Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Physical stress responsive
Reexamination Certificate
1999-12-23
2001-08-28
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Physical stress responsive
C438S052000, C438S739000, C216S002000, C216S092000
Reexamination Certificate
active
06281033
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for manufacturing a semiconductor physical quantity sensor that senses physical quantities such pressure, acceleration and angular velocity.
DESCRIPTION OF RELATED ART
FIGS.
7
(
a
)-(
b
) show the essential structure of a conventional semiconductor physical quantity sensor. FIG.
7
(
a
) is a plan view, and FIG.
7
(
b
) is a sectional view cut along line Y—Y in FIG.
7
(
a
).
As shown in FIGS.
7
(
a
)-(
b
), an SOI substrate
100
consists of a silicon substrate
1
, an oxide film
2
and a silicon layer
3
(a single crystal layer or a polysilicon layer). A semiconductor physical quantity sensor is formed in the silicon layer
3
, which is the third layer on the SOI substrate
100
. The semiconductor physical quantity sensor consists of a sensing element
103
, a digital adjustment circuit
104
, an analog amplifier circuit
105
, an input/output terminal
106
and a digital adjustment terminal
107
. The sensing element
103
is warped as indicated by an arrow in FIG.
7
(
b
) by pressure, acceleration and angular velocity. The semiconductor physical quantity sensor sensing physical quantities such as pressure, acceleration and angular velocity by amplifying electric signals generated by the warp.
FIGS.
8
(
a
)-(
b
) show the essential structure of a conventional sensing element. FIG.
8
(
a
) is a plan view, and FIG.
8
(
b
) is a sectional view cut along line B—B in FIG.
8
(
a
).
In FIGS.
8
(
a
)-(
b
), the oxide film
2
at the bottom of the sensing element
103
, which is arranged at the center of the silicon layer
3
, is removed in order to allow weight portions
110
a
,
110
b
of the sensing element
103
to move freely. The sensing element
103
comprises four beams
111
a
,
111
b
,
111
c
,
111
d
with semiconductor strain gauges
113
a
,
113
b
,
113
c
,
113
d
; the weight portions
110
a
,
110
b
with holes
15
for etching the oxide film as a sacrifice layer; and four beams
111
e
,
111
f
,
111
g
,
111
h
that support the weight portions
110
a
,
110
b
and have no semiconductor strain gauge. The weight portions
110
a
,
110
b
deform the eight beams. The semiconductor strain gauges
113
a
,
113
b
,
113
c
,
113
d
sense the deformations of the four beams
111
a
,
111
b
,
111
c
,
111
d
with the semiconductor strain gauges, and convert the deformations into electric signals. As shown in FIGS.
8
(
a
)-(
b
), the sensing element
103
is composed of the silicon layer
3
having the holes
15
, and the sensing element
103
sticks on the silicon substrate
1
through the oxide film
2
. The sensing element
103
is supported at a position where it sticks on the silicon substrate
1
(the position is not shown in FIG.
8
(
a
)).
FIG. 9
is a circuit diagram showing the semiconductor physical quantity sensor. An analog amplifier circuit
105
amplifies an output voltage of a Wheatstone bridge, which is composed of the four semiconductor strain gauges
113
a
,
113
b
,
113
c
,
11
3
d
. The digital adjustment circuit
104
adjusts the sensitivity and the temperature characteristics.
A description will now be given of the operation of an acceleration sensor, which is an example of the semiconductor physical quantity sensor. If a force generated by the vertical acceleration is applied to the semiconductor physical quantity sensor, a compressive stress acts on the two semiconductor strain gauges
113
b
,
113
d
of the four semiconductor strain gauges
113
a
,
113
b
,
113
c
,
113
d
to decrease their resistance. On the other hand, a tensile stress acts on the two semiconductor strain gauges
113
a
,
113
c
to increase their resistance. The change in the resistance causes the Wheatstone bridge circuit to output a sensor signal corresponding to the acceleration. Vcc indicates a high potential of a power supply voltage; GND indicates a ground potential; and V+ and Vindicate a positive potential and a negative potential, respectively.
FIGS. 10 and 11
are sectional views showing steps A-F in order in a conventional method for manufacturing the semiconductor physical quantity sensor.
At the step A, an insulating layer of the oxide film
2
such as BPSG film or PSG film is formed on the silicon substrate
1
, and the silicon layer
3
made of polysilicon or the like is formed on the oxide film
2
to thereby construct a SOI substrate
100
. Although not illustrated in the drawings, the previously-mentioned semiconductor strain gauges, the analog amplifier circuit
105
, the digital adjustment circuit
104
, the input/output terminal
106
, the digital adjustment terminal
107
, or the like are formed in the silicon layer
3
.
At the step B, a resist film
4
is coated and patterned on the silicon layer
3
. Then, a number of holes
15
are formed in the silicon layer
3
by wet etching using mixed acid of hydrofluoric acid (HF) or by dry etching using mixed gas of nitric acid (HNO
3
), and sulfur hexafluoride (SF
6
) and oxygen (O
2
), thus forming the sensing element
103
(indicated by an arrow). The sensing element
103
is formed in the silicon layer
3
including the weight portions
110
.
At the step C, the oxide film
2
, which is the sacrifice layer opposite to the bottom of the silicon layer
3
, is removed by an etching liquid
5
such as HF.
At the step D, the sensing element
103
is cleaned by a displacement liquid
6
such as pure water and isopropyl alcohol (IPA), and then the displacement liquid
6
is vaporized to dry the sensing element
103
. In the drying process, a surface tension of the displacement liquid
6
generates a suction force
7
toward the silicon substrate
1
.
At the step E, the weight portions
110
of the sensing element
103
formed in the silicon layer
3
made of polysilicon with low rigidity are sucked and stuck on the silicon substrate
1
by the suction force
7
. This is called a sticking phenomenon.
At the step F, the resist film is ashen and removed while the weight portions
110
stick on the silicon substrate
1
.
If the weight portions
110
stick on the silicon substrate
1
in the sticking phenomenon, the physical quantity sensor is useless.
A description will now be given of a manufacturing method that prevents the sticking phenomenon (Japanese Patent Publication No. 7-505743).
FIGS. 12 and 13
are sectional views showing steps A-F in order in a conventional method for manufacturing the semiconductor physical quantity sensor. This method is disclosed in Japanese Patent Publication No. 7-505743.
At the step A, a sacrifice layer of an oxide film
2
such as BPSG and PSG is formed on a silicon substrate
1
, and a silicon layer
3
made of polysilicon is formed on the oxide film
2
.
At the step B, a resist film
4
is coated and patterned on the silicon layer
3
, and a sensing element
103
is formed in the silicon layer
3
.
At the step C, an etching liquid
5
etches the oxide film
2
in such a manner as to partially remain that the oxide film
2
as the sacrifice layer just below the silicon layer
3
.
The silicon layer
3
sticks on the silicon substrate
1
through the remaining oxide film
2
.
At the step D, a photosensitive polymer
15
is coated and patterned in such a manner as to fill up a part A, from which the oxide film
2
as the sacrifice layer between the silicon layer
3
and the silicon substrate
1
has already been removed.
At the step E, an etching liquid
13
etches the remaining oxide film
2
in order to remove the oxide film
2
from a part B.
At the step F, the etching liquid
13
at the part where the oxide film
2
has already been removed is substituted with a displacement liquid
6
to dry the part B. At this time, a surface tension of the displacement liquid
6
causes a suction force
27
to act on the silicon substrate
1
as indicated by an arrow. This does not result in the sticking phenomenon in which the weight portions
100
of the sensing element
103
stick on the silicon substrate
1
at a position
30
inside the circle, because the photosensitive polymer
15
has a high rig
Katsumi Shiho
Nishikawa Mutsuo
Sasaki Mitsuo
Uayanagi Katsumichi
Fuji Electric & Co., Ltd.
Niebling John F.
Rossi & Associates
Simkovic Viktor
LandOfFree
Semiconductor dynamic quantity-sensor and method of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor dynamic quantity-sensor and method of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor dynamic quantity-sensor and method of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2501028