JP2001264672A - Optical polarizing element and method for manufacturing optical polarizing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light deflection element capable of high-speed driving having a reflecting mirror with the large effective area and the small moment of inertia, and its manufacturing method. SOLUTION: The optical polarizing element integrally formed of a single crystal semiconductor has a spring part of the shape of a beam serving as the center of the rotation of the optical polarizing element and a reflecting mirror supported by the spring part. The reflecting mirror consists of the first area extended in a vertical direction to the spring part and the second area. The first area and the second area are disposed alternately and the thickness of the first area is formed more thickly than the thickness of the second area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical deflecting element and a method of manufacturing the same, and more particularly, to an optical deflecting element having a large effective area and a reflecting mirror having a small moment of inertia and capable of high-speed driving and a method of manufacturing the same.

[0002]

2. Description of the Related Art Many attempts have been made to apply a so-called micromachine technique using a semiconductor manufacturing technique in order to reduce the size and enhance the performance of an optical deflection element.

As an example of such a light deflecting device,
A conventional technique based on a technique as disclosed in Japanese Patent Publication No. 60-5701 is known.

Hereinafter, an outline of the conventional optical deflector will be described with reference to FIGS. 10 to 12. FIG.

That is, as shown in FIGS. 10 and 11, in this optical deflector, a beam-shaped spring portion 101 and a reflecting plate 10 are formed by anisotropic etching of a silicon single crystal substrate.
2 is formed integrally with the lower substrate 10
4

The lower substrate 104 has a recess 106 having a projection 105 with a triangular cross section, and drive electrodes 107 and 108 are formed in this region.

The drive electrodes 107 and 108 are arranged so as to oppose both sides of the reflector 102 with the beam-shaped spring portion 101 as a central axis.

In this manner, by alternately applying a voltage to the electrodes 107 and 108 while grounding the reflector 102, the reflector 102 is vibrated by electrostatic attraction as shown in FIG.

At this time, by adjusting the frequency of the drive voltage alternately applied to the electrodes 107 and 108 to the resonance frequency determined by the spring constant of the beam-shaped spring portion 101 and the moment of inertia of the reflector 102, a relatively small voltage is applied. , A large amplitude can be obtained.

The above is an example in which electrostatic attraction is used for driving. As another method, an example of an optical scanner using a piezoelectric vibrator is disclosed in, for example, JP-A-10-197819. It is known as a conventional technique using a simple method.

Hereinafter, an outline of the conventional optical scanner will be briefly described with reference to FIG.

That is, as shown in FIG. 13, in this optical scanner, a micro mirror is formed by using a semiconductor manufacturing technique.
201, a beam-shaped spring portion 202 serving as an X-axis rotating support
And a frame 203 surrounding them are integrally formed, and the piezoelectric element 204 is attached to the bottom surface thereof.

Here, the center of gravity of the micromirror 201 is
The spring-shaped beam portion 202 is set to be shifted from the axis.

The driving of such an optical scanner is as follows.
This is performed by vibrating the piezoelectric element 204 in the Z-axis direction in the figure.

At this time, a proper resonance state is obtained.
By optimizing the structure of each part of the optical scanner, the micro mirror 201 can be vibrated.

[0016]

However, a light deflecting device according to the prior art as disclosed in Japanese Patent Publication No. Sho 60-5701 and Japanese Patent Laid-Open No.
In an optical scanner according to the related art disclosed in Japanese Patent Application Laid-Open No. 197819, for example, when applied to an optical deflection element for use requiring a large vibration frequency, for example, for displaying a video signal, the following is required. Several problems arise.

First, in order to increase the resonance frequency,
It is necessary to increase the rigidity of the beam-shaped spring portion 101 or the beam-shaped spring portion 202, and as a result, the force required for driving is increased.

To avoid this, the moment of inertia of the reflector 102 or the micro mirror 201 must be reduced.

Here, the moment of inertia Ip with respect to the central axis of a rectangular plate-like reflecting plate (micromirror) having a uniform thickness tm is:

[0020]

(Equation 1)

Is given by

Here, ρ, c, and b are the density, the axial length, and the width of the reflector (micromirror), respectively.

