CN112965239A - Stacked induction capacitor angle feedback galvanometer and manufacturing method thereof - Google Patents
Stacked induction capacitor angle feedback galvanometer and manufacturing method thereof Download PDFInfo
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- G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
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Abstract
The invention discloses a stacked induction capacitance angle feedback galvanometer, wherein a capacitance angle feedback sensor is integrated in a micro galvanometer, so that the angle feedback of the micro galvanometer is realized, the control precision can be obviously improved, the capacitance angle feedback sensor is vertically arranged with a driving comb tooth group of the micro galvanometer, the occupation of extra area is not needed, the area of the micro galvanometer is not needed to be increased, the micro galvanometer and the angle feedback sensor are integrated, the integrated flow sheet is manufactured, the process is stable, the consistency is high, the device volume is small, and the cost is low.
Description
Technical Field
The invention belongs to the field of three-dimensional imaging, and particularly relates to a stacked type induction capacitor angle feedback galvanometer.
Background
Micro-galvanometer mirrors based on MEMS technology are used in the field of three-dimensional imaging for the projection of light. The most widely used micromirrors include electrostatic, electromagnetic, piezoelectric, and electrothermal. Most of the current applied micromirrors adopt an open-loop control method without angle feedback, and a serious disadvantage of the micromirrors is that effective angle feedback is lacked, which causes inaccurate micromirror control. The prior partial micromirror adopts a certain angle feedback, but still has more problems.
In the currently used micromirror, an angle feedback method is to arrange an angle detection device outside the micromirror to measure the rotation angle of the micromirror, so that the angle feedback of the micromirror can be realized to a certain extent. For example, patent No. ZL200410085274.1 discloses a micromirror solution for angle measurement using optical components. However, in the detection device of the method, components such as a laser light source, a light path, a position sensor and the like need to be added into the micro-mirror module, so that the volume, the power consumption and the system complexity of the micro-mirror module are greatly increased. More importantly, due to factors such as installation errors, the detection method is difficult to realize accurate angle feedback, and the consistency of each micro mirror module is poor.
There are also angle sensors integrated in the micromirrors for angle detection, for example, a micromirror with electrothermal drive and plate capacitance detection is disclosed in the patent application publication No. CN 109814251A. According to the scheme, a capacitor plate is arranged on a substrate, and the relation between the capacitance value on the capacitor plate and the actual torsion angle of the micro lens is used as a feedback value to perform signal feedback on a controller. The proposal reduces the components of the light path and the position sensor in the micro mirror module, and reduces the complexity of the micro mirror module to a certain extent. However, in the scheme, the flat electrode element is used as an angle feedback capacitor, the distance between the output of the feedback capacitor and the corner of the micromirror is large, the flat electrode capacitor is small, the output signal is weak, the requirement on a processing circuit is high, and the signal-to-noise ratio is low. The proposal adopts an electrothermal driving mode, the working frequency of the micro mirror is low, and the micro mirror is difficult to be suitable for high-frequency scanning.
A piezoelectric driven Micromirror Integrated with a piezoelectric Angle sensor is disclosed in the paper "piezoelectric Actuated mirror Integrated with Angle Sensors" (Key Engineering Materials 2011, 483:437 442). However, the piezoelectric driving and piezoelectric sensors are made of PZT materials, so that the process compatibility is poor, the processing difficulty is high, and the chip production line is easily polluted. Meanwhile, the piezoelectric sensor has extremely high requirements on the input impedance of a processing circuit, the circuit is complex, and the cost is high. Piezoelectric transducers have poor performance at low frequencies and are difficult to adapt for low frequency scanning of the micromirror.
Reference 4-CN 107976871A-a dynamic deformation controllable comb tooth structure of micromirror mirror surface and its processing method, which discloses a micromirror comb tooth processing method and corresponding electrostatically driven micromirror with comb tooth structure. Meanwhile, the processing method of the micro-mirror comb tooth structure proposed by the document needs to perform photoetching after etching the deep groove structure, i.e. high-quality glue homogenizing needs to be performed on the surface of the deep groove structure, and complete equal-thickness covering of a glue layer is ensured, which is extremely difficult to realize in process.
In summary, the micromirror without feedback has poor control precision, and the angle measurement scheme of the existing micromirror with angle feedback has the problems of complex system, overlarge micro-vibration mirror surface area, low signal-to-noise ratio, poor process compatibility and the like.
Disclosure of Invention
Aiming at the problems of control and feedback of the existing micro-vibrating mirror, the invention provides a stacked induction capacitor angle feedback vibrating mirror, wherein a capacitive angle feedback sensor is integrated in the micro-vibrating mirror, so that the angle feedback of the micro-vibrating mirror is realized, the control precision can be obviously improved, the capacitive angle feedback sensor is vertically arranged with a driving comb tooth group of the micro-vibrating mirror, the occupied additional area is not needed, the area of the micro-vibrating mirror is not needed to be increased, the micro-vibrating mirror and the angle feedback sensor are integrally designed, and the integrated flow sheet is manufactured, so that the process is stable, the consistency is high, the device size is small, and the cost is low.
