JP2002267996A - Optical scanner and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a mirror substrate from curving in to an optical scanner which reciprocally vibrates a mirror substrate with electrostatic force. SOLUTION: On the reverse surface of the mirror substrate 101 where a mirror surface is not formed, a metal thin film 118 having compressive stress is formed as a stress adjusting layer. While the metal thin film 118 is not formed, the mirror substrate curves convexly, but after the metal thin film 18 is formed, the curvature of the mirror substrate is suppressed with its compressive stress and the mirror substrate becomes flat.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical scanning device, and more particularly to a mirror substrate (vibrator) supported by beams.
And an optical scanning device having a structure in which a beam is reciprocally oscillated using a beam as a torsional rotation axis. The optical scanning device of the present invention is applicable to an optical writing system of an image forming apparatus such as a digital copying machine and a laser printer, and a scanning system such as a barcode reader and a scanner.

[0002]

2. Description of the Related Art In an optical scanning device disclosed in IBM J. Res. Develop Vol. 24 (1980), a mirror substrate (vibrator) supported by two beams provided on the same straight line is used. The mirror substrate is driven by electrostatic attraction between an electrode provided at a position facing the mirror substrate and reciprocally oscillates the mirror substrate using the two beams as a torsional rotation axis. Compared to an optical scanning device that rotates a polygon mirror with a motor, this optical scanning device formed by micromachining technology has a simpler structure and can be formed at once in a semiconductor process, so it is easy to miniaturize and manufacture. Cost is low. In addition, since a single reflecting surface is used, there is no variation in accuracy as in an optical scanning device using a plurality of reflecting surfaces, and further, there is an advantage in that reciprocal scanning can cope with an increase in speed.

[0003] The 13th Annual International Wo
rkshop on MEMS2000 (2000) 473-478, MEMS1999 333-
No. 338 proposes an electrostatically driven torsional vibration optical scanning device in which a counter electrode is provided on the end face of the mirror substrate so that the electrode does not overlap the vibration region in order to increase the deflection angle of the mirror substrate.

In the former optical scanning device, a small asymmetry of a structure generated in a forming process is used to give an initial moment to a torsional rotation axis for starting a mirror substrate. In the scanning device,
A metal electrode film for activation is provided on a surface orthogonal to the drive electrodes.

[0005]

SUMMARY OF THE INVENTION As described above,
As one of the manufacturing methods of the torsional vibration type optical scanning device,
A part of a silicon substrate with a thickness of 200 μm to 500 μm is thinned to a thickness of several tens of μm by wet etching to form a diaphragm, and a part of the diaphragm region is fixed to the frame by penetrating the front and back by dry etching. There is a method of forming a vibrator (mirror substrate) with a beam that has been set. According to this method, the mirror surface of the vibrator is a polished surface of silicon, and the back surface of the vibrator is an etched surface of silicon. As a result, the vibrator bends in response to the stress, and the mirror surface on the vibrator also bends. Therefore, it is necessary to correct the effect of the mirror surface in an optical system that receives light reflected on the mirror surface. was there.

There is also a method in which a double-side polished SOI substrate is used as a vibrator. However, there is a problem that the formation of a mirror material on one side causes the same bending of the vibrator due to the internal stress.

Accordingly, an object of the present invention is to provide an optical scanning device having no curved mirror surface.

[0008]

According to a first aspect of the present invention, there is provided an optical scanning device comprising: a mirror substrate (vibrator);
An optical scanning device for reciprocatingly oscillating with a beam supporting it as a torsional rotation axis, wherein a stress adjustment layer having internal stress is formed on a mirror substrate to suppress the curvature of the mirror substrate. According to one embodiment, the stress adjusting layer having a compressive stress is formed on the surface of the mirror substrate opposite to the back surface, and according to another embodiment, the stress adjusting layer has a compressive stress. Is formed on the mirror surface side of the mirror substrate.

Another feature of the optical scanning device according to the present invention is that the internal stress for suppressing the curvature of the mirror substrate is generated by ion implantation on one surface of the mirror substrate. It is.

A feature of the method of manufacturing an optical scanning device according to the present invention is that the stress adjusting layer is formed by a sputtering method.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 A first embodiment of the present invention will be described with reference to FIG. FIG. 1A is a schematic center sectional view of the optical scanning device of the present embodiment, and FIG. 1B is a schematic plan view of the optical scanning device of the present embodiment as viewed from the back side.

