JP2002244063A - Laser beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser beam scanner which introduces the light from a laser beam source to a photosensitive drum surface to correct its curvature of the field by changing the curvature of a variable focus concave mirror. SOLUTION: A supporting member 26 having the rigidity of the concave mirror 28 is formed of single crystal Si and electrodes facing each other are formed on an Si substrate 21. A spacing 25 is formed in the Is substrate 21 and the counter electrodes 23 and a passivation oxidized film 24 are formed thereon. The concave mirror 28 is formed of a metallic thin film on the supporting member 26 of the concave mirror. The feeding of electricity to the counter electrodes 23 and the concave mirror 28 is effected by an extraction electrode pad 29 for the counter electrodes existing in a pad segment 31 and an extraction electrode pad 30 for the concave mirror 28. A voltage is impressed between the electrodes 23 facing each other and the supporting member 26 of the concave mirror to displace the concave mirror by electrostatic force. The supporting member 26 of the concave mirror is displaced within a range of about 1/3 of the spacing 25 by the impression of the voltage and the curvature of the concave mirror can be changed by increasing or decreasing the voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser beam scanning device for a laser printer.

[0002]

2. Description of the Related Art A laser beam scanning device used in a laser printer is configured so that a uniform spot diameter can be obtained on a photosensitive drum by a deflection by a polygon mirror and an fθ lens system. . In such a laser beam scanning device, the fθ lens is often made of plastic for cost reduction. However,
Plastic fθ lenses are easily deformed by heat,
As a result, a field curvature occurs on the photosensitive drum surface.

For this reason, in the technique disclosed in Japanese Patent Application Laid-Open No. 8-62522, the field curvature of the photosensitive drum surface is corrected by moving the lens position near the light source in parallel with the optical axis in accordance with the temperature change. are doing. That is, in the related art, the field curvature of the laser beam spot on the photosensitive drum surface due to the temperature deformation or the like of the fθ lens is corrected by moving the position of the lens system near the light source parallel to the optical axis.

A drive system using a small motor or a piezo actuator is used to drive such a lens system.
These drive systems are expensive and have the problem of offsetting the cost reduction by the plastic fθ lens.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is directed to a laser beam scanning apparatus that solves the problem by correcting the curvature of field of a photosensitive drum surface by changing the curvature of a variable focal length concave mirror. The purpose is to provide.

Another object of the present invention is to provide a laser beam scanning device capable of changing the optical axes of incident light and reflected light and easily extracting reflected light.

Another object of the present invention is to provide a laser beam scanning device which can be manufactured by micromachining technology, has a simple structure, is compatible with a general semiconductor manufacturing process, and can be manufactured in large quantities at low cost. I do.

[0008]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising a first optical component group between a laser light source and a deflecting means, and In the laser light scanning device having a second optical component group between the means and the medium to be scanned, the difference in spot diameter on the medium to be scanned due to a temperature change of the optical system formed by the second optical component group, In the first optical component group, a concave member and an electrode are provided on a support member having a predetermined rigidity, a voltage is applied between the electrode and an electrode facing the electrode via a gap, and the concave mirror member is deformed by electrostatic force. Correction by a concave mirror that can change the focal length.

According to a second aspect of the present invention, in order to achieve the above object, in the laser beam scanning device of the first aspect, the focal point of the concave mirror is offset.

According to a third aspect of the present invention, in order to achieve the above object, the laser beam scanning device of the first or second aspect further comprises a temperature detecting means, and corrects the spot diameter according to a temperature change. It is characterized by the following.

According to a fourth aspect of the present invention, in order to achieve the above object, in the laser beam scanning device of the second aspect, the electrode facing the support member of the concave mirror is divided to correspond to the displacement of the offset focal point movement. It is characterized by being made.

According to a fifth aspect of the present invention, in order to achieve the above object, in the laser beam scanning device of the second aspect, the concave mirror serves as an offset focus by changing the thickness of the supporting member. It is characterized by the following.

According to a sixth aspect of the present invention, in order to achieve the above object, in the laser scanning apparatus according to any one of the first to fourth aspects, the concave mirror comprises a single crystal S
i is a variable focal length concave mirror.

