MEMS galvanometer manufacturing method

Abstract

The present application provides an MEMS galvanometer and a manufacturing method therefor. The MEMS galvanometer comprises: a first mirror surface and a galvanometer driving structure which are arranged on top silicon of silicon-on-insulator; and a second mirror surface which is arranged in a back cavity formed by etching bottom silicon of the silicon-on-insulator and corresponds to the first galvanometer surface in position. According to the galvanometer, the number of mirror surfaces of the galvanometer is doubled while the structural complexity of a device is not increased, and a laser radar made on the basis of the galvanometer also achieves doubling of the field of view and the scanning efficiency, so that the problem of insufficient scanning efficiency of a scanning galvanometer in large-range scanning application scenarios can be solved.

Description

MEMS galvanometer preparation method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 11, 2023, with application number 202311690553.X and invention name “MEMS galvanometer preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a method for preparing a MEMS galvanometer mirror. Background Art

[0003] MEMS (Microelectromechanical System) galvanometers play a pivotal role in laser applications. Currently, MEMS galvanometers are widely used in consumer electronics, healthcare, military defense, communications, and other fields. Their main application areas are laser scanning, optical communications, and digital display. MEMS galvanometers are used in laser scanning applications such as lidar, 3D cameras, barcode scanning, laser printers, and medical imaging; in optical communications applications, they are used in optical add / drop multiplexers, optical attenuators, optical switches, and gratings; and in digital display applications, they are used in laser micro-projection, digital cinemas, automotive head-up displays (HUDs), laser keyboards, and augmented reality (AR).

[0004] Due to its inherent structure, current MEMS galvanometers typically have a mechanical rotation angle of 10° to 30°, with some even limited to just a few degrees. This limited rotation angle restricts the LiDAR's field of view, forcing LiDAR manufacturers to employ specialized structures such as light source beam expansion, splicing multiple lasers, or even using multiple MEMS galvanometers to expand the field of view. However, these methods are complex, inefficient, and difficult to manufacture.

[0005] Summary of the Invention

[0006] The purpose of this application is to solve at least one of the above-mentioned technical defects, especially the problem that the MEMS galvanometer with a large field of view in the prior art has a complex structure and is difficult to prepare.

[0007] In the first aspect, an embodiment of the present application provides a MEMS galvanometer, comprising: a first mirror and a galvanometer drive structure, which are arranged on the top silicon of a silicon-on-insulator sheet; a second mirror, which is arranged in a back cavity formed by etching the bottom silicon of the silicon-on-insulator sheet, corresponding to the position of the first mirror.

[0008] In a second aspect, an embodiment of the present application provides a method for preparing a MEMS galvanometer, comprising:

[0009] Prepare a first mirror and a galvanometer drive structure on the top silicon of the silicon-on-insulator;

[0010] preparing a protection structure for protecting the first mirror surface and the galvanometer drive structure;

[0011] etching the bottom silicon of the silicon-on-insulator to form a back cavity;

[0012] Prepare a second mirror surface at a position corresponding to the first mirror surface in the back cavity;

[0013] The protective structure is removed, and a release process is performed on the buried oxide layer of silicon on insulator to release the first mirror, the galvanometer drive structure and the second mirror.

[0014] In one embodiment, the galvanometer drive structure is a piezoelectric drive structure, and a first mirror surface and the galvanometer drive structure are fabricated on a top silicon of a silicon-on-insulator (SOI) film, including:

[0015] Performing 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;

[0016] A bottom electrode layer, a piezoelectric layer and a top electrode layer are sequentially deposited on the first oxide layer;

[0017] According to the pattern of the cantilever beam, the top electrode layer and the piezoelectric layer are etched to obtain the top electrode region and the piezoelectric driving region of the piezoelectric driving structure;

[0018] Etching the bottom electrode layer according to the pattern of the first mirror and the cantilever beam to obtain the bottom electrode region and the first mirror of the piezoelectric drive structure;

[0019] According to the patterns of the first mirror and the cantilever beam, the first oxide layer and the top silicon are etched to obtain a frame area, a first supporting area corresponding to the piezoelectric drive structure, and a second supporting area corresponding to the first mirror.

[0020] In one embodiment, etching the top electrode layer, the piezoelectric layer, and the bottom electrode layer adopts an ion beam etching process or a reactive ion etching process.

[0021] In one embodiment, the first oxide layer is etched using an inductively coupled enhanced plasma etching process or a reactive ion etching process; and the top silicon of the wafer is etched using a deep reactive ion etching process.

[0022] In one embodiment, etching the bottom silicon of a silicon-on-insulator to form a back cavity includes:

[0023] The second oxide layer and bottom silicon are etched in sequence to form a back cavity.

