JPH0749460A - Variable focus mirror and its manufacture - Google Patents

Abstract

PURPOSE:To provide a variable focus mirror which can be constituted in a size of a degree generally usable in an optical system, and constituted particularly in the state having no generation of distortion at non-deformation, and a method for manufacturing it. CONSTITUTION:An elastically isotropic thin film glass is adhered as a positive electrode on the surface of a single crystal silicon wafer, whereby a mirror body part holding a thin film diaphragm 11 by a ring base 12 is constituted. In the center part of the diaphragm 11 surrounded by the base 12, a metal layer 13 forming a light reflector and an electrode is evaporated. The ring base 12 is adhered to a base member 14 formed of a resin with an adhesive having a low Young's modulus, and a counter electrode 15 is formed on the position opposed to the metal layer 13 of the base member 14. A voltage generating circuit 18 is connected between the metal layer 13 and the counter electrode 15 so that a continuously variable DC voltage can be applied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a varifocal mirror whose focal length is variably controlled without initial distortion and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a varifocal mirror whose focal length can be variably adjusted, for example, Japanese Patent Laid-Open No. 4-212116
The technique disclosed in the spatial light modulation semiconductor device shown in Japanese Patent Publication is known. This semiconductor device is provided with a mirror array of a large number of mirrors formed by a thin film that is attracted by an electric field when the transistor is turned on. A thin film composed of a non-metal layer having high flexibility such as nitrocellulose and a metal layer is formed on a substrate, and the thin film constitutes the main body of the mirror.

This method of forming a thin film is suitable for forming a minute varifocal mirror, but for realizing a mirror having a size of, for example, 10 mm or more, which is used in an ordinary optical system. Inappropriate. The reason is that the bending elastic modulus of a thin film of a polymer having a thickness of 800 A (A is angstrom) is equal to “0”, and it is 10 mm used in a usual optical system.
In the case of the one having the above size, it is impossible to hold and fix the thin film without distortion when it is not deformed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in particular, it is necessary to fix and hold the mirror main body section without distortion when the mirror body section has an infinite focal length without deformation. Enabled, especially for example 10m
It is an object of the present invention to provide a varifocal mirror that can be configured without initial distortion in a size used in a normal optical system of m or more, and a manufacturing method thereof.

[0005]

A varifocal mirror according to the present invention comprises a concentric cylindrical ring-shaped substrate, and a thin film diaphragm is provided on one surface of the ring-shaped substrate to suppress stress strain asymmetrical to the central axis. In the state of being joined and supported,
A metal layer acting as a light reflecting member and an electrode member is formed in a region surrounded by the cylindrical portion of the ring-shaped substrate of the thin film diaphragm. Then, the ring-shaped substrate is attached to a pedestal member made of an insulating material, and a counter electrode is formed so as to face the thin film diaphragm of the pedestal member at small intervals to form a counter electrode. , A DC power source whose voltage value is variably controlled is connected.

Further, a thin film diaphragm layer made of an isotropic material is bonded and formed on one surface of the substrate member, and a circular ring-shaped portion is left on the surface of the substrate member opposite to the bonding surface of the diaphragm. A ring-shaped substrate is formed by forming an opening mask and etching the substrate member corresponding to the opening to reach the bonded diaphragm. A surface of the diaphragm surrounded by the ring-shaped substrate. A varifocal mirror is manufactured by forming a metal layer by vapor deposition.

[0007]

In the varifocal mirror configured as described above, the thin film diaphragm that constitutes the reflector is asymmetric with respect to the central axis with respect to the ring-shaped substrate made of, for example, single crystal silicon. It is joined and supported in a state in which stress and strain are suppressed, and therefore, it can be held and fixed in a strain-free state particularly when it is not deformed, and has a size of, for example, 10 mm or more used in a normal optical system. It is possible to realize a mirror having a variable focal length.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure, and the mirror reflector whose focal length is variable is composed of a thin film diaphragm 11. This thin film diaphragm 11 is made of, for example, Pyrex glass. Pyrex glass is quartz glass containing 3.5% of sodium ions and suitable for anodic bonding, and constitutes elastically isotropic glass. . The thin film diaphragm 11 is configured to be deformable as a mirror portion, and has a film thickness of about 10 μm and a diameter of about 10 mm.

The thin film diaphragm 11 is held by a cylindrical ring-shaped substrate 12 made of, for example, single crystal silicon, and one end face of the ring-shaped substrate 12 has an outer peripheral edge portion of the thin film diaphragm 11 as an anode. The thin film diaphragm 11 is bonded by bonding, and the flatness of the thin film diaphragm 11 is guaranteed by the ring-shaped substrate 12 when it is not deformed, and the thin film diaphragm 11 is held in a state of low stress strain so as to be deformed concentrically. Therefore, in this way, the thin film diaphragm 11
It is preferable that the ring-shaped substrate 12 that holds the film has a large thickness (the length in the axial direction of the cylinder).
It may be configured with about m.

On the surface of the thin film diaphragm 11 thus held by the ring-shaped substrate 12, a metal layer 13 is thinly vapor-deposited so as to act as a light reflection and an electrode. The metal layer 13 is made thin enough to allow deformation deformation of the thin film diaphragm 11 and to act as light reflection and an electrode. For example, the metal layer 13 has a film thickness of about 300A. It

The ring-shaped substrate 12 holding the thin film diaphragm 11 is held by a pedestal member 14 made of an insulating material such as synthetic resin. The pedestal member 14 is attached to the ring portion of the ring-shaped substrate 12. Corresponding ring-shaped support
141 and a facing portion 142 of the thin film diaphragm 11 formed in a bottom shape on the inner peripheral portion of the ring-shaped supporting portion 141. The facing portion 142 includes a metal layer of the thin film diaphragm 11.
A counter electrode layer 15 is formed so as to face 13 at a small interval. Then, a groove 16 for preventing current leakage is formed so as to surround the counter electrode layer 15, and the ring-shaped substrate 12 is integrally bonded to the pedestal member 14 with an adhesive having a low Young's modulus. .

Metal layer 1 formed on thin film diaphragm 11
Lead wires 171 and 172 are derived from the counter electrode layer 15 formed on the base member 14 and the counter electrode layer 3, respectively, and the voltage generation circuit 18 is connected to the lead wires 171 and 172. Then, the electrode formed of the metal layer 13 and the counter electrode layer 15
DC voltage that is continuously controlled to be changed between
An attraction force corresponding to the applied voltage value is set between the thin film diaphragm 11 in which the metal layer 13 is set and the pedestal member 14 in which the counter electrode 15 is set, so that the thin film diaphragm 11 is driven.

In the varifocal mirror configured as described above, when the DC voltage generated by the voltage generating circuit 18 is applied between the metal layer 13 and the counter electrode 15, the metal layer 13 and the counter electrode 15 are separated from each other. An electrostatic force is generated between the two, and for example, the gap between the metal layer 13 and the counter electrode 15 is 0.5 mm, and the applied voltage is 2
At 300 V, the thin film diaphragm 11 is deformed by suction by about 20 μm. This deformed thin film diaphragm 11
The focal length of the reflecting mirror is 30
It is 0 mm.

By changing the value of the DC voltage applied between the metal layer 13 and the counter electrode 15, the electrostatic force acting between the metal layer 13 and the counter electrode 15 is changed.
The deformation curvature of the thin film diaphragm 11 is changed according to the change of the electrostatic force, and the focal length as the reflecting mirror is continuously changed corresponding to the change of the deformation curvature. This focal length can be varied from 300 mm to infinity, for example.

The body of the reflecting mirror is a thin film diaphragm.
Since the thin film diaphragm 11 is held by the ring-shaped substrate 12, stress strain other than concentric circles is small and the material is isotropic. It deforms symmetrically with respect to the central axis, so that the condensing characteristics are good.

Metal layer 13 formed on thin film diaphragm 11
The electric field strength between the two electrodes with respect to the applied voltage changes depending on the distance between the electrode and the counter electrode 15 due to the change in the applied voltage. Therefore, it becomes necessary to monitor the electrostatic capacitance between the metal layer 13 of the thin film diaphragm 11 that constitutes the mirror and the counter electrode 15.

Since the metal layer 13 and the counter electrode 15 compose a capacitor, the capacitance between the metal layer 13 and the counter electrode 15 is monitored so that the diaphragm 11 is affected by a disturbance due to temperature or the like. It is also possible to correct the initial displacement of the diaphragm 11 and control the drive voltage so that the diaphragm 11 always has a constant deformation amount.

Next, a method of manufacturing the varifocal mirror having such a structure, particularly a mirror constituent portion will be described. First, an oxide film by thermal oxidation or a nitride film is formed by plasma CVD on both surfaces of a single crystal silicon wafer having a film thickness of about 200 μm and a plane orientation of (100). Figure 2
(A) shows a state in which an oxide film 22 is formed on the surface of the silicon wafer 21, and the oxide film 22 is patterned so as to expose a portion 221 to be an electrode for anodic bonding. The oxide film 22 to be patterned
The film thickness of 1 is set to about 1 μm because it needs to function in the silicon etching process described later. Further, a thin oxide film 23 that can be anodically bonded is formed on the back surface of the silicon wafer 21. This oxide film 23 is set to protect the mirror surface during etching, and preferably has a film thickness of about 1000A.

When the predetermined oxide films 22 and 23 are formed on both surfaces of the silicon wafer 21 in this way, as shown in FIG. 7B, the back surface portion of the silicon wafer 21 on which the oxide film 23 is formed. The glass plate 24 having a thickness of about 1 mm is anodically bonded. After that, the bonded glass plate 24 is ground,
As shown in FIG. (C), a glass thin film 24 having a film thickness of about 10 μm 24
Set to 1.

When the glass thin film 241 is bonded to the silicon wafer 21 in this way, the oxide film 22 is patterned in a circular shape having a diameter of about 10 mm at the center of the oxide film 22 as shown in FIG. It is removed to form the central exposed portion 222. Then, the ring-shaped exposed portion 223 is formed so as to surround the outer periphery of the central exposed portion 222.

In this way, a mask made of the oxide film 22 having the exposed portions 222 and 223 is formed on the surface of the silicon wafer 21. If such a mask is formed, as shown in FIG. As shown in (A) of FIG.
The silicon wafer 21 is etched corresponding to the area, and the oxide film
Silicon is etched away up to 23. For this etching, a mixed solution of potassium hydroxide and isopropyl alcohol is used. Through such an etching process, the thin film diaphragm 11 made of the glass thin film 241 having no distortion and held on the substrate 12 by the silicon ring can be obtained.

Then, as shown by the broken line in the figure, by cutting and separating from the etching portion corresponding to the ring-shaped exposed portion, the diaphragm made of the glass thin film 241 is formed on the surface of the ring-shaped substrate 12 as shown in FIG. This will form the mirror main body where 11 is joined.
A metal layer 13 made of aluminum is vapor-deposited on the surface of the glass thin film 241 corresponding to the cylindrical portion at the center of 12 to a thickness of about 300 A, whereby a mirror reflection surface and an electrode are formed.

The pedestal member 14 shown in FIG. 1 to which such a mirror body is attached may be deformed by a disturbance such as a temperature change. However, if the pedestal member 14 is deformed so that the central axis of the thin film diaphragm 11 is asymmetrical, the pedestal member 14 cannot sufficiently function as an optical mirror. Therefore, the ring-shaped substrate 12 is bonded and fixed to the pedestal member 14 with an adhesive having a low Young's modulus and sufficient adhesive strength so that the deformation of the resin material forming the pedestal member 14 can be sufficiently absorbed. To

When manufacturing such a variable focus mirror, the following material characteristics are required. First, in order to obtain the diaphragm 11 having a sufficient bonding strength and a small surface roughness, it is necessary to use one having a very good surface accuracy for the bonding surface between the thin film diaphragm 11 and the ring-shaped substrate 12. A mirror surface having a flatness of 10 μm or less is preferable.

Further, in order to obtain an axially symmetrical deformed shape, it is desirable that the thin film glass constituting the thin film diaphragm 11 has a uniform film thickness. However, since the parallelism of the glass thin plate is ground on the basis of the parallelism of the silicon wafer made of single crystal silicon, the parallelism of the wafer made of single crystal silicon should be as good as possible, preferably The parallelism of the entire 4-inch wafer is about 1 μm.

Furthermore, during anodic bonding between the silicon wafer forming the ring-shaped substrate 12 and the glass plate forming the diaphragm 11, the difference in the coefficient of thermal expansion between the two substances appears as stress strain of the thin film diaphragm 11.
It is necessary that the glass material used here has a coefficient of thermal expansion close to that of silicon.

In the embodiment shown in FIG. 1, the ring-shaped substrate 12 holding the thin film diaphragm 11 is adhered and fixed to the pedestal member 14 made of a resin material.
As shown in FIG. 5, a pedestal member for holding the ring-shaped substrate 12
Hold 14 between the glass ring 31 and the rubber ring 32,
The housing 33 made of resin or the like may be fixed by a screw ring 34 so as to be fixed.

That is, the ring-shaped substrate 12 holding the thin film diaphragm 11 which is a mirror reflector is held by an elastic material including a rubber ring 32, and the rubber ring 32 is made of conductive rubber. The metal layer 18 deposited on the surface of the diaphragm 11 by
Can be connected to the power supply via this rubber ring 32. Therefore, by adopting such a fixed holding structure, the assembly of the mirror main body can be facilitated, and the mirror main body can be fixed with high accuracy and certainty, and a structure that can endure mechanical vibration. To be done.

In the embodiment, the thin film diaphragm is used.
Although it has been described that 11 is made of thin film glass, it can be made of a polycrystalline metal film, an amorphous metal film, or an isotropic material such as polyimide.

When a polycrystalline metal is used as the thin film diaphragm 11, for example, the ring-shaped substrate 12 to which the diaphragm is attached is made of aluminum, and a metal which is not etched, preferably nickel, is formed on the ring-shaped substrate 12 made of aluminum. Is plated to about 10 μm. After that, a metal such as aluminum is patterned by mechanical grinding, and the entire surface is alkali-etched until the nickel serving as the diaphragm is exposed to form a nickel-plated film. Like glass, it is held on a ring-shaped substrate made of aluminum.

When a polyimide film is used, this polyimide material is applied to a metal such as aluminum by spin coating to a film thickness of about 10 μm. Then, a metal such as aluminum is patterned by mechanical grinding, and the entire surface is alkali-etched until the polyimide serving as the diaphragm is exposed, so that a polyimide film serving as the diaphragm is obtained.

[0032]

As described above, the varifocal mirror according to the present invention can be easily constructed to a size that can be used in an ordinary optical system, and in particular, when the mirror main body is not deformed, distortion is not generated. Since the thin film diaphragm constituting the reflector is fixedly held in the absence of the variable focus mirror, it is possible to provide a reliable variable focus mirror with a wide range of applications.

[Brief description of drawings]

1A and 1B show a variable focus mirror according to an embodiment of the present invention, in which FIG. 1A is a sectional view and FIG. 1B is a plan view.

2A to 2C are views sequentially illustrating a manufacturing process of the thin film diaphragm of the above embodiment.

3A and 3B show a diaphragm member manufactured in a process following FIG. 2C, in which FIG. 3A is a plan view and FIG.

4A is a diagram showing a state where the diaphragm member shown in FIG. 3 is etched, and FIG. 4B is a diagram showing a part of the diaphragm member in an enlarged manner.

FIG. 5 is a sectional configuration diagram of a varifocal mirror according to another example of the present invention.

[Explanation of symbols]

11 ... Thin film diaphragm, 12 ... Ring substrate, 13 ... Metal layer, 14 ... Pedestal member, 15 ... Counter electrode, 16 ... Groove, 171, 172
… Lead wire, 18… Voltage generator circuit.

Claims (2)

[Claims] 1. A concentric cylindrical ring-shaped substrate, a thin film diaphragm joined and supported on one surface of the ring-shaped substrate in a state in which stress strain asymmetrical to the central axis is suppressed, and the thin film diaphragm described above. A metal layer formed on one surface corresponding to a region surrounded by the cylindrical portion of the ring-shaped substrate and serving as a light reflecting member and an electrode member, and a pedestal composed of an insulator supporting the ring-shaped substrate A direct current power supply having a voltage value variably controlled between the metal layer and the counter electrode, the counter member being provided so as to face the thin film diaphragm of the pedestal member at a small interval. A variable-focus mirror characterized in that it is connected to. 2. A diaphragm bonding step of bonding and forming a thin film diaphragm layer made of an isotropic material on one surface of a substrate member, and a circular ring on the surface of the substrate member opposite to the bonding surface of the diaphragm. A mask forming step for forming an opening mask that leaves a ring-shaped portion, and an etching for forming a ring-shaped substrate by etching the substrate member corresponding to the opening formed in the mask forming step to reach the bonded diaphragm. A method of manufacturing a varifocal mirror, comprising: a step of forming a metal layer by vapor deposition on a surface of the diaphragm surrounded by the ring-shaped substrate.