Semiconductor sensor structure and method of manufacturing...

Details Semiconductor sensor structure and method of manufacturing... Semiconductor sensor structure and method of manufacturing...

2000-08-29

2002-02-12

Christianson, Keith (Department: 2813)

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Physical deformation

C438S052000

Reexamination Certificate

active

06346735

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a semiconductor structure used in sensors for sensing dynamic quantities. The present invention relates also to a method of manufacturing the semiconductor structure.
At first, conventional methods of manufacturing a semiconductor structure are explained with reference to FIGS.
6
(
a
) through
8
(
f
).
FIGS.
6
(
a
)-
6
(
e
) describe a first conventional method of manufacturing a semiconductor structure.
Referring now to FIGS.
6
(
a
)-
6
(
e
), an insulation layer
11
of boro-phospho silicate glass (BPSG) or phospho silicate glass (PSG) is formed on an Si substrate
10
in the step shown in FIG.
6
(
a
). A polysilicon layer
12
, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer
11
. Alternatively, silicon on an insulator (hereinafter referred to as “SOI”) wafer, including an oxide insulation layer
11
bonded onto the Si substrate
10
and the Si active layer
12
on the oxide insulation layer
11
, is used.
In the step of FIG.
6
(
b
), a resist film is formed on the polysilicon layer (or the Si active layer)
12
, and the resist film is patterned. Then, the polysilicon layer (or Si active layer)
12
with the patterned resist film thereon is etched, resulting in a sensor structure
13
.
In the step of FIG.
6
(
c
), the oxide insulation layer
11
or sacrificed layer, such as the BPSG insulation layer, PSG insulation layer, or Si oxide layer, is etched with buffered hydrofluoric acid (BHF) or such an etchant
20
.
Thus, a polysilicon structure
30
including the deformable sensor structure
13
formed of Si beams is formed above the central part of the substrate
10
. The polysilicon structure
30
is spaced apart from the Si substrate
10
in the central part of the Si substrate
10
. The polysilicon structure
30
is sustained by the beams on the Si substrate
10
in the peripheral part of the Si substrate
10
.
In the step of FIG.
6
(
d
), the etchant
20
is replaced by a cleaning liquid, such as pure water and isopropyl alcohol (IPA), and the region including the polysilicon sensor structure
13
is washed with the cleaning liquid.
In the drying step of FIG.
6
(
e
), surface tension
21
of the cleaning liquid occurs in the gap between the sensor structure
13
and the Si substrate
10
. The sensor structure
13
with low rigidity is attracted to the Si substrate
10
by the surface tension
21
.
FIGS.
7
(
a
)-
7
(
h
) describe a second conventional method of manufacturing a semiconductor structure.
Referring now to FIG.
7
(
a
), an insulation layer
11
of BPSG or PSG is formed on a Si substrate
10
. A polysilicon layer
12
, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer
11
. Alternatively, an SOI wafer, including an oxide insulation layer
11
bonded onto an Si substrate
10
and an Si active layer
12
on the oxide insulation layer
11
, is used.
In the step of FIG.
7
(
b
), a resist film is formed on the polysilicon layer (or Si active layer)
12
, and the resist film is patterned. Then, the polysilicon layer (or Si active layer)
12
with the patterned resist film thereon is etched, resulting in a sensor structure
13
.
In the step of FIG.
7
(
c
), a sacrificed layer (BPSG insulation layer, PSG insulation layer, or Si active layer) is etched with an etchant
20
to an extent that the sensor structure
13
does not become completely free.
In the step of FIG.
7
(
d
), the sensor structure
13
and the sacrificed layer remaining under the sensor structure are covered with a photosensitive polymer film
40
, and the photosensitive polymer film
40
is patterned so that the sensor structure
13
is sustained by the patterned photosensitive polymer film.
In the step of FIG.
7
(
e
), the remaining sacrificed layer is etched and the resulting sensor structure
13
is dried. Since the sensor structure
13
is sustained by the rigidity of the photosensitive polymer
40
, any sticking phenomenon does not occur between the sensor structure
13
and the substrate
10
.
In the step of FIG.
7
(
f
), the photosensitive polymer
40
is removed by ashing or such a dry process.
The sensor structure
13
is made free and deformable through the steps of FIGS.
7
(
g
) and
7
(
h
).
FIGS.
8
(
a
)-
8
(
f
) describe a third conventional method of manufacturing a semiconductor structure disclosed in Japanese Unexamined Laid Open Patent Publications No. H07-209105 and No. H07-245414.
Referring now to FIG.
8
(
a
), an insulation layer
11
of BPSG or PSG is formed on an Si substrate
10
. A polysilicon layer
12
, that will be a movable electrode and a stationary electrode later, is formed on the insulation layer
11
. Alternatively, an SOI wafer, including an oxide insulation layer
11
bonded onto the Si substrate
10
and the Si active layer
12
on the oxide insulation layer
11
, is used.
In the step of FIG.
8
(
b
), a resist film is formed on the polysilicon layer (or Si active layer)
12
, and the resist film is patterned. Then, the polysilicon layer (or Si active layer)
12
with the patterned resist film thereon is etched, resulting in a sensor structure
13
.
In the step of FIG.
8
(
c
), the insulation layer
11
or sacrificed layer (BPSG insulation layer, PSG insulation layer, or Si active layer) is etched with BHF or such an etchant
20
.
In the step of FIG.
8
(
d
), the etchant is replaced by a sublimable material
50
, such as paradichlorobenzene and naphthalene, in the liquid state thereof. The sublimable material
50
is solidified in the gap between the sensor structure
13
and the Si substrate
10
.
The sensor structure
13
is formed finally through the steps of FIGS.
8
(
e
) and
8
(
f
) by sublimating the sublimable material
50
.
The conventional semiconductor structures or the conventional methods of manufacturing the semiconductor structures have the problems described below.
As described in connection with the steps of FIGS.
6
(
d
) and
6
(
e
) in the first conventional manufacturing method, the surface tension
21
of the cleaning liquid occurs in the gap between the polysilicon structure
30
and the Si substrate
10
. The sensor structure
13
with low rigidity is attracted to the Si substrate
10
by the surface tension
21
, to cause the sticking phenomenon.
In the second conventional manufacturing method described with reference to FIGS.
7
(
a
)-
7
(
h
), it is difficult to precisely pattern the photosensitive polymer film
40
on the condition that unevenness of several &mgr;m is caused by the etching of the first sacrificed layer. It is also difficult to inject equally the photosensitive polymer down to the bottom surfaces of the trenches etched through the sacrificed layer.
Furthermore, it is difficult to completely remove the photosensitive polymer film
40
by ashing or such a dry process, causing low throughput for the manufacture. The incomplete removal of the photosensitive polymer film
40
is hazardous for securing the deformable range of the sensor structure
13
, causing a sensor with low reliability.
The second conventional manufacturing method increases the manufacturing costs, since the sacrificed layer is etched through two isolated steps and the step of burning (ashing) the photosensitive polymer film
40
is added.
According to the third conventional manufacturing method, the sublimable material
50
is not removed completely, remaining as foreign substances on the clean sensor surface. The remaining foreign substances impair the reliability of the sensor.
In view of the foregoing, it is an object of the invention to provide a highly reliable semiconductor structure.
It is another object of the invention to provide a method of manufacturing a reliable semiconductor structure, that facilitates, without employing any special step, preventing sticking phenomena, improving the throughput and reducing the manufacturing costs.
SUMMARY OF THE INVENTION
According to an aspect of the invention, there is provided a semiconductor struc

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