In order to realize the purpose, the following scheme is adopted:
the stacked sensing capacitor angle feedback galvanometer comprises a substrate layer 100, a first insulating layer 200, a device layer 300, a second insulating layer 400 and a sensing layer 500 which are sequentially stacked from bottom to top. The device layer 300 includes at least one set of rotating comb teeth 305 and at least one set of stationary comb teeth 306. The sensing layer comprises at least one set of sensing positive comb teeth 501 and at least one set of sensing negative comb teeth 503.
The substrate layer 100 is a frame structure with a cavity 101, the thickness is 100um-1000um, and the material is monocrystalline silicon, polycrystalline silicon, amorphous silicon, silicon oxide, silicon nitride and polymer.
The thickness of the first insulating layer 200 is 100nm-2um, the material is silicon oxide and silicon nitride, the resistivity is more than or equal to 103Ω·㎝。
The device layer 300 includes a mirror body 301, a mirror surface 302, a rotation shaft 303, an anchor body 304, a rotation comb 305, a fixed comb 306, a fixed frame 307, a ground pad 308, and a driving pad 309. The mirror surface 301 is a thin metal layer and covers the upper surface of the mirror body 301. The ground pad 308 is a small piece of thin metal that is attached to the upper surface of the anchor. The driving pad 309 is a small piece of thin metal attached to the upper surface of the fixing frame 307. The left side and the right side of the reflector body 301 are respectively connected with an anchor body 304 through a rotating shaft 303, the lower surface of the anchor body 304 is connected with the upper surface of the first insulating layer 200, and the lower surface of the first insulating layer 200 is connected with the upper surface of the substrate layer 100. Two sides of the rotating shaft 303 perpendicular to the axis direction are respectively provided with rotating comb teeth 305, and the rotating comb teeth and the fixed comb teeth 306 arranged on the inner side of the fixed frame 307 are staggered to form a driving capacitor.
The second insulating layer 400 has a thickness of 100nm-2um, is made of silicon oxide and silicon nitride, and has a resistivity of 10 or more3Ω·㎝。
The sensing layer 500 includes a positive comb 501, a positive fixed body 502, a negative comb 503, a negative fixed body 504, a sensing positive pad 505, and a sensing negative pad 506. The inductive positive pad 505 is a small piece of thin metal layer and is attached to the upper surface of the positive anchor 502. The inductive negative pad 506 is a small piece of thin metal that is attached to the upper surface of the negative anchor 504. One end of the positive electrode comb 501 is connected with the inner side of the positive electrode fixing body 502, and one end of the negative electrode comb is connected with the negative electrode fixing body 504. The lower surface of the sensing layer 500 is connected to the upper surface of the second insulating layer 400. The sensing layer 500 includes comb teeth that coincide with the orthographic projection of the fixed comb teeth 306 included in the device layer 300.
The working method of the stacked induction capacitor angle feedback galvanometer comprises the following steps:
The rotating comb 305 and the sensing positive comb 501 form a positive sensing capacitor (i.e., C1 in fig. 8), and the rotating comb 305 and the sensing negative comb 503 form a negative sensing capacitor (i.e., C2 in fig. 8). In the circumferential vibration process of the rotating comb teeth, the positive induction capacitance and the negative induction capacitance change along with the change of the rotation angles of the rotating comb teeth.
C1＝C10+f1(θ) (1)
C2＝C20+f2(θ) (2)
Wherein C10 and C20 are capacitance values of C1 and C2 at equilibrium positions, respectively, and according to structural symmetry, C10 ═ C20; theta is the angle of rotation of the rotating comb around the rotating shaft, f1 and f2 are functions of the rotation angle theta, and according to structural symmetry, f1 (theta) is f2 (-theta), f1 and f2 are each monotonic functions of the rotation angle theta. At the same time, since the capacitance C4 exists between the sensing positive comb 501 and the fixed comb 306, the capacitance C5 exists between the sensing negative comb 503 and the fixed comb 306, and C4 is equal to C5 due to structural symmetry, the driving signal U is a driving signal UdCoupling in the capacitive sense signal S through C4, C5c1And Sc2The same interference signal, namely:
Sc1＝C1+g(Ud) (3)
Sc2＝C2+g(Ud) (4)
the induction signal is processed by a differential circuit, then
Sc＝Sc1-Sc2＝C1-C2＝f1(θ)-f2(θ)＝f(θ) (5)
Namely, the interference caused by the coupling capacitor can be effectively eliminated by adopting the structure, and the output signal of the sensing capacitor is only a function of the rotation angle theta. And obtaining the induction capacitance value through the peripheral capacitance detection circuit, and obtaining the value of the rotation angle theta through reverse deduction.
The manufacturing method of the stacked type induction capacitor angle feedback galvanometer is characterized by comprising the following steps:
1) preparing a silicon on insulator wafer (SOI)
2) Thermal oxidation: performing thermal oxidation on the prepared SOI to form a layer of silicon oxide on the upper surface of the top silicon
3) Bonding: bonding a single crystal silicon on the oxide layer on the upper surface of the SOI top silicon processed in the step 2) to form a five-layer structure wafer of top monocrystalline silicon-second silicon dioxide layer-middle monocrystalline silicon layer-first silicon oxide layer-bottom monocrystalline silicon, namely SOIOI.
4) Preparing a metal layer on the induction layer: making a patterned metal layer on the upper surface of the top layer single crystal silicon of the SOIOI completed in the step 3), wherein the method comprises two steps: firstly, depositing a layer of metal, and forming a required graphical metal layer by photoetching and etching methods; and secondly, photoetching the surface of the top layer monocrystalline silicon, depositing metal, and finally forming a required patterned metal layer in a stripping mode.