[0024] In one embodiment, the galvanometer drive structure is an electrostatic drive structure, and the first mirror surface and the galvanometer drive structure are fabricated on top of silicon on insulator (SOI); the structure comprises:

[0025] Depositing a metal layer on the top silicon of the wafer;

[0026] Etching the metal layer according to the patterns of the electrode and the first mirror to obtain the electrode region and the first mirror of the electrostatic drive structure;

[0027] According to the patterns corresponding to the external frame, anchor points, comb teeth and the support base of the first mirror, the top silicon of the wafer is etched 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.

[0028] In one embodiment, etching the metal layer adopts an ion beam etching process.

[0029] In one embodiment, the material of the protection structure includes polymethyl methacrylate, polydimethylsiloxane or polyurethane.

[0030] In one embodiment, preparing a second mirror surface at a position corresponding to the first mirror surface in the back cavity includes:

[0031] determining a target position according to a projection of the first mirror surface in the back cavity;

[0032] According to the pattern of the first mirror surface, the pattern is transferred at the target position to prepare the second mirror surface.

[0033] In one embodiment, the release treatment process is a wet process or a hydrogen fluoride gaseous release process.

[0034] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0035] Based on the MEMS galvanometer in the above embodiment, it includes a first mirror, a galvanometer drive structure and a second mirror. The first mirror and the galvanometer drive structure are arranged on the top silicon of the silicon-on-insulator. The second mirror is arranged in a back cavity formed by etching the bottom silicon of the silicon-on-insulator, corresponding to the position of the first mirror. The second mirror shares the galvanometer drive structure of the first mirror, and the number of galvanometer mirror surfaces is doubled without increasing the complexity of the device structure. The laser radar made based on the galvanometer will also double the field of view angle and scanning efficiency, which can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-scale scanning. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0037] FIG1 is a schematic flow chart of a method for manufacturing a MEMS galvanometer mirror according to an embodiment of the present application;

[0038] FIG2 is a schematic cross-sectional view of a first mirror and a galvanometer drive structure manufactured using the manufacturing method in FIG1 ;

[0039] FIG3 is a schematic cross-sectional view of a protective structure prepared for the structure in FIG2 ;

[0040] FIG4 is a schematic cross-sectional view of the structure in FIG3 after etching the back cavity;

[0041] FIG5 is a schematic cross-sectional view of the structure in FIG4 for preparing a second mirror surface;

[0042] FIG6 is a schematic cross-sectional view of the structure in FIG5 after removing the protective structure and performing the release process;

[0043] FIG7 is a cross-sectional schematic diagram of a wafer used for preparing a MEMS galvanometer mirror having a piezoelectric drive structure using the preparation method in FIG1 ;

[0044] FIG8 is a schematic cross-sectional view of the structure in FIG7 after thermal oxidation treatment;

[0045] FIG9 is a schematic cross-sectional view of the structure in FIG8 after depositing a bottom electrode layer, a piezoelectric layer, and a top electrode layer;

[0046] FIG10 is a schematic cross-sectional view of the structure in FIG9 after etching;

[0047] FIG11 is a schematic cross-sectional view of the structure in FIG10 after etching;

[0048] FIG12 is a schematic cross-sectional view of the structure in FIG11 after etching;

[0049] FIG13 is a schematic cross-sectional view of the structure in FIG12 after etching;

[0050] FIG14 is a schematic cross-sectional view of the structure in FIG13 after the second mirror is grown;

[0051] FIG15 is a schematic cross-sectional view of the structure in FIG14 after release processing;

[0052] FIG16 is a top view of the MEMS galvanometer mirror of the piezoelectric drive structure formed in FIG15;

[0053] FIG17 is a cross-sectional view of a wafer used for preparing a MEMS galvanometer having an electrostatic drive structure using the preparation method in FIG1 ;

[0054] FIG18 is a schematic cross-sectional view of the structure in FIG17 after a metal layer is deposited;

[0055] FIG19 is a schematic cross-sectional view of the structure in FIG18 after etching;

[0056] FIG20 is a schematic cross-sectional view of the structure in FIG19 after etching;

[0057] FIG21 is a schematic cross-sectional view of the structure in FIG20 after etching and growing a second mirror surface;

[0058] FIG22 is a cross-sectional schematic diagram of the structure in FIG21 after release processing;

[0059] FIG. 23 is a top view of the MEMS galvanometer mirror of the electrostatic drive structure formed in FIG. 22 . DETAILED DESCRIPTION

[0060] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] The present application provides a method for preparing a MEMS galvanometer mirror, please refer to FIG. 1 , which includes steps S102 to S110 .

