Optical Scanning Device, Method for Manufacturing the Optical Scanning Device, and Adjustment Method

Abstract

To provide an optical scanner that can suppress generation of abnormal vibrations of a mirror part.SOLUTION: An optical scanner 1 includes a mirror part 9, semi-annular piezoelectric actuators 10a, 10b for resonance-driving the mirror part 9 around a Y-axial direction; and bellows-like piezoelectric actuator 6a, 6b for non-resonance-driving the mirror part 9 around an X-axial line. Since the reaction of the resonance frequency in the Y-axial direction and other frequencies of a plurality of unique vibration modes can cause an abnormal vibration of the mirror part 9, a weight structure 6c is provided which prevents reactions of frequencies of unique vibration modes by fixing a weight piece to the bellows-like piezoelectric actuator 6a, 6b.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an optical scanning device that operates a mirror unit to scan light, a manufacturing method thereof, and an adjustment method thereof.

Background Art

[0002] Conventionally, an optical deflector manufactured by MEMS (Micro Electro Mechanical Systems) technology and an optical scanning device including the optical deflector have been known. The optical deflector includes a mirror unit that rotates around a rotation axis, reflects light from a light source in a direction corresponding to the deflection angle of the mirror unit, and forms scanning light.

[0003] The vibrating mirror of Patent Document 1 has a mirror substrate that reflects an optical beam, two beams provided on the same straight line that support the mirror substrate, and a mirror driving means that generates a rotational force on the mirror substrate, and rotates the mirror substrate back and forth at a predetermined scanning frequency with the beam as a torsional rotation axis.

[0004] Further, a recess is formed on the surface of the mirror substrate opposite to the surface that reflects the optical beam, and a mass piece is attached to a corner of the recess at a position that is symmetric with respect to the rotation axis and symmetric with respect to the center of gravity of the mirror substrate, making the resonance frequency variable (Patent Document 1 / Paragraph 0012, FIG. 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the above vibrating mirror, variations generated in the semiconductor process during manufacturing can be corrected with the mass piece, so that the resonance frequencies of all elements within the wafer can be adjusted to the design values.

[0007] However, in a two-axis optical deflector composed of a resonance axis and a non-resonance axis, a plurality of natural vibration modes derived from a vibration system with a complex structure are generated. When the means of Patent Document 1 is applied to a two-axis optical deflector, the frequencies of other natural vibration modes that are not used for resonance driving cannot be corrected. Therefore, the frequencies of the other natural vibration modes may respond to the driving frequency of the resonance driving unit, resulting in abnormal vibrations. Furthermore, even if they do not match the frequency of a specific natural vibration mode, abnormal vibrations related to (coupled) the frequencies of a plurality of natural vibration modes may occur.

[0008] The present invention has been made in view of such circumstances, and an object thereof is to provide an optical scanning device capable of suppressing the occurrence of abnormal vibrations in a mirror unit.

Means for Solving the Problems

[0009] The optical scanning device of the first invention is an optical scanning device including a mirror unit that reflects light, a resonance driving unit that resonantly drives the mirror unit around a first axis, and a non-resonance driving unit that non-resonantly drives the mirror unit around a second axis perpendicular to the first axis, wherein the optical scanning device has a resonance frequency in the first axis direction and frequencies corresponding to a plurality of natural vibration modes different from the resonance frequency, and a weight piece having a weight that makes the frequencies of the plurality of natural vibration modes different is fixed to the non-resonance driving unit.

[0010] Since the optical scanning device of the present invention includes a resonance driving unit and a non-resonance driving unit, the mirror unit can be rotated in two axial directions to two-dimensionally scan light. When one frequency corresponding to the plurality of natural vibration modes or a frequency obtained by coupling them responds to the resonance frequency in the first axis direction, abnormal vibrations occur in the mirror unit and accurate optical scanning cannot be performed. Therefore, a weight piece is fixed to the non-resonance driving unit to adjust so that both frequencies do not respond. Thereby, the occurrence of abnormal vibrations in the mirror unit can be suppressed.

[0011] In the optical scanning device of the first invention, it is preferable that the non-resonant driving unit has a weight changing unit that houses the weight piece and changes the weight.

[0012] According to this configuration, the non-resonant driving unit includes a weight changing unit for changing the weight so that frequencies do not react with each other. Since the weight piece may be housed and fixed in the weight changing unit, frequency adjustment can be surely performed.

[0013] Further, in the optical scanning device of the first invention, it is preferable that the weight changing unit is composed of a plurality of holes to which the weight piece is fixed.

