Micro-electro-mechanical system (mems) scanning mirror and method of manufacturing the same

Abstract

The embodiment of the present disclosure relates to the technical field of micro-electro-mechanical system, and provides a micro-electro-mechanical system (MEMS) scanning mirror and a preparation method thereof, which comprises a mirror, a driving module comprising a fixed beam with fixed position, a rotating beam capable of rotating around an axis and a connecting piece, a first comb tooth arranged on the fixed beam, a second comb tooth arranged on the rotating beam, the first comb tooth formed on a first film layer, the second comb tooth formed on a second film layer, the first comb tooth and the second comb tooth capable of driving the rotating beam to swing under the action of a driving signal, the connecting piece connecting the mirror and the rotating beam, and the swinging rotating beam capable of driving the mirror to rotate through the connecting piece.In the embodiment of the present disclosure, on the one hand, different thicknesses of film layers can be used for processing according to the height requirements of the comb tooth, thereby improving the size consistency of the film layer; on the other hand, an etching blocking layer can be arranged in the preparation process, so that the rate and time of etching silicon do not need to be accurately controlled, the preparation efficiency of the chip is improved, and the chip is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and in particular to a MEMS scanning mirror and its fabrication method. Background Technology

[0002] Micro-Electro-Mechanical System (MEMS) scanning mirrors are optical devices that integrate a micro-light reflector with a MEMS actuator based on MEMS technology. The micro-light reflector can achieve translational motion or pivotal rotation in one or two dimensions under the action of the MEMS actuator.

[0003] In related technologies, the production process of MEMS scanning mirrors is complex and inefficient, making large-scale mass production difficult. Moreover, the dimensional consistency of the produced MEMS is poor. Summary of the Invention

[0004] This invention provides a microelectromechanical system (MEMS) scanning mirror and its fabrication method.

[0005] The first aspect of this disclosure provides a microelectromechanical system (MEMS) scanning mirror, comprising:

[0006] Mirror;

[0007] The drive module includes: a fixed beam with a fixed position, a rotating beam that can rotate around an axis, and connecting parts;

[0008] The fixed beam is provided with a first comb tooth; the rotating beam is provided with a second comb tooth; the first comb tooth is formed on a first film layer, and the second comb tooth is formed on a second film layer; the first comb tooth and the second comb tooth can drive the rotating beam to swing under the action of a driving signal;

[0009] The connector connects the mirror and the rotating beam; the swinging rotating beam can drive the reflector to rotate through the connector; the connector includes a link and a hinge connected to the link; the mirror, the link and / or the hinge each include an upper part and a lower part; the upper part is formed on the second film layer; the lower part is formed on the first film layer.

[0010] In one embodiment, the first film layer and the second film layer are made of the same material and / or have the same thickness.

[0011] In one embodiment, the driving module includes a plurality of stacked film layers; the plurality of stacked film layers include: a first film layer, a second film layer, and a bonding layer disposed between the first film layer and the second film layer.

[0012] In one embodiment, the upper part of the mirror is a mirror surface formed on the second film layer; and / or, the lower part of the mirror is a mirror reinforcing rib formed on the first film layer and the bonding layer; and / or, the connecting rod and / or the hinge are formed on the first film layer, the second film layer and the bonding layer.

[0013] A second aspect of this disclosure provides a method for fabricating a MEMS scanning mirror, comprising:

[0014] The first comb teeth, the lower part of the connecting rod, the lower part of the hinge and / or the mirror reinforcing rib are etched on the first film layer of the first wafer, wherein the first wafer includes the first film layer and a first etching barrier layer adjacent to a surface of the first film layer.

[0015] The second wafer is bonded to the first wafer on the other surface of the first film layer, wherein the second wafer includes a second film layer, a second etch barrier layer adjacent to one surface of the second film layer, and a bonding layer adjacent to the other surface of the second film layer;

[0016] The second comb teeth, the upper part of the connecting rod, the upper part of the hinge, and / or the mirror surface are etched on the second film layer of the second wafer.

[0017] In one embodiment, the method further includes:

[0018] After bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes:

[0019] Annealing at a first predetermined temperature;

[0020] After the predetermined time, stop the annealing and cool down to the second predetermined temperature at the predetermined cooling rate.

[0021] In one embodiment, after bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes:

[0022] The substrate layer and / or the second etch barrier layer on the second wafer are removed using a wet etching process;

[0023] And / or,

[0024] The SiO2 between the first comb teeth and / or the second comb teeth is removed by a wet etching process.