[0062] S102 , preparing a first mirror and a galvanometer drive structure on the top silicon of the silicon-on-insulator.

[0063] As can be understood, silicon-on-insulator (SOI) is a substrate technology that replaces traditional silicon substrates with engineered substrates. Refer to Figure 2 , which shows, from top to bottom, a top silicon layer 11, a buried oxide layer 12, and a bottom silicon layer 13. In microelectromechanical systems (MEMS), circuits are often fabricated on top of the top silicon layer 11. The buried oxide layer 12 acts as an insulator, while the bottom silicon layer 13, being thicker than the other two layers, primarily provides mechanical support for the upper two layers. The main structure of a MEMS galvanometer includes a mirror and a drive structure. The drive structure is used to drive the mirror to controllably rotate within a certain range, so that when a laser strikes the mirror, the reflected laser can scan within a certain range as the galvanometer rotates. This step involves fabricating a first mirror 14 and a galvanometer drive structure 15, which acts as a driver, on the top silicon layer 11 of the SOI. This galvanometer drive structure 15 can be based on principles such as electrostatic drive, piezoelectric drive, electrothermal drive, and electromagnetic drive. When preparing the first mirror 14 and the galvanometer drive structure 15 , their corresponding parts on the top silicon 13 will be retained, and the remaining parts of the top silicon 13 will be etched to facilitate the subsequent release of the first mirror 14 and the galvanometer drive structure 15 .

[0064] S104: Prepare a protection structure for protecting the first mirror and the galvanometer drive structure.

[0065] The side of the silicon on insulator close to the top silicon 11 is called the front side, and the side close to the bottom silicon 13 is called the back side. The traditional MEMS galvanometer only has a reflective effect on the front side. The idea of ​​this embodiment is to add a second mirror on the back side of the first mirror 14 so that both the front and back sides of the entire structure can participate in laser scanning. The process of preparing the second mirror may cause damage to the already prepared first mirror 14 and the galvanometer drive structure 15. Therefore, please refer to Figure 3. This step forms a protective structure 16 for protecting the first mirror 14 and the galvanometer drive structure 15. The protective structure 16 can accommodate the first mirror 14 and the galvanometer drive structure 15, and the material of the protective structure 16 can resist corrosion during the preparation of the second mirror, so that the first mirror 14 and the galvanometer drive structure 15 remain intact.

[0066] S106 , etching the bottom silicon of the silicon-on-insulator to form a back cavity.

[0067] As can be seen in Figure 5 , the back of the structure obtained in step S104 has its center silicon substrate 13 etched away, leaving a space enclosed by the remaining silicon substrate 13 to form a back cavity 17, which provides space for the galvanometer mirror to rotate. During the fabrication process in step S106, the protective structure 16 also resists corrosion during the process, thereby protecting the integrity of the first mirror surface 14 and the galvanometer mirror drive structure 15.

[0068] S108 , preparing a second mirror surface at a position corresponding to the first mirror surface in the back cavity.

[0069] It will be understood that the corresponding positions of the first mirror surface 14 here refer to the relative arrangement of the first mirror surface 14 and the second mirror surface 18, one located on the front side of the entire structure and the other located on the back side of the entire structure, scanning in two opposite directions. When the mirror drive structure 15 drives the first mirror surface 14 to rotate, the second mirror surface 18 will also be driven to rotate. Unlike step S102, since the second mirror surface 18 and the first mirror surface 14 share the mirror drive structure 15, there is no need to set up a separate drive structure. This step only requires the preparation of the second mirror surface 18 itself. The size and shape of the first mirror surface 14 and the second mirror surface 18 can be selected to be different, and they do not need to be coaxial, that is, the centers of the two mirror surfaces do not need to be on the same straight line. The purpose of improving scanning efficiency can be achieved by simply adding the second mirror surface 18 on the back side of the first mirror surface 14. However, in order to maximize scanning efficiency, the second mirror surface 18 can be arranged coaxially with the first mirror surface 14, that is, the centers of the two mirror surfaces are on the same straight line, and the size and shape of the two mirror surfaces can also be selected to be the same.

[0070] S110 , removing the protective structure and performing a release process on the buried oxide layer of silicon on insulator to release the first mirror, the galvanometer drive structure and the second mirror.

