U.S. patent application number 12/101648 was filed with the patent office on 2009-02-19 for systems and methods for processing thin films.
This patent application is currently assigned to THE TRUSTEES OF COLUMBIA UNIVERSITY IN THE CITY OF NEW YORK. Invention is credited to James S. IM.
Application Number | 20090045181 12/101648 |
Document ID | / |
Family ID | 34278963 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090045181 |
Kind Code |
A1 |
IM; James S. |
February 19, 2009 |
SYSTEMS AND METHODS FOR PROCESSING THIN FILMS
Abstract
The present disclosure is directed to methods and systems for
processing a thin film samples. In an exemplary method,
semiconductor thin films are loaded onto two different loading
fixtures, laser beam pulses generated by a laser source system are
split into first laser beam pulses and second laser beam pulses,
the thin film loaded on one loading fixture is irradiated with the
first laser beam pulses to induce crystallization while the thin
film loaded on the other loading fixture is irradiated with the
second laser beam pulses. In a preferred embodiment, at least a
portion of the thin film that is loaded on the first loading
fixture is irradiated while at least a portion of the thin film
that is loaded on the second loading fixture is also being
irradiated. In an exemplary embodiment, the laser source system
includes first and second laser sources and an integrator that
combines the laser beam pulses generated by the first and second
laser sources to form combined laser beam pulses. In certain
exemplary embodiments, the methods and system further utilize
additional loading fixtures for processing additional thin film
samples. In such methods and systems, the irradiation of thin film
samples loaded on some of the loading fixtures can be performed
while thin film samples are being loaded onto the remaining loading
fixtures. In certain exemplary methods and systems, the
crystallization processing of the semiconductor thin film samples
can consist of a sequential lateral solidification (SLS)
process.
Inventors: |
IM; James S.; (New York,
NY) |
Correspondence
Address: |
WilmerHale/Columbia University
399 PARK AVENUE
NEW YORK
NY
10022
US
|
Assignee: |
THE TRUSTEES OF COLUMBIA UNIVERSITY
IN THE CITY OF NEW YORK
New York
NY
|
Family ID: |
34278963 |
Appl. No.: |
12/101648 |
Filed: |
April 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10754133 |
Jan 9, 2004 |
7364952 |
|
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12101648 |
|
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60503346 |
Sep 16, 2003 |
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Current U.S.
Class: |
219/121.76 ;
219/121.66; 219/121.78; 257/E21.347; 438/795 |
Current CPC
Class: |
H01L 21/02678 20130101;
H01L 21/02532 20130101; B23K 26/0622 20151001; B23K 26/0604
20130101; H01L 21/02691 20130101; H01L 21/2636 20130101; H01L
21/02686 20130101; B23K 26/067 20130101; B23K 26/0673 20130101;
H01L 21/00 20130101; H01L 21/268 20130101; H01L 21/02683
20130101 |
Class at
Publication: |
219/121.76 ;
219/121.66; 219/121.78; 438/795; 257/E21.347 |
International
Class: |
H01L 21/268 20060101
H01L021/268; B23K 26/067 20060101 B23K026/067 |
Claims
1. A system for processing a plurality of thin films, comprising: a
laser source system for generating laser beam pulses each having a
pulse duration; a first loading fixture for securing a thin film; a
second loading fixture for securing a thin film; a beam splitting
element for splitting said generated laser beam pulses into at
least first laser beam pulses and second laser beam pulses; and
wherein a thin film loaded on said first loading fixture can be
irradiated with said first laser beam pulses and a thin film loaded
on said second loading fixture can be irradiated with said second
laser beam pulses, and wherein at least a portion of said thin film
loaded on said second loading fixture can be irradiated while said
thin film loaded on said first loading fixture is being
irradiated.
2. The system of claim 1, wherein said laser source system
comprises: a first laser source for generating first component
laser beam pulses each having a first pulse duration; a second
laser source for generating second component laser beam pulses each
having a second pulse duration; and an integrator for combining
said first component laser beam pulses with said second component
laser beam pulses to form said generated laser beam pulses.
3. The system of claim 2, wherein the integrator combines said
first component laser beam pulse with said second component laser
beam pulse with a time delay that exists between said first and
second component laser beam pulses.
4. The system of claim 2, wherein the integrator constructively
adds at least a portion of said first component laser beam to at
least a portion of said second component laser beam pulse.
5. The system of claim 1, further comprising: a third loading
fixture for securing a thin film; and wherein a thin film loaded on
said third loading fixture can be irradiated with said first laser
beam pulses.
6. The system of claim 5, wherein said beam splitting element is
capable of directing said first laser beam pulses to said first
loading fixture and said third loading fixture.
7. The system of claim 5, further comprising: a beam steering
element, wherein said beam steering element is capable of directing
said first laser beam pulses to said first loading fixture and said
third loading fixture.
8. The system of claim 5, further comprising a fourth loading
fixture for securing a thin film, and wherein a thin film loaded on
said fourth loading fixture can be irradiated with said second
laser beam pulses.
9. The system of claim 8, further comprising: a first beam steering
element, wherein said first beam steering element is capable of
directing said first laser beam pulses to said first loading
fixture and said third loading fixture; and a second beam steering
element, wherein said second beam steering element is capable of
directing said second laser beam pulses to said second loading
fixture and said fourth loading fixture.
10. The system of claim 1, wherein said system is utilized to
process semiconductor thin films.
11. The system of claim 10, wherein said semiconductor thin film
comprises silicon, germanium or silicon-germanium.
12. The system of claim 10, wherein said process comprises at least
one of the following: an excimer laser anneal (ELA) process, a
sequential lateral solidification (SLS) process and a uniform grain
structure (UGS) crystallization process.
13. The system of claim 1, wherein said system is utilized to
process thin films that are comprised of a metallic material.
14. The system of claim 13, wherein said metallic material
comprises at least one of the following: aluminum, copper, nickel,
titanium, gold and molybdenum.
15. The system of claim 1, wherein said laser source system
consists of at least one of the following: a continuous wave laser,
a solid-state laser and an excimer laser.
16. A system for processing a thin film, comprising: a laser source
system for generating laser beam pulses by generating initial laser
beam pulses having an initial pulse duration, and modifying said
initial laser beam pulses to generate laser beam pulses having a
pulse duration longer than said initial pulse duration; a loading
fixture for securing a thin film; a beam splitting element for
splitting said generated laser beam pulses into at least first
laser beam pulses and second laser beam pulses; and wherein a
region of a thin film that is loaded on said holding fixture can be
irradiated with said first laser beam pulses and another region of
said thin film can be simultaneously irradiated with said second
laser beam pulses.
17. The system of claim 16, wherein the laser source modifies said
initial laser beam pulses by extending said initial laser beam
pulses.
18. The system of claim 16, wherein the laser source generates
initial laser beam pulses by generating first and second component
laser beam pulses having first and second pulse durations, and
wherein the laser source modifies said initial laser beam pulses by
combining said first and second component laser beam pulses.
19. A system for processing a thin film, comprising: a laser source
system for generating laser beam pulses by generating initial laser
beam pulses having an initial pulse duration, and modifying said
initial laser beam pulses to generate laser beam pulses having a
pulse duration longer than said initial pulse duration; at least
one loading fixture for securing at least one thin film; a beam
splitting element for splitting said generated laser beam pulses
into at least first laser beam pulses and second laser beam pulses;
and wherein a first region of said at least one thin film can be
irradiated with said first laser beam pulses and a second region of
said at least one thin film can be simultaneously irradiated with
said second laser beam pulses.
20. The system of claim 19, wherein said first and second regions
are located on a single thin film.
21. The system of claim 19, wherein said first region is located on
a first thin film and said second region is located on a second
thin film.
22. The system of claim 19, wherein the laser source modifies said
initial laser beam pulses by extending said initial laser beam
pulses.
23. The system of claim 19, wherein the laser source generates
initial laser beam pulses by generating first and second component
laser beam pulses having first and second pulse durations, and
wherein the laser source modifies said initial laser beam pulses by
combining said first and second component laser beam pulses.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority under 35 U.S.C .sctn.120 to U.S. patent application
Ser. No. 10/754,133 filed on Jan. 9, 2004, and entitled "Systems
and Methods for Processing Thin Films," which claims priority under
35 U.S.C. .sctn.119(e) to U.S. Provisional Patent Application No.
60/503,346 filed on Sep. 16, 2003, and entitled "Systems and
Methods for Processing Thin Films," both of which are hereby
incorporated in their entirety by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a method and system for processing
thin films, and more particularly to forming crystalline thin films
from amorphous or polycrystalline thin films using laser
irradiation. In particular, the present disclosure relates to
systems and methods that utilize laser beam pulses to irradiate at
least two thin films at the same time.