[0025] In one embodiment, the first wafer includes a substrate layer; the method further includes:

[0026] Etch a portion of the substrate layer;

[0027] The support sheet is bonded to the substrate layer;

[0028] Perform surface treatment on the pads and / or mirror areas;

[0029] The support sheet is removed after the surface treatment is completed.

[0030] In one embodiment, the surface treatment of the pads and / or mirror areas includes:

[0031] Metal is sputtered and / or evaporated in the area corresponding to the pad on the upper surface of the second film layer, wherein the metal includes Ti and / or Al;

[0032] And / or,

[0033] The surface pads are annealed at a third predetermined temperature in a vacuum environment to form ohmic contacts;

[0034] And / or,

[0035] After annealing, metal is sputtered and / or evaporated onto the mirror region of the upper surface of the second film layer, wherein the metal includes Ti and / or Al.

[0036] A third aspect of this disclosure provides a lidar, which includes any of the MEMS scanning mirrors described in the embodiments of this disclosure.

[0037] The beneficial effects of the technical solution provided in this disclosure compared with the prior art are as follows:

[0038] In this embodiment, the fixed beam is provided with a first comb tooth; the rotating beam is provided with a second comb tooth; the first comb tooth is formed on a first film layer, and the second comb tooth is formed on a second film layer. Thus, in this MEMS scanning mirror, since the first and second comb teeth are formed on different film layers, compared to forming them on the same film layer, on the one hand, different thicknesses of film layers can be used for processing according to the height requirements of the comb teeth, improving the dimensional consistency of the comb teeth; on the other hand, an etching barrier layer can be set on the surface of the film layer during the fabrication process, thereby eliminating the need for precise control of the etching rate and time of silicon, improving the chip fabrication efficiency, and making it suitable for large-scale mass production.

[0039] The connector links the mirror and the rotating beam; the swinging rotating beam can drive the mirror to rotate via the connector; the connector includes a link and a hinge connected to the link; the mirror, the link, and / or the hinge each include an upper part and a lower part; the upper part is formed on the second film layer; the lower part is formed on the first film layer. Here, because the connector includes a link and a hinge connected to the link, compared to the case where the connector only includes a link, the hinge can increase the swing amplitude of the connector, thereby enabling the free movement of the mirror and making the movement of the mirror more sensitive. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure of a MEMS scanning mirror provided in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the film structure of a MEMS scanning mirror provided in an embodiment of the present invention.

[0042] Figure 3 This is a schematic diagram of the film structure of a MEMS scanning mirror provided in an embodiment of the present invention.

[0043] Figure 4 This is a schematic flowchart of a method for fabricating a MEMS scanning mirror according to an embodiment of the present invention.

[0044] Figure 5 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0045] Figure 6 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0046] Figure 7 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0047] Figure 8 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0048] Figure 9 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0049] Figure 10 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0050] Figure 11 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0051] Figure 12 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0052] Figure 13 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0053] Figure 14 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0054] Figure 15 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0055] Figure 16 This is a schematic diagram of the film structure during the fabrication process of a MEMS scanning mirror provided in an embodiment of the present invention.

[0056] Figure 17 This is a schematic flowchart of a method for fabricating a MEMS scanning mirror according to an embodiment of the present invention. Detailed Implementation

[0057] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0058] To better understand the embodiments of this disclosure, the following examples illustrate MEMS:

[0059] In some embodiments, the driving methods of MEMS scanning mirrors include electrostatic driving, piezoelectric driving, electromagnetic driving, and thermoelectric driving. Among these, electrostatically driven MEMS scanning mirrors have advantages such as small size, low power consumption, high reliability, and quasi-static operation, and are widely used in head-mounted displays, LiDAR, augmented reality, and other fields. However, compared with other driving methods, electrostatic driving has a smaller driving force. As a result, most MEMS scanning mirrors have a smaller deflection angle or can only operate in a resonant state, which limits the applicable scenarios of the scanning mirrors.

[0060] In one embodiment, a frameless electrostatic MEMS scanning mirror is provided. Unlike most electrostatic MEMS scanning mirrors, the mirror surface rotation direction is perpendicular to the drive shaft, and the two are connected by a linkage and a flexible hinge. The linkage and flexible hinge form a lever-like structure, and the rotation angle of the mirror surface can be increased by increasing the length of the linkage. In terms of the drive structure, the electrostatic comb teeth are designed with both high and low comb teeth, so that the mirror surface can still deflect even under DC drive, thereby achieving quasi-static operation of the scanning mirror. The advantages of large rotation angle and quasi-static operation greatly improve the applicable scenarios of this scanning mirror. However, this MEMS scanning mirror chip suffers from a serious shortage of production capacity. The reason is that the high and low comb teeth, linkage, flexible hinge, and mirror surface of the scanning mirror are designed on the same silicon layer in the film layer structure design of the scanning mirror chip. This requires precise control of the etching rate and etching time of silicon and silicon oxide during chip fabrication, resulting in complex chip fabrication processes and low processing efficiency, making it difficult to mass-produce.

