Electrostatic MEMS micromirror with independent electrode structure and manufacturing method thereof

Abstract

The application discloses an electrostatic comb-drive MEMS micro-mirror with independent electrode structure and a manufacturing method thereof, and belongs to the field of micro-opto-electromechanical systems. The electrostatic MEMS micro-mirror comprises a mirror surface, comb electrodes, comb support structures, torsion beams, pads, cavities and a fixed frame. Driving dynamic comb electrodes and detecting dynamic comb electrodes are connected with the pads through the torsion beams. The micro-mirror divides the comb electrodes into detecting comb electrodes and driving comb electrodes through filling isolation channels, and removes the silicon substrate at the bottom of the comb electrodes to reduce parasitic capacitance, thereby avoiding the feed-through interference of the driving signal on the detecting signal and improving the capacitance detecting precision of the electrostatic MEMS micro-mirror. According to the back cavity etching priority order, the application further discloses two kinds of manufacturing methods of the electrostatic MEMS micro-mirror with independent electrode structure. The manufacturing method of the electrostatic MEMS micro-mirror realizes the isolation and interconnection of different comb electrodes through polymer filling channels, insulating layers and metal wires.

Description

Technical Field

[0001] This invention belongs to the field of micro-opto-electro-mechanical systems (MOEMS) and relates to an electrostatic MEMS micromirror with an independent electrode structure and its fabrication method. Background Technology

[0002] Electrostatic MEMS micromirrors possess advantages such as high frequency, large angle, small size, and low power consumption, making them widely used in industrial and consumer electronics fields, such as LiDAR, AR display devices, and 3D cameras. However, the scanning stability of micromirrors is easily affected by ambient temperature, humidity, and atmospheric pressure, thus limiting their application in these fields. Therefore, position detection is needed to provide real-time and accurate angle and phase information for the micromirrors, thereby improving their scanning stability and accuracy.

[0003] For electrostatic MEMS micromirrors, the main position detection methods currently include optical detection, capacitive sensing, piezoresistive sensing, and piezoelectric sensing. Among these, capacitive sensing directly utilizes an electrostatic comb actuator as the detection structure. Compared to other detection methods, it requires no additional assembly or sensors, making it the preferred detection solution for electrostatic micromirrors. Currently, capacitive sensing methods primarily employ a shared comb electrode approach, where a set of comb actuators serves as both the driving and detection electrodes. In practice, a driving signal is applied to the moving comb electrode. This driving signal is converted into a detection signal containing capacitance change information through a variable capacitor between the moving and stationary comb teeth. This detection signal is then extracted by the stationary comb electrode. Because the driving and detection electrodes are shared, the driving signal is directly introduced into the detection signal through the variable capacitor, resulting in severe feedthrough interference. This leads to waveform distortion and a low signal-to-noise ratio, significantly reducing the accuracy of capacitive sensing and increasing the difficulty of extracting the sensing signal. Therefore, to improve the capacitive sensing accuracy of micromirrors, it is necessary to eliminate the feedthrough interference of the driving signal on the sensing signal. Summary of the Invention

[0004] To eliminate feedthrough interference during capacitance detection, the present invention aims to provide an electrostatic comb-driven MEMS micromirror with an independent electrode structure and its fabrication method. The micromirror divides the comb electrode into a detection comb electrode and a driving comb electrode by filling an isolation channel, and removes the silicon substrate at the bottom of the comb electrode to reduce parasitic capacitance, thereby avoiding feedthrough interference of the driving signal to the detection signal and improving the capacitance detection accuracy of the electrostatic MEMS micromirror.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention discloses an electrostatic MEMS micromirror with an independent electrode structure, comprising a mirror surface, comb electrodes, a comb support structure, a torsion beam, pads, a cavity, and a fixed frame. The moving comb electrodes are isolated by filled channels as driving and detecting moving comb electrodes. The driving and detecting moving comb electrodes are connected to the pads via the torsion beam. The fixed comb electrodes are located on the fixed frame and isolated by filled channels as driving, ground, and detecting fixed comb electrodes. The ground electrode is located between the driving and detecting fixed comb electrodes to avoid feedthrough interference of the driving signal to the detection signal. The bottom silicon substrate of the region connected to the fixed comb electrodes is removed and connected to the fixed frame through filled channels to eliminate parasitic capacitance introduced by the buried oxide layer and substrate layer in the SOI wafer, further reducing feedthrough interference of the driving signal to the detection signal. The pads are located on the fixed frame, and insulation between different pads is achieved through filled channels, and they are connected to different electrodes via metal wires. The comb electrode is divided into a detection comb electrode and a driving comb electrode by filling an isolation channel. The parasitic capacitance is reduced by removing the silicon substrate at the bottom of the comb electrode, thereby avoiding feedthrough interference of the driving signal to the detection signal and improving the capacitance detection accuracy of the electrostatic MEMS micromirror.

