A method for preparing a MEMS micromirror driven by an electrostatic comb, and a MEMS micromirror and a spectrometer

Abstract

The present invention provides a method for preparing a MEMS micromirror driven by an electrostatic comb, a MEMS micromirror and a spectrometer. The present invention utilizes semiconductor manufacturing technology to process the MEMS micromirror, thereby increasing the torsion angle of the micromirror and realizing light signal collection with a larger field angle. In addition, the grating of a traditional micro-spectrometer is combined with a rotating micromirror, thereby simplifying the optical path without affecting the distribution of light beams, thereby reducing energy loss. A design structure in which moving comb teeth electrodes are located on both sides of a grating mirror surface is adopted, and relatively insulated static comb teeth electrodes on both sides are used to allow the grating mirror surface to be deflected toward both sides, thereby increasing the deflection angle. A first silicon wafer and a second silicon wafer are of an integral structure, and only the first silicon wafer and the second silicon wafer need to be etched, thereby having a simpler processing technology.

Description

Technical Field

[0001] The invention relates to the technical field of MEMS micromirrors, and in particular to a method for preparing a MEMS micromirror driven by an electrostatic comb, a MEMS micromirror and a spectrometer. Background Art

[0002] Near infrared (NIR) spectrum has a wavelength range of 800-2500nm, mainly containing the absorption of hydrogen groups CH, OH, NH, SH, and contains rich information on the composition and molecular structure of most organic substances. NIR is fast, non-destructive, and can achieve simultaneous determination of multiple components. It is widely used in petrochemical, pharmaceutical, agricultural and other fields. These industries have the characteristics of on-site analysis and require portable spectrometers with compact structure, small size and light weight. Spectrometers based on microelectromechanical systems (MEMS) are the development trend of low-cost portable near-infrared spectrometers in the future. At present, preliminary promotion and application have been achieved, and small-scale attempts have been carried out in the manufacturing / consumption process of food, medicine and textiles, and good detection results have been achieved. The two major mainstream technical routes of MEMS near-infrared spectrometers include Fourier transform type based on Michelson interference principle and grating scanning type. The former has great difficulties in processing difficulty and cost due to its structural complexity, while the latter has a simple structure and easy optical path to build, but it is usually used with linear array detectors, which makes the equipment cost too high.

[0003] Optical scanning mirrors are important core components of optical application systems, which can guide a beam of light in different directions. Traditional optical scanning devices are designed with bulk optical components, and their large size and high price greatly limit their applications. With the development of micro-electromechanical (MEMS) technology, optical devices have gradually developed towards low cost, miniaturization and light weight, and have achieved a transition from static to dynamic. MEMS scanning mirrors have been widely used in fields including laser imaging, image digitization, quality inspection and medical imaging. MEMS scanning mirrors can be divided into electrostatic drive, electromagnetic drive, thermoelectric drive and piezoelectric drive according to their driving mode. Electrostatically driven MEMS scanning mirrors usually have simple manufacturing processes, compact structures, and are compatible with semiconductor micromachining technology. They do not require the use of rare materials like piezoelectric and electromagnetic devices, and have higher driving frequencies than thermoelectric drives. Electrostatic drive structures usually have flat-plate drive type and comb-tooth drive type. In the flat-plate drive structure, the micromirror surface twisting requires a higher driving voltage; while the comb-tooth drive can obtain a larger twisting angle at a lower driving voltage, so the comb-tooth drive structure has greater advantages in practical applications.