[0061] In one embodiment, the height of the comb teeth is controlled by mechanical thinning and / or dry etching processes. Since the above two processes have certain intra-chip and inter-chip inhomogeneities, the comb tooth heights of different chips are inconsistent, resulting in poor consistency of key characteristics of the scanning mirror such as resonant frequency and rotation angle. Therefore, individual calibration of the chips is required, which leads to greater development difficulty and longer development cycle for backend users.

[0062] To illustrate the technical solution described in this invention, specific embodiments are described below.

[0063] like Figure 1 and Figure 2 As shown, this disclosure provides a microelectromechanical system (MEMS) scanning mirror, including:

[0064] Mirror 107;

[0065] The drive module includes: fixed beams (113, 115 and 117) with fixed positions, a rotating beam 109 that can rotate about an axis, and connecting parts (including 105 and 122);

[0066] The fixed beams (113, 115, and 117) are provided with first comb teeth 112; the rotating beam 109 is provided with second comb teeth 111; the first comb teeth 112 are formed on the first film layer (e.g., Figure 2 (B), the second comb teeth 111 are formed on the second film layer (e.g. Figure 2 A); the first comb tooth 112 and the second comb tooth 111 can drive the rotating beam 109 to swing under the action of the driving signal;

[0067] The connector connects the mirror 107 and the rotating beam 109; the swinging rotating beam 109 can drive the mirror 107 to rotate through the connector; the connector includes connecting rods (105 and 122) and hinges (106 and 108) connected to the connecting rods; the mirror 107, the connecting rods (105 and 122) and / or the hinges (106 and 108) each include an upper part and a lower part; the upper part is formed in the second film layer B; the lower part is formed in the first film layer A.

[0068] In one embodiment, the first film layer B used to process the first comb tooth 112 and the second film layer A used to process the second comb tooth 111 are not the same film layer.

[0069] In one scenario embodiment, the MEMS scanning mirror can be applied to a lidar system. The lidar can detect the position, velocity, and other characteristics of a target object based on the MEMS scanning mirror and by emitting a laser beam. Exemplarily, the lidar system comprises a transmitting system, a receiving system, and a scanning system, and the MEMS scanning mirror can be applied to the aforementioned scanning system.

[0070] In one embodiment, the MEMS scanning mirror may be an electrostatic MEMS scanning mirror; please refer again to [link to previous document]. Figure 1 This is a top view of an electrostatic MEMS scanning mirror. In this disclosure, the MEMS scanning mirror can refer to a MEMS scanning mirror chip. The MEMS scanning mirror chip may include a driving module (101, 102, 103, and 104), a mirror 107, and a connector. It should be noted that one or more of the driving module, the mirror, and the connector can be formed based on film etching, and this is not limited thereto. Here, the film can be a Si device layer.

[0071] In some embodiments, the connector may also be a combination of links (105 and 122) and flexible hinges (106 and 108), without limitation.

[0072] In one embodiment, the drive module may include comb teeth, a rotating beam 109, a rotating shaft 110, a fixed anchor point 119, fixed beams (113, 115, and 117), and metal pads (114, 116, 118, 120, and 121). The comb teeth include first comb teeth 112 and second comb teeth 111; it should be noted that the first comb teeth 112 and the second comb teeth 111 may appear in pairs. The first comb teeth 112 and the second comb teeth 111 may be arranged in parallel and staggered positions in space. In this embodiment, the number, shape, and / or positional relationship of the first comb teeth 112 and the second comb teeth 111 are not limited.

[0073] In one embodiment, the comb teeth formed on the rotating beam 109 are second comb teeth 111, also referred to as moving teeth. The comb teeth formed on the fixed beams (113, 115, and 117) are first comb teeth 112, also referred to as fixed teeth. The rotating beam 109 and the fixed beams (113, 115, and 117) may be arranged in parallel.

[0074] In one embodiment, by applying voltages to the metal pads (114, 116, 118, and 121) respectively (metal pad 120 may be grounded), the second comb tooth 111 is attracted by the first comb tooth 112 and rotates, thereby driving the rotating beam 109 to swing about the rotation axis 110. The swinging of the rotation axis 109 drives the connecting rod 105 and the flexible hinge (106 and 108) to rotate, thereby driving the mirror surface of the reflector 107 to rotate.

