JP2018155798A - Inspection method of optical deflector, optical deflector and image projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical deflector that can be more efficiently manufactured.SOLUTION: An inspection method of an optical deflector is provided for inspecting an optical deflector. The optical deflector includes a substrate having a first silicon layer and a second silicon layer, a drive part disposed on the substrate and performing resonance driving, and a pattern part for measuring the thickness of the second silicon pattern. The method includes a measurement step of measuring the thickness of the second silicon layer by the pattern part and a determination step of determining whether abnormality in a resonant frequency of the resonance driving is present or not based on the thickness measured in the measurement step.SELECTED DRAWING: Figure 15

Description

  The present invention relates to an optical deflector inspection method, an optical deflector, and an image projection apparatus.

  2. Description of the Related Art A MEMS (Micro Electro Mechanical Systems) scanner using a resonance phenomenon that can be efficiently operated with a small driving source even when the operating frequency is high is known. Patent Document 1 proposes a technique for disposing a mass body in order to adjust the resonance frequency of the movable part, that is, the resonance frequency of the optical deflector.

  However, there is a problem that the resonance frequency of the conventional MEMS scanner tends to vary depending on the manufacturing process. The device chip may be packaged to protect the device chip, but the resonant frequency is often tested after the packaging process. For this reason, when a device chip whose resonance frequency is not specified is manufactured, there is a problem that not only the device chip but also the packaging cost is wasted.

  The present invention has been made in view of the above, and an object thereof is to make it possible to manufacture an optical deflector more efficiently.

  In order to solve the above-described problems and achieve the object, the present invention provides an optical deflector inspection method for inspecting an optical deflector, wherein the optical deflector includes a first silicon layer and a second silicon layer. A substrate having a layer, a drive unit that is provided on the substrate and performs resonance driving, and a pattern unit for measuring the thickness of the second silicon layer. A measurement step of measuring the thickness of the silicon layer, and a determination step of determining whether there is an abnormality in the resonance frequency of the resonance drive based on the thickness measured in the measurement step.

  According to the present invention, it is possible to produce an optical deflector more efficiently.

It is the schematic which shows an example of an optical scanning system. It is a hardware block diagram of an example of an optical scanning system. It is a functional block diagram of an example of a drive device. It is a flowchart of an example of the process which concerns on an optical scanning system. It is the schematic which shows an example of the motor vehicle carrying a head-up display apparatus. It is the schematic which shows an example of a head-up display apparatus. It is the schematic which shows an example of the image forming apparatus carrying an optical writing device. It is the schematic which shows an example of an optical writing device. It is the schematic which shows an example of the motor vehicle carrying a laser radar apparatus. It is the schematic which shows an example of a laser radar apparatus. It is the schematic which shows an example of the packaged optical deflector. It is a figure which shows the example which applied the level | step difference pattern to the cantilever type optical deflector. It is P-P 'sectional drawing of FIG. It is Q-Q 'sectional drawing of FIG. It is a flowchart which shows an example of the manufacturing process in the case of thickness estimation by a level | step difference pattern. It is a figure which shows the other example which applied the level | step difference pattern to the cantilever type optical deflector. It is R-R 'sectional drawing of FIG. It is a figure which shows the example which applied the level | step difference pattern to the double-ended optical deflector. It is a figure which shows the example which applied the level | step difference pattern to the double-ended optical deflector. It is a figure which shows the example which shared the address number with the level | step difference pattern. It is a figure which shows the example which applied the level | step difference pattern to the dicing line. It is a figure which shows the example which applied the cantilever pattern to the cantilever type optical deflector. It is Q-Q 'sectional drawing of FIG. It is a graph which shows the example of the relationship between thickness and a primary bending mode resonance frequency. It is a graph which shows the example of the relationship between length and a primary bending mode resonance frequency. It is a figure for demonstrating the measuring method of the primary bending mode resonance frequency of a cantilever. It is a flowchart which shows an example of the manufacturing process in the case of thickness estimation by a cantilever pattern. It is a figure which shows the other example which applied the cantilever pattern to the cantilever type optical deflector. It is P-P 'sectional drawing of FIG. It is a figure which shows the example which applied the cantilever pattern to the both-ends-type optical deflector. It is a figure which shows the other example which applied the cantilever pattern to the double-ended optical deflector. It is a figure which shows the example which applied adjustment of the resonant frequency by a protective film. It is a P-P 'cross section of FIG. It is a figure which shows an example of the relationship between a protective film thickness and a resonant frequency. It is a flowchart which shows an example of the manufacturing process at the time of applying frequency adjustment.

  Exemplary embodiments of an optical deflector inspection method, an optical deflector, and an image projection apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
In the first embodiment, the thickness of the silicon active layer is measured using the pattern portion (step pattern), and the presence or absence of abnormality in the resonance frequency, which is the characteristic value of the optical deflector, is determined based on the measured thickness ( Presumed. Since this thickness can be determined before the packaging process, for example, it is possible to prevent the waste of the manufacturing process such as packaging with a defective chip. That is, the optical deflector can be manufactured more efficiently.

[Optical scanning system]
First, an optical scanning system to which the drive device according to the present embodiment is applied will be described in detail with reference to FIGS.

  FIG. 1 is a schematic diagram illustrating an example of an optical scanning system according to the present embodiment. As shown in FIG. 1, the optical scanning system 10 optically scans the surface to be scanned 15 by deflecting the light emitted from the light source device 12 according to the control of the driving device 11 by the reflecting surface 14 of the optical deflector 13. It is. The optical scanning system 10 includes a driving device 11, a light source device 12, and an optical deflector 13 having a reflecting surface 14.

  The drive device 11 is an electronic circuit unit including, for example, a CPU (Central Processing Unit) and an FPGA (Field-Programmable Gate Array). The optical deflector 13 is a MEMS device that has, for example, a reflective surface 14 and can move the reflective surface 14. The light source device 12 is, for example, a laser device that irradiates a laser. The scanned surface 15 is, for example, a screen.

  The drive device 11 generates a control command for the light source device 12 and the optical deflector 13 based on the acquired optical scanning information, and outputs a drive signal to the light source device 12 and the optical deflector 13 based on the control command.

