Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates
Reexamination Certificate
2000-04-28
2001-12-18
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
C438S072000, C438S158000, C438S164000
Reexamination Certificate
active
06331473
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to silicon-on-insulator (SOI) substrates, and specifically to an SOI substrate using a transparent supporting substrate, a method for making the same, a liquid crystal panel, and an electronic device using the SOI substrate.
2. Description of Related Art
Since SOI technologies including formation of a silicon thin film on an insulating substrate and formation of a semiconductive device on the silicon thin film have advantages such as high speed response of devices, low electrical energy consumption, and high integration density, they have been widely studied.
One SOI technology is production of an SOI substrate including bonding single-crystal silicon substrates. The method, generally called a bonding method, includes bonding a single-crystal silicon substrate and a supporting substrate by means of hydrogen bonding, reinforcing the bonding strength by heat treatment, and forming a thin film single-crystal silicon layer by grinding, polishing or etching of the single-crystal silicon substrate. Since this method is capable of directly thinning the single-crystal silicon substrate, the resulting silicon thin film has high crystallinity and thus enables production of a high performance device.
Furthermore, applied bonding methods have been known, such as, for example, a method for doping hydrogen ions on a single-crystal silicon substrate, bonding it with a supporting substrate, and separating a thin film silicon layer from the hydrogen-doped region of the single-crystal silicon substrate by heat treatment (U.S. Pat. No. 5,374,564); and a method for epitaxially growing a single-crystal silicon layer on a silicon substrate with a porous surface, bonding it to a supporting substrate, removing the silicon substrate, and etching the porous silicon layer to form an epitaxial single crystal silicon thin film on the supporting substrate (Japanese Patent Application Laid-Open No. 4-346418). SOI substrates by bonding methods have been used in production of various devices, as well as general bulk semiconductive devices. An advantage of the SOI substrate not achieved by conventional bulk substrates is allowing the use of various materials as supporting substrates. That is, transparent quartz and glass substrates, in addition to general silicon substrates, can be used as supporting substrates. Formation of a single-crystal silicon thin film on a transparent substrate enables formation of devices requiring light transmissivity, for example, high-performance transistor devices using single crystal silicon in a transmissive liquid crystal display device.
In an SOI substrate including a transparent supporting substrate and a single-crystal silicon thin film bonded thereto, the single-crystal silicon layer is used as source and drain regions in transistor devices, such as metal oxide semiconductor field effect transistors (MOSFETs). When the substrate is transparent, light incident on the rear face of the substrate causes current leakage in the channel region of the MOSFET, and thus causes deterioration of device characteristics. (Herein the face of the substrate provided with the single-crystal silicon layer is called the front face, and the reverse face is called the rear face).
This will be described with reference to the drawings.
FIG. 2
is a cross-sectional view of an SOI substrate provided with a transparent substrate produced conventionally. The SOI substrate has a configuration in which a single-crystal silicon layer
2
is bonded to a supporting substrate
1
with an oxide layer
3
therebetween. Since the oxide layer
3
generally transmits light, a conventional SOI substrate using a transparent material, such as quartz and glass, as a supporting substrate is not provided with a light shielding layer under the single-crystal silicon layer
2
.
FIG. 3
is a cross-sectional view of a MOSFET produced using the conventional SOI substrate shown in FIG.
2
. The oxide layer
3
is provided on the supporting substrate
1
, and a source region
2
b
, a channel region
2
a
, and a drain region
2
c
of the MOSFET are formed by patterning of the single-crystal silicon layer. The single-crystal silicon layer is covered with a gate insulating film
2
d
formed by surface oxidation thereof. A gate electrode is provided on the gate insulating film
2
d
, and the single-crystal silicon layer and the gate electrode
6
of the MOSFET are covered with a first interlayer
7
. The source region
2
b
and the drain region
2
c
are connected to a source line
9
and a drain line
8
, respectively, through openings in the first interlayer
7
. A second interlayer
10
is formed thereon, and an upper light shielding layer
11
is formed on the second interlayer
10
. The upper light shielding layer
11
is formed of a nontransparent insulating material such as a polyimide resin or a metallic thin film such as aluminum. When light
12
a
is directly incident on the front face of the substrate, the upper light shielding layer
11
suppresses leakage of the light
12
a
to the channel region
2
a
of the MOSFET provided on the substrate. When light
12
c
is directly incident on the rear face of the substrate, leakage of the light to the channel region
2
a
of the MOSFET is not prevented. Light
12
b
reflected on the rear interface la of the substrate partly reaches the channel region
2
a
of the MOSFET and causes light leakage even if the light is incident on the front face of the substrate.
Since the conventional SOI substrate shown in
FIG. 2
has no light shielding layer between the supporting substrate
1
and the single-crystal silicon layer
2
, the channel region
2
a
of the MOSFET composed of a single-crystal silicon thin film using the SOI substrate is not shielded from the light
12
c
directly incident on the rear face of the substrate and the light
12
b
reflected on the rear face of the substrate. Thus, light leakage occurs in a MOSFET produced using an SOI substrate having the conventional configuration, resulting in a fundamental problem of deterioration of device characteristics. Accordingly, it is difficult to use a transparent SOI substrate for a device using light and the SOI substrate cannot be used generally.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an SOI substrate enabling production of a semiconductive device which does not cause light leakage when a transparent supporting substrate is used, and a method for making the same. It is another object of the present invention to provide a high-performance semiconductive device using an SOI substrate using a transparent substrate and which does not cause light leakage.
An SOI substrate in accordance with the present invention, for achieving the above-mentioned objects, is provided with an embedded-type light shielding layer, for preventing light leakage, between a transparent supporting substrate and a single-crystal silicon layer formed thereon. The light shielding layer is formed on one surface of the supporting substrate, and the single-crystal silicon layer is formed on an insulating layer deposited on the light shielding layer. The light shielding layer is patterned so as to cover the channel region of the MOSFETs constituting a device, and is not present in the portion other than the channel region of the MOSFETs. Thus, it can be used in an application requiring light transmittance of the substrate, for example, a transmissive liquid crystal display device. Use of a high melting point metal or a silicon compound (silicide) for the light shielding layer is capable of producing an SOI substrate which is sufficiently stable in a thermal process, such as impurity diffusion into the single-crystal silicon layer, essential for production of MOSFET.
REFERENCES:
patent: 4984033 (1991-01-01), Ishizu et al.
patent: 5281840 (1994-01-01), Sama
patent: 5374564 (1994-12-01), Bruel
patent: 5635707 (1997-06-01), Shimizu
patent: 5771110 (1998-06-01), Hirano et al.
patent: 5811866 (1998-09-01), Hirata
patent: 5886364 (1999-03-01
Niebling John F.
Oliff & Berridg,e PLC
Seiko Epson Corporation
Simkovik Viktor
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