Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1997-04-18
2001-02-27
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S151000
Reexamination Certificate
active
06194255
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a thin film transistor (in general, called “TFT”) and a method of manufacturing the same, and particularly to a method of forming source and drain regions in a thin film transistor.
In recent years, there have been known active matrix liquid-crystal display unit using a thin film transistor.
FIGS. 2A
to
2
D show a process of manufacturing a general thin film transistor. First, a silicon oxide film or silicon nitride is formed on a glass substrate
201
as a first coating film
202
. A Corning 7059 glass or the like is used as a glass substrate. After the formation of the first coating film
202
, a silicon semiconductor film which forms an active layer is formed on the first coating film
202
. An amorphous silicon film is usually formed through the plasma CVD technique or low pressure thermal CVD technique, and thereafter the amorphous silicon film is crystallized by heating or the application of laser beam. Then, a silicon film subjected to a crystal property (hereinafter referred to as “crystalline silicon film”) is patterned to thereby form an active layer
203
. (
FIG. 2A
)
After the formation of the active layer
203
, a silicon oxide film is formed as a gate insulating film
204
through the plasma CVD technique or the sputtering technique. Then, a gate electrode
205
is formed of material mainly containing metal or semiconductor. After the formation of the gate electrode
205
, impurity ions are injected thereinto so as to form a source region
207
as well as a drain region
209
. This process is executed using the gate electrode
205
as a mask. As the ions injected, P (phosphorus) is used in the manufacture of an n-channel thin film transistor, whereas B (boron) is used in the manufacture of a p-channel thin film transistor. Also, a channel formation region
208
is formed simultaneously during this process. (
FIG. 2B
)
After the formation of the source region
207
and the drain region
209
as well as the channel formation region
208
, the source region
207
and the drain region
209
are recrystallized by application of a laser beam or an infrared ray, and the impurity ions injected into those region are activated. The recrystallization of the source region
207
and the drain region
209
are made because the source region
207
and the drain region
209
have been made amorphous by the bombardment of injected ions at the time of the preceding ion injection.
The above-mentioned recrystallization and activation of the source and drain regions may be performed by heating. However, in the case of heating, its effect could not be obtained without heating at temperature of 700° C. or higher (preferably 800° C. or higher). Taking the heat-resistivity of a glass substrate (a substrate made of Corning 7059 glass must be dealt with at 600° C. or lower) into account, such a heat treatment is improper.
Subsequently, an interlayer insulating film
211
is formed of silicon oxide or other insulating materials. Further, after forming contact holes, a source electrode
212
and a drain electrode
213
are formed of a proper metallic material.
The thin film transistor manufactured through the foregoing processes suffers from such a problem that its characteristics are deteriorated or largely dispersed. This problem results from the fact that defects concentrate in the vicinity of interfaces between the source region
207
and the channel formation region
208
and between the drain region
209
and the channel formation region
208
.
In other words, the source region
207
and the drain region
209
, which have been made amorphous by the injection of ions in the process of
FIG. 2B
, are recrystallized by the application of a laser beam in the process of
FIG. 2C
, during which the channel formation region
208
remains crystalline. Therefore, the crystallization of the source and drain regions, which progresses by the application of a laser beam, stops at the interfaces between the source and drain regions and the channel formation region having the crystal property from the first. As a result, a large number of defects resulting from mismatching of lattices are produced in the vicinity of the interfaces between the source and drain regions and the channel formation region. The existence of those defects makes not only the characteristics dispersed and unstable but also an off-state current increase.
As a manner of solving the foregoing problem, it has been found that the recrystallization of the source and drain regions and the activation of the impurity ions are performed at a temperature of 700° C. or higher, preferably 800° C. or higher. If the recrystallization of the source and drain regions and the activation of the impurity ions are performed at a temperature of 700° C. or higher, preferably 800° C. or higher, energy is also applied to the channel formation region
208
. Hence, mismatching of lattices produced in the vicinity of the interfaces between the source and drain regions and the channel formation region can be released, as a result of which the defects can be prevented from concentrating in the vicinity of the interfaces between the source and drain regions and the channel formation region.
However, in order that processes for the recrystallization of the source and drain regions and the activation of impurity ions injected are performed by a process of heating at 700° C. or higher, a substrate capable of resisting a temperature of 700° C. or higher must be used. However, such a substrate is expensive, resulting in a large obstacle to the use of the thin film transistor in a liquid-crystal display apparatus. In other words, in the use of an inexpensive glass substrate having a heat-resistant temperature of 600° C. or lower, the processes for the recrystallization of the source and drain regions and the activation of impurity ions cannot be realized by heating for all practical purposes.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems with the prior art, and an object of the invention is to execute the recrystallization and activation of source and drain regions at a temperature lower than that in the prior art.
Another object of the invention is to provide a thin film transistor with a structure in which defects on interfaces between source and drain regions and a channel formation region are reduced.
A still another object of the invention is to provide a thin film transistor which is sufficiently high in a crystal property of the source and drain regions.
In order to achieve the above objects, according to one aspect of the invention, there is provided a method of manufacturing a thin film transistor, comprising the steps of:
introducing a metal element for promoting crystallization into an amorphous silicon film;
subjecting said amorphous silicon film to a heat treatment to form a crystalline silicon film;
forming an active layer using said crystalline silicon film;
selectively injecting impurity ions into a part of said active layer; and
subjecting said active layer to a heat treatment to grow crystal from a region into which said impurity ions have not been injected toward a region into which said impurity ions have been injected.
In the foregoing structure, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag and Au are applicable as the metal element which promotes crystallization. In particular, the use of Ni (nickel) makes it possible to obtain a remarkable effect.
An amorphous silicon film is formed on a glass substrate, a quartz substrate, or a semiconductor substrate or metal substrate having an insulating surface. The amorphous silicon film is formed through a vapor phase technique such as a plasma CVD technique or low pressure thermal CVD technique, or the sputtering technique.
As the impurity ions, ions of phosphorus or boron are used.
In the foregoing structure, it is effective to apply a laser beam or an intense light beam to the formed film before or after the heat treatment. In particular, the application of a laser bea
Hiroki Masamitsu
Takemura Yasuhiko
Teramoto Satoshi
Yamaguchi Naoaki
Yamamoto Mutsuo
Bowers Charles
Costellia Jeffrey L.
Nixon & Peabody LLP
Pert Evan
Semiconductor Energy Laboratry Co. Ltd
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