U.S. patent application number 11/554045 was filed with the patent office on 2007-03-08 for method of forming polysilicon film using a laser annealing apparatus.
This patent application is currently assigned to AU OPTRONICS CORPORATION. Invention is credited to I-Chang Tsao.
Application Number | 20070054478 11/554045 |
Document ID | / |
Family ID | 32322959 |
Filed Date | 2007-03-08 |
United States Patent
Application |
20070054478 |
Kind Code |
A1 |
Tsao; I-Chang |
March 8, 2007 |
METHOD OF FORMING POLYSILICON FILM USING A LASER ANNEALING
APPARATUS
Abstract
An excimer laser annealing apparatus and the application of the
same for stabilizing the atmosphere surrounding an area irradiated
by an excimer laser. The apparatus includes a chamber, a gas
diversion nozzle, an excimer laser and a gas supply device. The gas
diversion nozzle is positioned inside the chamber. The laser beam
produced by the excimer laser passes through the gas diversion
nozzle. The gas supply device connects with the gas diversion
nozzle for providing a jet of gas to the laser-irradiated area and
carrying away any pollutants from the irradiated area.
Inventors: |
Tsao; I-Chang; (Hsinchu,
TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Assignee: |
AU OPTRONICS CORPORATION
No. 1, Li-Hsin Rd. II, Science-Based Industrial Park
Hsinchu
TW
|
Family ID: |
32322959 |
Appl. No.: |
11/554045 |
Filed: |
October 30, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10250172 |
Jun 10, 2003 |
|
|
|
11554045 |
Oct 30, 2006 |
|
|
|
Current U.S.
Class: |
438/487 ;
257/E21.141; 257/E21.347; 438/482 |
Current CPC
Class: |
H01L 21/268 20130101;
H01L 21/223 20130101; C23C 16/56 20130101 |
Class at
Publication: |
438/487 ;
438/482 |
International
Class: |
H01L 21/20 20060101
H01L021/20 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2002 |
TW |
91134040 |
Claims
1. A method of forming polysilicon film, comprising the steps of:
providing a substrate; forming an amorphous silicon film on the
substrate; aiming a beam of laser on a location of the amorphous
silicon film and targeting the laser-irradiated location with a gas
comprising at least a doping element at the same time, so that the
amorphous silicon film is recrystallized into a polysilicon film
doped with the doping element.
2. The method of claim 1, wherein the gas further comprises
nitrogen.
3. The method of claim 1, wherein the gas further comprises an
inert gas.
4. The method of claim 1, wherein the doping element comprises
phosphine.
5. A method of forming polysilicon film, comprising the steps of:
providing a laser annealing apparatus comprising a chamber, a
movable device positioned inside the chamber, a gas diversion
nozzle positioned inside the chamber close to the movable device, a
laser source for emitting a beam of laser which passing through the
gas diversion nozzle to target at a location on the movable device,
and a gas supply device connected with the gas diversion nozzle for
delivering a jet of gas comprising at least a doping element to the
laser-irradiated location on the movable device; forming an
amorphous layer on a substrate; placing the substrate having the
amorphous layer thereon on the movable device inside the chamber;
and aiming the beam of laser emitted from the laser source on a
location of the amorphous silicon film and targeting the
laser-irradiated location with the gas diversion nozzle for
delivering the jet of gas comprising the doping element at the same
time, so that the amorphous silicon film is re-crystallized into a
polysilicon film doped with the doping element.
6. The method of claim 5, wherein the gas further comprises
nitrogen.
7. The method of claim 5, wherein the gas further comprises an
inert gas.
8. The method of claim 5, wherein the doping element comprises
phosphine.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of a prior
application Ser. No. 10/250,172, filed Jun. 10, 2003 which claims
the priority benefit of Taiwan application Ser. No. 91134040, filed
on Nov. 22, 2002. All disclosures are incorporated herewith by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a laser annealing apparatus
and its applications. More particularly, the present invention
relates to a laser annealing apparatus that can stabilize the
surrounding atmosphere of a laser-irradiated region and the
application of the same.