[0075] In one embodiment, the mirror 107 can be connected to multiple drive modules, for example, such as... Figure 1 The four drive modules shown.

[0076] In one embodiment, multiple drive modules may have the same structure. The locations of the multiple drive modules may differ. For example, the drive modules are arranged in pairs along different dimensions of the mirror 107; for instance, the drive modules are arranged along both the x and y dimensions of the mirror 107.

[0077] In one embodiment, the MEMS scanning mirror is a two-dimensional scanning mirror, wherein the driving modules 101 and 102 form a group that can drive the mirror 107 to rotate in the first dimension; and the driving modules 103 and 104 form a group that can drive the mirror 107 to rotate in the second dimension.

[0078] In this embodiment, the fixed beam is provided with a first comb tooth; the rotating beam is provided with a second comb tooth; the first comb tooth is formed on a first film layer, and the second comb tooth is formed on a second film layer. Thus, in this MEMS scanning mirror, since the first and second comb teeth are formed on different film layers, compared to forming them on the same film layer, on the one hand, different thicknesses of film layers can be used for processing according to the height requirements of the comb teeth, improving the dimensional consistency of the comb teeth; on the other hand, an etching barrier layer can be set on the surface of the film layer during the fabrication process, thereby eliminating the need for precise control of the etching rate and time of silicon, improving the chip fabrication efficiency, and making it suitable for large-scale mass production.

[0079] The connector links the mirror and the rotating beam; the swinging rotating beam can drive the mirror to rotate via the connector; the connector includes a link and a hinge connected to the link; the mirror, the link, and / or the hinge each include an upper part and a lower part; the upper part is formed on the second film layer; the lower part is formed on the first film layer. Here, because the connector includes a link and a hinge connected to the link, compared to the case where the connector only includes a link, the hinge can increase the swing amplitude of the connector, thereby enabling the free movement of the mirror and making the movement of the mirror more sensitive.

[0080] In one embodiment, see Figure 2 The first film layer B and the second film layer A are made of the same material and / or have the same thickness.

[0081] In one embodiment, the driving module includes multiple stacked film layers; the multiple stacked film layers include: a first film layer B, a second film layer A, and a bonding layer disposed between the first film layer B and the second film layer A. Here, the bonding layer may be a SiO2 bonding layer. The bonding layer may be a film layer obtained after bonding the first film layer B and the second film layer A.

[0082] In one embodiment, the upper part of the mirror 107 is a mirror surface formed on the second film layer A; and / or, the lower part of the mirror 107 is a mirror reinforcing rib formed on the first film layer B and the bonding layer. The mirror reinforcing rib may be used to support the mirror 107.

[0083] In one embodiment, the link 105 and / or the hinge (106 and 108) are formed on the first film layer B, the second film layer A, and the bonding layer.

[0084] In one embodiment, the connector is fabricated based on the first film layer B, the second film layer A, and the bonding layer. Here, the connector can be fabricated using a predetermined etching process.

[0085] In one embodiment, Figure 2 This is a schematic diagram of the cross-sectional film layers of a multi-layer electrostatic MEMS scanning mirror based on silicon-on-insulator (SOI) substrate (along...). Figure 1 (Section cut along the AA direction). Figure 2In the direction of the middle arrow, the layers are, in sequence, a first Si device layer 201, a SiO2 bonding intermediate layer (also called a bonding layer) 202, a second Si device layer 203, a SiO2 insulating layer 204, and a substrate Si layer 205. The first film layer B can be the first Si device layer 201, and the second film layer A can be the second Si device layer 203. The bonding layer can be the SiO2 bonding intermediate layer 202.

[0086] In one embodiment, the first Si device layer 201 and the second Si device layer 203 are made of the same material. For example, both are N-type doped low-resistivity silicon.

[0087] In one embodiment, the first Si device layer 201 and the second Si device layer 203 have the same thickness. For example, the thickness is 30 μm.

[0088] For example, the thickness of the SiO2 bonding intermediate layer 202 is 1 μm.

[0089] For example, the thickness of the substrate Si layer 205 is 450 μm.

[0090] In one embodiment, the electrostatic comb teeth are divided into two types: high teeth 206 (i.e., the second comb teeth 111) and low teeth 207 (i.e., the first comb teeth 112). The high teeth 206 are formed on the first Si device layer 201, and the height of the high teeth 206 is the same as the thickness of the first Si device layer 201. The low teeth are formed on the second Si device layer 203, and the height of the low teeth is the same as the thickness of the second Si device layer 203.

