U.S. patent application number 14/055632 was filed with the patent office on 2014-02-13 for systems and methods for processing a film, and thin films.
This patent application is currently assigned to The Trustees Of Columbia University In The City Of New York. The applicant listed for this patent is The Trustees Of Columbia University In The City Of New York. Invention is credited to James S. IM.
Application Number | 20140045347 14/055632 |
Document ID | / |
Family ID | 38123429 |
Filed Date | 2014-02-13 |
United States Patent
Application |
20140045347 |
Kind Code |
A1 |
IM; James S. |
February 13, 2014 |
SYSTEMS AND METHODS FOR PROCESSING A FILM, AND THIN FILMS
Abstract
In some embodiments, a method of processing a film is provided,
the method comprising defining a plurality of spaced-apart regions
to be pre-crystallized within the film, the film being disposed on
a substrate and capable of laser-induced melting; generating a
laser beam having a fluence that is selected to form a mixture of
solid and liquid in the film and where a fraction of the film is
molten throughout its thickness in an irradiated region;
positioning the film relative to the laser beam in preparation for
at least partially pre-crystallizing a first region of said
plurality of spaced-apart regions; directing the laser beam onto a
moving at least partially reflective optical element in the path of
the laser beam, the moving optical element redirecting the beam so
as to scan a first portion of the first region with the beam in a
first direction at a first velocity, wherein the first velocity is
selected such that the beam irradiates and forms the mixture of
solid and liquid in the first portion of the first region, wherein
said first portion of the first region upon cooling forms
crystalline grains having predominantly the same crystallographic
orientation in at least a single direction; and crystallizing at
least the first portion of the first region using laser induced
melting.
Inventors: |
IM; James S.; (New York,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Trustees Of Columbia University In The City Of New
York |
New York |
NY |
US |
|
|
Assignee: |
The Trustees Of Columbia University
In The City Of New York
New York
NY
|
Family ID: |
38123429 |
Appl. No.: |
14/055632 |
Filed: |
October 16, 2013 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12095450 |
Sep 16, 2008 |
8598588 |
|
|
PCT/US06/46405 |
Dec 5, 2006 |
|
|
|
14055632 |
|
|
|
|
60742276 |
Dec 5, 2005 |
|
|
|
Current U.S.
Class: |
438/795 |
Current CPC
Class: |
H01L 27/1296 20130101;
H01L 21/02532 20130101; H01L 21/02422 20130101; H01L 21/268
20130101; H01L 21/02683 20130101; H01L 29/04 20130101; H01L 27/1285
20130101; H01L 21/02691 20130101 |
Class at
Publication: |
438/795 |
International
Class: |
H01L 21/268 20060101
H01L021/268 |
Claims
1. A method of processing a film, the method comprising: (a)
defining a plurality of spaced-apart regions to be pre-crystallized
within the film, the film being disposed on a substrate and capable
of laser-induced melting; (b) generating a laser beam having a
fluence that is selected to form a mixture of solid and liquid in
the film and where a fraction of the film is molten throughout its
thickness in an irradiated region; (c) positioning the film
relative to the laser beam in preparation for at least partially
pre-crystallizing a first region of said plurality of spaced-apart
regions; (d) directing the laser beam onto a moving at least
partially reflective optical element in the path of the laser beam,
the moving optical element redirecting the beam so as to scan a
first portion of the first region with the beam in a first
direction at a first velocity, wherein the first velocity is
selected such that the beam irradiates and forms the mixture of
solid and liquid in the first portion of the first region, wherein
said first portion of the first region upon cooling forms
crystalline grains having predominantly the same crystallographic
orientation in at least a single direction; and (e) crystallizing
at least the first portion of the first region using laser-induced
melting.
2. The method of claim 1, wherein the laser beam is
continuous-wave.
3. The method of claim 1, further comprising re-positioning the
film relative to the laser beam in preparation for at least
partially pre-crystallizing a second region of the plurality of
spaced-apart regions; and moving the optical element so as to scan
a first portion of the second region with the laser beam in the
first direction at the first velocity, wherein the first portion of
the second region upon cooling forms crystalline grains having
predominantly the same crystallographic orientation in said at
least a single direction.
4. The method of claim 1, wherein said first velocity is further
selected such that heat generated by the beam substantially does
not damage the substrate.
5. The method of claim 1, wherein the moving optical element
comprises a rotating disk that comprising a plurality of facets
that reflect said laser beam onto the film.
6. The method of claim 1, wherein the first velocity is at least
about 0.5 m/s.
7. The method of claim 1, wherein the first velocity is at least
about 1 m/s.
8. The method of claim 1, further comprising, after redirecting the
beam with the moving optical element so as to scan the first
portion of the first region, translating the film relative to the
laser beam in a second direction so as to scan a second portion of
the first region with the laser beam in the first direction at the
first velocity, wherein the second portion of the first region upon
cooling forms crystalline grains having predominantly the same
crystallographic orientation in said at least a single
direction.