  The light source device 12 irradiates the light source based on the input drive signal. The optical deflector 13 moves the reflecting surface 14 in at least one of the uniaxial direction and the biaxial direction based on the input drive signal.

  For example, by controlling the driving device 11 based on image information (image data) that is an example of optical scanning information, the reflecting surface 14 of the optical deflector 13 is reciprocally movable in a biaxial direction within a predetermined range. An arbitrary image can be projected onto the scanned surface 15 by deflecting the incident light from the light source device 12 and performing optical scanning.

  Details of the optical deflector 13 and details of control by the driving device 11 will be described later.

  Next, an exemplary hardware configuration of the optical scanning system 10 will be described with reference to FIG. FIG. 2 is a hardware configuration diagram of an example of the optical scanning system 10. As shown in FIG. 2, the optical scanning system 10 includes a driving device 11, a light source device 12, and an optical deflector 13, and each is electrically connected.

[Driver]
The driving device 11 includes a CPU 20, a RAM 21 (Random Access Memory), a ROM 22 (Read Only Memory), an FPGA 23, an external I / F (interface) 24, a light source device driver 25, and an optical deflector driver 26.

  The CPU 20 is an arithmetic device that reads out programs and data from a storage device such as the ROM 22 onto the RAM 21 and executes processing to realize the overall control and functions of the drive device 11.

  The RAM 21 is a volatile storage device that temporarily stores programs and data. The ROM 22 is a nonvolatile storage device that can retain programs and data even when the power is turned off, and stores processing programs and data that the CPU 20 executes to control each function of the optical scanning system 10. Yes.

  The FPGA 23 is a circuit that outputs control signals suitable for the light source device driver 25 and the optical deflector driver 26 in accordance with the processing of the CPU 20.

  The external I / F 24 is an interface with, for example, an external device or a network. The external device includes, for example, a host device such as a PC (Personal Computer) and a storage device such as a USB memory, an SD card, a CD, a DVD, an HDD, and an SSD. The network is, for example, an automobile CAN (Controller Area Network), a LAN (Local Area Network), and the Internet. The external I / F 24 may be configured to enable connection or communication with an external device, and the external I / F 24 may be prepared for each external device.

  The light source device driver 25 is an electric circuit that outputs a drive signal such as a drive voltage to the light source device 12 in accordance with the input control signal. The optical deflector driver 26 is an electric circuit that outputs a drive signal such as a drive voltage to the optical deflector 13 in accordance with the input control signal.

  In the driving device 11, the CPU 20 acquires optical scanning information from an external device or a network via the external I / F 24. The CPU 20 may be configured so that the optical scanning information can be acquired. The optical scanning information may be stored in the ROM 22 or the FPGA 23 in the driving device 11, or a new SSD or the like may be included in the driving device 11. A storage device may be provided, and the optical scanning information may be stored in the storage device.

  Here, the optical scanning information is information indicating how the scanned surface 15 is optically scanned. For example, when an image is displayed by optical scanning, the optical scanning information is image data. For example, when optical writing is performed by optical scanning, the optical scanning information is writing data indicating the writing order and writing location. In addition, for example, when object recognition is performed by optical scanning, the optical scanning information is irradiation data indicating the timing and irradiation range for irradiating light for object recognition.

  The drive device 11 according to the present embodiment can realize the functional configuration described below by the instruction of the CPU 20 and the hardware configuration shown in FIG.

[Functional configuration of drive unit]
Next, a functional configuration of the driving device 11 of the optical scanning system 10 will be described with reference to FIG. FIG. 3 is a functional block diagram of an example of a driving device of the optical scanning system. As shown in FIG. 3, the drive device 11 includes a control unit 30 and a drive signal output unit 31 as functions.

  The control unit 30 is realized by, for example, the CPU 20 and the FPGA 23, and acquires optical scanning information from an external device, converts the optical scanning information into a control signal, and outputs the control signal to the drive signal output unit 31. For example, the control unit 30 constitutes a control unit, acquires image data as optical scanning information from an external device or the like, generates a control signal from the image data by a predetermined process, and outputs the control signal to the drive signal output unit 31.

  The drive signal output unit 31 constitutes an application unit and is realized by the light source device driver 25, the optical deflector driver 26, and the like, and outputs a drive signal to the light source device 12 or the optical deflector 13 based on the input control signal. Output. The drive signal output unit 31 (applying unit) may be provided for each target that outputs a drive signal, for example.

  The drive signal is a signal for controlling driving of the light source device 12 or the optical deflector 13. For example, in the light source device 12, the drive signal is a drive voltage for controlling the irradiation timing and irradiation intensity of the light source. Further, for example, in the optical deflector 13, the drive signal is a drive voltage for controlling the timing and movable range at which the reflecting surface 14 of the optical deflector 13 is movable. The driving device 11 may acquire the irradiation timing and the light receiving timing of the light source from external devices such as the light source device 12 and the light receiving device, and synchronize them with the driving of the optical deflector 13.

[Optical scanning processing]
Next, a process in which the optical scanning system 10 optically scans the scanned surface 15 will be described with reference to FIG. FIG. 4 is a flowchart of an example of processing according to the optical scanning system.

  In step S11, the control unit 30 acquires optical scanning information from an external device or the like. In step S <b> 12, the control unit 30 generates a control signal from the acquired optical scanning information, and outputs the control signal to the drive signal output unit 31. In step S <b> 13, the drive signal output unit 31 outputs a drive signal to the light source device 12 and the optical deflector 13 based on the input control signal. In step S <b> 14, the light source device 12 performs light irradiation based on the input drive signal. The optical deflector 13 moves the reflecting surface 14 based on the input drive signal. By driving the light source device 12 and the optical deflector 13, light is deflected in an arbitrary direction and optically scanned.

  In the optical scanning system 10, one drive device 11 has a device and a function for controlling the light source device 12 and the optical deflector 13. However, the drive device for the light source device 12 and the drive for the optical deflector 13 are used. It may be provided separately from the device.

  In the optical scanning system 10, the function of the control unit 30 and the function of the drive signal output unit 31 of the light source device 12 and the optical deflector 13 are provided in one drive device 11, but these functions exist separately. You may do it. For example, a drive signal output device having a drive signal output unit 31 may be provided separately from the drive device 11 having the control unit 30. In the optical scanning system 10, an optical deflection system that performs optical deflection may be configured by the optical deflector 13 having the reflecting surface 14 and the driving device 11.