[0004] 2. Description of Related Art
[0005] With the rapid development in technologies, high tech
products including video, especially digital video or imaging
devices has become an indispensable part in our everyday life. At
present, liquid crystal display (LCD) is one of the commonest video
and image display devices. In recent years, a type of thin film
transistor liquid crystal display (TFT-LCD) manufactured using
polysilicon fabrication technique is produced. The TFT-LCD
fabricated using polysilicon has electron mobility considerably
greater than a conventional TFT-LCD device made from amorphous
silicon. Consequently, a smaller thin film transistor with a larger
aperture ratio can be built so that brightness level of the display
is increased and power consumption of the device is reduced.
Moreover, due to an increase in electron mobility, a portion of the
driving circuit may be fabricated on the glass substrate along with
the thin film transistors. Ultimately, reliability and performance
of the liquid crystal display panel is improved and production cost
of the display is reduced considerably. Due to a lower production
cost of a polysilicon TFT-LCD considerable improvements in the
resolution, thickness and weight of the polysilicon TFT-LCD
compared with the amorphous silicon TFT-LCD, polysilicon TFT-LCD is
routinely used in mobile and portable products to take advantage of
its light weight and low power consumption.
[0006] Formerly, the polysilicon thin film transistors are
fabricated through solid phase crystallization (SPC). However, to
withstand the high re-crystallization temperature of up to
1,000.degree. C. , quartz substrate must be used. Yet, quartz
substrate costs considerably more than a glass substrate. Moreover,
due to limitations in the size of substrate, a panel having a
dimension of at most 2 to 3 inches can be produced. Hence, only
small polysilicon display panels are produced. With the advent of
laser technologies, the transformation of amorphous silicon film
into polysilicon film is carried out through laser irradiation. For
example, an amorphous silicon film is scanned by a laser source in
a laser crystallization or excimer laser annealing (ELA) process so
that the amorphous silicon re-crystallizes into polysilicon at a
temperature around 600.degree. C. Since a lower temperature is used
to transform the silicon, ordinary glass panel used in most
conventional amorphous silicon TFT can be used to fabricate the
polysilicon TFT. Thus, the fabrication of a polysilicon TFT display
panel having a larger size is possible. This type of low
temperature re-crystallization technique of manufacturing
polysilicon is often referred to as a low temperature polysilicon
(LTPS) process.
[0007] FIG. 1 is a schematic diagram of a conventional laser
annealing apparatus for transforming amorphous silicon film into
polysilicon film. As shown in FIG. 1, a laser annealing apparatus
100 principally includes a laser source 102 and a chamber 104. An
incoming laser plate 106 made from quartz glass is located above
the chamber 104. A beam of laser 102a from the laser source 102
penetrates the laser plate 106 and irradiates the interior of the
chamber 104. In addition, a movable apparatus 108 is placed inside
the chamber 104. A substrate 110 is normally placed over the
movable apparatus 108 so that the substrate 110 is able to shift
position when irradiated by the laser.
[0008] In general, liquefied silicon may react with moisture and
oxygen in surrounding atmosphere to form contaminants when
amorphous silicon film is irradiated with a laser in a
re-crystallization process. To prevent contaminants produced inside
the chamber 104 from contaminating the polysilicon film and
resulting in some unforeseen effects, gaseous nitrogen or inert gas
is passed into the chamber 104.
[0009] Nevertheless, the aforementioned method can hardly stabilize
the atmosphere around a laser-illuminated region so that all kinds
of unwanted gaseous contaminants may still pollute the surrounding
atmosphere during the laser annealing process. The unwanted gas
includes silicon vapor evaporated from the amorphous silicon film
at high temperature. One of the components inside the chamber 104
that can be easily polluted by the silicon vapor is the laser plate
106. With too much pollution, working life of the incoming laser
plate 106 may be greatly reduced. To prevent this from happening,
an inert gas inlet 104a and an inert gas outlet 104b are installed
on each side of the chamber 104 as shown in FIG. 1. Utilizing the
purging effect of inert gases, quality of the atmosphere inside the
chamber 104 may be conditioned. However, because size of the
chamber 104 for carrying out laser annealing process is usually
large, a lot of inert gas must be used to purge the atmosphere.