A mirror substrate (vibrator) 101 is supported on a frame 104 having a thickness of 200 μm by two beams 102 and 103 on the same straight line at the center thereof, and reciprocates using the beams 102 and 103 as torsional rotation axes. Vibration is possible. The dimensions of the beams 102 and 103 are set so as to be rigid enough to obtain a required deflection angle of the mirror substrate 101.

The ends 105 and 106 of the mirror substrate 101 which are not supported by the beams 102 and 103 are in the form of comb teeth, and are provided with a step in the plate thickness direction on the inner end face of the frame 104. 5 fixed electrodes 107 and 108
They oppose each other with a gap of μm. The frame 104 is made of a mirror substrate 101 made of a conductive material.
The frame 104 is formed integrally with the beams 102 and 103, and an insulating coating 113 is formed on the surface of the frame 104. The fixed electrodes 107 and 108 are formed on the insulating film 113. A part of the insulating film 113 of the frame 104 is removed, and a pad 114 for leading out an electrode is formed there. This pad 114 is electrically connected to the mirror substrate 101. The fixed electrodes 107 and 108 extend to electrode pads 116 and 117 formed on the frame surface, respectively.

On the mirror substrate 101, a metal thin film 115 having a sufficient reflectivity for light to be scanned is formed as a mirror surface. On the back surface of the mirror substrate 101, as a stress adjusting layer, a metal thin film 118 having a compressive stress
Are formed.

Before forming the metal thin film 118 (stress adjusting layer), the mirror substrate 101 has a processing strain caused by polishing in the manufacturing process, a compressive stress of the metal thin film 115 as a mirror surface, and an etching stop surface on the back side. As shown in the cross-sectional view of FIG. If this curvature is left undisturbed, there is the above-mentioned disadvantage.

In order to avoid such inconvenience, in this embodiment, the thickness of the mirror substrate 101 is reduced by forming a metal thin film 118 having a compressive stress on the back surface of the mirror substrate 101 as a stress adjusting layer. Plane mirror substrate 10 which balances internal stresses on both sides of the center plane in the
1 is realized.

The operation of the optical scanning device according to the present embodiment is as follows. When a voltage is alternately applied to the electrode pads 116 and 117 using the electrode lead pad 114 as a common electrode, electrostatic force between the fixed electrodes 107 and 108 and the mirror substrate ends 105 and 106 which are in close proximity to the fixed electrodes 107 and 108 causes the mirror substrate 10
1 is driven, and the mirror substrate 101 reciprocally oscillates using the beams 102 and 103 as torsional rotation axes. The incident light is reflected by the metal thin film 115 as the mirror surface on the mirror substrate 101, and the reflected light is swung according to the reciprocating vibration of the mirror substrate 101. The function of the metal thin film 118 as a stress adjusting layer suppresses the curvature of the mirror substrate 101 and thus also suppresses the curvature of the mirror surface composed of the metal thin film 115, so that the reflected light of the mirror surface is corrected by the curvature of the mirror surface. No optical system is required.

Next, an example of a method of manufacturing the above-described optical scanning device of the present embodiment will be described. (A) to (i) of FIG.
FIG. 3 is a cross-sectional view for explaining a manufacturing process.

[FIG. 2 (a)] Mirror substrate, torsion beam,
As a material for forming the frame, a low-resistance silicon substrate containing a high concentration of impurities is used. Thickness 200
Such a silicon substrate 201 polished on both sides of μm
, A high-viscosity heat-resistant resist 202 is applied in a thickness of 100 μm. This resist 202 is used as a mask for deeply etching silicon in the step of FIG. The material used as the mask may be any material that has good adhesion to silicon, is large enough to remain as a mask even during silicon etching with an etching selectivity of 100 μm, and can be easily removed after etching. Instead of 202, a Ni plating film or the like can be used.

[FIG. 2 (b)] The resist 202 is exposed,
The pattern is formed into the shape of the frame 104 by developing.

[FIG. 2C] Using the resist 202 after patterning as a mask, a silicon substrate 201 is formed into a frame 104 in a shape of 100 μm using a dry etching apparatus (ICP-RIE) having a high etching rate and high anisotropy.
Etching to a depth of.

[FIG. 2D] The resist 202 is dissolved,
After the removal, a high-viscosity heat-resistant resist 203 is applied in a thickness of 100 μm on a surface (upper surface in the figure) opposite to the surface etched into the frame shape of the silicon substrate.
04, the shape of the mirror substrate 101, the beam 102,
Pattern 103 into a shape. At this time, the thickness of the resist on the mirror surface and the beams 102 and 103 is made thinner than the surrounding frame portion, and the mirror surface and the beams 102 and 10 are formed.
The mask of the portion 3 has a transmittance of 50%.