[0071] It can be understood that the first mirror surface 14, the galvanometer drive structure 15, and the second mirror surface 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 surface 14, the galvanometer drive structure 15, and the second mirror surface 18 are in a suspended state. The process of removing the buried oxide 12 layer is the release process. The protective structure 16 is also irrelevant to the function of the galvanometer itself and needs to be removed. The order of removing the protective structure 16 and releasing the buried oxide layer 12 is mainly determined by the release process. If the release process has no corrosive effect on the first mirror surface 14 and the galvanometer drive structure 15, the protective structure can be removed first. Otherwise, the protective structure 16 should be retained. If the second mirror surface 18 is also corroded by the release process, it should also be aligned and protected by certain means. Please refer to Figure 6. The area where the buried oxide layer 12 is released in Figure 6 is only schematically drawn and may be different in galvanometers with different structures. It is worth mentioning that the first mirror 14, the galvanometer drive structure 15 and the second mirror 18 in Figures 2 to 6 are only drawn for schematic purposes, and only show the relative position relationship between them and the silicon on the insulating top, and do not represent the specific materials, structures, etc. of the first mirror 14, the galvanometer drive structure 15 and the second mirror 18.

[0072] Based on the MEMS galvanometer preparation method in this embodiment, after the original first mirror and the mirror drive structure are prepared, they are covered and protected by certain means to ensure that the subsequent process does not pollute or damage the first mirror. The wafer is turned over to the back to prepare the second mirror. After the second mirror is prepared, the overall movable structure is released. This solution doubles the number of galvanometer mirrors without increasing the complexity of the device structure. The laser radar made based on the galvanometer will also double the field of view angle and scanning efficiency, which can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in large-scale scanning applications. In addition, the structure and preparation process of the galvanometer are simple, which can greatly improve the preparation efficiency.

[0073] In one embodiment, the galvanometer drive structure is a piezoelectric drive structure. A first mirror surface and a galvanometer drive structure are prepared on a first surface of silicon-on-insulator, including:

[0074] (1) The silicon on insulator is thermally oxidized 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.

[0075] Referring to Figure 7 , the silicon-on-insulator (SOI) layer comprises, from top to bottom, top silicon 101, buried oxide 102, and bottom silicon 103. Referring to Figure 8 , after thermal oxidation, both top silicon 101 and bottom silicon 103 come into contact with oxygen and react to form a first oxide layer 104 and a second oxide layer 105, respectively.

[0076] (2) A bottom electrode layer, a piezoelectric layer and a top electrode layer are sequentially deposited on the first oxide layer.

[0077] It can be understood that in a piezoelectric drive structure, the inverse piezoelectric effect that occurs on piezoelectric materials is utilized. This is because piezoelectric materials deform when a voltage is applied. Therefore, the magnitude and frequency of this deformation can be controlled by controlling the electrical signal applied to the piezoelectric material. To utilize this effect, as shown in FIG9 , a bottom electrode layer 106, a piezoelectric layer 107, and a top electrode layer 108 are sequentially deposited and grown on the first oxide layer 104. The bottom electrode layer 106 and the top electrode layer 108 serve as media for applying an electric field to the piezoelectric layer 107 and have good electrical conductivity. The bottom electrode layer 106 will serve as the foundation for the first mirror in subsequent processes, so its material selection should also consider its laser reflectivity. Therefore, materials for the bottom electrode layer 106 and the top electrode layer 108 include, but are not limited to, metals with strong laser reflectivity, 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, lithium barium lead 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.

[0078] (3) According to the pattern of the cantilever beam, the top electrode layer and the piezoelectric layer are etched to obtain the top electrode region and the piezoelectric driving region of the piezoelectric driving structure.

[0079] It can be understood that one end of the cantilever beam is fixed to the external frame of the entire galvanometer, and the other end is connected to the first mirror surface. Its function is to suspend the mirror surface and drive the mirror surface to twist and rotate through elastic deformation. The piezoelectric drive structure includes the cantilever beam. According to the principle of the inverse piezoelectric effect, the piezoelectric drive structure should include a top electrode area, a piezoelectric drive area and a bottom electrode area. The elastic deformation is generated by applying an electric field to the piezoelectric drive area by energizing the top electrode area and the bottom electrode area. The shape of the cantilever beam will affect the rotation angle, frequency, etc. of the mirror surface. Therefore, the shape of the cantilever beam will be designed according to the functional requirements of the product. When the shape of the cantilever beam is observed from a top-down perspective, there will be a corresponding pattern. In order to prepare a cantilever beam of 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 pattern portion corresponding to the cantilever beam needs to be retained. Based on the pattern corresponding to the cantilever beam and the designed position, photolithography can be performed to form a first mask covering the area where the cantilever beam is located. Referring to Figure 10 , the area covered by the first mask will be protected during etching, the remaining portion of the top electrode layer 108 will be retained as the top electrode region 109 of the piezoelectric drive structure, and the remaining portion of 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.