BACKGROUND OF THE INVENTION
[0003] In recent years, various techniques for crystallizing or
improving the crystallinity of an amorphous or polycrystalline
semiconductor film have been investigated. This technology is used
in the manufacture of a variety of devices, such as image sensors
and active-matrix liquid-crystal display (AMLCD) devices. In the
latter, a regular array of thin-film transistors (TFT) is
fabricated on an appropriate transparent substrate such that the
TFTs serve as integration regions and pixel regions.
[0004] Semiconductor films can be processed using excimer laser
annealing (ELA), also known as line beam ELA, in which a region of
the film is irradiated by an excimer laser to partially melt the
film and then crystallized. The process typically uses a long,
narrow beam shape that is continuously advanced over the substrate
surface, so that the beam can potentially irradiate the entire
semiconductor thin film in a single scan across the surface. ELA
produces homogeneous small grained polycrystalline films; however,
the method often suffers from microstructural non-uniformities
which can be caused by pulse to pulse energy density fluctuations
and/or non-uniform beam intensity profiles. In addition, it may
take approximately 200 second to 600 seconds to completely process
the semiconductor film sample using the ELA techniques, without
even taking into consideration the time it takes to load and unload
such sample.
[0005] Sequential lateral solidification (SLS) using an excimer
laser is one method that has been used to form high quality
polycrystalline films having large and uniform grains. A
large-grained polycrystalline film can exhibit enhanced switching
characteristics because the reduced number of grain boundaries in
the direction of electron flow provides higher electron mobility.
SLS processing also provides controlled grain boundary location.
U.S. Pat. Nos. 6,322,625 and 6,368,945 issued to Dr. James Im, and
U.S. patent application Ser. Nos. 09/390,535 and 09/390,537, the
entire disclosures of which are incorporated herein by reference,
and which are assigned to the common assignee of the present
application, describe such SLS systems and processes.
[0006] In an SLS process, an initially amorphous (or small grain
polycrystalline) silicon film is irradiated by a very narrow laser
beamlet, e.g., laser beam pulse. The beamlet is formed by passing a
laser beam pulse through a slotted mask, which is projected onto
the surface of the silicon film. The beamlet melts the amorphous
silicon and, upon cooling, the amorphous silicon film
recrystallizes to form one or more crystals. The crystals grow
primarily inward from edges of the irradiated area toward the
center. After an initial beamlet has crystallized a portion of the
amorphous silicon, a second beamlet is directed at the silicon film
at a location less than the lateral growth length from the previous
beamlet. Translating a small amount at a time, followed by
irradiating the silicon film, promotes crystal grains to grow
laterally from the crystal seeds of the polycrystalline silicon
material formed in the previous step. As a result of this lateral
growth, the crystals produced tend to attain high quality along the
direction of the advancing beamlet. The elongated crystal grains
are separated by grain boundaries that run approximately parallel
to the long grain axes, which are generally perpendicular to the
length of the narrow beamlet. See FIG. 6 for an example of crystals
grown according to this method. One of the benefits of these SLS
techniques is that the semiconductor film sample and/or sections
thereof can be processed (e.g., crystallized) much faster that it
would take for the processing the semiconductor film by the
conventional ELA techniques. Typically, the
processing/crystallization time of the semiconductor film sample
depends on the type of the substrates, as well as other factors.
For example, it is possible to completely process/crystallize the
semiconductor film using the SLS techniques in approximately 50 to
100 seconds not considering the loading and unloading times of such
samples.
[0007] When polycrystalline material is used to fabricate
electronic devices, the total resistance to carrier transport is
affected by the combination of barriers that a carrier has to cross
as it travels under the influence of a given potential. Due to the
additional number of grain boundaries that are crossed when the
carrier travels in a direction perpendicular to the long grain axes
of the polycrystalline material or when a carrier travels across a
larger number of small grains, the carrier will experience higher
resistance as compared to the carrier traveling parallel to long
grain axes. Therefore, the performance of devices fabricated on
polycrystalline films formed using SLS, such as TFTs, will depend
upon the crystalline quality and crystalline orientation of the TFT
channel relative to the long grain axes, which corresponds to the
main growth direction.
[0008] In order to uniformly process the semiconductor films, it is
important for the beam pulse to be stable. Thus, to achieve the
optimal stability, it is preferable to pulse or fire the beam
constantly, i.e., without stopping the pulsing of the beam. Such
stability may be reduced or compromised when the pulsed beams are
turned off or shut down, and then restarted. However, when the
semiconductor sample is loaded and/or unloaded from a stage, the
pulsed beam would be turned off, and then turned back on when the
semiconductor sample to be processed was positioned at the
designated location on the stage. The time for loading and
unloading is generally referred to as a "transfer time." The
transfer time for unloading the processed sample from the stage,
and then loading another to-be-processed sample on the stage is
generally the same for the ELA techniques and the SLS techniques.
Such transfer time can be between 50 and 100 seconds.
[0009] In addition, the costs associated with processing
semiconductor samples are generally correlated with the number of
pulses emitted by the beam source. In this manner, a "price per
shot/pulse" is established. If the beam source is not shut down
(i.e., still emit the beam pulses) when the next semiconductor
sample is loaded unto the stage, or unloaded from the stage, the
number of such irradiations by the beam source when the sample is
not being irradiated by the beam pulse and corresponding time
therefore is also taken into consideration for determining the
price per shot. For example, when utilizing the SLS techniques, the
time of the irradiation, solidification and crystallization of the
semiconductor sample is relatively short as compared to the sample
processing time using the ELA techniques. In such case,
approximately half of the beam pulses are not directed at the
sample since such samples are being either loaded into the stage or
unloaded from the stage. Therefore, the beam pulses that are not
impinging the samples are wasted.
[0010] Accordingly, it is preferable to reduce the price per shot,
without stopping the emission of the beam pulses. It is also
preferable to be able to process two or more semiconductor samples
at the same time, without the need to stop or delay the emission of
the laser beam pulses generated by the laser source until the
samples are loaded on the respective stages.
SUMMARY OF THE INVENTION
[0011] Laser systems are capable of generating laser beam pulses
that have sufficient energy and pulse durations to process more
than one thin film sample at a time. To efficiently utilize the
generated laser beam pulses to process thin film samples, such
laser beam pulses can be split into component laser beam pulses.
Thin film samples can then be irradiated with the component laser
beam pulses. By generating and splitting laser beam pulses that
have sufficient energy and pulse durations to process more than one
thin film sample at a time, the energy generated by the laser
system can be more efficiently utilized in processing the thin film
samples. By efficiently utilizing the energy that is produced by
the laser system, the manufacturing costs for producing thin films
can be reduced, e.g., the price per shot/pulse can be reduced.
[0012] The present invention is directed to systems and methods for
inducing the melting and subsequent crystallization (upon cooling)
of thin films. Generated laser beam pulses can be split into two or
more component laser beam pulse that can be used to simultaneously
irradiate, via different optical paths, a plurality of thin film
samples or, alternatively, can be used simultaneously to irradiate
different regions of one thin film sample. An optical path, as that
term is used herein, refers to the trajectory of a laser beam pulse
as the laser beam pulse travels from a laser beam source to a thin
film sample. Optical paths thus extend through both the
illumination and projection portions of the exemplary systems. Each
optical path has at least one optical element that is capable of
manipulating the energy beam characteristics of a laser beam pulse
that is directed along that optical path. Thus, by having optical
paths that include different optical elements, laser beam pulses
having different energy beam characteristics can be directed via
the different optical paths to different regions of the thin film
sample or, alternatively, to different thin film samples
[0013] In one aspect of the invention, a method of processing a
plurality of thin films includes: loading a first thin film onto a
first loading fixture; loading a second thin film onto a second
loading fixture; generating laser beam pulses each having a pulse
duration; splitting the generated laser beam pulses into at least
first laser beam pulses and second laser beam pulses, wherein the
first laser beam pulses and the second laser beam pulses each have
pulse durations which are substantially equal to the pulse duration
of the generated laser beam pulses; directing the first laser beam
pulses onto a first optical path and directing the second laser
beam pulses onto a second optical path; irradiating the first thin
film with the first laser beam pulses to induce the melting and
subsequent crystallization of at least a portion of the first thin
film; and irradiating the second thin film with the second laser
beam pulses to induce the melting and subsequent crystallization of
at least a portion of the second thin film.
[0014] In certain embodiments, at least a portion of the step of
irradiating the first thin film and at least a portion of the step
of irradiating the second thin film occur simultaneously.
[0015] In accordance with another aspect of the invention, the step
of generating the laser beam pulses includes: generating first
component laser beam pulses each having a first pulse duration;
generating second component laser beam pulses each having a second
pulse duration; and combining the first component laser beam pulses
with the second component laser beam pulses to form the generated
laser beam pulses.
