Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1998-08-28
2001-04-24
Bowers, Charles (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S149000, C438S007000
Reexamination Certificate
active
06221702
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method of fabricating a thin film transistor in which a metal silicide line generated from Metal Induced Lateral Crystallization is located at the outside of a channel region.
2. Discussion of Related Art
A polycrystalline silicon TFT (Thin Film Transistor) is used rather than an armophous silicon TFT for high resolution and fast operation speed in a liquid crystal display. The development of laser crystallization enables fabrication of polysilicon TFT's on a large-sized glass substrate under a temperature similar to a temperature in aprocess of fabricating armophous silicon TFT's. However, the TFT fabricated by laser crystallization requires a long processing time and the related process equipments, cause difficulties in mass production.
Armophous silicon under a metal layer become crystallized by thermal treatment in MIC(Metal Induced Crystallization) after a specific metal layer has been formed on an armophous silicon layer. MIC enables low temperature crystallization and needs no equipments of high expenses. In spite of the merit of the low temperature crystallization, MIC causes metal contamination which deteriorates and changes the intrinsic characteristics of silicon due to the introduction of metal into the crystallized film.
A new crystallization method called Metal Induced Lateral Crystallization (MILC) [S. W. Lee & S. K. Joo, IEEE Electron Device Lett., 17(4), P.160, (1996)] has been proposed. MILC enables the crystallization of armophous silicon under a low temperature of about 400° C. A crystallization of armophous silicon progresses laterally as the boundary of the silicon crystallizedbyMIC inMILC. Namely, the crystallization of silicon is induced laterally against the crystallization by MIC.
FIG. 1A
to
FIG. 1D
show cross-sectional views of fabricating a TFT in which a silicon layer crystallized by MILC is used as a channel region.
Referring to
FIG. 1A
, an armophous silicon layer is deposited on an insulated substrate
100
on which a buffer layer has been formed. An active layer
10
is formed by patterning the armophous silicon layer by photolithography. A gate insulating layer
11
and a gate electrode
12
are formed on the active layer
10
by a conventional method.
Referring to
FIG. 1B
, a nickel film
13
having a thickness of 20 Å is deposited on the whole surface by sputtering. Accordingly, the portion of active layer on which the gate electrode 12 is not formed contacts the nickel film
13
.
Referring to
FIG. 1C
, a source region
10
S and a drain region
10
D which are doped heavily with impurity are formed in the active layer
10
by ion-implantation. A channel region
10
C lies between the source
10
S and the drain
10
D.
Referring to
FIG. 1D
, the active layer of amorphous silicon
10
is crystallized by a thermal treatment of 300 to 500° C. to the substrate 100 after the above step. Consequently, A portion of armophous silicon of the source
10
S and drain
10
D on which the nickel film has been formed is crystallized by MIC, while the other portion of armophous silicon where the channel
10
C has been formed is crystallized by MILC.
FIG. 2A
shows a TEM picture of a nickel-silicide line formed in the middle of the channel, and
FIG. 2B
shows a layout of a TFT after the crystalization by a conventional method wherein the arrows indicate the directions of crystallization by MILC. As shown in
FIGS. 2A and 2B
, an Ni-silicide line is formed in the middle of the channel region in the active layer. The thin Ni-silicide precipitates formed in the source and the drain crystallize silicon and move to the channel region. Accordingly, the Ni-silicide precipitates started to move from both ends of the source and the drain meet each other at the middle of the channel region, resulting in a Ni-silicide line. The Ni-silicide line becomes a defect deteriorating device characteristics, such as the field effect mobility and the threshold voltage to lower the electrical characteristics of polysilicon TFT's.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of fabricating a thin film transistor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide a method of fabricating TFT which prevents the metal-silicide from being a defect in the channel region by means of locating the metal-silicide line outside the channel region.
Another object of the present invention is to provide a method of fabricating TFT which improves the characteristics of the TFT by means of crystallizing the semiconductor layer by MILC and simultaneously locating the metal-silicide line generated therein outside the channel region.
Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes the steps of forming a semiconductor layer on a substrate, said semiconductor layer having a first region, a channel region and a second region in order; forming a gate insulating layer and a gate electrode on said channel region; doping said first and said second region heavily with impurity; forming a metal film pattern making said first region a metal-offset; and crystallizing said semiconductor layer through thermal treatment of said semiconductor layer having said metal film.
Also, the present invention includes a method of fabricating a thin film transistor comprising the steps of forming a semiconductor layer on a substrate, said semiconductor layer having a first region, a channel region and a second region in order, forming a gate insulating layer and a gate electrode on said channel region, forming a metal film pattern making said first region a metal-offset, doping said first and said second region heavily with impurity, and crystallizing said semiconductor layer through thermal treatment of said semiconductor layer having said metal film.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
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Lee, Seok-Woon, Yoo-Chan Jeon, and Seung-Ki Joo, “Pd Induced Lateral Crystallization of Amorphous Si Thin Films,” Appl. Phys. Lett. 66 (13), Mar. 27, 1995, pp. 1671-1673.
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Kawazu, Yunosuke, Hiroshi Kudo, Seinosuke Onari and Toshihiro Arai, “Low-Temperature Crystallization of Hydrogenated Amorphous Silicon Induced by Nickel Silicide Formation,”Japanese Journal of Applied Physics. vol. 29, No. 12, Dec., 1990, pp. 2698-2704.
Joo Seung-Ki
Kim Tae-Kyung
Bowers Charles
Hawranek Scott
LG. Philips LCD Co. Ltd.
Long Aldridge & Norman LLP
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