[0004] The existing MEMS scanning mirror generally only has the function of a scanning mirror, and needs to be used in conjunction with a grating. When building a spectrometer, the optical path is relatively complex and the energy loss of light is relatively large. In addition, the MEMS scanning mirror in the prior art generally uses a single-sided moving comb tooth electrode and a stationary comb tooth electrode to cooperate, and can only be deflected to one side, and the deflection angle is small. If deflection to both sides is to be achieved, it is necessary to separately etch multiple sets of moving comb tooth electrodes and stationary comb tooth electrodes, which makes the processing process complicated. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a MEMS micromirror driven by an electrostatic comb, a MEMS micromirror and a spectrometer, so as to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a MEMS micromirror driven by an electrostatic comb, the specific steps comprising:

[0008] S1: etching a deep square active groove on a first silicon wafer as a rotation space for the mirror, and etching a comb tooth structure on the front and rear side walls of the active groove as a static comb tooth electrode;

[0009] S2: Along the symmetry axis direction of the stationary comb-tooth electrodes on both sides of the active groove, the side walls of the active groove are symmetrically thermally oxidized to form an insulating layer of a certain width, so that the stationary comb-tooth electrodes on both sides are relatively insulated;

[0010] S3: thermally oxidizing the upper surface of the first silicon wafer or the lower surface of the second silicon wafer to form a thermal oxidation layer, and bonding the oxide layers of the two silicon wafers together using a bonding process after fully cleaning the surface, with the second silicon wafer being located above the first silicon wafer;

[0011] S4: etching a grating mirror in the middle on the second silicon wafer, etching a torsion beam at both ends of the grating mirror, etching a comb-tooth structured moving comb-tooth electrode at both ends of the grating mirror perpendicular to the torsion beam, wherein the moving comb-tooth electrode is located directly above the gap between adjacent stationary comb-tooth electrodes, and the width of the gap between adjacent stationary comb-tooth electrodes is greater than the width of the moving comb-tooth electrode;

[0012] S5: etching a plurality of groups of mutually parallel grating lines on the upper surface of the grating mirror;

[0013] S6: Using the photoresist as a mask, deposit an aluminum metal layer on the upper surface of the grating mirror by magnetron sputtering, and remove the photoresist.

[0014] In one of the embodiments, the etching method used when etching the first silicon wafer and the second silicon wafer is deep silicon etching technology.

[0015] In one embodiment, the thickness of the first silicon wafer is 200 μm, and after bonding the oxide layers of the two silicon wafers together in step S3, the second silicon wafer is thinned to 75 μm.

[0016] In one embodiment, the grating line direction and the torsion beam orientation etched in step S5 remain the same.

[0017] In one of the embodiments, in step S6, an aluminum metal layer is deposited on the surfaces of the stationary comb-tooth electrode and the moving comb-tooth electrode by magnetron sputtering, and the thickness of the aluminum metal layer deposited on the surfaces of the grating mirror, the stationary comb-tooth electrode and the moving comb-tooth electrode is 300 nm.

[0018] The present invention further provides a MEMS micromirror driven by an electrostatic comb, wherein the MEMS micromirror driven by an electrostatic comb is prepared by the above-mentioned preparation method, comprising:

[0019] A first silicon wafer layer, the first silicon wafer layer comprising a first frame, a static comb-tooth electrode and an insulating layer connected in one piece, the first frame having two groups symmetrically arranged and connected through the insulating layer, and a static comb-tooth electrode being arranged on the inner side of the first frame;

[0020] a second silicon wafer layer, wherein the second silicon wafer layer comprises an integrally connected second frame, a moving comb-tooth electrode, a grating mirror and a torsion beam, a grating mirror is arranged in the middle of the second frame, two sides of the grating mirror are connected to the inner side of the second frame through a torsion beam, two sides of the grating mirror are arranged with moving comb-tooth electrodes perpendicular to the torsion beam, a gap width between adjacent static comb-tooth electrodes is greater than a width of the moving comb-tooth electrode, and a plurality of groups of mutually parallel grating lines are arranged on the grating mirror;

[0021] An oxide layer, wherein the oxide layer is formed by thermally oxidizing the upper surface of the first silicon wafer or the lower surface of the second silicon wafer, the first silicon wafer layer and the second silicon wafer layer are bonded together with the oxide layer through a bonding process, and the dynamic comb-tooth electrode is located directly above the gap between adjacent stationary comb-tooth electrodes;

[0022] The metal layer is an aluminum metal layer, which is deposited on the upper surface of the grating mirror.

[0023] In one embodiment, the thickness of the first silicon wafer layer is 200 μm, and the thickness of the second silicon wafer layer is 75 μm.