[0080] (4) According to the pattern of the first mirror and the cantilever beam, the bottom electrode layer is etched to obtain the bottom electrode region and the first mirror of the piezoelectric drive structure.

[0081] It can be understood that in this embodiment, the bottom electrode layer 106 is used as the basis to form the first mirror. The shape of the first mirror can be designed according to the functional requirements of the product. When the first mirror is observed from a top view, a corresponding pattern will exist. In order to prepare the first mirror of the designed shape and retain the top electrode region 109 and the piezoelectric drive region 110 prepared 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 and the cantilever beam. Specifically, the pattern portions corresponding to the first mirror and the cantilever beam need to be retained. Based on the patterns corresponding to the first mirror and the cantilever beam, photolithography can be performed at the selected position to form a second mask covering the area where the first mirror and the cantilever beam are located. Please refer to Figure 11. The area covered by the second mask will be protected during etching, and the remaining portion of the bottom electrode layer 106 will be retained as the first mirror 113 and the bottom electrode region 112 of the piezoelectric drive structure respectively. The bottom electrode layer 106 in the area not covered by the second mask will be etched as the second etching area 114.

[0082] (5) According to the pattern of the first mirror and the cantilever beam, the first oxide layer and the top silicon are etched to obtain a frame area, a first support area corresponding to the piezoelectric drive structure, and a second support area corresponding to the first mirror.

[0083] It will be appreciated that further etching is required to support the piezoelectric drive structure and first mirror 113 formed in the above steps. Specifically, the patterned portions of the first mirror 113 and the cantilever beam need to be retained. Photolithography can be performed at selected locations based on the patterns corresponding to the first mirror 113 and the cantilever beam to form a third mask covering the areas where the first mirror 113 and the cantilever beam are located. Referring to Figure 12 , the areas covered by the third mask will be protected during etching, while the remaining portions of the first oxide layer 104 and the top silicon 101 will serve as the frame area 115, the first support area 117 corresponding to the piezoelectric drive structure, and the second support area 116 corresponding to the first mirror 113, respectively. The remaining portions of the first oxide layer 104 and the top silicon 101 below the outermost bottom electrode region 112 will serve as the frame area 115, the remaining portions of the first oxide layer 104 and the top silicon 101 below the first mirror 113 will serve as the second support area 116, and the remaining portions will serve as the first support area 117 corresponding to the piezoelectric drive structure. The first oxide layer 104 and the top silicon 101 in the area not covered by the third mask will be etched as the third etching area 118 .

[0084] 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.

[0085] In one embodiment, the first oxide layer 104 is etched using an inductively coupled enhanced plasma process or a reactive ion etching process; and the top silicon 101 is etched using a deep reactive ion etching process.

[0086] In one embodiment, etching the bottom silicon of the silicon-on-insulator to form a back cavity includes: etching the second oxide layer and the bottom silicon in sequence to form the back cavity.

[0087] Refer to Figure 13 . Reference numeral 119 in Figure 13 is protective structure 119. The outermost portion of the back surface in Figure 12 that requires protection can be marked using photolithography, and a fourth mask can be formed based on this marking. The second oxide layer 105 and the bottom silicon substrate 103 in the area not covered by the fourth mask will be etched away, and the cavity formed by these removals will become the back surface cavity 120. Etching the second oxide layer 105 can be performed using an inductively coupled enhanced plasma process or a reactive ion etching process. Etching the bottom silicon substrate 103 can be performed using a deep reactive ion etching process.

[0088] In one preferred embodiment, preparing a second mirror surface at a position corresponding to the first mirror surface within the back cavity includes: determining a target position based on a projection of the first mirror surface within the back cavity; and performing pattern transfer based on a pattern of the first mirror surface at the target position to prepare the second mirror surface.

[0089] Please refer to Figure 14. The target position is symmetrical to the first mirror 113. The second mirror 121 is set at this position, and the shapes of the two are also set to be the same, so that the two can have the same scanning effect. The pattern transfer process here can be deposited according to the material selected for the bottom electrode layer 106, and then the second mirror 121 is generated according to the pattern of the first mirror 113 using a stripping or etching process. Based on the structure of Figure 14, the protective structure 119 is removed and released, and the resulting structure is shown in Figure 15. The area removed during release is the first release area 122. The top view of the galvanometer corresponding to Figure 15 is shown in Figure 16. The cutting lines selected for the various cross-sectional views of Figures 7 to 15 are shown as the dotted lines in Figure 16. In Figure 16, the points on both sides of the galvanometer used to connect to the external circuit are called the upper electrode 123 and the lower electrode 124, respectively. The upper electrode 123 is the lead-out point for the top electrode area 109 to connect to the external circuit, and the lower electrode 123 is the lead-out point for the bottom electrode area 112 to connect to the external circuit. In the figure, the various regions of the piezoelectric drive structure are combined to form a cantilever beam 125. The cantilever beam 125 is in the shape of a planar spring. The distance between the various spring units can be set as needed, and a non-uniform spacing structure can be used to achieve different swing frequencies.