[0091] In one embodiment, the mirror surface 208 of the MEMS scanning mirror is formed on the first Si device layer 201, and the mirror reinforcing rib 212 is jointly formed by the bonding intermediate layer 202 and the second Si device layer 203. Here, the mirror surface 208 can be the mirror 107.

[0092] In one embodiment, the connecting rod 213 and the flexible hinge 214 are jointly composed of a first Si device layer 201, a second Si device layer 203, and a bonding intermediate layer 203.

[0093] In one embodiment, metal pads 210 are formed on the upper surface of the first Si device layer 201, and metal pads 211 are formed on the upper surface of the second Si device layer 202, serving as access points for drive signals, respectively. The drive signals can be electrical signals.

[0094] In one embodiment, the metal pad 210 may be made of Ti and / or Al, and exemplaryly, may form an ohmic contact with the Si of the device layer. In another embodiment, the upper surface of the mirror 208 is also covered with Ti and / or Al to enhance the reflectivity of the mirror.

[0095] In one embodiment, the second Si device layer 203, the SiO2 insulating layer 204, and the substrate Si layer 205 are derived from the same SOI wafer, while the first Si device layer 201 is derived from another SOI wafer. Here, the SOI wafer can correspond to one film layer.

[0096] To better understand Figure 2 The film structure shown below illustrates the film structure of a MEMS scanning mirror in the related art through an embodiment:

[0097] Please see Figure 3 The diagram shows a cross-sectional film layer schematic of a MEMS scanning mirror product in the related technology. It should be noted that... Figure 3 The example structures shown are not intended to limit the scope of this disclosure and are merely illustrative examples for understanding purposes.

[0098] exist Figure 3In the diagram, following the arrow direction, from top to bottom, are the Si device layer 301, the SiO2 insulating layer 302, and the Si substrate layer 303. It can be seen that the MEMS scanning mirror has only one silicon layer as the Si device layer. The functional components of the scanning mirror include high teeth 304, low teeth 305, connecting rods 309, and flexible hinges 320, all formed on the same Si device layer 301. The heights of the high teeth 304 and low teeth 305 (e.g., 21 μm) are inconsistent with the thickness of the device layer (e.g., 40 μm). Therefore, during the fabrication of the comb teeth, the Si device layer 301 needs to be etched from both the top and bottom directions. Since there is no silicon oxide layer in the middle of the Si device layer as an etching barrier, the etching rate and time need to be precisely controlled during the etching of both the high and low teeth, and the etching program may even need to be repeatedly modified, resulting in low chip fabrication efficiency. Furthermore, the thickness of device layer 301 is achieved by thinning the silicon wafer from approximately a first thickness (e.g., 500 μm) to a second thickness (e.g., 40 μm) using mechanical thinning and chemical mechanical polishing (CMP) processes. Mechanical polishing and CMP consume significant time, further reducing chip fabrication efficiency. Moreover, both mechanical thinning and dry etching processes exhibit intra-wafer / inter-wafer inhomogeneities, leading to inconsistencies in the height of the comb teeth (304, 305), the thickness of the connecting rod 309, the flexible hinge 320, and the mirror 306 across different chips. This, in turn, causes inconsistencies in the scanning mirror's rotation angle and resonant frequency, reducing the scanning mirror's yield. These two issues make it difficult to mass-produce this electrostatic scanning mirror chip, resulting in a high price and limiting its widespread application in fields such as LiDAR. Therefore, this disclosure proposes... Figure 2 The MEMS scanning mirror shown.

[0099] like Figure 4 As shown, this disclosure provides a method for fabricating a MEMS scanning mirror, including:

[0100] Step 41: Etch a first comb tooth, a lower part of a connecting rod, a lower part of a hinge, and / or a mirror-finish reinforcing rib on a first film layer of a first wafer, wherein the first wafer includes the first film layer and a first etching barrier layer adjacent to a surface of the first film layer.

[0101] Step 42: Bond the second wafer to the first wafer on the other surface of the first film layer, wherein the second wafer includes a second film layer, a second etch barrier layer adjacent to one surface of the second film layer, and a bonding layer adjacent to the other surface of the second film layer;

[0102] Step 43: Etch the second comb teeth, the upper part of the connecting rod, the upper part of the hinge, and / or the mirror surface on the second film layer of the second wafer.

