JP5934621B2 - Manufacturing method of optical deflector - Google Patents

Description

  The present invention relates to a method of manufacturing a MEMS (Micro Electro Mechanical Systems) optical deflector equipped in an optical scanner or the like.

  2. Description of the Related Art In recent years, as one form of an image display device, a projection display has been proposed in which light from a light source is deflected and projected onto a screen using an optical deflector, and an image is projected on the screen. Examples of the optical deflector include a MEMS optical deflector in which mechanical parts such as a mirror and a piezoelectric actuator are integrally formed on a semiconductor substrate as a MEMS device using a semiconductor process or a micromachine technique (for example, patent document). 1).

  In this optical deflector, one end of the piezoelectric actuator is connected to and supported by a frame portion (support portion), and torque generated by the piezoelectric actuator is transmitted to a torsion bar (elastic beam) connected to the other end. The previously installed mirror is swung (reciprocating). Such an optical deflector has an advantage that a large driving force can be obtained with a small and simple structure. Each optical deflector element is processed into a pattern after batch processing of a silicon wafer, and then cut out as a single piece by a dicing process, and then mounted on a package such as a ceramic product.

  The element structure of the optical deflector is connected to an actuator by supporting a mirror having a diameter of about 1 mm with a thin torsion bar. As the torsion bar is twisted by the movement of the actuator, the mirror swings. By irradiating the oscillating mirror with a laser beam, a one-dimensional or two-dimensional scanning beam is obtained. A relatively wide space is provided around the mirror so as not to prevent the mirror from swinging. In particular, in a two-dimensional optical deflector that simultaneously swings one mirror around two orthogonal rotation axes, the ratio of the area of the movable portion to the entire element is large.

  In the process of dividing a processed wafer into chips by the most general blade dicing for such an element structure, the element structure of the MEMS optical deflector is broken when high-pressure pure water hits the processed wafer. This problem occurs.

  In order to avoid this problem, there is a method of attaching a protective tape to the surface of the processed wafer. However, when the tape is peeled later, there is a problem that the element structure of the MEMS optical deflector is broken. Even if a tape whose adhesive strength is weakened by ultraviolet irradiation or heat treatment is used, 100% element damage cannot be prevented for a complicated structure on the processed wafer surface. Even when a resist is applied without using a tape to form a protective layer, there is a problem in that the element structure is damaged in the process of removing the resist later.

  As means for solving such a problem, a wafer level package has been recently developed in which dicing is performed after securing a mirror swing space by bonding to a glass wafer or the like at the wafer level.

  FIG. 11 shows a schematic diagram of a wafer level package. 11A is a perspective view of the packaged wafer 400 of the MEMS optical deflector, and FIG. 11B is a cross-sectional view of the optical deflector 405 as one chip as one section of the packaged wafer 400.

  In FIG. 11A, the packaged wafer 400 has a sandwich structure in which the main body wafer 401 is sandwiched between the front side glass wafer 402 and the back side glass wafer 403 as transparent sealing material wafers from both the front and back sides. The packaged wafer 400 of FIG. 11A is diced vertically and horizontally along the dicing line 404, whereby a plurality of optical deflectors 405 are cut out.

  In FIG. 11B, the main body wafer 401 includes a BOX (Buried Oxide) layer 414, an SOI (Silicon on Insulator) layer 415 and a handle layer 416 that are stacked on the front and back sides of the BOX layer 414. The internal space 410 is formed inside the optical deflector 405, and the mirror unit 411 and the actuator element 412 are formed by etching the SOI layer 415. The internal space 410 is formed on the lower surface and the back side of the front glass wafer 402. It is defined by the upper surface of the glass wafer 403 and the inner peripheral surface of the main body wafer 401, and has a volume that accommodates the mirror portion 411 and the like and allows the displacement of the mirror portion 411.

  In the case of the optical deflector 405 having the structure shown in FIG. 11, there is no problem of structural damage of the mirror unit 411 and the actuator element 412 in the dicing process. However, in the optical deflector 405, it is necessary to form a silicon through electrode (TSV) 409 or to form a through electrode 413 on the glass wafers 402 and 403, which complicates the process and increases the manufacturing cost. There is.