[0016] In certain embodiment, the method further includes: loading
a third thin film onto a third loading fixture while the first thin
film is being irradiated; irradiating the third thin film with the
first laser beam pulse to induce the melting and subsequent
crystallization of at least a portion of the third thin film upon
completing the processing of the first thin film; unloading the
first thin film from the first loading fixture; and loading another
thin film onto the first loading fixture, wherein the steps of
unloading the first thin film from the first loading fixture and
loading another thin film onto the first loading fixture
substantially occur while the third thin film is being
irradiated.
[0017] In certain other embodiments, the method further includes:
loading a fourth thin film onto a fourth loading fixture while the
second thin film is being irradiated; irradiating the fourth thin
film with the second laser beam pulses to induce the melting and
subsequent crystallization of at least a portion of the fourth thin
film upon completing the processing of the second thin film;
unloading the second thin film from the second loading fixture; and
loading another thin film onto the second loading fixture, wherein
the steps of unloading the second thin film from the second loading
fixture and loading another thin film onto the second loading
fixture substantially occur while the fourth thin film is being
irradiated.
[0018] In accordance with another aspect of the invention, a method
of processing a thin film includes: loading a thin film onto a
loading fixture; generating a laser beam pulse having a pulse
duration; splitting the generated laser beam pulses into at least a
first laser beam pulse and a second laser beam pulse, wherein the
first laser beam pulse and the second laser beam pulse have pulse
durations which are substantially equal to the pulse duration of
the generated laser beam pulse; irradiating a first region of the
thin film with the first laser beam pulse to induce the melting and
subsequent crystallization of the first region of the thin film;
and irradiating a second region of the thin film with the second
laser beam pulse to induce the melting and subsequent
crystallization of the second region of the thin film, wherein at
least portions of the steps of irradiating the first region and
irradiating the second region occur simultaneously.
[0019] In one aspect of the invention, the methods of processing
thin films can be utilized to perform excimer laser anneal (ELA)
processing, sequential lateral solidification (SLS) processing or
uniform grain structure (UGS) crystallization processing.
[0020] In one aspect of the invention, a system for processing a
plurality of thin films includes: a laser source system for
generating laser beam pulses each having a pulse duration; a first
loading fixture for securing a thin film; a second loading fixture
for securing a thin film; a beam splitting element for splitting
the generated laser beam pulses into at least first laser beam
pulses and second laser beam pulses, wherein the first laser beam
pulses and second laser beam pulses each have pulse durations which
are substantially equal to the pulse duration of the generated
laser beam pulses; and wherein a thin film loaded on the first
loading fixture can be irradiated with the first laser beam pulses
and a thin film loaded on the second loading fixture can be
irradiated with the second laser beam pulses.
[0021] In accordance with another aspect of the invention, the
laser source system includes: a first laser source for generating
first component laser beam pulses each having a first pulse
duration; a second laser source for generating second component
laser beam pulses each having a second pulse duration; and an
integrator for combining the first component laser beam pulses with
the second component laser beam pulses to form the generated laser
beam pulses.
[0022] In certain embodiments, the system further includes a third
loading fixture for securing a thin film wherein a thin film loaded
on the third loading fixture can be irradiated with the first laser
beam pulses. A beam steering element can be utilized to direct the
first laser beam pulses to the first loading fixture and the third
loading fixture.
[0023] In certain other embodiments, the system additionally
includes a fourth loading fixture for securing a thin film wherein
a thin film loaded on the fourth loading fixture can be irradiated
with the second laser beam pulses.
[0024] In accordance with yet another aspect of the invention, a
system for processing a thin film includes: a laser source system
for generating a laser beam pulse having a pulse duration; a
holding fixture for securing a thin film; a beam splitting element
for splitting the generated laser beam pulses into at least first
laser beam pulses and second laser beam pulses, wherein the first
laser beam pulses and second laser beam pulses have pulse durations
which are substantially equal to the pulse duration of the
generated laser beam pulses; and wherein a region of a thin film
that is loaded on the holding fixture can be irradiated with the
first laser beam pulses and a different region of the thin film
loaded on the loading fixture can be simultaneously irradiated with
the second laser beam pulses.
[0025] According to one aspect of the invention, the laser source
system consists of at least one continuous wave laser, solid-state
laser or excimer laser.
BRIEF DESCRIPTION OF THE DRAWING
[0026] Various objects, features, and advantages of the present
invention can be more fully appreciated with reference to the
following detailed description of the invention when considered in
connection with the following drawing, in which like reference
numerals identify like elements. The following drawings are for the
purpose of illustration only and are not intended to be limiting of
the invention, the scope of which is set forth in the claims that
follow.
[0027] FIG. 1 illustrates the process of excimer laser annealing
according to one or more embodiments of the present invention.
[0028] FIG. 2 shows a diagram of an exemplary system for performing
a sequential lateral solidification according to one or more
embodiments of the present invention.
[0029] FIG. 3 shows a mask for using in a sequential lateral
solidification according to one or more embodiments of the present
invention
[0030] FIG. 4 illustrates a step in the process of sequential
lateral solidification according to one or more embodiments of the
present invention.
[0031] FIG. 5 illustrates a step in the process of sequential
lateral solidification according to one or more embodiments of the
present invention.
[0032] FIG. 6 illustrates a step in the process of sequential
lateral solidification according to one or more embodiments of the
present invention.
[0033] FIG. 7A through FIG. 7C illustrate a sequential lateral
solidification process according to one or more embodiments of the
present invention.
[0034] FIG. 8 is a prior art system for processing a thin film
sample.
[0035] FIG. 9 is a flow chart of an exemplary embodiment of a
process according to the present invention in which more than one
thin film sample is irradiated at a time.
[0036] FIG. 10 depicts an exemplary system for processing a
plurality of thin film sample in accordance with the present
invention.
[0037] FIG. 11 depicts an exemplary laser source system for
generating laser beam pulses in accordance with the present
invention.
[0038] FIG. 12A through FIG. 12C depict exemplary laser beam pulses
generated by the laser source system of FIG. 11.
[0039] FIG. 13 depicts another exemplary system for processing a
plurality of thin film sample in accordance with the present
invention.
[0040] FIG. 14 depicts an exemplary system for processing a
plurality of thin film sample in accordance with the present
invention where thin film samples are loaded and unloaded onto a
loading fixture while thin film samples are being processed on
other loading fixtures.
[0041] FIG. 15 depicts an exemplary system for processing a
plurality of thin film sample in accordance with the present
invention where thin film samples are loaded and unloaded onto
third and fourth loading fixtures while thin film samples are being
processed on other loading fixtures.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The quality of a film that has been crystallized using a
laser-induced crystallization growth technique depends, in part, on
the energy beam characteristics of the laser beam pulse that is
used to irradiate the film and in the manner in which these laser
beams are delivered, e.g., continuous scan, two-shot, n-shot, to
the film. This observation is used to crystallize different regions
of the films with laser beams having different energy beam
characteristics in an energy- and time-efficient manner and to
provide the film performance characteristics needed in device to be
fabricated. Laser-induced crystallization is typically accomplished
by laser irradiation using a wavelength of energy that can be
absorbed by the film. The laser source may be any conventional
laser source, including but not limited to, excimer laser,
continuous wave laser and solid-state laser. The irradiation beam
pulse can be generated by another known source or short energy
pulses suitable for melting a semiconductor can be used. Such known
sources can be a pulsed solid state laser, a chopped continuous
wave laser, a pulsed electron beam and a pulsed ion beam, etc.
[0043] The systems and methods of the present disclosure can be
utilized to process a wide variety of types of thin films. In
certain embodiments, for example, the described systems and methods
can be used to process (e.g., induce and achieve desired
crystallization) semiconductor thin films. Such semiconductor thin
films can be comprised of silicon, germanium or silicon germanium.
Other semiconductor materials, however, may also be used to make up
a semiconductor thin film. In certain other embodiments, the
described systems and methods may be used to process thin films
that are comprised of a metallic material, such as aluminum,
copper, nickel, titanium, gold and molybdenum, for example. In
certain embodiments, an intermediate layer located beneath the thin
film is utilized to protect the substrate from the heat and to
prevent impurities from able to diffuse into the thin film. The
intermediate layer can be comprised of silicon oxide, silicon
nitride and/or mixtures of oxide, nitride or a wide variety of
other suitable materials.
[0044] Improvements in crystal properties are typically observed
regardless of the specific crystallization process employed. The
films can be laterally or transversely crystallized, or the films
can crystallize using spontaneous nucleation. By "lateral crystal
growth" or "lateral crystallization," as those terms are used
herein, it is meant a growth technique in which a region of a film
is melted to the film/surface interface and in which
recrystallization occurs in a crystallization front moving
laterally across the substrate surface. By "transverse crystal
growth" or "transverse crystallization," as those terms are sued
herein, it is meant a growth technique in which a region of film is
partially melted, e.g., not through its entire thickness, and in
which recrystallization occurs in a crystallization front moving
across the film thickness, e.g., in a direction transverse to that
of the above-described lateral crystallization. In spontaneous
nucleation, crystal growth is statistically distributed over the
melted regions and each nucleus grows until it meets other growing
crystals. Exemplary crystallization techniques include excimer
laser anneal (ELA), sequential lateral solidification (SLS), and
uniform grain structure (UGS) crystallization.