[FIG. 2 (e)] Using the resist 203 with the step as a mask, a dry etching apparatus (ICP-RIE) having a large etching rate and high anisotropy is used.
The mirror substrate 101 and the beams 102 and 103 are formed by dry-etching the silicon substrate until the beam and the periphery of the mirror substrate penetrate. At this time, since the resist mask in the region of the beam and the mirror substrate disappears before the surrounding frame portion, the region of the beam and the mirror substrate is also etched, so that a step is provided between the beam and the mirror substrate and the frame. be able to.

[FIG. 2 (f)] After the resist is dissolved and removed, the entire substrate is thermally oxidized to form S as an insulating film 113.
An iO2 film 204 is formed to a thickness of 1 .mu.m.

[FIG. 2 (g)] Si on inner end face of frame
Metal thin films 205 and 206 as fixed electrodes 107 and 108 are formed on the O2 film. For example, Ti
A thin film is formed to a thickness of 300 °, and a Pt thin film is formed thereon by a sputtering method to a thickness of 1200 °. Ti thin film is S
This is for improving the adhesion of the Pt thin film on the iO2 film. As an electrode material, a material other than Pt, which has high conductivity and can secure adhesion to SiO2, for example, A
u, Ti or the like may be used. Further, an Al thin film 207 is formed on the mirror substrate surface as a mirror surface, that is, a metal thin film 115 by a sputtering method. In the above-described film formation, a region where a metal thin film is not formed is shielded by a metallic stencil mask. As a film formation method, a method capable of obtaining a sufficient shielding effect with a mask may be used, and a vacuum evaporation method, a sputtering method, an ion plating method, or the like can be used.

[FIG. 2 (h)] SiO2 on the back of the frame
A part of the film is etched away using a metal mask to form a contact hole 208.

[FIG. 2 (i)] Contact hole 208
Next, a metal thin film 209 as an electrode lead pad 114 of the mirror substrate and a metal thin film 210 as a metal thin film 118 as a stress adjustment layer are formed on the back surface of the mirror substrate using a metal mask. The thickness of the metal thin film 210 is set to have a stress that cancels the curvature of the mirror substrate. Then, heat treatment is performed at 400 ° C. in order to reduce the resistance between the metal thin film 209 and the silicon substrate. The metal thin film is formed by a sputtering method. In the sputtering method, the internal stress of a formed metal thin film can be adjusted by power, pressure, gas flow rate, and the like during film formation. Generally, a metal thin film formed by a sputtering method has a compressive stress.

<< Embodiment 2 >> A second embodiment of the present invention will be described. The optical scanning device of the present embodiment has the same overall configuration as the optical scanning device of the first embodiment, except for a part of the configuration of the mirror substrate. This difference will be described with reference to FIG. FIG. 3 is a schematic center sectional view of the optical scanning device;
The same reference numerals as in FIG. 1 indicate the same or corresponding elements.

In the first embodiment, the metal thin film 118 having a compressive stress as a stress adjusting layer is formed on the back surface of the mirror substrate. However, in the present embodiment, it is not formed. Instead, in this embodiment, on the metal thin film 115 as a mirror surface on the mirror substrate 101, an oxide thin film 312 having a tensile stress transparent to the light to be scanned is formed as a stress adjusting layer. Is done. The oxide thin film 312 is, for example, a silicon nitride thin film formed by a sputtering method.

Before the oxide thin film 312 was formed, the mirror substrate 101 was curved in an upwardly convex shape due to the processing strain due to polishing and the compressive stress of the metal thin film 115 as a mirror surface as described above. Oxide thin film 3 with stress
12, the internal stresses on the mirror substrate surface cancel each other, the internal stresses on both sides of the center plane in the thickness direction are balanced, and the flat mirror substrate 10 having no curvature is formed.
1 can be realized. Since the metal thin film 115 as a mirror surface is shielded from the outside air by the oxide thin film 312, it is possible to prevent the reflectance of the mirror surface from decreasing with time due to oxidation.

<< Embodiment 3 >> A third embodiment of the present invention will be described. The optical scanning device of the present embodiment has the same overall configuration as the optical scanning device of the first embodiment, except for a part of the configuration of the mirror substrate. This difference will be described with reference to FIG. FIG. 4 is a schematic center sectional view of the optical scanning device;
The same reference numerals as in FIG. 1 indicate the same or corresponding elements.

