JP2009093105A - Micromirror device, and mirror part forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a strength and rigidity required practically for a mirror part, while reducing the weight of the mirror part. <P>SOLUTION: This micromirror device is provided with the mirror part for reflecting the light from a light source as a scanning light, and is formed to reduce the film thickness at the central part of the mirror part than the film thickness at the peripheral part of the mirror part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a micromirror device that scans light from a light source on an object to be scanned, and a method of forming a mirror portion included in the micromirror device.

  In recent years, with the development of MEMS (Micro Electro Mechanical Systems) technology, micro devices such as micro mirror devices have been developed and put into practical use. The micromirror device is mounted on various devices such as a barcode reader and a laser printer, and is used as an optical scanner. As an example of the micromirror device, an electrostatic drive type device that vibrates the mirror portion using an electrostatic attractive force generated between the mirror portion and the electrode is disclosed in, for example, Patent Document 1 below.

Here, in the semiconductor process, for example, the mirror part of the micromirror device can be formed thin. The thinner the mirror part is, the lighter the mirror part becomes, so that the response of the mirror part can be improved. For this reason, there is a constant demand for forming the mirror part of the micromirror device as thin as possible.
JP 2003-57575 A

  However, as the mirror portion becomes thinner, there is a concern that the mirror portion may be easily broken or easily broken due to a decrease in the compressive strength or breaking strength of the mirror portion. In addition, since the bending rigidity and shear rigidity of the mirror portion are reduced, for example, the mirror portion is easily deformed during vibration of the mirror portion, and there is a concern that the surface accuracy of the mirror surface cannot be guaranteed. At present, there is such a concern, and in order to satisfy the specifications of the micromirror device, there is a substantial limit to the reduction in the thickness of the mirror portion. That is, the method of reducing the film thickness of the mirror portion for improving the response has a limit in securing the strength and rigidity of the mirror portion that are practically necessary. On the other hand, the user wants a product with a better specification (here, a product with quick response).

  Therefore, in view of the above circumstances, the present invention provides a micromirror device including a mirror portion that can ensure the practically necessary strength and rigidity of the mirror portion while realizing the weight reduction of the mirror portion, and the It is an object of the present invention to provide a method for forming a mirror part.

  A micromirror device that scans light according to one embodiment of the present invention that solves the above problems includes a mirror portion that reflects light from a light source as scanning light, and the thickness of the central portion of the mirror portion is the mirror. The apparatus is characterized in that it is formed to be thinner than the film thickness of the peripheral part of the part.

  According to the micromirror device configured as described above, since the peripheral portion of the mirror portion is formed as a rib structure that is one step higher than the central portion, the strength and rigidity of the entire mirror portion is increased, and the central portion of the mirror portion is Since the thin wall is formed, the mirror portion can be reduced in weight.

  In the mirror part, at least a part of the peripheral part protrudes from the center part of the mirror part on at least one of the mirror surface that reflects light from the light source and the back surface of the mirror surface. It may be a configuration.

  The central part of the mirror part includes, for example, an optically effective area on the mirror surface.

  Moreover, the mirror part formation method which concerns on 1 aspect of this invention which solves said subject is a method of forming the mirror part supported so that rocking | fluctuation with respect to a base is possible. The mirror part forming method corresponds to the mirror part by removing a region exposed from the first mask pattern, and a first mask pattern forming step for forming a first mask pattern in a predetermined region on the surface of the base. A mirror shape forming step for forming a mirror shape; a second mask pattern forming step for forming a second mask pattern only in a peripheral region of the mirror shape in a region corresponding to the mirror shape; and the second mask A thin-wall forming step of removing the central region of the mirror shape exposed from the pattern by a predetermined depth and forming the film thickness of the central region to be thinner than the film thickness of the peripheral region of the mirror shape.

  According to such a mirror part forming method, since the peripheral part of the mirror part is formed as a rib structure that is one step higher than the central part, the strength and rigidity of the entire mirror part is increased, and the central part of the mirror part is formed thin. Therefore, the mirror part can be reduced in weight.

  The base includes, for example, an etch stop layer. In this case, in the thin film forming step, the film thickness of the central region is defined by the etch stop layer.

  According to the micromirror device and the mirror portion forming method of the present invention, since the peripheral portion of the mirror portion is formed as a rib structure that is one step higher than the central portion, the strength and rigidity of the entire mirror portion is increased, and Since the central part is formed thin, the mirror part can be reduced in weight.

  The configuration and operation of the micromirror device according to the embodiment of the present invention will be described below with reference to the drawings.

  FIG. 1 is an exploded perspective view showing the configuration of a micromirror device 1 according to an embodiment of the present invention. FIG. 2 is a sectional view showing the configuration of the micromirror device 1. For convenience of explanation, the X, Y, and Z axes orthogonal to each other are attached to FIGS. Referring to FIG. 2, the cut surface view is a view showing the micromirror device 1 cut along a YZ plane including the axis Ax in FIG. 1.

  The micromirror device 1 is mounted on various devices such as a barcode reader and a laser printer, and is supported on a support substrate (not shown) inside the device. The micromirror device 1 includes a micromirror device unit 100, a lid unit 200, and a lower substrate 300.

  The micromirror device part 100 has a frame part 110 formed in a hollow rectangle. In the hollow part of the frame part 110, a movable part of the micromirror device part 100 is formed. The movable part includes a mirror part 120 and a pair of torsion bars 130 having an axis Ax as a central axis. One end of each torsion bar 130 is supported by the frame part 110, and the other end supports the mirror part 120 so as to be swingable around the axis Ax.

  Here, with reference to FIG. 3, the manufacturing process of the micromirror device unit 100 will be described. The micromirror device unit 100 is formed by the following manufacturing process using a wafer having a five-layer structure.

  As shown in FIG. 3A, the wafer has a layer structure in which a single crystal silicon layer 10, an SiO 2 layer 20, a single crystal silicon layer 30, an SiO 2 layer 40, and a single crystal silicon layer 50 are sequentially deposited. Note that FIG. 3 shows only a single die, not the entire wafer, for convenience of explanation. FIGS. 3A, 3B, 3D, 3F, and 3G show sectional views of the wafer, and FIGS. 3C and 3E show perspective views of the wafer. Further, the film thickness in the Z-axis direction of the wafer before the manufacturing process of FIG. 3 is t0 as shown in FIG.

  According to the manufacturing process of FIG. 3, first, for example, formation of a SiO 2 film by thermal oxidation, patterning of the SiO 2 film, etc. are performed on the wafer of FIG. 3A, and a mask pattern is formed on the single crystal silicon layer 10. Is formed. This mask pattern is formed in a region corresponding to the upper surface 112 of the frame portion 110 shown in FIGS. Next, an etching process is performed using, for example, KOH (potassium hydroxide), and a portion of the single crystal silicon layer 10 corresponding to the region exposed from the mask pattern (hereinafter referred to as “hollow region portion”) has a predetermined depth. Removed until t.

  The above-described series of processing (SiO 2 film formation, patterning, and etching) applied to the single crystal silicon layer 10 is also applied to the back surface of the wafer, that is, the single crystal silicon layer 50. The mask pattern on the single crystal silicon layer 50 is formed in a region corresponding to the lower surface 114 of the frame portion 110 shown in FIG.

  By performing the above-described series of processes on both the single crystal silicon layer 10 and the single crystal silicon layer 50, the wafer is in the state shown in FIGS. That is, the hollow region portion is removed by the etching process, and the film thickness of the wafer corresponding to the hollow region portion becomes t1. The removal depth t is a depth that does not expose the SiO 2 layers 20 and 40. The removal depth in the etching process in this step can be controlled by managing the etching time. For simplification of the drawing, the mask pattern is not shown in each drawing of FIG.

  Next, a mask pattern is formed in a region corresponding to the mirror portion 120 and the pair of torsion bars 130 (hereinafter referred to as “movable portion region”) in the hollow region portion. Then, an etching process for the single crystal silicon layer (for example, an etching process using KOH) and an etching process for the SiO 2 layer (for example, reactive ion etching (RIE)) are sequentially performed. All the five layers other than the region are removed (see FIGS. 3D and 3E).

  Further, in the movable part region, the mask pattern of the region corresponding to the mirror surface 122 and the mirror back surface 124 shown in FIGS. 1 and 2 is removed, and the mask pattern removal region is subjected to an etching process using KOH or the like. The Here, the SiO2 layers 20 and 40 function as an etch stop layer. Therefore, the film thickness of the removal region is the layer thickness t2 between the SiO2 layer 20 and the SiO2 layer 40, as shown in FIG.

  Next, the SiO2 layers 20 and 40 on the mask pattern removal region are removed by RIE or the like, and a metal film is formed in the region after the removal by metallization or the like. For simplification of the drawings, illustration of the metal film is omitted in each drawing. Further, the surface on the SiO 2 layer 20 side after the metal film is formed is referred to as “mirror surface 122”, and the surface on the SiO 2 layer 40 side is referred to as “mirror back surface 124”.

  The film thickness t3 between the mirror surface 122 and the mirror back surface 124 is precisely defined by the film thickness of the single crystal silicon layer 30 and the metal films on both sides thereof by the etch stop of the SiO2 layers 20 and 40. Moreover, the film thickness uniformity between the mirror surface 122 and the mirror back surface 124 can be obtained by the etch stop. For this reason, even when the film thickness between the mirror surface 122 and the mirror back surface 124 is thin, the die yield is relatively stable.

  Next, when all the mask patterns are removed, the manufacturing process of FIG. 3 is completed, and the wafer is in the state shown in FIG. 3G and FIG. That is, the wafer is formed in a shape in which each die has a frame portion 110 and a mirror portion 120 and a pair of torsion bars 130 in the hollow portion. In addition, ribs 126 having a shape protruding from the mirror surface 122 and the mirror back surface 124 are formed on the mirror portion 120 by etching the mask pattern removal region in the movable part region.

  The film thickness t3 between the mirror surface 122 and the mirror back surface 124 is very thin. Therefore, for example, when the film thickness of the entire mirror part 120 is t3, the strength and rigidity of the mirror part 120 may be lowered to such a degree that practical problems (for example, cracks, breakage, deformation, etc.) may occur. In the present embodiment, in order to prevent the occurrence of such a problem, a configuration is adopted in which ribs 126 are formed on the periphery of the mirror surface 122 in the above manufacturing process. That is, according to the present embodiment, the center portion of the mirror portion 120 is thinly formed to reduce the weight of the mirror portion 120, and the rib 126 is formed on the entire circumference of the mirror portion 120 so that the strength and rigidity of the entire mirror portion 120 are improved. Securement has also been achieved.

  Next, the description returns to FIGS. 1 and 2. In the following description, the operation of the movable part is also described while further explaining the configuration of the micromirror device 1.

  As shown in FIG. 2, the upper surface 112 and the lower surface 114 of the frame portion 110 are bonded to the lid portion 200 and the lower substrate 300, respectively. The lid 200 is formed of a glass substrate, and the lower substrate 300 is formed of a silicon substrate, for example, similarly to the frame 110, and is bonded by, for example, anodic bonding. At this time, each bonded portion is bonded with a strong bonding force by anodic bonding.

  Further, as in the manufacturing process of FIG. 3, the frame portion 110 is a portion that is not removed on the wafer, and has a thickness (film thickness t0) that is greater than the mirror portion 120 and the torsion bar 130 (film thickness t1, t3). And it is formed in the rectangle so that the mirror part 120 and the torsion bar 130 may be covered from four side surfaces. Therefore, when the lid part 200 and the lower substrate 300 are joined to the upper surface and the lower surface of the frame part 110 in the joining process, the mirror part 120 and the torsion bar 130, as shown in FIG. The portion 200 is housed in a cavity formed by the lower substrate 300.

  Further, the film thickness t0 is designed so that the movable range of the mirror part 120 is completely contained in the cavity. Therefore, according to the present embodiment, a cavity can be formed without interposing a separate component such as a spacer between the micromirror device unit 100 and the lid unit 200 and between the micromirror device unit 100 and the lower substrate 300. It becomes possible. This has an advantage of reducing steps such as bonding between separate components such as spacers and the micromirror device unit 100 and alignment for the bonding.

  Note that the atmosphere of the cavity is preferably a vacuum. By making the atmosphere of the cavity a vacuum, for example, it is not necessary to consider the viscous resistance of the air received when the mirror unit 120 is moved, and the performance of the micromirror device 1 such as the Q value of the mirror unit 120 is stabilized. This is because a stable effect can be obtained.

  The lid part 200 is formed of a light transmitting member and functions as a laser light entrance / exit window for the mirror part 120. This laser light is light for scanning the object to be scanned, and is emitted from a light source (not shown). The laser light transmitted through the lid part 200 enters the mirror surface 122 and is reflected in a direction corresponding to the tilt angle of the mirror surface 122. The reflected light is again transmitted through the lid 200 and emitted, and scans the object to be scanned as scanning light from the micromirror device 1.

  On the upper surface 310 of the lower substrate 300, the electrodes 322 and 324 are arranged facing each other with a YZ plane including the axis Ax interposed therebetween. The electrodes 322 and 324 are electrically connected to wiring (not shown) drawn from the back surface of the upper surface 310 via through holes 332 and 334, respectively. Further, wiring is also drawn from the mirror part 120 (single crystal silicon layer 30) of the micromirror device part 100. These wirings are connected to a drive control circuit (not shown) that drives and controls the micromirror device 1. Single crystal silicon layer 30 is insulated from other layers by SiO 2 layers 20 and 40.

  When the drive control circuit applies a voltage so as to generate an asymmetric potential difference between the mirror unit 120 and each electrode, the mirror unit 120 tilts around the axis Ax. For example, when the drive control circuit drives and controls the mirror unit 120 and the electrode 324 so that a potential difference V is generated between the ground and the mirror back surface 124 -the electrode 322, the mirror unit 120 generates the electrostatic charge generated between the mirror back surface 124 and the electrode 322. In response to the moment of force around the axis Ax due to the attractive force, it tilts around the axis Ax so as to rotate in the direction of arrow R in FIG. For example, when the drive control circuit controls the mirror 120 and the electrode 322 so that the potential difference V is generated between the ground and the mirror back surface 124 and the electrode 324, the mirror 120 has an arrow around the axis Ax by the same operation as described above. Tilt to rotate in the opposite direction to the R direction. By alternately repeating the two patterns of voltage application, the mirror unit 120 vibrates, and the scanning light can be scanned on the object to be scanned.

  That is, according to the present embodiment, the center part of the mirror part 120 is formed thin and the peripheral part is formed one step higher than the center part, so that the entire mirror part 120 is reduced in weight and is practically necessary. It is possible to ensure strength and rigidity. Moreover, the effect of raising the resonance frequency of the mirror part 120 by forming the rib 126 is also expected.

  The above is the embodiment of the present invention. The present invention is not limited to these embodiments and can be modified in various ranges. For example, various patterns are assumed for the shape and formation position of the rib 126. For example, in this embodiment, the rib 126 is formed on the entire circumference of the mirror unit 120, but in another embodiment, a part of the periphery of the mirror unit 120 (for example, the side on the mirror unit 120 where the torsion bar 130 is formed). ). Further, the rib 126 may be formed only on one side instead of both the mirror surface 122 and the mirror back surface 124.

  In the present embodiment, the mirror unit 120 and the mirror surface 122 are rectangular, but in other embodiments, other shapes (for example, a circle or an ellipse) may be used. With respect to the mirror surface 122, the function is sufficiently fulfilled if at least the effective region used as the optical element surface has high surface accuracy such as etch stop.

  Further, although the uniaxial micromirror device has been described in the present embodiment, the same configuration as that of the mirror unit 120 of the present embodiment can be applied to the mirror unit of a biaxial or multiaxial micromirror device. .

  In addition, the wafer may be a single monocrystalline silicon layer that does not have an SiO2 layer, or an SiO2 layer interposed between two monocrystalline silicon layers (hereinafter referred to as “SOI substrate”). There may be. That is, if the etching time of the single crystal silicon layer is precisely managed, the film thickness of the mirror portion 120 can be precisely defined, and the surface accuracy of the mirror surface 122 and the mirror back surface 124 can be increased. Therefore, even if the wafer is a single-crystal silicon layer or an SOI substrate, it is possible to manufacture an equivalent to the micromirror device 1 of this embodiment.

  The present invention is not limited to the flat plate type micromirror device of the present embodiment, but can be applied to a comb-shaped electrostatic drive mirror or a mirror of another drive system.

It is a disassembled perspective view which shows the structure of the micromirror device of embodiment of this invention. It is a sectional view showing the composition of the micromirror device of an embodiment of the invention. It is a figure for demonstrating the manufacturing process of the micromirror device part of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Micromirror apparatus 100 Micromirror device part 110 Frame part 120 Mirror part 122 Mirror surface 124 Mirror back surface 126 Rib 130 Torsion bar 200 Cover part 300 Lower substrate

Claims (5)

In a micromirror device that scans light,
A mirror unit that reflects light from the light source as scanning light;
A micromirror device characterized by being formed so that the film thickness of the central part of the mirror part is thinner than the film thickness of the peripheral part of the mirror part.   In the mirror part, at least a part of the peripheral part protrudes from the center part of the mirror part on at least one of a mirror surface that reflects light from the light source and a back surface of the mirror surface. The micromirror device according to claim 1.   The micromirror device according to claim 1, wherein a central portion of the mirror portion includes an optically effective area on the mirror surface. In a mirror part forming method for forming a mirror part supported to be swingable with respect to a base,
A first mask pattern forming step for forming a first mask pattern in a predetermined region on the surface of the base;
A mirror shape forming step of removing a region exposed from the first mask pattern to form a mirror shape corresponding to the mirror portion;
A second mask pattern forming step of forming a second mask pattern only in a peripheral region of the mirror shape among regions corresponding to the mirror shape;
A thin-wall forming step of removing the mirror-shaped central region exposed from the second mask pattern by a predetermined depth and forming the film thickness of the central region to be thinner than the film thickness of the peripheral region of the mirror shape And a mirror part forming method. The base includes an etch stop layer;
The method for forming a mirror part, wherein in the thin-wall forming step, the film thickness of the central region is defined by an etch stop layer.

Images