[Image projection device]
Next, with reference to FIG. 5 and FIG. 6, an image projection apparatus to which the drive device 11 of the present embodiment is applied will be described in detail. FIG. 5 is a schematic diagram showing an example of an automobile 400 equipped with a head-up display device 500 that is an example of an image projection device. FIG. 6 is a schematic view showing an example of the head-up display device 500.

  The image projection device is a device that projects an image by optical scanning, for example, a head-up display device 500. As shown in FIG. 5, the head-up display device 500 is installed, for example, in the vicinity of a windshield (a windshield 401 or the like) of the automobile 400. The projection light L emitted from the head-up display device 500 is reflected by the windshield 401 and travels toward the observer (driver 402) who is the user.

  Accordingly, the driver 402 can visually recognize an image or the like projected by the head-up display device 500 as a virtual image. In addition, you may make it the structure which installs a combiner in the inner wall face of a windshield, and makes a user visually recognize a virtual image with the projection light reflected by a combiner.

  As shown in FIG. 6, in the head-up display device 500, laser light is emitted from red, green, and blue laser light sources 501R, 501G, and 501B. The emitted laser light passes through an incident optical system including collimator lenses 502, 503, and 504 provided for each laser light source, two dichroic mirrors 505 and 506, and a light amount adjustment unit 507. The light is deflected by an optical deflector 13 having a reflecting surface 14.

  The deflected laser light is projected onto a screen through a projection optical system including a free-form surface mirror 509, an intermediate screen 510, and a projection mirror 511.

  In the head-up display device 500, the laser light sources 501R, 501G, and 501B, the collimator lenses 502, 503, and 504 and the dichroic mirrors 505 and 506 are unitized as an optical housing as a light source unit 530.

  The head-up display device 500 projects the intermediate image displayed on the intermediate screen 510 onto the windshield 401 of the automobile 400 so that the driver 402 can visually recognize the intermediate image as a virtual image.

  The respective color laser beams emitted from the laser light sources 501R, 501G, and 501B are substantially collimated by the collimator lenses 502, 503, and 504, and are combined by the two dichroic mirrors 505 and 506. The combined laser light is two-dimensionally scanned by the optical deflector 13 having the reflecting surface 14 after the light amount is adjusted by the light amount adjusting unit 507. The projection light L that has been two-dimensionally scanned by the optical deflector 13 is reflected by the free-form surface mirror 509, corrected for distortion, and then condensed on the intermediate screen 510 to display an intermediate image. The intermediate screen 510 includes a microlens array in which microlenses are two-dimensionally arranged, and enlarges the projection light L incident on the intermediate screen 510 in units of microlenses.

  The optical deflector 13 reciprocally moves the reflecting surface 14 in the biaxial direction, and two-dimensionally scans the projection light L incident on the reflecting surface 14. The drive control of the optical deflector 13 is performed in synchronization with the light emission timings of the laser light sources 501R, 501G, and 501B.

  The head-up display device 500 as an example of the image projection device has been described above. However, the image projection device is any device that projects an image by performing optical scanning with the optical deflector 13 having the reflective surface 14. Good.

  For example, it is mounted on a projector that is placed on a desk or the like and projects an image on a display screen, or a mounting member that is mounted on an observer's head or the like, and is projected on a reflective transmission screen that the mounting member has, or an eyeball as a screen The present invention can be similarly applied to a head-mounted display device that projects an image.

  The image projection apparatus is not only a vehicle or a mounting member, but also, for example, a moving body such as an aircraft, a ship, and a mobile robot, and a work robot that operates a driving target such as a manipulator without moving from the spot. It may be mounted on a non-moving body.

[Optical writing device]
Next, with reference to FIG. 7 and FIG. 8, an optical writing device to which the driving device 11 of this embodiment is applied will be described in detail. FIG. 7 is an example of an image forming apparatus incorporating the optical writing device 600. FIG. 8 is a schematic diagram showing an example of an optical writing device.

  As shown in FIG. 7, the optical writing device 600 is used as a constituent member of an image forming apparatus represented by a laser printer 650 having a printer function using laser light. In the image forming apparatus, the optical writing device 600 performs optical writing on the photosensitive drum by optically scanning the photosensitive drum which is the surface to be scanned 15 with one or a plurality of laser beams.

  As shown in FIG. 8, in the optical writing device 600, the laser light from the light source device 12 such as a laser element passes through an imaging optical system 601 such as a collimator lens, and is then transmitted by the optical deflector 13 having the reflecting surface 14. Deflection is performed in one or two axial directions.

  Then, the laser beam deflected by the optical deflector 13 passes through the scanning optical system 602 including the first lens 602a, the second lens 602b, and the reflection mirror unit 602c, and then the scanned surface 15 (for example, a photosensitive drum or a photosensitive drum). (Paper) and write optically. The scanning optical system 602 forms a light beam in a spot shape on the scanned surface 15.

  The light source device 12 and the optical deflector 13 having the reflecting surface 14 are driven based on the control of the driving device 11.

  As described above, the optical writing device 600 can be used as a constituent member of an image forming apparatus having a printer function using laser light. Also, by making the scanning optical system different so that optical scanning is possible not only in one axis direction but also in two axis directions, a laser label device that performs printing by deflecting laser light to a thermal medium, optical scanning, and heating. It can be used as a component of the image forming apparatus.

  Since the optical deflector 13 having the reflecting surface 14 applied to the optical writing device 600 consumes less power for driving than a rotary polygon mirror using a polygon mirror or the like, power saving of the optical writing device 600 is achieved. It is advantageous to make. Further, since the wind noise during vibration of the optical deflector 13 is smaller than that of the rotary polygon mirror, it is advantageous for improving the quietness of the optical writing device 600. The optical writing device 600 requires much less installation space than the rotary polygon mirror, and the optical deflector 13 generates only a small amount of heat. Therefore, the optical writing device 600 can be easily downsized, and thus the image forming apparatus can be downsized. It is advantageous.

[Object recognition device]
Next, with reference to FIG. 9 and FIG. 10, the object recognition apparatus to which the drive device 11 of this embodiment is applied will be described in detail. FIG. 9 is a schematic diagram of an automobile equipped with a laser radar device which is an example of an object recognition device. FIG. 10 is a schematic diagram showing an example of a laser radar device. The object recognition device is a device that recognizes an object in a target direction, for example, a laser radar device.

  As shown in FIG. 9, a laser radar device 700 is mounted on, for example, an automobile 701, optically scans the target direction, and receives reflected light from the target object 702 existing in the target direction, thereby receiving the target object. 702 is recognized.

  As shown in FIG. 10, the laser light emitted from the light source device 12 is reflected through an incident optical system including a collimating lens 703 that is an optical system that makes diverging light substantially parallel light, and a plane mirror 704. Scanning is performed in one or two axial directions by an optical deflector 13 having a surface 14.

  Then, the laser light is irradiated onto the object 702 in front of the apparatus through a light projecting lens 705 that is a light projecting optical system. Driving of the light source device 12 and the optical deflector 13 is controlled by the driving device 11. The reflected light reflected by the object 702 is detected by the photodetector 709. That is, the reflected light is received by the image sensor 707 via the condenser lens 706 that is a light receiving optical system, and the image sensor 707 outputs a detection signal to the signal processing circuit 708. The signal processing circuit 708 performs predetermined processing such as binarization and noise processing on the input detection signal, and outputs the result to the distance measurement circuit 710.

  The distance measuring circuit 710 determines whether the light source device 12 emits a laser beam and the timing at which the photodetector 709 receives the laser beam, or the phase difference of each pixel of the received image sensor 707. The presence or absence of the object 702 is recognized, and further distance information with respect to the object 702 is calculated.

  Since the optical deflector 13 having the reflecting surface 14 is less likely to be damaged than a polygonal mirror and is small in size, it is possible to provide a small and highly durable radar device.

  Such a laser radar device 700 is attached to, for example, a vehicle, an aircraft, a ship, a robot, and the like, and can optically scan a predetermined range to recognize the presence or absence of an obstacle and the distance to the obstacle.

  Although the laser radar device 700 has been described as an example of the object recognition device, the object recognition device performs optical scanning by controlling the optical deflector 13 having the reflection surface 14 with the driving device 11 and reflects the light by the photodetector 709. Any device that recognizes the object 702 by receiving light may be used, and is not limited to the above-described example.

  For example, a biometric authentication device that recognizes an object by calculating object information such as a shape from distance information obtained by optically scanning a hand or face and referring to the record, and recognizes an intruder by optical scanning of the target range The present invention can be applied in the same manner to a security sensor and a component of a three-dimensional scanner that calculates and recognizes object information such as a shape from distance information obtained by optical scanning and outputs it as three-dimensional data.

[Packaging]
Next, with reference to FIG. 11, the packaging of the optical deflector 13 controlled by the driving device 11 of the present embodiment will be described. FIG. 11 is a schematic diagram illustrating an example of a packaged optical deflector.

  As shown in FIG. 11, the optical deflector 13 is attached to an attachment member 802 disposed inside the package member 801, and a part of the package member is covered with a transmission member 803 and sealed to achieve packaging. Is done. Further, an inert gas such as nitrogen is sealed in the package. As a result, deterioration of the optical deflector 13 due to oxidation is suppressed, and durability against changes in the environment such as temperature is improved.

  Next, details of the optical deflector 13 used in the optical deflection system, the optical scanning system, the image projection apparatus, the optical writing apparatus, and the object recognition apparatus described above and the control by the driving apparatus 11 of the present embodiment. Details will be described. 1 to 11 can also be applied to optical deflectors of second to third embodiments described later.

[Details of optical deflector]
First, the optical deflector 13 will be described in detail with reference to FIG. 12, FIG. 13, and FIG. FIG. 12 is a plan view of a cantilever type optical deflector 13 capable of deflecting light in two axial directions. 13 is a cross-sectional view taken along the line PP ′ of FIG. 14 is a cross-sectional view taken along the line QQ ′ of FIG.

  As shown in FIG. 12, the optical deflector 13 includes a mirror unit 101, first drive units 110a and 110b, a movable frame 120 as a support member, second drive units 130a and 130b, and a fixed support member. It has a frame 140 and an electrode connection part 150. The mirror unit 101 reflects incident light. The first drive units 110a and 110b are connected to the mirror unit 101 and drive (resonance drive) the mirror unit 101 around a first axis parallel to the Y axis. The movable frame 120 supports the mirror unit 101 and the first drive units 110a and 110b. The second drive units 130a and 130b are connected to the movable frame 120, and drive the mirror unit 101 and the movable frame 120 around a second axis parallel to the X axis (resonance [sawtooth wave] drive). The fixed frame 140 supports the second driving units 130a and 130b. The electrode connection unit 150 is electrically connected to the first driving units 110 a and 110 b, the second driving units 130 a and 130 b, and the driving device 11.

  The optical deflector 13 is formed, for example, by an etching process or the like on one SOI (Silicon On Insulator) substrate. By forming the reflecting surface 14, the first piezoelectric drive units 112a and 112b, the second piezoelectric drive units 131a to 131f, 132a to 132f, the electrode connection unit 150, and the like on the molded substrate, the respective components are integrated. Is formed. Note that each component may be formed after the SOI substrate is formed or during the formation of the SOI substrate.

  In the SOI substrate, a silicon oxide layer 162 is provided on a first silicon layer made of single crystal silicon (Si), and a second silicon layer made of single crystal silicon is further provided on the silicon oxide layer 162. It is a substrate. Hereinafter, the first silicon layer is referred to as a silicon support layer 161, and the second silicon layer is referred to as a silicon active layer 163.

  Since the silicon active layer 163 has a smaller thickness in the Z-axis direction with respect to the X-axis direction or the Y-axis direction, a member formed only of the silicon active layer 163 has a function as an elastic part having elasticity.

  The mirror unit 101 includes, for example, a circular mirror unit base 102 and a reflective surface 14 formed on the + Z side surface of the mirror unit base 102. The mirror part base | substrate 102 is comprised from the silicon | silicone active layer 163, for example. The reflecting surface 14 is made of a metal thin film containing, for example, aluminum, gold, silver or the like.

  Further, the mirror portion 101 may have reinforcing ribs formed on the surface of the mirror portion base 102 on the −Z side. The rib is composed of, for example, a silicon support layer 161 and a silicon oxide layer 162, and can suppress distortion of the reflecting surface 14 caused by movement.

  The first drive units 110a and 110b include two torsion bars 111a and 111b and first piezoelectric drive units 112a and 112b. The torsion bars 111a and 111b have one ends connected to the mirror base 102 and extend in the first axial direction to support the mirror 101 movably. The first piezoelectric drive units 112 a and 112 b have one end connected to the torsion bars 111 a and 111 b and the other end connected to the inner peripheral part of the movable frame 120.

  As shown in FIG. 13 (P-P ′ cross-sectional view), the torsion bars 111 a and 111 b are composed of a silicon active layer 163. The first piezoelectric driving units 112a and 112b are configured by forming a lower electrode 201, a piezoelectric unit 202, and an upper electrode 203 in this order on the surface of the silicon active layer 163 that is an elastic part on the + Z side.

  The upper electrode 203 and the lower electrode 201 are made of, for example, gold (Au) or platinum (Pt). The piezoelectric portion 202 is made of, for example, PZT (lead zirconate titanate) that is a piezoelectric material.

  Returning to FIG. 12, the movable frame 120 is, for example, a rectangular support formed of a silicon support layer 161, a silicon oxide layer 162, and a silicon active layer 163 so as to surround the mirror unit 101.

  The second drive units 130a and 130b are constituted by, for example, a plurality of second piezoelectric drive units 131a to 131f and 132a to 132f connected so as to be folded back. One end of each of the second drive units 130 a and 130 b is connected to the outer peripheral part of the movable frame 120, and the other end is connected to the inner peripheral part of the fixed frame 140.

  At this time, the connection location between the second drive unit 130a and the movable frame 120, the connection location between the second drive unit 130b and the movable frame 120, the connection location between the second drive unit 130a and the fixed frame 140, and the second drive unit 130b are fixed. The connection location of the frame 140 is point-symmetric with respect to the center of the reflection surface 14.

  As shown in FIG. 14 (QQ ′ cross-sectional view), the second driving units 130a and 130b have a lower electrode 201, a piezoelectric unit 202, and an upper electrode 203 on the surface on the + Z side of the silicon active layer 163 that is an elastic unit. It is formed and configured in this order. The upper electrode 203 and the lower electrode 201 are made of, for example, gold (Au) or platinum (Pt). The piezoelectric unit 202 is made of, for example, PZT that is a piezoelectric material.

  Returning to FIG. 12, the fixed frame 140 includes, for example, a silicon support layer 161, a silicon oxide layer 162, and a silicon active layer 163. The mirror unit 101, the first driving units 110a and 110b, the movable frame 120, and the second driving unit. It is a rectangular support formed so as to surround 130a and 130b.

  As shown in FIG. 12 and the QQ ′ cross-sectional view of FIG. 12 (FIG. 14), holes are formed in the silicon active layer 163 in the fixed frame 140, and the silicon oxide layer 162 and the silicon support layer 161 are formed. In contrast, a step pattern 1201 is formed. As a result, the thickness of the silicon active layer 163 can be accurately measured. The step pattern 1201 shown in FIG. 12 is an example, and the present invention is not limited to this. For example, a step pattern in which a side surface is a second silicon layer and a bottom surface is a first silicon layer may be used.

  The electrode connection unit 150 is formed, for example, on the surface of the fixed frame 140 on the + Z side, and the upper electrodes 203 and the lower electrodes 201 of the first piezoelectric driving units 112a and 112b and the second piezoelectric driving units 131a to 131f, and The drive device 11 is electrically connected to the drive device 11 through an electrode wiring such as aluminum (Al).

  Each of the upper electrode 203 or the lower electrode 201 may be directly connected to the electrode connecting portion 150 or may be indirectly connected by connecting the electrodes to each other.

  In the present embodiment, the case where the piezoelectric portion 202 is formed only on one surface (the surface on the + Z side) of the silicon active layer 163 that is an elastic portion has been described as an example. The piezoelectric portion 202 may be provided on the other surface of the elastic portion (for example, the surface on the −Z side), or may be provided on both one surface and the other surface of the elastic portion.

  In addition, as long as the mirror unit 101 can be driven around the first axis or the second axis, the shape of each component is not limited to the shape of the embodiment. For example, the torsion bars 111a and 111b and the first piezoelectric drive units 112a and 112b may have a curved shape.

  Furthermore, on the + Z side surface of the upper electrode 203 of the first drive units 110a and 110b, on the + Z side surface of the movable frame 120, on the + Z side surface of the upper electrode 203 of the second drive units 130a and 130b, and An insulating layer made of a silicon oxide film may be formed on at least one of the surfaces of the fixed frame 140 on the + Z side.

  At this time, an electrode wiring is provided on the insulating layer, and the insulating layer is not partially removed or formed as an opening at a connection spot where the upper electrode 203 or the lower electrode 201 and the electrode wiring are connected. This increases the degree of freedom in designing the first drive units 110a and 110b, the second drive units 130a and 130b, and the electrode wiring, and can further suppress a short circuit due to contact between the electrodes. The insulating layer may be any member having an insulating property, and may have a function as an antireflection material.

[Details of control of drive unit]
Next, details of control of the driving device 11 that drives the first driving units 110a and 110b and the second driving units 130a and 130b of the optical deflector 13 will be described.

  When the voltage is applied in the polarization direction, the piezoelectric parts 202 included in the first driving parts 110a and 110b and the second driving parts 130a and 130b are deformed in proportion to the potential of the applied voltage, and exhibit a so-called reverse piezoelectric effect. To do. The piezoelectric part 202 has a unimorph structure fixed only to one side of the silicon active layer 163. While the piezoelectric portion 202 expands and contracts, the silicon active layer 163 does not deform, so that warping deformation occurs in the first driving portions 110a and 110b and the second driving portions 130a and 130b due to voltage application. In this way, the mirror unit 101 is moved using the inverse piezoelectric effect.

  At this time, the angle at which the light beam incident on the reflecting surface 14 of the mirror unit 101 is deflected is called a deflection angle. The deflection angle when no voltage is applied to the piezoelectric portion 202 is zero, and the deflection angle larger than that angle is defined as a positive deflection angle, and the deflection angle is defined as a negative deflection angle.

  First, control of the drive device 11 that drives the first drive units 110a and 110b will be described. In the first driving units 110a and 110b, when a driving voltage is applied in parallel to the piezoelectric units 202 included in the first piezoelectric driving units 112a and 112b via the upper electrode 203 and the lower electrode 201, the respective piezoelectric units 202 are connected. Deform. Due to the action of the deformation of the piezoelectric portion 202, the first piezoelectric driving portions 112a and 112b are bent and deformed.

  As a result, the driving force around the first axis acts on the mirror portion 101 via the twist of the two torsion bars 111a and 111b, and the mirror portion 101 moves around the first axis. The driving voltage applied to the first driving units 110 a and 110 b is controlled by the driving device 11.

  Therefore, the drive unit 11 applies the drive voltage having a predetermined sine waveform in parallel to the first piezoelectric drive units 112a and 112b included in the first drive units 110a and 110b, so that the mirror unit 101 is moved around the first axis. Can be moved at a period of a drive voltage having a predetermined sine waveform.

  In particular, for example, when the frequency of the sinusoidal waveform voltage is set to about 20 kHz, which is about the same as the resonance frequency of the torsion bars 111a and 111b, utilizing the mechanical resonance caused by the torsion of the torsion bars 111a and 111b, The mirror unit 101 can be resonantly oscillated at about 20 kHz.

  Here, when the mechanical resonance of the torsion bars 111a and 111b is utilized using a silicon material, the resonance peak is steep, so that a very large amplitude can be obtained with a small voltage. In particular, the resonance operation is indispensable for vibrating the mirror at a high speed and a large amplitude. However, on the other hand, mechanical resonance in the silicon structure has a big problem that manufacturing variation is large.

  Further, in the optical deflector 13 which is a packaged MEMS as shown in FIG. 11, the resonance frequency of the mirror is often inspected after the packaging process for reasons of handling and wiring. It may occur after packaging that is found to be out of specification. In this case, not only the optical deflector 13 but also the package cost is wasted.

  In the present embodiment, the cause of the variation in resonance frequency due to torsion torsion is considered, and the contribution ratio of the thickness of the silicon active layer 163 is very large (60% or more under certain conditions depending on design parameters and process capability). By managing the thickness of the silicon active layer 163, the present inventors have focused on efficiently managing the resonance frequency during mass production.

  Here, an example of a manufacturing process of the optical deflector 13 will be described. FIG. 15 is a flowchart illustrating an example of a manufacturing process of the optical deflector 13. The manufacturing process includes a process of inspecting the manufactured optical deflector 13 (optical deflector inspection method).

  First, an SOI substrate is delivered (step S101). A film such as the lower electrode 201, the piezoelectric portion 202 (PZT), and the upper electrode 203 is formed on the SOI substrate (step S102). Next, patterning of the piezoelectric part 202 (PZT) and electrodes is executed (step S103). For example, etching is performed while leaving a necessary portion of the electrode, the piezoelectric portion 202 (PZT), and a wiring pattern.

  Next, etching is performed leaving the shape of the silicon active layer 163 (step S104). In this step, a step pattern 1201 is formed. Next, the electrical characteristics are inspected (step S105). For example, a continuity check and an inspection of electrical characteristics of the piezoelectric part 202 (PZT) are performed. Further, inspection (measurement) of important dimension values such as the thickness of the silicon active layer 163 is performed (step S106).

  Next, the SOI substrate is inverted (step S107). Then, the silicon support layer 161 and the silicon oxide layer 162 are etched (step S108). Next, dicing (chip formation) is performed, and each device chip is divided into pieces (step S109).

  Next, the selection of the chip is performed depending on whether there is an abnormality (step S110). For example, various dimensions including electrical characteristics and the thickness of the silicon active layer 163 are inspected. For example, whether or not there is an abnormality is determined based on whether or not the thickness of the silicon active layer 163 is a value within a predetermined range. This step corresponds to determining (estimating) whether there is an abnormality in the resonance frequency based on the thickness of the silicon active layer 163 before the packaging step. For example, when the thickness of the silicon active layer 163 is not within the range, it is determined (estimated) that the resonance frequency is abnormal.

  When an abnormal value is obtained in the electrical characteristics and dimensional inspection (step S110: Yes), the chip having the abnormal value is excluded (step S111). If there is no abnormality (step S110: No), packaging is performed (step S112).

  Next, it is inspected whether the device characteristics (resonance frequency, amplitude, etc.) are abnormal (step S113). When there is an abnormality (step S113: Yes), the chip with the abnormality is excluded (step S114). If there is no abnormality (step S113: No), the corresponding chip is shipped (step S115).

  Thus, according to the present embodiment, the thickness of the silicon active layer 163 can be inspected after the etching process. As a result, it is possible to exclude chips that have a high possibility that the resonance frequency will be abnormal before the packaging process, and to prevent useless packaging costs.

(Modification 1)
In order to obtain a higher effect, a modification example in which the step pattern 1201 is arranged in the vicinity of the torsion bars 111a and 111b (for example, a position where the distance from the torsion bars 111a and 111b is equal to or less than a predetermined value) is shown in FIG. As shown in FIG. As shown in FIG. 16, in this modification, the step pattern 1201 by the silicon active layer 163 is disposed on both sides of the pair of torsion bars 111a and 111b. Thereby, since the thickness in the vicinity of the torsion bars 111a and 111b that contribute to the resonance frequency of the mirror can be measured, it is possible to perform discrimination with higher accuracy.

(Modification 2)
In the above embodiment and the modification, as shown in FIG. 12, the optical deflector 13 includes a cantilever type optical deflector 13 in which the first piezoelectric drive units 112a and 112b extend from the torsion bars 111a and 111b toward the + X direction. Used. The configuration is not limited to this as long as the reflecting surface 14 is movable by the piezoelectric unit 202 to which a voltage is applied.

  For example, as shown in FIGS. 18 and 19, first torsion bars 211a and 211b have first piezoelectric drive parts 212a and 212b extending in the + X direction and first piezoelectric drive parts 212c and 212d extending in the −X direction. A both-end type optical deflector 13 may be used.