[0090] In one embodiment, the galvanometer drive structure is an electrostatic drive structure, and a first mirror surface and the galvanometer drive structure are prepared on a first surface of silicon-on-insulator, including:

[0091] (1) A metal layer is deposited on the top silicon of the wafer.

[0092] Referring to Figure 17 , the silicon-on-insulator (SOI) layer comprises, from top to bottom, top silicon 201, buried oxide 202, and bottom silicon 203. Referring to Figure 18 , a metal layer 204 is formed on top silicon 201 using a metal material with good conductivity and strong laser reflectivity. Materials for metal layer 204 include, but are not limited to, gold, silver, titanium, platinum, aluminum, copper, and molybdenum, all of which have strong laser reflectivity. Physical vapor deposition (PVD) can be used as the deposition process.

[0093] (2) According to the patterns of the electrode and the first mirror, the metal layer is etched to obtain the electrode region and the first mirror of the electrostatic drive structure.

[0094] It can be understood that the electrostatic drive structure mainly includes an electrode area, an outer comb tooth area, and an inner comb tooth area. Among them, the outer comb tooth area is a static comb tooth, which is integrated with the external frame. The inner comb tooth area is a dynamic comb tooth, which is integrated with the first mirror and connected to the anchor point of the external frame. The electrode area is used to connect to the external circuit, so that a voltage difference is generated between the comb teeth corresponding to the outer comb tooth area and the inner comb tooth area, thereby generating an electrostatic force, so that the inner comb tooth area drives the first mirror to swing. The electrode area and the first mirror have corresponding patterns when viewed from above. In order to prepare the electrode area and the first mirror of the designed shape, the metal layer 204 will be etched. Specifically, the pattern portion corresponding to the electrode area and the first mirror needs to be retained. Based on the pattern corresponding to the electrode area and the first mirror and the designed position, photolithography can be performed to form a fifth mask for the area where the electrode and the first mirror are located. Please refer to Figure 19. The area covered by the fifth mask will be protected during etching, and the remaining portion of the metal layer 204 will be retained as the electrode area 206 and the first mirror 205 respectively. The metal layer 204 in the area not covered by the fifth mask will be etched as the fourth etching area 207 .

[0095] (3) Etching the top silicon of the wafer according to the corresponding patterns of the external frame, anchor points, comb teeth and the support base of the first mirror 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.

[0096] It is understood that in order to further improve the electrostatic drive structure, further etching is required on the top silicon 201. Specifically, the patterns corresponding to the external frame, anchor points, comb teeth, and the support base of the first mirror 205 need to be retained. Based on the patterns corresponding to the external frame, anchor points, comb teeth, and the support base of the first mirror 205, photolithography can be performed at selected locations to form a sixth mask covering the frame area, anchor point area, comb tooth area, and the third support area corresponding to the first mirror 205. Referring to Figure 20, the areas covered by the sixth mask will be protected during etching, and the remaining portions of the top silicon 201 will serve as the frame area 208, the anchor point area (not shown in Figure 20 because it is an off-center cross-sectional view and the anchor point is located in the middle), the third support area 209 corresponding to the first mirror 205, and the comb tooth area 210. The top silicon 201 areas not covered by the sixth mask will be etched as the fifth etch area 211.

[0097] In one embodiment, steps S104 to S108 are performed based on the structure of FIG20 , and as shown in FIG21 , a back cavity 213 and a second mirror surface 214 are formed. The description thereof can be referred to above. Based on the structure of FIG21 , the protective structure is removed and released, and the resulting structure is shown in FIG22 . The area removed during release is the second release area 215. The top view of the galvanometer mirror corresponding to FIG22 is shown in FIG23 , wherein the section lines selected for each cross-sectional view of FIG17 to FIG22 are shown as the dotted lines in FIG23 . The comb tooth area 210 can be divided into an outer comb tooth area 210A and an inner comb tooth area 210B. The outer comb tooth area 210A is part of the frame area 208 and remains fixed during use. The inner comb tooth area 210B is the area that drives the mirror surface to rotate and is movable during use. The gap between the outer comb tooth area 210A and the inner comb tooth area 210B generates electrostatic induction, thereby driving the mirror surface to rotate. The anchor point area 216 is located in the middle of the galvanometer, and is connected to the inner comb tooth area 210B, the first mirror surface 205 and its corresponding third support area 209 .