[0014]

Embodiments and examples of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a laser beam scanning device according to the present invention. As shown in the figure, the laser beam from a laser element 1 passes through a collimator lens system 2 and then enters a varifocal concave mirror 3,
If necessary, the direction is changed by the mirror 4, and the reflected light is condensed by the cylinder lens 5 and supplied to the polygon mirror 6. In other respects, as in a general laser beam scanning device, the photosensitive drum 1 is an fθ lens system including a first lens 7 and a second lens 8.
0 is supplied with laser light.

If a temperature change occurs in the fθ lens system, the lens is deformed due to thermal expansion, and a field curvature occurs in the spot diameter. Then, the temperature change is detected by the temperature detecting means 9,
The driving voltage of the variable focal length concave mirror 3 is changed by the driving circuit of the variable focal length concave mirror so as to compensate for the laser spot diameter on the photosensitive drum due to the temperature change. It is also possible to adopt a configuration in which a laser beam is received by a CCD or the like, the spot diameter is measured, and the spot diameter is fed back to the variable focal length concave mirror for correction.

FIG. 2 shows the structure of the variable focal length concave mirror of the laser beam scanning device used in this embodiment. For example, the support member 26 having the rigidity of the concave mirror is formed of single crystal Si. Opposing electrodes are formed on the Si substrate 21. It is possible to use borosilicate glass for the substrate 21. A gap 25 is formed in the Si substrate 21, and a counter electrode 23 and a passivation oxide film 24 are formed thereon. A concave mirror 28 is formed of a metal thin film on a support member 26 of the concave mirror. The power supply to the counter electrode 23 and the concave mirror 28 is performed by the counter electrode lead electrode pad 29 and the concave mirror lead electrode pad 30 in the pad portion 31.

The distance between the opposing electrodes 23 and the support member 2 for the concave mirror
A voltage is applied to 6, and the concave mirror is displaced by electrostatic force. At this time, the rigidity and the electrostatic force of the support member 26 of the concave mirror are balanced. By applying the voltage, the support member 26 of the concave mirror is displaced in a range of about 1/3 of the gap 25, and the curvature of the concave mirror can be changed by adjusting the voltage. FIG. 3 shows a schematic diagram of the displacement. 3A and 3B are cross-sectional views taken along line DD in FIG. 2C. FIG. 3A shows a state where no voltage is applied, and FIG. 3B shows a state where a voltage is applied.

FIG. 4 shows a manufacturing process of the variable focal length concave mirror.
In this example, the concave mirror has a diameter of 5 mm and the concave mirror support member 2 μm.
m, the case where the gap between the counter electrode and the concave mirror supporting member was 30 μm was taken as an example. In this manufacturing process, (a) a single-crystal Si substrate 21 is coated with a photoresist of 10 μm
Apply, pattern by photolithography,
RIE (reactive, ion, etching) is performed with a mixed gas of SF6 + Ar. The etching depth is 30 μm. Thermal oxidation is performed to form a 1 μm oxide film 22. (B) A TiN film is formed by a 150 nm sputtering method using N2 added Ar, and then N2O and SiH are formed by a plasma CVD method.
An oxide film is formed with the mixed gas of No. 4. The TiN and oxide film are patterned by photolithography. After patterning the organic resist by photolithography, the oxide film is etched and ashing is performed. Further, etching is performed with a mixed solution of hydrogen peroxide and ammonia to form a TiN electrode. Thus, the counter electrode 23 and the passivation oxide film 24 were formed. As the electrode material, a high melting point metal or a compound thereof can be used. W, WSix, Mo, etc. can also be used. (C) For example, S having a thickness of 400 μm and a thin Si of 2 μm
The OI wafer is used as a support member for a concave mirror. The thin Si side of the SOI wafer is used for the counter electrode S manufactured in the above step (b).
Direct bonding is performed by stacking on an i-electrode substrate in a vacuum and treating at 1050 ° C. On a Si substrate on which a high concentration B layer is formed,
An etching stop layer with a high concentration B layer can also be used. In this case, high-concentration B of 1E20 cm-3 or more is diffused to a depth corresponding to the thickness of the diaphragm, and then directly joined. (D) Next, a SiN film is formed by a thermal CVD method, and is patterned by photolithography to form a SiN film mask. Anisotropic etching of Si is performed with a KOH aqueous solution. A portion surrounded by the 111 surface having a low etching rate remains as the Si partition wall 27. In the etched portion, the Si etching proceeds, and the etching stops at the oxide film, so that the concave mirror support member 26 can be left. When the high-concentration B layer is used, the etching rate is rapidly reduced by the high-concentration B layer, and a Si concave mirror support member having a predetermined thickness is formed. Next, the SiN film is removed by treatment with hot phosphoric acid. (E) If an SOI substrate is used, the oxide film is removed with buffered hydrofluoric acid or the like, and a metal thin film 28 serving as a concave mirror is formed using a metal mask. For example, a film of a metal such as Al or Cr is formed on a substrate by a sputtering device or a vapor deposition device using a metal mask. As shown by reference numeral 30 in FIG. 5, a metal mask is used so that the electrodes remain on the pad portions. (F) Using a mask made of quartz glass or the like, Si on the counter electrode take-out pad is etched away by RIE of SF6 gas to remove it. Further, the oxide film 24 on the TiN electrode is removed by RIE using CHF3 gas. (G) A state in which the extraction electrode pad 29 is exposed.