[0045] Referring to FIG. 1, the ELA process uses a long and narrow
shaped beam 100 to irradiate the thin film. In ELA, a line-shaped
and homogenized excimer laser beam pulses are generated and scanned
across the film surface. For example, the width 124 of the center
portion of the ELA beam can be up to about 1 cm (typically about
0.4 mm) and the length 120 can be up to about 70 cm (typically
about 400 mm) so that the beam can potentially irradiate the entire
semiconductor thin film 126 in a single pass. The excimer laser
light is very efficiently absorbed in, for example, an amorphous
silicon surface layer without heating the underlying substrate.
With the appropriate laser pulse duration (approx. 20-50 ns) and
intensity (350-400 mJ/cm.sup.2), the amorphous silicon layer is
rapidly heated and melted; however, the energy dose is controlled
so that the film is not totally melted down to the substrate. As
the melt cools, recrystallization into a polycrystalline structure
occurs. Line beam exposure is a multishot technique with an overlay
of 90% to 99% between shots. The properties of silicon films are
dependent upon the dose stability and homogeneity of the applied
laser light. Line-beam exposure typically produces films with an
electron mobility of 100 to 150 cm.sup.2/V-s.
[0046] Referring to FIG. 2, an apparatus 200 is shown that may be
used for sequential lateral solidification and/or for uniform grain
structure crystallization. Apparatus 200 has a laser source 270.
Laser source 270 may include a laser (not shown) along with optics,
including mirrors and lens, which shape a laser beam pulse 272
(shown by dotted lines) and direct it toward a substrate 274, which
is supported by a stage 278. The laser beam pulse 272 passes
through a mask 280 supported by a mask holder 282. The laser beam
pulses 272 generated by the beam source 270 provide a beam
intensity in the range of 10 mJ/cm.sup.2 to 1 J/cm.sup.2, a pulse
duration in the range of 20 to 300 nsec, and a pulse repetition
rate in the range of 10 Hz to 300 Hz. Currently available
commercial lasers such as Lambda STEEL 1000 available from Lambda
Physik, Ft. Lauderdale, Fla., can achieve this output. As the power
of available lasers increases, the energy of the laser beam pulses
272 will be able to be higher, and the mask size will be able to
increase as well. After passing through the mask 280, the laser
beam pulse 272 passes through projection optics 284 (shown
schematically). The projection optics 284 reduces the size of the
laser beam, and simultaneously increases the intensity of the
optical energy striking the substrate 274 at a desired location
276. The demagnification is typically on the order of between
3.times. and 7.times. reduction, preferably a 5.times. reduction,
in image size. For a 5.times. reduction the image of the mask 280
striking the surface at the location 276 has 25 times less total
area than the mask, correspondingly increasing the energy density
of the laser beam pulse 272 at the location 276.
[0047] The stage 278 is a precision x-y stage that can accurately
position the substrate 274 under the beam 272. The stage 278 can
also be capable of motion along the z-axis, enabling it to move up
and down to assist in focusing or defocusing the image of the mask
280 produced by the laser beam pulses 272 at the location 276. In
another embodiment of the method of the present invention, it is
preferable for the stage 278 to also be able to rotate.
[0048] In uniform grain structure (UGS) crystallization, a film of
uniform crystalline structure is obtained by masking a laser beam
pulse so that non-uniform edge regions of the laser beam pulse do
not irradiate the film. The mask can be relatively large, for
example, it can be 1 cm.times.0.5 cm; however, it should be smaller
than the laser beam size, so that edge irregularities in the laser
beam are blocked. The laser beam pulse provides sufficient energy
to partially or completely melt the irradiated regions of the thin
film. UGS crystallization provides a semiconductor film having an
edge region and a central region of uniform fine-grained
polycrystals of different sizes. In the case where the laser
irradiation energy is above the threshold for complete melting, the
edge regions exhibit large, laterally grown crystals. In the case
where the laser irradiation energy is below the threshold for
complete melting, grain size will rapidly decrease from the edges
of the irradiated region. For further detail, see U.S. application
Ser. No. 60/405,084, filed Aug. 19, 2002 and entitled "Process and
System for Laser Crystallization Processing of Semiconductor Film
Regions on a Substrate to Minimize Edge Areas, and Structure of
Such Semiconductor Film Regions," which is hereby incorporated by
reference.
[0049] Sequential lateral solidification is a particularly useful
lateral crystallization technique because it is capable of grain
boundary location-controlled crystallization and provides crystal
grain of exceptionally large size. Sequential lateral
solidification produces large grained semiconductor, e.g., silicon,
structures through small-scale translations between sequential
pulses emitted by an excimer laser. The invention is described with
specific reference to sequential lateral solidification of an
amorphous silicon film; however, it is understood that the benefits
of present invention can be readily obtained using other lateral
crystallization techniques or other film materials.
[0050] FIG. 3 shows a mask 310 having a plurality of slits 320 with
slit spacing 340. The mask can be fabricated from a quartz
substrate and includes a metallic or dielectric coating that is
etched by conventional techniques to form a mask having features of
any shape or dimension. The length of the mask features is chosen
to be commensurate with the dimensions of the device that is to be
fabricated on the substrate surface. The width 360 of the mask
features also may vary. In some embodiments it is chosen to be
small enough to avoid small grain nucleation within the melt zone,
yet large enough to maximize lateral crystalline growth for each
excimer pulse. By way of example only, the mask feature can have a
length of between about 25 and 1000 micrometers (.mu.m) and a width
of between about two and five micrometers (.mu.m).
[0051] An amorphous silicon thin film sample is processed into a
single or polycrystalline silicon thin film by generating a
plurality of excimer laser pulses of a predetermined fluence,
controllably modulating the fluence of the excimer laser pulses,
homogenizing the modulated laser pulses, masking portions of the
homogenized modulated laser pulses into patterned beamlets,
irradiating an amorphous silicon thin film sample with the
patterned beamlets to effect melting of portions thereof irradiated
by the beamlets, and controllably translating the sample with
respect to the patterned beamlets (or vice versa) to thereby
process the amorphous silicon thin film sample into a single or
grain boundary-controlled polycrystalline silicon thin film.
[0052] In one or more embodiments of the sequential lateral
solidification process, highly elongated crystal grains that are
separated by grain boundaries that run approximately parallel to
the long grain axes are produced. The method is illustrated with
reference to FIG. 4 through FIG. 6.
[0053] FIG. 4 shows the region 440 prior to crystallization. A
laser pulse is directed at the rectangular area 460 causing the
amorphous silicon to melt. Crystallization is initiated at solid
boundaries of region 460 and continues inward towards centerline
480. The distance the crystal grows, which is also referred to as
the lateral growth length, is a function of the amorphous silicon
film thickness, the substrate temperature, the energy beam
characteristics, the buffer layer material, if any, the mask
configuration, etc. A typical lateral growth length for 50 nm thick
films is approximately 1.2 micrometers. After each pulse the image
of the opening is advanced by an amount not greater than the
lateral growth length. In order to improve the quality of the
resultant crystals, the sample is advanced much less than the
lateral crystal growth length, e.g., not more than one-half the
lateral crystal growth length. A subsequent pulse is then directed
at the new area. By advancing the image of the slits 460 a small
distance, the crystals produced by preceding steps act as seed
crystals for subsequent crystallization of adjacent material. By
repeating the process of advancing the image of the slits and
firing short pulses the crystal grows in the direction of the
slits' movement.
[0054] FIG. 5 shows the region 440 after several pulses. As is
clearly shown, the area 500 that has already been treated has
formed elongated crystals that have grown in a direction
substantially perpendicular to the length of the slit.
Substantially perpendicular means that a majority of lines formed
by crystal boundaries 520 could be extended to intersect with
dashed center line 480.
[0055] FIG. 6 shows the region 440 after several additional pulses
following FIG. 5. The crystals have continued to grow in the
direction of the slits' movement to form a polycrystalline region.
The slits preferably continue to advance at substantially equal
distances. Each slit advances until it reaches the edge of a
polycrystalline region formed by the slit immediately preceding
it.
[0056] The sequential lateral solidification process can produce a
film having highly elongated, low defect grains. In one or more
embodiments, this process is used to process those regions of the
semiconductor thin film that are used for high performance devices.
The polycrystalline grains obtained using this process are
typically of high mobility, e.g., 300-400 cm.sup.2/V-s. These
highly elongated grains are well suited for the integrated
circuitry regions on an AMLCD device.