(Modification 3)
Further, it is not necessary to provide a step pattern for measuring the thickness of the silicon active layer 163. As shown in FIG. 20, an address number (wafer address number) indicating a position in the wafer is used as an etching pattern for the silicon active layer 163. The depth of this portion may be measured as the thickness. Although FIG. 20 shows an example of a double-sided type optical deflector 13, the present invention can be similarly applied to a cantilevered type optical deflector 13.

(Modification 4)
If you do not want to leave a functionally unnecessary shape in the final product, it is possible to eliminate the step pattern after dicing by providing a step pattern in the dicing line part that makes chips smaller as shown in FIG. It is. Although FIG. 21 shows an example of a double-sided type optical deflector 13, the invention can be similarly applied to a cantilevered type optical deflector 13.

  As described above, in the first embodiment, the pattern portion (step pattern) for measuring the thickness of the silicon active layer (second silicon layer) is provided, and the thickness of the silicon active layer is determined by this pattern portion. Measure. Since the thickness of the silicon active layer greatly contributes to variations in the resonance frequency, it is determined whether the resonance frequency is abnormal by determining whether the thickness is abnormal, for example, before the packaging process ( Estimate). As a result, for example, it is possible to prevent wasteful manufacturing processes such as packaging with a defective chip, and to suppress generation of unnecessary costs.

(Second Embodiment)
In the first embodiment, after the substrate is inverted, the silicon support layer 161 is etched, and the silicon oxide layer 162 is etched to form a pattern in which the entire SOI substrate is completely removed. Since the etching speed of the silicon oxide layer 162 has a distribution within the wafer surface, the portion where the silicon oxide layer 162 disappears before the etching of all the in-plane etching is damaged from the back surface of the silicon active layer 163. The thickness may become thinner. For this reason, the thickness of the silicon active layer 163 also varies during the etching of the silicon oxide layer 162 in the process flow of FIG. Therefore, in the thickness measurement using the step pattern, the thickness variation due to the over-etching on the back surface is not reflected, and the variation in the resonance frequency may be affected accordingly.

  In the second embodiment, an example that can cope with variations including thickness variations during the process will be described. In the second embodiment, a cantilever pattern supported by the silicon active layer is formed as a pattern portion for measuring the thickness of the silicon active layer. Further, the resonance frequency of the cantilever pattern is measured, and the thickness of the silicon active layer is calculated from this resonance frequency. Based on the calculated thickness of the silicon active layer, it is determined (estimated) whether there is an abnormality in the resonance frequency, which is a characteristic value of the optical deflector, before inspecting the characteristics of the device chip.

  FIG. 22 is a plan view of a cantilever type optical deflector 13-2. 23 is a cross-sectional view taken along the line Q-Q ′ of FIG.

As shown in FIG. 22, a cantilever (cantilever) pattern 2201 formed of only the silicon active layer 163 is formed on a part of the fixed frame 140. The resonance frequency f of the first-order bending mode in the cantilever pattern 2201 is obtained by a theoretical expression such as the following expressions (1) and (2). t is the thickness, L is the length, w is the width, E is the Young's modulus, ρ is the density, A is the cross-sectional area (= w · t), and I is the cross-sectional second moment (= w / t ³ ).
f = (1.875 / L) ² / 2π√ (EI / ρA) (1)
t = (L / 1.875) ² / (2πf) · √ (12ρ / E) (2)

  FIG. 24 is a graph showing an example of the relationship between the thickness and the primary bending mode resonance frequency. FIG. 25 is a graph showing an example of the relationship between the length and the primary bending mode resonance frequency. The numerical values in the graph represent values obtained by dividing the primary bending mode resonance frequency (Hz) by the thickness (μm).

  Although depending on the dimension value, the resonance frequency of the optical deflector 13-2 depends on the thickness and length of the silicon active layer 163, and the influence of the thickness is particularly large. The thickness of the silicon active layer 163 can be obtained by calculating backward from the primary bending mode resonance frequency of the cantilever according to the equations (1) and (2).

  Although the influence of the length is slight, the equation may be corrected by measuring the dimensions in the wafer state. The primary bending mode resonance frequency of the cantilever can be measured as it is in the wafer state before dicing, and defective chips can be excluded before packaging.

  FIG. 26 is a diagram for explaining a method of measuring the primary bending mode resonance frequency of the cantilever. The entire wafer including the chip on which the cantilever pattern 2201 is formed is fixed to a vibration table 2902, and vibration is applied by external vibration. The vibration in the Z direction (arrow 2911) is adjusted by the frequency sweep. The sensor 2901 detects that the amplitude of the cantilever suddenly increases when the first bending mode resonance frequency is met. The sensor 2901 can collectively measure the wafer surface by using a scanning Doppler vibrometer or the like.

  Next, an example of a manufacturing process of the optical deflector 13-2 will be described. FIG. 27 is a flowchart illustrating an example of a manufacturing process of the optical deflector 13-2.

  Step S201 to Step S205 and Step S207 to Step S208 are the same as Step S101 to Step S105 and Step S107 to Step S108 of FIG. 15 showing the manufacturing process of the optical deflector 13 of the first embodiment. Therefore, explanation is omitted.

  In the dimension inspection of this embodiment, dimension values such as the width of the torsion bars 111a and 111b and the length of the cantilever are inspected (step S206). In this embodiment, the primary bending mode resonance frequency of the cantilever is measured by the method shown in FIG. 26, and the thickness of the silicon active layer 163 is calculated from the primary bending mode resonance frequency by the equations (1) and (2). Is calculated (step S209).

  Steps S210 to S216 are the same as steps S109 to S115 of FIG. 15 showing the manufacturing process of the optical deflector 13 of the first embodiment, and thus the description thereof is omitted.

(Modification 5)
FIG. 28 and FIG. 29 show modifications in which the cantilever pattern 2201 is arranged in the vicinity of the torsion bars 111a and 111b so that a higher effect can be obtained. As shown in FIG. 28, in this modification, a cantilever pattern 2201 made of a silicon active layer 163 is disposed adjacent to the pair of torsion bars 111a and 111b. As a result, the thickness in the vicinity of the torsion bars 111a and 111b that contribute to the mirror resonance frequency is obtained, so that a more accurate determination can be made.

