Semiconductor dynamic quantity-sensor and method of...

Details Semiconductor dynamic quantity-sensor and method of... Semiconductor dynamic quantity-sensor and method of...

2001-05-09

2002-11-19

Le, N. (Department: 2858)

Electricity: measuring and testing

Determining nonelectric properties by measuring electric...

Semiconductors for nonelectrical property

C438S461000

Reexamination Certificate

active

06483283

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,
113
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 grand potential; and V+ and V− indicate 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 rigidity.
FIG.
13
(
c

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