Therefore, it is effective to reduce the size of the reflection plate, especially the width b of the mirror, in order to reduce the moment of inertia Ip.

However, considering applications such as display of video signals, it is desirable that the reflector be somewhat large in view of the optical system if it is used for displaying high-definition images.

On the other hand, it is effective to reduce the moment of inertia Ip by reducing the thickness tm of the reflector, but there is a problem that a reflector driven at high speed causes distortion due to torque fluctuation. Reducing the thickness tm makes this problem apparent.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide an optical deflecting element having a reflecting mirror having a large effective area and a small moment of inertia, which can be driven at high speed, and a method of manufacturing the same. I have.

Further, in order to realize a reflector having a small moment of inertia, it is necessary to form a semiconductor thin plate which is very thin, has a small internal stress, and has no distortion.

Another object of the present invention is to provide an optical deflecting element employing a method for stably producing a semiconductor thin plate satisfying the above-mentioned requirements, and a method for producing the same.

[0029]

According to the present invention, in order to solve the above-mentioned problems, (1) an optical polarization element integrally formed from a single crystal semiconductor, which is a center of rotation of the optical polarization element. A beam-shaped spring portion, and a reflecting mirror supported by the spring portion, wherein the reflecting mirror includes a first region and a second region extending in a direction perpendicular to the spring portion. And the second region are alternately arranged, and the thickness of the first region is formed to be thicker than the thickness of the second region.

(Corresponding Embodiment) The first embodiment described below corresponds to this.

(Operation) In FIG. 1, the reflecting mirror 4 is composed of thick regions 2 and thin regions 3 which are alternately arranged.

By appropriately setting the thickness of the reflecting mirror 4 and the ratio between the thick region and the thin region, the moment of inertia Ip can be reduced without increasing the distortion of the reflecting mirror due to torque fluctuation. It is.

This means that when trying to obtain the same resonance frequency, the rigidity of the beam-shaped spring portion can be reduced by the smaller the moment of inertia Ip.

According to the present invention, in order to solve the above problems, (2) the outer peripheral shape of the reflecting mirror is symmetrical with respect to the beam-shaped spring portion as an axis. The light polarizing element according to (1) is provided, wherein one side of the divided reflecting mirror is different from the other side in an area ratio of the first region and the second region. .

(Corresponding Embodiment) A second embodiment described later corresponds to this.

(Operation) In FIG. 2, the reflecting mirror 4 is composed of thick regions 2 and thin regions 3 alternately arranged, and the ratio of the thick region to the thin region is determined on both sides of the beam-shaped spring portion. The same effect as the difference (1) can also be applied to an optical deflecting element that uses piezoelectric vibration as a driving force that needs to shift the center of gravity from the center axis of rotation. (3) a first step of forming an N-type diffusion layer on a first main surface of a P-type semiconductor substrate;
A second step of performing electrochemical etching from the second main surface of the P-type semiconductor substrate using an alkaline solution to integrally form a beam-shaped spring portion and a reflecting mirror supported by the spring portion; And a method for manufacturing a light polarizing element.

(Corresponding Embodiment) The fourth embodiment described below corresponds to this.

(Operation) In FIGS. 4 to 6, N-type diffusion regions 52 and 5 left by electrochemical etching are shown.
With the 2 ', 53, the reflecting mirror and the beam-shaped spring portion are integrally formed.

Since the thickness of the reflector is determined by the junction depth of the diffusion layer and the depletion layer generated at the time of bias from the junction, it is possible to obtain a reflector that is very thin and has a small internal stress with good controllability.

[0040]

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

(First Embodiment) A light polarizing element according to a first embodiment of the present invention will be described with reference to FIG.

That is, the light polarizing element according to the first embodiment of the present invention comprises a beam-shaped spring portion 1 integrally formed by electrochemically etching a single crystal semiconductor, as described later, It has a reflecting mirror 4 including a thick region 2 having a thickness tm1 and a thin region 3 having a thickness tm2.

FIG. 1 shows the optical polarizing element viewed from the back, and at least the front side of the reflecting mirror 4 has a smooth mirror surface.

Although not shown in particular, similar to the case of FIGS. 10 and 13 according to the prior art described above,
The periphery of the reflecting mirror 4 is assumed to be supported by a frame made of a semiconductor substrate.

According to the present embodiment, if the ratio of the thick region 2 of the reflecting mirror 4 to the length of the mirror in the direction of the beam-shaped spring portion 1 is R,

[0046]

(Equation 2)

Is as follows.

On the other hand, the distortion ε of the reflecting mirror due to the torque fluctuation is because the rigidity of the reflecting mirror is proportional to the square of its thickness.

[0049]

(Equation 3)

Is as follows.

Here, A is a coefficient determined by the Young's modulus and driving frequency of the material of the reflector, the width and length of the reflector, and the like.

Then, the reflecting mirror 4 of the present embodiment comprising the thick region 2 having a thickness tm1 and the thin region 3 having a thickness tm2.
And a reflector having a uniform thickness tm, R =
When 0.2, tm1 = 2tm, tm2 = tm / 2, the distortion ε of the reflecting mirror caused by the torque fluctuation does not change. However, in the reflecting mirror 4 of the present embodiment, the reflecting mirror 4 having a uniform thickness tm. The moment of inertia Ip can be reduced by 20% compared to a mirror.

As described above, according to the present embodiment, the thickness of the reflecting mirror 4 is provided in the direction perpendicular to the beam-shaped spring portion 1 so that the thickness, the thick region and the thin region can be obtained. By appropriately setting the ratio, it is possible to reduce the moment of inertia Ip without increasing the distortion ε of the reflector due to the torque fluctuation.

This means that when trying to obtain the same resonance frequency, if the moment of inertia Ip is small, the rigidity of the beam-shaped spring portion 1 can be reduced by that much, so that the force required for driving is small. As a result, the driving voltage can be reduced and the current consumption can be reduced.

(Second Embodiment) In the case where a piezoelectric vibrator is used for driving, as shown in FIG. 13, the center of gravity of the reflecting mirror is a beam-shaped spring serving as the center of rotation. Although it is necessary to be displaced from the axis of the section, a second embodiment applied in such a case will be described with reference to FIG.

That is, the basic configuration of the light polarizing element according to the second embodiment of the present invention is the same as that of the first embodiment. t
A reflecting mirror 4 including a thick region 2 having a thickness m1 and a thin region 3 having a thickness tm2 is integrally formed.

FIG. 2 shows the light polarizing element as viewed from the back, and at least the front side of the reflecting mirror 4 has a smooth mirror surface.

The light polarizing element according to the second embodiment of the present invention is different from that of the first embodiment in that the ratio of the thick region 2 to the thin region 3 is different from that of the first embodiment. (The ratio of the thick region 2 on the upper side in FIG. 2 is smaller than the ratio of the thick region 2 on the lower side).

As a result, the center of gravity of the reflecting mirror 4 is displaced from the axis of the beam-shaped spring portion 1, and the reflecting mirror 4 is moved by piezoelectric vibration.
Can be vibrated.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
The embodiment will be described with reference to FIG.

That is, the light polarizing element according to the third embodiment of the present invention has a beam-shaped spring portion 1 made of a single crystal semiconductor formed by electrochemical etching, which will be described later, and a thick region 2 and a thin region 3. And a plurality of reflecting mirrors 4 formed integrally with each other.

FIG. 3 shows the light polarizing element as viewed from the back, and at least the front side of each reflecting mirror 4 has a smooth mirror surface.

In particular, although not shown, the plurality of reflecting mirrors 4 are driven in the same phase by resonance due to electrostatic attraction or piezoelectric vibration, and function similarly to one reflecting mirror 4 having a substantially large area. .

In this case, the width of each reflecting mirror 4 in a direction perpendicular to the axis of the beam-shaped spring portion 1 can be made very small as compared with the case where one reflecting mirror is used.

As described above, the moment of inertia Ip of the reflecting mirror is proportional to the cube of the width of the reflecting mirror. Therefore, by adopting the configuration as in the present embodiment, the moment of inertia Ip of the reflecting mirror 4 is greatly reduced. Can be reduced.

Also, in this embodiment,
Since the rigidity of the beam-shaped spring portion 1 can be reduced,
As a result, the force required for driving can be reduced.

In the case where the optical polarizing element according to the present embodiment uses an electrostatic attraction for driving as shown in FIG. 10, a secondary deflection that can provide a large deflection angle even at the same distance between the electrodes. Significant benefits also arise.

(Fourth Embodiment) Next, the first embodiment will be described.
A method of manufacturing each light deflecting element according to the third to third embodiments will be described as a fourth embodiment with reference to FIGS.

FIG. 4A is a front view of a main part of the optical deflecting element according to the present invention, and FIG.
(A) is an AA ′ sectional view of FIG.

That is, as shown in FIGS. 4A and 4B, a deep N-type diffusion layer 52 and a shallow N-type diffusion layer 53 are formed in a predetermined region on the surface side of a P-type semiconductor substrate 51. Then, a protective film 54 of polyimide or the like is formed on the surface side.

On the other hand, on the back side of the P-type semiconductor substrate 51,
A silicon nitride film 55 is formed in a region left as a frame in a later step.

Next, as shown in FIG. 5, using the silicon nitride film 55 as a mask pattern, the N-type diffusion layers 52 and 5 are formed.
By performing electrochemical etching with an alkaline aqueous solution while a positive voltage is applied to the N-type diffusion layer 3,
Areas 2 and 53 are selectively left.

The region to be left corresponds to the reflecting mirror 4 in each of the above-described embodiments, but a difference in thickness occurs on the back surface in accordance with the junction depth of the N-type diffusion layers 52 and 53. .

After this step, as shown in FIG. 6, the surface protection film 54 made of polyimide or the like is removed by a method such as oxygen plasma etching or the like, so that the beam-like spring portion 1 of the thick N-type diffusion layer 52 is formed. Corresponding area 52 '(see FIG. 4A)
Then, the reflecting mirror 4 supported by the frame portion 51 'remaining in the electrochemical etching step using the alkaline aqueous solution by the silicon nitride film 55 is obtained.

In this method, the thickness of the reflecting mirror 4 is determined by the junction depth of the diffusion layer and the depletion layer generated at the time of biasing from the diffusion layer. The reflecting mirror 4 having a small internal stress can be obtained with good controllability.

In addition, since the difference in thickness between the deep N-type diffusion layer 52 and the shallow N-type diffusion layer 53 can be defined by the junction depth of the diffusion layer, even a very thin reflecting mirror 4 can be used. It can be formed with high accuracy.

(Fifth Embodiment) Next, as a modification of the fourth embodiment, a fifth embodiment will be described with reference to FIG.
This will be described with reference to FIGS.

FIG. 7A is a front view of a main part of the optical deflecting element according to the present invention, and FIG.
(A) is an AA ′ sectional view of FIG.

That is, as shown in FIGS. 7A and 7B, an N-type diffusion layer 62 and a high-concentration P-type A diffusion layer 63 is formed, and a protective film 54 of polyimide or the like is formed on the surface side.

On the other hand, a silicon nitride film 55 is formed on the back surface of the P-type semiconductor substrate 61 in a region to be left as a frame in a later step.

Next, as shown in FIG. 8, using the silicon nitride film 55 as a mask pattern, electrochemical etching is performed with an alkaline aqueous solution in a state where a positive voltage is applied to the N-type diffusion layer 62, and the N-type diffusion layer 62 is formed. A region corresponding to a depletion layer (not shown) generated in the low-concentration P-type semiconductor substrate 61 therefrom selectively remains.

At this time, in the region where the high-concentration buried diffusion layer 63 is formed, the extension of the depletion layer is suppressed, so that the thickness of the remaining portion in this region is reduced, as shown in FIG. Thus, a reflecting mirror 4 having a shape similar to that of the fourth embodiment can be obtained.