[0014] The weight changing unit is composed of a plurality of holes, and the weight is changed by fixing the weight piece in the holes. Thereby, the weight and balance of the non-resonant driving unit can be adjusted to suppress the occurrence of abnormal vibration.

[0015] Further, in the optical scanning device of the first invention, it is preferable that the weight piece is a solidified resin, metal, or resin in which fine particles are dispersed.

[0016] For example, when the weight piece is a liquid resin, the required amount is landed on the hole and solidified when it is in a liquid state. Thereby, a desired weight can be obtained.

[0017] Further, in the optical scanning device of the first invention, it is preferable that the hole is made of a material with a lyophilic bottom surface and a liquid-repellent side surface.

[0018] Since the hole is made of a material with a lyophilic bottom surface and a liquid-repellent side surface, the liquid weight piece can be repelled by the side surface and landed on the lyophilic bottom surface, and the weight can be accurately added to a desired position.

[0019] In the optical scanning device of the first invention, the non-resonant driving unit is arranged such that beams each having a plurality of piezoelectric members on the second axis are arranged adjacent to each other, and is a meander structure in which one end of adjacent beams is mechanically connected so as to be folded back, and it is preferable that the weight piece is fixed to the folded-back portion of the beam.

[0020] Since the non-resonant driving unit has the meander structure, when a voltage is applied, the displacement amounts of the minute piezoelectric members are integrated and greatly bent and deformed. Thereby, the mirror unit can be rotated non-resonantly around the second axis by non-resonant driving.

[0021] In the meander-type non-resonant driving unit, the central portion of each beam coincides with the rotation axis of the second axis, and the folded-back portions of adjacent beams have the maximum amplitude. Therefore, by providing a weight piece or a weight-changing portion at the folded-back portion, the weight balance can be efficiently changed.

[0022] The manufacturing method of the optical scanning device of the second invention is a manufacturing method of an optical scanning device including a resonant driving unit that resonantly drives a mirror unit around a first axis and a non-resonant driving unit that non-resonantly drives the mirror unit around a second axis perpendicular to the first axis, a step of forming a recess having a vertical side wall by repeating etching of a base on the back side of the non-resonant driving unit of the substrate and formation of a protective film; a step of coating the bottom surface and side surface of the recess with a polymer film; a step of removing the polymer film of the recess; and a step of fixing a weight piece having a weight that makes the frequencies of a plurality of natural vibration modes of the optical scanning device different to a hole portion from which the polymer film has been removed from the recess.

[0023] In the method for manufacturing an optical scanning device of the present invention, first, the substrate on the back side of the non-resonant driving part of the optical scanning device is etched to form a recess having a side surface substantially perpendicular to the substrate. For forming the side surface, formation of a protective film on the side surface of the recess and processing of the bottom surface of the recess are repeated. After the recess is completed, plasma treatment is performed to form a polymer film on the entire back surface of the substrate. The polymer film has low wettability with respect to almost all liquids such as water and organic solvents, and the entire back surface of the substrate becomes liquid-repellent.

[0024] Thereafter, by treatment with argon ions or the like accelerated in the direction perpendicular to the substrate, in a region parallel to the substrate, that is, the bottom surface and the side surface of the recess, the liquid-repellent thin film is removed and becomes lyophilic. Since the accelerated ions hardly collide with the side surface of the recess, most of the liquid-repellent thin film on the side surface of the recess remains. Then, by heating the substrate (200 ° C or higher), the liquid repellency of the fluorocarbon resin film on the side wall damaged by argon ions is restored. As a result, a lyophilic silicon film is exposed on the bottom surface, and a hole portion having completely changed to liquid repellency is formed on the side surface. Finally, a weight piece is fixed to the hole portion. In this way, by forming the hole portion and adjusting the weight, it is possible to manufacture an optical scanning device capable of suppressing the occurrence of abnormal vibration of the mirror portion.

[0025] The adjustment method of the optical scanning device of the third invention is an adjustment method of an optical scanning device including a mirror portion that reflects light, a resonance driving portion that resonantly drives the mirror portion around a first axis, and a non-resonance driving portion that non-resonantly drives the mirror portion around a second axis perpendicular to the first axis, A plurality of the optical scanning devices are manufactured in a wafer plane, the optical scanning device has a resonance frequency in the first axis direction and frequencies corresponding to a plurality of natural vibration modes different from the resonance frequency, and the non-resonance driving portion has a meander structure in which beams having a plurality of piezoelectric members on the second axis are arranged side by side so as to be adjacent to each other, and one end portion is mechanically connected to the adjacent beam so as to be folded back. A step of forming a plurality of optical scanning devices having a weight change portion formed of a hole portion at a folded portion of the beam; a step of measuring the weight of each of the weight change portions of the plurality of optical scanning devices; and a step of adding a weight piece to the hole portion so that the weight of the weight change portion falls within a predetermined ideal weight range.

[0026] In the adjustment method of the optical scanning device of the present invention, an optical scanning device including a resonance driving portion and a non-resonance driving portion, and rotating a mirror portion in two axial directions to two-dimensionally scan light is manufactured in a plurality on one wafer surface. The non-resonance driving portion of the optical scanning device has a meander structure. Further, a weight change portion formed of a hole portion is formed at a folded portion of the beam of the meander structure.

[0027] First, by measuring the weight of each of the weight change portions of the plurality of optical scanning devices, the weight difference between the optical scanning devices is examined. Then, a weight piece is added to the hole portion and adjusted so that the weight of the weight change portion of each optical scanning device falls within a predetermined ideal weight range. Thereby, each optical scanning device in the wafer surface can be given equivalent characteristics.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0029] Hereinafter, the optical scanning device of the present invention will be described with reference to the drawings.

[0030] (Overall Configuration) FIG. 1 shows the overall configuration of an optical scanning device 1 according to an embodiment of the present invention. The optical scanning device 1 is used, for example, in a ultra-small projector, an interactive projector, smart glasses, LiDAR (Light Detection and Ranging), an ADB (Adaptive Driving Beam) system, etc., and mainly includes an optical deflector 2, a laser light source 3, and a control device 5.

[0031] (Optical Deflector) The optical deflector 2 is manufactured using semiconductor processes and MEMS technology, and reflects light incident from a certain direction with a micromirror (mirror portion 9) that rotates, and emits it as scanning light.

[0032] A mirror portion 9, a piezoelectric actuator 10, a torsion bar 13, etc. are provided on a movable frame 8 which is an inner frame of the optical deflector 2. The laser light 4a incident from the laser light source 3 is reflected by the mirror portion 9, and the reflected light (laser light 4b) scans, for example, the projection surface of a picoprojector.

[0033] (Control Device) The control device 5 transmits control signals to the movable frame 8 and the laser light source 3. By this control signal, the piezoelectric actuator 10 in the movable frame 8 is driven, and the torsion bar 13 coupled thereto is twisted, thereby reciprocally rotating the mirror portion 9. Also, the laser light 4a of the laser light source 3 has its on / off state and brightness controlled by the control signal.

[0034] Next, with reference to FIGS. 2 and 3, the details of the optical deflector 2 will be described. First, FIG. 2 shows the front side of the optical deflector 2.

[0035] (Mirror Portion) In the stationary state, the mirror unit 9 is arranged such that the normal line extending from the center O toward the front side is directed straight ahead of the optical deflector 2. The mirror unit 9 is supported by a torsion bar 13 in the Y-axis (the “first axis” of the present invention) direction and is arranged at the center of the movable frame 8.

[0036] The reflecting surface of the mirror unit 9 is formed of a metal thin film such as Au, Pt, Al, etc. by, for example, sputtering or electron beam evaporation. Note that the shape of the mirror unit 9 is not limited to a circular shape and may be an elliptical shape or other shapes.

[0037] (Semicircular piezoelectric actuator, torsion bar) As shown in the figure, the movable frame 8 has a double structure of an inner frame body 8a and an outer frame body 8b. The piezoelectric actuator 10 is composed of a semi-circular piezoelectric actuator 10a on the left side in the front view and a semi-circular piezoelectric actuator 10b on the right side in the front view, and is placed on the upper surface of the inner frame body 8a. That is, the inner frame body 8a is an annular drive part in which piezoelectric parts are arranged side by side in an annular shape.

[0038] Also, the torsion bar 13 is composed of a torsion bar 13a on the upper side in the front view and a torsion bar 13b on the lower side in the front view. One end of the torsion bars 13a and 13b is connected to the mirror unit 9, and the other end is connected to the inner frame body 8a. By connecting the torsion bars 13a and 13b in this way, the reciprocating rotation (resonance drive according to the resonance frequency) of the mirror unit 9 in the Y-axis direction is stabilized.

[0039] The inner frame body 8a provided with the semi-circular piezoelectric actuators 10a and 10b (the “resonance drive part” of the present invention) is arranged so as to surround the mirror unit 9 from the outside. The inner frame body 8a provided with the semi-circular piezoelectric actuators 10a and 10b is connected to the torsion bars 13a and 13b on the Y-axis and is connected to the outer frame body 8b on the X-axis.

[0040] Note that the semi-circular piezoelectric actuators 10a and 10b have a structure in which a piezoelectric film of lead zirconate titanate (PZT) is sandwiched between a lower electrode and an upper electrode. By applying a voltage to the piezoelectric film through the lower electrode and the upper electrode, the semi-circular piezoelectric actuators 10a and 10b are bent and deformed, and the torsion bars 13a and 13b are twisted. Resonant driving is performed by driving the semi-circular piezoelectric actuators 10a and 10b at the frequency of the natural vibration mode in which the mirror unit 9 rotates in the Y-axis direction.

[0041] (Bellows-shaped piezoelectric actuator, beam) In the optical deflector 2, a movable frame 8 (an inner frame body 8a and an outer frame body 8b) is disposed at the center of the outer frame support 11, and bellows-shaped piezoelectric actuators 6a and 6b are disposed on both sides of the movable frame 8. The bellows-shaped piezoelectric actuators 6a and 6b (the "non-resonant driving unit" of the present invention) are coupled to the ends of the outer frame body 8b and the outer frame support 11 on the X-axis (the "second axis" of the present invention).

[0042] The bellows-shaped piezoelectric actuators 6a and 6b have a meander structure in which a plurality of piezoelectric members having beams 12 are arranged side by side with their longitudinal directions adjacent to each other and are mechanically coupled by folding back at the upper and lower ends. When voltages with different polarities are applied to the piezoelectric members of the forward path side (the odd-numbered beams from the side closer to the mirror unit 9) and the return path side (the even-numbered beams from the side closer to the mirror unit 9) of the bellows-shaped piezoelectric actuator, reverse deformations (deflections) occur in the forward path side beam and the return path side beam, respectively, and these deflections are accumulated, causing the movable frame 8 to reciprocally rotate (non-resonant driving) around the X-axis.

[0043] Alternatively, it is also possible to drive by applying sine waves, triangular waves, sawtooth waves, etc. with opposite phases to the piezoelectric members of the forward path side beam and the return path side beam. Note that there are natural vibration frequencies corresponding to a plurality of other natural vibration modes different from the frequency at which resonant driving is performed by the semi-circular piezoelectric actuators 10a and 10b.

[0044] As a result, when the optical deflector 2 reflects the laser beam 4a by the mirror portion 9, the light can be emitted forward of the optical deflector 2 and scanned in two directions of the X-axis direction and the Y-axis direction. The resonance drive around the Y-axis may be performed by an electrostatic method, an electromagnetic method, or the like in addition to the piezoelectric method.

[0045] (Electrode pad) On the left side in the front view of the outer frame support 11, electrode pads 7a-1 to 7a-8 (hereinafter referred to as electrode pads 7a) are disposed, and on the right side in the front view of the outer frame support 11, electrode pads 7b-1 to 7b-8 (hereinafter referred to as electrode pads 7b) are disposed. The electrode pads 7a and 7b are electrically connected so that a drive voltage can be applied to the electrodes of the bellows piezoelectric actuators 6a and 6b and the semi-annular piezoelectric actuators 10a and 10b.

[0046] Next, FIG. 3 shows the back side of the optical deflector 2.

[0047] (Weight structure) As shown in the figure, a weight structure 6c (the "weight changing portion" of the present invention) is provided at the folded-back portion of the piezoelectric cantilever of the bellows piezoelectric actuators 6a and 6b. In the present embodiment, the weight structure 6c is provided at all the folded-back portions, but it may be provided only at a part of the folded-back portions.

[0048] The weight structure 6c is a weight adjusting mechanism for adjusting the weights of the bellows piezoelectric actuators 6a and 6b so that the natural frequencies of a plurality of natural vibration modes not used for driving are frequencies that do not respond to the resonance frequency on the resonance axis side.

[0049] Depending on the manufacturing variations of the optical deflector 2, at least one of the frequencies of the natural vibration modes or the frequencies obtained by combining a plurality of natural vibration modes may respond to the resonance frequency and induce abnormal vibrations. The optical deflector 2 is usually formed simultaneously in a plurality of pieces on a single wafer, but the variations within the wafer surface differ in degree depending on the position, and it is difficult to design so as to prevent abnormal vibrations over the entire surface. Therefore, it is necessary to adjust the weight by the weight structure 6c.

[0050] (Rib of the mirror part) As shown in the figure, a rib 9a is provided on the back side of the mirror part 9. The rib 9a has a circular shape along the shape of the mirror part 9, and further has a cross structure that divides the circular shape into four parts in order to suppress deformation of the mirror part 9. A weight structure (additional weight accommodation hole) may be provided at the center part (small circle) of the rib 9a.

[0051] (Method for manufacturing an optical scanning device) As a feature of the present invention, adding a weight piece to the non-resonant drive part can be mentioned. The weight structure 6c is composed of a plurality of additional weight accommodation holes 14, and a liquid resin (such as epoxy resin), a liquid resin in which fine particles are dispersed, or a metal such as solder is landed and solidified at the bottom of the additional weight accommodation hole 14 using an inkjet dispenser. This operation is performed at a stage prior to singulating the chip for the optical deflector 2.

[0052] The optical deflector 2 is manufactured with a plurality of devices arranged in parallel on one wafer. Before adding the weight piece, each device is manufactured except for the part of the weight piece. Then, the resonance frequency used for driving the semi-circular piezoelectric actuators 10a and 10b of the mirror part 9 of the chip for the optical deflector 2 (the electrode pads 7a and 7b are already formed) and the natural vibration modes not used for driving are measured with a laser Doppler meter (for example, MSA600 manufactured by Polytec).

[0053] Thereafter, the relationship between the bellows-shaped piezoelectric actuators 6a and 6b, the weight of the mirror part 9 (the abdomen of the vibrating element), and the frequencies of each natural vibration mode is obtained by the finite element method, and a necessary and sufficient weight range (ideal weight range) is acquired so that abnormal vibration is not induced. Note that as the ideal weight range, the ideal design values of devices in which pre-designed abnormal vibration does not occur may be used.

[0054] Next, the weight structures 6c provided on the bellows-shaped piezoelectric actuators 6a and 6b, and the height and area of the ribs 9a on the mirror part 9 (back side) are measured with a shape inspection device, and for all the devices on the wafer, it is determined whether the weight of the "vibration elements (especially the folded parts of the mirror part 9 and the bellows-shaped piezoelectric actuators 6a and 6b)" is within the ideal weight range. Note that, anticipating that weight will ultimately be added to match the appropriate value, the design weight of each device may be made lighter than the ideal weight.

[0055] Regarding the weights of the multiple "vibration elements" each device has, if even one is not within the ideal weight range, ink (droplets that will become weight pieces) is selectively driven into the additional weight accommodation holes 14 with a non-contact inkjet dispenser (for example, AEROJET manufactured by Musashi Engineering) to bring all the "vibration elements" within the ideal weight range.

[0056] Note that by forming additional weight accommodation holes 14 or providing weight pieces at the folded parts of the bellows-shaped piezoelectric actuators 6a and 6b, the natural vibration modes not used for driving can be adjusted, and weight pieces can be provided to the weight structure (additional weight accommodation hole) at the center of the rib 9a on the back side of the mirror part 9 to adjust the resonance frequency used for resonance driving.

[0057] FIG. 4 is an enlarged view of the region R of the optical deflector 2 (back side) in FIG. 3. As shown in the figure, a weight structure 6c is provided at the folded part of the piezoelectric cantilever of the bellows-shaped piezoelectric actuator 6b, and the weight structure 6c is composed of five additional weight accommodation holes 14a to 14e. Note that the shapes of the additional weight accommodation holes 14 and the weight structure at the center of the rib 9a may be elliptical or rectangular.

[0058] Also, FIG. 5 is a cross-sectional view taken along the line V-V of the region R in FIG. 4. The position where the weight structure 6c is provided is on the back side of the bellows-shaped piezoelectric actuator 6b. The additional weight accommodation hole 14b of the weight structure 6c is a hole part capable of accommodating ink.

[0059] Since the minimum droplet diameter (ink dimension) of a commercially available inkjet dispenser is about 50 μm and the landing accuracy is about ±50 μm, in order to land the ink in the additional weight accommodation hole 14 and the weight structure at the center of the rib 9a, it is preferable that the hole diameter is at least twice the ink dimension. Further, in order for the landed ink to be fixed near the center of the additional weight accommodation hole 14, it is preferable that the hole diameter is not more than four times the ink dimension. The details of the method for forming the additional weight accommodation hole 14 will be described later.

[0060] The weight of the ink discharge unit is preferably in the range of 0.01 to 1.00% with respect to the weight of the weight structure 6c added to the bellows piezoelectric actuator 6b. A plurality of additional weight accommodation holes 14 can be provided for one weight structure 6c (not limited to five), and the arrangement can be one-dimensional (linear) or two-dimensional (triangular or square matrix). Further, a plurality of inks can be accommodated in the additional weight accommodation hole 14.

[0061] When there are a plurality of additional weight accommodation holes 14, in order to maintain the weight balance of the folded portion, it is preferable to land the ink from the center of gravity position (in the example of FIG. 4, the central additional weight accommodation hole 14c) and then land the ink sequentially in the direction away from it. When it is found that there is an inherent lack of balance due to the misalignment of the lithography alignment, it is possible to adjust the landing position according to the amount of misalignment of the alignment of the weight structure 6c.

[0062] After the ink has landed on each device, the entire wafer is heated to solidify the ink in the additional weight accommodation hole 14. As the material of the ink, any material may be used as long as it is liquid at a temperature of 150° C. or lower and is irreversibly cured (solidified) by means such as heating or light irradiation.

[0063] Specifically, a thermosetting organic substance such as a liquid epoxy resin, a silicone resin, or a urethane resin, a photocurable organic substance such as a UV-curable acrylic resin, or a solution in which fine solder balls are dispersed can be used. It is also possible to disperse a high-density substance such as metal fine particles or ceramic fine particles in the curable organic substance to enhance the effect of the weight load.

[0064] If necessary, a chip on the wafer can be randomly selected by a laser Doppler meter, the driving frequency of the natural vibration mode and other natural vibration frequencies can be measured, and it can be confirmed whether the deviation amount is within a predetermined range. If it exceeds the predetermined range, a weight-frequency calibration curve is drawn again, an additional weight for recorrection is calculated, and the weight is added by an inkjet dispenser.

[0065] (Method for forming a weight structure) Next, with reference to FIGS. 6 and 7, among the manufacturing methods of the optical scanning device 1, a method for forming the weight structure 6c in particular will be described. Note that the following forming method can also be applied to the weight structure at the center of the rib 9a of the mirror unit 9.

[0066] As a preparation step 1 (STEP1), an SOI (Silicon On Insulator) substrate 20 shown in FIG. 6 is prepared. The SOI substrate 20 is composed of a silicon oxide (SiO2) film 21 (1 μm), a silicon device layer 22 (50 μm), a silicon oxide (SiO2) film 23 (1 μm), a silicon handle layer 24 (350 μm), and a silicon oxide (SiO2) film 25 (1 μm). The silicon device layer 22 and the silicon handle layer 24 are lyophilic (contact angle is 20° or less) with respect to the resin-based ink.

[0067] Note that the lower silicon oxide (SiO2) film 21 side in FIG. 6 is the surface side of the optical deflector 2, and it is assumed that processing of the bellows-shaped piezoelectric actuators 6a and 6b, the mirror unit 9, the semi-annular piezoelectric actuators 10a and 10b, etc. has already been completed.

[0068] In order to form the weight structure 6c (additional weight accommodation hole 14) on the silicon handle layer 24 side of the SOI substrate 20, each of the following semiconductor process steps is performed. As step 2 (STEP2), a photoresist 26 is applied to the surface of the silicon handle layer 24 (silicon oxide film 25), and a pattern is drawn using a photomask.

[0069] Next, reactive ion etching using CF4 (carbon tetrafluoride) gas or the like is performed to selectively remove the silicon oxide film 25 on the back surface, and the photoresist is removed by oxygen plasma treatment. Then, a shallow recess 14' is formed by reactive ion etching (RIE: Reactive Ion Etching) of the plasmaized SF6 (sulfur hexafluoride) gas using the patterned silicon oxide film 25 as a mask.

[0070] As step 3 (STEP3), the entire recess 14' is coated with a protective film (coating with a CxFy polymer) by plasma treatment of C4F8 (cyclobutane octafluoride) gas. Subsequently, reactive ion etching treatment of the plasmaized SF6 gas is performed. As a result, the ionized SF6 component accelerated in the vertical direction collides and the protective film 30 at the bottom of the recess 14' is removed, and the silicon handle layer 24 is etched. Note that since the protective film 30 on the side surface of the recess 14' does not collide with the SF6 component, the etching does not proceed.

[0071] By repeating the formation of the protective film 30 by C4F8 gas plasma and the removal of the protective film 30 at the bottom surface of the recess 14' and the etching of the silicon handle layer 24 by reactive ion etching treatment of the plasmaized SF6 gas several tens to several hundreds of times, the recess 14' is dug vertically downward.

[0072] As step 4 (STEP4), the above deep etching anisotropy etching is performed until reaching the silicon oxide film 23. Since the reactivity of the plasmaized SF6 gas with respect to the silicon oxide film 23 is significantly lower than the reactivity with respect to silicon, the etching spontaneously stops when it reaches the silicon oxide film 23.

[0073] Next, reactive ion etching is performed using CF4 (carbon tetrafluoride) gas or the like to remove the silicon oxide film 23 on the bottom surface of the recess 14'. At this time, the surface of the protective film 30 on the side surface of the recess 14' is altered, and part of it maintains liquid repellency (contact angle of 50° or more), while part of it becomes hydrophilic. Note that if left in this state, the ratio of liquid repellency to hydrophilicity will vary greatly depending on the processing conditions, so the stability as an ink receptor cannot be maintained. Note that in STEP4 of FIG. 6, the altered protective film 30 on the side surface of the recess 14' is omitted.

[0074] Next, as step 5 (STEP5) shown in FIG. 7, again, a plasma treatment of C4F8 (cyclobutane octafluoride) gas is performed to form and coat a carbon fluoride polymer film 31 on the entire surface (side surface, upper surface, and bottom surface) of the recess 14'.

[0075] The plasma treatment in step 5 (STEP5) is preferably performed for a longer time than the plasma treatment in step 3 (STEP3), and particularly preferably for 10 times or more the time. The polymer film 31 is preferably thicker than the protective film 30 immediately after being formed in step 3 (STEP3), and particularly preferably has a thickness of 10 times or more.

[0076] As step 6 (STEP6), the polymer film 31 on the bottom surface and the upper surface (excluding the side surface) of the recess 14' is selectively removed by argon ion treatment accelerated by an electric field in the vertical direction. Here, since the polymer film 31 on the side surface of the recess 14' does not collide with argon ions, etching does not progress.

[0077] Note that the surface of the polymer film 31 on the side surface of the recess 14' may be altered by a small amount of argon ions other than the vertical component, resulting in deterioration of liquid repellency. Therefore, as step 7 (STEP7), the SOI substrate 20 is heated at 200°C or higher to restore the liquid repellency of the polymer film 31 (side surface).

[0078] Through the above steps, the side surface of the concave portion 14’ becomes completely liquid-repellent, and the hydrophilic silicon device layer 22 is exposed on the bottom surface. Note that when the substrate (silicon handle layer 24) is extremely thick, depending on the thickness of the silicon oxide film 25, the silicon oxide film 25 may disappear in the process of repeating step 3 (STEP3).

[0079] In step 2 (STEP2), the process can be advanced without removing the photoresist 26, and after step 4 (STEP4) in which the concave portion 14’ is completed, the photoresist 26 can be removed by oxygen plasma to avoid the consumption of the silicon oxide film 25. As a result, the additional weight accommodation hole 14 is formed, and a weight piece is fixed to the additional weight accommodation hole 14.

[0080] FIG. 8 shows a state in which the weight piece 15 solidified in the additional weight accommodation hole 14 is fixed. If the contact angle between the ink and the bottom surface is 20° or less, the ink wets and spreads on the bottom surface, and the end of the ink is constrained by the liquid-repellent side surface. Therefore, in the additional weight accommodation hole 14, a weight piece with an arc-shaped cross section is fixed to the silicon device layer 22.

[0081] The weight piece 15 has a shape obtained by cutting a part of a sphere in the circular additional weight accommodation hole 14. The weight piece 15 is an organic substance such as resin or a metal such as solder, and is a different material from the silicon device layer 22, the silicon oxide film 23, and the silicon handle layer 24. The weight piece 15 is separated from the polymer film 31 on the side surface and is not fixed. In this way, the optical scanning device 1 capable of suppressing the occurrence of abnormal vibration of the mirror unit 9 can be manufactured.

[0082] The optical scanning device 1 of the present embodiment is manufactured in a plurality on one wafer surface. Specifically, by executing the above-described STEP1 to STEP7, a plurality of optical scanning devices 1 are formed in the wafer surface. However, since the weight of each optical scanning device 1 is slightly different, the frequencies of the natural vibration modes are also different.

[0083] Each optical scanning device 1 has a weight structure 6c formed by additional weight accommodation holes 14 at the folding parts of the beams of bellows-shaped piezoelectric actuators 6a, 6b (meander structure). Therefore, the weight can be adjusted using the weight structure 6c (additional weight accommodation holes 14).

[0084] First, by measuring the weight of each of the weight structures 6c of the plurality of optical scanning devices 1, the weight difference between the optical scanning devices 1 is examined. Then, a weight piece 15 is added to the additional weight accommodation hole 14 so that the weight of the weight structure 6c of each optical scanning device 1 falls within a predetermined ideal weight range for adjustment. Thereby, each optical scanning device 1 within the wafer surface can be given equivalent characteristics.

[0085] As described above, the embodiments for carrying out the present invention have been explained, but the present invention is not limited to the above embodiments, and can be appropriately modified without departing from the gist of the present invention.

[0086] The weight structure 6c is preferably provided at the folding part of the piezoelectric cantilever of the bellows-shaped piezoelectric actuators 6a, 6b (on the back side), but is not limited to this position. However, the position on the X-axis line becomes a vibration node and the displacement amount is the smallest, so it is not suitable as the position of the weight structure 6c.

Explanation of reference numerals

[0087] 1... optical scanning device, 2... optical deflector, 3... laser light source, 4a, 4b... laser light, 5... control device, 6a, 6b... bellows-shaped piezoelectric actuator, 6c... weight structure, 7a1~7a8, 7b1~7b8... electrode pads, 8... movable frame, 8a... inner frame body, 8b... outer frame body, 9... mirror part, 9a... rib, 10... piezoelectric actuator, 10a, 10b... semi-annular piezoelectric actuator, 11... outer frame support, 12... (bellows-shaped) beam, 13, 13a, 13b... torsion bar, 14... additional weight accommodation hole, 14’... recess, 15... weight piece, 20... SOI substrate, 30... protective film, 31... polymer film.

Claims

1. A mirror unit that reflects light, A resonance driving unit that resonantly drives the mirror unit, A non-resonance driving unit that non-resonantly drives the mirror unit, and an optical scanning device comprising: A weight piece having a weight is fixed to the non-resonance driving unit, The non-resonance driving unit has a weight changing unit that houses the weight piece and changes the weight, The weight changing unit is composed of a plurality of holes to which the weight piece is fixed, The resonance driving unit and the non-resonance driving unit rotate the mirror unit in directions orthogonal to each other. An optical scanning device characterized by this.

2. The optical scanning device according to claim 1, wherein the weight piece is a solidified resin, metal, or resin in which fine particles are dispersed.

3. The optical scanning device according to claim 1 or 2, wherein the hole is made of a material with a lyophilic bottom surface and a liquid-repellent side surface.

4. The non-resonance driving unit is a meander structure in which beams having a plurality of piezoelectric members are arranged side by side so as to be adjacent to each other, and one end portion is mechanically connected to the adjacent beam so as to fold back, The optical scanning device according to any one of claims 1 to 3, wherein the weight piece is fixed to the folded-back portion of the beam.

5. A method for manufacturing an optical scanning device including a resonance driving unit that resonantly drives a mirror unit and a non-resonance driving unit that non-resonantly drives the mirror unit, wherein the resonance driving unit and the non-resonance driving unit rotate the mirror unit in directions orthogonal to each other, A step of forming a recess having a vertical side wall by repeating etching of the substrate on the back side of the non-resonance driving unit and forming a protective film, A step of coating the bottom surface and the side surface of the recess with a polymer film, A step of removing the polymer film on the bottom surface while leaving the polymer film on the side surface of the recess, A step of fixing a weight piece having a weight that makes the frequencies of a plurality of natural vibration modes of the optical scanning device different to a hole formed by removing the polymer film from the concave portion; A method for manufacturing an optical scanning device, characterized by comprising the above.

6. An adjustment method for an optical scanning device including a mirror unit that reflects light, a resonance drive unit that resonantly drives the mirror unit, and a non-resonance drive unit that non-resonantly drives the mirror unit, wherein the resonance drive unit and the non-resonance drive unit rotate the mirror unit in directions orthogonal to each other, comprising: A plurality of the optical scanning devices are manufactured within a wafer surface; The non-resonance drive unit has a meander structure in which beams each having a plurality of piezoelectric members are arranged side by side such that adjacent beams are adjacent to each other, and one end portion thereof is mechanically connected so as to be folded back with respect to the adjacent beam; A step of forming a plurality of optical scanning devices each having a weight change portion formed of a hole portion at a folded-back portion of the beam; A step of adding a weight piece to the hole portion; An adjustment method for an optical scanning device, characterized by comprising the above.

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