Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1994-09-19
2001-02-13
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S022000, C438S030000
Reexamination Certificate
active
06187605
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device for a light valve and a production method thereof. More specifically, the present invention relates to a transparent semiconductor device and a production method of the same which is utilized as a driving substrate of a flat light valve such as an active matrix liquid crystal display device.
FIG. 26
shows a general construction of the driving substrate used in the active matrix liquid crystal display device. The driving substrate
1001
is formed integrally thereon with a pixel array
1002
and a peripheral drive circuit including an X-drive
1003
and a Y-drive
1004
by an IC fabrication process.
FIG. 27
schematically shows the pixel array. A thin film transistor (TFT)
1007
is formed for switching a pixel at each intersection between plural scan lines
1005
and plural signal lines
1006
. The TFT
1007
is connected at its gate electrode to corresponding scan line
1005
, connected at its source electrode to a corresponding signal line, and connected at its drain electrode to a corresponding liquid crystal pixel
1008
. The liquid crystal pixel
1008
is composed of a liquid crystal layer sandwiched between the driving substrate and a counter substrate. While the scan lines
1005
are scanned to select and open the TFTs
1007
, the signal lines
1006
are accessed to write an image signal into the corresponding liquid crystal pixels
1008
.
The TFT is composed of a semiconductor thin film material conventionally selected from polysilicon or amorphous silicon. However, these materials have a relatively low mobility, hence it would be difficult to utilize the TFT for a transistor element of the peripheral drive circuit. In view of this, recently another technology has been developed such that a single crystal silicon (monosilicon) transistor is formed to constitute a peripheral drive circuit element, as disclosed for example in Tokkaihei 3-100516. This prior art utilizes a composite substrate comprised of a monosilicon wafer laminated on another wafer composed of a transparent insulating material such as quartz glass. The monosilicon wafer is partly removed by etching so that a pixel array is formed on an exposed surface of the quartz glass wafer, while a peripheral drive circuit is formed in the remaining part of the monosilicon wafer.
However, when a high temperature IC process over
1000
is applied to the composite substrate comprised of a laminate of the quartz glass wafer and the monosilicon wafer, the substrate is deformed due to thermal expansion difference to thereby disadvantageously hinder a yield rate and reliability. In view of such a problem of the prior art, an object of the invention is to construct a semiconductor device for a light valve by using a stable substrate free of thermal deformation.
SUMMARY OF THE INVENTION
Referring to
FIG. 1
, description is given for means to solve the above noted problem of the prior art and to achieve the object of the invention. First, as shown in FIG.
1
(B), the inventive semiconductor device for a light value is formed of a semiconductor substrate
3
having an opaque portion
1
having a certain thickness, and a transparent portion
2
free of said thickness. The semiconductor substrate in the opaque portion has a thickness thick enough to prevent light transmitting, e.g., over 10 &mgr;m in thickness. For example, the semiconductor substrate
3
is composed of a bulk monosilicon (single crystal silicon) wafer. A pixel array is formed in the transparent portion
2
along a major face
4
of the semiconductor substrate
3
, while a drive substrate is formed in the opaque portion
1
along the same major face
4
. Further, a transparent support substrate
5
composed of, for example, quartz glass is superposed on the major face
4
of the semiconductor substrate where the pixel array and the drive circuit are provided.
Preferably, the support substrate
5
is bonded to the semiconductor substrate
3
through a protective film
6
and an adhesive layer
7
. The transparent support substrate
5
can be constituted by the adhesive layer
7
itself or both the adhesive layer
7
and a leveling layer, not shown in
FIG. 1
, which is interposed between the adhesive layer
7
and the protective layer
6
.
A pre-complete form of the semiconductor device shown in FIG.
1
(B) is illustrated in FIG.
1
(A). As described before, the high temperature IC process is applied to the semiconductor substrate
3
composed of the bulk monosilicon wafer to form concurrently the drive substrate
8
and the pixel array
9
. In this construction, the drive circuit
8
contains a single crystal transistor
10
formed directly in the major face
4
of the semiconductor substrate
3
. The pixel array
9
contains a switching element in the form of a TFT
11
and a pixel electrode
12
. This pixel array
9
is formed on an underlying insulative film
13
provisionally provided along the major face
4
of the semiconductor substrate
3
. The pixel array
9
and the drive circuit
8
are interconnected to each other through a metal lead
14
on the same substrate.
FIG.
1
(C) shows an active matrix liquid crystal display device constructed of the semiconductor device for a light valve in FIG.
1
(B). The liquid crystal display device is constructed by using a cavity formed in the transparent portion of the semiconductor substrate
3
. An orientation film
21
is formed on a back of the underlying insulative film
13
exposed in the transparent portion. Further, a transparent counter substrate
16
is laminated through a spacer
15
composed of a seal material. A common electrode
17
and an orientation film
18
are formed on an inner face of the counter substrate
16
. A liquid crystal layer
19
is filled between the pair of orientation films
14
,
18
. Though not shown in FIG.
1
(B), a leveling layer
20
is preferably interposed between the protective film
6
and the adhesive layer
7
. Further, a periphery of the transparent support substrate
5
is partly removed to expose an electrode terminal for external connection (pad electrode)
23
.
Further referring to
FIG. 1
, the description is given for a production method of the inventive semiconductor device for a light valve. As shown in FIG.
1
(A), the first step is carried out such that the pixel array
9
and the drive circuit
8
are formed on the major face
4
of the semiconductor substrate
3
. Since the semiconductor substrate
3
is composed of, for example, a bulk monosilicon wafer, a high temperature IC process is directly applied in manner similar to a rectangular LSI fabrication technology. Further, the TFT
11
contained in the pixel array
9
and the single crystal transistor
10
contained in the drive circuit
8
can be fabricated by the same process. In this first step, the underlying insulative film
13
is provisionally formed under the pixel array
9
, which will be served as an etching stopper in a later step. The underlying insulative film
13
is composed of, for example, a silicon oxide film, a silicon nitride film or a composite film thereof.
Next, as shown in FIG.
1
(B), the second step is undertaken to bond the transparent support substrate
5
to the major face
4
of the semiconductor substrate
3
by means of the adhesive layer
7
. The transparent support substrate
5
is composed of, for example, glass, quartz or sapphire, and preferably has a thermal expansion coefficient comparable to that of the semiconductor substrate
3
. Further preferably, the leveling layer is interposed between the transparent adhesive layer
7
and the semiconductor substrate
3
to absorb unevenness of the major face. Although the transparent support substrate
5
is formed adhesively over the whole portion of the major face on which the drive circuit
8
is formed, as shown in FIG.
1
(B), the transparent support substrate
5
can be bonded adhesively with slightly enlarging from the transparent portion
2
and slightly covering over the opaque portion
1
because the pixel array
9
in the transp
Iwaki Tadao
Kojima Yoshikazu
Takahashi Kunihiro
Takasu Hiroaki
Yamazaki Tsuneo
Adam & Wilks
Bowers Charles
Pert Evan
Seiko Instruments Inc.
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