[0007] The comb tooth support structure is connected to the mirror plate, and the detection moving comb tooth is located at the end of the comb tooth support structure. The shape of the comb tooth support structure can be trapezoidal or rectangular. Preferably, the shape of the comb tooth support structure is trapezoidal, and the detection moving comb tooth is located on one side of the short side of the trapezoid. The strength of the capacitive sensing signal is improved by increasing the overlapping area of ​​the comb teeth.

[0008] The moving comb electrode is isolated by a filled channel as a driving moving comb electrode and a sensing moving comb electrode, and is connected to the pad via metal wires and a torsion beam. Preferably, the total ratio of sensing moving comb teeth to driving moving comb teeth is between 1:1 and 2:5.

[0009] The arrangement of the moving comb teeth electrodes includes the following three methods: Method 1: Both the driving moving comb teeth and the detection moving comb teeth are located on the mirror plate, which can reduce the chip size and thus reduce production costs; Method 2: Both the driving moving comb teeth and the detection moving comb teeth are located on the comb tooth support structure, which can avoid the interference effect of the comb teeth on the mirror plate on the light; Method 3: The driving moving comb teeth are located on the mirror plate and the detection moving comb teeth are located on the comb tooth support structure. By increasing the driving force, the driving voltage is reduced. At the same time, the overlapping area of ​​the detection moving comb teeth and the detection stationary comb teeth is increased, thereby improving the capacitance sensing signal strength and further improving the capacitance sensing accuracy.

[0010] The driving and detecting moving comb electrodes are connected to the pads via a torsion beam. The torsion beam structure can be a single torsion beam or a double torsion beam. When a single torsion beam structure is used, the driving and detecting moving comb electrodes are connected to the two pads respectively via the single torsion beam and the metal wire above it. When a double torsion beam structure is used, the driving and detecting moving comb electrodes are connected to the two pads respectively via the two torsion beams in the double torsion beam.

[0011] The fixed comb-tooth electrode is isolated from the fixed frame by a filler channel and connected to the pads by metal wires. The pads are surrounded by the filler channel, achieving electrical isolation between different pads. The number of filler channel turns around the pads is between 1 and 4, preferably 2 turns, and multiple openings are made around the filler channel around the pads to release stress inside the filler channel and reduce parasitic capacitance introduced by the filler channel.

[0012] This invention also discloses two methods for fabricating electrostatic MEMS micromirrors with independent electrode structures, used to fabricate the aforementioned electrostatic MEMS micromirror with an independent electrode structure. These two methods are categorized based on the priority of back cavity etching:

[0013] Regarding the fabrication method of the post-etched back cavity, the electrostatic MEMS micromirror fabrication method with independent electrode structure disclosed in this invention includes the following steps:

[0014] Step (a): The electrostatic MEMS micromirror with an independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer, a buried oxide layer, and a substrate layer. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, a deep silicon etching process is used to etch the SOI wafer device layer down to the SOI wafer insulating layer to form deep trenches for filling the insulating material.

[0015] Step (b): The insulating material is a polymer. Preferably, the polymer is PI, BCB, SOG, LCP or a combination of the above polymer materials. The polymer is filled into the channel by spin coating, and the air bubbles inside the channel are removed by vacuum treatment. The channel is then placed in a nitrogen oven for high-temperature curing.