[0024] In one of the embodiments, the grating line direction and the torsion beam orientation remain the same.

[0025] In one of the embodiments, an aluminum metal layer is also deposited on the surfaces of the stationary comb-tooth electrode and the moving comb-tooth electrode, and the thickness of the aluminum metal layer deposited on the surfaces of the grating mirror, the stationary comb-tooth electrode and the moving comb-tooth electrode is 300 nm.

[0026] The present invention further provides a spectrometer, wherein the spectrometer comprises an optical fiber, a collimating mirror, a grating micromirror, a focusing mirror and a photodetector. The light emitted by the optical fiber is reflected to the grating micromirror through the collimating mirror, reflected to the focusing mirror after being split by the grating micromirror, and reflected to the photodetector after being focused by the focusing mirror. The grating micromirror adopts the above-mentioned MEMS micromirror driven by the electrostatic comb.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention utilizes semiconductor manufacturing technology to process MEMS micromirrors, which can increase the deflection angle of the micromirrors and realize light signal collection with a larger field angle. In addition, the grating of a traditional micro-spectrometer is combined with a rotating micromirror to simplify the optical path without affecting the light beam distribution, thereby reducing energy loss. The design structure in which moving comb-tooth electrodes are located on both sides of the grating mirror surface is adopted, and relatively insulated static comb-tooth electrodes on both sides are used to allow the grating mirror surface to be deflected toward both sides, making the deflection angle larger. The first silicon wafer and the second silicon wafer are an integral structure, and only the first silicon wafer and the second silicon wafer need to be etched, which has a simpler processing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the process of the preparation method of the present invention;

[0030] Figure 2 It is a schematic diagram of the exploded structure of the MEMS micromirror of the present invention;

[0031] Figure 3 It is a schematic diagram of the top view of the structure of the stationary comb-tooth electrode and the movable comb-tooth electrode in the present invention;

[0032] Figure 4 is a schematic structural diagram of the first silicon wafer layer in the present invention;

[0033] Figure 5 is a schematic structural diagram of the second silicon wafer layer in the present invention;

[0034] Figure 6 It is a schematic diagram of the overall structure of the MEMS micromirror of the present invention.

[0035] In the figure: 100 first silicon wafer layer, 110 first frame, 120 active groove, 130 insulating layer, 140 static comb-tooth electrode, 200 second silicon wafer layer, second frame 210, 220 grating mirror, 230 torsion beam, 240 dynamic comb-tooth electrode, 250 grating line, 300 oxide layer, 400 metal layer. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example:

[0038] See also Figure 1 , the present invention provides a technical solution:

[0039] A method for preparing a MEMS micromirror driven by an electrostatic comb, the specific steps comprising:

[0040] S1: A deep square active groove is etched on the first silicon wafer as a rotation space for the mirror, and a comb tooth structure is etched on the front and rear side walls of the active groove as a static comb tooth electrode.

[0041] The thickness of the first silicon wafer is 200 μm, and the size of the active groove is larger than the size of the grating mirror, so as to ensure that the grating mirror can rotate in the active groove.

[0042] S2: Along the symmetry axis direction of the stationary comb-tooth electrodes on both sides of the active groove, the side walls of the active groove are symmetrically thermally oxidized to form an insulating layer of a certain width, so that the stationary comb-tooth electrodes on both sides are relatively insulated.

[0043] Among them, the oxidized insulating layer is made of silicon dioxide, which is obtained by oxidizing a silicon wafer and has a width of 600nm, which can effectively insulate the static comb teeth electrodes on both sides.

[0044] S3: thermally oxidize the upper surface of the first silicon wafer or the lower surface of the second silicon wafer to form a thermal oxide layer, and after fully cleaning the surface, use a bonding process to bond the oxide layers of the two silicon wafers together, with the second silicon wafer being located above the first silicon wafer.