[0098] In one embodiment, the process used to etch the metal layer is an ion beam etching process.

[0099] In one embodiment, the material of the protective structure includes polymethyl methacrylate (PMMA), polydimethylsiloxane (PDMS) or polyurethane (PI). These materials have strong acid and alkali corrosion resistance and high temperature resistance and are suitable for use as the material of the protective structure.

[0100] In one embodiment, the release treatment process is a wet process or a hydrogen fluoride gaseous release process. The wet process uses a liquid corrosive medium and has simple equipment, while the hydrogen fluoride gaseous release process uses gaseous HF, which can achieve a faster and more uniform release effect. The choice can be based on actual needs.

[0101] 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 14 and a galvanometer drive structure 15, which are arranged on the top silicon 11 of the silicon-on-insulator; the second mirror 18 is arranged in the back cavity 17 formed by etching the bottom silicon 13 of the silicon-on-insulator, corresponding to the position of the first mirror 14. The first mirror 14 and the second mirror 18 share the same galvanometer drive structure 15, and the second mirror 18 can move in the back cavity 17. When in use, 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 galvanometer mirror surfaces is doubled. The laser radar made based on the galvanometer will also double the field of view angle and scanning efficiency, which can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-scale scanning.

[0102] Based on the MEMS galvanometer in the above embodiment, it includes a first mirror, a galvanometer drive structure and a second mirror. The first mirror and the galvanometer drive structure are arranged on the top silicon of the silicon-on-insulator. The second mirror is arranged in a back cavity formed by etching the bottom silicon of the silicon-on-insulator, corresponding to the position of the first mirror. The second mirror shares the galvanometer drive structure of the first mirror, and the number of galvanometer mirror surfaces is doubled without increasing the complexity of the device structure. The laser radar made based on the galvanometer will also double the field of view angle and scanning efficiency, which can well solve the problem of insufficient scanning efficiency of the scanning galvanometer in the application scenario of large-scale scanning.

[0103] The first mirror 14, the galvanometer drive structure 15, and the second mirror 18 in FIG6 are only schematically depicted, and only illustrate their relative positional relationship with the silicon-on-insulator (SOI) and do not represent the specific materials, structures, etc. of the first mirror 14, the galvanometer drive structure 15, and the second mirror 18. The specific structures of the MEMS galvanometer in different drive structures can be found below:

[0104] In a specific embodiment, the MEMS oscillator can be piezoelectrically driven. Please refer to Figures 7 to 16. The silicon-on-insulator comprises, from top to bottom, a top silicon 101, a buried oxide layer 102, and a bottom silicon 103. On top of the top silicon 101, the oscillator also 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. A second oxide layer 105 is also included on the bottom silicon 103. 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. And after the bottom electrode layer 106 is etched according to the pattern of the first mirror 113 and the cantilever beam 125, it will include a first mirror 113 and a bottom electrode region 112 of the piezoelectric drive structure. After the first oxide layer 104 and the top silicon 101 are etched according to the patterns of the first mirror 113 and the cantilever beam 125, they will include a frame area 115, a first support area 117 corresponding to the piezoelectric drive structure, and a second support area 116 corresponding to the first mirror 113. The frame area 115 is the main body of the entire galvanometer, while the first support area 117 and the second support area 116 respectively support the piezoelectric drive structure and the first mirror 113 located thereon. Due to the presence of the second oxide layer 105, when etching the back cavity 120, the bottom silicon 103 and the second oxide layer 105 will be etched at the same time. After all 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 various areas of the piezoelectric drive structure. The top electrode area 109 includes an upper electrode 123, which is the lead-out point for connecting the top electrode area 109 to the external circuit. The bottom electrode region 112 includes a lower electrode 123 , which is a lead-out point for connecting the bottom electrode region 112 to an external circuit.

