Method of producing polycrystalline silicon

Details Method of producing polycrystalline silicon Method of producing polycrystalline silicon

1999-10-06

2001-07-03

Lee, Eddie C. (Department: 2815)

Semiconductor device manufacturing: process

Formation of semiconductive active region on any substrate

Amorphous semiconductor

C438S487000, C438S795000, C438S798000, C427S554000

Reexamination Certificate

active

06255199

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of fabricating thin film transistors to be used in pixel switches of a liquid crystal display and in a driving circuit therefore, and, more particularly, to a method of producing polycrystalline silicon of which a thin film transistor is comprised.
Today, liquid crystal displays to whose pixel switches insulated gate thin film transistors using amorphous silicon are adapted are mass-produced. Since the field-effect mobility of amorphous silicon is equal to or less than 1 cm
2
/Vs, however, such a liquid crystal display has a difficulty in outputting a high-chroma image at a high speed.
As a solution to this problem, liquid crystal displays to whose pixel switches thin film transistors using polycrystalline silicon having a relatively high field-effect mobility are adapted are being put to a practical use. This polycrystalline silicon (hereinafter called “polysilicon”) is produced by laser annealing which irradiates a laser beam from an excimer laser on amorphous silicon to crystallize it. It is known through experiments that the polysilicon shows a field-effect mobility of about 100 cm
2
/Vs to 200 cm
2
/Vs. Therefore, a liquid crystal display whose thin film transistors use polycrystalline silicon having a high field-effect mobility can output a high-chroma image fast.
It is known that the greater the particle size of polysilicon becomes, the higher the field-effect mobility of polysilicon gets. It is also known that the particle size of polysilicon depends on the energy density (fluence) of a laser beam which is irradiated on amorphous silicon by laser annealing. In other words, increasing the fluence of the laser beam can increase the particle size of polysilicon, thereby making the field-effect mobility higher.
When the fluence of a laser beam exceeds a certain value, the particles of polysilicon have a microcrystal size, so that the desired field-effect mobility cannot be acquired. The fluence of a laser beam should therefore be adjusted to fall within a range which can achieve the desired field-effect mobility. That is, the fluence of a laser beam is adjusted to range from a fluence F1 at which the minimum field-effect mobility needed for fast output of a high-chroma image can be obtained to a fluence F2 over which the particle size of polysilicon becomes a microcrystal size.
At present, however, the fluence margin from F1 to F2 is so narrow that a slight variation of the oscillation intensity of a laser causes the fluence to go off this fluence margin. This makes it difficult to acquire the desired particle size or the desired field-effect mobility. This results in a poor yield and an increase in the production cost at the time of producing the aforementioned high-performance polysilicon.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of producing polysilicon, which can make the fluence margin of a laser beam in laser annealing to crystallize amorphous silicon wide enough to achieve a high field-effect mobility and a high yield.
To achieve this object, the present inventors have studied the correlation between a beam profile along the scan direction of a laser beam to be irradiated on amorphous silicon and the fluence margin and found out that the fluence margin can be made sufficiently wide when a laser beam having the following beam profile is used.
A method of producing polycrystalline silicon according to this invention comprising the step of: depositing a non-monocrystalline silicon layer on a substrate; and scanning a region of the non-monocrystalline silicon layer with a laser beam in a first direction, thereby crystallizing the non-monocrystalline silicon of the region, the laser beam forming an elongated beam spot on the non-monocrystalline silicon layer, the beam spot extending in a second direction perpendicular to the first direction, wherein the laser beam has an intensity distribution in the first direction, the distribution being one indicated by a convex curve which includes a peak representing a maximum intensity and which has a radius of curvature of 0.2 &mgr;m to 4 &mgr;m when maximum intensity is represented by a distance of 1 m.
According to this method, the peak on the curve is shifted form a midpoint of the curve.
Alternatively, the peak on the curve is shifted from a midpoint of the curve in the first direction.
The method according to this invention may further comprises a step of scanning another region of the non-monocrystalline silicon layer with the laser beam in the first direction, the other region being adjacent to the region already scanned, with respect to the second direction.
According to this method, the curve has a shape quantified by applying laser beams to different regions of a target at predetermined pulse rates, respectively, the laser beams having different energy densities gradually varying from an energy density of the laser beam to be applied to the non-monocrystalline silicon layer, by acquiring distributions of energy densities of the laser beams from conditions of the regions applied with the laser beams and by combining the distributions of energy densities on the regions.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.


REFERENCES:
patent: 4330363 (1982-05-01), Biegesen et al.
patent: 5529937 (1996-06-01), Zhang et al.
patent: 5529951 (1996-06-01), Noguchi et al.
patent: 5614426 (1997-03-01), Funada et al.
patent: 5712191 (1998-01-01), Nakajima et al.
patent: 5756364 (1998-05-01), Tanaka et al.
patent: 5766989 (1998-06-01), Maegawa et al.
patent: 5834071 (1998-10-01), Lin
patent: 5837569 (1998-11-01), Makita et al.
patent: 5970368 (1999-10-01), Sasaki et al.
patent: 5970369 (1999-10-01), Hara et al.
patent: 9-129573 (1997-05-01), None
Jhon et al. (Crystallization of Amorphous Silicon by Excimer Laser Annealing with a Line Shape Beam Having a Gaussian Profile, Jpn. J. Appl. Phys. vol. 33 (1994), pp. L1438-L1441).*
Brotherton, et al. (Beam Shape Effects with Excimer Layer Crystallisation of Plasma Enhanced and Low Pressure Chemical Vapor Deposited Amorphous Silicon, Solid State Phenomena vols. 37-38 (1994) pp. 299-304).

Affiliated with

Also associated with

Rating

Method of producing polycrystalline silicon does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of producing polycrystalline silicon, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing polycrystalline silicon will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2518991