional requirements of the product. And the shape of the cantilever beam will have a corresponding pattern when viewed from the top view. In order to fabricate the cantilever beam with the designed shape, etching will be performed on the overall structure formed in the above step (2) according to the pattern corresponding to the cantilever beam. Specifically, the part of the pattern corresponding to the cantilever beam needs to be retained. Lithography can be performed based on the pattern corresponding to the cantilever beam and the designed position to form a first mask covering the area where the cantilever beam is located. Please refer to Figure 10 , the area covered by the first mask will be protected during etching, and the remaining part in the top electrode layer 108 will be retained as the top electrode region 109 of the piezoelectric drive structure, and the remaining part in the piezoelectric layer 107 will be retained as the piezoelectric drive region 110 of the piezoelectric drive structure. The top electrode layer 108 and the piezoelectric layer 107 in the area not covered by the first mask will be etched as the first etching region 111.

[0078] (4) According to the patterns of the first mirror and the cantilever beam, etch the bottom electrode layer to obtain the bottom electrode region of the piezoelectric drive structure and the first mirror.

[0079] It can be understood that in this embodiment, a first mirror surface will be formed based on the bottom electrode layer 106. The shape of the first mirror surface can be designed according to the functional requirements of the product. When observing the first mirror surface from a top view angle, there will be a corresponding pattern. In order to fabricate the first mirror surface with the designed shape and retain the top electrode region 109 and the piezoelectric driving region 110 fabricated in the previous step, etching will be performed on the overall structure formed in the above step (3) according to the patterns corresponding to the first mirror surface and the cantilever beam. Specifically, the pattern parts corresponding to the first mirror surface and the cantilever beam need to be retained. Lithography can be performed at the selected positions based on the patterns corresponding to the first mirror surface and the cantilever beam to form a second mask covering the regions where the first mirror surface and the cantilever beam are located. Please refer to Figure 11 , the regions covered by the second mask will be protected during etching, and the remaining parts in the bottom electrode layer 106 will be retained as the first mirror surface 113 and the bottom electrode region 112 of the piezoelectric driving structure respectively. The bottom electrode layer 106 in the regions not covered by the second mask will be etched as the second etching region 114.

[0080] (5) According to the patterns of the first mirror surface and the cantilever beam, etch the first oxide layer and the top silicon wafer to obtain the frame region, the first support region corresponding to the piezoelectric driving structure, and the second support region corresponding to the first mirror surface.

[0081] It can be understood that in order to support the piezoelectric driving structure and the first mirror surface 113 formed in the above step, further etching is required. Specifically, the pattern parts corresponding to the first mirror surface 113 and the cantilever beam need to be retained. Lithography can be performed at the selected positions based on the patterns corresponding to the first mirror surface 113 and the cantilever beam to form a third mask covering the regions where the first mirror surface 113 and the cantilever beam are located. Please refer to Figure 12 , the regions covered by the third mask will be protected during etching, and the remaining parts of the first oxide layer 104 and the top silicon wafer 101 will be retained as the frame region 115, the first support region 117 corresponding to the piezoelectric driving structure, and the second support region 116 corresponding to the first mirror surface 113 respectively. Among them, the remaining parts of the first oxide layer 104 and the top silicon wafer 101 under the outermost bottom electrode region 112 will be used as the frame region 115, the remaining parts of the first oxide layer 104 and the top silicon wafer 101 under the first mirror surface 113 will be used as the second support region 116, and the rest will be used as the first support region 117 corresponding to the piezoelectric driving structure. The first oxide layer 104 and the top silicon wafer 101 in the regions not covered by the third mask will be etched as the third etching region 118.

[0082] In one embodiment, the top electrode layer 108, the piezoelectric layer 107, and the bottom electrode layer 106 are etched using an ion beam process or a reactive ion process.

[0083] In one embodiment, the first oxide layer 104 is etched using an inductively coupled plasma enhanced process or a reactive ion process; the top silicon 101 is etched using a deep reactive ion etching process.

[0084] In one embodiment, the bottom silicon of the silicon-on-insulator is etched to form a back cavity, including: etching the second oxide layer and the bottom silicon in sequence to form a back cavity.

[0085] Please refer to Figure 13 , Figure 13 in which 119 is the protection structure 119. The parts that need to be protected at the outermost periphery of the back in Figure 12 are marked by photolithography, and a fourth mask is formed based on this marking. Among them, the second oxide layer 105 and the bottom silicon 103 in the area not covered by the fourth mask will be etched, and the cavity formed by the removal is the back cavity 120. The second oxide layer 105 can be etched using an inductively coupled plasma enhanced process or a reactive ion process. The bottom silicon 103 can be etched using a deep reactive ion etching process.

[0086] In one preferred embodiment, a second mirror surface is prepared at a position corresponding to the first mirror surface in the back cavity, including: determining a target position according to the projection of the first mirror surface in the back cavity. According to the pattern of the first mirror surface, pattern transfer is performed at the target position to prepare the second mirror surface.

[0087] Please refer to Figure 14 , the target position is symmetric with the first mirror surface 113. Setting the second mirror surface 121 at this position and setting their shapes to be the same can make them have the same scanning effect. Here, the pattern transfer process can be deposited according to the material selected for the bottom electrode layer 106, and then according to the pattern of the first mirror surface 113 and using a lift-off or etching process, the second mirror surface 121 is generated. Based on Figure 14 the structure, the protection structure 119 is removed and released, and the obtained structure is as shown in Figure 15 . The area removed during release is the first release area 122. Figure 15 The top view perspective of the corresponding galvanometer is as shown in Figure 16 . Figures 7 to 15 The cutting lines selected for the respective cross-sectional views of Figure 16 are as shown by the dashed lines in Figure 16Among them, the points on both sides of the galvanometer mirror used to connect the external circuit are respectively called the upper electrode 123 and the lower electrode 124. Among them, the upper electrode 123 is the lead-out point for the connection between the top electrode region 109 and the external circuit, and the lower electrode 123 is the lead-out point for the connection between the bottom electrode region 112 and the external circuit. In the figure, each region of the piezoelectric drive structure is combined to form a cantilever beam 125. The shape of the cantilever beam 125 is a planar spring shape, and the distance between each spring unit can be set as required, and a non-uniform spacing structure can be adopted to achieve different swing frequencies.

[0088] In one embodiment, the galvanometer mirror drive structure is an electrostatic drive structure. A first mirror surface and the galvanometer mirror drive structure are fabricated on the first surface of silicon-on-insulator, including:

[0089] (1) Deposit a metal layer on the top silicon wafer.

[0090] Please refer to Figure 17 , the silicon-on-insulator from top to bottom is the top silicon wafer 201, the buried oxide layer 202, and the bottom silicon wafer 203. Please refer to Figure 18 , a metal layer 204 is formed on the top silicon wafer 201 using a metal material with good electrical conductivity and strong laser reflection ability. The materials of the metal layer 204 include but are not limited to metals with strong laser reflection ability such as gold, silver, titanium, platinum, aluminum, copper, and molybdenum. The deposition process here can select physical vapor deposition.

[0091] (2) According to the patterns of the electrodes and the first mirror surface, etch the metal layer to obtain the electrode region and the first mirror surface of the electrostatic drive structure.

[0092] It can be understood that the electrostatic drive structure mainly includes an electrode region, an outer comb region, and an inner comb region. Among them, the outer comb region is a static comb, which is integrated with the external frame. The inner comb region is a moving comb, which is integrated with the first mirror surface and connected to the anchor points of the external frame. The electrode region is used to connect with the external circuit, so that a voltage difference is generated between the corresponding combs in the outer comb region and the inner comb region, thereby generating an electrostatic force, so that the inner comb region drives the first mirror surface to swing. There are corresponding patterns for the electrode region and the first mirror surface in the top view. In order to fabricate the designed-shaped electrode region and the first mirror surface, the metal layer 204 will be etched. Specifically, the graphic parts corresponding to the electrode region and the first mirror surface need to be retained. Lithography can be performed based on the patterns corresponding to the electrode region and the first mirror surface and the designed positions to form the fifth mask for the regions where the electrodes and the first mirror surface are located. Please refer to Figure 19 , the regions covered by the fifth mask will be protected during etching, and the remaining parts in the metal layer 204 will be retained as the electrode region 206 and the first mirror surface 205 respectively. The metal layer 204 in the regions not covered by the fifth mask will be etched as the fourth etching region 207.

[0093] (3) According to the corresponding graphics of the outer frame, anchor points, comb teeth, and the support base of the first mirror surface, etch the top silicon of the chip to obtain the frame region, anchor point region, comb tooth region of the electrostatic drive structure, and the third support region corresponding to the first mirror surface.

[0094] It can be understood that in order to further improve the electrostatic drive structure, it is necessary to further etch the top silicon 201. Specifically, the corresponding graphics of the outer frame, anchor points, comb teeth, and the support base of the first mirror surface 205 need to be retained. Lithography can be performed at the selected positions based on the corresponding graphics of the outer frame, anchor points, comb teeth, and the support base of the first mirror surface 205 to form a sixth mask covering the frame region, anchor point region, comb tooth region, and the third support region corresponding to the first mirror surface 205. Please refer to Figure 20 , the areas covered by the sixth mask will be protected during etching, and the remaining parts of the top silicon 201 will be used as the frame region 208, anchor point region (since Figure 20 is an eccentric cross-sectional view and the anchor points are located in the middle, so they are not shown in the figure), the third support region 209 corresponding to the first mirror surface 205, and the comb tooth region 210 respectively. The top silicon 201 in the area not covered by the sixth mask will be etched as the fifth etching region 211.

[0095] In one embodiment, steps S104 to S108 are performed based on the Figure 20 structure, as shown in Figure 21 , a back cavity 213 and a second mirror surface 214 will be formed. The description can refer to the above text. Then, based on the Figure 21 structure, the protection structure is removed and released, and the resulting structure is as shown in Figure 22 . The area removed during release is the second release region 215. Figure 22 The top view perspective of the corresponding galvanometer is as shown in Figure 23 , where Figures 17 to 22 The selected cutting lines for each cross-sectional view are as shown by the dashed lines in Figure 23 . The comb tooth region 210 can be divided into an outer comb tooth region 210A and an inner comb tooth region 210B. Among them, the outer comb tooth region 210A is a part of the frame region 208 and remains fixed during use. The inner comb tooth region 210B is the region that drives the mirror to rotate and is movable during use. The gap between the outer comb tooth region 210A and the inner comb tooth region 210B generates electrostatic induction, thereby driving the mirror to rotate. The anchor point region 216 is located in the middle of the galvanometer and is connected to the inner comb tooth region 210B, the first mirror surface 205, and its corresponding third support region 209.

[0096] In one embodiment, the process used for etching the metal layer is the ion beam etching process.

[0097] In one embodiment, the material of the protection structure includes polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS), or polyimide (PI). These materials all have strong resistance to acid and alkali corrosion and high temperature, and are suitable for use as the material of the protection structure.

[0098] In one embodiment, the process of the release treatment is a wet process or a hydrogen fluoride gas release process. The wet process uses a liquid corrosion medium and has simple equipment, while the hydrogen fluoride gas release utilizes gaseous HF and can achieve a faster and more uniform release effect, and can be selected according to actual needs.

[0099] Please refer to Figure 6 , the embodiment of the present application also provides a MEMS galvanometer, which can be obtained by using the preparation method in the above embodiment. The galvanometer includes a first mirror surface 14 and a galvanometer driving structure 15, which are disposed on the top silicon 11 of the silicon-on-insulator; a second mirror surface 18 is disposed in the back cavity 17 etched from the bottom silicon 13 of the silicon-on-insulator, corresponding to the position of the first mirror surface 14. The first mirror surface 14 and the second mirror surface 18 share the same galvanometer driving structure 15, and the second mirror surface 18 can move in the back cavity 17. When in use, both the front and back of the entire MEMS galvanometer can be used for scanning. Without increasing the complexity of the device structure, the number of mirror surfaces of the galvanometer is doubled, and the lidar made based on this galvanometer will also double the field of view angle and scanning efficiency, and can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-range scanning.

[0100] Based on the MEMS galvanometer in the above embodiment, it includes a first mirror surface, a galvanometer driving structure, and a second mirror surface. The first mirror surface and the galvanometer driving structure are disposed on the top silicon of the silicon-on-insulator. The second mirror surface is disposed in the back cavity etched from the bottom silicon of the silicon-on-insulator, corresponding to the position of the first mirror surface. The second mirror surface shares the galvanometer driving structure of the first mirror surface. Without increasing the complexity of the device structure, the number of mirror surfaces of the galvanometer is doubled, and the lidar made based on this galvanometer will also double the field of view angle and scanning efficiency, and can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-range scanning.

[0101] Figure 6 The first mirror surface 14, the galvanometer driving structure 15, and the second mirror surface 18 in [[ ]] are only schematically drawn, only showing the relative position relationship with the silicon-on-insulator, and do not represent the specific materials, structures, etc. of the first mirror surface 14, the galvanometer driving structure 15, and the second mirror surface 18. The specific structure of the MEMS galvanometer in different driving structures can be seen below:

[0102] In a specific embodiment, the MEMS galvanometer can be piezoelectrically driven. Please refer to Figures 7 to 16Silicon-on-insulator includes, from top to bottom, a top silicon layer 101, a buried oxide layer 102, and a bottom silicon layer 103. Above the top silicon layer 101, the galvanometer further includes, from top to bottom, a top electrode layer 108, a piezoelectric layer 107, a bottom electrode layer 106, and a first oxide layer 104. Above the bottom silicon layer 103, there is also a second oxide layer 105. Among them, after the top electrode layer 108 and the piezoelectric layer 107 are etched according to the pattern of the cantilever beam 125, they will include a top electrode region 109 and a piezoelectric drive region 110 of the piezoelectric drive structure. After the bottom electrode layer 106 is etched according to the patterns of the first mirror 113 and the cantilever beam 125 respectively, it will include the first mirror 113 and a bottom electrode region 112 of the piezoelectric drive structure. After the first oxide layer 104 and the top silicon layer 101 are etched according to the patterns of the first mirror 113 and the cantilever beam 125 respectively, they will include a frame region 115, a first support region 117 corresponding to the piezoelectric drive structure, and a second support region 116 corresponding to the first mirror 113. The frame region 115 is the main body of the entire galvanometer, and the first support region 117 and the second support region 116 support the piezoelectric drive structure and the first mirror 113 located thereon respectively. Due to the presence of the second oxide layer 105, when etching the back cavity 120, the bottom silicon layer 103 and the second oxide layer 105 will be etched together. After all the structures are etched, the buried oxide layer 102 can be etched to release the first mirror 113, the second mirror 121, and the cantilever beam 125 composed of each region of the piezoelectric drive structure to be suspended. The top electrode region 109 includes an upper electrode 123, which is the lead-out point for connecting the top electrode region 109 to the external circuit. The bottom electrode region 112 includes a lower electrode 123, which is the lead-out point for connecting the bottom electrode region 112 to the external circuit.

[0103] In a specific embodiment, the MEMS galvanometer can be electrostatically driven. Please refer to Figures 17 to 23Silicon on insulator, from top to bottom, successively includes top silicon 201, buried oxide layer 202, and bottom silicon 203. Above the top silicon 201, there is also a metal layer 204. Among them, after the metal layer 204 is etched according to the patterns of the electrodes and the first mirror 205, it will include the electrode region 206 of the electrostatic drive structure and the first mirror 205. After the top silicon 201 is etched according to the corresponding patterns of the external frame, anchor points, comb teeth, and the support base of the first mirror respectively, it will include the frame region 208, the anchor point region 216, the comb tooth region 210 of the electrostatic drive structure, and the third support region 209 corresponding to the first mirror 205. Thereafter, the bottom silicon 203 is etched to obtain a back cavity 213, and a second mirror 214 corresponding to the first mirror 205 can be fabricated on the buried oxide layer 202 within the back cavity 213. Then, the buried oxide layer 202 is etched to release the first mirror 205, the second mirror 214, and the inner comb tooth region 210B for driving the first mirror 205 and the second mirror 214 to be suspended. Among them, the inner comb tooth region 210B is connected to the frame region 208 through the anchor point region 216. The frame region 208 includes an outer comb tooth region 210A that cooperates with the inner comb tooth region 210B. An electrostatic induction is generated in the gap between the outer comb tooth region 210A and the inner comb tooth region 210B, thereby driving the mirror to rotate.

[0104] Finally, it should also be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the element.

[0105] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The various embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0106] The foregoing description of the disclosed embodiments enables those skilled in the art to practice or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A MEMS galvanometer mirror, characterized in that, it includes: A first mirror surface and a galvanometer mirror driving structure, disposed on the top silicon of silicon-on-insulator; A second mirror surface, disposed in a back cavity etched in the bottom silicon of the silicon-on-insulator, corresponding to the position of the first one.

2. A method for manufacturing a MEMS galvanometer mirror, characterized in that, it includes: Fabricating a first mirror surface and a galvanometer mirror driving structure on the top silicon of silicon-on-insulator; Fabricating a protection structure for protecting the first mirror surface and the galvanometer mirror driving structure; Etching the bottom silicon of the silicon-on-insulator to form a back cavity; Fabricating a second mirror surface at a position corresponding to the first mirror surface in the back cavity; Removing the protection structure and performing a release treatment on the buried oxide layer of the silicon-on-insulator to release the first mirror surface, the galvanometer mirror driving structure, and the second mirror surface.

3. The method for manufacturing a MEMS galvanometer mirror according to claim 2, characterized in that, the galvanometer mirror driving structure is a piezoelectric driving structure, and fabricating a first mirror surface and a galvanometer mirror driving structure on the top silicon of silicon-on-insulator includes: Performing thermal oxidation treatment on the silicon-on-insulator to form a first oxide layer on the surface of the top silicon and a second oxide layer on the surface of the bottom silicon; Sequentially depositing a bottom electrode layer, a piezoelectric layer, and a top electrode layer on the first oxide layer; Etching the top electrode layer and the piezoelectric layer according to the pattern of the cantilever beam to obtain the top electrode region and the piezoelectric driving region of the piezoelectric driving structure; Etching the bottom electrode layer according to the patterns of the first mirror surface and the cantilever beam to obtain the bottom electrode region of the piezoelectric driving structure and the first mirror surface; Etching the first oxide layer and the top silicon according to the patterns of the first mirror surface and the cantilever beam to obtain a frame region, a first support region corresponding to the piezoelectric driving structure, and a second support region corresponding to the first mirror surface.

4. The method for manufacturing a MEMS galvanometer mirror according to claim 3, characterized in that, ion beam etching process or reactive ion etching process is used for etching the top electrode layer, the piezoelectric layer, and the bottom electrode layer.

5. The method for manufacturing a MEMS galvanometer mirror according to claim 3, characterized in that, inductively coupled plasma enhanced etching process or reactive ion etching process is used for etching the first oxide layer; deep reactive ion etching process is used for etching the top silicon.

6. The method for manufacturing a MEMS galvanometer mirror according to claim 3, characterized in that, etching the bottom silicon of the silicon-on-insulator to form a back cavity includes: Sequentially etching the second oxide layer and the bottom silicon to form the back cavity.

7. The method for manufacturing a MEMS galvanometer mirror according to claim 2, characterized in that, the galvanometer mirror driving structure is an electrostatic driving structure, and fabricating a first mirror surface and a galvanometer mirror driving structure on the top silicon of silicon-on-insulator includes: Depositing a metal layer on the top silicon; Etching the metal layer according to the patterns of the electrode and the first mirror surface to obtain the electrode region of the electrostatic driving structure and the first mirror surface; Etch the top silicon wafer according to the corresponding patterns of the outer frame, anchor points, comb teeth, and the support base of the first mirror to obtain a frame region, an anchor point region, a comb tooth region of the electrostatic drive structure, and a third support region corresponding to the first mirror.

8. The method for manufacturing a MEMS galvanometer according to claim 7, wherein, the ion beam etching process is used to etch the metal layer.

9. The method for manufacturing a MEMS galvanometer according to any one of claims 2-8, wherein, the material of the protection structure includes polymethyl methacrylate, polydimethylsiloxane, or polyurethane.

10. The method for manufacturing a MEMS galvanometer according to any one of claims 2-8, wherein, fabricating a second mirror at a position corresponding to the first mirror in the back cavity includes: determining a target position according to the projection of the first mirror in the back cavity; performing pattern transfer at the target position according to the pattern of the first mirror to fabricate the second mirror.

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