[0105] In one specific embodiment, the MEMS galvanometer can be electrostatically driven. See Figures 17 to 23. From top to bottom, the silicon-on-insulator (SOI) comprises top silicon 201, a buried oxide layer 202, and bottom silicon 203. A metal layer 204 is also included above the top silicon 201. After etching the metal layer 204 according to the patterns of the electrodes and first mirror 205, it will include an electrode region 206 for the electrostatic drive structure and the first mirror 205. After etching the top silicon 201 according to the patterns corresponding to the external frame, anchor points, comb teeth, and support base of the first mirror, it will include a frame region 208, an anchor point region 216, a comb tooth region 210 for the electrostatic drive structure, and a third support region 209 corresponding to the first mirror 205. Subsequently, etching the top silicon 203 will form a back cavity 213. A second mirror 214 corresponding to the first mirror 205 can be fabricated on the buried oxide layer 202 within the back cavity 213. The buried oxide layer 202 is then etched, releasing the first mirror 205, the second mirror 214, and the inner comb-tooth region 210B that drives the first and second mirrors 205 and 214. The inner comb-tooth region 210B is connected to the frame region 208 via the anchor region 216. The frame region 208 includes an outer comb-tooth region 210A that mates with the inner comb-tooth region 210B. The gap between the outer comb-tooth region 210A and the inner comb-tooth region 210B generates electrostatic induction, thereby driving the mirrors to rotate.

[0106] Finally, it should be noted that, in this document, relational terms such as first and second, etc., are used only 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 terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising the element.

[0107] The various embodiments in this specification are described in a progressive manner, and 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 referenced to each other.

[0108] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one 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. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A MEMS galvanometer, characterized in that: include: A first mirror and a galvanometer drive structure are disposed on top of the silicon on insulator; The second mirror is arranged in a back cavity formed by etching the bottom silicon of the silicon-on-insulator, corresponding to the first position.

2. A method for preparing a MEMS galvanometer, characterized in that: include: Prepare a first mirror and a galvanometer drive structure on the top silicon of the silicon-on-insulator sheet; Preparing a protection structure for protecting the first mirror surface and the galvanometer drive structure; Etching the bottom silicon of the silicon-on-insulator to form a back cavity; Preparing a second mirror surface at a position in the back cavity corresponding to the first mirror surface; The protection structure is removed, and a release process is performed on the buried oxide layer of silicon on the insulator to release the first mirror, the galvanometer drive structure, and the second mirror.

3. The method for preparing a MEMS galvanometer according to claim 2, characterized in that: The galvanometer drive structure is a piezoelectric drive structure, and the first mirror surface and the galvanometer drive structure are prepared on the top silicon of the silicon-on-insulator sheet, including: Performing 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; A bottom electrode layer, a piezoelectric layer and a top electrode layer are sequentially deposited on the first oxide layer; According to the pattern of the cantilever beam, etching the top electrode layer and the piezoelectric layer to obtain the top electrode region and the piezoelectric driving region of the piezoelectric driving structure; According to the patterns of the first mirror surface and the cantilever beam, etching the bottom electrode layer to obtain the bottom electrode region of the piezoelectric drive structure and the first mirror surface; According to the patterns of the first mirror and the cantilever beam, the first oxide layer and the top silicon are etched to obtain a frame area, a first supporting area corresponding to the piezoelectric drive structure, and a second supporting area corresponding to the first mirror.

4. The method for preparing a MEMS galvanometer according to claim 3, characterized in that: The top electrode layer, the piezoelectric layer and the bottom electrode layer are etched by using an ion beam etching process or a reactive ion etching process.

5. The method for preparing a MEMS galvanometer according to claim 3, characterized in that: The first oxide layer is etched by using an inductively coupled enhanced plasma etching process or a reactive ion etching process; and the top silicon is etched by using a deep reactive ion etching process.

6. The method for preparing a MEMS galvanometer according to claim 3, characterized in that: The etching of the bottom silicon of the silicon on insulator to form a back cavity comprises: The second oxide layer and the bottom silicon are etched in sequence to form the back cavity.

7. The method for preparing a MEMS galvanometer according to claim 2, characterized in that: The galvanometer drive structure is an electrostatic drive structure, and the first mirror surface and the galvanometer drive structure are prepared on the top silicon of the silicon-on-insulator sheet; comprising: Depositing a metal layer on the top silicon of the wafer; According to the patterns of the electrode and the first mirror, the metal layer is etched to obtain the electrode region and the first mirror of the electrostatic drive structure; According to the patterns corresponding to the external frame, anchor points, comb teeth and the support base of the first mirror, the top silicon of the sheet is etched to obtain the frame area, the anchor point area, the comb tooth area of ​​the electrostatic drive structure and the third support area corresponding to the first mirror.

8. The method for preparing a MEMS galvanometer according to claim 7, characterized in that: The metal layer is etched using an ion beam etching process.

9. The method for preparing a MEMS galvanometer according to any one of claims 2 to 8, characterized in that: The material of the protection structure includes polymethyl methacrylate, polydimethylsiloxane or polyurethane.

10. The method for preparing a MEMS galvanometer according to any one of claims 2 to 8, characterized in that: The step of preparing a second mirror surface at a position corresponding to the first mirror surface in the back cavity comprises: determining a target position according to a 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.

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