[0016] Step (c): Use chemical mechanical polishing (CMP) to remove excess filler material from the surface to obtain a smooth surface, which facilitates subsequent processes.

[0017] Step (d): A layer of SiO2 is grown by enhanced plasma chemical vapor deposition (PECVD) for insulation between the metal wire and the device layer, and excess SiO2 is removed by wet etching process.

[0018] Step (e): Deposit a metal film on the front side of the device layer and pattern it to form metal wires, metal pads and a specular reflection layer for interconnection.

[0019] Step (f): The SOI device layer surface is coated with adhesive and patterned, and deep silicon is etched down to the insulating layer to form a micromirror device structure.

[0020] Step (g): Photoresist is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed down to the insulating layer to form a cavity structure.

[0021] Step (h): Remove the SOI buried oxide layer using a dry or wet method, and then remove the photoresist on the surface to form an electrostatic micromirror with an independent detection electrode.

[0022] Regarding the fabrication method of first etching the back cavity, the electrostatic MEMS micromirror fabrication method with independent electrode structure disclosed in this invention includes the following steps:

[0023] Step (a): The electrostatic MEMS micromirror with an independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer, a buried oxide layer, and a substrate layer. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, a deep silicon etching process is used to etch the SOI wafer device layer down to the SOI wafer insulating layer to form deep trenches for filling the insulating material.

[0024] Step (b): The insulating material is a polymer. Preferably, the polymer is PI, BCB, SOG, LCP or a combination of the above polymer materials. The polymer is filled into the channel by spin coating, and the air bubbles inside the channel are removed by vacuum treatment. The channel is then placed in a nitrogen oven for high-temperature curing.

[0025] Step (c): Use CMP process to remove excess filler material from the surface to obtain a smooth surface, which facilitates subsequent processes.

[0026] Step (d): Photoresist is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed to the insulating layer to form a cavity structure.

[0027] Step (e): A layer of photoresist is spin-coated onto the surface of the SOI device layer to protect the front structure, and then a wet etching process is used to remove SiO2 from the buried oxide layer.

[0028] Step (f): The glass is bonded to the SOI substrate using an anodic bonding process.

[0029] Step (g): A layer of SiO2 is grown on the surface of the SOI device layer using PECVD process for insulation between the metal wires and the device layer, and excess SiO2 is removed using wet etching process.

[0030] Step (h): Deposit a metal film on the front side of the device layer and pattern it to form metal wires, metal pads and a specular reflection layer for interconnection.

[0031] Step (i): The SOI device layer surface is coated with adhesive and patterned, and deep silicon is etched down to the buried oxide layer to form a micromirror device structure.

[0032] Beneficial effects:

[0033] 1. The present invention discloses an electrostatic micromirror with an independent detection comb tooth structure, which isolates the driving comb tooth electrode and the detection comb tooth electrode by filling the channel, eliminating the feedthrough interference of the driving signal to the detection signal, and significantly improving the capacitance detection accuracy of the electrostatic MEMS micromirror.

[0034] 2. The present invention discloses an electrostatic micromirror with an independent detection comb tooth structure. By removing the silicon substrate at the bottom of the comb tooth electrode and placing a ground electrode between the driving fixed comb tooth electrode and the detection fixed comb tooth electrode, the parasitic capacitance is reduced, thereby further improving the capacitance detection accuracy of the electrostatic MEMS micromirror.

[0035] 3. The present invention discloses an electrostatic micromirror with an independent detection comb structure, which realizes a low-voltage, small-volume electrostatic MEMS micromirror with an independent detection comb structure through various comb layouts, and improves the capacitance sensing accuracy by increasing the overlapping area between the detection combs.

[0036] 4. The electrostatic micromirror disclosed in this invention has an independent detection comb tooth structure. It uses a double torsion beam to electrically interconnect the electrodes of different comb teeth, avoiding the deformation of the torsion beam caused by the metal wire covering the torsion beam, and improving the reliability of the torsion beam.