[0103] In one embodiment, the wafer can be an SOI wafer. Here, the first wafer can be a first SOI wafer; the first film layer can be a Si device layer 401; the etch barrier layer can be a SiO2 intermediate layer 402; the second wafer can be a second SOI wafer; the second film layer can be a Si device layer 405; the bonding layer can be a SiO2 layer 407; the first comb tooth 112 can be a low tooth or a lower tooth 404; the second comb tooth 112 can be a high tooth or an upper tooth 409.

[0104] Please see Figure 5 The first SOI wafer used in the fabrication process was then produced. For example, the diameter of the first SOI wafer can be 6 inches or 8 inches.

[0105] In one embodiment, the first SOI wafer may include a Si device layer 401, a SiO2 intermediate layer 402, and a Si substrate 403. Exemplarily, the Si device layer 401 may have a thickness of 30 μm and may be an N-type low-resistivity single-crystal silicon layer. Exemplarily, the SiO2 intermediate layer 402 may have a thickness of 2 μm. Exemplarily, the Si substrate 403 may be a high-resistivity single-crystal silicon with a thickness of 450 μm.

[0106] In one embodiment, the method further includes:

[0107] The mirror reinforcement ribs of the MEMS scanning mirror are etched on the first film layer B of the first wafer.

[0108] In one embodiment, see Figure 6 The low-tooth 404 (corresponding to the aforementioned first comb tooth 112) and mirror-finish reinforcing rib 418 structure are etched on the Si device layer of the first SOI wafer using reactive ion deep etching (DRIE) technology. The resulting structure also includes a connecting rod 419 and the lower half (half the height) of a flexible hinge 330. In one embodiment, the DRIE etching rate ratio of Si to SiO2 is approximately 100:1. Therefore, the SiO2 intermediate layer 402 can serve as the first etching barrier layer. Over-etching is allowed for a period of time during the DRIE etching process, thus reducing the requirements for controlling the etching rate and time. Furthermore, the height of the low-tooth 404 and other structures is determined by the thickness of the Si device layer 401 and is not affected by the DRIE process, resulting in high structural consistency.

[0109] In one embodiment, see Figure 7The second SOI wafer used in the fabrication process has the same characteristics as the first SOI wafer. In one embodiment, to improve bonding power, a layer of SiO2 (407, corresponding to the aforementioned bonding layer) is deposited on the surface of the Si device layer 401 of this SOI. Exemplarily, the thickness of this SiO2 layer can be 1 μm.

[0110] In one embodiment, after bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes:

[0111] Step a: Anneal at a first predetermined temperature;

[0112] Step b: Stop annealing after the predetermined time and cool down to the second predetermined temperature at the predetermined cooling rate.

[0113] For example, the first predetermined temperature may be 1100℃±100℃.

[0114] For example, the scheduled duration can be 4 hours ± 2 hours.

[0115] For example, the second predetermined temperature can be 25°C ± 5°C.

[0116] In one embodiment, see Figure 8 Two SOI wafers are bonded together using a SiO2 layer (407) as an intermediate bonding layer. In one embodiment, the pre-bonding process is hydrophilic bonding. After pre-bonding, the wafers are annealed in a high-temperature furnace at 1100°C for 4 hours and then slowly cooled to room temperature to complete the high-strength bonding of the wafers.

[0117] In one embodiment, after bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes: removing the substrate layer and / or etch barrier layer on the second wafer using a wet etching process.

[0118] In one embodiment, see Figure 9 The substrate layer 408 and the SiO2 layer 406 of the second SOI wafer are removed by wet etching, leaving only the Si device layer 405.

[0119] In one embodiment, see Figure 10 The upper tooth 409 (corresponding to the second comb tooth 111), the mirror structure 420, and the upper part of the connecting rod 419 and the flexible hinge 420 are etched on the device layer 405 using the DRIE process. Here, the SiO2 layer 407 acts as an etching barrier layer, which has low requirements for etching process control precision and good dimensional consistency of the etched structure.

[0120] In one embodiment, see Figure 11The Si substrate layer 403 is etched using DRIE etching down to the SiO2 insulating layer 402, creating the cutout area on the back of the chip. The SiO2 insulating layer 402 also acts as an etching barrier layer during the etching process.

[0121] In one embodiment, a wet etching process is used to remove SiO2 between the first comb teeth and / or the second comb teeth.

[0122] In one embodiment, see Figure 12 Wet etching is used to remove SiO2 between the comb teeth and other structures, thereby releasing the comb teeth.

[0123] It should be noted that, in one embodiment, the following can be performed sequentially: Figure 6 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 The implementation of this disclosure solution can also be carried out in other sequences that embody the technical concept of this disclosure, and no limitation is made here.