[0057] According to the above-described method of sequential
lateral solidification, the entire mask area is crystallized using
multiple pulses. This method is hereinafter referred to as an
"n-shot" process, alluding to the fact that a variable, or "n",
number of laser pulses ("shots") are required for complete
crystallization. Further detail of the n-shot process is found in
U.S. Pat. No. 6,322,625, entitled "Crystallization Processing of
Semiconductor Film Regions on a Substrate and Devices Made
Therewith," and in U.S. Pat. No. 6,368,945, entitled "System for
Providing a Continuous Motion Sequential Lateral Solidification,"
both of which are incorporated in their entireties by
reference.
[0058] In one or more embodiments, regions of the semiconductor
film are processed using a sequential lateral solidification
process that produces shorter crystal grains than those of the
preceding "n-shot" method. The film regions are therefore of lower
electron mobility; however the film is processed rapidly and with a
minimum number of passes over the film substrate, thereby making it
a cost-efficient processing technique. These crystallized regions
are well suited for the regions of the semiconductor thin film that
are used for making pixel control devices of an AMLCD device.
[0059] The process uses a mask such as that shown in FIG. 3, where
closely packed mask slits 320 having a width 360, of about by way
of example 4 .mu.m, are each spaced apart by spacing 340 of about,
by way of example, 2 .mu.m. The sample is irradiated with a first
laser pulse. As shown in FIG. 7A, the laser pulse melts regions
710, 711, 712 on the sample, where each melt region is
approximately 4 .mu.m wide 720 and is spaced approximately 2 .mu.m
apart 721. This first laser pulse induces crystal growth in the
irradiated regions 710, 711, 712 starting from melt boundaries 730
and proceeding into the melt region, so that polycrystalline
silicon 740 forms in the irradiated regions, as shown in FIG.
7B.
[0060] The sample is then translated approximately half the
distance (or greater) of the sum of the width 360 and spacing 340,
and the film is irradiated with a second excimer laser pulse. The
second irradiation melts the remaining amorphous regions 742
spanning the recently crystallized region 740 and initial crystal
seed region 745 to melt. As shown in FIG. 7C, the crystal structure
that forms the central section 745 outwardly grows upon
solidification of melted regions 742, so that a uniform long grain
polycrystalline silicon region is formed.
[0061] According to the above-described method of sequential
lateral solidification, the entire mask area is crystallized using
only two laser pulses. This method is hereinafter referred to as a
"two-shot" process, alluding to the fact that only two laser pulses
("shots") are required for complete crystallization. Further detail
of the two-shot process is found in Published International
Application No. WO 01/18854, entitled "Methods for Producing
Uniform Large-Grained and Grain Boundary Location Manipulated
Polycrystalline Thin Film Semiconductors Using Sequential Lateral
Solidification," which is incorporated in its entirety by
reference.
[0062] FIG. 8 illustrates a typical system 10 that can be used to
induce the melting and subsequent crystallization of a thin film
sample. Referring to FIG. 8, the system 10 includes a laser source
12, an attenuator 14 which is utilized in conjunction with a pulse
duration extender 16, a telescope 18, a homogenizer 20, a condenser
lens 22, a mirror 24, a variable-focus field lens 26, a mask 28,
mirrors 30 and 32, a projection lens 34 and a handling stage 38
(i.e., a loading fixture). The laser source 12 is capable of
generating laser beam pulses 42 that have set pulse durations. The
attenuator 14 can be a variable attenuator, e.g., having a dynamic
range of 10 to 1, capable of adjusting the energy density of the
generated laser beam pulses 42. Since crystal growth can be a
function of the duration of the pulse, a pulse duration extender 16
is often used to lengthen the duration of each generated laser beam
pulse 42 to achieve a desired pulse duration. The telescope 18 can
be used to efficiently adapt the beam profile of the laser beam
pulse 42 to the aperture of the homogenizer 20. The homogenizer 20
can consist of two pairs of lens arrays (two lens arrays for each
beam axis) that are capable of generating a laser beam pulses 42
that have uniform energy density profiles. The condenser lens 22
can condense the laser beam pulse 42 onto the variable-focus field
lens 26. The mask 28 is typically mounted to a mask stage (not
shown) that is capable of accurately positioning the mask 28 (e.g.,
in three dimensions) in relationship to the incoming laser beam
pulse 42.
[0063] The energy beam characteristics of the laser beam pulses 42
generated by the laser source 12 are modified by the optical
elements of system 10 to produce laser beam pulses 42a that have
desired energy beam characteristics, e.g., beam energy profile
(density), beam shape, beam orientation, beam pulse duration, etc.
As previously discussed, the amorphous silicon film 36 can be
deposited in a controlled manner upon a surface of a substrate (not
shown). The handling stage 38 is capable of accurately positioning
the thin film 36 (e.g., in three dimensions) in relation to the
incoming laser beam pulses 42a. The handling stage 38 can operate
in a continuous scanning mode or, alternatively, a stepper mode.
Laser beam pulses 42a thus are directed to portions of the thin
film sample to induce the melting and subsequent crystallization of
the thin film sample, e.g., via two-shot or n-shot SLS
processing.
[0064] As discussed above, to achieve a laser beam pulse 42a that
has acceptable energy beam characteristics, many systems today
utilize a pulse duration extender 16 to extend the pulse duration
of the laser beam pulses 42 that are generated by the laser source
12. When using a pulse duration extender, however, some of the
energy of the generated laser beam pulse 42 will become lost during
the "extension" process since pulse duration extenders tend to be
inefficient (e.g., the efficiencies of a pulse duration extender
may range from between 50-80%). This inability to utilize all of
the energy which is generated by the laser source can lead to
increased processing times and, thus, lower manufacturing
throughput. System 10 also suffers from the disadvantage that only
a single thin film sample can be processed (i.e., irradiated) at a
time.
[0065] Exemplary systems and processes according to the present
invention can employ principles and components thereof to process
more than one thin film sample at a time. An exemplary process is
set forth in the flow diagram 900 of FIG. 9. Flow diagram 900
illustrates a method for simultaneously irradiating two thin film
samples that are located on separate handling stages (i.e., loading
fixtures) while other thin film samples are being unloaded from and
loaded onto other handling stages.
[0066] In steps 910a and 910b, thin film samples (which may be
mounted on substrates) are loaded onto a first loading fixture and
a second loading fixture, respectively. The deposition and/or
fabrication of a thin film on a substrate is well known in the art.
In step 912 laser beam pulses are generated. In step 914 the
generated laser beam pulses are split into first laser beam pulses
and second laser beam pulses. In certain preferred embodiments, the
first and second laser beam pulses have pulse durations that are
substantially the same. In step 916a the first laser beam pulses
are directed to the first loading fixture and the thin film sample
loaded on the first loading fixture is irradiated with the first
laser beam pulses to induce the melting and subsequent
crystallization of the thin film sample, step 918a. In step 916b
the second laser beam pulses are directed to the second loading
fixture and the thin film sample loaded on the second loading
fixture is irradiated with the second laser beam pulses to induce
the melting and subsequent crystallization of the thin film sample,
step 918b. In an exemplary embodiment, at least a portion of the
thin film loaded on the first loading fixture is also being
irradiated (steps 916a and 918a) while at least a portion of the
thin film loaded on the second loading fixture is also being
irradiated (steps 916b and 918b). Thus, in this manner, more than
one thin film sample can be processed simultaneously. The
processing of the thin film sample loaded on the first loading
fixture is continued until the processing is complete, step 920a.
Similarly, the processing of the thin film sample loaded on the
second loading fixture is also continued until the processing is
complete, step 920b. In certain embodiments, the (total) processing
of the thin film sample loaded on the first loading fixture
coincides with the processing of the thin film sample loaded on the
second loading fixture. In other embodiments, however, the
processing of the thin film sample loaded on the first loading
fixture does not coincide with the processing of the thin film
sample loaded on the second loading fixture.
[0067] While the processing of the thin film samples loaded on the
first and second loading fixtures is underway, other thin film
samples are loaded onto a third loading fixture, step 922a, and
onto a fourth loading fixture, step 922b. Thus, while a thin film
sample is being processed (i.e., irradiated), the unloading/loading
of another thin film sample onto an inactive (i.e., receiving no
irradiation) loading fixture can be accomplished. Upon completing
the processing of the thin film sample which is loaded on the first
loading fixture, the first laser beam pulses are then directed to
the third loading fixture, step 924a, (where a thin film sample has
already been loaded (step 922a)) and the unloading of the processed
thin film sample and the loading of a new thin film sample onto the
first loading fixture, step 930a, begins. Upon completing the
processing of the thin film sample which is loaded on the second
loading fixture, the second laser beam pulses are directed to the
fourth loading fixture, step 924b, (where a thin film sample has
already been loaded (step 922b)) and the unloading of the processed
thin film sample and the loading of a new thin film sample onto the
second loading fixture, step 930b, begins.
[0068] In step 926a the thin film sample loaded on the third
loading fixture is then irradiated with the first laser beam pulses
to induce the melting and subsequent crystallization of the loaded
thin film sample. In step 926b the thin film sample loaded on the
fourth loading fixture is then irradiated with the second laser
beam pulses to induce the melting and subsequent crystallization of
this thin film sample. The processing of the thin film samples
loaded on the third and fourth loading fixtures is then continued
until the processing is complete, steps 928a and 928b,
respectively. Preferably, a new thin film sample is already loaded
onto the first loading fixture, step 930a, before the processing of
the thin film sample loaded on the third loading fixture is
completed. And, preferably, a new thin film sample is already
loaded onto the second loading fixture, step 930b, before the
processing of the thin film sample loaded on the fourth loading
fixture is completed. This method of unloading/loading thin film
samples from/onto inactive loading fixtures, while other thin film
samples are being processed on active loading fixtures, is
continued until all the thin film samples have been processed, step
940. Flow diagram 900 thus provides a method for optimally using
the power provided by the laser source and for maximizing the
manufacturing throughput of the thin film processing. This is
accomplished by maximizing the laser (irradiation) source's duty
cycle, e.g., the laser source can remain on and its generated
energy is continuously being utilized to facilitate the processing
of thin film samples, and minimizing any downtime that may be
necessary for the loading and unloading of the thin film samples
onto and from the loading fixtures.
[0069] An exemplary embodiment of a system constructed in
accordance with the present invention is depicted in FIG. 10.
System 1000 of FIG. 10 includes a laser source system 50, a beam
splitting element 70 and two loading fixtures 122, 142. Thin film
samples 118, 138 are loaded onto loading fixtures 122 and 142,
respectively. System 1000 may further include an automatic handling
system(s) (not shown) that is capable of loading the thin film
samples onto the loading fixtures, so that the thin film samples
may be processed, and removing the thin film samples from the
loading fixtures when processing has been completed. The laser
source system 50 is capable of generating laser beam pulses 52 that
have sufficient energy to process (upon splitting) at least two
thin film samples at the same time. Moreover, in most preferred
embodiments, the laser source system 50 is capable of generating
laser beam pulses 52 which have pulse durations that are sufficient
to induce the desired crystallization processing of the thin film
samples. Thus, in most preferred embodiments, a pulse duration
extender does not need to be utilized to extend the pulse duration
of the laser beam pulses 52 generated by the laser source system
50.
[0070] System 1000 further includes a variable-focus field lens
112, a mask 114, a projection lens 116, a mirror 144, a second
variable-focus field lens 132, a second mask 134 and a second
projection lens 136. Variable-focus field lens 112, mask 114 and
projection lens 116 are disposed between the beam splitting element
70 and the loading fixture 122, while variable-focus field lens
132, mask 134 and projection lens 136 are disposed between the beam
splitting element 70 and the loading fixture 142. In other
embodiments, system 1000 may include different (or fewer) optical
elements. Moreover, different optical elements may be present
within the different optical paths that are located downstream of
the beam splitting element 70. Accordingly, the energy beam
characteristics of the laser beam pulses that are used to irradiate
the thin film samples can be tailored to meet the processing
requirements of the thin samples that are to be processed. System
1000 further includes an attenuator 14, a telescope 18, a
homogenizer 20 and a condenser lens 22, which are located between
the laser source system 50 and the beam splitting element 70.
[0071] After traveling through the attenuator 14, telescope 18,
homogenizer 20 and condenser lens 22 (where the energy beam
characteristics of the laser beam pulses 52 are accordingly
modified), laser beam pulses 52 are then split by the beam
splitting element 70 into first laser beam pulses 58 and second
laser beam pulses 56 which are directed to the first loading
fixture 122 and the second loading fixture 142, respectively. The
beam splitting element 70 "splits" the laser beam pulses 52 by
distributing the energy density of the laser beam pulses 52 into
separate component laser beam pulses 56 and 58. The component laser
beam pulses 56 and 58 produced by the beam splitting element 70
generally will have the same pulse durations as the laser beam
pulses 52 which are generated by the laser source system 50.
Component laser beam pulses 56 and 58, however, need not have the
same energy densities. For example, in some embodiments, 60% of the
energy density of the laser beam pulses 52 may be used to form the
first laser beam pulses 58 while, in other embodiments, the energy
densities of the component laser beam pulses 56 and 58 may be
substantially the same. While the beam splitting element 70 of
system 1000, as shown, only generates two component laser beam
pulses, in other embodiments the beam splitting element 70 is
capable of producing several (e.g., three, four, etc.) component
laser beam pulses from the laser beam pulses 52 that are generated
by the laser source system 50.
[0072] First laser beam pulses 58 travel through variable-focus
lens 112, mask 114 and projection lens 116 to form first laser beam
pulses 58a (e.g., the energy beam characteristics of laser beam
pulses 58a will be different than that of laser beam pulses 58).
Thin film 118, which is loaded on loading fixture 122, is then
irradiated with the laser beam pulses 58a. The loading fixture 122
is capable of accurately positioning the thin film 118 (e.g., in
three dimensions) in relation to the incoming first laser beam
pulses 58a. The loading fixture 122 can operate in a continuous
scanning mode or, alternatively, a stepper mode. Laser beam pulses
58a thus are directed to portions of thin film 118 to induce the
melting and subsequent crystallization of the thin film 118, e.g.,
via two-shot or n-shot SLS processing. Upon completing the
processing of the thin film 118 loaded on loading fixture 122, the
thin film 118 is then removed from loading fixture 122 and another
thin film sample is substituted in its place.
[0073] Second laser beam pulses 56 similarly travel through
variable-focus lens 132, mask 134 and projection lens 136 to form
second laser beam pulses 56a (e.g., the energy beam characteristics
of laser beam pulses 56a will be different than that of laser beam
pulses 56). Thin film 138, which is loaded on loading fixture 142,
is then irradiated with the laser beam pulses 56a. The loading
fixture 142 is capable of accurately positioning the thin film 138
(e.g., in three dimensions) in relation to the incoming second
laser beam pulses 56a. Loading fixture 142 can operate in a
continuous scanning mode or, alternatively, a stepper mode. Laser
beam pulses 56a thus are directed to portions of thin film 138 to
induce the melting and subsequent crystallization of the thin film
138, e.g., via two-shot or n-shot SLS processing. Upon completing
the processing of the thin film 138 loaded on loading fixture
142--which need not coincide with the processing of the thin film
118 that is loaded on loading fixture 122--thin film 138 can be
removed from the loading fixture 142 and another can be substituted
in its place. The operations of the laser source system 50, the
beam steering element 70, and the handling stages 122, 142, along
with the systems (e.g., actuators, conveyors, etc) necessary for
loading and unloading the thin film samples onto and from the
loading fixtures 122, 142, and the other optical elements (if
present) can be controlled by a programmable computer system (not
shown). FIG. 10 thus illustrates a system for processing thin film
samples where two thin film samples can be processed at the same
time.
[0074] In an alternate embodiment, system 1000 can be configured so
as to simultaneously irradiate different portions of a single thin
film sample (loaded on a loading fixture). In other words, in
certain embodiments, system 1000 may only include a single loading
fixture and laser beam pulses 56a and 58a can be directed to
different regions of the thin film that is loaded on the loading
fixture. Thus, simultaneous processing of different regions of a
thin film sample can be accomplished in accordance with the
teachings of the present invention.
[0075] As previously discussed, laser source system 50 is
preferably capable of generating laser beam pulses 52 that have
sufficient energy to process (upon splitting) more than one thin
film samples at a time. In most exemplary embodiments, the laser
source system 50 has a high pulse-to-pulse stability, e.g., less
than 3% and preferable less than 1.5%. Moreover, in most preferred
embodiments, the laser source system 50 is capable of generating
laser beam pulses 52 which have pulse durations that are sufficient
to induce the desired crystallization processing of the thin film
samples. Thus, in certain preferred embodiments, a pulse duration
extender does not need to be utilized to extend the pulse duration
of the laser beam pulses 52 generated by the laser source system
50. Appropriate laser source systems that are capable of producing
laser beam pulses 52 which have sufficient energy to process more
than one thin film sample at a time are commercially available. For
example, in certain embodiments, the laser source system 50 of the
present invention can be a high-pulse-energy excimer laser, such as
the Lambda STEEL systems that are available from Lambda Physik or
the SOPRA VEL 1510 that is available from SOPRA S.A.
[0076] In other exemplary embodiments, the laser source system 50
includes two or more laser sources that generate component laser
beam pulses that are integrated together to form the laser beam
pulses 52. FIG. 11 illustrates one exemplary embodiment of a laser
source system 50 that utilizes two or more laser sources. FIGS.
12A-C illustrate various ways in which the component laser beam
pulses of the laser source system 50 of FIG. 11 can be integrated
to form laser beam pulses 52. The laser source system 50 of FIG. 11
includes a first laser source 60a, a second laser source 60b,
mirrors 63 and an integrator 66. Referring to FIGS. 11 and 12A, the
first laser source 60a generates component laser beam pulses 62a
that have an energy profile, pulse cycle and pulse duration 64a as
shown. The second laser source 60b generates component laser beam
pulses 62b that have an energy profile, pulse cycle and pulse
duration 64b as shown. In certain preferred embodiments, the energy
profiles, pulse cycles and pulse durations 64a, 64b of the
component laser sources 60a, 60b are substantially similar, while
in other embodiments, the energy profiles, pulse cycles and/or
pulse durations are different. The laser beam pulses 62a, 62b are
directed to the integrator 66 via mirrors 63. The integrator 66
combines laser beam pulses 62a, 62b together to form laser beam
pulses 52 having an effective pulse duration as shown in FIGS.
12A-C. The integrator 66 can include reflective elements that
direct the laser beam pulses 62a, 62b onto the same optical path.
As seen in FIGS. 12A-C, each component laser beam pulse 62a (having
a pulse duration 64a) is integrated (i.e., paired) with a
corresponding component laser beam pulse 62b (having a pulse
duration 64b) to effectively form a laser beam pulse 52. The
component laser beam pulses 62a, 62b can be integrated together so
that (1) there is a small time delay between a laser beam pulse 62a
and a corresponding laser beam pulse 62b, (2) a portion of a laser
beam pulse 62a overlies a portion of a corresponding laser beam
pulse 62b so that the laser beam pulse 62a, 62b are constructively
added where they overlie each other, or (3) a laser beam pulse 62a
completely overlies a corresponding laser beam pulse 62b (and,
thus, laser beam pulse 62a, 62b constructively add to each other).
The integration of the component laser beam pulses 62a, 62b (to
form a laser beam pulse 52) can be controlled, for example, by
varying the timing of the generation of the component laser beam
pulses 62a, 62b (with respect to each other), the pulse cycle at
which the component laser beam pulses 62a, 62b are being generated,
the length of the pulse durations 64a, 64b of the component laser
beam pulses 62a, 62b, the path lengths found between the laser
sources 60a, 60b and the integrator 60, the operations of the
integrator 60 (e.g., delayed biases, if present), or the energy
densities of the component laser beam pulses 62a, 62b.
[0077] As shown in FIG. 12A, in certain exemplary embodiments, a
time delay d is inter-disposed between corresponding component
laser beam pulses 62a, 62b. In one preferred embodiment, the laser
sources 60a, 60b are synchronized to produce laser beam pulses 62a,
62b at substantially identical frequencies (e.g., 300 hz) with a
timed separation delay (e.g. 50-500 nanoseconds) occurring between
the generation of a laser beam pulse 62a and a corresponding laser
beam pulse 62b. In other words, laser source 60a generates a first
laser beam pulse 62a while laser source 60b generates a first laser
beam pulse 62b shortly thereafter. The integrator 66 then combines
the first laser beam pulse 62a with the first laser beam pulse 62b
to form a first laser beam pulse 52, as shown in FIG. 12A. In the
embodiment depicted in FIG. 12A, the resulting pulse duration of a
generated laser beam pulse 52 is thus the sum of the pulse
durations 64a, 64b (corresponding to laser beam pulses 62a, 62b,
respectively) and the time delay d. Laser sources 60a, 60b then
continue to generate additional laser beam pulses 62a, 62b,
respectively, and the integrator 66 combines the corresponding
laser beam pulses 62a, 62b together to form the laser beam pulses
52.
[0078] FIG. 12B shows an embodiment where a component laser beam
pulse 62b partially overlaps a corresponding laser beam pulse 62b
to form an integrated laser beam pulse 52, while FIG. 12C shows an
embodiment where a component laser beam pulse 62b completely
overlaps a corresponding laser beam pulse 62b to form an integrated
laser beam pulse 52. In the area where the component laser beam
pulses 62a, 62b are constructively added (i.e., where they
overlap), the resulting energy profile of the laser beam pulse 52
is indicated with a dashed line. In the embodiment depicted in FIG.
12B, since the component laser beams pulse 62a only partially
overlap with the corresponding component laser beam pulses 62b, the
resulting pulse durations of the integrated laser beam pulses 52
will be less than the sum of the pulse durations 64a, 64b
(corresponding to laser beam pulses 62a, 62b, respectively). In the
embodiment depicted in FIG. 12C, the resulting pulse durations of
the integrated laser beam pulses 52 will be equal to the longer of
the two pulse durations 64a, 64b (corresponding to laser beam
pulses 62a, 62b, respectively) since the component laser beams
pulse 62a fully overlap with the corresponding component laser beam
pulses 62b.
[0079] FIG. 13 depicts another exemplary embodiment of a system
constructed in accordance with the present invention. System 1100
of FIG. 13 is similar to system 1000 of FIG. 10 except that the
optical elements (e.g., attenuators, telescopes, homogenizers,
condenser lenses, etc.) have been moved downstream of the beam
splitting element 70. Thin films 230 and 260 are loaded onto
loading fixtures 232 and 262, respectively. Mirrors 212, 222,
attenuator 214, telescope 216, homogenizer 218, condenser lens 220,
variable-focus field lens 224, mask 226, and projection lens 228
are disposed (along an optical path) between the beam splitting
element 70 and the loading fixture 232. Attenuator 244, telescope
246, homogenizer 248, condenser lens 250, mirror 252,
variable-focus field lens 254, mask 256, and projection lens 258
are similarly disposed (along a different optical path) between the
beam splitting element 70 and the loading fixture 262. The laser
source system 50 is capable of generating laser beam pulses 52 that
have sufficient energy to process (upon splitting) at least two
thin film samples at the same time. Moreover, the laser source
system 50 is capable of generating laser beam pulses 52 which have
pulse durations that are sufficient to induce the desired
crystallization processing of the thin film samples.
[0080] Laser beam pulses 52 are split by the beam splitting element
70 into first laser beam pulses 58 and second laser beam pulses 56
which are directed to the first loading fixture 232 (and thin film
230 which is disposed thereon) and the second loading fixture 262
(and thin film 260 which is disposed thereon), respectively. First
laser beam pulses 58 travel through attenuator 214, telescope 216,
homogenizer 218, condenser lens 220, variable-focus field lens 224,
mask 226, and projection lens 228 to form first laser beam pulses
58a (e.g., the energy beam characteristics of laser beam pulses 58a
will tend to be different than that of laser beam pulses 58). The
thin film 230 that is loaded on loading fixture 232 is then
irradiated by the laser beam pulses 58a. Upon completing the
processing of thin film 230, the thin film 230 can be removed from
the loading fixture 232 and another can be substituted in its
place. Second laser beam pulses 56 similarly travel through
attenuator 244, telescope 246, homogenizer 248, condenser lens 250,
variable-focus field lens 254, mask 256, and projection lens 258 to
form second laser beam pulses 56a (e.g., the energy beam
characteristics of laser beam pulses 56a will tend to be different
than that of laser beam pulses 56). The thin film 260 that is
loaded on loading fixture 262 is then irradiated by the laser beam
pulses 56a. The loading fixtures 232, 262 (and thus the
corresponding thin films 230, 262) may be located within the same
irradiation chamber or separate irradiation chambers depending, for
example, upon the operational conditions (e.g., pressure,
temperature, etc.) that are to be maintained at the different
loading fixtures 232 and 262. Upon completing the processing of
thin film 260--which need not coincide with the processing of the
thin film 230--the thin film 260 can be removed from the loading
fixture 262 and another can be substituted in its place. System
1100 provides additional flexibility in controlling the energy beam
characteristics of the laser beam pulses 58a and 56a to match the
irradiation processing requirements of the thin film samples that
are being irradiated on loading fixtures 232 and 262, respectively.
In other words, by placing more of the optical elements downstream
of the beam splitting element 70, the energy beam characteristics
of the laser beam pulses 56a, 58a can be more easily tailored to
meet the (e.g., different) operational requirements of the thin
film samples that are being processed.
[0081] FIG. 14 depicts yet another exemplary embodiment of a system
constructed in accordance with the present invention. System 1200
of FIG. 14 is different from the systems of FIGS. 10 and 13 in that
it includes a third loading fixture. Preferably, at any given
moment, two of the loading fixtures are being utilized for
processing (i.e., irradiating) thin film samples while other thin
film samples are being unloaded and loaded onto the third loading
fixture. System 1200 includes a laser source system 50, an
attenuator 14, a telescope 18, a homogenizer 20, a condenser lens
22, a beam splitting element 70 and three loading fixtures,
fixtures 232, 262 and 372. Other optical elements (not shown),
e.g., masks, projection lens, etc, as previously discussed, can be
disposed between the beam splitting element 70 and the respective
loading fixtures 232, 262, and 372. The laser beam pulses 52 that
are generated by the laser source system 50 enter the beam
splitting element 70 after passing through the optical elements as
shown. Beam splitting element 70 splits the laser beam pulses 52
into first laser beam pulses 58 and second laser beam pulses 56 as
previously discussed. However, in addition to splitting laser beam
pulses 52, beam splitting element 70 of system 1200 is also capable
of directing the spilt laser beam pulses 56, 58 along the different
optical paths which lead to the thin film samples that are loaded
on the loading fixtures 232, 262, and 372. Since the beam splitter
element 70 of system 1200 only produces two component laser beam
pulses 56, 58 and there are three loading fixtures, at any given
moment at least one of the loading fixtures 232, 262, 372 is not
receiving a component laser beam pulse 56 or 58.
