CN113534442A

CN113534442A - Micro-mirror device and preparation method thereof

Info

Publication number: CN113534442A
Application number: CN202010315540.4A
Authority: CN
Inventors: 马宏
Original assignee: Juexin Electronics Wuxi Co ltd
Current assignee: Juexin Electronics Wuxi Co ltd
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-10-22

Abstract

The application provides a micro-mirror device and a preparation method thereof, wherein the micro-mirror device comprises a substrate layer, a first buried layer and a device structure layer, wherein the substrate layer, the first buried layer and the device structure layer are sequentially connected in a laminated manner; the device structure layer comprises a movable structure, and the movable structure comprises a movable mirror and a driving plate; the front surface of the movable mirror surface and the driving plate are both provided with weight reduction parts, and the back surface of the movable mirror surface is provided with a metal reflecting layer; a back cavity structure is arranged on the substrate layer and can provide a movement space for the movable structure; the first buried layer is provided with a light-transmitting area, and the metal reflecting layer can be exposed outside by the back cavity structure and the light-transmitting area. The micro-mirror device provided by the application can reduce the oscillator mass and the torsional axis stiffness coefficient of the MEMS micro-mirror system by lightening the mass of the movable structure, ensure that the resonant frequency of the mirror surface is unchanged, namely the reliability of the device is unchanged, and simultaneously realize larger motion amplitude of the mirror surface under the same driving voltage.

Description

Micro-mirror device and preparation method thereof

Technical Field

The present disclosure relates to optical technologies, and in particular, to a micromirror device and a method for manufacturing the same.

Background

In recent years, with the development of technology, many emerging optical application fields such as vehicle-mounted laser radar, portable laser projection, three-dimensional measurement, and the like have appeared in succession. These emerging applications have a broad and good market prospect, but at the same time face many technical problems. In the process of commercialization, whether the process technology is mature and repeatable large-scale production with low cost can be realized is a problem to be considered by each manufacturer. The emerging applications set forth rather high requirements on integration level, reliability, optical field of view, and the like of the product devices. Among the existing technical solutions, a solution based on a Micro Electro Mechanical Systems (MEMS) plays an important role.

Unlike the conventional large-scale optical mechanical structure, the MEMS technology is based on the semiconductor integrated circuit technology and the microfabrication technology. Therefore, the sensor based on the MEMS technology has features of miniaturization, high reliability, high integration, low cost, mass production, etc., and has been widely used in many fields. For example, micro-accelerometers and micro-gyroscopes applied to inertial navigation and precision guidance; the micro-microphone and the micro-pressure sensor are applied to a smart phone. In the field of optical applications, the MEMS sensor represented by the MEMS micro-mirror has not only a very mature commercial product in the traditional imaging display field, such as DMD chip of texas instruments, but also an important application prospect in the advanced field of in vivo medical imaging, such as various optical endoscopes.

The MEMS micro-mirror mainly comprises 2 functional structures, namely an optical mirror structure, and is used for spatially modulating incident beams in a light path; the second is a driving structure, including a torsion shaft, etc., which can make the optical mirror surface move in a certain mode in space according to the input driving signal. Among them, the resonant motion and the quasi-static motion are the most basic 2 motion modes of the optical mirror structure. When the micromirror moves in the quasi-static mode, its mirror surface no longer moves in a sinusoidal fashion, which is of great significance for the spatial modulation of the light beam. In addition, the MEMS micro-mirror can be mainly classified into 4 types of pyroelectric type, piezoelectric type, electromagnetic type, and electrostatic type according to a driving method. The electrostatic MEMS micro-mirror is mature in manufacturing process, does not need an external magnetic field, and has the characteristics of high integration level, good reliability and the like. However, the motion range of the existing electrostatic MEMS micro-mirror capable of performing quasi-static operation is usually small, and cannot meet the requirement of applications such as vehicle-mounted laser radar, three-dimensional measurement and portable laser projection on the field of view.

In order to realize a larger field of view of the electrostatic MEMS micromirror in the quasi-static mode, the prior art includes increasing the driving voltage, directly reducing the stiffness coefficient of the torsion axis, and realizing field-of-view stitching by cooperating multiple chips. However, the above solutions all have obvious drawbacks. The driving voltage is increased, so that the driving structure is easy to generate electrostatic damage, the service life of the device is shortened, the driving structure is easy to generate phenomena of electrostatic adsorption, breakdown, ablation and the like under the use scenes of vehicle-mounted carrying, daily carrying and the like, and the reliability of the device is difficult to meet the application requirement. Directly reducing the stiffness coefficient of the torsion shaft can result in the reduction of the resonant frequency of the device, and the device is easily affected by external vibration in daily use or transportation, resulting in the reduction of the reliability of the device. And the field-of-view splicing based on multi-chip cooperation also increases the production cost of the product.

Disclosure of Invention

The application aims to solve the technical problem that the electrostatic MEMS micro-mirror has small motion amplitude in a quasi-static mode.

In order to solve the technical problem, the embodiment of the application discloses a micromirror device, which comprises a substrate layer, a first buried layer and a device structure layer, wherein the substrate layer, the first buried layer and the device structure layer are sequentially connected in a laminated manner;

the device structure layer comprises a movable structure, and the movable structure comprises a movable mirror and a driving plate;

the front surface of the movable mirror surface and the driving plate are both provided with weight reduction parts, and the back surface of the movable mirror surface is provided with a metal reflecting layer;

a back cavity structure is arranged on the substrate layer and can provide a movement space for the movable structure;

the first buried layer is provided with a light-transmitting area, and the metal reflecting layer can be exposed outside by the back cavity structure and the light-transmitting area.

Further, the weight-reduced portion includes an etched groove.

Further, the device structure layer comprises a first device layer, a second buried layer and a second device layer, wherein the first device layer, the second buried layer and the second device layer are sequentially connected in a stacked mode;

the movable structure is arranged on the first device layer;

the weight reduction part is arranged on one surface of the movable mirror surface, which is spaced from the first buried layer, and the metal reflection layer is arranged on one surface of the movable mirror surface, which is connected with the first buried layer.

the movable structure is arranged on the second device layer;

the weight reduction part is arranged on one surface of the movable mirror surface, which is separated from the second buried layer, and the metal reflection layer is arranged on one surface of the movable mirror surface, which is connected with the second buried layer.

Further, the depth of the etched groove on the movable mirror is smaller than the thickness of the first device layer.

Optionally, the depth of the etched trench in the movable mirror is less than the thickness of the second device layer.

Further, the device also comprises a reinforcing frame;

the movable structure is arranged on the first device layer, the reinforcing frame is arranged on the second device layer, the reinforcing frame and the movable structure are bonded into a whole, and the reinforcing frame can reinforce the movable structure;

optionally, the movable structure is arranged on the first device layer, and the reinforcing frame is etched on the movable structure; the reinforcing frame can reinforce the movable structure.

Optionally, the movable structure is arranged on the second device layer, and the reinforcing frame is etched on the movable structure; the reinforcing frame can reinforce the movable structure.

Another aspect of the present invention provides a method for manufacturing a micromirror device, including:

obtaining an SOI wafer, wherein the SOI wafer comprises a substrate layer, a first buried layer and a first device layer;

preparing and forming a device layer structure, comprising:

if the movable structure is arranged on the first device layer and the reinforcing frame is arranged on the second device layer, the method comprises the following steps: etching the first device layer by using a subtractive process, and defining a movable structure and an alignment mark; the movable structure comprises a movable mirror surface, a driving plate and a movable comb tooth structure; preparing and forming a weight reduction part on the movable structure; obtaining a second device layer, and preparing and forming a second buried layer on the second device layer; bonding the second buried layer with the first device layer to form an integral wafer; etching the second buried layer and the second device layer to expose the alignment mark; etching the second device layer to form a reinforcing frame and a static comb structure;

depositing a layer of metal film on the first device layer and the second device layer, and patterning to prepare and form a metal bonding pad structure;

coating photoresist on the front surface of the whole wafer, and curing to form a protective layer structure;

the whole wafer is reversely buckled, and the substrate layer is etched to form a back cavity structure;

removing exposed areas of the first buried layer and the second buried layer;

and depositing a metal film on the back of the whole wafer, wherein the metal film formed on the back of the movable mirror serves as a metal reflecting layer, and the metal film formed on the bottom of the substrate layer can be used for chip welding.

Optionally, preparing and forming a device layer structure further includes:

if the movable structure is arranged on the first device layer and the reinforcing frame is formed on the movable structure through etching, the method comprises the following steps:

performing dry etching treatment on the first device layer by using a subtractive process, forming device layer structures with different etching depths on the first device layer and defining alignment marks; the device layer structure comprises a movable mirror surface, a driving plate, a movable comb tooth structure, a reinforcing frame and a weight reduction part, wherein the reinforcing frame can be formed on the movable mirror surface by designing the appearance, the size and the arrangement range of the weight reduction part;

obtaining a second device layer, and preparing and forming a second buried layer on the second device layer; bonding the second buried layer with the first device layer to form an integral wafer;

etching the second buried layer and the second device layer to expose the alignment mark; etching the second device layer to form a static comb structure;

optionally, if the movable structure is set to be disposed on the second device layer and the reinforcing frame is etched on the movable structure, the method includes the following steps:

etching the first device layer to form a fixed frame structure and a static comb structure; the static comb tooth structure is arranged on the fixed frame structure; the fixed frame structure also comprises an alignment mark;

etching the second buried layer and the second device layer to expose the alignment mark;

according to the alignment mark, etching the second device layer by using a mass reduction process, and simultaneously forming a movable structure, a weight reduction part and a reinforcing frame on the second device layer; the reinforcing frame can be formed on the movable mirror surface by designing the appearance, the size and the arrangement range of the weight reduction part.

Further, the subtractive process includes dry etching based on a loading effect or a double-layer glue process.

By adopting the technical scheme, the application has the following beneficial effects:

the application provides a micro mirror device, with the metal reflecting layer setting at the back of movable mirror surface, will subtract heavy portion setting in movable structure's front, can realize the quality at bigger proportional range and subtract, through the quality that alleviates movable structure, can reduce MEMS micro mirror system's oscillator quality and torsion axis coefficient of stiffness simultaneously, guarantee that the resonant frequency of mirror surface is unchangeable, the reliability of device is unchangeable promptly, simultaneously, make the mirror surface realize bigger amplitude of motion under the same driving voltage.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a schematic view of a micro-mirror device according to embodiment 1 of the present application;

FIG. 2 is a schematic illustration of the loading effect of etching;

FIG. 3 is a three-dimensional view of the back side of a micro-mirror device according to embodiment 1 of the present application; (ii) a

FIG. 4 is a detailed view of a micromirror device according to embodiment 1 of the present application;

FIG. 5 is a schematic view illustrating an operating micro-mirror device according to embodiment 1 of the present application;

FIG. 6 is a schematic flow chart illustrating a method for fabricating a micro-mirror device according to embodiment 1 of the present application;

FIG. 7 is a schematic view of a micro-mirror device according to embodiment 2 of the present application;

fig. 8 is a schematic diagram of a double-layer photoresist etching process in embodiment 2 of the present application;

FIG. 9(a) is a three-dimensional view of the front surface of a micromirror device according to embodiment 3 of the present application;

FIG. 9(b) is a three-dimensional view of the back surface of a micromirror device according to embodiment 3 of the present application;

FIG. 9(c) is a schematic view of a micromirror device according to embodiment 3 of the present application in operation;

fig. 10 is a flowchart illustrating a method for fabricating a micro mirror device according to embodiment 3 of the present application.

The following is a supplementary description of the drawings:

110-a substrate layer; 111-a back cavity structure; 120-a first device layer; 130-a second device layer; 140-a second buried layer; 150 — a first buried layer; 160-metal reflective layer; 121-a movable mirror surface; 122-movable comb tooth structure, 123-driving plate, 124-torsion shaft and 125-fixed anchor point; 126-first metal pad; 127-a weight-reducing portion; 128-a fixed frame structure; 131-a reinforcing frame; 132-static comb structure, 133-electric isolation groove; 134-second metal pad; 360-protective layer structure; 1-a movable structure; 2-para position marking.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic may be included in at least one implementation of the present application. In the description of the embodiments of the present application, it is to be understood that the terms "upper", "lower", "top", "bottom", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present application and simplifying the description, and do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," and the like are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in sequences other than those illustrated or described herein.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a micromirror device according to an embodiment of the present application, in which the micromirror device in fig. 1 includes a substrate layer 110, a first buried layer 150, and a device structure layer, and the substrate layer 110, the first buried layer 150, and the device structure layer are sequentially stacked and connected;

the device structure layer comprises a first device layer 120, a second buried layer 140 and a second device layer 130, wherein the first device layer 120, the second buried layer 140 and the second device layer 130 are sequentially connected in a stacked mode;

the first device layer 120 and the second device layer 130 sandwich a second buried layer 140 therebetween, and the first device layer 120 and the substrate layer 110 further sandwich a first buried layer 150 therebetween for maintaining the respective layers independent of each other in potential. The first buried layer 150 and the second buried layer 140 may be silicon dioxide buried layers, the first device layer 120 and the second device layer 130 may be single crystal silicon device layers, the substrate layer 110 may be a single crystal silicon substrate layer, the thickness of the single crystal silicon device layers is between 10 and 100 μm, the thickness of the silicon dioxide buried layers is between 0.1 and 3 μm, and the thickness of the single crystal silicon substrate layer 110 is between 100 μm and 1 mm.

The device structure layer includes a movable structure including a movable mirror 121 and a driving plate 123;

the weight reduction part 127 is arranged on the front surface of the movable mirror 121 and the driving plate 123, and the metal reflecting layer 160 is arranged on the back surface of the movable mirror 121; in the embodiments of the present application, the movable structures may be arranged in various ways, and two of them are described as follows:

in one implementation, the moveable structure is disposed on the first device layer 120;

the weight reduction portion 127 is provided on a surface of the movable mirror 121 spaced from the first buried layer 150 (i.e., a front surface of the movable mirror 121), and the metal reflection layer 160 is provided on a surface of the movable mirror 121 connected to the first buried layer 150 (i.e., a rear surface of the movable mirror 121).

In another embodiment, the movable structure is disposed on the second device layer 130;

the weight reduction portion 127 is disposed on a surface of the movable mirror 121 spaced from the second buried layer 140, and the metal reflection layer 160 is disposed on a surface of the movable mirror 121 connected to the second buried layer 140.

In an embodiment of the present application, the micromirror device further comprises a reinforcing frame; the reinforcing frame can be arranged in various ways, three of which are described below by way of example:

in a first possible implementation, the reinforcing frame is arranged on the second device layer 130, the movable structure is arranged on the first device layer, the reinforcing frame and the movable structure are bonded into a whole, and the reinforcing frame can reinforce the movable structure;

in a second implementable solution, the movable structure is disposed on the first device layer, and the reinforcing frame is formed on the movable structure by etching;

in a third possible implementation, the movable structure is disposed on the second device layer, and the reinforcing frame is formed on the movable structure by etching. The shape and size of the reinforcing frame can be designed according to needs, and in some other embodiments, the reinforcing frame can be omitted from the micro-mirror device.

In the embodiment of the present application, the weight-reducing portion 127 may be a large number of etching grooves or etching cavities with small characteristic lengths (CDs) for reducing the mass of the movable structure, and the CD value range is usually between 1um and 20 um. When the movable structure is arranged on the first device layer 120, the depth of the etched groove or the etched cavity on the movable mirror 121 is smaller than the thickness of the first device layer 120; when the movable structure is arranged on the second device layer 130, the depth of the etched groove or the etched cavity on the movable mirror 121 is smaller than the thickness of the second device layer 130; namely, the etching groove or the etching cavity on the movable mirror surface is not a perforation structure; since the back side of the driver board does not need to be kept optically flat, the etched grooves or etched cavities in the driver board can be designed as a relatively large CD through structure.

A back cavity structure 111 is arranged on the substrate layer 110, and the back cavity structure 111 can provide a movement space for the movable structure;

the first buried layer 150 is provided with a light-transmitting region, and the back cavity structure 111 and the light-transmitting region can expose the metal reflective layer 160.

Compared with the prior art, the invention provides the MEMS micro-mirror structure with reduced quality and the manufacturing method thereof, simultaneously reduces the mass of the oscillator and the stiffness coefficient of the torsional axis, maintains the resonance frequency of the mirror surface unchanged, and can realize a larger deflection angle under the same driving voltage, thereby simultaneously meeting the requirements of optical performance, reliability and cost. By the formula

It is known that the movable structure is turned after the mass of the movable structure is reducedThe moment of inertia J is reduced accordingly, and the stiffness coefficient k can be scaled down to keep the resonant frequency f constant. For quasi-statically operating micromirrors, the angle of deflection is linear with time during the active time of operation, and the static torque remains equal to the restoring force of the spring provided by the torsion axis, i.e., the moment of inertia remains equal to the restoring force of the spring provided by the torsion axis

Wherein C is comb capacitance. By adopting the technical scheme provided by the invention, as the stiffness coefficient k is reduced, the deflection angle theta can be increased by only adopting the same or even smaller driving voltage U to drive the micromirror. In addition, since the resonant frequency f of the device is not changed, the reliability of the micromirror is not deteriorated due to the decrease of the stiffness coefficient of the torsion axis.

The embodiment of the application also discloses a preparation method of the micro-mirror device, which comprises the following steps:

obtaining an SOI wafer comprising a substrate layer 110, a first buried layer 150, and a first device layer 120;

there are various ways of fabricating the structure forming the device layer, three of which are described below by way of example:

in a first embodiment, the step of setting the movable structure on the first device layer 120 and the reinforcing frame 131 on the second device layer 130 includes:

dry etching the first device layer 120 by using a subtractive process, i.e., a load effect or double-layer glue etching process, to define a movable structure and an alignment mark; the movable structure comprises a movable mirror 121, a driving plate 123 and a movable comb tooth structure 122; preparing and forming a lightening portion 127 on the movable structure; obtaining a second device layer 130, and forming a second buried layer 140 on the second device layer 130; bonding the second buried layer 140 to the first device layer 120 to form an integral wafer; etching the second buried layer 140 and the second device layer 130 to expose the alignment mark; etching the second device layer 130 to form a reinforcing frame 131 and a static comb structure 132;

in a second possible implementation, the step of setting the movable structure on the first device layer 120 and the step of forming the reinforcing frame 131 on the movable structure by etching includes the following steps:

spin-coating a negative photoresist on the upper surface of the SOI wafer, and carrying out first photoetching to form a thin photoresist layer; after photoetching development, covering the defined weight-reduced part with a thin photoresist layer;

spin-coating a positive photoresist on the upper surface of the SOI wafer, and carrying out second photoetching, wherein a local area covered by the positive photoresist is overlapped with a local area covered by the thin photoresist layer to form a thick photoresist layer;

dry etching the first device layer 120 by using a subtractive process, namely a load effect or double-layer glue etching process, forming device layer structures with different etching depths on the first device layer 120 and defining alignment marks; the device layer structure comprises a movable mirror 121, a driving plate 123, a movable comb tooth structure 122, a reinforcing frame 131 and a weight reducing part 127, wherein the reinforcing frame 131 can be formed on the movable mirror 121 by designing the shape, size and arrangement range of the weight reducing part 127;

obtaining a second device layer 130, and forming a second buried layer 140 on the second device layer 130; bonding the second buried layer 140 to the first device layer 120 to form an integral wafer;

etching the second buried layer 140 and the second device layer 130 to expose the alignment mark; etching the second device layer 130 to form a static comb structure 132;

in a third possible implementation, the step of setting the movable structure on the second device layer 130 and etching the reinforcing frame on the movable structure includes the following steps:

etching the first device layer 120 to form a fixed frame structure 128 and a static comb structure 132; stationary comb structure 132 is arranged on fixed frame structure 128; the fixed frame structure 128 further includes alignment marks;

etching the second buried layer 140 and the second device layer 130 to expose the alignment mark;

according to the alignment mark, dry etching processing is carried out on the second device layer by using a mass reduction process, namely a load effect or a double-layer glue etching process, and a movable structure, a mass reduction part 127 and a reinforcing frame 131 are formed on the second device layer at the same time; wherein, the reinforcing frame 131 can be formed on the movable mirror 121 by designing the shape, size and arrangement range of the lightening part 127;

the steps after preparing and forming the device layer structure are as follows:

depositing a metal film on the first device layer 120 and the second device layer 130, and patterning to prepare and form a metal pad structure;

and coating photoresist on the front surface of the whole wafer, and curing to form a protective layer structure 360.

The whole wafer is reversely buckled, and the substrate layer 110 is etched to form a back cavity structure 111;

removing the exposed regions of the first buried layer 150 and the second buried layer 140 by a BHF wet etching process;

a metal film is deposited on the back of the bulk wafer, wherein the metal film formed on the back of the movable mirror 121 serves as the metal reflective layer 160, and the metal film formed on the bottom of the substrate layer 110 can be used for die bonding.

In the present application, the weight reduction portion 127 may be prepared by selecting a process such as a loading effect of etching or double-layer glue etching according to actual conditions.

The conventional micromirror device requires the integration of the metal reflective layer 160 on the front surface of the movable mirror 121, and thus the front surface of the movable mirror 121 must be kept flat. Meanwhile, since the device layers are stacked on the buried layer and the substrate layer 110, it is difficult for the existing process technology to etch the back of the movable mirror 121, so the existing quality reduction scheme has a very limited effect, and the quality of the driving plate 123 structure can only be reduced by etching on the front side, and the quality of the movable mirror 121 cannot be reduced.

In the prior art, there is a method for etching the back of a movable structure to reduce mass: before bonding to form an SOI wafer, etching the upper surface of a top silicon wafer to form a microstructure, and removing part of the mass; simultaneously etching the upper surface of the silicon wafer at the bottom layer to form a cavity and provide a movement space for the movable structure; aligning and bonding the surfaces of the two layers of silicon wafers with microstructures to form an SOI wafer; and processing and manufacturing the metal reflecting layer and the mirror surface movable structure on the front surface of the bonded top layer silicon. However, the technical process of the technical scheme is complicated, two times of etching are needed to respectively realize the mass reduction and the manufacture of the movable structure, and the cost is high. In addition, because the surfaces of the two wafers are provided with the microstructures during bonding, the requirement on the alignment precision of wafer bonding is high, certain technical difficulty exists during implementation, and the repeatability is poor.

The micromirror devices proposed in this application are completely different. First, in the micromirror device of the present invention, the metal reflective layer 160 is integrated on the back of the movable mirror 121. The movable structure of the micromirror device of the present invention, including the movable mirror 121 and the driving plate 123, has etched deep grooves on the front surface, which can greatly reduce the mass of the movable structure. Therefore, the technical scheme provided by the invention can realize mass reduction in a larger proportion range, and the proportion range of mass reduction covers 1-90%. And secondly, the process method provided by the invention is simpler and more convenient, and has better process stability and higher repeatability. When the etching groove is etched, the load effect of etching and the double-layer glue etching process are utilized, and the etching groove with controllable depth and relatively shallow depth and other device structures can be formed simultaneously in one-step etching process, so that the movable structure quality is reduced, the back of the movable mirror surface 121 is kept flat, an extra etching step is not needed, and the production cost is not increased. In addition, the process method provided by the invention has the advantages of low requirement on the alignment precision of wafer bonding, better process stability and higher repeatability. Compared with the prior art, the MEMS micro-mirror structure with reduced quality and the manufacturing method thereof provided by the invention can simultaneously reduce the mass of the oscillator and the stiffness coefficient of the torsion axis on the basis of maintaining the resonance frequency of the mirror surface unchanged so as to realize a larger deflection angle under the same driving voltage, thereby simultaneously meeting the requirements of optical performance, reliability and cost.

Several micromirror devices and methods for making them are detailed below by way of example:

example 1:

the movable structure is arranged on the first device layer, and the reinforcing frame is arranged on the second device layer:

fig. 1 is a schematic structural diagram of a micromirror device according to an embodiment of the present application, in which the micromirror device in fig. 1 includes a substrate layer 110, a first buried layer 150, and a device structure layer, and the substrate layer 110, the first buried layer 150, and the device structure layer are sequentially stacked and connected from bottom to top;

the device structure layer comprises a first device layer 120, a second buried layer 140 and a second device layer 130, wherein the first device layer 120, the second buried layer 140 and the second device layer 130 are sequentially connected in a stacked mode from bottom to top;

the second device layer 130 is provided with a static comb structure 132, an electrical isolation groove 133, and a second metal pad 134. The electrically isolated slots 133 serve to divide the static comb structure 132 into two parts that are electrically independent of each other. In addition to the divided electrical isolation trenches shown in fig. 1, filled electrical isolation trenches may be used, with electrical isolation being achieved by filling the etched trenches with an electrically insulating material.

The first device layer 120 is provided with a movable mirror 121, a movable comb-tooth structure 122, a driving plate 123, a torsion shaft 124, a fixed anchor 125, and a first metal pad 126. The weight reduction part 127 is arranged on the upper surface of the movable mirror 121 and the driving plate 123; in embodiment 1 of the present application, the weight reducing portion 127 is formed by using an etching load effect, the weight reducing portion 127 is an etching cavity, and the depth of the etching cavity on the movable mirror surface does not exceed the thickness of the first device layer 120; the back of movable mirror 121 remains flat. In order to increase the light reflectivity, a metal reflective layer 160 is deposited or sputtered on the back of the movable mirror 121, and the material is gold or aluminum with a thickness of 20-200 nm. The reinforcing frame 131 is arranged on the second device layer, the reinforcing frame 131 is bonded with the movable structure into a whole through the second buried layer 140, and the reinforcing frame 131 can reinforce the movable structure;

fig. 2 is a schematic diagram of the loading effect of etching, and the process principle is as shown in the figure: a photoresist 202 is applied to the upper surface of the single crystal silicon, and patterned by photolithography to form openings (202a, 202b, 202c) having a difference in the characteristic dimension CD. The patterned photoresist layer 202 is used as a mask for the single crystal silicon layer 201, and the single crystal silicon layer 201 is dry etched. Due to the loading effect of etching, the etching speed of the exposed monocrystalline silicon of the openings with different CDs is different. The CD of the opening 202c is minimized and the etch rate of the single crystal silicon layer exposed by the opening 202c is relatively slow. Etching cavities (201a, 201b, 201c) with different depths can be formed in the same etching time.

The movable comb-tooth structures 122 are arranged on the driving plate 123 and are staggered in the horizontal direction with the static comb-tooth structures 132 provided on the second device layer 130 to form a comb-tooth pair. Because the static comb-tooth structures 132 and the movable comb-tooth structures 122 are respectively arranged on the second device layer 130 and the first device layer 120 and are not arranged in the same horizontal plane, a vertical comb-tooth pair structure can be formed for driving the movable structure to perform quasi-static motion.

The driving plate 123 is connected to the movable mirror 121, and the upper surface of the driving plate 123 is also provided with etching cavities with smaller CDs for reducing the mass of the movable structure. Alternatively, the etched cavities in the driver board may be designed as relatively large CD through structures, since the back side of the driver board need not be optically flat. Torsion shaft 124 connects movable mirror 121 and fixed anchor 125 to provide a spring restoring force for movement of the movable structure. A first metal pad 126 is disposed on the fixed anchor 125 for electrical interconnection with an external circuit by wire bonding.

Fig. 3 is a three-dimensional view of the back side of a micromirror device in embodiment 1 of the present application. It can be seen that the movable structure of the micromirror device has a smooth back surface.

FIG. 4 is a detailed view of a micromirror device according to embodiment 1 of the present application. As can be seen, the reinforcing frame 131 is bonded to the upper surface of the movable structure, which is lined with a large number of smaller CD etching cavities. The ratio of the total volume of the etching cavity to the total volume of the movable structure is called occupancy, and the larger the occupancy is, the better the mass reduction effect is. The occupancy can be adjusted by controlling the CD, the arrangement number and the etching time of the etching cavity, thereby adjusting the effect of reducing the mass according to the design requirement.

Fig. 5 is a schematic view of a micromirror device in accordance with embodiment 1 of the present application during operation. As can be seen, in operation, a light beam is incident from the back of the micro mirror device and strikes the metal reflective layer 160 on the back of the movable mirror 121. The movable mirror 121 moves under the control of a drive signal while reflecting a light beam incident from the back surface, thereby realizing spatial modulation of the light beam.

FIG. 6 is a schematic process flow diagram for fabricating a micromirror device according to the present invention

As shown in fig. 6(a), the SOI wafer to be etched is subjected to conventional pretreatment including cleaning, drying, and the like. The embodiment of the application adopts a single-layer SOI wafer, which comprises a first device layer 120, a first buried layer 150 and a monocrystalline silicon substrate layer 110, wherein three layers of structures are stacked from top to bottom in sequence. The first buried layer 150 is a silicon dioxide buried layer, the first device layer 120 is a monocrystalline silicon device layer, the substrate layer 110 is a monocrystalline silicon substrate layer, the thickness of the monocrystalline silicon device layer is between 10 and 100 micrometers, the thickness of the silicon dioxide buried layer is between 0.1 and 3 micrometers, and the thickness of the monocrystalline silicon substrate layer is between 100 micrometers and 1 mm. The micromirror of the present invention can be fabricated using other types of single-crystal silicon wafers in addition to the single-layer SOI wafer.

As shown in fig. 6(b), the first device layer 120 is etched for the first time by using a dry etching process, and the movable structure 1 and the alignment mark 2 are defined. The movable structure includes a movable mirror 121, a drive plate 123, and movable comb tooth structures 122 arranged on both sides. Meanwhile, a weight-reduced portion 127, i.e., a large number of etching cavities with small CDs, is formed in the central areas of the movable mirror and the driving plate by the load effect of etching. Due to the loading effect of the etching, under the same etching conditions, the single crystal silicon around the movable structure is completely etched, exposing the first buried layer 150 at the bottom, while the single crystal silicon in the middle of the movable structure is not completely etched through.

As shown in fig. 6(c), another single crystal silicon wafer (second device layer 130) is prepared, and a dense oxide film (second buried layer 140) is formed on the surface thereof by a thermal oxidation process. The second device layer 130 is bonded to the first device layer 120 of the SOI wafer using a fusion bonding process, and then the top second device layer 130 is polished to reduce its thickness to a design value.

As shown in fig. 6(d), the second device layer 130 and the second buried layer 140 are dry etched to expose the alignment mark 2.

As shown in fig. 6(e), the second device layer 130 is etched using a conventional dry etching process to form a reinforcing frame 131 and a static comb tooth structure 132.

As shown in fig. 6(f), a metal film is deposited on the second device layer 130 and the exposed first device layer 120 by a sputtering or evaporation process, and patterned to form a metal pad structure, i.e., a first metal pad 126 and a second metal pad 134. The metal film is made of Cr/Au and has a thickness of 20-200 nm. Because the surface of the wafer is fully distributed with deep grooves, thick photoresist photoetching and developing processes are needed, and stripping process is adopted to realize metal patterning.

As shown in fig. 6(g), a photoresist (or other kind of organic polymer) is coated on the front surface of the whole wafer and cured to form a protection layer structure 360.

As shown in fig. 6(h), the whole wafer is flipped over, and the substrate layer 110 of the SOI wafer is etched by using a conventional dry etching process or a conventional wet etching process to form a back cavity structure 111.

As shown in fig. 6(i), after the protective layer structure 360 on the front surface is removed, the exposed regions of the first buried layer 150 and the second buried layer 140 are removed by BHF wet etching process to release the movable structure and form a light transmission region.

As shown in fig. 6(j), a metal film is deposited on the back side of the entire wafer. The metal film formed on the back of the movable mirror serves as a metal reflective layer 160 for the beam, and the metal film formed on the bottom of the substrate layer can be used for subsequent die bonding. The metal film is made of Ti/Au and has a thickness of 20-200 nm.

Example 2:

the movable structure is arranged on the first device layer 120, and the reinforcing frame 131 is formed on the movable structure through etching;

the difference from embodiment 1 is that, as shown in fig. 7(a), a reinforcing frame 131 is provided on the first device layer 120, the reinforcing frame 131 is formed on the movable structure by etching the first device layer 120; the whole mass of the movable structure is reduced while the reinforcement effect is realized.

As shown in FIG. 7(b), the lower surface of the movable structure of the micromirror device is kept smooth and flat, and a metal reflective layer 160 is formed by plating a metal thin film through a metal evaporation or sputtering process, wherein the material is Ti/Au, and the thickness is 20-200 nm.

Different from embodiment 1, the micromirror device of embodiment 2 of the present application is fabricated by a double-layer glue etching process. Device layer structures having different etch depths are formed on the first device layer 120 by one dry etch. The device layer structure includes a movable mirror 121, a torsion shaft 124, a driving plate 123, a movable comb-tooth structure 122, a reinforcing frame 125, and a weight-reduced portion 127.

The preparation process of the micromirror device of embodiment 2 of this application is as follows:

obtaining an SOI wafer; the wafer to be etched is subjected to conventional pre-treatment including cleaning, drying, etc. In embodiment 2 of the present application, a single-layer SOI wafer is adopted, and includes a first device layer 120, a first buried layer 150, and a monocrystalline silicon substrate layer 110, where the three layers are stacked in sequence from top to bottom. The first buried layer 150 is a silicon dioxide buried layer, the first device layer 120 is a monocrystalline silicon device layer, the substrate layer 110 is a monocrystalline silicon substrate layer, the thickness of the monocrystalline silicon device layer is between 10 and 100 micrometers, the thickness of the silicon dioxide buried layer is between 0.1 and 3 micrometers, and the thickness of the monocrystalline silicon substrate layer is between 100 micrometers and 1 mm. The micromirrors provided by embodiments of the present application can be fabricated using other types of single-crystal silicon wafers in addition to single-layer SOI wafers.

In embodiment 2 of the present application, a double-layer photoresist etching process is used for preparing the device layer structure, and fig. 8 is a schematic diagram of the double-layer photoresist etching process in embodiment 2 of the present application.

Spin-coating a negative photoresist on the upper surface of the SOI wafer, and performing first photoetching to form a thin photoresist layer 501; after photoetching development, the thin photoresist layer 801 covers the defined weight-reduced part;

spin-coating a positive photoresist on the upper surface of the SOI wafer, and carrying out second photoetching, wherein a local area covered by the positive photoresist is overlapped with a local area covered by the thin photoresist layer 801 to form a thick photoresist layer 802; as shown in fig. 8 (a).

Performing dry etching processing on the first device layer 120, forming device layer structures with different etching depths on the first device layer 120, and defining alignment marks; the device layer structure comprises a movable mirror 121, a driving plate 123, a movable comb tooth structure 122, a reinforcing frame 131 and a weight reducing part 127, wherein the reinforcing frame 131 can be formed on the movable mirror 121 by designing the shape, size and arrangement range of the weight reducing part 127;

in the embodiment of the application, the weight reduction part can be an etching groove, and in the etching process, the etching selection ratio of the negative photoresist is assumed to be N: 1, thickness a, then when the negative is completely consumed, the etching depth that has been performed for the area not covered by the negative is na. And continuing etching until the first buried layer below the first device layer is exposed. Due to the protective effect of the negative photoresist at the initial stage of etching, the etching depth of the etching groove for reducing the mass is less than the thickness of the first device layer by Na, and the etching depth does not reach the first buried layer. By designing and controlling the appearance of the deep groove, the movable structure can be lightened, and meanwhile, a reinforcing frame with a reinforcing effect can be manufactured. As shown in fig. 8 (b).

etching the second buried layer 140 and the second device layer 130 to expose the alignment mark 2; etching the second device layer 130 to form a static comb structure 132;

a metal film is deposited on the second device layer 130 and the exposed first device layer 120 by a sputtering or evaporation process and patterned to form metal pad structures, i.e., a first metal pad 126 and a second metal pad 134. The metal film is made of Cr/Au and has a thickness of 20-200 nm. Because the surface of the wafer is fully distributed with deep grooves, thick photoresist photoetching and developing processes are needed, and stripping process is adopted to realize metal patterning.

A photoresist (or other kind of organic polymer) is applied to the front side of the bulk wafer and cured to form a protective layer structure 360.

And reversing the whole wafer, and etching the substrate layer 110 of the SOI wafer by using a traditional dry etching process or a traditional wet etching process to form a back cavity structure 111.

After the front protective layer structure 360 is removed, the exposed regions of the first buried layer 150 and the second buried layer 140 are removed by BHF wet etching process to release the movable structure and form a light transmission region.

And depositing a metal film on the back of the whole wafer. The metal film formed on the back of the movable mirror serves as a metal reflective layer 160 for the beam, and the metal film formed on the bottom of the substrate layer can be used for subsequent die bonding. The metal film is made of Ti/Au and has a thickness of 20-200 nm.

Example 3:

the movable structure is arranged on the second device layer:

unlike

embodiments

1 and 2, the movable structure of the micromirror device shown in embodiment 3 of the present application is mainly integrated in the second device layer, and the reinforcing frame is formed on the movable structure by etching the second device layer;

fig. 9(a) is a three-dimensional view of the front surface of a micromirror device in embodiment 3 of the present application. The micromirror device comprises 1 layer of single crystal

silicon substrate layer

110 and 2 layers of single crystal silicon device layer structure: a first device layer 120 and a second device layer 130. The first device layer 120 and the second device layer 130 sandwich a second buried layer 140 therebetween, and the first device layer 120 and the substrate layer 110 further sandwich a first buried layer 150 therebetween for maintaining the respective layers independent of each other in potential. The first buried layer 150 and the second buried layer 140 may be silicon dioxide buried layers. The thickness of the monocrystalline silicon device layer is 10-100 mu m, the thickness of the silicon dioxide buried layer is 0.1-3 mu m, and the thickness of the monocrystalline silicon substrate layer 110 is 100 mu m-1 mm.

The second device layer 130 is provided with a movable mirror 121, a movable comb-tooth structure 122, a driving plate 123, a torsion shaft 124, a fixed anchor 125, and a first metal pad 126. The movable mirror 121 is integrally connected to the driving plate 123, and movable comb structures 122 are arranged on both sides of the driving plate 123. Torsion shaft 124 connects movable mirror 121 and fixed anchor 125, providing a spring restoring force to the movable structure when in motion. The fixed anchor 125 is further provided with a first metal pad 126 for electrical interconnection with an external circuit.

The movable mirror 121 and the driving plate structure 123 are also provided with weight reducing portions 127 (etching grooves) on the upper surfaces thereof. Since the depth of the etched trench is less than the thickness of the second device layer 130, the back of the movable mirror 121 remains flat, as shown in FIG. 9 (b). In order to increase the light reflectivity, a metal reflective layer 160 is deposited or sputtered on the back of the movable mirror surface, and the material is gold or aluminum, and the thickness is 20-200 nm.

In addition, optionally, by designing and controlling the shape, size and arrangement range of the etching grooves, the reinforcing frame 131 can be formed on the upper surface of the movable mirror 121, so that the movable structure can be lightened, and simultaneously, the reinforcing effect can be achieved, and the performance of the device can be further improved. The etching groove can be manufactured by using a double-layer glue etching process or an etching load effect.

An electrical isolation trench 133, a first metal pad 134, and a static comb structure 132 are disposed on the first device layer 120. Static comb tooth structures 132 are arranged horizontally staggered from movable comb tooth structures 122, but are located at different levels in the vertical direction, and thus together constitute a vertical comb tooth pair structure for driving the movable structure to perform quasi-static motion. The electrically isolated tank 133 separates the stationary comb-tooth structure 132 into two sections whose potentials are independent of each other. In addition to the divided electrical isolation trenches shown in fig. 9(a), filled electrical isolation trenches may be used, where electrical isolation is achieved by filling an electrical insulating material in the etched trenches. Since a buried layer of silicon dioxide is sandwiched between the first device layer 120 and the second device layer 130, and the potentials of the two device layers are independent, the movable comb-tooth structure 122 and the stationary comb-tooth structure 132 have 3 independent potentials, respectively.

Substrate layer 110 has a back cavity structure 111 disposed thereon to provide a space for movement of the movable structure while exposing a metal reflective layer 160 on the back of movable mirror 121.

Fig. 9(b) is a three-dimensional view of the back surface of the micromirror device in embodiment 3 of the present application. It can be seen that the movable structure of the micromirror device has a smooth back surface.

FIG. 9(c) is a schematic diagram of a micromirror device in accordance with embodiment 3 of the present application during operation. As can be seen, the movable mirror 121 of the micro mirror device is located in the second device layer 130. In operation, a light beam is incident from the back of the micro mirror device and illuminates the metal reflective layer 160 on the back of the movable mirror 121. The movable mirror 121 moves under the control of a drive signal while reflecting a light beam incident from the back surface, thereby realizing spatial modulation of the light beam.

Fig. 10 is a schematic flow chart illustrating a process for fabricating a micro-mirror device according to embodiment 3 of the present application.

As shown in fig. 10(a), the SOI wafer to be etched is subjected to conventional pretreatment including cleaning, drying, and the like. The embodiment of the application adopts a single-layer SOI wafer, which comprises a first device layer 120, a first buried layer 150 and a monocrystalline silicon substrate layer 110, wherein the three layers are stacked in sequence. The first buried layer 150 is a silicon dioxide buried layer, the first device layer 120 is a monocrystalline silicon device layer, the substrate layer 110 is a monocrystalline silicon substrate layer, the thickness of the monocrystalline silicon device layer is between 10 and 100 micrometers, the thickness of the silicon dioxide buried layer is between 0.1 and 3 micrometers, and the thickness of the monocrystalline silicon substrate layer is between 100 micrometers and 1 mm. The micromirror of the present invention can be fabricated using other types of single-crystal silicon wafers in addition to the single-layer SOI wafer.

As shown in fig. 10(b), the first device layer 120 is dry etched until the bottom first buried layer 150 is exposed, forming the fixed frame structure 128 and the static comb tooth structure 132. Static comb structures 132 are arranged on the fixed frame structure 128 and are separated by electrical isolation slots 133. The fixed frame structure 128 further includes alignment marks 3.

As shown in fig. 10(c), another single crystal silicon wafer (second device layer 130) is prepared, and a dense oxide film (second buried layer) 140 is formed on the surface thereof by a thermal oxidation process. The single crystal silicon wafer 130 is bonded to the first device layer 120 of the SOI wafer by a fusion bonding process, and then the top single crystal silicon 130 is polished to reduce its thickness to a design value.

As shown in fig. 10(d), the second device layer 130 and the second buried layer 140 are dry etched to expose the alignment mark 3.

As shown in fig. 10(e), the wafer bonded as a whole is dry etched according to the alignment mark until the single crystal silicon around the movable structure is completely etched and the second buried layer 140 at the bottom is exposed. When the double-layer glue etching process is adopted, the monocrystalline silicon in the middle of the movable structure is not completely etched under the same etching condition. Therefore, the movable structure and the lightening portion 127 can be simultaneously formed on the second device layer 130 through one-step dry etching, the lightening portion 127 is an etching groove, and the etching depth of the etching groove is smaller than the thickness of the second device layer 130. The movable structure comprises a movable mirror 121, a driving plate 123 and movable comb teeth 122. Alternatively, the loading effect of etching can be used for processing.

As shown in fig. 10(f), a metal film is deposited on the second device layer 130 and the exposed first device layer 120 by a sputtering or evaporation process and patterned to form a first metal pad 126 and a second metal pad 134. The metal film is made of Cr/Au and has a thickness of 20-200 nm.

As shown in fig. 10(g), a photoresist is coated on the front surface of the whole wafer and cured to form a protection layer structure 360.

As shown in fig. 10(h), the whole wafer is flipped over, and the substrate layer 110 of the SOI wafer is etched by using a conventional dry etching process or a conventional wet etching process to form a back cavity structure 111.

As shown in fig. 10(i), the whole wafer is flipped over, the substrate layer 110 of the SOI wafer is etched by using a conventional dry etching process or a wet etching process to form the back cavity structure 111, and as shown in fig. 3(i), after the front protective layer structure 360 is removed, the exposed regions of the first buried layer 150 and the second buried layer 140 are removed by using a BHF wet etching process, so as to release the movable structure and form a light-passing region.

As shown in fig. 10(j), a metal film is deposited on the backside of the entire wafer. The metal film formed on the back of the movable mirror serves as a metal reflective layer 160 for the beam, and the metal film formed on the bottom of the substrate layer can be used for subsequent die bonding. The metal film is made of Ti/Au and has a thickness of 20-200 nm.

The micromirror device and the manufacturing method of the invention are also suitable for designing and manufacturing a two-dimensional micromirror device. On the basis of the one-dimensional micro-mirror, the movable mirror surface can perform two-dimensional movement by arranging an additional balance structure and an additional driving structure. The weight reduction part of the invention can be integrated on the two-dimensional micro-mirror device through the load effect of etching or the double-layer glue etching process, thereby reducing the whole mass of the movable structure, keeping the resonance frequency unchanged and increasing the motion amplitude of the quasi-static mode. Therefore, the micromirror structure and fabrication method of the present invention can be equally applied in designing and fabricating two-dimensional micromirror devices without departing from the scope of the present invention.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features herein disclosed.

Claims

1. A micro-mirror device, comprising a substrate layer (110), a first buried layer (150) and a device structure layer, wherein the substrate layer (110), the first buried layer (150) and the device structure layer are sequentially connected in a stacked manner;

the device structure layer comprises a movable structure, and the movable structure comprises a movable mirror (121) and a driving plate (123);

a weight reduction part (127) is arranged on the front surface of the movable mirror surface (121) and the driving plate (123), and a metal reflecting layer is arranged on the back surface of the movable mirror surface (121);

a back cavity structure is arranged on the substrate layer (110), and the back cavity structure can provide a movement space for the movable structure;

and a light-transmitting area is arranged on the first buried layer (150), and the metal reflecting layer can be exposed outside by the back cavity structure and the light-transmitting area.

2. The micro-mirror device of claim 1, wherein the lightening features (127) comprise etched grooves.

3. The micro mirror device according to claim 2, wherein the device structure layer comprises a first device layer (120), a second buried layer (140), and a second device layer (130), the first device layer (120), the second buried layer (140), and the second device layer (130) being sequentially stacked and connected;

the movable structure is arranged on the first device layer (120);

the weight reduction part (127) is arranged on one surface of the movable mirror surface (121) spaced from the first buried layer (150), and the metal reflection layer is arranged on one surface of the movable mirror surface (121) connected with the first buried layer (150).

4. The micro mirror device according to claim 2, wherein the device structure layer comprises a first device layer (120), a second buried layer (140), and a second device layer (130), the first device layer (120), the second buried layer (140), and the second device layer (130) being sequentially stacked and connected;

the movable structure is arranged on the second device layer (130);

the weight reduction part (127) is arranged on one surface of the movable mirror surface (121) spaced from the second buried layer (140), and the metal reflection layer is arranged on one surface of the movable mirror surface (121) connected with the second buried layer (140).

5. The micro mirror device according to claim 3, wherein a depth of the etched groove on the movable mirror surface (121) is less than a thickness of the first device layer (120).

6. The micro mirror device according to claim 4, wherein a depth of the etched groove on the movable mirror (121) is less than a thickness of the second device layer (130).

7. The micro-mirror device according to claim 3, further comprising a reinforcing frame (131);

the reinforcing frame (131) is arranged on the second device layer (130), the reinforcing frame (131) is bonded with the movable structure into a whole, and the reinforcing frame (131) can reinforce the movable structure;

or;

the reinforcing frame (131) is etched on the movable structure; the reinforcing frame (131) is capable of reinforcing the movable structure.

8. The micro-mirror device according to claim 4, further comprising a reinforcing frame (131);

9. A method of fabricating a micro-mirror device, comprising the steps of:

obtaining an SOI wafer comprising a substrate layer (110), a first buried layer (150) and a first device layer (120);

preparing and forming a device layer structure, comprising:

if the movable structure is set on the first device layer (120) and the reinforcing frame (131) is set on the second device layer (130), the method comprises the following steps: etching the first device layer (120) by using a subtractive process to define a movable structure and a contraposition mark; the movable structure comprises a movable mirror surface (121), a driving plate (123) and a movable comb tooth structure (122); preparing and forming a lightening portion (127) on the movable structure; obtaining a second device layer (130), and preparing and forming a second buried layer (140) on the second device layer (130); bonding the second buried layer (140) with the first device layer (120) to form a monolithic wafer; etching the second buried layer (140) and the second device layer (130) to expose an alignment mark; etching the second device layer (130) to form a reinforcing frame (131) and a static comb structure (132);

depositing a layer of metal film on the first device layer (120) and the second device layer (130) and patterning to prepare and form a metal pad structure;

reversely buckling the integral wafer, and etching the substrate layer (110) to form a back cavity structure (111);

removing bare regions of the first buried layer (150) and the second buried layer (140);

and depositing a metal film on the back of the whole wafer, wherein the metal film formed on the back of the movable mirror (121) is used as a metal reflecting layer (160), and the metal film formed on the bottom of the substrate layer (110) can be used for chip welding.

10. The method of manufacturing a micro mirror device according to claim 9, wherein the manufacturing forming a device layer structure further comprises:

if a movable structure is set on the first device layer (120) and a reinforcing frame (131) is formed on the movable structure by etching, the method comprises the following steps:

etching the first device layer (120) by using a subtractive process, forming device layer structures with different etching depths on the first device layer (120), and defining alignment marks; the device layer structure comprises a movable mirror surface (121), a driving plate (123), a movable comb tooth structure (122), a reinforcing frame (131) and a weight reducing part (127), wherein the reinforcing frame (131) can be formed on the movable mirror surface (121) by designing the shape, size and arrangement range of the weight reducing part (127);

obtaining a second device layer (130), and preparing and forming a second buried layer (140) on the second device layer (130); bonding the second buried layer (140) with the first device layer (120) to form a monolithic wafer;

etching the second buried layer (140) and the second device layer (130) to expose the alignment mark; etching the second device layer (130) to form a static comb structure (132);

or;

if the movable structure is set to be arranged on the second device layer (130) and the reinforcing frame is etched on the movable structure, the method comprises the following steps:

etching the first device layer (120) to form a fixed frame structure (128) and a static comb structure (132); the static comb structure (132) is arranged on the fixed frame structure (128); the fixed frame structure (128) further comprises alignment indicia;

etching the second buried layer (140) and the second device layer (130) to expose the alignment mark;

according to the alignment mark, etching the second device layer by using a weight reduction process, and simultaneously forming a movable structure, a weight reduction part (127) and the reinforcing frame (131) on the second device layer; wherein the reinforcing frame (131) can be formed on the movable mirror (121) by designing the shape, size, and arrangement range of the weight-reduced portion (127).

11. The method of claim 10, wherein the subtractive process comprises a dry etch based on a loading effect or a double glue process.