JP 2010-128116 A

  In order to solve this problem, Deep-RIE processing is performed first on the back side of the optical deflector (on the side opposite to the light incident side and the reflection side) instead of the packaged wafer 400 as shown in FIG. The back side is bonded to the support substrate, and after the front side resist pattern is formed, blade dicing is performed first, and then front side deep-RIE processing is performed, while preventing element damage during dicing, There are also proposals to be able to use this package.

  On the other hand, prevention of mirror deformation during mirror scanning has recently been discussed as a required specification for MEMS optical deflectors. This is because the deformation of the mirror widens or distorts the spot diameter of the laser beam to be scanned, thereby causing the quality of the projected image on the screen to deteriorate. As a general countermeasure, it is widely known that a reinforcing rib structure as shown in Patent Document 1 / FIG. 2 is formed on the back side of a mirror. By designing the rib thickness to be 3 to 4 times the mirror thickness, the rib structure increases the rigidity against the bending stress of the mirror and can suppress mirror deformation during scanning.

  However, the introduction of the rib structure may cause a new problem in the manufacturing process of the MEMS optical deflector. By forming a heavy structure called a rib structure on the back side of the mirror, it was composed of a thin SOI layer of 50 μm or less when the back side was deep-RIE processed following the Deep-RIE processing on the front side of the MEMS optical deflector. The element structure is damaged in the Deep-RIE apparatus due to stress caused by the weight of the rib structure. Since this defect occurs in the wafer process step before the dicing step, none of the above-described element damage prevention measures in the dicing step is useful. Establishment of a manufacturing process of a MEMS optical deflector having a rib structure has been an issue.

  An object of the present invention is to provide a method of manufacturing an optical deflector that can appropriately prevent breakage of a mirror section during wafer backside etching and dicing.

  According to a first aspect of the present invention, there is provided an optical deflector manufacturing method comprising: a mirror part having a mirror surface on the front side; a front side space part that accommodates the mirror part; and a back side space part that allows displacement of the mirror part; A wafer having an SOI layer, a BOX layer and a handle layer in order from the front side to the back side, by etching the SOI layer from the front side, on the front side of each section of the wafer, A first step of forming the front side space portion and the front side portion of the mirror portion, and a liquid coating agent that is soluble in a predetermined solution is applied to the front side of the wafer after the first step. A second step of forming a coating layer covering the front side and applying a support substrate covering the front side of the coating layer; and the support substrate via the coating layer with respect to the wafer after the second step. And fixing the coating layer The third step to be solidified, and the wafer after the third step are etched on the back side of each section of the wafer by etching the handle layer and the BOX layer from the back side, and the back side portion of the mirror part, A first step of attaching the first tape to the front side of the support substrate and then dicing from the back side of the wafer along each partition line of the wafer. 5 steps, a sixth step of attaching a second tape to the back side of the wafer after the fifth step, and a wafer after the sixth step, dipping the wafer in the predetermined solution, And a seventh step of removing the coating layer and the support substrate.

  According to the first invention, after forming the front side portion of the mirror portion from the front side, the wafer is subjected to etching from the back side and dicing from the back side in a state where the liquid coating agent is applied to the front side and the support substrate is fixed. This is followed by immersion in a solution to separate the coating layer and the support substrate, so that the mirror part can be prevented from being damaged during backside etching and dicing.

  In the method of manufacturing the optical deflector according to the second aspect of the invention, the back side portion of the mirror portion formed in the fourth step of the first aspect is a rib.

  According to the second invention, when a rib is added to the mirror portion for reinforcing the mirror portion, the rib is formed on the back side of the mirror portion. The addition of this rib increases the weight of the mirror part and increases the possibility of breakage of the mirror part during dicing. However, after the front side of the wafer is supported by the support substrate in the third step, from the back side of the wafer in the fourth step. By forming ribs by etching and performing dicing in the fifth step, it is possible to reliably prevent the mirror portion from being damaged in the fourth and fifth steps.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the support substrate is a silicon wafer or glass.

  According to the third invention, an inexpensive and highly reliable support substrate can be used.

  According to a fourth aspect of the present invention, there is provided the method for manufacturing an optical deflector according to any one of the first to third aspects, wherein the liquid coating agent is a liquid wax, and the predetermined solution is isopropyl alcohol or an alkaline solution.

  According to the fourth invention, the reliability of the liquid coating agent and the solution can be improved, and the fixing and separation of the liquid coating agent and the support substrate can be facilitated.

  According to a fifth aspect of the present invention, there is provided a method of manufacturing an optical deflector according to any one of the first to fourth aspects, wherein the first and second tapes have a property that adhesive strength is reduced by ultraviolet rays.

  According to the fifth aspect of the invention, the reliability of the tape can be improved with respect to capturing and separating the chips.

The block diagram of an optical deflector. The detailed structure figure of a mirror part. The chip structure figure of a MEMS optical deflector. The process drawing of the front side part of the whole main process of the manufacturing method of a MEMS optical deflector. The process figure of the back side part of the whole main process of the manufacturing method of a MEMS optical deflector. Process drawing of the 1st part of the preparation methods of a biaxial MEMS optical deflector. Process drawing of the 2nd part following the process of FIG. Process drawing of the 3rd part following the process of FIG. Process drawing of the 4th part following the process of FIG. FIG. 10 is a process diagram of a fifth part following the process of FIG. 9. The schematic diagram of the wafer level package as a prior art is shown.

  The configuration of the optical deflector 1 will be described with reference to FIG. The optical deflector 1 includes a mirror part 2 disposed at the center, an inner rectangular frame part 3 surrounding the mirror part 2 from the outside, and an outer rectangular frame part 4 surrounding the inner rectangular frame part 3 from the outside. . The outer rectangular frame portion 24 (corresponding to the support of the present invention) of the optical deflector 1 is composed of a front outer rectangular frame portion 4 and a back outer rectangular frame portion 23 of FIG.

  For convenience of explanation, the vertical direction and the horizontal direction of the optical deflector 1 are defined as a direction parallel to the short side and a direction parallel to the long side of the outer rectangular frame part 4, respectively. In FIG. 1, the left diagonally lower-right diagonally upward is the vertical direction of the optical deflector 1, and the left diagonally upper-right diagonally downward is the lateral direction of the optical deflector 1. Further, the side on which the light deflector 1 enters and reflects light is defined as the front side of the light deflector 1, and the side opposite to the front side is defined as the back side of the light deflector 1. Furthermore, the front side and the back side of the optical deflector 1 are referred to as the front side and the back side of the optical deflector 1 as appropriate.

  The pair of torsion bars 5 are arranged on both sides in the vertical direction with respect to the mirror part 2 with their axes aligned in the vertical direction, and the tip side is coupled to the mirror part 2. The base end side of the torsion bar 5 is coupled to the central portion on the inner peripheral side of the lateral side of the inner rectangular frame portion 3. The base end side of the torsion bar 5 may be separated from the inner rectangular frame portion 3. In that case, the base end portion of the torsion bar 5 is supported by the inner rectangular frame portion 3 only by the inner actuator 6.

  The pair of inner actuators 6 are cantilever-type piezoelectric actuators, which are disposed on both lateral sides of each torsion bar 5, the distal end side is coupled to the proximal end portion of the torsion bar 5, and the proximal end side is an inner rectangular frame. It is coupled to the vertical side of the part 3. The inner actuator 6 reciprocates the base end portion of the torsion bar 5 around the axis of the torsion bar 5 at a predetermined frequency, and reciprocates the mirror unit 2 around the first rotation axis.

  Here, the first rotation axis is defined as a straight line that passes through the center of the mirror portion 2 and is parallel to the axis of the torsion bar 5. The second rotation axis described later is defined as a straight line that is substantially orthogonal to the first rotation axis at the center of the mirror unit 2. The first and second rotation axes are straight lines defined on a mirror surface 10 described later.

  The pair of piezoelectric outer actuators 7 is arranged on both sides in the lateral direction with respect to the inner rectangular frame portion 3 and has a structure in which four cantilevers are connected in series. 4 is coupled to the vertical side portion of the inner rectangular frame portion 3 on the front end side. Each outer actuator 7 bends the front end side of all the cantilevers constituting the same to either the front side or the back side alternately at a predetermined cycle with respect to the base end side, and causes the mirror unit 2 to move to the second rotation axis. Reciprocate around.

  The electrode pads 8 and 9 are respectively provided on the front side surfaces of one and the other vertical sides of the outer rectangular frame portion 4, and are electrode terminals of the inner actuator 6 and the outer actuator 7 via wiring in the optical deflector 1. It is connected to the.

  The structure of the mirror unit 2 will be described in detail with reference to FIG. 2A is a rear view of the mirror unit 2, and FIG. 2B is a side view of the mirror unit 2. The mirror surface 10 is formed as a surface on the front side of the mirror portion 2 and reflects incident light from a certain direction on the front side to the front side at a reflection angle corresponding to the direction of the normal. The annular rib 11 is erected on the back side of the mirror part 2 and is formed in a circumferential wall shape along the circular peripheral edge of the main body of the mirror part 2. The annular rib 11 reinforces the mirror part 2 and suppresses distortion of the mirror surface 10 during the reciprocating rotation of the mirror part 2.

  The operation of the optical deflector 1 will be briefly described. The mirror unit 2 reciprocally rotates around the first and second rotation axes by the operation of the inner actuator 6 and the outer actuator 7, respectively, from a light source (not shown) (for example, a laser light source). Light in a certain direction is incident on the mirror surface 10 from the front side, and the light is reflected at an angle corresponding to the rotation angle around the first and second rotation axes and emitted to the front side. The outgoing light from the optical deflector 1 becomes scanning light that reciprocates in a predetermined scanning angle range and a predetermined frequency in the horizontal and vertical directions.

  The optical deflector 1 and its light source are mounted on an optical scanner, and the optical scanner is installed in, for example, a projector, a barcode reader, a laser printer, a laser head amplifier, or a head-up display.

  The chip structure of the MEMS optical deflector 1 will be described with reference to FIG. The optical deflector 1 includes a laminate 15, an SOI layer 16, a BOX layer 17, a handle layer 18, a bonding layer 19, and a support substrate 20 in order from the front side to the back side.

The laminated body 15 is composed of a lower electrode adhesion layer 31 made of Ti (titanium, TiOx), a lower electrode layer 32 made of Pt (platinum), PZT (titanate) in order from the back side (lower side in FIG. 3) to the front side. A piezoelectric element layer 33 made of lead zirconate) and an upper electrode layer 34 made of Pt (platinum) are provided. The covering layer 37 is made of SiO ₂ (silicon dioxide) and covers the surfaces of the lower electrode adhesion layer 31, the lower electrode layer 32, the piezoelectric element layer 33 and the upper electrode layer 34.

The SOI layer 16 is made of Si (silicon). The BOX layer 17 is made of SiO ₂ (silicon dioxide) as an oxide film. The handle layer 18 is made of Si (silicon). The bonding layer 19 is made of SiO ₂ (silicon dioxide). The support substrate 20 is made of a Si (silicon) layer.

  From the laminate 15 and the SOI layer 16, the mirror part 2, the outer rectangular frame part 4, the inner actuator 6, the outer actuator 7, and the electrode pads 8 and 9 are produced as MEMS structures. From the handle layer 18, the annular rib 11 and the back outer side rectangular frame part 23 are formed as a MEMS structure. The back outer rectangular frame portion 23 has the same inner and outer contours as the outer rectangular frame portion 4. The front outer rectangular frame portion 4 and the back outer rectangular frame portion 23 are joined to each other to form an outer rectangular frame portion 24.

  The inner peripheral space 27 is defined on the inner peripheral side of the outer rectangular frame portion 24, and a front side space portion is formed by the SOI layer 16 from the front side, and by etching of the BOX layer 17 and the handle layer 18 from the back side A back space part is formed. The inner circumferential space 27 is a space that accommodates the movable portions of the mirror portion 2, the inner actuator 6, and the outer actuator 7 and allows displacement of these movable portions.

  With reference to FIG.4 and FIG.5, main process S1-S10 of the manufacturing method of a MEMS optical deflector is demonstrated. For the sake of easy understanding, the fabrication process of the electrodes, wiring, interlayer insulating film, actuator and mirror of the MEMS optical deflector is omitted, and only the silicon processing (Deep-RIE process) portion of the MEMS processed wafer is illustrated. Yes.

  In the following, the MEMS processed wafer at the end stage of each of the steps S1 to S10 is indicated by reference numerals “101” to “110”.

  The MEMS processed wafer before the start of step S1 includes an oxide film layer 125, a handle layer 126, a BOX layer 127, an SOI layer 128, and a stacked body 129 in order from the back side. The oxide film layer 125, the handle layer 126, the BOX layer 127, the SOI layer 128, and the stacked body 129 correspond to the bonding layer 19, the handle layer 18, the BOX layer 17, the SOI layer 16, and the stacked body 15 in FIG. .

  4, the SOI layer 128 and the stacked body 129 as the front side portion are etched from the front side by Deep-RIE to form the element forming portion 132 and the front side frame forming portion 133 surrounding the element forming portion 132. The element forming portion 132 corresponds to the entire movable portion of the mirror portion 2, the inner actuator 6, and the outer actuator 7 in FIG. 3, and the front side frame forming portion 133 corresponds to the front outer rectangular frame portion 4 in FIG. Step S1 corresponds to the first step of the present invention.

  In step S2, a liquid wax as the liquid coating agent of the present invention is applied on the processed SOI layer 128 and laminate 129, and the step formed on the front side by the etching process in step S1 is filled, and the flat wax layer 135 is filled. (Corresponding to the coating layer of the present invention). As an example of the liquid wax, there is Nichika Seiko Co., Ltd. Sky Coat (trade name. Tempen resin type) and the company's Space Liquid (registered trademark: Tempen Phenol resin type). Step S2 corresponds to the second step of the present invention.

  In step S <b> 3, the support substrate 137 is placed on the MEMS processed wafer 102 in step S <b> 2 and heated under load to solidify the wax layer 135 and temporarily bond the MEMS processed wafer 102 to the support substrate 137. Step S3 corresponds to the third step of the present invention. The material of the support substrate 137 is, for example, a silicon wafer or glass.

  In step S4, the oxide film layer 125 and the handle layer 126 are etched to an intermediate depth by Deep-RIE. In Step S5, the oxide film layer 125, the handle layer, and the handle layer are digged down to the BOX layer 127 by further Deep-RIE. 126 and the corresponding portions of the BOX layer 127 are removed, and the rib forming part 145 and the back side frame forming part 146 are formed.

  The rib forming portion 145 corresponds to the annular rib 11 in FIG. 3, and the back side frame forming portion 146 corresponds to the back outside rectangular frame portion 23 in FIG. The internal space 147 defined by the back frame forming portion 146 corresponds to the back side portion of the inner circumferential space 27 of FIG. Steps S4 and S5 correspond to the fourth step of the present invention.

  In step S6 of FIG. 5, a dicing tape 151 of UV type (having a property that the adhesive strength of the tape is weakened by irradiation of ultraviolet rays) stretched on the rim is attached to the support substrate side of the MEMS processed wafer 105 in step S5. As an example of a UV type dicing tape 151 (corresponding to the first tape of the present invention) and a dicing tape 157 (corresponding to the second tape of the present invention) described later, for example, D-176 / 181/185 (product of Lintec Corporation) Name). Step S6 corresponds to the fifth step of the present invention.

  In step S7, the full dice 154 are formed on each chip (of the present invention) along each partition line together with the temporarily bonded support substrate 137 using a blade dicing apparatus with the back side of the handle layer 126 facing upward. Step S7 corresponds to the fifth step of the present invention.

  In step S8, the back side of the handle layer 126 is attached to another UV type dicing tape 157 stretched on the rim, and then the dicing tape 151 attached to the support substrate 137 side is irradiated with UV light, thereby dicing tape 151. Is peeled off and removed. This means that the MEMS processed wafer is transferred from the dicing tape 151 to the dicing tape 157. Step S8 corresponds to the sixth step of the present invention.

  In step S9, the MEMS processed wafer 108 after the replacement in step S8 is immersed in an IPA (isopropyl alcohol) solution together with the dicing tape 157. By immersion for several tens of minutes to several hours, the liquid wax of the wax layer 135 (see step S8) is dissolved in the IPA solution, and the support substrate 137 temporarily bonded to the MEMS processed wafer 108 is peeled and removed together with the wax. Step S9 corresponds to the seventh step of the present invention.

  In step S10, the MEMS processed wafer 109 in step S9 is washed with an organic solution such as IPA together with the dicing tape 157 and dried to obtain the workpiece 110 in which the MEMS optical deflector chips 160 are aligned on the dicing tape 157. It is done.

  Thereafter, the dicing tape 157 is expanded to increase the distance between the chips 160 of the MEMS optical deflector, and then the UV light is applied to the dicing tape 157 to reduce the adhesive force. The camera can be picked up.

  After this, an electrical inspection is performed before the die bonding step, and a non-defective chip and a defective chip are selectively marked, and only the non-defective chip is picked up and finished as a package product. The liquid wax is not limited to those soluble in IPA, and any liquid wax may be used as long as it does not adversely affect the MEMS processed wafer and the dicing tape. For example, a liquid wax that is soluble in a certain alkaline aqueous solution (corresponding to the alkaline solution of the present invention) can be sufficiently used.

  According to the manufacturing method of FIG. 4 and FIG. 5, it is possible to prevent damage to the element during deep-RIE processing on the back side by a combination of simple processes, and to use a mirror and torsion while using normal blade dicing at a low production cost. Dividing into chips by dicing can be performed without damaging each movable part of the bar and actuator.

  Further, although temporarily bonded to the support substrate, it is finally removed, so that it can be mounted on a general package. Since the wafer level package is not a premise, the element structure of the MEMS optical deflector does not need to form a through silicon via (FIG. 11) and can be a general electrode structure. As a result, the yield is high and the cost is low. Further, unlike the wafer level package (see FIG. 11), since testing can be performed before packaging, even defective chips are not formed into a package, and efficient production is possible.

  Next, referring to FIG. 6 to FIG. 10, a process for manufacturing a piezoelectric drive type two-axis MEMS optical deflector using a piezoelectric material lead zirconate titanate (PZT) thin film as an actuator is further performed. This will be specifically described below. The structure of the piezoelectric drive MEMS optical deflector described with reference to FIGS. 6 to 10 is obtained by removing the support substrate 20 from the element structure shown in FIG. In addition, the MEMS processed wafers at the end stage of the respective steps S21 to S35 are designated by reference numerals “221” to “235”. All the explanatory diagrams of each step correspond to the cross section of one MEMS optical deflector chip.

  The SOI wafer 240 before step S1 includes an oxide film layer 241, a handle layer 242, a BOX oxide film layer 243, and an SOI layer 244 in order from the back side. The oxide film layer 241, the handle layer 242, the BOX oxide film layer 243, and the SOI layer 244 correspond to the bonding layer 19, the handle layer 18, the BOX layer 17, and the SOI layer 16 of FIG. For example, the SOI layer 244 has a thickness of 50 μm, the BOX oxide film layer 243 has a thickness of 2 μm, and the handle layer 242 has a thickness of 400 μm.

  In step S21 of FIG. 6, a thermal silicon oxide film 245 having a thickness of 500 nm was formed on the surface of the initial SOI wafer 240 by a diffusion furnace.

  In step S22, a Ti layer and a Pt layer were sequentially formed on the front side of the Si wafer 221 by sputtering so that the respective thicknesses were 50 nm and 150 nm, thereby forming the lower electrode 251. The Ti layer and the Pt layer of the lower electrode 251 correspond to the lower electrode adhesion layer 31 and the lower electrode layer 32 of FIG.

  Next, a film of lead zirconate titanate (hereinafter referred to as PZT), which is a piezoelectric material, was formed on the lower electrode 251 by a reactive arc discharge ion plating method to form a piezoelectric PZT film 255. Thereafter, a Pt layer 257 having a thickness of 150 nm was formed on the piezoelectric PZT film 255 by sputtering to form an upper electrode. The piezoelectric PZT film 255 and the Pt layer 257 correspond to the piezoelectric element layer 33 and the upper electrode layer 34 in FIG.

  In step S23, a pattern corresponding to the outer actuator 7 that drives the inner rectangular frame portion 3 by non-resonance driving and the inner actuator 6 for resonance driving of the mirror portion 2 is formed on the substrate surface by photolithography and dry etching techniques. To do. Step S23 corresponds to the first step of the present invention.

  First, the Pt layer 257 and the PZT film 255 were patterned to form a pattern of the upper electrode and piezoelectric PZT film corresponding to the outer actuator 7 and the upper electrode and piezoelectric PZT film corresponding to the inner actuator 6. Similarly, the lower electrode 251 and the underlying silicon oxide film were also patterned, and the lower electrode and silicon oxide film for the outer actuator 7 and the lower electrode and silicon oxide film pattern for the inner actuator 6 were produced.

  In step S24, a silicon oxide film 273 having a thickness of 500 nm is formed on the entire surface of the wafer 223 in step S23 by plasma CVD.

  In step S25 of FIG. 7, a resist pattern is formed on the substrate surface by photolithography, a part of the silicon oxide film is removed by dry etching, and the contact hole 276 corresponding to the lower electrode and the upper electrode and the single crystal silicon are processed. The silicon oxide at the location 277 to be removed is removed by dry etching.

  In step S26, a resist pattern is formed by photolithography, an AlCu (1% Cu) film is formed by sputtering, and a wiring pattern is formed by lift-off. That is, the lower electrode and the upper electrode of the PZT actuator are electrically connected to the electrode pad on the outer periphery of the optical deflector via the AlCu film wiring 280.

  In step S27, after forming a resist pattern with photolithography, Ti and Ag are sequentially formed by sputtering, and a layer 287 of the mirror surface 10 of the mirror portion 2 is formed by lift-off.

  With the steps so far, the pre-process of silicon processing by deep-RIE is completed. Subsequent silicon processing steps will be described below.

  In step S28, the front SOI layer is etched by Deep-RIE to form element structures of the mirror part 2, the outer rectangular frame part 4, the torsion bar 5, the inner actuator 6, and the outer actuator 7.

  In step S29 of FIG. 8, a liquid wax is applied on the processed SOI layer using a spinner apparatus or the like to fill the steps of the structure formed by etching, and a flat wax layer 290 is formed. Step S29 corresponds to the second step of the present invention.

  In step S30, the support substrate 292 is placed on the wax layer 290 of the MEMS processed wafer 229 heated to 100 ° C. to 150 ° C., and is supported on the MEMS processed wafer 229 by cooling while applying an appropriate load (eg, 1 kN). The substrate 292 is temporarily joined. At this time, if bonded together in a vacuum, it is possible to form a good bonding state that does not include air voids. Step S30 corresponds to the third step of the present invention.

  In step S31, the oxide film layer 241 and the handle layer 242 are etched by deep-RIE to form a rib structure portion 297 on the back side of the mirror and a swinging space portion 298 of the mirror. Step S31 corresponds to part of the fourth step of the present invention.

  In step S32, the buried oxide film (BOX) 242 is also removed by BOE (Buffered Oxide Etch) processing. As a result, the rib structure portion 300 on the back side of the mirror and the oscillating space portion 302 of the mirror are completed. The rib structure portion 300 corresponds to the annular rib 11 (FIG. 3), and the swing space portion 302 corresponds to the back side portion of the inner circumferential space 27 (FIG. 3). Step S32 corresponds to part of the fourth step of the present invention.

  In step S33 of FIG. 9, UV type dicing tape 304 stretched on the rim is attached to the support substrate 292 side. Step S33 corresponds to part of the fifth step of the present invention.

  In step S34, full dice 308 is performed on each chip (corresponding to each section of the wafer of the present invention) of the temporarily bonded support substrate by a blade dicing apparatus with the back side of the handle layer facing upward. Step S34 corresponds to part of the fifth step of the present invention.

  In step S35, the back side of the handle layer 242 is attached to another UV type dicing tape 310 stretched on the rim, and the dicing tape 304 attached to the support substrate 292 side is irradiated with UV light, and the dicing tape is irradiated. 304 is peeled and removed. This means that the MEMS processed wafer is transferred from the dicing tape 304 to the dicing tape 310. Step S35 corresponds to the sixth step of the present invention.

  In step S36 in FIG. 10, the MEMS processed wafer 235 in step S35 is immersed in the IPA solution together with the dicing tape 310. The liquid wax is dissolved in the IPA solution by immersion for several tens of minutes to several hours, and the support substrate 292 temporarily bonded to the MEMS processed wafer 235 is peeled off and removed. Step S36 corresponds to the seventh step of the present invention.

  In step S37, the MEMS processed wafer 236 is washed with an organic solution such as IPA together with the dicing tape 310 and dried to obtain a workpiece 237 in which the chips 315 of the MEMS optical deflector are aligned on the dicing tape 310.

  After that, if the dicing tape 310 is expanded to increase the distance between the MEMS chips and the adhesive force is reduced by irradiating the tape with UV light, each chip 315 can be picked up as a single piece.

  Thereafter, the electrical characteristics of the PZT film and the wiring are evaluated by electrical inspection to mark a defective chip, and then only the good chip 315 is mounted on the ceramic package, thereby completing the MEMS optical deflector package.

  In this embodiment, the simplest open-air package form is adopted. The laser light from the light source is directly reflected and scanned by the movable mirror of the MEMS optical deflector and used for image projection.

  Assuming that the thickness of the mirror body is λ, as a result of introducing the reinforcing rib structure on the back side of the mirror, the static surface deformation of the mirror body changes from (1/4) λ or less before introduction to (1/8) λ. The following was improved and the spread and distortion of the scanning laser beam were reduced. Moreover, since the processing structure of the SOI layer was protected with wax, the mirror surface reflectivity was 85% or more without being affected by high-pressure pure water during dicing.

  For this MEMS optical deflector package, an AC voltage of Vpp = 20 V and a drive frequency (resonance frequency) of 27 kHz is applied to the horizontal axis scanning resonant actuator, and Vpp = 20 V is applied to the vertical axis scanning non-resonant actuator. When an AC voltage with a driving frequency of 60 Hz was applied, a mechanical deflection angle of ± 12 ° on the horizontal axis and ± 8 ° on the vertical axis was observed. Since there was no damage at the periphery of the mirror in the dicing process, the yield rate within the wafer exceeded 90%, and the variation in deflection angle and resonance frequency was within ± 3%, indicating a very good yield.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the embodiment, and can be implemented in various ways within the scope of the gist.

  In the embodiment, the part processed from the back side of the mirror part is a rib, but the back side part of the mirror part formed by etching from the back side in the fourth step of the present invention is not limited to the rib of the mirror part, It can also be a back side part other than the rib, for example, the back side itself.

  As a liquid coating, if the condition that the step generated by etching from the front side is smoothed and the support substrate is fixed to the wafer main body and can be dissolved by immersion in a predetermined solution is satisfied, Coating agents other than liquid wax in the form can be employed.

DESCRIPTION OF SYMBOLS 1 ... Optical deflector, 2 ... Mirror part, 10 ... Mirror surface, 16 ... SOI layer, 17 ... BOX layer, 18 ... Handle layer, 24 ... Outside rectangular frame Part (support), 27 ... inner peripheral side space (front side space part and back side space part), 137 ... support substrate, 151 ... dicing tape (first tape), 157 ... dicing tape ( Second tape).

Claims (5)

A method of manufacturing an optical deflector comprising: a mirror part having a mirror surface on the front side; a front side space part that accommodates the mirror part; and a back side space part that allows displacement of the mirror part;
For the wafer having the SOI layer, the BOX layer, and the handle layer in order from the front side to the back side, the front side space portion and the front side portion of the mirror portion are formed on the front side of each section of the wafer by etching the SOI layer from the front side. A first step of forming
On the front side of the wafer after the first step, a liquid coating agent that is soluble in a predetermined solution is applied to form a coating layer that covers the front side, and the front side of the coating layer is A second step of applying a covering support substrate;
A third step of fixing the support substrate to the wafer after the second step via the coating layer and solidifying the coating layer;
A fourth step of forming the back side space portion and the back side portion of the mirror portion on the back side of each section of the wafer by etching the handle layer and the BOX layer from the back side of the wafer after the third step; ,
A fifth step in which the first tape is attached to the front side of the support substrate on the wafer after the fourth step, and then dicing is performed along each partition line of the wafer from the back side of the wafer;
A sixth step of sticking a second tape on the back side of the wafer after the fifth step;
A method of manufacturing an optical deflector, comprising: a seventh step of immersing the wafer in the predetermined solution with respect to the wafer after the sixth step and removing the coating layer and the support substrate. The optical deflector according to claim 1.
The method of manufacturing an optical deflector, wherein a back side portion of the mirror portion formed in the fourth step is a rib. In the manufacturing method of the optical deflector of Claim 1 or 2,
The method of manufacturing an optical deflector, wherein the support substrate is a silicon wafer or glass. In the manufacturing method of the optical deflector of any one of Claims 1-3,
The liquid coating agent is a liquid wax,
The method for manufacturing an optical deflector, wherein the predetermined solution is isopropyl alcohol or an alkaline solution. In the manufacturing method of the optical deflector given in any 1 paragraph of Claims 1-4,
The method of manufacturing an optical deflector, wherein the first and second tapes have a property that adhesive strength is reduced by ultraviolet rays.