[0037] 5. The present invention discloses a method for fabricating an electrostatic micromirror with an independent detection comb tooth structure, which achieves isolation and interconnection of different comb tooth electrodes by filling channels with polymer, insulating layers and metal wires.

[0038] 6. The present invention discloses a method for fabricating an electrostatic micromirror with an independent detection comb structure. The post-etching back cavity process uses a single SOI wafer for processing, eliminating the need for multi-wafer bonding. The process is simple, easy to implement, and has good repeatability.

[0039] 7. The present invention discloses a method for fabricating an electrostatic micromirror with an independent detection comb tooth structure. The back cavity etching process uses SOI wafers bonded to glass anodes to avoid photoresist residue inside the comb teeth. The process yield is high and it is easy to mass-produce. Attached Figure Description

[0040] Figure 1 A schematic diagram of an embodiment of an electrostatic micromirror with an independent detection electrode structure;

[0041] Figure 2 Schematic diagrams of pads with different structures, where: Figure 2 (a) is a pad with a single-ring filler channel. Figure 2 (b) Pads with double-ring fill channels. Figure 2 (c) is a pad with a filled channel opening;

[0042] Figure 3 A schematic diagram of an embodiment of an electrostatic micromirror with an independent detection electrode structure;

[0043] Figure 4 Schematic diagram of embodiment three of an electrostatic micromirror with an independent detection electrode structure;

[0044] Figure 5 Schematic diagrams of different comb tooth support structures, wherein: Figure 5 (a) is a rectangular comb tooth support structure. Figure 5 (b) is a trapezoidal comb tooth support structure;

[0045] Figure 6 Schematic diagram of embodiment four of an electrostatic micromirror with an independent detection electrode structure;

[0046] Figure 7 (a)~ Figure 7 (j) is a schematic diagram of the post-etching back cavity process steps based on a single SOI wafer;

[0047] Figure 8 (a)~ Figure 8 (j) is a schematic diagram of the pre-etching back cavity process steps based on silicon glass anodic bonding;

[0048] Among them, 100-fixed frame, 101-detection moving comb tooth, 102-detection fixed comb tooth, 103-drive moving comb tooth, 104-drive fixed comb tooth, 105-comb tooth support structure, 106-mirror plate, 107-single torsion beam, 108-metal wire, 109-first filling channel, 110-second filling channel, 111-third filling channel, 112-fourth filling channel, 113-drive negative electrode pad, 114-detection positive electrode pad, 115-ground electrode pad, 116-drive positive electrode pad, 117-detection negative electrode pad Disk, 118-Double torsion beam, 119-First torsion beam, 120-Second torsion beam, 121-Fifth filling trench, 122-Sixth filling trench, 123-Seventh filling trench, 124-Eighth filling trench, 125-Ninth filling trench, 201-Filling trench opening, 701-Device layer, 701-Buried oxide layer, 703-Substrate layer, 704-Trench, 705-Trench filler, 706-Silicon dioxide, 707-Metal, 708-Micromirror structure, 709-Cavity, 710-Photoresist, 801-Glass. Detailed Implementation

[0049] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment discloses an electrostatic micromirror with an independent electrode detection structure, fabricated using an SOI wafer. It includes a driving comb structure, a detection comb structure, a mirror plate 106, a single torsion beam 107, pads, metal wires 108, and filling channels. The driving comb structure includes a driving movable comb tooth 103 and a driving fixed comb tooth 104, used to drive the mirror plate 106 to rotate. The driving movable comb tooth 103 is connected to the mirror plate 106, and the driving fixed comb tooth 104 is connected to the fixed frame 100. The driving movable comb tooth 103 forms an independent electrically isolated region by being electrically isolated from the comb tooth support structure through a second filling channel 110, and is connected to the driving negative electrode pad 113 through the metal wire 108 above the single torsion beam 107. The driving fixed comb tooth 104 forms an independent electrically isolated region by being electrically isolated from the fixed frame 100 through a third filling channel 111, and is connected to the driving positive electrode pad 116 through the metal wire 108.

