Light deflector and method for manufacturing the same

Abstract

The present invention provides an optical deflector and a method for manufacturing the same. The optical deflector and the method for manufacturing the same can suppress the splitting of the R portion of the coupling portion of the torsion bar (12). The optical deflector (10) comprises a mirror portion (11), a pair of torsion bars (12), an inner piezoelectric actuator (13) and a movable frame portion (14). The axial direction of the torsion bar (12) is set to a crystal orientation. <100> An R portion (31a, 31bb) is formed on the joint edge of the torsion bar (12) and the inner piezoelectric actuator (13), and the R portion is formed to face <110> The curved surface is concave inward. The waviness of the roughness curve derived from the curved surface is set within 600 nm.

Description

Technical Field

[0001] The invention relates to a MEMS light deflector and a manufacturing method thereof. Background Art

[0002] A piezoelectric MEMS optical deflector is known (for example, Patent Document 1).

[0003] In the light deflector of Patent Document 1, in order to prevent damage to the joint portion between the mirror portion and the torsion bar, an R portion recessed inward is formed at the joint edge between the mirror portion and the torsion bar.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-151476 Summary of the invention

[0007] Problems to be solved by the invention

[0008] As a general piezoelectric MEMS optical deflector, an SOI (Silicon on Insulator) wafer is used as a substrate. The crystal plane index of the main surface of a general SOI wafer is (100) or (110).

[0009] On the other hand, when the frequency of the reciprocating rotation of the mirror portion around the axis of the torsion bar is increased, it is preferred to increase the rigidity of the torsion bar in the torsion direction. <100> The light deflector is manufactured in a consistent manner.

[0010] However, when the axial crystal orientation of the torsion bar is set to <100> When the normal line on the bending line of the R part is generated, it becomes the cleavage direction of the single crystal silicon. <110> The split direction is the direction in which cracks are likely to occur and expand, so cracks will occur in this part and the torsion bar is likely to be damaged.

[0011] An object of the present invention is to provide a light deflector and a method for manufacturing the same that can suppress the splitting of an R portion provided on a coupling edge portion of a torsion bar.

[0012] Means for solving problems

[0013] The optical deflector of the present invention has:

[0014] A mirror portion capable of reciprocating about a predetermined rotation axis;

[0015] a pair of torsion bars extending from both sides of the mirror portion along the rotation axis of the mirror portion;

[0016] a frame portion surrounding the mirror portion and the pair of torsion bars;

[0017] A plurality of piezoelectric actuators are interposed between each torsion bar and the frame portion, causing each torsion bar to torsionally vibrate around the rotation axis, thereby causing the mirror portion to reciprocate around the rotation axis;

[0018] a first R portion, which is formed by a cylindrical curved surface that is recessed inward and is formed at a junction edge of each torsion bar and the mirror portion;

[0019] The second R portion is formed by a cylindrical curved surface that is recessed inward and is formed at a joint edge between each piezoelectric actuator and each torsion bar on a side facing the mirror portion.

[0020] The mirror portion, the torsion bar, and the substrate layer of the piezoelectric actuator are composed of a common single crystal silicon layer.

[0021] The crystal plane index of the main surface of the single crystal silicon layer is one of (100) and (110),

[0022] The axial direction of the torsion bar is the crystal orientation of the single crystal silicon layer. <100> ,

[0023] A predetermined portion of at least one of the first R portion and the second R portion is formed so that the unevenness with respect to the cylindrical surface is 600 nm or less.

[0024] According to the present invention, the concavity and convexity of a predetermined portion of at least one of the first R portion and the second R portion is within 600 nm relative to the cylindrical surface. This can suppress the occurrence of cleavage in at least one of the R portions.

[0025] In the light deflector of the present invention, it is preferable that both ends of the predetermined portion are set outside both ends of a central divided portion when the cylindrical surface is divided into three equal parts.

[0026] Since the axial direction of the torsion bar is the crystal orientation of the single crystal silicon layer <100> Therefore, the cleavage direction of the first R portion and the second R portion exists in the central divided portion when the cylindrical surface is divided into three equal parts. According to this structure, it is possible to ensure that cleavage in the range including the cleavage direction is suppressed in at least one of the first R portion and the second R portion.

[0027] In the light deflector of the present invention, it is preferable that a contour line when the at least one R portion is cut through a plane parallel to the main surface is set to a corrugated curve.

[0028] A mean line based on the least square method is set for the ripple curve.

[0029] The interval between the adjacent peaks of the ripple curve is set as the period,

[0030] The distance from the average line at each position on the ripple curve is set as the ripple amount,

[0031] With respect to all the periods included in the predetermined portion, the difference between the maximum ripple amount and the minimum ripple amount in each period is 600 nm or less.

[0032] According to this configuration, the amount of waviness in a predetermined portion can be suppressed, thereby suppressing the splitting of the first R portion and the second R portion.

[0033] In the light deflector of the present invention, it is preferable that the flat surface is a surface of the at least one R portion.

[0034] The surfaces of the first R portion and the second R portion exist at a shallower position than the surface of the light deflector. According to this structure, the contours of the first R portion and the second R portion can be easily detected.

[0035] In the light deflector of the present invention, it is preferable that the at least one R portion is the second R portion.

[0036] The torsion bar receives a torsion force about the rotation axis from the piezoelectric actuator and transmits it to the mirror portion. Therefore, in the operation of the light deflector, a stronger torsion force is applied to the second R portion than to the first R portion.

[0037] According to this configuration, the life of the torsion bar can be extended by suppressing unevenness in the first R portion with priority over the second R portion.

[0038] The manufacturing method of the present invention comprises the following steps:

[0039] a coating step of coating the surface of a substrate including an active layer of single crystal silicon and having a main surface with a crystal plane index of one of (100) and (110) with a photoresist film having a film thickness of 5 μm or more and 10 μm or less,

[0040] an exposure step of exposing the surface side of the substrate after the coating step through a photomask, the photomask including the mirror portion of the light deflector, the torsion bar, the piezoelectric actuator, and an outline pattern including outlines of the first R portion and the second R portion; and

[0041] The outline forming step is to form the outlines of the mirror portion, the torsion bar, the piezoelectric actuator, the first R portion, and the second R portion of the light deflector on the active layer by etching the surface side of the substrate.

[0042] According to the manufacturing method of the present invention, the amount of waviness of the curved surfaces of the first R portion and the second R portion can be kept within 600 nm, thereby suppressing the splitting of the R portion of the coupling portion of the torsion bar. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a front view of the MEMS light deflector.

[0044] Figure 2A This is a front view of an SOI wafer used for manufacturing an optical deflector.

[0045] Figure 2B This is a front view of another SOI wafer used for manufacturing an optical deflector.

[0046] Figure 3 This is an enlarged view of the range including the torsion bar.

[0047] Figure 4 This is an image of the surface stress distribution of a torsion bar based on simulation.

[0048] Figure 5 This is an image of the cross-sectional stress distribution of a torsion bar based on simulation.

[0049] Figure 6 This is a microscope observation image showing damage in a light deflector in which no measures were taken to reduce the amount of ripples in the R portion.

[0050] Figure 7 Observe from a specified direction Figure 6 SEM observation image of the fracture surface.

[0051] Figure 8 This is an explanatory diagram of the waviness amount when the JIS standard on surface roughness is applied to the curved surface of the R portion.

[0052] Fig. 9 This is a graph showing the relationship between the amount of ripples in the R portion and the H critical deflection angle.

[0053] Fig.10 This is a process diagram of a method for manufacturing a light deflector.

[0054] Fig.11 is to use Fig.10 A cross-sectional view of a light deflector manufactured by the manufacturing method.

[0055] Fig. 12A These are SEM observation images of a cross section of a resist film layer having a film thickness greater than a predetermined 10 μm and the amount of waviness when an R portion is formed using the resist film layer.

[0056] Fig. 12B These are SEM observation images of a cross section of a resist film layer having a film thickness within a predetermined range of 10 μm and an amount of waviness when an R portion is formed using the resist film layer. DETAILED DESCRIPTION

[0057] Hereinafter, a preferred embodiment of the present invention will be described in detail. In the following description, for substantially the same or equivalent elements and parts, common reference symbols are used. In addition, for elements or parts with the same structure but only different configuration positions, reference symbols with the same numbers and only different letters in the letter markings are used. Furthermore, for elements or parts with the same numbers and only different letters in the letter markings, when no distinction is made, the letters in the letter markings are omitted and only the symbols of the numbers are used for general reference.

[0058] [MEMS light deflector]

[0059] Figure 1 1 is a front view (viewed from the front side) of a MEMS optical deflector 10. The optical deflector 10 includes a mirror 11, torsion bars 12a, 12b, inner piezoelectric actuators 13a, 13b, a movable frame 14, outer piezoelectric actuators 15a, 15b, and a fixed frame 16 as main elements.

[0060] For the sake of convenience, a three-axis coordinate system consisting of an X-axis, a Y-axis, and a Z-axis is defined below. The X-axis and the Y-axis are arranged to be horizontal and vertical when viewed from the front of the light deflector 10. The Z-axis is the thickness direction of the light deflector 10. O is the center of the circular mirror portion 11.

[0061] The mirror portion 11 can reciprocate around rotation axes 22x and 22y that are orthogonal to the center O. When the mirror portion 11 faces straight ahead, the rotation axes 22x and 22y are parallel to the X-axis and the Y-axis, respectively.

[0062] A pair of torsion bars 12a and 12b extend from both sides of the mirror portion 11 along the rotation axis 22y. A pair of inner piezoelectric actuators 13a and 13b are coupled to each other in the X-axis direction to form a vertically long elliptical wheel as a whole. The elliptical wheel surrounds the mirror portion 11 and the torsion bar 12.

[0063] The movable frame 14 has an elliptical wheel shape larger than the elliptical wheel formed by the pair of inner piezoelectric actuators 13a and 13b. The elliptical wheel surrounds the elliptical wheels of the pair of inner piezoelectric actuators 13a and 13b. Each inner piezoelectric actuator 13 is connected to the inner periphery of the movable frame 14 on a straight line in the X-axis direction passing through the center O.

[0064] Each outer piezoelectric actuator 15 is disposed between the movable frame portion 14 and the fixed frame portion 16. Each outer piezoelectric actuator 15 has a plurality of cantilevers 19 whose longitudinal direction is adjusted to coincide with the Y-axis. Cantilevers 19 adjacent to each other in the X-axis direction are coupled to each other at one end and the other end in the Y-axis direction. According to the arrangement order of the cantilevers 19 in the X-axis direction, the coupling parts are alternately switched to one end and the other end in the Y-axis direction. In this way, the plurality of cantilevers 19 on each outer piezoelectric actuator 15 as a whole constitute a combination of a zigzag pattern.

[0065] The outer piezoelectric actuator 15 is driven by a driving voltage from a driving voltage supply unit (not shown) to reciprocate the movable frame portion 14 at a non-resonant frequency around a rotation axis (≠rotation axis 22x) in the X-axis direction passing through the center O. As a result, the mirror portion 11 reciprocates around the rotation axis 22x at a non-resonant frequency.

[0066] The inner piezoelectric actuator 13 is driven by another driving voltage from a driving voltage supply unit (not shown) to torsionally vibrate the torsion bar 12 about the rotation axis 22y at a resonance frequency. As a result, the mirror portion 11 reciprocates about the rotation axis 22y at the resonance frequency.

[0067] [SOI wafer]

[0068] Figure 2A and Figure 2B 1 is a front view of SOI wafers 25 a and 25 b used for manufacturing the light deflector 10 . The front surface of each SOI wafer 25 constitutes a main surface on the front side of each SOI wafer 25 .

[0069] Figure 2A and Figure 2B The coordinate axis in the figure represents the active layer 28d formed of single crystal silicon of the SOI wafer 25 ( Fig.11 The orientation plane 26 indicates the crystal orientation of the active layer 28d (single crystal silicon layer) of the SOI wafer 25.

[0070] A plurality of light deflectors 10 are cut out from each SOI wafer 25. Figure 2A and Figure 2B In FIG. 1 , the outer shape of the light deflector 10 is represented by a dotted rectangular line. The long side and the short side of the rectangle are Figure 1 The horizontal sides (long sides) and the vertical sides (short sides) of the fixing frame portion 16 in the front view of the light deflector 10 correspond to each other.

[0071] Orientation plane 26a is located at <100> Therefore, the crystal plane index of the main surface of SOI wafer 25a is (100). On the other hand, orientation plane 26b is in <110> Therefore, the crystal plane index of the main surface of the supporting layer 28b is (110).

[0072] As described later Fig.11 As described in FIG. 2 , the substrate layer of the light deflector 10 is composed of the active layer 28d of the SOI wafer 25. The dotted rectangle in FIG. 2 represents the outer shape of each light deflector 10. Therefore, the axial direction (= extension direction) of the torsion bar 12 is formed together with the SOI wafers 25a and 25b. <100> This is because, in order to increase the resonance frequency of the mirror portion 11 around the rotation axis 22y, the axial direction of the torsion bar 12 is adjusted to be consistent with <100> The axial direction of the torsion bar 12 is adjusted to be consistent with <100> When they coincide, the torsional rigidity of the torsion bar 12 becomes high.

[0073] Therefore, in the SOI wafer 25a, the axial direction of the torsion bar 12 is perpendicular to the orientation flat surface 26a. In the SOI wafer 25b, the axial direction of the torsion bar 12 is at an angle of 45° to the orientation flat surface 26b.

[0074] [Part R]

[0075] Figure 3 yes Figure 1 The center portion includes the movable frame portion 14, the mirror portion 11 surrounding the movable frame portion 14, the torsion bar 12, and the internal piezoelectric actuator 13. Figure 3 The three-axis coordinate system of X-axis, Y-axis and Z-axis and the direction of crystal orientation are shown in FIG. <100> The direction at 45° relative to the X-axis and Y-axis is consistent with <110> Consistent.

[0076] Each torsion bar 12 is coupled to the peripheral edge of the mirror portion 11 on the center O side, and is coupled to the movable frame portion 14 on the side opposite to the center O. Each inner piezoelectric actuator 13 is coupled to the torsion bars 12a and 12b at both ends of the semi-elliptical wheel shape, and is coupled to the inner periphery of the movable frame portion 14 at the center of the outer periphery of the shape.

[0077] In order to improve the strength, the edge of each torsion bar 12 that is connected to the mirror portion 11, the inner piezoelectric actuator 13, and the movable frame portion 14 is formed with an R portion 31. The R portion 31 is formed of a curved surface that is recessed inward.

[0078] In detail, the R portions 31aa and 31ba constitute the joining edge portion between each torsion bar 12 and the mirror portion 11. The R portions 31ab and 31bb constitute the joining edge portion between each torsion bar 12 and the mirror portion 11 side of the inner piezoelectric actuator 13. The R portions 31ac and 31bc constitute the joining edge portion between each torsion bar 12 and the movable frame portion 14 side of the inner piezoelectric actuator 13. The R portions 31ad and 31bd constitute the joining edge portion between each torsion bar 12 and the inner peripheral side of the movable frame portion 14.

[0079] The R portion 31 is formed to reinforce the corner portion (corner portion), but this may cause a problem in the light deflector 10. Figure 2A and Figure 2B In order to align the axial direction of the torsion bar 12 with the active layer 28d, <100> The curved surface of the R portion 31 formed on each joint edge of the torsion bar 12 includes a curved surface toward <110> The generatrix (face element) of the cleavage direction, in other words, including the normal line becomes <110> As a result, on the curved surface, splitting easily starts from the position of the generatrix.

[0080] Figure 4 : is a distribution diagram of the surface stress of the torsion bar 12 based on simulation. Figure 5 This is a diagram showing the distribution of stress in the cross section of the torsion bar 12 based on simulation. The whiter the area, the higher the stress.

[0081] from Figure 4 and Figure 5 It can be seen that, with R part 31aa, 31ba, 31ab, 31bb ( Figure 3 )The stress in the corresponding part is obviously higher than that in other parts.

[0082] Figure 6 This is a microscope observation image showing the destruction of the torsion bar 12 in the light deflector 10 in which no measures are taken to reduce the amount of waviness in the R portion 31 described later. Figure 7 Observe from a specified direction Figure 6 SEM observation image of the fracture surface 37.

[0083] exist Figure 6 In the embodiment, due to the destruction of the R portion 31, the torsion bar 12b is damaged between the mirror portion 11 and the inner piezoelectric actuator 13. Figure 7 In FIG. 1 , the fracture surface 37 and the adjacent surface 35 (the surface on the front side) and the curved surface 36 (the curved surface) are reflected together.

[0084] [Ripple Amount]

[0085] Figure 8 This is an explanatory diagram regarding the amount of waviness when the JIS standard regarding surface roughness is applied to the R portion 31. This is an explanatory diagram regarding the amount of waviness when the JIS standard regarding surface roughness is applied to the curved surface of the R portion. The JIS standard is specifically "JIS B0601-1994" and includes standards based on the JIS standard.

[0086] In "JIS B 0601-1994", regarding surface roughness, a measurement cross-sectional curve, a cross-sectional curve, a reference length, a roughness curve, a peak, a valley, a peak top, a valley bottom, and an average line are defined. Figure 8 The statements of are based on the above definitions.

[0087] The measured cross-sectional curve is a contour line when the curved surface of the R portion 31 is cut with a predetermined cross section parallel to the XY plane (e.g., a cross section passing through the center of the thickness of the Z axis). Here, the two ends of the contour line are set as the contour of the R portion 31 and the <100> The measured cross-sectional curve is in the direction of the reference length ( Figure 8 The horizontal axis of the reference length is divided into three equal parts. The length of each divided interval in the direction of the reference length is set to L.

[0088] Here, the above-mentioned JIS standard defines "ripple curve", "period" and "ripple amount" separately.

[0089] The waviness curve refers to the contour line when the R portion 31 is cut by a plane parallel to the main surface of the SOI wafer 25. In the above-mentioned JIS standard, an average line based on the least square method is set for the measured cross-sectional curve. In the next calculation of the waviness amount, an average line based on the least square method is set for the waviness curve. And, the distance from the average line at each position on the waviness curve is defined as the waviness amount.

[0090] The cycle is Figure 8 The plane is the surface of the R portion 31. The surface of the R portion 31 is located at a shallow position from the surface of the light deflector 10, and the contour of the R portion 31 is easy to measure.

[0091] exist Figure 8 In the figure, Ta, Ba represent the maximum and minimum ripple amounts in the period in which the difference between the maximum and minimum ripple amounts in the entire period of the R portion 31 is the largest. Tb, Bb represent the maximum and minimum ripple amounts in the period in which the difference between the maximum and minimum ripple amounts in the period included in the central interval when divided into three equal parts is the largest. The difference between Tb and Bb is ≤ the difference between Ta and Ba.

[0092] Fig. 9 31 and the H critical deflection angle. Here, the "H critical deflection angle" refers to the maximum deflection angle of the mirror portion 11 around the rotation axis 22y when the torsion bar 12 breaks. In order to prevent the torsion bar 12 from breaking, the light deflector 10 must be used when the deflection angle of the mirror portion 11 around the rotation axis 22y is less than the H critical deflection angle.

[0093] It should be noted that the deflection angle of the mirror portion 11 includes two deflection angles: a deflection angle around the rotation axis 22y and a deflection angle around the rotation axis 22x. When distinguishing between the two deflection angles, the deflection angle around the rotation axis 22y is referred to as the "H deflection angle", and the deflection angle around the rotation axis 22x is referred to as the "V deflection angle". When the mirror portion 11 faces straight ahead, the H swing angle and the V swing angle are both defined as 0°. In addition, the respective deflection angles are mechanical deflection angles.

[0094] exist Fig. 9 In the figure, the values ​​on the vertical axis refer to the relative values ​​of the critical deflection angle H. The critical deflection angle H = 1.0 refers to the maximum allowable value of the critical deflection angle H when the optical deflector 10 is used as a vehicle-mounted product. When the optical deflector 10 is actually sold as a product, the critical deflection angle H = 0.8 or above, which is 20% lower, needs to be guaranteed. Therefore, according to Fig. 9 It can be seen that the waviness of the curved surface of the R portion 31 only needs to be set within 600 nm.

[0095] [Suppress Cleave]

[0096] The structure for suppressing the splitting of the R portion 31 in the light deflector 10 is described. The difference between the maximum and minimum ripple amounts of each period in the predetermined portion of the R portion 31 (particularly, the R portions 31aa, 31ba and at least one of the R portions 31ab, 31bb) is 600 nm or less. Thus, even if the R portion 31 has a normal line oriented toward the crystal orientation, the R portion 31 is not more than 600 nm. <110> The part in the direction of can also effectively prevent the splitting from this part. It should be noted that at least one R part is typically R part 31ab, 31bb.

[0097] In other words, each R portion 31 is formed by a cylindrical curved surface that is recessed inward as a connecting edge between the elements. A predetermined portion of the R portion 31 is formed so that the concavity and convexity relative to the cylindrical curved surface is 600 nm or less.

[0098] Both ends of the specified part (e.g. equivalent to Figure 8 The extraction length of the two ends) is set to the outside of the two ends of the central segment when the cylindrical surface is divided into three equal parts. Figure 8 In the roughness curve, the central curve portion corresponds to the three curve portions in the direction of the reference length (horizontal axis direction).

[0099] The cylindrical surface includes the standard side surface of the cylinder (the side surface with a concave-convex 0). Further, the cylindrical surface also includes a concave-convex side surface that converges within a specified first threshold value relative to the standard side surface of the cylinder, or a concave-convex side surface that converges within a specified first threshold value and the amount of protrusion or subsidence per unit length in any direction of the side surface is within a second threshold value.

[0100] The reason for setting the two ends of the predetermined portion outside the two ends of the central divided portion is as follows. That is, the axial direction of the torsion bar 12 is the crystal orientation of the single crystal silicon layer. <100> Therefore, the cleavage direction at the R portion 31 exists in the central divided portion when the cylindrical surface is divided into three equal parts.

[0101] [Manufacturing method]

[0102] Fig.10 This is a process diagram of a method for manufacturing the optical deflector 10 in which the waviness of the R portion 31 is within 600 nm, and particularly relates to an example of an SOI processing process.

[0103] In step (STEP) 1, prepare SOI wafer 25 ( Figure 2A SOI wafer 25a or Figure 2B SOI wafer 25b).

[0104] In the next step (STEP) 2, an element formation layer 42 is formed on the surface 40 of the SOI wafer 25. Specifically, the element formation layer 42 is Fig.11 The electrode layer 42a, the piezoelectric film layer 42b and the electrode layer 42c.

[0105] Step 3 corresponds to the coating process. In step 3, the photosensitive agent 44 is dripped from the nozzle 43 onto the SOI wafer 25 with the surface 40 while the spin 45 is operated. Thus, the photosensitive agent 44 is uniformly spread on the surface of the element formation layer 42 .

[0106] In the conventional photosensitive agent coating process, AZ4620 (viscosity: 400 cSt) is used as the photosensitive agent. In addition, the spin rotation 45 is 1000 rpm to 2000 rpm. As a result, the film thickness of the resist film layer formed on the surface of the element forming layer 42 is greater than 10 μm. If the rotation speed of the spin rotation 45 is increased to reduce the film thickness of the resist film layer 48, the degree of uneven film thickness becomes greater.

[0107] On the other hand, in step 3, AZ6130 (viscosity: 70 cSt) is used as the photosensitive agent 44. In addition, the spin rotation 45 is 500 rpm to 1000 rpm. Thus, in step (STEP) 4, a resist film layer 48 having a uniform film thickness is formed on the surface side of the element formation layer 42. Thus, the film thickness of the resist film layer 48 is 5 μm or more and 10 μm or less.

[0108] It should be noted that when the film thickness is less than 5 μm, the concave and convex height difference structure of the MEMS cannot be ensured. In addition, when the film thickness exceeds 10 μm, the photosensitive agent 44 cannot be evenly coated on the surface of the element forming layer 42, and the ripple amount of the curved surface of the R portion 31 cannot be within 600 nm.

[0109] In step (STEP) 5 , a photomask 50 is covered with the SOI wafer 25 with the resist film layer 48 . The photomask 50 has a pattern 52 corresponding to the number and arrangement of the light deflectors 10 to be manufactured using one SOI wafer 25 .

[0110] In step 5 , as an exposure step of the present invention, ultraviolet light 51 is further irradiated from the surface side of the photomask 50 . The region of the pattern 52 of the photomask 50 in the resist film layer 48 is exposed to the ultraviolet light 51 .

[0111] Fig.11 This is a cross-sectional view of the light deflector 10 manufactured by further performing an etching process after step 5. The SOI wafer 25 has the following structure: a SiO2 layer 28a, a support layer 28b, a SiO2 layer 28c, an active layer 28d, and a SiO2 layer 28e are stacked from the back side to the front side of the SOI wafer 25. The element formation layer 42 is stacked with an electrode layer 42a, a piezoelectric film layer 42b, and an electrode layer 42c in this order from the SOI wafer 25 side.

[0112] The mirror portion 11 has a metal layer 54 covering the surface of the SiO2 layer 28e. The surface of the metal layer 54 constitutes a reflection surface for reflecting light incident from a light source (not shown) to the mirror portion 11. The active layer 28d forms a common substrate layer for the mirror portion 11, the inner piezoelectric actuator 13, and the outer piezoelectric actuator 15.

[0113] Fig. 12A This is an SEM observation image of a cross section of the resist film layer 48 where the film thickness of the resist film layer 48 exceeds a predetermined 10 μm and the amount of ripples on the curved surface of the R portion 31 manufactured with this film thickness. Fig. 12B The SEM observation image shows a cross section of the resist film layer 48 in which the film thickness of the resist film layer 48 is within a predetermined 10 μm, and the amount of ripples on the curved surface of the R portion 31 manufactured with this film thickness.

[0114] from Fig. 12A and Fig. 12B From the comparison of the SEM observation images, it can be understood that when the film thickness of the resist film layer 48 is less than the prescribed 10 μm, the curved surface of the R portion 31 manufactured with this film thickness can be suppressed to within the desired 600 nm.

[0115] [Variations and Supplements]

[0116] The optical deflector 10 of the embodiment is a two-axis optical deflector, that is, a scanning light from a mirror scans two-dimensionally. The optical deflector of the present invention may be a uniaxial optical deflector, that is, a scanning light from a mirror scans one-dimensionally.

[0117] The torsion bar of the optical deflector 10 of the embodiment exceeds the connection portion with the inner piezoelectric actuator 13 as a piezoelectric actuator in the Y-axis direction, reaches the inner periphery of the movable frame portion 14 (movable frame), and is connected to the inner periphery. In the optical deflector of the present invention, the torsion bar may not be connected to the movable frame portion 14 as a support portion.

[0118] In the embodiment, AZ6130 (viscosity: 70 cSt) is used as the photosensitive agent 44 of the resist film layer 48, wherein the resist film layer 48 is a photoresist film. The photosensitive agent forming the photoresist film of the present invention is not limited to any type of photosensitive agent as long as it can cover the surface side of the substrate before the exposure process with a photoresist film having a uniform film thickness of 5 μm or more and 10 μm or less.

[0119] The R portions 31aa and 31ba of the embodiment correspond to the first R portion of the present invention. The R portions 31ab and 31bb correspond to the second R portion of the present invention. Fig.10 As described in step 4 of , the entire surface 40 of the SOI wafer 25 is covered with a resist film layer 48 having a film thickness of 5 μm or more and 10 μm or less. Therefore, the amount of corrugation of not only the R portions 31aa, 31ba, 31ab, 31bb but also the other R portions 31ac, 31bc, 31ad, 31bd and the R portion of the connecting portion of the cantilever 19 connected in a zigzag pattern is within 600nm. In the present invention, the R portions whose amount of corrugation is within 600nm may be only the R portions 31ab and 31bb.

[0120] In an embodiment, as in Fig.10 As described in step 4 of , the entire surface 40 of the SOI wafer 25 is covered with a resist film layer 48 having a film thickness of 5 μm or more and 10 μm or less. Therefore, it is not limited to each cycle included in the range of the extraction length of the roughness curve of the R portion, and the difference between the maximum waviness amount and the minimum waviness amount of each cycle included in the full length of the roughness curve of the R portion can also be made less than 600 nm.

[0121] Description of symbols

[0122] 10…light deflector; 11…mirror; 12…torsion bar; 13…inner piezoelectric actuator; 14…movable frame; 22x, 22y…rotation axis; 25…SOI wafer; 28d…active layer; 31…R portion; 36…curved surface; 40…surface; 42…element forming layer; 44…photosensitive agent; 45…spin rotation; 48…resist film layer; 52…pattern.

Claims

1. A light deflector, characterized in that: have: A mirror portion capable of reciprocating about a predetermined rotation axis; a pair of torsion bars extending from both sides of the mirror portion along the rotation axis of the mirror portion; a frame portion surrounding the mirror portion and the pair of torsion bars; A plurality of piezoelectric actuators are interposed between each torsion bar and the frame portion, causing each torsion bar to torsionally vibrate around the rotation axis, thereby causing the mirror portion to reciprocate around the rotation axis; a first R portion, which is formed by a cylindrical curved surface that is recessed inward and is formed at a junction edge of each torsion bar and the mirror portion; The second R portion is formed by a cylindrical curved surface that is recessed inward and is formed at a joint edge between each piezoelectric actuator and each torsion bar on a side facing the mirror portion. The mirror portion, the torsion bar, and the substrate layer of the piezoelectric actuator are composed of a common single crystal silicon layer. The crystal plane index of the main surface of the single crystal silicon layer is one of (100) and (110), The axial direction of the torsion bar is the crystal orientation of the single crystal silicon layer. <100> , A predetermined portion of at least one of the first R portion and the second R portion is formed as follows: A contour line when a predetermined portion of at least one of the first R portion and the second R portion is cut through a plane parallel to the main surface is defined as a corrugation curve, The interval between the adjacent peaks of the ripple curve is defined as a period, A mean line based on the least square method is set for the ripple curve, and the distance of the period at each position on the ripple curve from the mean line is defined as the ripple amount. The maximum ripple amount in each cycle is defined as the maximum ripple amount. The minimum ripple amount in each cycle is defined as the minimum ripple amount. The difference between the maximum ripple amount and the minimum ripple amount of all cycles included in the specified portion is less than 600nm, Both ends of the predetermined portion are set outside both ends of a central divided portion when the cylindrical surface is divided into three equal parts.

2. The light deflector according to claim 1, characterized in that The at least one is the second R portion.

3. A method for manufacturing an optical deflector, characterized in that: The light deflector has: A mirror portion capable of reciprocating about a predetermined rotation axis; a pair of torsion bars extending from both sides of the mirror portion along the rotation axis of the mirror portion; a frame portion surrounding the mirror portion and the pair of torsion bars; A plurality of piezoelectric actuators are interposed between each torsion bar and the frame portion, causing each torsion bar to torsionally vibrate around the rotation axis, thereby causing the mirror portion to reciprocate around the rotation axis; a first R portion, which is formed by a cylindrical curved surface that is recessed inward and is formed at a junction edge of each torsion bar and the mirror portion; The second R portion is formed by a cylindrical curved surface that is recessed inward and is formed at a joint edge between each piezoelectric actuator and each torsion bar on a side facing the mirror portion. The mirror portion, the torsion bar, and the substrate layer of the piezoelectric actuator are composed of a common single crystal silicon layer. The crystal plane index of the main surface of the single crystal silicon layer is one of (100) and (110), The axial direction of the torsion bar is the crystal orientation of the single crystal silicon layer. <100> , A predetermined portion of at least one of the first R portion and the second R portion is formed such that: A contour line when a predetermined portion of at least one of the first R portion and the second R portion is cut through a plane parallel to the main surface is defined as a corrugation curve, The interval between the adjacent peaks of the ripple curve is defined as a period, A mean line based on the least square method is set for the ripple curve, and the distance of the period at each position on the ripple curve from the mean line is defined as the ripple amount. The maximum ripple amount in each cycle is defined as the maximum ripple amount. The minimum ripple amount in each cycle is defined as the minimum ripple amount. The difference between the maximum ripple amount and the minimum ripple amount of all cycles included in the specified portion is less than 600nm, The two ends of the predetermined portion are set outside the two ends of the central divided portion when the cylindrical surface is divided into three equal parts. The manufacturing method comprises the following steps: a coating step of coating the surface of a substrate including an active layer of single crystal silicon and having a main surface with a crystal plane index of one of (100) and (110) with a photoresist film having a film thickness of 5 μm or more and 10 μm or less, an exposure step of exposing the surface side of the substrate after the coating step through a photomask, the photomask including the mirror portion of the light deflector, the torsion bar, the piezoelectric actuator, and an outline pattern including outlines of the first R portion and the second R portion; and The outline forming step is to form the outlines of the mirror portion, the torsion bar, the piezoelectric actuator, the first R portion, and the second R portion of the light deflector on the active layer by etching the surface side of the substrate.

4. The method for manufacturing a light deflector according to claim 3, characterized in that: At least one of the first R portion and the second R portion is the second R portion.

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