FIG. 5 shows the measurement results of the relationship between the applied voltage and the radius of curvature of the varifocal concave mirror device manufactured as described above. It can be seen that the radius of curvature decreases as the voltage increases.

Next, a second embodiment of the present invention will be described.
As shown in FIG. 6, the opposite electrode of the concave mirror support member is denoted by reference numeral 2.
It is divided as shown by 3a, 23b, 23c, 23d and 23e, and the voltage is distributed and controlled. Then, the curvature of the concave mirror can be partially changed, and the offset focal point can be easily obtained. FIG. 6B is a schematic diagram thereof. The electrodes 23a and 23 are applied to the divided electrodes 23d and 23e.
When a voltage higher than b and 23c is applied, the portion to which the higher voltage is applied is more displaced, so that the curvature can be partially changed.

Next, a third embodiment of the present invention will be described. As shown in FIG. 8, the thickness of the concave mirror supporting member is changed in the radial direction to easily obtain an offset focal point. Since the rigidity of the support member is proportional to the cube of the thickness, if the thickness differs in the radial direction, the thin portion is more deformed. It is manufactured according to the manufacturing process of FIG. 5, but as shown in FIG. 9, the following processing is performed on the concave mirror supporting member before the joining in the process (c). (C-1) A substrate having a thin SOI to be a concave mirror supporting member is processed. An organic resist is applied, for example, at 5 μm, and a resist pattern is formed on a curved surface corresponding to the offset focus using a gradation mask. (C-2) The concave mirror support member is processed so as to be deformed into a curved surface corresponding to the offset focus by performing RIE with, for example, SF6 + O2 + Ar gas. (C-3) Joining is performed in the same manner as in the manufacturing process of FIG.

[0022]

As described above, the laser beam scanning device according to the first aspect of the present invention includes a rigid supporting member provided with a concave mirror and an electrode. A concave mirror capable of changing the focal length by applying a voltage in between and deforming the concave mirror member by electrostatic force can be mass-produced by a micromachining technology equivalent to a semiconductor device manufacturing process, and cost can be reduced. And there is an effect that a laser beam scanning device having a highly accurate field curvature correction function can be provided at low cost.

As described above, the laser beam scanning device according to the second aspect of the present invention can change the optical axes of the incident light and the reflected light by using the variable focus concave mirror having the offset focus, In addition to the above-mentioned common effect, there is an effect that the reflected light can be easily taken out and the cost of the laser beam scanning device having a highly accurate field curvature correction function can be reduced.

In the laser beam scanning device according to the third aspect of the present invention, as described above, by providing the second optical system with the temperature detecting means, in addition to the above-mentioned common effect, a more actual optical element can be obtained. There is an effect that correction for a temperature change can be performed and more accurate field curvature correction can be performed.