5) And (3) conducting photoetching on a guide mode selection area: and 4) conducting guided mode selection area photoetching on the wafer finished in the step 4), and forming an unexposed photoresist area, a partially exposed photoresist area and a fully exposed photoresist area on the surface of the top layer of monocrystalline silicon.
6) Etching top monocrystalline silicon: etching the SOIOI completed in the step 5) until the area of the top monocrystalline silicon uncovered by the photoresist is completely etched to expose the second oxide layer.
7) Etching the second oxide layer: and etching the second oxide layer until the second oxide layer below the monocrystalline silicon region uncovered by the photoresist is completely removed to expose the monocrystalline silicon in the middle layer. At this time, the photoresist in the original partially exposed area is completely removed, and only the original unexposed photoresist remains.
8) Etching the monocrystalline silicon of the middle layer: and (4) continuing to etch the monocrystalline silicon, wherein the photoresist of the original complete exposure area and the photoresist of the original partial exposure area do not exist, and the monocrystalline silicon below the two areas are etched at the same time until the monocrystalline silicon in the middle layer is etched to be through, so that the first oxide layer is exposed.
9) Spraying glue: and spraying glue by adopting a hard mask mode to cover the area of the first oxidation layer, which needs to be reserved.
10) Etching the first oxide layer: and etching the second oxide layer until the exposed second oxide layer is completely removed.
11) Manufacturing device layer metal: a patterned metal layer is formed on the surface of the intermediate layer of single crystal silicon by a hard mask method to form a mirror surface 301, a ground pad 308 and a driving pad 309.
12) Back cavity etching: and etching the SOIOI bottom silicon to form a cavity on the back of the micro-mirror device.
13) Releasing: and removing the first oxide layer in the cavity on the back surface by adopting a reactive ion etching mode.
And (3) conducting photoetching on a guide mode selection area:
superposing a guide mold above the mask plate, and then carrying out exposure, development and subsequent etching processes;
the guide mold is a specially designed optical super-surface template, and the whole area range of the template comprises a full-transmission area and a fractional-transmission area. The transmittance of the total transmittance region to the wavelength used by the photoetching machine is more than or equal to 95 percent, and the transmittance of the fractional transmittance region to the wavelength used by the photoetching machine is 1 to 99 percent of the transmittance of the total transmittance region.
In the photoetching, a guide mold is arranged above a mask plate and is parallel to the mask plate, the partial transmission area projection of the guide mold is positioned in the projection range of the light transmission area of the mask plate, and the area of the guide mold is smaller than that of the mask plate; the outside of the transmission region of the guided modulus is the full projection region.
The mask plate is positioned above the photoresist, and the guide mold is arranged above the mask plate; during exposure, the photoresist which is positioned in the light transmission area of the mask plate and is right below the range outside the guide mode fraction transmission area is completely exposed to generate complete reaction, and the photoresist which is positioned right below the guide mode fraction transmission area is partially exposed to generate incomplete reaction. And the photoresist which is completely reacted is completely removed in the development, the thickness of the photoresist which is not completely reacted is unchanged, but the density is reduced, and the etching rate selectivity of the masked substrate is reduced.
The etching process and effect after the photoetching of the guide mode selection area are as follows:
in the etching process, the photoresist is used as a masking layer, and the etching rate selectivity ratio of the partially exposed photoresist to the masked material is 1-99% of the selectivity ratio of the photoresist in the unexposed area to the masked material. In the initial etching stage, the substrate below the photoresist complete exposure area is exposed to etching gas, and only the part of the substrate is etched; the photoresist in the partially exposed region remains blocked from the etching gas and the substrate beneath this region is not etched. The etching rate of the partially exposed photoresist is higher than that of the unexposed photoresist, so that the partially exposed photoresist is completely etched away as the etching is carried out for a certain time, the substrate below the partially exposed photoresist is exposed to the etching gas and begins to be etched, and the unexposed photoresist still exists to protect the substrate below the partially exposed photoresist from being etched. At this time, as the etching continues, the substrate under the original fully exposed area and the original partially exposed area is etched until the etching is finished. Because the substrate below the original complete exposure area is etched to a certain depth before the substrate below the original partial exposure area starts etching, the etching depths of the two areas are different after etching is finished, and a stepped groove is formed. According to different design requirements of the device, the transmittance of the guide module fraction transmission area is designed, and the etching of the induction layer and the device layer can be completed.
The working principle is as follows:
the grounding pad is grounded via a lead, and a driving signal U is applied to the driving pad via the leaddWherein U isdThe periodic voltage signal includes square wave, sawtooth wave, sine wave, triangle wave, the waveform listed here is only used as illustration, and is not limited to the listed waveforms, and other periodic signals are also included. The device layer bonding pad is made of metal, the part outside the bonding pad is made of low-resistivity materials, and the bonding pad is in ohmic contact with the surface attached to the bonding pad, so that the reflector body 301, the rotating shaft 303, the anchor body, the rotating comb teeth and the grounding bonding pad are in an equi-potential body in the lead connection mode, namely, the rotating comb teeth and the grounding bonding pad are all grounded; similarly, the fixed comb teeth, the frame and the driving welding disc are equi-potential bodies, and the electric potentials of the fixed comb teeth, the frame and the driving welding disc are U-shapedd. The rotating comb teeth and the fixed comb teeth form a driving capacitor, and a signal U is periodically drivendUnder the action, the comb teeth are rotated to generate circumferential vibration around the rotating shaft, so that circumferential torsional vibration of the rotating shaft is driven, and the reflector body is further driven to vibrate around the rotating shaft in the circumferential direction.