Moreover, this arrangement can only produce partial improvement in
the atmospheric quality. In fact, little is done to stabilize the
atmosphere close to the laser-irradiated region.
SUMMARY OF THE INVENTION
[0010] Accordingly, one object of the present invention is to
provide a laser annealing apparatus and an application of the same
that can stabilize a laser-irradiated region.
[0011] A second object of this invention is to provide a laser
annealing apparatus and an application of the same that uses a
smaller volume of gases.
[0012] A third object of this invention is to provide a laser
annealing apparatus and an application of the same that can
minimize any variation in the electrical properties of a
polysilicon thin film transistor.
[0013] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a laser annealing apparatus. The
laser annealing apparatus includes a laser source, a gas supply
device, a chamber and a movable device inside the chamber and a gas
diversion nozzle. The air diversion nozzle is wider at both ends
and narrower in the middle and hence has a funnel-shape profile. A
substrate having an amorphous silicon layer thereon can be placed
on the top of the movable device inside the chamber. The gas
diversion nozzle is positioned close to the substrate on the
movable device. A beam of laser emitted from the laser source
enters the chamber and impinges upon the substrate on the movable
device via the gas diversion nozzle so that the amorphous silicon
film on the substrate is subjected to the scanning laser beam.
Hence, the irradiated amorphous silicon film re-crystallizes into a
polysilicon film. The gas supply device in the laser annealing
apparatus is connected to the gas diversion nozzle inside the
chamber through a tube so that gas from the gas supply device is
brought to the laser-irradiated location via the tube and the air
diversion nozzle. Due to the special profile of the gas diversion
nozzle, any unwanted vapor produced from the laser-irradiated
region is carried away from the substrate along with the gas
flow.
[0014] This invention also provides a laser annealing method. An
annealing substrate such as an amorphous silicon film is provided.
A beam of laser is shone onto a particular location on the
substrate and a jet of nitrogen or inert gas is blown over the
laser-irradiated region so that the atmosphere surrounding the
laser-irradiated region is stabilized.
[0015] If the laser-irradiated substrate is an amorphous silicon
film, the amorphous silicon film will re-crystallize into a
polysilicon film. Hence, this invention can be applied to the
fabrication of polysilicon thin film transistor. In addition, the
nitrogen or inert gas blowing over the annealing substrate may be
replaced using a gas with dopants therein so that the
laser-irradiation operation is accompanied by a doping
implantation.
[0016] Due to the deployment of a special gas diversion nozzle in
this invention, nitrogen, inert gas or some dopants infused gas may
target at a laser-irradiated region with great accuracy and carry
away any harmful gases produced by the laser in the stream of
outflow. Therefore, this invention is particularly useful in
setting up a stable environment surrounding a laser-irradiated
region with a minimum gas flow and hence reduces gases charges
substantially. When the apparatus according to this invention is
applied to the production of polysilicon thin film transistor,
possible contaminants such as the ones resulting from a reaction
between liquefied silicon with moisture and oxygen in the air will
no longer contaminates the polysilicon thin film transistor.
Ultimately, the polysilicon thin film transistor will have
electrical properties according to design.
[0017] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0019] FIG. 1 is a schematic diagram of a conventional laser
annealing apparatus for transforming amorphous silicon film into
polysilicon film;
[0020] FIG. 2 is a schematic diagram of a laser annealing apparatus
according to one preferred embodiment of this invention;
[0021] FIG. 3 is a magnified view of section III in FIG. 2; and
[0022] FIG. 4 is a flow chart showing the steps of using the laser
annealing apparatus in FIG. 2 to produce a polysilicon thin
film.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0024] Although a laser annealing apparatus is used in the
embodiment of this invention, this invention can be applied to
other beam-illuminating apparatus to stabilize the atmosphere
surrounding a beam-illuminated region.
