Semiconductor device manufacturing: process – Chemical etching – Combined with coating step
Reexamination Certificate
2001-07-30
2003-06-10
Chen, Kin-Chan (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Combined with coating step
C438S702000, C438S706000
Reexamination Certificate
active
06576556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device which is aimed at forming a three-dimensional structure having a space therein and, more particularly, to a method of manufacturing an infrared image sensor.
2. Description of the Related Art
A description is given of a conventional method of manufacturing a semiconductor device to which the invention relates with reference to a structure of a pixel of an uncooled infrared image sensor as an example.
FIG. 14A
is a cross sectional view showing a structure of a unit element or a pixel of an uncooled infrared image sensor that is a type disclosed in Japanese Laid-Open Patent Publication 209418/1998 or Proceedings of SPIE, No. 3698, pp. 556-564 in which an infrared ray absorbing portion for absorbing infrared rays to increase the temperature of a photodetector portion and a temperature detecting portion that forms a temperature sensor to detect the temperature rise are formed as separate structures.
FIG. 14B
is a plane view of the structure shown in
FIG. 14A
with the infrared ray absorbing portion removed.
FIG. 14A
is a cross sectional view along the line XIVA—XIVA in
FIG. 14B
taken before removing the infrared ray absorbing portion.
FIGS. 14A and 14B
omit a signal readout circuit which is formed on a silicon substrate
1
, as it is not directly related to the invention. In those figures, reference numeral
1
represents a silicon substrate; reference numeral
10
represents a temperature detecting portion which is supported above a hollow portion
200
provided in the silicon substrate
1
with support legs
21
and
22
; reference numeral
11
represents a temperature sensor constituted by a bolometer or the like for detecting a temperature change; reference numeral
12
represents an insulating film constituted by a silicon dioxide film or the like that covers the temperature sensor
11
; and reference numerals
13
and
14
represent metal wirings for readout of signals from the temperature sensor
11
. The support legs
21
and
22
are constituted by insulating films that are silicon dioxide films
23
and
24
similar to that of the temperature detecting portion, and metal wirings
25
and
26
are provided in the insulating films. Reference numeral
130
represents an infrared ray absorbing portion for absorbing infrared rays and converting them into heat, and reference numeral
140
represents a splicing pillar for holding the infrared ray absorbing portion at a certain interval from the temperature detecting portion
10
and for thermally integrating the infrared ray absorbing portion
130
and temperature detecting portion
10
. Reference numerals
31
and
32
represent insulating films constituted by silicon dioxide films or the like formed on the substrate
1
, and reference numerals
33
and
34
represent metal wirings formed in the insulating films
31
and
32
.
An operation of a pixel of the uncooled infrared image sensor will now be described. Infrared rays impinge upon the infrared ray absorbing portion
130
. The incident infrared rays are absorbed by the infrared ray absorbing portion
130
to increase the temperature of the infrared ray absorbing portion
130
. The temperature change of the infrared ray absorbing portion
130
is conducted to the temperature detecting portion
10
through the splicing pillar
140
to increase the temperature of the temperature detecting portion
10
. The splicing pillar
140
is designed such that it has thermal resistance lower than that of the support legs
21
and
22
. A time constant determined by the total thermal capacity of the three structures, that is, temperature detecting portion
10
, splicing pillar
140
and infrared ray absorbing portion
130
, and the thermal resistance of the support legs
21
and
22
is shorter than a frame time during which the uncooled infrared image sensor operates. Since the support legs
21
and
22
are designed such that they have thermal conductance sufficiently lower than that of the splicing pillar
140
, the temperature rise at the temperature detecting portion
10
substantially coincides with the temperature rise at the infrared ray absorbing portion
130
. It is therefore possible to detect infrared rays by measuring the temperature rise with the temperature sensor
11
.
A method of manufacturing the pixel structure shown in
FIGS. 14A and 14B
will now be with reference to
FIGS. 15 through 19
.
A signal readout circuit (not shown) is firstly formed on a silicon substrate
1
having a (100)-plane orientation, and an insulating film
2
(which will become insulating films
12
,
23
,
24
,
31
and
32
at the next step), metal wirings
13
,
14
,
25
,
26
,
33
and
34
and a temperature sensor
11
are thereafter formed (see FIG.
15
).
Subsequently, etching holes
41
,
42
,
43
, and
44
for forming a hollow portion in the silicon substrate
1
are formed by means of etching in the insulating film
2
which is constituted by a silicon dioxide film; a sacrificial layer
110
made of amorphous silicon or the like which is to be removed at a later step is thereafter formed on the wafer; photolithography and etching techniques are then used to form a hole penetrating through the sacrificial layer
110
in a region of the sacrificial layer
110
where a splicing pillar is to be formed; and the hole is filled with a material which will become a splicing pillar
140
(see FIG.
16
).
The above-described step separates the insulating film
2
into regions
12
,
23
,
24
,
31
and
32
. At this step, it is preferable to flatten the top surface using an etch-back technique, CMP (chemical mechanical polishing) or the like. The splicing pillar
140
may be constituted by the same material that constitutes an infrared ray absorbing portion
130
as disclosed in Japanese Laid-Open Patent Publication 209418/1998, and the infrared ray absorbing portion
130
is formed concurrently with the splicing pillar
140
in this case.
A thin film to become the infrared ray absorbing portion
130
is formed on the sacrificial layer
110
and is patterned into a separated infrared ray absorbing portion for each pixel (see
FIG. 17
The sacrificial layer
110
is etched from an opening around the infrared ray absorbing portion
130
to separate the infrared absorbing portion
130
above the substrate
1
with the splicing pillar
140
left between them (see FIG.
18
).
The silicon substrate
1
is etched from the exposed regions of the silicon substrate
1
at the bottom of the etching holes
41
,
42
,
43
and
44
. As a result, a hollow portion
200
is formed in the silicon substrate
1
(see FIG.
19
).
When the sacrificial layer
110
is formed of amorphous silicon, the sacrificial layer
110
and the silicon substrate
1
can be simultaneously etched. When the silicon is etched using an etchant, such as potassium hydroxide (KOH), tetramethyl ammonium hydroxide (TMAH), or the like, the etching rate decreases as (111)-crystal planes are exposed in so-called anisotropic etching. It is therefore possible to form an etched section having a configuration as shown in
FIG. 19
without expanding the surface configuration of the hollow portion
200
beyond a certain size by using a silicon substrate whose surface is a (100)-plane which is commonly used for MOS (metal oxide semiconductor) and CMOS (complimentary metal oxide semiconductor) devices.
While the removal of the sacrificial layer
110
and the formation of the hollow portion
200
in the silicon substrate
1
is carried out using an etchant, that is, using a wet process in the above-described example of the prior art, such a wet process had a possibility of deformation of a constituent part of a pixel attributable to the surface tension of a residue of the liquid on the surface of the pixel structure at the final drying step. For example, there is a high possibility of a problem referred to as “sticking” in which the silicon substrate
1
stays in contact with the infrared ray absorbing layer
Kimata Masafumi
Nakaki Yoshiyuki
Chen Kin-Chan
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
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