[0052] The detection comb structure includes a moving detection comb tooth 101 and a fixed detection comb tooth 102 for capacitive sensing of the micromirror. The moving detection comb tooth 101 is connected to the comb tooth support structure 105, and the fixed detection comb tooth 102 is connected to the fixed frame 100. The moving detection comb tooth 101 forms an independent electrically isolated region with the mirror plate 106 and the fixed frame 100 through the first filling channel 109 and the second filling channel 110, respectively, and is connected to the negative detection pad 117 through a single torsion beam 107 and a metal wire 108. The fixed detection comb tooth 102 forms an independent electrically isolated region with the fixed frame 100 through the third filling channel 111, and is connected to the positive detection pad 114 through a metal wire 108.

[0053] The third filling channel 111 isolates an independent isolation region connected to the ground electrode pad 115 between the driving fixed comb tooth region and the detection fixed comb tooth region to avoid feedthrough interference of the driving positive signal to the detection positive signal. At the same time, the substrate silicon at the bottom of the independent electrically isolated region connected to the third filling channel 111 is completely hollowed out to avoid feedthrough interference caused by parasitic capacitance introduced by the substrate silicon.

[0054] The pads are surrounded by a fourth fill channel 112, which electrically isolates different pads for applying corresponding voltages. The fourth fill channel 112 can surround the pads completely, such as... Figure 2 As shown in (a); the fourth fill channel 112 can also wrap around the pad multiple times, for example, two times, to reduce parasitic capacitance. Figure 2As shown in (b); multiple filling channel openings 201 can be opened around the fourth filling channel 112, and the silicon at the openings is etched away to release the stress inside the filling channel and further reduce parasitic capacitance, such as Figure 2 As shown in (c).

[0055] An electrical signal is input through the pads. A driving signal is applied to the driving positive pad 116, and a signal to be detected is applied to the detection positive pad 114. The driving negative pad 113 and the ground electrode pad 115 are grounded. The detection negative pad 117 is connected to the detection circuit to obtain the capacitance detection signal of the micromirror movement.

[0056] Example 2

[0057] This embodiment discloses another electrostatic micromirror with an independent electrode detection structure, such as... Figure 3 As shown. In this embodiment, the dual torsion beam 118 is used to support the mirror and electrical connections. The dual torsion beam consists of a first torsion beam 119 and a second torsion beam 120, and the two torsion beams can transmit different electrical signals respectively. The first torsion beam 119 forms an independent electrical isolation area through the fifth filling channel 121 and the sixth filling channel 122, and is connected to the mirror plate 106 and the drive negative electrode pad 113 through the metal wire 108. The second torsion beam 120 forms an independent electrical isolation area through the fifth filling channel 121 and the second filling channel 110, and is connected to the detection negative electrode pad 117 through the metal wire 108. The dual torsion beam 118 on the other side is directly connected to the comb tooth support structure 105, forms an independent electrical isolation area through the first filling channel 109 and the second filling channel 110, and is then connected to the detection negative electrode pad 117 through the metal wire 108.

[0058] Example 3

[0059] This embodiment discloses another electrostatic micromirror with an independent electrode detection structure, such as... Figure 4 As shown. In this embodiment, both the driving comb tooth 103 and the detecting comb tooth 101 are located on the comb tooth support structure 105. The driving comb tooth 103 and the detecting comb tooth 101 are divided into two independent electrically isolated regions by the seventh filling channel 123, and are electrically interconnected by a double torsion beam electrical system. The double torsion beam electrical interconnection layout in this embodiment can also be replaced by the single torsion beam electrical interconnection layout in Embodiment 1.

[0060] Meanwhile, the comb tooth support structure 105 has two layouts, such as Figure 5 As shown. One structure is rectangular, such as... Figure 5 As shown in (a), the detection movable comb tooth 101 is fixed to one end connected to the torsion beam, and the driving movable comb tooth 103 is fixed to one end connected to the mirror plate 106. The width of this structure is preferably 30μm to 100μm; another structure is trapezoidal, as shown in (a). Figure 5As shown in (b), the detection comb tooth 101 is located on the short base side of the trapezoidal structure, which is connected to the torsion beam. The driving comb tooth 103 is located on the long base side of the trapezoidal structure, which is connected to the mirror plate 106. This structure is beneficial for improving the amplitude of the capacitive sensing signal and increasing the accuracy of capacitive sensing.