9. The method of claim 8, wherein the second portion of the first
region partially overlaps the first portion of the first
region.
10. The method of claim 9, comprising continuously translating the
film in the second direction with a second velocity selected to
provide a pre-determined amount of overlap between the first and
second portions of the first region.
11. The method of claim 8, comprising continuously translating the
film in the second direction with a second velocity for a period of
time selected to sequentially irradiate and a plurality of portions
of the first region, wherein each of said plurality of portions
upon cooling forms crystalline grains having predominantly the same
crystallographic orientation in said at least a single
direction.
12. The method of claim 1, wherein said crystallographic
orientation in said at least a single direction is substantially
normal to the surface of the film.
13. The method of claim 1, wherein said crystallographic
orientation in said at least a single direction is a <100>
orientation.
14. The method of claim 1, wherein crystallizing at least the first
portion of the first region comprises performing uniform sequential
lateral crystallization.
15. The method of claim 14, wherein the uniform sequential lateral
crystallization comprises line-scan sequential lateral
crystallization.
16. The method of claim 1, wherein crystallizing at least the first
portion of the first region comprises performing Dot sequential
lateral crystallization.
17. The method of claim 1, wherein crystallizing at least the first
portion of the first region comprises performing controlled
super-lateral growth crystallization.
18. The method of claim 1, wherein crystallizing at least the first
portion of the first region comprises forming crystals having a
pre-determined crystallographic orientation suitable for a channel
region of a driver TFT.
19. The method of claim 1, further comprising fabricating at least
one thin film transistor in at least one of the first and second
regions.
20. The method of claim 1, further comprising fabricating a
plurality of thin film transistors in at least the first and second
regions.
21. The method of claim 1, wherein defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a device or
circuit intended to be later fabricated in that region.
22. The method of claim 1, wherein defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a width of a thin
film transistor intended to be later fabricated in that region.
23. The method of claim 1, wherein the spaced-apart regions are
separated by amorphous film.
24. The method of claim 1, wherein the film comprises at least one
of a conductor and a semiconductor.
25. The method of claim 1, wherein the film comprises silicon.
26. The method of claim 1, wherein the substrate comprises
glass.
27. The method of claim 1, comprising shaping said laser beam using
focusing optics.
28. A method of processing a film, the method comprising: (a)
defining at least one region within the film, the film being
disposed on a substrate and capable of laser-induced melting; (b)
generating a laser beam having a fluence that is selected to form a
mixture of solid and liquid in the film and where a fraction of the
film is molten throughout its thickness in an irradiated region;
(c) directing the laser beam onto a moving optical element that is
at least partially reflective, said moving optical element
directing the laser beam across a first portion of the first region
in a first direction at a first velocity; (d) moving the film
relative to the laser beam in a second direction and at a second
velocity to displace the film along the second direction during
laser irradiation of the first portion in step (c), wherein said
first portion of the first region upon cooling forms crystalline
grains having predominantly the same crystallographic orientation
in at least a single direction, wherein the first velocity is
selected such that the beam irradiates and forms a mixture of solid
and liquid in the first portion of the film; and (e) repeating
steps (c) and (d) at least once to crystallize the first
region.
29. The method of claim 28, wherein the laser beam is
continuous-wave.
30. The method of claim 28, further comprising re-positioning the
film relative to the laser beam in preparation for at least
partially pre-crystallizing a second region of the plurality of
spaced-apart regions; and moving the optical element so as to scan
a first portion of the second region with the laser beam in the
first direction at the first velocity, wherein the first portion of
the second region upon cooling forms crystalline grains having
predominantly the same crystallographic orientation in said at
least a single direction.
31. The method of claim 28, wherein said first velocity is further
selected to avoid heat generation by the beam that damages the
substrate.
32. The method of claim 28, wherein directing the moving optical
element comprises rotating a disk that comprises a plurality of
facets that reflect said laser beam onto the film.
33. The method of claim 28, wherein the first velocity is at least
about 0.5 m/s.
34. The method of claim 28, wherein the first velocity is at least
about 1 m/s.
35. The method of claim 28, wherein steps (c) and (d) provide first
and second portions of the first region having predominantly the
same crystallographic orientation and the second portion of the
first region partially overlaps the first portion of the first
region.
36. The method of claim 35, comprising continuously translating the
film in the second direction with a second velocity selected to
provide a pre-determined amount of overlap between the first and
second portions of the first region.
37. The method of claim 35, comprising continuously translating the
film in the second direction with a second velocity for a period of
time selected to sequentially irradiate and partially melt a
plurality of portions of the first region, wherein each of said
plurality of portions upon cooling forms crystalline grains having
predominantly the same crystallographic orientation in said at
least a single direction.
38. The method of claim 28, wherein said crystallographic
orientation in said at least a single direction is substantially
normal to the surface of the film.
39. The method of claim 28, wherein said crystallographic
orientation in said at least a single direction is a <100>
orientation.