(Modification 6)
In the embodiment and the modification, the optical deflector 13-2 is a cantilever type in which the first piezoelectric driving units 112a and 112b extend from the torsion bars 111a and 111b toward the + X direction as shown in FIGS. An optical deflector is used. The configuration is not limited to this as long as the reflecting surface 14 is movable by the piezoelectric unit 202 to which a voltage is applied.

  For example, as shown in FIGS. 30 and 31, the first piezoelectric drive units 212a and 212b extending from the torsion bars 211a and 211b in the + X direction and the first piezoelectric drive units 212c and 212d extending in the −X direction are provided. A dual-support type optical deflector 13-2 may be used.

  As described above, in the second embodiment, the primary bending mode resonance frequency of the cantilever is measured, and the thickness of the silicon active layer 163 is calculated from the primary bending mode resonance frequency. The thickness of the silicon active layer 163 can be calculated including the processing error after the etching process of the silicon oxide layer 162. In addition, chips having an abnormal resonance frequency can be excluded before the packaging process, and generation of useless packaging costs can be prevented.

(Third embodiment)
In the third embodiment, when the resonance frequency, which is the characteristic value of the optical deflector grasped in the first embodiment and the second embodiment, is out of the specification range, the protective film on the torsion bar is etched. The resonance frequency can be adjusted with. That is, in this embodiment, the main factor of the variation of the resonance frequency characteristic is measured (inspected) during the manufacturing process, the resonance frequency is grasped in advance, and the resonance frequency is adjusted before packaging, thereby avoiding loss. .

  Below, the example which applied the method of this embodiment based on the modification 5 (FIG. 28, FIG. 29) of 2nd Embodiment is demonstrated. The same technique can be applied to other forms (first embodiment, modified example of the first embodiment, second embodiment, and other modified example of the second embodiment).

  FIG. 32 is a plan view of the optical deflector 13-3 to which adjustment of the resonance frequency by the protective film is applied. 33 is a cross-sectional view taken along the line P-P ′ in FIG. 32. As shown in FIG. 33, a protective film 3301 that is a silicon oxide layer is formed on the uppermost surface of the device. The protective film 3301 is also laminated on the torsion bars 111a and 111b, and affects the resonance frequency although not as much as the silicon active layer 163.

  FIG. 34 is a diagram illustrating the relationship between the thickness of the protective film 3301 and the resonance frequency (torsion torsional resonance) of the optical deflector 13-3 when the material of the protective film 3301 is SiO2 (silicon dioxide). As shown in FIG. 34, although the degree of influence of the protective film thickness on the resonance frequency is small, a change of 0.36 Hz per unit film thickness (nm) is expected. Utilizing this fact, the protective film 3301 is formed thick in advance, and after estimating the resonance frequency, the protective film 3301 on the torsion bars 111a and 111b is additionally etched. The protective film 3301 is etched so as to have a thickness adjusted according to the thickness of the silicon active layer 163, for example. The amount of etching may be determined based on, for example, the relationship shown in FIG. As a result, the resonance frequency can be corrected to an appropriate value.

  Next, an example of a manufacturing process of the optical deflector 13-3 will be described. FIG. 35 is a flowchart illustrating an example of a manufacturing process of the optical deflector 13-3.

  Step S301 and step S303 to step S309 are the same as step S201 and step S203 to step S209 of FIG. 27 showing the manufacturing process of the optical deflector 13-2 of the second embodiment, so description thereof will be omitted.

  In the present embodiment, a protective film 3301 is formed on the SOI substrate in addition to the lower electrode 201, the piezoelectric portion 202 (PZT), the upper electrode 203, and the like (step S302). In the present embodiment, an etching process for the protective film 3301 is added (step S310).

  Since step S311 is the same as step S210 of the second embodiment, a description thereof will be omitted.

  In this embodiment, after the cantilever inspection, additional etching of the protective film 3301 is performed to adjust the resonance frequency, so that it is not necessary to perform chip selection. That is, for example, the processing of step S211 and step S212 of the second embodiment is not necessary.

  Subsequent steps S312 to S315 are the same as steps S213 to S216 of FIG. 27 showing the manufacturing process of the optical deflector 13-2 of the second embodiment, and thus description thereof is omitted.

  As described above, in this embodiment, it is possible to avoid the occurrence of defective products and prevent loss in the manufacturing process by adjusting the resonance frequency to normal characteristics.

DESCRIPTION OF SYMBOLS 10 Optical scanning system 11 Drive apparatus 12 Light source device 13, 13-2, 13-3 Optical deflector 14 Reflecting surface 20 CPU
21 RAM
22 ROM
23 FPGA
24 External I / F
25 Light source device driver 26 Optical deflector driver

JP 2014-235244 A

Claims (7)

An optical deflector inspection method for inspecting an optical deflector,
The optical deflector includes a substrate having a first silicon layer and a second silicon layer, a drive unit provided on the substrate for performing resonance driving, and a thickness of the second silicon layer. A pattern portion for measuring,
A measuring step of measuring the thickness of the second silicon layer by the pattern portion;
A determination step of determining whether there is an abnormality in the resonance frequency of the resonance drive based on the thickness measured in the measurement step;
An optical deflector inspection method including: A substrate having a first silicon layer and a second silicon layer;
A drive unit provided on the substrate for performing resonance drive;
A pattern portion for measuring the thickness of the second silicon layer;
An optical deflector comprising: The pattern portion is a concave portion whose side surface is the second silicon layer and whose bottom surface is the first silicon layer.
The optical deflector according to claim 2. The pattern portion is a cantilever supported by the second silicon layer.
The optical deflector according to claim 2. A mirror portion having a light reflecting surface;
A support member for supporting the mirror part,
The pattern portion is formed in the vicinity of the support member.
The optical deflector according to claim 2. A mirror portion having a light reflecting surface;
A support member for supporting the mirror part;
A protective film formed on the support member and having a thickness adjusted according to the thickness of the second silicon layer,
The optical deflector according to claim 2. An optical deflector according to any one of claims 2 to 6,
A light source for irradiating the light deflector with light;
An image projection apparatus comprising: