Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal
Reexamination Certificate
2000-10-03
2003-02-04
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
C438S049000
Reexamination Certificate
active
06514786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing an acceleration sensor having a fixed electrode and a movable electrode to be displaced according to an acceleration and serving to measure an acceleration based on a change in an electrostatic capacity between both electrodes.
2. Description of the Background Art
FIG. 13
is a sectional view showing an example of a structure of an acceleration sensor. The acceleration sensor comprises fixed electrodes
2
a
and
2
b
, a movable electrode
1
, a surface side substrate
3
, a back side substrate
4
and a frame portion
7
.
The movable electrode
1
is displaced upon receipt of an acceleration. Accordingly, respective distances between the movable electrode
1
and the fixed electrodes
2
a
and
2
b
are changed. The change is detected as a variation in the electrostatic capacitance. Thus, the acceleration sensor converts the acceleration into an electric signal.
Moreover,
FIGS. 14 and 15
are perspective views showing the acceleration sensor seen from the surface and back sides, respectively.
FIG. 13
is a sectional view taken along the line A—A in
FIGS. 14 and 15
. In order to clearly illustrate an internal structure of the acceleration sensor, the back side substrate
4
and the surface side substrate
3
are separated from the acceleration sensor in
FIGS. 14 and 15
, respectively. Furthermore,
FIG. 16
is a plan view showing the fixed electrodes
2
a
and
2
b
, the movable electrode
1
and the frame portion
7
in which the surface side substrate
3
is separated from the acceleration sensor.
As shown in
FIGS. 13
to
16
, the movable electrode
1
takes the shape of a rectangular parallelepiped having an H-shaped projection
1
e
on one surface. Then, beam-shaped portions
1
a
and
1
c
are extended from a set of opposite sides of the rectangular parallelepiped and the beam-shaped portions
1
a
and
1
c
are connected to movable electrode support portions
1
b
and
1
d
, respectively.
The projection
1
e
is provided on the movable electrode
1
for the following reason. The weight of the movable electrode
1
should be reduced to increase a sensitivity to the acceleration, and furthermore, the distance between the back side substrate
4
and the movable electrode
1
should not be greatly increased as compared with the distance between the surface side substrate
3
and the movable electrode
1
.
The movable electrode support portions
1
b
and
1
d
are joined to the back side substrate
4
and the surface side substrate
3
, and the movable electrode
1
is maintained in a floating state by the joined portions and the beam-shaped portions
1
a
and
1
c
. The back side substrate
4
and the surface side substrate
3
are provided with concave portions
4
a
and
3
d
such that the back side substrate
4
and the surface side substrate
3
do not come in contact with the movable electrode
1
, respectively.
Moreover, the fixed electrodes
2
a
and
2
b
and the frame portion
7
are also joined to the back side substrate
4
and the surface side substrate
3
. The movable electrode
1
is provided to be interposed between the two fixed electrodes
2
a
and
2
b
. The movable electrode
1
is not in contact with the two fixed electrodes
2
a
and
2
b
through a void
5
.
The surface side substrate
3
is provided with contact holes
3
a
and
3
b
to be connected to the fixed electrodes
2
a
and
2
b
respectively and a contact hole
3
c
to be connected to the movable electrode support portion
1
d
. Electric potentials of the respective electrodes are detected from the contact holes
3
a
to
3
c
. Then, a change in an electrostatic capacity is detected between the electrodes. Only one fixed electrode can also be operated in the same manner. In that case, it is enough that the surface side substrate
3
should be provided with the contact hole
3
a
or
3
b
and the contact hole
3
c.
A method of manufacturing the acceleration sensor will be described below.
First of all, a silicon substrate for forming the movable electrode
1
, the fixed electrodes
2
a
and
2
b
and the frame portion
7
and two glass substrates to be the surface side substrate
3
and the back side substrate
4
are prepared. The contact holes
3
a
to
3
c
and the concave portion
3
d
are formed in one glass substrate and the concave portion
4
a
is formed in another glass substrate. Thus, the surface side substrate
3
and the back side substrate
4
are formed.
In the silicon substrate, moreover, patterns of the movable electrode
1
, the beam-shaped portions
1
a
and
1
c
, the movable electrode support portions
1
b
and
1
d
, the fixed electrodes
2
a
and
2
b
and the frame portion
7
are formed from the side of the surface side substrate
3
to the middle of a thickness of the substrate (corresponding to a thickness of the movable electrode
1
) by using a photolithographic technique and an anisotropic etching technique.
Next, the silicon substrate and the surface side substrate
3
are joined to each other by using an anode junction method. As shown in
FIG. 17
, the silicon substrate
11
and the surface side substrate
3
are provided in alignment, and electrodes
13
and
15
are connected thereto and are heated, respectively. When a temperature suitable for the anode junction method is reached, a voltage is applied to the electrodes
13
and
15
. At this time, a ground potential GND is applied to the electrode
13
connected to the silicon substrate
11
, and an electric potential which is lower than the ground potential GND by an electric potential difference E is applied to the electrode
15
connected to the surface side substrate
3
. In order to generate the electric potential difference E, it is preferable that a DC power supply
14
should be connected to the electrodes
13
and
15
. By properly regulating the value of the electric potential difference E, a time required for application thereof, a temperature for junction and the like, a junction current is caused to flow to both electrodes so that the silicon substrate
11
and the surface side substrate
3
can be joined to each other.
Next, the voltage application is stopped and the electrodes
13
and
15
are removed from the silicon substrate
11
and the surface side substrate
3
. By using the photolithographic technique and the anisotropic etching technique, the patterns of the projection
1
e
of the movable electrode
1
, the movable electrode support portions
1
b
and
1
d
, the fixed electrodes
2
a
and
2
b
and the frame portion
7
are formed in a surface of the silicon substrate
11
which is opposite to the surface side substrate
3
. Consequently, the movable electrode
1
is brought into a floating state.
Then, the anode junction method is used again to join the silicon substrate
11
to the back side substrate
4
. As shown in
FIG. 18
, the silicon substrate
11
having the movable electrode
1
, the fixed electrodes
2
a
and
2
b
and the frame portion
7
formed thereon and the back side substrate
4
are provided in alignment, and electrodes
13
and
15
are connected to the surface side substrate
3
and the back side substrate
4
and are heated, respectively. When a temperature suitable for the anode junction method is reached, a voltage is applied to the electrodes
13
and
15
. At this time, a ground potential GND is applied to the electrode
13
connected to the surface side substrate
3
, and an electric potential which is lower than the ground potential GND by the electric potential difference E is applied to the electrode
15
connected to the back side substrate
4
. The same electric potential as that of the electrode
13
is applied to the frame portion
7
in the silicon substrate
11
. By properly regulating the value of the electric potential difference E, a time required for application thereof, a temperature for junction and the like, a junction current is caused to flow to both electrodes so that the silicon substrate
11
and the back side subst
Fukaura Teruya
Nakamura Kunihiro
Yamaguchi Yasuo
Le Dung A
Mitsubishi Denki & Kabushiki Kaisha
Nelms David
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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