Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Light responsive structure
Reexamination Certificate
2002-03-08
2004-08-10
Pham, Long (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Light responsive structure
C257S200000
Reexamination Certificate
active
06774409
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is related to Japanese Patent Application No. 2001-064950 filed on Mar. 8, 2001, whose priority is claimed under 35 USC §119, the disclosure of which is incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, more particularly, a semiconductor device having a semiconductor substrate on which a silicon germanium film, a carbon-containing silicon film and a silicon film are formed.
2. Description of Related Art
In recent years, for increasing the operating speed of silicon MOS transistors, techniques of producing high-electron-mobility transistors are now under active development in place of conventional transistors having Si—SiO
2
MOS interfaces as channels. In high electron-mobility transistor techniques, hetero interfaces are formed by epitaxially growing, on a Si substrate, films of materials having different lattice constants from the lattice constant of the Si substrate with a view to taking advantage of compression or tensile distortion in a horizontal direction and/or discontinuity in a band structure in the films.
For example, as shown in
FIG. 2
, IEDM (International Electron Device Meeting), 1994 proposed, on page 373 thereof, a transistor wherein a SiGe film
22
having a Ge concentration gradient of 0% to 20% is formed to have a thickness of 2.1 &mgr;m on a p-type Si substrate
21
, a SiGe film
23
having a Ge concentration of 20% is formed to have a thickness of 0.6 &mgr;m on the SiGe film
22
, a Si film
24
is epitaxially grown to have a thickness of 13 nm on the SiGe film
23
, and as in ordinary MOSs, a SiO
2
film
25
to be a gate oxide film and a polysilicon film
26
to be a gate electrode are formed on the Si film
24
. In the transistor of this structure, the thick SiGe film
22
having the concentration gradient and the SiGe film
23
having a Ge concentration of 20% are formed to reduce strained distortion, so that distortion is completely reduced on the top surface of the SiGe film
23
. By forming the thin Si film
24
on the SiGe film
23
, is realized the strained Si film
24
. Thereby the effective electron mobility in an N-channel MOS can be improved by about 50% with respect to a non-strained Si film.
For improving the mobility in a pMOS, as shown in
FIG. 3
, IEDM, 1994 proposed, on page 735 thereof, a transistor wherein a SiGe film
32
having a Ge concentration of 30% and a thickness of 10 nm and a Si film
33
having a thickness of 7 nm are sequentially formed on an n-type Si substrate
31
by epitaxial growth, and further, as in ordinary MOSs, a SiO
2
film
34
to be a gate oxide film and a polysilicon film
35
to be a gate electrode are formed on the Si film
33
. In the transistor of this structure, the SiGe film
32
having compression distortion therein is formed under the thin Si film
33
. By forming a channel in the Si film
33
, can be obtained a hole mobility about 1.2 times better than a non-strained Si film.
Further, referring to
FIG. 4
, Japanese Unexamined Patent Publication No. HEI 10(1998)-321733 proposes, as a technique for forming both an nMOS and a pMOS simultaneously, an nMOS transistor and a pMOS transistor wherein a SiGe film
42
and a Si film
43
are sequentially formed on a Si substrate
41
with an n-well and a p-well formed therein, respectively, and further gate insulating films
44
and gate electrodes
45
are formed thereon. Here, the channel of the nMOS is formed in the strained Si film
43
, and the channel of the pMOS is formed in the compressed SiGe film
42
.
As shown in
FIG. 5
, Japanese Unexamined Patent Publication No. HEI 9(1997)-219524 proposes a transistor using a SOI (silicon on insulator) substrate in which a buried oxide film
52
and a SOI film
53
are formed on a Si substrate
51
. With regard to this transistor, the SOI film
53
and the buried oxide film
52
are removed from a pMOS region in the SOI substrate, and thereafter a SiGe film
54
having a Ge concentration of 30% and a thickness of 30 nm is epitaxially grown over the resulting SOI substrate and annealed at a high temperature. Thereby distortion is reduced in the SiGe film
54
on the SOI film
53
in the nMOS region. Thereafter a Si film
55
is epitaxially grown to a thickness of about 30 nm, and further a gate insulating film and a gate electrode
57
are formed thereon. Thereby, in the nMOS, the strained Si film
55
on the SOI film
53
is used as a channel, and in the pMOS, the compressed SiGe film
54
on the Si substrate
51
is used as a channel.
Of the above-mentioned transistors, the mobility of the transistor shown in
FIG. 2
is improved by forming the SiGe films
22
and
23
having sequentially raised Ge concentrations to reduce the compression distortion on the top face of the SiGe film
23
and also increasing the lattice constant to give a strong strain distortion to the Si film
24
formed thereon. However, this transistor requires the formation of the thick SiGe films
22
and
23
, which results in an increase in production costs.
In the CMOS transistor shown in
FIG. 4
, the nMOS and the pMOS are formed to have the same construction by forming the SiGe films
42
having a Ge concentration of 25 to 50% and a thickness of 5 to 10 nm and forming the Si films
43
thereon. Accordingly, since the SiGe films
42
under the Si films
43
have the compression distortion therein, the electron mobility is not sufficiently improved, especially in the nMOS.
That is, in the CMOS, for improving the electron mobility in the nMOS, the strained Si film
43
is formed on the SiGe film
42
whose distortion is reduced. For this purpose, the thick SiGe film
42
is required to be formed to reduce distortion. However, since the channel of the pMOS and the channel of the nMOS have greatly different structures, it is difficult to produce a CMOS having high effective electron and hole mobilities at the same time.
In the transistor shown in
FIG. 5
, the SOI substrate is used, and in the nMOS, the thin SiGe film
54
whose distortion is reduced is formed above the buried oxide film
52
. However, this transistor requires an SOI substrate, and it has the disadvantage in production since a step is formed between the nMOS and the pMOS due to the removal of the buried oxide film
52
and the SOI layer
53
from the channel region of the pMOS. Also, in the epitaxial growth, the crystallinity is impaired at the step, and therefore, it is difficult to produce a CMOS having high effective electron and hole mobility simultaneously.
SUMMARY OF THE INVENTION
The present invention provides an n-channel semiconductor device comprising a semiconductor substrate on which a silicon germanium film, a carbon-containing silicon film and a silicon film are formed in this order and a gate electrode on the semiconductor substrate with intervention of a gate oxide film, wherein a channel region of the semiconductor device is formed in the carbon-containing silicon film, i.g., wherein the carbon-containing silicon film functions as a channel region.
The present invention also provides a p-channel semiconductor device comprising a semiconductor substrate on which a silicon germanium film, a carbon-containing silicon film and a silicon film are formed in this order and a gate electrode on the semiconductor substrate with intervention of a gate oxide film, wherein a channel region of the semiconductor device is formed in the silicon germanium film, i.g., wherein the silicon germanium film functions as a channel region.
Further, the present invention provides a complementary metal-oxide semiconductor device provided with the above-described n-channel semiconductor device and the above-described p-channel semiconductor device on the same substrate.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments o
Baba Tomoya
Fujii Katsumasa
Mutou Akiyoshi
Nixon & Vanderhye P.C.
Pham Long
Sharp Kabushiki Kaisha
Trinh Hoa B.
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