As can be seen from FIG. 4, in this embodiment, the metal thin film 118 (FIG. 1) formed as a stress adjusting layer on the back surface of the mirror substrate 101 in the first embodiment.
Is not formed. Further, a thin film corresponding to the oxide thin film 312 formed as a stress adjusting layer on the mirror surface in the second embodiment is not formed.

In this embodiment, instead of forming the stress adjusting layer, the P
Ions are implanted at high concentrations. The mirror substrate 101 before this ion implantation is curved in an upwardly convex shape due to processing strain due to polishing and compressive stress of the metal thin film 115 as a mirror surface. However, after ion implantation, the mirror substrate back surface 41 on which ions were implanted at a high concentration was used.
Since a large compressive stress is generated in 2, a flat mirror substrate 101 having no curvature can be realized by balancing the compressive stress on the front and back of the mirror substrate 101.

The optical scanning device of the present invention is not limited to the configuration of each of the above embodiments. For example, the shape, arrangement, and number of the fixed electrodes, the shape of the end of the mirror substrate facing the fixed electrode and the like may be changed as necessary.

Further, by using the optical scanning device of the present invention, a photosensitive member is scanned with a laser beam modulated by an image signal to form an electrostatic latent image, and the electrostatic latent image is developed and transferred and fixed on recording paper. An image forming apparatus such as a printer or a copying machine that outputs a hard copy by doing so is also included in the present invention.

Also, in the optical scanning device according to the present invention,
By adjusting the stress of the stress adjustment layer according to the film thickness determined by time management, there is an advantage that the mirror substrate can be flattened under different conditions without changing the film formation conditions that affect the film quality. is there. Further, in the manufacturing process of the optical scanning device of the present invention, it is preferable to perform a heat treatment for lowering the stress of the mirror substrate and making the stress distribution uniform, in order to enhance the reliability of the optical scanning device.

[0038]

In the optical scanning device according to the first to fourth aspects, since the curvature of the mirror substrate can be suppressed, it is necessary to provide an optical system or the like for performing a curvature correction on the light reflected by the mirror surface of the mirror substrate. Disappears. In the optical scanning device according to the third aspect, the stress adjustment layer achieves the stress adjustment for flattening the mirror substrate, and at the same time, shields the mirror surface from the outside air and decreases the reflectance of the mirror surface over time due to oxidation. Can be prevented. In the optical scanning device according to the fourth aspect, since the internal stress of the mirror substrate itself is directly adjusted by ion implantation, there is no fear of peeling as in a stress adjustment layer of a different material formed on the mirror substrate. . In the manufacturing method according to the fifth aspect, since the degree of freedom of the internal stress of the stress adjustment layer to be formed is large, it is possible to obtain effects such as being able to cope with flattening of the mirror substrate under various conditions.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view and a schematic plan view for explaining a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining a manufacturing process of the optical scanning device according to the first embodiment.

FIG. 3 is a schematic sectional view for explaining a second embodiment of the present invention.

FIG. 4 is a schematic sectional view for explaining a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Mirror substrate 102, 103 Beam 104 Frame 107, 108 Fixed electrode 115 Metal thin film as a mirror surface 118 Metal thin film as a stress adjustment layer 312 Oxide thin film as a stress adjustment layer 412 Mirror substrate back surface on which P ions are implanted

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Claims (5)

[Claims] 1. An optical scanning device for reciprocating a mirror substrate using a beam supporting the mirror substrate as a torsion rotation axis, the stress adjustment layer having an internal stress on the mirror substrate to suppress the curvature of the mirror substrate. An optical scanning device characterized by having a film formed thereon. 2. The optical scanning device according to claim 1, wherein a stress adjusting layer having a compressive stress is formed on the back side of the mirror substrate. 3. The method according to claim 1, wherein the stress adjusting layer having a tensile stress is formed on the mirror surface side of the mirror substrate.
The optical scanning device according to claim 1. 4. An optical scanning device for reciprocatingly oscillating a mirror substrate using a beam supporting the mirror substrate as a torsion rotation axis, wherein an internal stress for suppressing the curvature of the mirror substrate is ion-implanted into one surface of the mirror substrate. An optical scanning device produced by: 5. The method according to claim 1, wherein the stress adjustment layer is formed by a sputtering method.