[0045] Among them, the oxide layer is obtained by thermally oxidizing the upper surface of the first silicon wafer, the lower surface of the second silicon wafer, or oxidizing both. After the first silicon wafer and the second silicon wafer are bonded together through the oxide layer, the thickness of the oxide layer is 600nm, which effectively ensures the relative insulation between the first silicon wafer and the second silicon wafer, and after bonding, the second silicon wafer is thinned to 75μm. The size of the first silicon wafer is the same as that of the second silicon wafer.

[0046] S4: A grating mirror is etched in the middle on the second silicon wafer, and a torsion beam is etched at both ends of the grating mirror. Comb-tooth structured movable comb-tooth electrodes are etched at both ends of the grating mirror perpendicular to the torsion beam, wherein the movable comb-tooth electrode is located directly above the gap between adjacent stationary comb-tooth electrodes, and the width of the gap between adjacent stationary comb-tooth electrodes is greater than the width of the movable comb-tooth electrode.

[0047] Among them, the grating mirror can rotate around the torsion beam, the gap depth between adjacent static comb tooth electrodes is greater than the length of the moving comb tooth electrode, and when the static comb tooth electrode is grounded and a voltage is applied to the moving comb tooth electrode, a capacitance effect is formed vertically between the comb teeth, thereby forming an electrostatic force to drive the moving comb tooth electrode to move vertically. Since this embodiment provides relatively insulated symmetrical static comb tooth electrodes, when in use, when the grating mirror needs to be rotated to a certain side, a voltage can be applied to the mirror comb tooth electrode on the same side, so that the rotation amplitude of the grating mirror is larger.

[0048] S5: Etch several sets of parallel grating lines on the upper surface of the grating mirror

[0049] The direction of the etched grating lines and the orientation of the torsion beam remain the same. The incident light is dispersed along the rotation direction of the torsion beam under the action of the grating diffraction. At the same time, the scanning grating micromirror also rotates around the torsion beam under the action of the electrostatic force. The grating lines are used to combine the grating and the rotating micromirror of the traditional miniature spectrometer, which simplifies the optical path without affecting the beam distribution, thereby reducing energy loss.

[0050] S6: Using the photoresist as a mask, deposit an aluminum metal layer on the upper surface of the grating mirror by magnetron sputtering, and remove the photoresist.

[0051] Among them, an aluminum metal layer is also deposited on the surface of the stationary comb tooth electrode and the moving comb tooth electrode by magnetron sputtering, and the thickness of the aluminum metal layer deposited on the surface of the grating mirror, the stationary comb tooth electrode and the moving comb tooth electrode is 300nm. The role of the aluminum metal layer on the grating mirror is to enhance the surface flatness and improve the surface reflectivity, and the role of the stationary comb tooth electrode and the moving comb tooth electrode is to be used as a conductive electrode.

[0052] Furthermore, in the above steps, the etching method used for etching the first silicon wafer and the second silicon wafer is deep silicon etching technology, and the MEMS micromirror is processed by semiconductor manufacturing technology, which can increase the torsion angle of the micromirror and achieve larger field angle light signal collection. The first silicon wafer and the second silicon wafer are an integral structure, and only the first silicon wafer and the second silicon wafer need to be etched, which has a simpler processing technology.

[0053] See also Figure 2-6The present invention also provides an electrostatic comb-driven MEMS micromirror, which is prepared by the above-mentioned preparation method, and includes a first silicon wafer layer 100, a second silicon wafer layer 200, an oxide layer 300 and a metal layer 400, wherein:

[0054] The first silicon wafer layer 100 includes a first frame 110, an insulating layer 130 and a static comb-tooth electrode 140 which are integrally connected. The first frame 110 is symmetrically arranged in two groups and connected through the insulating layer 130. The static comb-tooth electrode 140 is arranged on the inner side of the first frame 110. The middle part of the first silicon wafer layer 100, that is, between the static comb-tooth electrodes 140 on both sides, is an active groove 120. The size of the active groove 120 is larger than the size of the grating mirror 220, ensuring that the grating mirror 220 can rotate in the active groove 120. The insulating layer 130 is obtained by partially oxidizing the first silicon wafer layer 100 into silicon dioxide, and has a width of 600nm, which can effectively make the static comb-tooth electrodes 140 on both sides relatively insulated.

[0055] Furthermore, the thickness of the first silicon wafer layer 100 is 200 μm.

[0056] The second silicon wafer layer 200 includes a second frame 210, a grating mirror 220, a torsion beam 230 and a moving comb-tooth electrode 240 which are integrally connected. A grating mirror 220 is arranged in the middle of the second frame 210. Both sides of the grating mirror 220 are connected to the inner side of the second frame 210 through the torsion beam 230. Both sides of the grating mirror 220 are arranged with moving comb-tooth electrodes 240 which are perpendicular to the torsion beam 230. The width of the gap between adjacent static comb-tooth electrodes 140 is greater than the width of the moving comb-tooth electrode 240. A plurality of groups of mutually parallel grating lines 250 are arranged on the upper surface of the grating mirror 22.

[0057] Furthermore, the thickness of the second silicon wafer 200 is 75 μm, and the direction of the grating lines 250 and the orientation of the torsion beam 230 remain the same.

[0058] The oxide layer 300 is formed by thermal oxidation of the upper surface of the first silicon wafer 100 or the lower surface of the second silicon wafer 200 or both, the first silicon wafer layer 100 and the second silicon wafer layer 200 are bonded together with the oxide layer 300 through a bonding process, and the moving comb tooth electrode 240 is located directly above the gap between adjacent stationary comb tooth electrodes 140, the width of the gap between adjacent stationary comb tooth electrodes 140 is greater than the width of the moving comb tooth electrode 240, and the depth of the gap between adjacent stationary comb tooth electrodes 140 is greater than the length of the moving comb tooth electrode 240.

[0059] The grating mirror 220 can rotate around the torsion beam 230. When the stationary comb electrode 140 is grounded and a voltage is applied to the moving comb electrode 240, a capacitance effect is formed vertically between the comb teeth, thereby generating an electrostatic force to drive the moving comb electrode 240 to move vertically.

[0060] The metal layer 400 is an aluminum metal layer, which is deposited on the upper surface of the grating mirror 220 .

[0061] Furthermore, an aluminum metal layer is also deposited on the surfaces of the stationary comb-tooth electrode 140 and the moving comb-tooth electrode 240 , and the thickness of the aluminum metal layer deposited on the surfaces of the grating mirror 220 , the stationary comb-tooth electrode 140 and the moving comb-tooth electrode 240 is 300 nm.

[0062] The present invention further provides a spectrometer, wherein the spectrometer comprises an optical fiber, a collimating mirror, a grating micromirror, a focusing mirror and a photodetector. The light emitted by the optical fiber is reflected to the grating micromirror through the collimating mirror, reflected to the focusing mirror after being split by the grating micromirror, and reflected to the photodetector after being focused by the focusing mirror. The grating micromirror adopts the above-mentioned MEMS micromirror driven by the electrostatic comb.

[0063] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a MEMS micromirror driven by an electrostatic comb, characterized in that: The specific steps include: S1: etching a deep square active groove on a first silicon wafer as a rotation space for the mirror, and etching a comb tooth structure on the front and rear side walls of the active groove as a static comb tooth electrode; S2: Along the symmetry axis direction of the stationary comb-tooth electrodes on both sides of the active groove, the side walls of the active groove are symmetrically thermally oxidized to form an insulating layer of a certain width, so that the stationary comb-tooth electrodes on both sides are relatively insulated; S3: thermally oxidizing the upper surface of the first silicon wafer or the lower surface of the second silicon wafer to form a thermal oxidation layer, and bonding the oxide layers of the two silicon wafers together using a bonding process after fully cleaning the surface, with the second silicon wafer being located above the first silicon wafer; S4: etching a grating mirror in the middle on the second silicon wafer, etching a torsion beam at both ends of the grating mirror, etching a comb-tooth structured moving comb-tooth electrode at both ends of the grating mirror perpendicular to the torsion beam, wherein the moving comb-tooth electrode is located directly above the gap between adjacent stationary comb-tooth electrodes, and the width of the gap between adjacent stationary comb-tooth electrodes is greater than the width of the moving comb-tooth electrode; S5: etching a plurality of groups of mutually parallel grating lines on the upper surface of the grating mirror, wherein the directions of the etched grating lines and the orientation of the torsion beam are kept the same; S6: Using the photoresist as a mask, deposit an aluminum metal layer on the upper surface of the grating mirror by magnetron sputtering, and remove the photoresist.

2. The method for preparing a MEMS micromirror driven by an electrostatic comb according to claim 1, characterized in that: The etching method used when etching the first silicon wafer and the second silicon wafer is deep silicon etching technology.

3. The method for preparing a MEMS micromirror driven by an electrostatic comb according to claim 1, characterized in that: The thickness of the first silicon wafer is 200 μm. After the oxide layers of the two silicon wafers are bonded together in step S3, the second silicon wafer is thinned to 75 μm.

4. The method for preparing a MEMS micromirror driven by an electrostatic comb according to claim 1, characterized in that: In the step S6, an aluminum metal layer is also deposited on the surface of the stationary comb-tooth electrode and the moving comb-tooth electrode by magnetron sputtering, and the thickness of the aluminum metal layer deposited on the surface of the grating mirror, the stationary comb-tooth electrode and the moving comb-tooth electrode is 300 nm.

5. A MEMS micromirror driven by an electrostatic comb, characterized in that: The electrostatic comb driven MEMS micromirror is prepared by the preparation method according to any one of claims 1 to 4, comprising: A first silicon wafer layer, the first silicon wafer layer comprising a first frame, a static comb-tooth electrode and an insulating layer connected in one piece, the first frame having two groups symmetrically arranged and connected through the insulating layer, and a static comb-tooth electrode being arranged on the inner side of the first frame; a second silicon wafer layer, wherein the second silicon wafer layer comprises an integrally connected second frame, a moving comb-tooth electrode, a grating mirror and a torsion beam, a grating mirror is arranged in the middle of the second frame, two sides of the grating mirror are connected to the inner side of the second frame through a torsion beam, two sides of the grating mirror are arranged with moving comb-tooth electrodes perpendicular to the torsion beam, a gap width between adjacent static comb-tooth electrodes is greater than a width of the moving comb-tooth electrode, and a plurality of groups of mutually parallel grating lines are arranged on the grating mirror; An oxide layer, wherein the oxide layer is formed by thermally oxidizing the upper surface of the first silicon wafer or the lower surface of the second silicon wafer, the first silicon wafer layer and the second silicon wafer layer are bonded together with the oxide layer through a bonding process, and the dynamic comb-tooth electrode is located directly above the gap between adjacent stationary comb-tooth electrodes; The metal layer is an aluminum metal layer, which is deposited on the upper surface of the grating mirror.

6. The electrostatic comb driven MEMS micromirror according to claim 5, characterized in that: The thickness of the first silicon wafer layer is 200 μm, and the thickness of the second silicon wafer layer is 75 μm.

7. The electrostatic comb driven MEMS micromirror according to claim 5, characterized in that: The grating line direction and torsion beam orientation remain the same.

8. The electrostatic comb driven MEMS micromirror according to claim 5, characterized in that: The surfaces of the stationary comb-tooth electrodes and the moving comb-tooth electrodes are also deposited with an aluminum metal layer, and the thickness of the aluminum metal layer deposited on the surfaces of the grating mirror, the stationary comb-tooth electrodes and the moving comb-tooth electrodes is 300 nm.

9. A spectrometer, characterized in that: The spectrometer comprises an optical fiber, a collimating mirror, a grating micromirror, a focusing mirror and a photodetector. The light emitted by the optical fiber is reflected to the grating micromirror through the collimating mirror, reflected to the focusing mirror after being split by the grating micromirror, and reflected to the photodetector after being focused by the focusing mirror. The grating micromirror adopts a MEMS micromirror driven by an electrostatic comb as described in claim 5.

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