[0124] In one embodiment, the first wafer includes a substrate layer; the method further includes:

[0125] Step a: Etch a portion of the substrate layer;

[0126] Step b: Bond the support sheet to the substrate layer;

[0127] Step c: Perform surface treatment on the pads and / or mirror areas;

[0128] Step d: Remove the support sheet after the surface treatment is completed.

[0129] Surface treatment includes coating treatment.

[0130] In one embodiment, the surface treatment of the pads and / or mirror areas includes:

[0131] Metal is sequentially sputtered and / or evaporated in the area corresponding to the pads on the upper surface of the second film layer, wherein the metal includes Ti and / or Al;

[0132] And / or,

[0133] The surface pads are annealed at a third predetermined temperature in a vacuum environment to form ohmic contacts;

[0134] And / or,

[0135] After annealing, metal is sequentially sputtered and / or evaporated onto the mirror region of the upper surface of the second film layer, wherein the metal includes Ti and / or Al.

[0136] For example, the third predetermined temperature can be 450℃±100℃.

[0137] In one embodiment, see Figure 13 Since most areas of the wafer are hollowed out, in order to enhance the strength and maneuverability of the wafer, a piece of glass 411 must be temporarily bonded to the lower surface of the substrate layer 403 as a support sheet before coating.

[0138] In one embodiment, see Figure 14 10nm Ti (412, 415) and 200nm Al (413, 414) were sputtered / deposited sequentially in the area corresponding to the pads on the upper surface of device layer 405, and annealed at 400℃ in a vacuum environment to form ohmic contacts.

[0139] In one embodiment, see Figure 15 After annealing, 10nm Ti (416) and 200nm Al (417) are sequentially sputtered / deposited on the mirror area of ​​the Si device layer 405 to form a reflective film. Figure 14 He Ru Figure 15 The reason for separating the two coating processes is that the annealing process increases the roughness of the metal film and reduces its reflectivity.

[0140] In one embodiment, see Figure 16 The diagram shows the process of removing the support sheet, thus completing the fabrication of the entire MEMS scanning mirror.

[0141] To better understand the embodiments of this disclosure, the following exemplary embodiment will be used to illustrate the embodiments of this disclosure:

[0142] Example 1:

[0143] This disclosure uses at least two SOI wafers, namely a first SOI wafer and a second SOI wafer. The first SOI wafer (corresponding to the second film layer in this disclosure) has a diameter of 6 inches or 8 inches, a 30 μm Si device layer, and is an N-type low-resistivity single-crystal silicon layer. The SiO2 intermediate layer has a thickness of 2 μm, and the substrate layer is a high-resistivity single-crystal silicon layer with a thickness of 450 μm. The second SOI wafer (corresponding to the first film layer in this disclosure) can be the same as the first SOI wafer, and a layer of SiO2 is deposited on the surface of the Si device layer of the second SOI wafer.

[0144] Please see Figure 17 This disclosure provides a method for fabricating a MEMS scanning mirror, comprising:

[0145] Step 171: Using reactive ion etching, low teeth (corresponding to the first comb teeth) and mirror-finish reinforcing ribs are etched on the Si device layer (corresponding to the first film layer) of the first SOI wafer. The structure formed also includes the lower half (half the height) of the connecting rod and the flexible hinge.

[0146] Step 172: Using the SiO2 layer as an intermediate layer, bond the first SOI wafer and the second SOI wafer together. The pre-bonding process is hydrophilic bonding. After pre-bonding, anneal in a high-temperature furnace at 1100℃ for 4 hours, and then slowly cool to room temperature to complete the high-strength bonding of the wafers.

[0147] Step 173: Remove the substrate layer and SiO2 layer of the second SOI wafer using a wet etching process, leaving only the Si device layer.

[0148] Step 174: Using the DRIE process, etch the upper teeth, mirror surface, and the upper half of the connecting rod and flexible hinge onto the Si device layer of the second SOI wafer.

[0149] Step 175: DRIE etching of the Si substrate layer down to the SiO2 insulating layer to create the cutout area on the back of the chip. The SiO2 insulating layer also acts as an etching barrier layer during the etching process.

[0150] Step 176: Use wet etching to remove SiO2 between the comb teeth and other structures, thus releasing the comb teeth. This completes the fabrication of the mechanical structure of the rotating mirror chip.

[0151] Step 177: Before coating, temporarily bond a piece of glass as a support sheet to the lower surface of the substrate.