The rotating comb teeth and the sensing positive electrode comb teeth form a positive sensing capacitor (namely C1 in figure 8), and the rotating comb teeth and the sensing negative electrode comb teeth form a negative sensing capacitor (namely C2 in figure 8). In the circumferential vibration process of the rotating comb teeth, the positive induction capacitance and the negative induction capacitance change along with the change of the rotation angles of the rotating comb teeth.
C1＝C10+f1(θ) (I)
C2＝C20+f2(θ) (2)
Wherein C10 and C20 are capacitance values of C1 and C2 at equilibrium positions, respectively, and according to structural symmetry, C10 ═ C20; theta is the angle of the rotating comb teeth rotating around the rotating shaft, f1 and f2 are functions of the rotating angle theta, and according to structural symmetry, f1 (theta) is f2 (-theta), and f1 and f2 are both monotone functions of the rotating angle theta. At the same time, since the capacitance C4 exists between the sensing positive comb teeth and the fixed comb teeth, the capacitance C5 exists between the sensing negative comb teeth and the fixed comb teeth, and the C4 is equal to C5 due to structural symmetry, the driving signal UdCapacitive sense signals coupled in through C4, C5Sc1And Sc2The same interference signal, namely:
Sc1＝C1+g(Ud) (3)
St2＝C2+g(Ud) (4)
the induction signal is processed by a differential circuit, then
Sc＝Sc1-Sc2＝C1-C2＝f1(θ)-f2(θ)＝f(θ) (5)
That is to say, the interference caused by the coupling capacitor can be effectively eliminated by adopting the structure, and the output signal of the sensing capacitor is only a function of the rotation angle theta. And obtaining the induction capacitance value through the peripheral capacitance detection circuit, and obtaining the value of the rotation angle theta through reverse deduction.
Advantageous effects
1. The micro-vibration mirror integrates an angle feedback sensor, so that the control precision is high;
2. the angle feedback sensor is vertically arranged with the micro-vibration mirror driving comb tooth group, and the angle feedback sensor is integrated in the micro-mirror chip on the premise of not increasing the area of the micro-vibration mirror;
3. the angle feedback sensor and the micro-vibration mirror are integrally designed and integrated with a flow sheet, and the device has the advantages of stable process, high consistency, small device volume and low cost.
Drawings
FIG. 1 shows an overall structure of a stacked type sensing capacitor angle feedback galvanometer;
FIG. 2 a substrate structure;
FIG. 3 a first insulating layer;
FIG. 4 device layer structure;
FIG. 5 a second insulating layer;
FIG. 6 a sense layer structure;
FIG. 7 shows a schematic drawing of the galvanometer circuit;
FIG. 8 is a schematic diagram of the operation of a stacked capacitive sensing angle feedback galvanometer, wherein (a) the balanced position, (b) the positive rotation, and (c) the negative rotation;
FIG. 9 is an equivalent circuit diagram;
FIG. 10 depicts one embodiment of a gated area lithography;
figure 11 shows a process flow of the stacked sensing capacitor angle feedback galvanometer.
Detailed Description
Referring to fig. 1, the stacked induction capacitance angle feedback galvanometer comprises a substrate layer 100, a first insulating layer 200, a device layer 300, a second insulating layer 400 and an induction layer 500 which are stacked in sequence from bottom to top.
As shown in fig. 2, the substrate layer 100 is a frame structure having a cavity 101.
As shown in fig. 3, the first insulating layer has a ring-shaped thin layer structure.
As shown in fig. 1 and 4, the device layer 300 includes a mirror body 301, a mirror surface 302, a rotation shaft 303, an anchor body 304, a rotation comb 305, a fixed comb 306, a fixed frame 307, a ground pad 308, and a driving pad 309. The mirror surface 301 is a thin metal layer and covers the upper surface of the mirror body 301. The ground pad 308 is a small piece of thin metal that is attached to the upper surface of the anchor. The driving pad 309 is a small piece of thin metal attached to the upper surface of the fixing frame 307. The reflector body 301, the rotating shaft 303, the anchor body 304 and the rotating comb teeth 305 are connected with each other and electrically conducted; the fixed comb teeth 306 and the fixed frame 307 are connected to each other and electrically conducted. The reflector body 301, the rotating shaft 303, the anchor body 304 and the rotating comb teeth 305 are electrically isolated from the fixed comb teeth 307 and the fixed frame 307; the reflector body 301, the rotating shaft 303 and the rotating comb teeth 305 are all suspended, the left side and the right side of the reflector body 301 are respectively connected with the anchor body 304 through the rotating shaft 303, the lower surface of the anchor body 304 is connected with the upper surface of the first insulating layer 200, and the lower surface of the first insulating layer 200 is connected with the upper surface of the substrate layer 100. Two sides of the rotating shaft 303 perpendicular to the axis direction are respectively provided with rotating comb teeth 305, and the rotating comb teeth and the fixed comb teeth 306 arranged on the inner side of the fixed frame 307 are staggered to form a driving capacitor.