In FIG. 7A, reference numeral 6
2 'is a region of the thick N-type diffusion layer 62 corresponding to the beam-shaped spring portion 1.

In FIGS. 8 and 9, reference numeral 61 'denotes a frame portion left in the electrochemical etching step.

In the present specification described in the above-described embodiment, in addition to claims 1 to 3 described in the claims, the inventions described as appendices 1 to 5 below will be described. include.

(Supplementary Note 1) An optical polarization element integrally formed from a single crystal semiconductor, comprising a beam-shaped spring portion serving as a rotation center of the optical polarization element, and a reflecting mirror supported by the spring portion. A length of a direction parallel to the beam-shaped spring portion of the reflecting mirror is longer than a direction perpendicular to the beam-shaped spring portion, and a plurality of the reflecting mirrors are arranged so as to form the same plane; .

(Corresponding Embodiment) The third embodiment corresponds to the third embodiment.

(Supplementary Note 2) A first step of forming a deep N-type diffusion layer and a shallow N-type diffusion layer on a first main surface of a P-type semiconductor substrate, and from a second main surface of the P-type semiconductor substrate. Electrochemical etching using an alkaline solution, and a second step of integrally forming a beam-shaped spring portion and a reflecting mirror supported by the spring portion. Production method.

(Corresponding Embodiment) The fourth embodiment corresponds to this.

(Supplementary Note 3) A first step of forming an N-type diffusion layer and a P-type buried diffusion layer on a first main surface of a P-type semiconductor substrate; A method of manufacturing an optical polarization element, comprising: performing electrochemical etching using a solution to form a beam-shaped spring portion and a reflecting mirror integrally supported by the spring portion. .

(Corresponding Embodiment) The fifth embodiment corresponds to the fifth embodiment.

(Supplementary Note 4) A first step of forming a deep N-type diffusion layer and a shallow N-type diffusion layer on a first main surface of a P-type semiconductor substrate; A second step of forming a protective film, a third step of forming a silicon nitride film on the second main surface of the P-type semiconductor substrate, and applying a positive voltage to the deep N-type diffusion layer and the shallow N-type diffusion layer. A fourth step of integrally forming a beam-shaped spring portion and a reflector supported by the spring portion, and a fifth step of removing the protective film. And a process for producing a light polarizing element.

(Corresponding Embodiment) The fourth embodiment corresponds to the fourth embodiment.

(Supplementary Note 5) A first step of forming an N-type diffusion layer and a P-type buried diffusion layer on the first main surface of the P-type semiconductor substrate, and protecting the first main surface of the P-type semiconductor substrate. A second step of forming a film, a third step of forming a silicon nitride film on the second main surface of the P-type semiconductor substrate, and an alkaline aqueous solution with a positive voltage applied to the N-type diffusion layer. A fourth step of performing electrochemical etching to integrally form a beam-shaped spring portion and a reflecting mirror supported by the spring portion;
And a fifth step of removing the protective film.

(Corresponding Embodiment) The fifth embodiment corresponds to the fifth embodiment.

[0096]

According to the first aspect of the present invention, it is possible to reduce the moment of inertia Ip without increasing the distortion of the reflecting mirror due to the torque fluctuation, thereby obtaining the same resonance frequency. In this case, if the moment of inertia Ip is small, the rigidity of the beam-shaped spring portion can be reduced accordingly, so that the force required for driving is reduced. As a result, the driving voltage is reduced and the current consumption is reduced. Reduction can be realized.

According to the second aspect of the present invention, the reflecting mirror is constituted by alternately arranged thick regions and thin regions, and the ratio of the thick region to the thin region is equal to the both sides of the beam-shaped spring portion. The same effect as that of the first aspect of the present invention can be applied to an optical deflecting element using piezoelectric vibration as a driving force, which needs to shift the center of gravity from the rotation center axis.

According to the third aspect of the present invention, with the N-type diffusion region left by the electrochemical etching,
Since the thickness of the reflector is determined by the junction depth of the diffusion layer and the depletion layer generated at the time of bias from the junction depth of the reflector, as a result of the reflector and the beam-shaped spring portion being integrally formed,
A very thin reflecting mirror with small internal stress can be obtained with good controllability.

Therefore, as described above, according to the present invention, it is possible to provide an optical deflecting element having a large effective area and a reflecting mirror having a small moment of inertia, which can be driven at high speed, and a method of manufacturing the same.

Further, according to the present invention, in order to realize a reflecting mirror having a small moment of inertia, an optical deflecting element and a light deflecting element adopting a method of stably manufacturing a semiconductor thin plate having a very small thickness and a small internal stress without distortion. The manufacturing method can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a main part of a light polarizing element according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of a main part of a light polarizing element according to a second embodiment of the present invention.

FIG. 3 is a perspective view showing a configuration of a main part of a light polarizing element according to a second embodiment of the present invention.

FIG. 4 shows a process chart of a method for manufacturing an optical polarizing element according to a fourth embodiment of the present invention, and FIG.
FIG. 4 is a front view of a main part of the light deflecting element according to the present invention, and FIG. 4B is a sectional view taken along the line AA ′ of FIG.

FIG. 5 is a diagram showing a process chart of a method for manufacturing an optical polarizing element according to a fourth embodiment of the present invention.

FIG. 6 is a diagram showing a process chart of a method for manufacturing an optical polarizing element according to a fourth embodiment of the present invention.

FIG. 7 shows a process chart of a method for manufacturing an optical polarizing element according to a fifth embodiment of the present invention, and FIG.
FIG. 7 is a front view of a main part of the optical deflecting element according to the present invention, and FIG. 7B is a sectional view taken along the line AA ′ of FIG.

FIG. 8 is a view showing a process chart of a method for manufacturing an optical polarizing element according to a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a process chart of a method for manufacturing an optical polarizing element according to a fifth embodiment of the present invention.

FIG. 10 is a perspective view for explaining a schematic configuration of a light deflecting device according to a conventional technique.

FIG. 11 is an exploded perspective view for explaining a schematic configuration of a conventional optical deflection device.

FIG. 12 is a cross-sectional view of a main part for describing a schematic configuration of an optical deflection device according to a conventional technique.

FIG. 13 is a perspective view for explaining a schematic configuration of an optical scanner according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Spring part, 2 ... Thick area, 3 ... Thin area, 4 ... Reflector, 51 ... P-type semiconductor substrate, 52 ... Deep N-type diffusion layer, 53 ... Shallow N-type diffusion layer, 54 ... Protective film of polyimide etc. 55, a silicon nitride film; 52 ', a region corresponding to the beam-shaped spring portion 1; 51', a frame portion remaining in the electrochemical etching step; 61, a low-concentration P-type semiconductor substrate; 62, an N-type diffusion layer 63, a P-type buried diffusion layer; 62 ', a region corresponding to the beam-shaped spring portion 1; 61', a frame portion remaining in the electrochemical etching step;

Claims (3)

[Claims] 1. An optical polarizing element integrally formed from a single crystal semiconductor, comprising: a beam-shaped spring portion serving as a rotation center of the optical polarizing element; and a reflecting mirror supported by the spring portion. The reflecting mirror comprises a first region and a second region extending in a direction perpendicular to the spring portion, and the first region and the second region are alternately arranged, and the thickness of the first region is changed. Is a light polarizing element formed to be thicker than the thickness of the second region. 2. An outer peripheral shape of the reflecting mirror is symmetrical about the beam-shaped spring portion, and one side of the reflecting mirror divided by the beam-shaped spring portion is the other side, First
2. The light polarizing element according to claim 1, wherein the area ratio of the second region is different from that of the second region. 3. The method according to claim 1, wherein the first main surface of the P-type semiconductor substrate has N
A first step of forming a mold diffusion layer; and performing electrochemical etching from the second main surface of the P-type semiconductor substrate using an alkaline solution to form a beam-shaped spring portion and a reflection supported by the spring portion. A second step of integrally forming the mirror and the mirror; and a method for manufacturing a light polarizing element.