[0082] While a particular loading fixture is not receiving a
component laser beam pulse 56 or 58, a previously processed thin
film sample can be unloaded from this loading fixture and an
unprocessed thin film sample can then be loaded. Once a thin film
sample has been loaded onto this loading fixture and the
irradiation processing of a thin film sample that is loaded on a
different loading fixture has been completed, the component laser
beam pulses previously directed to the other loading fixture can
then be directed, via the beam splitting element 70, to the now
loaded thin film sample. For example, as shown in FIG. 14, first
laser beam pulses 58 are initially directed to loading fixture 262
(having thin film 260 disposed thereon) and second laser beam
pulses 56 are initially directed to loading fixture 232 (having
thin film 230 disposed thereon). While thin films 230 and 260 are
being irradiated on loading fixtures 232 and 262, respectively, a
thin film can be unloaded (if a processed thin film is present) and
new thin film 370 can be loaded onto the inactive loading fixture
372. The processing of the thin films 230, 260 loaded on loading
fixtures 232, 262 can be performed concurrently or, alternatively,
the processing of thin film 230 loaded on loading fixture 232 may
be independent of the processing of thin film 260 loaded on loading
fixture 262, e.g., the processing times may be the same or
different, and if the same the processing sequences may be
staggered from each other, etc. Upon completing the irradiation
processing of thin film 230, the beam splitter element 70 can then
direct the second laser beam pulses 56 to loading fixture 372
(having thin film 370 disposed thereon), as shown by the dotted
lines in FIG. 14. The processed thin film 230 can then be removed
from the loading fixture 232 and a new unprocessed thin film sample
can be loaded and readied (on loading fixture 232) for
processing.
[0083] FIG. 15 depicts a further exemplary embodiment of a system
constructed in accordance with the present invention. System 1300
of FIG. 15 includes four loading fixtures, fixtures 232, 262, 372,
and 382. Preferably, at any given moment, two of the loading
fixtures are being utilized to process thin film samples while
other thin film samples are being unloaded and loaded onto the two
remaining loading fixtures. System 1300 includes a laser source
system 50, an attenuator 14, a telescope 18, a homogenizer 20, a
condenser lens 22, a beam splitting element 70 and four loading
fixtures, fixtures 232, 262, 372, and 382. Other optical elements
(not shown), e.g., masks, projection lens, etc, as previously
discussed, can be utilized downstream of the beam splitting element
70 between the loading fixtures 232, 262, 372, and 382 and the beam
splitting element 70. Laser beam pulses 52 generated by the laser
source system 50 enter the beam splitting element 70 after passing
through the optical elements as shown. Beam splitting element 70
splits the laser beam pulses 52 into first laser beam pulses 58 and
second laser beam pulses 56 as previously discussed. However,
unlike system 1200, system 1300 also includes beam steering
elements 80a and 80b. Beam steering elements 80a, 80b can act as
switches for directing the second laser beam pulses 56 and first
laser beam pulses 58, respectively. Such beam steering elements are
readily known in the art. So, unlike the beam splitting element 70
of system 1200, which was capable of both splitting laser beam
pulse 52 and directing the component laser beam pulses 56, 58 along
a plurality of optical paths, system 1300 provides beam steering
elements 80a and 80b that are separate from the beam splitting
element 70.
[0084] The first laser beam pulses 58 are directed from the beam
splitting element 70 to beam steering elements 80b. Beam steering
elements 80b controls whether first laser beam pulses 58 are to be
delivered to loading fixture 262 or, alternatively, to loading
fixture 382. The second laser beam pulses 56 are directed from the
beam splitting element 70 to beam steering elements 80a. Beam
steering elements 80a controls whether second laser beam pulses 56
are to be delivered to loading fixture 232 or, alternatively, to
loading fixture 372. Since the beam splitter element 70 of system
1300 only "produces" two component laser beam pulses 56, 58 and
there are four loading fixtures (each of which may hold a thin film
sample), at any given moment at least two of the loading fixtures
232, 262, 372, 382 are thus not receiving a component laser beam
pulse 56, 58. Based upon the arrangement of system 1300, at any
given moment, one of the loading fixtures 232 or 372 and one of the
loading fixtures 262 or 382 are preferably receiving first laser
beam pulses 58 and second laser beam pulses 56, respectively.
Moreover, while one of the loading fixtures 232, 372 is receiving
first laser beam pulses 58, thin film samples can be
unloaded/loaded onto the other loading fixture. Similarly, while
one of the loading fixtures 262, 382 is receiving second laser beam
pulses 56, thin film samples can be unloaded/loaded on the other
load fixture.
[0085] For example, as shown in FIG. 15, first laser beam pulses 58
are initially directed via beam steering element 80b to loading
fixture 262 (having thin film 260 disposed thereon) and second
laser beam pulses 56 are initially directed via beam steering
element 80a to loading fixture 232 (having thin film 230 disposed
thereon). While thin films 230, 260 of loading fixtures 232, 262,
respectively, are being irradiated, thin film samples can be
unloaded (if a processed thin film sample is present) and thin
films 370, 380 can be loaded onto inactive loading fixtures 372,
382, respectively. The processing of thin films 230, 260 loaded on
loading fixtures 232, 262 can be performed concurrently or,
alternatively, the processing of thin film 230 loaded on loading
fixture 232 may be independent of the processing of thin film 260
that is loaded on loading fixture 262, e.g., the processing times
may be the same or different, and if the same the processing
sequences may be staggered from each other, etc. Upon completing
the irradiation processing of thin film 230 (loaded on loading
fixture 232), the beam steering element 80a then directs the second
laser beam pulses 56 to loading fixture 372, as shown by the dotted
lines in FIG. 15, where thin film 370 has already been loaded. The
processed thin film 230 can then be removed from loading fixture
232 and a new unprocessed thin film sample can be loaded on loading
fixture 230 and readied for processing. Similarly, upon completing
the irradiation processing of thin film 260 (loaded on leading
fixture 262), the beam steering element 80b then directs the first
laser beam pulses 58 to loading fixture 382, as shown by the dotted
lines in FIG. 15, where thin film 380 has already been loaded. The
processed thin film 260 can then be removed from loading fixture
262 and a new unprocessed thin film sample can be loaded on loading
fixture 260 and readied for processing.
[0086] The methods of irradiating thin film samples loaded on a
plurality of loading fixtures while unloading/loading thin film
samples on the other loading fixtures which are not currently
receiving irradiation can continue until the processing of all the
thin film samples is completed. Thus the manufacturing throughput
of systems 1200 and 1300 are further increased (e.g., over systems
1000 and 1100) because at least a portion of the sample handling
times of loading thin film samples onto and from the loading
fixtures are done in parallel with the irradiation processing of
other thin film samples. Depending upon the time it takes to unload
and load thin film samples onto a loading fixture and the amount of
time that is required to process a thin film sample, in certain
embodiments the handling processing times can be completely
absorbed within the irradiation processing times so that the
handling times do not contribute to the total manufacturing
processing time. Accordingly, in certain embodiments, laser beam
pulses that are generated by a laser source system that is
constantly "on" can be fully utilized in the processing of thin
film samples.
[0087] Further detail is provided in co-pending provisional patent
application entitled "Laser-Irradiated Thin Films Having Variable
Thickness" filed concurrently with the present disclosure, and in
co-pending provisional patent application entitled "Systems And
Methods For Inducing Crystallization of Thin Films Using Multiple
Optical Paths" filed concurrently with the present disclosure, the
contents of which are incorporated by reference.
[0088] The semiconductor device fabricated by the present invention
includes not only an element such as a TFT or a MOS transistor, but
also a liquid crystal display device (TFT-LCDs), an EL (Electro
Luminescence) display device, an EC (Electro Chromic) display
device, active-matrix organic light emitting diodes (OLEDs), static
random access memory (SRAM), three-dimensional integrated circuits
(3-D ICs), sensors, printers, and light valves, or the like, each
including a semiconductor circuit (microprocessor, signal
processing circuit, high frequency circuit, etc.) constituted by
insulated gate transistors.
[0089] Although various embodiments that incorporate the teachings
of the present invention have been shown and described in detail
herein, those skilled in the art can readily devise many other
varied embodiments that incorporate these teachings.
* * * * *