As shown in fig. 5, the second insulating layer has a thin layer structure having a porous shape inside.
As shown in fig. 1 and 6, the sensing layer includes positive comb teeth 501, a positive fixed body 502, negative comb teeth 503, a negative fixed body 504, a sensing positive pad 505, and a sensing negative pad 506. The inductive positive pad 505 is a small piece of thin metal layer and is attached to the upper surface of the positive anchor 502. The inductive negative pad 506 is a small piece of thin metal that is attached to the upper surface of the negative anchor 504. One end of the positive electrode comb teeth 501 is connected with the inner side edge of the positive electrode fixing body 502, and one end of the negative electrode comb teeth 503 is connected with the negative electrode fixing body 504; the positive comb teeth 501 and the positive fixing body 502 are structurally separated from the negative comb teeth 503 and the negative fixing body 504, and are electrically isolated. The lower surface of the sensing layer 500 is connected to the upper surface of the second insulating layer 400. The sensing layer 500 includes comb teeth that coincide with the orthographic projection of the fixed comb teeth 306 included in the device layer 300.
The working principle is as follows:
referring to fig. 7, 8 and 9, the ground pad 308 is grounded via a lead, and a driving signal U is applied to the driving pad 309 via the leaddWherein U isdThe periodic voltage signal includes square wave, sawtooth wave, sine wave, triangle wave, the waveform listed here is only used as illustration, and is not limited to the listed waveforms, and other periodic signals are also included. The bonding pad of the device layer 300 is made of metal, the portion outside the bonding pad is made of low-resistivity material, and the bonding pad forms ohmic contact with the surface to which the bonding pad is attached, so that the reflector 301, the rotating shaft 303, the anchor 304, the rotating comb 305, and the grounding bonding pad 308 are equi-potential bodies, namely are all grounded; similarly, the fixed comb 306, the frame 307 and the driving pad 309 are equivalent bodies, and the potentials thereof are all Ud. The rotating comb 305 and the fixed comb 306 form a driving capacitor for periodically driving the signal UdUnder the action, the comb teeth are rotated to generate circumferential vibration around the rotating shaft 303, so that circumferential torsional vibration of the rotating shaft 303 is driven, and the reflector body 301 is further driven to vibrate around the rotating shaft 303 in the circumferential direction.
The rotating comb 305 and the sensing positive comb 501 form a positive sensing capacitor (i.e., C1 in fig. 8), and the rotating comb 305 and the sensing negative comb 503 form a negative sensing capacitor (i.e., C2 in fig. 8). In the circumferential vibration process of the rotating comb teeth, the positive induction capacitance and the negative induction capacitance change along with the change of the rotation angles of the rotating comb teeth.
C1＝C10+f1(θ) (I)
C2＝C20+f2(θ) (2)
Wherein C10 and C20 are capacitance values of C1 and C2 at equilibrium positions, respectively, and according to structural symmetry, C10 ═ C20; theta is the angle of rotation of the rotating comb about the rotation axis, f1 and f2 are functions of the rotation angle theta, and f1 (theta) is f2 according to structural symmetry(-) f1 and f2 are each monotonic functions of the rotation angle θ. At the same time, since the capacitance C4 exists between the sensing positive comb 501 and the fixed comb 306, the capacitance C5 exists between the sensing negative comb 503 and the fixed comb 306, and C4 is equal to C5 due to structural symmetry, the driving signal U is a driving signal UdCoupling in the capacitive sense signal S through C4, C5 c1 and Sc2The same interference signal, namely:
Sc1＝C1+g(Ud) (3)
Sc2＝C2+g(Ud) (4)
the induction signal is processed by a differential circuit, then
Sc＝Sc1-Sc2＝C1-C2＝f1(θ)-f2(θ)＝f(θ) (5)
That is to say, the interference caused by the coupling capacitor can be effectively eliminated by adopting the structure, and the output signal of the sensing capacitor is only a function of the rotation angle theta. And obtaining the induction capacitance value through the peripheral capacitance detection circuit, and obtaining the value of the rotation angle theta through reverse deduction.
Referring to fig. 10, an implementation method and effect of the guided mode selection area lithography are as follows:
a layer of selective area photoresist 820 with the thickness of 2um is coated on the upper surface of a monocrystalline silicon substrate 810, then a mask plate 830 is covered on the photoresist 820, a guide mold 840 is superposed above the mask plate 830, and then exposure, development and subsequent etching processes are carried out.
Here the lithography uses an i-line (wavelength 365nm) light source and a corresponding i-line photoresist.
The reticle includes a light transmissive region 831 and a light opaque region 832; the transmission rate of the light-transmitting region 831 to the used i-ray light wave was 100%, and the transmission rate of the light-transmitting region to the used i-ray light wave was 0%.
The guiding mold 840 is a specially designed optical super-surface template, and the whole area of the guiding mold comprises a full-transmission area 841 and a fractional-transmission area 842, wherein the full-transmission area 841 has a transmission rate of 97% for i-line light waves, and the fractional-transmission area 842 has a transmission rate of 48.5% for i-line light waves used by a photoetching machine.
In the photoetching process, the guide module 840 is arranged above the mask plate 830 and is parallel to the mask plate 830, the projection of the fractional transmission area 842 of the guide module 840 is positioned in the projection range of the transmission area 831 of the mask plate 830, and the area of the former is smaller than that of the latter; the transmissive regions 841 are all the other than the fractional transmissive regions 842 of the guide mold 840, as shown in FIG. 10 (a).
The mask plate is positioned above the photoresist, and the guide mold is arranged above the mask plate; the photoresist which is positioned in the light transmission area of the mask plate and is right below the range outside the guide modulus transmission area completely reacts during exposure to form a complete exposure area 821; the photoresist directly beneath the guided mode fraction transmission region is partially exposed to light and undergoes an incomplete reaction to form a partially exposed region 822. Completely removing the photoresist which is completely reacted during development; the incompletely reacted photoresist has a constant thickness, but the density is reduced, the etching resistance is reduced, and the selectivity to the substrate is reduced to 20% of the unexposed photoresist, as shown in fig. 10 (b).
The photoresist is used as a masking layer in the etching process, the selection ratio of the partially removed photoresist to the masked material is 20% of the selection ratio of the photoresist to the masked material in an unexposed area, namely, the etching rate of the monocrystalline silicon substrate is 10um/min, the etching rate of the unexposed photoresist is 0.2um/min, and the etching rate of the photoresist in a partial exposure area 822 is 2 um/min. In the etching process, the monocrystalline silicon substrate which is not covered by the photoresist is etched all the time; in the etching stage of 0-120 seconds, the monocrystalline silicon substrate covered by the partial exposure area 822 can not be etched due to the protection of the photoresist; and when the etching is finished for 120 seconds, the partially exposed photoresist is completely removed by the etching gas, and the monocrystalline silicon substrate originally covered by the partially exposed region 822 is exposed to the etching gas and also begins to be etched until the etching is stopped for 240 seconds. The substrate etch depth under the partial exposure area 822 is 20um and the substrate etch depth under the full exposure area 821 is 40um, as shown in FIG. 10 (c). Namely, a step-shaped groove is formed on the monocrystalline silicon substrate through one-time photoetching and etching.
As shown in fig. 11, a process flow of the stacked type induced capacitance angle feedback galvanometer includes the following steps:
1) preparing a silicon on insulator wafer (SOI)
2) Thermal oxidation: performing thermal oxidation on the prepared SOI to form a layer of silicon oxide on the upper surface of the top silicon
3) Bonding: bonding a single crystal silicon on the oxide layer on the upper surface of the SOI top silicon processed in the step 2) to form a five-layer structure wafer of top monocrystalline silicon-second silicon dioxide layer-middle monocrystalline silicon layer-first silicon oxide layer-bottom monocrystalline silicon, namely SOIOI.
4) Preparing a metal layer on the induction layer: making a patterned metal layer on the upper surface of the top layer single crystal silicon of the SOIOI completed in the step 3), wherein the method comprises two steps: firstly, depositing a layer of metal, and forming a required graphical metal layer by photoetching and etching methods; and secondly, photoetching the surface of the top layer monocrystalline silicon, depositing metal, and finally forming a required patterned metal layer in a stripping mode.
5) And (3) conducting photoetching on a guide mode selection area: and 4) conducting guided mode selection area photoetching on the wafer finished in the step 4), and forming an unexposed photoresist area, a partially exposed photoresist area and a fully exposed photoresist area on the surface of the top layer of monocrystalline silicon.
6) Etching top monocrystalline silicon: etching the SOIOI completed in the step 5) until the area of the top monocrystalline silicon uncovered by the photoresist is completely etched to expose the second oxide layer.
7) Etching the second oxide layer: and etching the second oxide layer until the second oxide layer below the monocrystalline silicon region uncovered by the photoresist is completely removed to expose the monocrystalline silicon in the middle layer. At this time, the photoresist in the original partially exposed area is completely removed, and only the original unexposed photoresist remains.
8) Etching the monocrystalline silicon of the middle layer: and (4) continuing to etch the monocrystalline silicon, wherein the photoresist of the original complete exposure area and the photoresist of the original partial exposure area do not exist, and the monocrystalline silicon below the two areas are etched at the same time until the monocrystalline silicon in the middle layer is etched to be through, so that the first oxide layer is exposed.
9) Spraying glue: and spraying glue by adopting a hard mask mode to cover the area of the first oxidation layer, which needs to be reserved.
10) Etching the first oxide layer: and etching the second oxide layer until the exposed second oxide layer is completely removed.
11) Manufacturing device layer metal: a patterned metal layer is formed on the surface of the intermediate layer of single crystal silicon by a hard mask method to form a mirror surface 301, a ground pad 308 and a driving pad 309.
12) Back cavity etching: and etching the SOIOI bottom silicon to form a cavity on the back of the micro-mirror device.
Releasing: and removing the first oxide layer in the cavity on the back surface by adopting a reactive ion etching mode.
Claims (9)
1. The utility model provides a heap response electric capacity angle feedback galvanometer which characterized in that: the capacitive angle feedback sensor is integrated in the micro-galvanometer, so that the angle feedback of the micro-galvanometer is realized, and the capacitive angle feedback sensor is vertically arranged with the driving comb tooth group of the micro-galvanometer.
2. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the device comprises a substrate layer, a first insulating layer, a device layer, a second insulating layer and an induction layer which are sequentially stacked from bottom to top; the device layer comprises at least one group of rotating comb teeth and at least one group of fixed comb teeth; the induction layer comprises at least one group of induction positive comb teeth and at least one group of induction negative comb teeth.
3. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the substrate layer is of a frame structure with a cavity, the thickness of the substrate layer is um-0um, and the substrate layer is made of monocrystalline silicon, polycrystalline silicon, amorphous silicon, silicon oxide, silicon nitride and polymer.
4. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the device layer comprises a reflector body, a reflector surface, a rotating shaft, an anchor body, rotating comb teeth, fixed comb teeth, a fixed frame, a grounding bonding pad and a driving bonding pad; the reflecting mirror surface is a thin metal layer and covers the upper surface of the reflecting mirror body; the grounding pad is a small piece of thin-layer metal and is attached to the upper surface of the anchor body; the driving bonding pad is a small piece of thin-layer metal and is attached to the upper surface of the fixing frame; the left side edge and the right side edge of the reflector body are respectively connected with the anchor body through a rotating shaft, the lower surface of the anchor body is connected with the upper surface of the first insulating layer, and the lower surface of the first insulating layer is connected with the upper surface of the substrate layer; the two sides of the rotating shaft perpendicular to the axis direction are respectively provided with rotating comb teeth, and the rotating comb teeth and the fixed comb teeth arranged on the inner side edge of the fixed frame are staggered to form a driving capacitor.
5. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the induction layer comprises positive comb teeth, a positive fixing body, negative comb teeth, a negative fixing body, an induction positive bonding pad and an induction negative bonding pad; the induction anode bonding pad is a small piece of thin-layer metal and is attached to the upper surface of the anode fixing body; the induction negative electrode bonding pad is a small piece of thin-layer metal and is attached to the upper surface of the negative electrode fixing body; one end of the positive electrode comb tooth is connected with the inner side of the positive electrode fixing body, and one end of the negative electrode comb tooth is connected with the negative electrode fixing body; the lower surface of the induction layer is connected with the upper surface of the second insulating layer; the comb teeth included in the sensing layer coincide with the orthographic projection of the fixed comb teeth included in the device layer.
6. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the first insulating layer is nm-2um thick, is made of silicon oxide and silicon nitride, and has a resistivity not less than 103Omega cm; the thickness of the second insulating layer is nm-2um, the second insulating layer is made of silicon oxide and silicon nitride, and the resistivity is more than or equal to 103Ω·cm。
7. The stacked type induction capacitance angle feedback galvanometer of claim 1, wherein: the grounding pad is grounded via a lead, and a driving signal U is applied to the driving pad via the leaddWherein U isdThe voltage signal is a periodic voltage signal and comprises square waves, sawtooth waves, sine waves and triangular waves; the device layer bonding pad is made of metal, the part outside the bonding pad is made of low-resistivity materials, and the bonding pad is in ohmic contact with the surface attached to the bonding pad, so that the reflector body, the rotating shaft, the anchor body, the rotating comb teeth and the grounding bonding pad are in an equal-potential body in the lead connection mode, namely, the reflector body, the rotating shaft, the anchor body, the rotating comb teeth and the grounding bonding pad are all grounded; in the same way, the comb teeth, the frame and the driving welding disc are fixedIs an equipotential body, and has a uniform potential Ud(ii) a The rotating comb teeth and the fixed comb teeth form a driving capacitor, and a signal U is periodically drivendUnder the action of the vibration, the comb teeth are rotated to generate circumferential vibration around the rotating shaft, so that circumferential torsional vibration of the rotating shaft is driven, and the reflector body is further driven to vibrate around the rotating shaft in the circumferential direction;
the rotating comb teeth and the inductive positive electrode comb teeth form positive inductive capacitance, and the rotating comb teeth and the inductive negative electrode comb teeth form negative inductive capacitance; in the circumferential vibration process of the rotating comb teeth, the positive induction capacitance and the negative induction capacitance change along with the change of the rotation angles of the rotating comb teeth;
C1＝C10+f1(θ) (1)
C2＝C20+f2(θ) (2)
wherein C10 and C20 are capacitance values of C1 and C2 at equilibrium positions, respectively, and according to structural symmetry, C10 ═ C20; theta is the angle of the rotating comb teeth rotating around the rotating shaft, f1 and f2 are functions of the rotating angle theta, according to structural symmetry, f1 (theta) is f2 (-theta), and f1 and f2 are both monotone functions of the rotating angle theta; at the same time, since the capacitance C4 exists between the sensing positive comb teeth and the fixed comb teeth, the capacitance C5 exists between the sensing negative comb teeth and the fixed comb teeth, and the C4 is equal to C5 due to structural symmetry, the driving signal UdCoupling in the capacitive sense signal S through C4, C5c1And Sc2The same interference signal, namely:
Sc1＝C1+g(Ud) (3)
Sc2＝C2+g(Ud) (4)
the induction signal is processed by a differential circuit, then
Sc＝Sc1-Sc2＝C1-C2＝f1(θ)-f2(θ)＝f(θ) (5)
Namely, the structure can effectively eliminate the interference caused by the coupling capacitor, and the output signal of the sensing capacitor is only a function of the rotation angle theta; and obtaining the induction capacitance value through the peripheral capacitance detection circuit, and obtaining the value of the rotation angle theta through reverse deduction.