[0025] FIG. 2 is a schematic diagram of a laser annealing apparatus
according to one preferred embodiment of this invention. As shown
in FIG. 2, a laser annealing apparatus 200 includes a laser source
202, a gas supply device 220, a chamber 204 and a movable device
208 inside the chamber and a gas diversion nozzle 222. The laser
annealing device 200 may further include an optical system 203
between the laser light source 202 and the chamber 204 for
channeling a beam of laser 202a from the laser source 202 into the
chamber 204. An incoming laser plate 206 is also mounted on top of
the chamber 204 so that the laser beam 202a is able to pass into
the chamber 204 via the incoming laser plate 206. In general, the
laser plate 206 is made from a material such as quartz glass.
[0026] A substrate 210 having an amorphous silicon film thereon is
placed over the movable device 208 inside the chamber 204. The gas
diversion nozzle 222 is positioned close to the substrate 210 on
the movable device 208 such that the laser beam 202a from the laser
source 202 passes through the gas diversion nozzle 222 to irradiate
the substrate 210. After scanning the laser beam 202a across the
amorphous silicon film on the substrate 210, the amorphous silicon
film re-crystallizes into a polysilicon film.
[0027] The gas supply device 220 inside the laser annealing
apparatus 200 connects with the gas diversion nozzle 222 inside the
chamber 204 through a tube 224. Thus, the gas from the gas supply
device 220 is transported to the laser beam 202a irradiated region
through the gas diversion nozzle 222. Through the stream of gas
provided by the gas supply device 220, any harmful gases generated
when the substrate 210 is laser-irradiated are carried away. Since
the harmful gases include silicon vapor evaporated from the
amorphous silicon film at a high temperature, the gas diversion
nozzle 222 according to this invention also draws away the silicon
vapor and hence lowers the probability of having the incoming laser
plate 206 contaminated.
[0028] To explain the relationships between the gas diversion
nozzle, the laser beam and the gas supply device, refer to FIG. 3.
FIG. 3 is a magnified view of section III in FIG. 2. As shown in
FIG. 3 the substrate 210 on the movable device 208 has an amorphous
silicon film 310. When the laser beam 202a passes through the gas
diversion nozzle 222 to illuminate the substrate 210, the amorphous
silicon film 310 will re-crystallize into a polysilicon film. In
the meantime, the gas 320 provided by the gas supply device 220
(refer to FIG. 2) will pass through the gas diversion nozzle 222
and impinges upon the laser-irradiated amorphous silicon film 310
over substrate 210. In this embodiment, the gas diversion nozzle
222 is narrow in the middle but wider at both ends. In other word,
the gas diversion nozzle 222 has a funnel shape. After bringing a
jet of gas 320 to the substrate 210, any harmful gases generated
during the laser beam 202a irradiated substrate 210 will be carried
away by the outgoing gas stream.
[0029] FIG. 4 is a flow chart showing the steps of using the laser
annealing apparatus in FIG. 2 to produce a polysilicon thin film.
In step 400, a substrate is provided. In step 402, an amorphous
silicon film is formed over the substrate. Thereafter, in step 404,
a beam of laser is shone on a particular location of the amorphous
silicon film. In the meantime, a gas containing some doping
elements is passed over the laser-irradiated region of the
amorphous silicon film so that the amorphous silicon film melts and
re-crystallizes into polysilicon film. The gas containing doping
element includes phosphene (PH.sub.3). Since the doping element
within the gas transforms the amorphous silicon film into a doped
polysilicon film, a doping operation such as a low density channel
doping is saved from the process of forming the polysilicon thin
film transistor.
[0030] One major aspect of this invention is the deployment of a
gas diversion nozzle inside a reaction chamber that can deliver a
jet of nitrogen, inert gas or a gas containing doping elements
accurately onto a laser-irradiated region. Aside from providing an
inert atmosphere around a processing film or doping the processing
film, any harmful gases produced by the irradiation can also be
carried away along with the gas outflow. Consequently, this
invention not only stabilizes the atmosphere surrounding the
laser-irradiated region, but also wastes very little gas. This
invention also prevents any products that result from the reaction
of vaporized silicon with moisture and oxygen in the process of
fabricating polysilicon thin film transistor from contaminating the
laser annealing apparatus.
[0031] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *