JP7447594B2 - Device manufacturing method and device - Google Patents

Description

The present invention relates to a device manufacturing method and a device.

BACKGROUND ART MEMS (Micro Electro Mechanical Systems) devices that use magnetic materials, piezoelectric films, electrostatic forces, or the like as actuators are known. For example, a scanner device having a reflective surface for the purpose of optical scanning, a pressure sensor using a membrane structure, an acceleration sensor/gyro that detects fluctuations in the weight of a double-supported beam, and the like are known. These are mainly manufactured by forming minute movable parts using SOI (Silicon On Insulator) wafers, and by forming various members such as functional films or protective films on the surface layer of SOI wafers. .

Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2017-074625) discloses that in order to arbitrarily change the thickness of the active layer, a local thick film of SiO ₂ is formed by performing oxidation after forming grooves by microloading. , a technique using a sacrificial layer is disclosed.

However, there is room for improvement in that the formation of various members on the surface layer of a structure obtained using an SOI wafer causes local stress and strain in the structure.

Furthermore, in the case of the structure disclosed in Patent Document 1, the thick SiO ₂ film is formed as a sacrificial layer and is therefore removed during the manufacture of the structure. Therefore, when a member is formed on the surface of the structure disclosed in Patent Document 1, there is a concern that distortion may occur due to local stress.

The present invention has been made in view of the above-mentioned problems, and aims to provide a method for manufacturing a device and a device that can suppress defects such as distortion in a structure.

In order to solve the above-mentioned problems and achieve the objects, the present invention provides a method for manufacturing a device having a stress-targeted portion, which comprises a first silicon layer, a first silicon oxide layer, and a second silicon layer. a first step of forming a groove pattern in a second silicon layer of a stacked body having a second silicon layer, and a second silicon oxide layer and a common silicon layer on the second silicon layer from the second silicon layer side. A second step of laminating and forming a second silicon oxide layer to form a common silicon layer, and a third step of forming a stress target portion at a position where at least a portion of the common silicon layer faces the groove pattern. a fourth step of removing the first silicon layer; and a fifth step of oxidizing the second silicon layer in which the groove pattern is formed, The second silicon oxide layer at a position overlapping with the stress target part includes a thicker region than the second silicon oxide layer at a position not overlapping with the stress target part .

According to the present invention, it is possible to suppress inconveniences such as distortion in the structure.

FIG. 1 is a diagram showing the system configuration of an optical scanning system according to a first embodiment. FIG. 2 is a diagram showing the hardware configuration of the optical scanning system according to the first embodiment. FIG. 3 is a diagram showing the functional configuration of the control device. FIG. 4 is a flowchart showing the flow of optical scanning of a surface to be scanned in the optical scanning system of the first embodiment. FIG. 5 is a diagram for explaining the packaging of the optical deflector provided in the optical scanning system of the first embodiment. FIG. 6 is a plan view of the optical deflector, and is a view of the optical deflector viewed from the front side (reflecting surface side). FIG. 7 is a perspective view of the optical deflector viewed from the front side. FIG. 8 is a diagram for explaining the configuration and function of a mirror section that is a movable section of the optical deflector. FIG. 9 is a diagram showing the flow of a formation process for forming a local SiO ₂ layer for a mirror portion. FIG. 10 is a perspective view showing the positional relationship between the dielectric multilayer film, the groove pattern section, and the step pattern section. FIG. 11 is a diagram for explaining a modification of the mirror section. FIG. 12 is a diagram showing an example in which a MEMS device of a displacement detection system such as an acceleration sensor or a gyro sensor is provided with two SiO ₂ layers. FIG. 13 is a diagram showing an example in which a membrane type pressure sensor is provided with two SiO ₂ layers. FIG. 14 is a diagram showing a car equipped with a head-up display device including an optical deflector according to the second embodiment. FIG. 15 is a block diagram showing the configuration of the head-up display device 500. FIG. 16 is a diagram showing an optical writing device in the third embodiment. FIG. 17 is a diagram showing the configuration of main parts of the optical writing device. FIG. 18 is a diagram showing an automobile equipped with a laser radar device according to the fourth embodiment. FIG. 19 is a block diagram of the main parts of the laser radar device.

Hereinafter, an optical scanning system according to an embodiment will be described with reference to the accompanying drawings.

(overview)
First, in explaining the optical scanning system of the embodiment, an outline of a MEMS (Micro Electro Mechanical Systems) device will be explained. MEMS devices have been developed in which functional structures are formed on silicon wafers (Si wafers) using semiconductor technology. To give an example, such MEMS devices include, for example, an acceleration sensor, a pressure sensor, a mirror device, and the like.

In the case of an acceleration sensor, a weight structure supported on all sides by beams is formed by penetrating or thinning a part of the Si wafer through a process such as etching. Acceleration is then detected by detecting the displacement of the weight due to inertial force in response to external acceleration by the deformation of the beams on all sides.

In the case of a pressure sensor, it is formed by forming a membrane portion on a thin film and sealing one side of the membrane portion to create a vacuum. The pressure sensor formed in this manner detects pressure by detecting deformation of the membrane due to pressure fluctuations.

As a mirror device, a scanning mirror device, etc., which scans a mirror portion supported by a beam structure in one axis or two axes, and the like are known.

Such MEMS devices are required to perform large displacements with small forces. For this reason, it is desirable to make the movable part (beam part or membrane part) as thin as possible. In addition, in order to detect mechanical displacement by converting it into an electrical signal, or to convert an electrical signal into mechanical force and drive it, the surface layer of the structure is equipped with wiring, a protective film, and a functional layer. It is common to form a member such as a membrane.

However, since this thinning is made to a thickness of several to several tens of um, it is greatly influenced by the stress of the members themselves, such as the surface protective film and functional film. This stress causes an offset output due to displacement to occur in the sensor system even under normal conditions. Further, in the drive system, deviations from desired drive characteristics occur.

In order to alleviate the influence of such stress, film structure design is performed to bring the stress of the surface protective film close to zero. In the case of semiconductor processes such as general circuit wiring, stress control is also possible. However, it is practically difficult to apply the above structural design to members such as ceramic materials such as piezoelectric films, upper and lower electrodes thereof, or thick laminated film constituent materials such as mirror reflection films.

In such a case, there is a method of optimizing the thickness of the BOX layer of the SOI (Silicon on Insulator) wafer to alleviate the stress. However, in that case, the entire BOX layer becomes thicker, which causes process problems due to substrate warpage. Moreover, distortion occurs in the entire chip due to stress from the BOX layer.

In the embodiment described below, a three-layer cavity SOI is used, and a narrow gap groove pattern is locally formed in the intermediate layer. The groove pattern is formed in a region of the MEMS device where a member to which strong stress is applied, such as the piezoelectric film or antireflection film described above, is formed. When this groove pattern portion is oxidized, Si (silicon) forming the groove pattern portion becomes SiO ₂ (silicon dioxide) and expands in volume. A wide SiO ₂ region is formed by this Si oxidation treatment. Then, it becomes possible to form a thick SiO ₂ layer only at desired locations, that is, only at locations where the narrow gap groove pattern portions are formed.

Since the thickness of the SiO ₂ layer can be adjusted by adjusting the thickness of the intermediate layer of the 3-layer SOI, the stress value can be adjusted freely. In addition, since a standard BOX layer may be used except for this thick SiO ₂ layer forming portion, it is possible to avoid warping during the process and distortion when chipping is performed.

[First embodiment]
Hereinafter, as a first embodiment, an optical scanning system to which a scanning mirror device, which is one of such MEMS devices, is applied will be described.

(System configuration)
FIG. 1 is a diagram showing the system configuration of an optical scanning system according to a first embodiment. As shown in FIG. 1, the optical scanning system 10 includes a control device 11, a light source device 12, and an optical deflector 13 having a reflective surface 14. The optical deflector 13 is a scanning mirror device. Such an optical scanning system 10 deflects the light emitted from the light source device 12 by the reflective surface 14 of the optical deflector 13 under the control of the control device 11 to optically scan the surface to be scanned 15 .

The control 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, for example, a MEMS (Micro Electromechanical Systems) device that has a reflective surface 14 and that the reflective surface 14 is movable. The light source device 12 is, for example, a laser device that emits laser light. Note that the scanned surface 15 is, for example, a screen.

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

The light source device 12 irradiates light based on the input drive signal.

The optical deflector 13 moves the reflective surface 14 in at least one of a uniaxial direction and a biaxial direction based on the input drive signal.

As a result, the optical scanning system 10 reciprocates the reflective surface 14 of the optical deflector 13 in two axial directions under the control of the control device 11 based on image information, which is an example of optical scanning information, so that the reflective surface 14 By deflecting and optically scanning the irradiation light from the light source device 12 that enters the surface, an arbitrary image can be projected onto the surface to be scanned 15 .

(Hardware configuration)
Next, FIG. 2 is a diagram showing the hardware configuration of the optical scanning system 10. As shown in FIG. 2, the optical scanning system 10 includes a control device 11, a light source device 12, and an optical deflector 13, each of which is electrically connected.

Among these, the control 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 24, a light source device driver 25, and an optical deflector driver 26.

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

The RAM 21 is a volatile storage device that temporarily holds 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. There is.

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

The external I/F 24 is an interface with, for example, an external device or a network. External devices include, for example, host devices such as PCs (Personal Computers), storage devices such as USB memory, SD cards, CDs, DVDs, HDDs, and SSDs. Further, the network is, for example, a CAN (Controller Area Network) of an automobile, a LAN (Local Area Network), the Internet, or the like. The external I/F 24 may have any configuration as long as it enables connection or communication with an external device, and an external I/F 24 may be provided for each external device.

The light source device driver is an electric circuit that outputs a drive signal such as a drive voltage to the light source device 12 according to an input control signal.

The optical deflector driver 26 is an electric circuit that outputs a driving signal such as a driving voltage to the optical deflector 13 according to an input control signal.

In the control device 11, the CPU 20 acquires optical scanning information from an external device or network via the external I/F 24. Note that any configuration may be sufficient as long as the CPU 20 can acquire the optical scanning information, and the optical scanning information may be stored in the ROM 22 or FPGA 23 in the control device 11. A configuration may also be adopted in which a storage device is provided and the optical scanning information is stored in the storage device.

Here, the optical scanning information is information indicating how to scan the scanned surface 15 with light. For example, when displaying an image by optical scanning, the optical scanning information is image data. Further, for example, when optical writing is performed by optical scanning, the optical scanning information is write 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 that indicates the timing and irradiation range of irradiation with light for object recognition.

(Functional configuration of control device)
FIG. 3 is a diagram showing the functional configuration of the control device 11. As shown in FIG. The control device 11 realizes the functions of the control section 30 and the drive signal output section 31 using instructions from the CPU 20 and the hardware configuration shown in FIG.

The control unit 30 is realized by, for example, the CPU 20, the FPGA 23, etc., 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 section 30 constitutes a control means, acquires image data as optical scanning information from an external device, etc., generates a control signal from the image data through predetermined processing, and outputs it to the drive signal output section 31.

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

The drive signal is a signal for controlling the drive of the light source device 12 or the optical deflector 13. For example, in the light source device 12, it is a drive voltage that controls the irradiation timing and irradiation intensity of light emitted from the light source. Further, for example, in the optical deflector 13, it is a driving voltage that controls the timing and operating range of operating the reflective surface 14 of the optical deflector 13. Note that the control device may acquire the irradiation timing and light reception timing of the light emitted from the light source from an external device such as the light source device 12 and the light receiving device, and synchronize these with the drive of the optical deflector 13.

(Light scanning processing)
FIG. 4 is a flowchart showing the flow of optical scanning of the surface to be scanned 15 by the optical scanning system 10. In the flowchart of FIG. 4, in step S11, the control unit 30 acquires optical scanning information from an external device or the like.

In step S12, the control section 30 generates a control signal from the acquired optical scanning information, and outputs the control signal to the drive signal output section 31.

In step S13, the drive signal output section 31 outputs a drive signal to the light source device 12 and the optical deflector 13 based on the input control signal.

In step S14, the light source device 12 performs light irradiation based on the input drive signal. Further, the optical deflector 13 operates the reflective 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 control device 11 has the device and function of controlling the light source device 12 and the optical deflector 13, but the control device for the light source device and the control device for the optical deflector, It may be provided separately.

Further, in the optical scanning system 10, the functions of the control section 30 of the light source device 12 and the optical deflector 13 and the function of the drive signal output section 31 are provided in one control device 11, but these functions are provided as separate units. For example, a drive signal output device having a drive signal output section 31 may be provided separately from the control device 11 having the control section 30. Note that in the optical scanning system 10, the optical deflector 13 having the reflective surface 14 and the control device 11 may constitute an optical deflection system that performs optical deflection.

(Packaging)
FIG. 5 is a diagram for explaining the packaging of the optical deflector 13. As shown in FIG. 5, the optical deflector 13 is attached to a mounting member 802 disposed inside a package member 801, and a part of the package member is covered with a transparent member 803 to seal the package. will be processed.

Furthermore, the inside of the package is sealed with an inert gas such as nitrogen. This suppresses deterioration of the optical deflector 13 due to oxidation, and further improves durability against environmental changes such as temperature.

(Configuration of optical deflector)
FIG. 6A is a plan view of the optical deflector 13, and is a view of the optical deflector viewed from the front side (reflecting surface side). FIG. 7 is a perspective view of the optical deflector 13 viewed from the front side. In FIGS. 6(a) and 7, the optical deflector 13 rotates a movable part having a reflective surface to direct light incident on the reflective surface in one axis direction (around axis A parallel to the X axis). This is an optical deflector with a support structure at both ends.

The optical deflector 13 has a structure that allows the mirror section 110 to rotate around the axis A. That is, the optical deflector 13 deflects the light incident on the mirror section 110 by rotating the mirror section 110 in the uniaxial direction, thereby enabling scanning in the uniaxial direction.

The optical deflector 13 includes a mirror section 110 having a reflective surface 112 that reflects incident light, torsion beams 120a and 120b, connecting sections 131a and 131b, connecting sections 132a and 132b, and driving sections 140a and 140b. It has a fixing part 150 and an electrode connecting part 160.

The optical deflector 13 is constructed by, for example, molding a single SOI (Silicon On Insulator) substrate by etching or the like, and forming the reflective surface 112 and the driving parts 140a and 140b on the molded substrate, so that each component is It is integrally formed. Note that the formation of each of the above components may be performed after molding the SOI substrate, or may be performed during molding of the SOI substrate.

The mirror section 110 is rotatable about the axis A, and has a mirror section base 111 having a circular, elliptical, polygonal, etc. shape, and a mirror section formed on the +Z side surface of the mirror section base 111. It has a reflective surface 112. The mirror base 111 is composed of, for example, a silicon active layer 103. The reflective surface 112 is made of a metal thin film containing, for example, aluminum, gold, silver, or the like.

Further, in the mirror portion 110, ribs for reinforcing the mirror portion may be formed on the -Z side surface of the mirror portion base 111. The rib is composed of, for example, a silicon support layer 101 and a silicon oxide layer 102, and suppresses distortion of the reflective surface 112 caused by movement.

The center (center of gravity) of the mirror portion 110 is located, for example, on the axis A, which is the central axis of the torsion beams 120a and 120b. However, the center (center of gravity) of the mirror portion 110 may be offset with respect to the axis A, which is the central axis of the torsion beams 120a and 120b.

The connecting portion 131a and the connecting portion 131b are rectangular cantilevers provided in a straight line so as to bridge the opposing inner peripheral surfaces of the fixing portion 150. One end of the connecting parts 131a and 131b is connected to the fixing part 150, and the other ends of the connecting parts 131a and 131b are connected to each other.

Similarly, the connecting portion 132a and the connecting portion 132b are rectangular cantilevers provided in a straight line so as to bridge the opposing inner peripheral surfaces of the fixing portion 150. One ends of the connecting parts 132a and 132b are connected to the fixing part 150, and the other ends of the connecting parts 132a and 132b are connected to each other. The connecting portions 131a and 131b and the connecting portions 132a and 132b are arranged with the mirror portion 110 in between, for example, so as to be axisymmetric with respect to an axis parallel to the Y-axis passing through the center of the reflective surface 112.

The connecting portions 131a, 131b, 132a, and 132b can be formed from a material selected from, for example, Si, Al2O3, SiC, and SiGe. The connecting portions 131a, 131b, 132a, and 132b are preferably made of Si, since an SOI substrate can be used for manufacturing the optical deflector 13. When the optical deflector 13 is formed from an SOI substrate, the connecting portions 131a, 131b, 132a, and 132b are formed from the silicon active layer 103, for example.

The torsion beams 120a and 120b are a pair of elastic support parts that have one end connected to the mirror base 111, extend in the axis A direction, and support the mirror part 110 movably around the axis A. Torsion beams 120a and 120b are composed of silicon active layer 103, for example.

The other end of the torsion beam 120a is connected to a connection point between the connecting portion 131a and the connecting portion 131b. The other end of the torsion beam 120b is connected to a connection point between the connecting portion 132a and the connecting portion 132b. The longitudinal direction of the torsion beam 120a and the longitudinal direction of the connecting parts 131a and 131b are perpendicular, and the longitudinal direction of the torsion beam 120b and the longitudinal direction of the connecting parts 132a and 132b are perpendicular.

In this way, the connecting part 131a and the connecting part 131b are arranged on both sides of the axis A which is the central axis of the torsion beam 120a, and the connecting part 132a and the connecting part 132b are the central axis of the torsion beam 120b. They are arranged on both sides of axis A. The mirror part 110 and the torsion beams 120a and 120b are supported from both sides of the fixed part 150 by the connecting parts 131a and 131b and the connecting parts 132a and 132b. The four connection points between the connecting parts 131a and 131b and the connecting parts 132a and 132b and the fixed part 150 are fixed ends.

The drive unit 140a has strip-shaped drive elements 141a and 141b whose longitudinal direction is perpendicular to the axis A (direction parallel to the Y-axis). The drive element 141a is formed on the surface of the connection part 131a (the surface on which the reflective surface 112 is formed), and the drive element 141b is formed on the surface of the connection part 131b. The driving elements 141a and 141b are arranged symmetrically with respect to the axis A, for example.

Similarly, the drive unit 140b has strip-shaped drive elements 142a and 142b whose longitudinal direction is perpendicular to the axis A (direction parallel to the Y-axis). The drive element 142a is formed on the surface of the connection part 132a, and the drive element 142b is formed on the surface of the connection part 132b. The drive elements 142a and 142b are arranged symmetrically with respect to the axis A, for example.

Drive elements 141a, 141b, 142a, and 142b are piezoelectric elements. The fixing part 150 is, for example, a rectangular support body formed to surround the mirror part 110. Note that the fixing part 150 does not need to be formed to completely surround the mirror part 110, and for example, it is also possible to provide an open part in the vertical direction in FIG. 6(a).

The electrode connection part 160 is formed, for example, on the +Z side surface of the fixing part 150. The electrode connection portion 160 is electrically connected to, for example, each upper electrode and each lower electrode of the drive elements 141a, 141b, 142a, and 142b via an electrode arrangement made of aluminum (Al) or the like. The electrode connection section 160 is electrically connected to, for example, a control device placed outside the optical deflector 13. Note that the upper electrode and/or the lower electrode may each be directly connected to the electrode connecting portion 160, or may be indirectly connected by, for example, connecting the electrodes to each other. Note that in FIGS. 6A and 7, illustration of electrode wiring including the wiring 108 and the like is omitted.

Further, as long as the mirror section 110 can be driven around the axis A, the shape of each component is not limited to the shape of the embodiment. For example, the torsion beams 120a and 120b, the connecting portions 131a and 131b, and the connecting portions 132a and 132b may have a shape with curvature.

Alternatively, the mirror section 110 may be directly connected between the connecting sections 131a and 131b and the connecting sections 132a and 132b without providing the torsion beams 120a and 120b. In the example of the first embodiment, the mirror section 110 and the torsion beams 120a and 120b are the movable sections, but if the torsion beams 120a and 120b are not provided, only the mirror section 110 is the movable section.

Further, an insulating layer made of a silicon oxide layer or the like may be formed on at least one of the +Z side surfaces of the upper electrodes of the drive parts 140a and 140b and the +Z side surface of the fixed part 150.
Although FIG. 6A shows an optical deflector 13 having a so-called double-end type structure in which the mirror portion 110 and torsion beams 120a and 120b are arranged on both sides with respect to the axis A, the optical deflector 13 is As shown in FIG. 6(b), it may be a so-called cantilever type structure that does not have the connecting portions 131b and 132b and the driving elements 141b and 142b.

At this time, the electrode wiring is provided on the insulating layer, and the insulating layer may be partially removed or no insulating layer formed as an opening only at the connection spot where the upper electrode or the lower electrode and the electrode wiring are connected. preferable. This improves the degree of freedom in designing the driving portions 140a and 140b as well as the electrode wiring, and further suppresses short circuits due to contact between electrodes. Further, the silicon oxide layer 102 may have a function as an antireflection material.

In this way, in the optical deflector 13, the mirror part 110 and the torsion beams 120a and 120b, which are movable parts, are attached to the fixed part 150 to swing around the axis A via the connecting parts 131a and 131b and the connecting parts 132a and 132b. Possibly supported. By using the inverse piezoelectric effect of the driving elements 141a, 141b, 142a, and 142b of the driving parts 140a and 140b, the connecting parts 131a and 131b and the connecting parts 132a and 132b are vibrated, and the connecting parts 131a and 131b and the connecting parts are vibrated. The vibration of the portions 132a and 132b can be converted into torsion of the torsion beams 120a and 120b, thereby exciting the vibration of the mirror portion 110. That is, the driving parts 140a and 140b can swing the movable parts by deforming the connecting parts 131a and 131b and the connecting parts 132a and 132b.

Specifically, when a voltage is applied to the drive elements 141a, 141b, 142a, and 142b in the Z direction, the drive elements 141a, 141b, 142a, and 142b contract in the in-plane direction. Thereby, as a bimorph with the silicon active layer 103, displacement in the rotational direction about the axis A can be applied to the torsion beams 120a and 120b.

(Configuration and function of mirror part)
Next, the configuration and function of the mirror section 110, which is the movable section of the optical deflector 13, will be explained. First, FIG. 8(a) shows a cross-sectional view of a general mirror portion as a comparative example. As shown in FIG. 8(a), the mirror section usually has a structure in which an active layer 211, a support layer 213, and a BOX layer 212 of an SOI wafer 210 are laminated, and a weight section 232 is supported by a beam section 233. ing.

In the mirror section of this comparative example, since the mirror member 209 is supported by a beam structure, there is a problem in that the beam section 233 is deflected, as shown in FIG. 8(b). Further, a reflection improving member may be provided on the mirror member 209 in order to improve reflectance. As this reflection improving member, for example, Al (aluminum), Au (gold), Ag (silver), or the like is used. Further, the reflection improving member may be formed of a reflection increasing film made of a dielectric multilayer film.

However, since the dielectric multilayer film forming the reflection improving member has a total thickness of more than 1 μm, the reflection improving member is disposed at a position in the supporting layer 213 opposite to the active layer 211. It is difficult to suppress surface deformation using only the ribs 238, which are the frame. When surface deformation occurs, the mirror becomes a convex mirror as shown in FIG. 8(b), causing the inconvenience that the reflected light diverges. Furthermore, if the frame area is increased, the weight of the entire mirror section increases, which may make it difficult to drive the optical deflector 13 at high speed and at a wide angle.

Therefore, in the case of the mirror unit 110 of the optical scanning system according to the embodiment, as shown in _FIG . 243 locally. Thereby, surface deformation of the entire mirror portion 110 can be suppressed. Furthermore, the thick SiO ₂ layer 243 has a smaller effect on the overall weight of the mirror section 110 than the frame region, and suppresses surface deformation of the entire mirror section 110 with a lighter member compared to the case where the frame region is provided. be able to. Therefore, high-speed driving and wide-angle driving of the optical deflector 13 can be maintained.

(Formation process of mirror part)
FIG. 9 is a diagram showing the flow of the formation process for forming the local SiO ₂ layer 243 for the mirror section 110. The example shown in FIG. 9 is a process for forming the mirror section 110 that controls stress on the dielectric multilayer film (reflection increasing film) 222, which is a reflection improving member. This is also a process for forming a semiconductor device with a three-layer SOI structure in which a silicon film is formed on an insulator layer inside a silicon wafer.

First, as shown in FIG. 9A, a support layer 213, a BOX layer 216 (an example of an insulator layer), and an SOI active layer 215 are stacked to form an SOI wafer 210. The combined thickness of the SOI active layer 215 and the BOX layer 216 is equal to the thickness of the SiO ₂ layer 245 that generates stress corresponding to the stress applied to the dielectric multilayer film 222 (an example of a stress target part) formed in a later process. Almost equivalent.

Next, as shown in FIG. 9(b), a groove pattern portion 234 (an example of a groove portion) is also removed at the location where the thick SiO ₂ layer 243 of the SOI wafer 210 is to be formed. A step pattern portion 235 is formed at each location by etching. As the etching method, photolithography in a semiconductor process, anisotropic etching using ICP etching, etc. can be used. Note that the formation of the step pattern portion 235 is optional.

Here, although this is just an example, it is desirable that the groove pattern formed in the groove pattern section 234 has a narrow pitch. For example, the Si width is preferably about 0.1 um to 0.5 um. Further, as an example, it is desirable that the ratio of Si and groove width be close to "1:1.3". In this case, the groove pattern portion 234 is formed with Line/Space=0.1 um/0.13 um.

Next, as shown in FIG. 9(c), a Si wafer 270 provided with SiO ₂ films 271 and 272 is attached to the surface layer of the SOI wafer 210 on which groove pattern portions 234 and step pattern portions 235 are formed at desired locations. match. Direct bonding can be used as this bonding method. Other bonding techniques may also be used, such as thermal diffusion bonding, plasma activated bonding, or room temperature activated bonding. Note that depending on the Si bonding method using the bonding method, the SiO ₂ films (thermal oxide films) 271 and 272 may be omitted.

Next, as shown in FIG. 9(d), the bonded Si wafers 270 are polished to a desired thickness to form a three-layer cavity SOI.

Next, a pattern is formed on the three-layer cavity SOI to form a reflection improving member (reflection increasing film) 222, as shown in FIG. 9(e). As a method for forming this pattern, in addition to formation by photolithography and etching, lift-off using a resist pattern, etc. can be used. Note that pattern formation is performed after alignment with respect to the groove pattern portion 234 and the dielectric multilayer film 222.

Next, as shown in FIGS. 9(f) and 9(g), a structure is formed by an etching process from the back side of the SOI wafer 210. At this time, as shown in FIG. 9(f), an etching stop occurs due to the BOX layer 216 (SiO ₂ film). Therefore, as shown in FIG. 9(g), the BOX layer 216 and the SiO ₂ film 272 at two locations, one where the groove pattern is provided and the other where the step pattern is provided, are removed at once. do.

Finally, as shown in FIG. 9H, the groove pattern portion 234 (the groove pattern portion 234 on the back side of the dielectric multilayer film 222) corresponding to the stress-applied portion of the dielectric multilayer film 222 is oxidized. As a result, Si is combined with O, that is, Si is oxidized, and the volume expands (2.3 times the theoretical value), so that the groove pattern portion 234 is filled with SiO ₂ . In other words, the thickness of the SiO ₂ layer 245 expanded in the groove pattern portion 234 is thicker than the SiO ₂ film 272, which is an insulator layer.

Since the thickness of the SiO ₂ layer 245 can be set by the thickness of the SOI active layer 215, the thickness of the SiO ₂ layer 245 can be changed according to the stress of the dielectric multilayer film 222, making stress control easy.

Furthermore, since the region other than the groove pattern portion 234 is oxidized to only about 50% of the Si line width of the groove pattern portion 234, it is not easily affected by stress due to the newly formed SiO ₂ layer 245.

Further, the oxidation treatment shown in FIG. 9(h) may be performed by heat treatment in an oxygen atmosphere, or by oxidation treatment by exposure to a hydrogen peroxide solution or an ozone atmosphere.

Further, the thickness of the uppermost silicon layer forming the three-layer cavity SOI structure (thickness of the silicon layer on which the dielectric multilayer film 222 is placed) is thinner than the silicon layer forming the lowermost support layer 213. . This allows the mirror section 110 to be moved easily.

FIG. 10 is a perspective view showing the positional relationship among the dielectric multilayer film 222, the groove pattern section 234, and the step pattern section 235. As an example, the dielectric multilayer film 222, the groove pattern section 234, and the step pattern section 235 have an elliptical overall shape. The groove pattern portions 234 and the step pattern portions 235 are alternately formed to have an elliptical shape having substantially the same center as the center of the ellipse that is the shape of the dielectric multilayer film 222 . As described above, by oxidizing the groove pattern portion 234, the SiO ₂ layer 245 is formed and the groove pattern portion 234 is filled. This SiO ₂ layer 245 can cope with the stress of the dielectric multilayer film 222.

Note that it is possible to counteract the stress of the dielectric multilayer film by increasing the thickness of the entire BOX layer of the SOI wafer and leaving beams or the like on the back side of the structure. However, in this case, a strong stress is always applied to the entire wafer, resulting in disadvantages such as inhibiting process flow due to the effects of warping, or causing the entire chip to warp when it is made into chips.

On the other hand, in the case of the above-mentioned example of the embodiment, since the thick SiO ₂ layer 234 is formed only in necessary locations, the stress when looking at the entire wafer and chip is lower than that of the conventional SOI wafer. Since the stress is equivalent to only the stress generated from the BOX layer, there will be no problem such as inhibition of process flow due to warping or the like, or warping of the entire chip when it is made into chips.

(Modified example of mirror part)
The above embodiment was an example in which the SiO ₂ layer 244 was provided so that the dielectric multilayer film 222 would not be deformed due to stress. In contrast, as shown in FIG. 11, a concave mirror portion 260 with a predetermined radius of curvature is formed on the front side of the structure, and a thick layer is formed on the back side of the structure to support this mirror portion 260. A membrane SiO ₂ layer may also be provided. This allows it to function as a condensing lens, for example.

(Application example for other MEMS devices)
The above-described embodiment was an example in which the SiO ₂ layer 243 was provided for the optical deflector 13, which is a scanning mirror device, but even if the SiO ₂ layer 243 is provided for other MEMS devices, the above-mentioned You can get the same effect as .

For example, FIG. 12 shows an example in which an SiO ₂ layer 243 is provided in a MEMS device for displacement detection such as an acceleration sensor or a gyro sensor. A displacement detection MEMS device such as an acceleration sensor or a gyro sensor shown in FIG. A structure is formed that is supported by beam portions 233 that are part of the structure. Acceleration, angular acceleration, etc. are detected from the amount of strain in the beam portion when the piezoelectric film 221 is displaced in a specific direction due to acceleration or inertial force.

Regarding the amount of strain mentioned above, a piezoelectric film 221 made of a ferroelectric material (PZT) or a non-ferroelectric material (AlN) is formed on the upper surface of the beam 233, and electric charges are generated as the beam 233 is displaced. In addition to the method of detecting strain from the amount, there is a method of injecting B (boron) or P (phosphorus) into a part of the beam portion 211 to form a strain resistance.

Here, the beam portion 233 needs to be formed thin or thin so that even a slight displacement can be detected through the piezoelectric film 221. Therefore, when the piezoelectric film 221 or a protective film for strain resistance is formed on the upper surface of the beam 233, the beam 233 is deflected due to the stress from the piezoelectric film 221, as shown in FIG. 12(b). Occur.

If the beam portion 233 is deflected in a steady state where no acceleration is applied, an offset will occur in the output of the piezoelectric film 221, and the linearity of the output signal will be impaired due to the structural imbalance, which is not desirable.

For this reason, as shown in FIG. 12(c), a SiO ₂ layer (oxide film) 243 is formed on the opposite side of the piezoelectric film 221 of the beam portion 233 and the active layer 211 so as to generate the same stress. establish. Thereby, stress from the piezoelectric film 221 can be suppressed by the SiO ₂ layer (oxide film) 243, and deflection of the beam portion can be prevented.

Moreover, FIG. 13 is an example in which a SiO ₂ layer 243 is provided in a membrane type pressure sensor. This pressure sensor has a membrane structure, as shown in FIG. 13(a), and one side of the membrane structure is vacuum-sealed using a sealing package 250. Thereby, the inside of the space 251 can be brought into a vacuum state, and a pressure difference is created via the membrane 236.

The membrane 236 is displaced toward the space 251 according to the pressure difference, as shown in FIG. 13(b). At this time, the amount of displacement changes in response to pressure fluctuations on the space 237 side, so it functions as a pressure sensor.

However, like the above-mentioned acceleration sensor, etc., in the membrane type pressure sensor, pressure is always applied to the edge of the membrane 236, so the membrane 236 may be displaced even in a steady state. . This makes it difficult to accurately detect small pressure changes, resulting in a problem of unreliable detection accuracy.

For this reason, as shown in FIG. 13(c), a thick SiO ₂ layer 243 is provided on the space 237 side of the membrane 236. Thereby, the state of the membrane 236 in a steady state can be maintained in a flat state in which no displacement occurs. Therefore, small pressure changes can be detected accurately, and detection accuracy can be improved.

(Effects of the first embodiment)
As is clear from the above description, the optical scanning system of the first embodiment uses a three-layer cavity SOI for the optical deflector 13, which is a scanning mirror device, and has a narrow gap groove pattern section in the intermediate layer. 234 (see FIG. 9) is formed locally. The groove pattern portion 234 is located at a position on the Si wafer 270 that is opposite to a region of the optical deflector 13 where a strong stress film such as the dielectric multilayer film (return-enhancing film) 222 is formed (a region where stress occurs). formed so that at least a portion of the After forming the groove pattern portion 234, the groove pattern portion 234 is subjected to oxidation treatment.

As a result, in the narrow gap groove pattern portion 234, Si (silicon) is converted to SiO ₂ (silicon dioxide), and a wide SiO ₂ region is formed by volume expansion. Then, a thick SiO ₂ layer 243 is formed only at desired locations. Therefore, the stress applied to the dielectric multilayer film (return increasing film) 222 can be suppressed (cancelled) by the stress of the thick SiO ₂ layer 243. Therefore, by forming various films on the surface layer of the SOI wafer, it is possible to prevent the disadvantage of distortion occurring in the structure due to local stress.

Moreover, since the thickness of the SiO ₂ layer can be adjusted by adjusting the thickness of the intermediate layer of the 3-layer SOI, the stress value can be adjusted freely. In addition, since a standard BOX layer may be used except for this thick SiO ₂ layer forming portion, it is possible to avoid the influence of warpage during the process or the influence of strain when chipping is performed.

[Second embodiment]
Next, the second embodiment will be explained. This second embodiment is an example in which the above-described optical deflector 13 is applied to an image projection device. FIG. 14 is a diagram showing an automobile 400 equipped with a head-up display device 500, which is an example of an image projection device. Further, FIG. 15 is a block diagram showing the configuration of the head-up display device 500.

As shown in FIG. 14, the head-up display device 500 is installed, for example, near a windshield (windshield 401, etc.) of an automobile 400. Projection light L emitted from the head-up display device 500 is reflected by the windshield 401 and is directed toward the viewer (driver 402) who is the user.

Thereby, the driver 402 can visually recognize the image projected by the head-up display device 500 as a virtual image. Note that a combiner may be installed on the inner wall surface of the windshield, and a configuration may be adopted in which the user can visually recognize the virtual image by the projection light reflected by the combiner.

As shown in FIG. 15, in the head-up display device 500, laser light is emitted from red, green, and blue laser light sources 501R, 501G, and 501B. After the emitted laser light passes through an input optical system consisting of collimator lenses 502, 503, 504 provided for each laser light source, two dichroic mirrors 505, 506, and a light amount adjustment section 507, The light is deflected by the above-mentioned optical deflector 13 having a reflective surface 14.

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

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

The head-up display device 500 projects the intermediate image displayed on the intermediate screen 510 onto the windshield 401 of the automobile 400, thereby allowing the driver 402 to view the intermediate image as a virtual image.

Laser beams of each color emitted from laser light sources 501R, 501G, and 501B are made into substantially parallel beams by collimator lenses 502, 503, and 504, respectively, and combined by two dichroic mirrors 505 and 506. The light intensity of the combined laser beams is adjusted by a light intensity adjustment unit 507, and then two-dimensionally scanned by an optical deflector 13 having a reflective surface 14. The projection light L that has been two-dimensionally scanned by the optical deflector 13 is reflected by the free-form mirror 509 to correct distortion, and then is focused on the intermediate screen 510 to display an intermediate image. The intermediate screen 510 is composed of a microlens array in which microlenses are two-dimensionally arranged, and magnifies the projected light L incident on the intermediate screen 510 in units of microlenses.

The optical deflector 13 moves the reflective surface 14 back and forth in two axial directions, and scans the projection light L incident on the reflective surface 14 two-dimensionally. The drive control of this optical deflector 13 is performed in synchronization with the emission timing of the laser light sources 501R, 501G, and 501B.

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

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

In addition, image projection devices can be used not only for vehicles and mounting parts, but also for mobile objects such as aircraft, ships, and mobile robots, or for work robots that operate drive objects such as manipulators without moving from the location. It may also be mounted on a non-mobile object.

As described above, by using the semiconductor device according to this embodiment in an image projection apparatus, an image projection apparatus can be realized in which various disadvantages resulting from distortion of the semiconductor device caused by local stress on a certain member are suppressed. can do.

[Third embodiment]
Next, a third embodiment will be explained. This third embodiment is an example in which the above-described optical deflector 13 is applied to an optical writing device. FIG. 16 is an example of an image forming apparatus incorporating an optical writing device 600. Further, FIG. 17 is a diagram showing the configuration of main parts of the optical writing device.

As shown in FIG. 16, the optical writing device 600 is used as a component of an image forming apparatus, such as 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 photoreceptor drum by optically scanning the photoreceptor drum, which is the scanned surface 15, with one or more laser beams.

As shown in FIG. 17, in an optical writing device 600, a laser beam from a light source device 12 such as a laser element passes through an imaging optical system 601 such as a collimator lens, and then passes through an optical deflector 13 having a reflective surface 14. Deflected in one or two axes.

The laser beam deflected by the optical deflector 13 then passes through a scanning optical system 602 consisting of a first lens 602a, a second lens 602b, and a reflective mirror section 602c, and then passes through a scanning optical system 602 that includes a surface to be scanned 15 (for example, a photoconductor drum or a photoconductor). paper) to perform optical writing. The scanning optical system 602 forms a spot-shaped light beam on the surface to be scanned 15 .

Further, the light source device 12 and the optical deflector 13 having the reflective surface 14 are driven under the control of the control device 11 .

In this way, the optical writing device 600 can be used as a component of an image forming apparatus having a laser beam printer function.

In addition, by changing the scanning optical system to enable light scanning not only in one axis but also in two directions, laser label devices that print by deflecting laser light onto thermal media, scanning it, and heating it, etc. It can be used as a component of an image forming apparatus.

The optical deflector 13 with the reflective surface 14 applied to the above-mentioned optical writing device consumes less power for driving than a rotating polygon mirror using a polygon mirror, etc., so it can save power in the optical writing device. advantageous to

Further, since the wind noise generated when the optical deflector 13 vibrates is smaller than that of a rotating polygon mirror, it is advantageous for improving the quietness of the optical writing device. The optical writing device requires much less installation space than a rotating polygon mirror, and the amount of heat generated by the optical deflector 13 is small, so it is easy to miniaturize the optical writing device. It's advantageous.

As described above, by using the semiconductor device according to this embodiment in an optical writing device, an optical writing device can be obtained in which various disadvantages resulting from distortion of the semiconductor device caused by local stress on a certain member are suppressed. can be realized.

[Fourth embodiment]
Next, a fourth embodiment will be described. This fourth embodiment is an example in which the above-described optical deflector 13 is provided in a laser radar device that is an example of an object recognition device. FIG. 18 is a diagram showing an automobile 701 equipped with a laser radar device 700. In FIG. 18, a laser radar device 700 recognizes a target object 702 by optically scanning the target direction and receiving reflected light from the target object 702 existing in the target direction.

FIG. 19 is a block diagram of main parts of the laser radar device 700. As shown in FIG. 19, the laser beam emitted from the light source device 12 passes through an input optical system consisting of a collimator lens 703, which is an optical system that converts diverging light into substantially parallel light, and a plane mirror 704. Scanning is performed in one or two axial directions by an optical deflector 13 having a reflective surface 14.

The light is then irradiated onto a target object 702 in front of the apparatus through a light projecting lens 705, which is a light projecting optical system. The driving of the light source device 12 and the optical deflector 13 is controlled by the control device 11. The reflected light reflected by the target object 702 is detected by a photodetector 709.

That is, the reflected light is received by the image sensor 707 through a condenser lens 706 or the like 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 ranging circuit 710.

The distance measuring circuit 710 determines the target object based on the time difference between the timing when the light source device 12 emits the laser beam and the timing when the photodetector 709 receives the laser beam, or the phase difference between each pixel of the image sensor 707 that receives the laser beam. The presence or absence of the target object 702 is recognized, and further distance information to the target object 702 is calculated.

The optical deflector 13 having the reflective surface 14 is less likely to be damaged than a polygon mirror and is smaller, so it is possible to provide a compact radar device with high durability.

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

In the object recognition device described above, the laser radar device 700 was explained as an example, but the object recognition device performs optical scanning by controlling the optical deflector 13 having the reflective surface 14 with the control device 11, and performs optical detection. Any device may be used as long as the device recognizes the target object 702 by receiving reflected light by a device, and is not limited to the embodiment described above.

For example, biometric authentication that recognizes objects by calculating object information such as shape from distance information obtained by optically scanning a hand or face and recording and referencing it, and recognizing intruders by optically scanning a target area. The present invention can also be similarly applied to security sensors that calculate and recognize object information such as shape from distance information obtained by optical scanning, and components of three-dimensional scanners that output as three-dimensional data.

As described above, by using the semiconductor device according to this embodiment in an object recognition device, an object recognition device can be realized in which various disadvantages resulting from distortion of the semiconductor device caused by local stress on a certain member are suppressed. can do.

Finally, each of the embodiments described above is presented as an example, and is not intended to limit the scope of the present invention. Each of the novel embodiments can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the gist of the invention. Further, each embodiment and modifications of each embodiment are included within the scope and gist of the invention, and are included within the scope of the invention described in the claims and its equivalents.

10 Optical scanning system 11 Control device 12 Light source device 13 Light polarizer 14 Reflection surface 15 Scanning surface 110 Mirror portion 210 SOI wafer 213 Support layer 214 SiO ₂ film 215 SOI active layer 216 BOX layer 234 Groove pattern portion 271 SiO ₂ film 272 SiO ₂ film 222 Dielectric multilayer film (reflection improvement member)
243 SiO ₂ layer

JP2017-074625A

Claims (7)

A method of manufacturing a device having a stressed portion, the method comprising:
a first step of forming a groove pattern in the second silicon layer of a stacked body including a first silicon layer, a first silicon oxide layer, and a second silicon layer;
A second silicon oxide layer and a common silicon layer are stacked on the second silicon layer so that the second silicon oxide layer and the common silicon layer are stacked from the second silicon layer side. The process of
a third step of forming the stress target portion on the common silicon layer at a position at least partially facing the groove pattern;
a fourth step of removing the first silicon layer;
a fifth step of oxidizing the second silicon layer on which the groove pattern is formed;
including;
In the stacking direction of the laminate, the second silicon oxide layer at a position overlapping with the stress target part includes a thicker region than the second silicon oxide layer at a position not overlapping with the stress target part.
A method of manufacturing a device having a stressed portion. The method for manufacturing a device having a stress-targeted portion according to claim 1, wherein in the groove pattern, the groove width is wider than the silicon width. 3. The method of manufacturing a device having a stressed portion according to claim 2, wherein the silicon width is 0.1 um to 0.5 um. 3. The method of manufacturing a device having a stressed portion according to claim 1, wherein the common silicon layer is formed in the second step so that the thickness is thinner than the first silicon layer. a common silicon layer;
a first member provided on one surface of the common silicon layer; a second member provided on one surface of the common silicon layer;
a stress target portion provided on the other surface of the common silicon layer,
The first member is
having a structure in which a first silicon layer, a first silicon oxide layer, a second silicon layer, and a second silicon oxide layer are stacked toward the common silicon layer,
The second member is a third silicon oxide layer,
At least a portion of the second member is provided at a position facing the stress target portion with respect to the common silicon layer ,
In the stacking direction, the second silicon oxide layer at a position overlapping with the stress target part includes a thicker region than the second silicon oxide layer at a position not overlapping with the stress target part. device. 6. The device of claim 5, wherein the third silicon oxide layer is thicker than the second silicon oxide layer. 7. A device according to claim 5 or claim 6, characterized in that the common silicon layer has a thickness thinner than the first silicon layer.

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