As described above, the laser beam scanning device according to the fourth aspect of the present invention divides the opposing electrode of the variable focal-length concave mirror so that, in addition to the above-mentioned common effect, it is also necessary to cope with the offset focus. There is an effect that a curved surface can be easily obtained, and cost reduction of a laser beam scanning device having a highly accurate field curvature correction function using a variable focal length concave mirror can be realized.

As described above, the laser beam scanning device according to the fifth aspect of the present invention, in addition to the above-described common effects, partially changes the thickness of the concave mirror supporting member of the variable focal length concave mirror. There is an effect that a curved surface corresponding to the variable focal length concave mirror of the offset focal point can be easily obtained, and the cost of the laser beam scanning device having a highly accurate field curvature correction function can be reduced.

According to the laser beam scanning device of the fifth aspect of the present invention, as described above, the supporting member of the variable focal length concave mirror is made of single crystal Si. Therefore, a micromachine device manufacturing method based on the above manufacturing process can be used, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a laser beam scanning device according to the present invention.

FIGS. 2A and 2B are sectional views (A), (B) and a plan view (C) showing the structure of a variable focal length concave mirror of the laser beam scanning device used in the embodiment of FIG.

FIG. 3 is a sectional view showing a schematic view of the displacement of the variable focal length concave mirror of FIG. 2;

FIG. 4 is a sectional view showing a manufacturing process of the variable focal length concave mirror of FIG. 2;

FIG. 5 is a view showing a measurement result of a relationship between an applied voltage and a radius of curvature of the variable focal length concave mirror device manufactured as in FIG. 4;

FIG. 6 is a sectional view (A) showing a second embodiment of the present invention,
(B) and a plan view (C).

FIG. 7 is a sectional view of the same.

FIG. 8 is a sectional view showing a third embodiment of the present invention.

FIG. 9 is a view showing a manufacturing process of the embodiment of FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Laser element 2 Collimator lens system 3 Variable focal length concave mirror 4 Mirror 5 Cylinder lens 6 Polygon mirror 7 First lens 8 Second lens 10 Photosensitive drum 21 Si substrate 23 Counter electrode 23a, 23b, 23c, 23d, 23e Split counter electrode 24 Passivation oxide film 25 Gap 26 Support member 28 Concave mirror 29 Leader electrode pad for counter electrode 30 Leader electrode pad for concave mirror 31 Pad part

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 7/198 G02B 7/18 BFterm (Reference) 2C362 AA21 BB14 2H042 DA02 DA03 DA12 DA20 DA21 DB14 DC02 DC08 DC11 DD08 DD11 DE07 2H043 BC00 2H045 CB13 CB22 DA22 DA41

Claims (6)

[Claims] 1. A laser beam scanning apparatus comprising: a first optical component group between a laser light source and a deflecting unit; and a second optical component group between the deflecting unit and a medium to be scanned. The difference in the spot diameter on the medium to be scanned due to the temperature change of the optical system formed by the two optical component groups, the first optical component group, the supporting member having a predetermined rigidity provided with a concave mirror and an electrode, A laser beam scanning apparatus, wherein a voltage is applied between the electrode and a facing electrode through a gap, and the concave mirror member is deformed by electrostatic force to correct the focal length with a concave mirror. 2. The laser beam scanning device according to claim 1, wherein
A laser beam scanning apparatus, wherein the focal point of the concave mirror is offset. 3. A laser beam scanning apparatus according to claim 1, further comprising a temperature detecting means, wherein said spot diameter is corrected according to a temperature change. 4. The laser beam scanning device according to claim 2, wherein
A laser beam scanning device characterized in that an electrode facing a support member of the concave mirror is divided so as to correspond to the displacement of the offset focal point movement. 5. The laser beam scanning device according to claim 2, wherein
A laser beam scanning device, wherein the concave mirror serves as an offset focus by changing the thickness of the support member. 6. A laser beam scanning apparatus according to claim 1, wherein said concave mirror is a variable focal length concave mirror whose support member is made of single-crystal Si.