Optical: systems and elements – Mirror – Including specified control or retention of the shape of a...
Reexamination Certificate
2001-11-07
2004-04-27
Sikder, Mohammad (Department: 2872)
Optical: systems and elements
Mirror
Including specified control or retention of the shape of a...
C359S847000, C359S848000, C359S883000
Reexamination Certificate
active
06726338
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-349925, filed Nov. 16, 2000; and No. 2000-349926 filed Nov. 16, 2000, the entire contents of both of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable shape mirror and its manufacturing method, and more particularly to a small variable shape mirror applying the semiconductor technology and its manufacturing method, in a variable shape mirror capable of varying the curvature continuously.
2. Description of the Related Art
In a micro optical system applied in photo pickup or other micro optics, hitherto, for the purpose of simplifying the mechanism relating to focusing by using electromagnetic actuator, an ultrasmall variable focus mirror capable of varying the curvature of the reflection plane has been proposed.
In a small photographic optical system, application of variable focus mirror contributes to reduction of size.
Such variable focus mirror is expected to be manufactured at low cost and high precision by applying the so-called MEMS (Micro Electro-Mechanical System) based on the semiconductor manufacturing technology.
As an example of such technology, a reflecting mirror device as a variable focus mirror is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
The reflecting mirror device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402 is explained briefly by referring to
FIGS. 8A and 8B
, and
FIGS. 9A
to
9
E.
FIGS. 8A and 8B
are sectional view and perspective view showing the configuration of the reflecting mirror device of electrostatic attraction driving system disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
In
FIGS. 8A and 8B
, reference numeral
11
is a glass or other insulating substrate (hereinafter called glass substrate), and a fixed side electrode layer
12
of conductive thin film is applied on the top of the glass substrate
11
.
Reference numeral
13
is a silicon or other semiconductor substrate (hereinafter called silicon substrate), and a silicon dioxide thin film
14
is formed as a insulating film on a principal plane of the silicon substrate
13
.
Reference numeral
15
is a vacancy formed on other principal plane in the central part of the silicon substrate
13
, and this vacancy
15
is to set the central part of the silicon dioxide thin film
14
displaceably in the thickness direction.
Reference numeral
16
is a movable side electrode layer, and this variable side electrode layer
16
is laminated on the thin silicon dioxide film
14
.
The central parts of the silicon dioxide thin film
14
and movable side electrode layer
16
form a reflecting mirror section
17
.
The reflecting mirror section
17
is recessed and deformed to the fixed side electrode layer
12
side by the voltage applied both electrode layers of the fixed side electrode layer
12
and movable side electrode layer
16
.
The silicon substrate
13
is bonded to the glass substrate
11
by way of a spacer member
18
, with the silicon dioxide thin film
14
side downward.
Also, in
FIGS. 8A and 8B
, reference numeral
19
is a silicon dioxide thin film formed on other principal plane of the silicon substrate
13
.
This reflecting mirror device is manufactured according to the manufacturing process diagrams shown in
FIGS. 9A
to
9
E.
FIGS. 9A
to
9
E are sectional views for explaining the manufacturing process of the reflecting mirror device of electrostatic attraction driving system disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.
First, as shown in
FIG. 9A
, silicon dioxide thin films
19
and
14
of 400 to 500 nm in thickness are formed on both sides of a silicon substrate
13
of plane azimuth <100> of which both sides are polished to mirror smoothness.
A gold thin film
16
of about 100 nm in thickness is applied on the silicon dioxide thin film
14
of the lower side.
Next, as shown in
FIG. 9B
, a photo resist
20
of specified pattern is applied on the silicon dioxide thin film
19
, and a circular window opening
21
is formed by photolithography.
With the lower side of the substrate in protected state, a window is opened in the silicon dioxide thin film
14
by a hydrofluoric acid solution, using the photo resist
20
as mask.
Further, as shown in
FIG. 9C
, the silicon substrate
13
is immersed in an aqueous solution of ethylene diamine pyrocatechol, and the silicon substrate is etched from the area of the window opening
21
.
At this time, as shown in the drawing, etching is stopped when the silicon dioxide
16
at the lower side is exposed.
Thus, a thin film of reflecting mirror section
17
composed of silicon dioxide film
14
and gold thin film
16
is left over.
On the other hand, in other process than mentioned above, as shown in
FIG. 9D
, a metal film of 100 nm in thickness is formed as a fixed side electrode layer
12
on the top of a glass substrate
11
of 300 nm in thickness.
Then, as shown in
FIG. 9E
, a silicon substrate
13
is adhered on the glass substrate
11
by way of a polyethylene spacer member
18
of about 100 &mgr;m in thickness, so that a reflecting mirror device is manufactured as shown in
FIGS. 8A and 8B
.
This variable focus mirror manufactured by adhering substrates as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402 involves the following first and second problems when applied in the optical system where a high focusing performance is required such as a high definition camera.
The first problem is about the opening shape of the upper substrate on which the reflecting plane is formed.
That is, to form an opening, it is most preferable to etch by using an alkaline solution such as aqueous solution of ethylene diamine pyrocatechol mentioned above or potassium hydroxide from the viewpoint of cost and combination with thin film members.
By etching, however, due to crystal azimuth dependence of the silicon substrate, an accurate circular or elliptical opening shape cannot be obtained.
If the opening is square or polygonal, the deformation of the reflecting plane due to stress is asymmetrical, and the astigmatism increases, and the focusing performance is lowered.
The second problem is distortion of the upper substrate in the assembling process.
That is, the upper substrate is a single crystal silicon substrate, and a high mirror flatness is achieved, but when bonding with the lower substrate, or due to stress caused in the connection process for leading out the electrode of the upper substrate to the external lead, the upper substrate is slightly deformed, and an adverse effect is caused on the mirror focusing performance.
This problem may be somewhat avoided by keeping the junction position of the substrates or the connection position of the electrode of the upper substrate to the external part sufficiently away from the mirror opening area, but, as a result, the entire size of the mirror element is increased, which is contradictory to requirements of smaller size and lower cost of the optical system.
Incidentally, as the driving method of this kind of variable shape mirror, aside from the method of using electrostatic attraction force disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402, a method of using piezoelectric effect disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 3-81132, and a method of using fluid pressure disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-219801 are known.
These methods have their own merits and demerits, but the method of using fluid pressure is advantageous in an application where very high response is not required but a relatively large displacement is needed from the concave surface to the convex surface.
As an example of a variable shape mirror of such fluid pressure drive, the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 1-219801 is briefly explained by referring to FIG.
10
.
This variable focus mirror
1
is composed of a shell
2
, chamber pressure
Frishauf Holtz Goodman & Chick P.C.
Olympus Optical Co,. Ltd.
Sikder Mohammad
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