[0152] Step 178: Sputter or vapor-deposit 10nm Ti and 200nm Al sequentially on the area corresponding to the pads on the upper surface of the Si device layer, and anneal at 400℃ in a vacuum environment to form ohmic contacts. After annealing, sputter or vapor-deposit 10nm Ti and 200nm Al sequentially on the mirror area on the upper surface of the Si device layer to form a reflective film.

[0153] Step 179: Remove the support sheet to complete the fabrication of the entire MEMS rotating mirror.

[0154] It should be noted that the specific structure of the above embodiments can be illustrated in any of the accompanying drawings or descriptions shown in this disclosure, and no limitation is made herein.

[0155] In one embodiment, this disclosure also provides a lidar, which includes a MEMS scanning mirror as described in any of the embodiments of this disclosure.

[0156] Those skilled in the art will understand that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0157] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A microelectromechanical system (MEMS) scanning mirror, characterized in that, include: Mirror; The drive module includes: a fixed beam with a fixed position, a rotating beam that can rotate around an axis, and connecting parts; The fixed beam is provided with a first comb tooth; the rotating beam is provided with a second comb tooth; the first comb tooth is formed on a first film layer, and the second comb tooth is formed on a second film layer; both ends of the rotating beam are respectively connected to fixed anchor points through rotating shafts, and metal pads are provided on the fixed anchor points; voltage is applied to the metal pads respectively, the first comb tooth attracts the second comb tooth to rotate, and the second comb tooth drives the rotating beam to swing around the rotating shaft after rotating; The connector connects the mirror and the rotating beam; the oscillating rotating beam can drive the mirror to rotate through the connector; the connector includes a link and a hinge connected to the link; the mirror, the link and / or the hinge each include an upper part and a lower part; the upper part is formed on the second film layer; the lower part is formed on the first film layer.

2. The MEMS scanning mirror according to claim 1, characterized in that, The first film layer and the second film layer are made of the same material and / or have the same thickness.

3. The MEMS scanning mirror according to claim 1, characterized in that, The driving module includes multiple stacked film layers; the multiple stacked film layers include: a first film layer, a second film layer, and a bonding layer disposed between the first film layer and the second film layer.

4. The MEMS scanning mirror according to claim 3, characterized in that, The upper part of the mirror is a mirror surface, which is formed on the second film layer; and / or, the lower part of the mirror is a mirror reinforcing rib, which is formed on the first film layer and the bonding layer; and / or, the connecting rod and / or the hinge are formed on the first film layer, the second film layer and the bonding layer.

5. A method for fabricating a MEMS scanning mirror, characterized in that, For fabricating a MEMS scanning mirror as described in any one of claims 1 to 4, comprising: The first comb teeth, the lower part of the connecting rod, the lower part of the hinge and / or the mirror reinforcing rib are etched on the first film layer of the first wafer, wherein the first wafer includes the first film layer and a first etching barrier layer adjacent to a surface of the first film layer. The second wafer is bonded to the first wafer on the other surface of the first film layer, wherein the second wafer includes a second film layer, a second etch barrier layer adjacent to one surface of the second film layer, and a bonding layer adjacent to the other surface of the second film layer; The second comb teeth, the upper part of the connecting rod, the upper part of the hinge, and / or the mirror surface are etched on the second film layer of the second wafer.

6. The preparation method according to claim 5, characterized in that, After bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes: Annealing at a first predetermined temperature; After the predetermined time, stop the annealing and cool down to the second predetermined temperature at the predetermined cooling rate.

7. The preparation method according to claim 5, characterized in that, After bonding the second wafer to the first wafer on another surface of the first film layer, the method further includes: The substrate layer and / or the second etch barrier layer on the second wafer are removed using a wet etching process; And / or, The SiO2 between the first comb teeth and / or the second comb teeth is removed by a wet etching process.

8. The preparation method according to claim 5, characterized in that, The first wafer includes a substrate layer; the method further includes: Etch a portion of the substrate layer; The support sheet is bonded to the substrate layer; Perform surface treatment on the pads and / or mirror areas; The support sheet is removed after the surface treatment is completed.

9. The preparation method according to claim 8, characterized in that, The surface treatment of the pads and / or mirror areas includes: Metal is sputtered and / or evaporated in the area corresponding to the pad on the upper surface of the second film layer, wherein the metal includes Ti and / or Al; And / or, The surface pads are annealed at a third predetermined temperature in a vacuum environment to form ohmic contacts; And / or, After annealing, metal is sputtered and / or evaporated onto the mirror region of the upper surface of the second film layer, wherein the metal includes Ti and / or Al.

10. A lidar, characterized in that, The lidar includes a MEMS scanning mirror as described in any one of claims 1 to 4.

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