[0061] Example 4

[0062] This embodiment discloses another electrostatic micromirror with an independent electrode detection structure, such as... Figure 6 As shown. In this embodiment, both the driving comb tooth 103 and the detection comb tooth 101 are located on the mirror plate 105. The driving comb tooth 103 and the detection comb tooth 101 are divided into two independent electrically isolated regions by the eighth filling channel 124, and are connected to the driving negative electrode pad 113 and the detection negative electrode pad 117 respectively by a single torsion beam 107 and a metal wire 108. The third filling channel 111 isolates an independent isolation region connected to the ground electrode pad 115 between the driving fixed comb tooth region and the detection fixed comb tooth region to avoid feedthrough interference of the driving positive electrode signal to the detection positive electrode signal.

[0063] To achieve the fabrication of electrostatic micromirrors with independent electrode detection structures, in one embodiment, this invention proposes a post-etching back cavity fabrication method based on a single SOI wafer, such as... Figure 7 As shown

[0064] (a) The electrostatic MEMS micromirror with an independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer 701, a buried oxide layer 701, and a substrate layer 703. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, a deep silicon etching process is used to etch the SOI wafer device layer down to the SOI wafer insulating layer to form trenches 704 for filling with insulating material.

[0065] (b) The channel filler 705 is a polymer. Preferably, the polymer is selected from PI, BCB, SOG, LCP or a combination of the above polymer materials. The polymer is filled into the channel by spin coating and the air bubbles inside the channel are removed by vacuum treatment and then cured at high temperature in a nitrogen oven.

[0066] (c) The excess groove filler 705 on the surface is removed by CMP process to obtain a smooth surface, which facilitates subsequent processes.

[0067] (d) A layer of silicon dioxide 706 is grown by PECVD for insulation between the metal wire and the device layer. The thickness of the silicon dioxide is preferably 300 nm to 1000 nm.

[0068] (e) Remove excess silicon dioxide using a wet etching process;

[0069] (f) A layer of metal 707 is deposited on the front side of the device layer, and metal wires, metal pads and a mirror reflection layer for interconnection are formed by stripping or dry etching. The metal is preferably Au or Al.

[0070] (g) The surface of the SOI device layer is coated with adhesive and patterned, and deep silicon etching is performed to the buried oxide layer to form a micromirror structure 708.

[0071] (h) Photoresist is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed to the buried oxide layer to form cavity 709;

[0072] (i) Photoresist 710 is sprayed onto the surface of the SOI device layer to protect the front structure;

[0073] (j) The SOI buried oxide layer is removed by dry or wet method, and then the photoresist on the surface is removed to form an electrostatic micromirror with an independent detection electrode.

[0074] To achieve the fabrication of electrostatic micromirrors with independent electrode detection structures, in another embodiment, this invention proposes a pre-etching back cavity fabrication process based on silicon glass anodic bonding, such as... Figure 8 As shown

[0075] (a) The electrostatic MEMS micromirror with an independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer 701, a buried oxide layer 701, and a substrate layer 703. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, a deep silicon etching process is used to etch the SOI wafer device layer down to the SOI wafer insulating layer to form trenches 704 for filling with insulating material.

[0076] (b) The channel filler 705 is a polymer. Preferably, the polymer is selected from PI, BCB, SOG, LCP or a combination of the above polymer materials. The polymer is filled into the channel by spin coating and the air bubbles inside the channel are removed by vacuum treatment and then cured at high temperature in a nitrogen oven.

[0077] (c) The excess groove filler 705 on the surface is removed by CMP process to obtain a smooth surface, which facilitates subsequent processes.

[0078] (d) Photoresist 710 is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed to the buried oxide layer to form a cavity 709.

[0079] (e) Remove the SOI buried oxygen layer using dry or wet methods;

[0080] (f) Bonding the SOI substrate to the 801 glass anode;

[0081] (g) A layer of silicon dioxide 706 is grown by PECVD for insulation between the metal wire and the device layer. The thickness of the silicon dioxide is preferably 300 nm to 1000 nm.

[0082] (h) Remove excess silicon dioxide using a wet etching process;

[0083] (i) A layer of metal 707 is deposited on the front side of the device layer, and metal wires, metal pads and a mirror reflection layer for interconnection are formed by stripping or dry etching. The metal is preferably Au or Al.

[0084] (j) The surface of the SOI device layer is coated with adhesive and patterned, and deep silicon is etched to the buried oxide layer to form a micromirror structure 708, thus completing the electrostatic micromirror fabrication with an independent detection electrode.

[0085] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrostatic MEMS micromirror with an independent electrode structure, characterized in that: It includes a mirror, comb tooth electrodes, comb tooth support structure, torsion beam, pads, cavity, and fixed frame; the moving comb tooth electrodes are isolated by filled channels as driving moving comb tooth electrodes and detection moving comb tooth electrodes; the driving moving comb tooth electrodes and detection moving comb tooth electrodes are connected to the pads through the torsion beam; the fixed comb tooth electrodes are located on the fixed frame and isolated by filled channels as driving fixed comb tooth electrodes, ground electrodes, and detection fixed comb tooth electrodes; the ground electrode is located between the driving fixed comb tooth electrodes and the detection fixed comb tooth electrodes to avoid feedthrough interference of the driving signal to the detection signal; The bottom silicon substrate of the area connected to the fixed comb electrode is removed and connected to the fixed frame through a filled channel. The silicon substrate at the bottom of the independent electrically isolated section of the channel used to isolate the driving fixed comb electrode, the ground electrode and the detection fixed comb electrode is hollowed out to eliminate the parasitic capacitance introduced by the buried oxide layer and the substrate layer in the SOI wafer, and reduce the feedthrough interference of the driving signal to the detection signal. The pads are located on the fixed frame, and insulation between different pads is achieved by filling the channel, and they are connected to different electrodes through metal wires. The comb electrode is divided into the detection comb electrode and the driving comb electrode by filling the isolation channel, and the removal of the silicon substrate at the bottom of the comb electrode is used to reduce parasitic capacitance, avoid the feedthrough interference of the driving signal to the detection signal, and improve the capacitance detection accuracy of the electrostatic MEMS micromirror.

2. The electrostatic MEMS micromirror with an independent electrode structure as described in claim 1, characterized in that: The comb support structure is trapezoidal in shape, with the detection moving comb tooth located on one side of the short side of the trapezoid. The strength of the capacitive sensing signal is improved by increasing the overlapping area of ​​the comb teeth. The ratio of the total number of detected moving comb teeth to the total number of driving moving comb teeth is between 1:1 and 2:

5.

3. The electrostatic MEMS micromirror with an independent electrode structure as described in claim 1, characterized in that: The arrangement of the moving comb teeth electrodes includes the following three methods: Method 1: Both the driving moving comb teeth and the detection moving comb teeth are located on the mirror plate, thereby reducing production costs by shrinking the chip size; Method 2: Both the driving moving comb teeth and the detection moving comb teeth are located on the comb tooth support structure, avoiding interference effects on light caused by the comb teeth on the mirror plate; Method 3: Both the driving moving comb teeth and the detection moving comb teeth are located on the comb tooth support structure, thereby reducing the driving voltage by increasing the driving force, and increasing the overlapping area of ​​the detection moving comb teeth and the detection stationary comb teeth to improve the capacitance sensing signal strength and improve the capacitance sensing accuracy.

4. The electrostatic MEMS micromirror with an independent electrode structure as described in claim 1, characterized in that: The driving and detecting moving comb electrodes are connected to the pads via a torsion beam; the torsion beam structure can be a single torsion beam or a double torsion beam; when a single torsion beam structure is used, the driving and detecting moving comb electrodes are connected to the two pads respectively via the single torsion beam and the metal wire above the single torsion beam; when a double torsion beam structure is used, the driving and detecting moving comb electrodes are connected to the two pads respectively via the two torsion beams in the double torsion beam.

5. An electrostatic MEMS micromirror with an independent electrode structure as described in claim 1, characterized in that: The fixed comb electrode is isolated from the fixed frame by a filling channel and connected to the pads by a metal wire; the pads are surrounded by the filling channel to achieve electrical isolation between different pads; the number of filling channels around the pads is between 1 and 4.

6. The electrostatic MEMS micromirror with an independent electrode structure as described in claim 5, characterized in that: The fill channel has two turns, and multiple openings are made around the fill channel of the pad to release stress inside the fill channel and reduce parasitic capacitance introduced by the fill channel.

7. An electrostatic MEMS micromirror with an independent electrode structure as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: The production method includes the following steps: Step (a): The electrostatic MEMS micromirror with independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer, a buried oxide layer, and a substrate layer. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, the SOI wafer device layer is etched down to the SOI wafer insulating layer using a deep silicon etching process to form deep trenches for filling with insulating material. Step (b): The insulating material is a polymer; the polymer is filled into the channel by spin coating, and the air bubbles inside the channel are removed by vacuum treatment, and then cured at high temperature in a nitrogen oven. Step (c): Use chemical mechanical polishing (CMP) to remove excess filler material from the surface to obtain a smooth surface, which facilitates subsequent processes. Step (d): A layer of SiO2 is grown by enhanced plasma chemical vapor deposition (PECVD) for insulation between the metal wire and the device layer, and excess SiO2 is removed by wet etching process. Step (e): Deposit a metal film on the front side of the device layer and pattern it to form metal wires, metal pads and a specular reflective layer for interconnection; Step (f): The surface of the SOI device layer is coated with adhesive and patterned, and deep silicon is etched down to the insulating layer to form a micromirror device structure; Step (g): Photoresist is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed down to the insulating layer to form a cavity structure; Step (h): Remove the SOI buried oxide layer using a dry or wet method, and then remove the photoresist on the surface to form an electrostatic micromirror with an independent detection electrode.

8. An electrostatic MEMS micromirror with an independent electrode structure as described in claims 1, 2, 3, 4, 5, or 6, characterized in that: The production method includes the following steps: Step (a): The electrostatic MEMS micromirror with independent electrode structure is fabricated using SOI wafers. Each SOI wafer consists of a device layer, a buried oxide layer, and a substrate layer. Photoresist is coated on the surface of the SOI wafer device layer and patterned with electrically isolated channels. Then, the SOI wafer device layer is etched down to the SOI wafer insulating layer using a deep silicon etching process to form deep trenches for filling with insulating material. Step (b): The insulating material is a polymer; the polymer is filled into the channel by spin coating, and the air bubbles inside the channel are removed by vacuum treatment, and then cured at high temperature in a nitrogen oven. Step (c): Use CMP process to remove excess filler material from the surface to obtain a smooth surface, which facilitates subsequent processes; Step (d): Photoresist is coated and patterned on the surface of the SOI substrate, and deep silicon etching is performed down to the insulating layer to form a cavity structure; Step (e): Spin-coat a layer of photoresist onto the surface of the SOI device layer to protect the front structure, and then use a wet etching process to remove SiO2 from the buried oxide layer; Step (f): The glass is bonded to the SOI substrate using an anodic bonding process; Step (g): A layer of SiO2 is grown on the surface of the SOI device layer using PECVD process for insulation between the metal wires and the device layer, and excess SiO2 is removed using wet etching process. Step (h): Deposit a metal film on the front side of the device layer and pattern it to form metal wires, metal pads and a specular reflection layer for interconnection; Step (i): The SOI device layer surface is coated with adhesive and patterned, and deep silicon is etched down to the buried oxide layer to form a micromirror device structure.

9. An electrostatic MEMS micromirror with an independent electrode structure as described in claim 7, characterized in that: The polymer is selected from PI, BCB, SOG, LCP or a combination of the above polymer materials.

10. An electrostatic MEMS micromirror with an independent electrode structure as described in claim 8, characterized in that: The polymer is selected from PI, BCB, SOG, LCP or a combination of the above polymer materials.

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