8. A manufacturing method of a stack type induction capacitor angle feedback galvanometer is characterized by comprising the following steps: the method comprises the following steps:
preparing a silicon on insulator wafer (SOI);
thermal oxidation: carrying out thermal oxidation on the prepared SOI, and forming a layer of silicon oxide on the upper surface of the top silicon;
bonding: bonding a single crystal silicon on the oxide layer on the upper surface of the SOI top silicon processed in the step 2) to form a five-layer structure wafer of top monocrystalline silicon, a second silicon dioxide layer, a middle monocrystalline silicon layer, a first silicon oxide layer and bottom monocrystalline silicon, namely SOIOI;
preparing a metal layer on the induction layer: making a patterned metal layer on the upper surface of the top layer single crystal silicon of the SOIOI completed in the step 3), wherein the method comprises two steps: firstly, depositing a layer of metal, and forming a required graphical metal layer by photoetching and etching methods; firstly, photoetching the surface of a top layer single crystal silicon, then depositing metal, and finally forming a required patterned metal layer in a stripping mode;
and (3) conducting photoetching on a guide mode selection area: performing guided mode selection area photoetching on the wafer finished in the step 4), and forming an unexposed photoresist area, a partially exposed photoresist area and a fully exposed photoresist area on the surface of the top layer of monocrystalline silicon;
etching top monocrystalline silicon: etching the SOIOI completed in the step 5) until the area of the top monocrystalline silicon which is not covered by the photoresist is completely etched to expose the second oxide layer;
etching the second oxide layer: etching the second oxide layer until the second oxide layer below the monocrystalline silicon region uncovered by the photoresist is completely removed to expose the monocrystalline silicon in the middle layer; at the moment, the photoresist of the original partial exposure area is completely removed, and only the unexposed photoresist is remained;
etching the monocrystalline silicon of the middle layer: continuing to etch the monocrystalline silicon, wherein the monocrystalline silicon below the complete exposure area and the partial exposure area are etched simultaneously until the monocrystalline silicon in the middle layer is etched through and the first oxide layer is exposed because the photoresist of the complete exposure area and the photoresist of the partial exposure area do not exist;
spraying glue: spraying glue by adopting a hard mask mode to cover the area needing to be reserved of the first oxidation layer;
etching the first oxide layer: etching the second oxide layer until the exposed second oxide layer is completely removed;
manufacturing device layer metal: manufacturing a graphical metal layer on the upper surface of the intermediate layer monocrystalline silicon by adopting a hard mask method to form a reflecting mirror surface, a grounding bonding pad and a driving bonding pad;
back cavity etching: etching the SOIOI bottom silicon to form a cavity on the back of the micro-mirror device;
releasing: and removing the first oxide layer in the cavity on the back surface by adopting a reactive ion etching mode.
9. The method of manufacturing of claim 8, wherein:
photoetching the guide mode selection area:
superposing a guide mold above the mask plate, and then carrying out exposure, development and subsequent etching processes;
the guide mold is an optical super-surface template, and the whole area range of the template comprises a full-transmission area and a fractional-transmission area; the transmittance of the total transmittance area to the wavelength used by the photoetching machine is more than or equal to 95 percent, and the transmittance of the fractional transmittance area to the wavelength used by the photoetching machine is 1 to 99 percent of the transmittance of the total transmittance area:
in the photoetching, a guide mold is arranged above a mask plate and is parallel to the mask plate, the partial transmission area projection of the guide mold is positioned in the projection range of the light transmission area of the mask plate, and the area of the guide mold is smaller than that of the mask plate; the outside of the guide modulus transmission area is a full projection area;
the mask plate is positioned above the photoresist, and the guide mold is arranged above the mask plate; when in exposure, the photoresist which is positioned in the light transmission area of the mask plate and is right below the range outside the fractional transmission area of the guide mode is completely exposed to generate complete reaction, and the photoresist which is positioned right below the fractional transmission area of the guide mode is partially exposed to generate incomplete reaction; the photoresist which is completely reacted is completely removed during development, the thickness of the photoresist which is not completely reacted is unchanged, but the density is reduced, and the etching rate selectivity of the masked substrate is reduced;
in the etching process, the photoresist is used as a masking layer, and the etching rate selection ratio of the partially exposed photoresist to the masked material is 1-99% of the selection ratio of the photoresist in the unexposed area to the masked material; in the initial etching stage, the substrate below the photoresist complete exposure area is exposed to etching gas, and only the part of the substrate is etched; the photoresist of the partial exposure area still exists and blocks etching gas, so that the substrate below the area is not etched; the etching rate of the partially exposed photoresist is higher than that of the unexposed photoresist, so that the partially exposed photoresist is completely etched away when the etching is carried out for a certain time, the substrate below the partially exposed photoresist is exposed in etching gas and begins to be etched, and the unexposed photoresist still exists to protect the substrate below the partially exposed photoresist from being etched; at the moment, as the etching continues, the substrate below the original complete exposure area and the original partial exposure area is etched until the etching is finished; because the substrate below the original complete exposure area is etched to a certain depth before the substrate below the original partial exposure area starts to be etched, the etching depths of the two areas are different after the etching is finished, and a stepped groove is formed; according to different design requirements of the device, the transmittance of the guide module fraction transmission area is designed, and the etching of the induction layer and the device layer can be completed.
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