40. The method of claim 28, further comprising subjecting the film
to a subsequent sequential lateral crystallization process to
generate location controlled grains having wherein crystallizing at
least the first portion of the first region comprises performing
uniform sequential lateral crystallization.
41. The method of claim 40, wherein the uniform sequential lateral
crystallization comprises line-scan sequential lateral
crystallization.
42. The method of claim 28, wherein crystallizing at least the
first portion of the first region comprises performing Dot
sequential lateral crystallization.
43. The method of claim 28, wherein crystallizing at least the
first portion of the first region comprises performing controlled
super-lateral growth crystallization.
44. The method of claim 28, wherein crystallizing at least the
first portion of the first region comprises forming crystals having
a pre-determined crystallographic orientation suitable for a
channel region of a driver TFT.
45. The method of claim 28, further comprising fabricating at least
one thin film transistor in at least one of the first and second
regions.
46. The method of claim 28, further comprising fabricating a
plurality of thin film transistors in at least the first and second
regions.
47. The method of claim 28, wherein defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a device or
circuit intended to be later fabricated in that region.
48. The method of claim 28, wherein defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a width of a thin
film transistor intended to be later fabricated in that region.
49. The method of claim 28, wherein the spaced-apart regions are
separated by amorphous film.
50. The method of claim 28, wherein the film comprises at least one
of a conductor and a semiconductor.
51. The method of claim 28, wherein the film comprises silicon.
52. The method of claim 28, wherein the substrate comprises
glass.
53. The method of claim 28, comprising shaping said laser beam
using focusing optics.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of and claims the benefit
under 35 U.S.C. .sctn.121 of U.S. application Ser. No. 12/095,450,
filed on Sep. 16, 2008, entitled "Systems and Methods for
Processing a Film, and Thin Film," the contents of which are
incorporated herein by reference, which is a U.S. National Phase
application under 35 U.S.C. .sctn.371 of International Patent
Application No. PCT/US2006/046405, filed Dec. 5, 2006, entitled
"SYSTEMS AND METHODS FOR PROCESSING A FILM, AND THIN FILMS," which
claims the benefit under 35 U.S.C. .sctn.119(e) of the following
application, the entire contents of which are incorporated herein
by reference: [0002] U.S. Provisional Patent Application Ser. No.
60/742,276, filed Dec. 5, 2005 and entitled "Scheme for
Crystallizing Films Using a Continuous-Wave Light Source Compatible
With Glass Substrates And Existing Precision Stages."
FIELD
[0003] Systems and methods for processing a film, and thin films,
are provided.
BACKGROUND
[0004] In recent years, various techniques for crystallizing or
improving the crystallinity of an amorphous or polycrystalline
semiconductor film have been investigated. Such crystallized thin
films may be 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
("TFTs") is fabricated on an appropriate transparent substrate, and
each transistor serves as a pixel controller.
[0005] Crystalline semiconductor films, such as silicon films, have
been processed to provide pixels for liquid crystal displays using
various laser processes including excimer laser annealing ("ELA")
and sequential lateral solidification ("SLS") processes. SLS is
well suited to process thin films for use in AMLCD devices, as well
as organic light emitting diode ("OLED") devices.
[0006] In ELA, a region of the film is irradiated by an excimer
laser to partially melt the film, which subsequently crystallizes.
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. The Si film is irradiated multiple
times to create the random polycrystalline film with a uniform
grain size. ELA produces 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.
FIG. 6A illustrates a random microstructure that may be obtained
with ELA. This figure, and all subsequent figures, are not drawn to
scale, and are intended to be illustrative in nature.
[0007] SLS is a pulsed-laser crystallization process that can
produce high quality polycrystalline films having large and uniform
grains on substrates, including substrates that are intolerant to
heat such as glass and plastics. SLS uses controlled laser pulses
to fully melt a region of an amorphous or polycrystalline thin film
on a substrate. The melted regions of film then laterally
crystallize into a solidified lateral columnar microstructure or a
plurality of location-controlled large single crystal regions.
Generally, the melt/crystallization process is sequentially
repeated over the surface of a large thin film, with a large number
of laser pulses. The processed film on substrate is then used to
produce one large display, or even divided to produce multiple
displays, each display being useful for providing visual output in
a given device. FIGS. 6B-6D shows schematic drawings of TFTs
fabricated within films having different microstructures that can
be obtained with SLS. SLS processes are described in greater detail
below.
[0008] The potential success of SLS systems and methods for
commercial use is related to the throughput with which the desired
microstructure and texture can be produced. The amount of energy
and time it takes to produce a film having the microstructure is
also related to the cost of producing that film; in general, the
faster and more efficiently the film can be produced, the more
films can be produced in a given period of time, enabling higher
production and thus higher potential revenues.
SUMMARY
[0009] The application describes systems and methods for processing
thin films, and thin films.
[0010] In some embodiments, a method of processing a film is
provided, the method comprising defining a plurality of
spaced-apart regions to be pre-crystallized within the film, the
film being disposed on a substrate and capable of laser-induced
melting; generating a laser beam having a fluence that is selected
to form a mixture of solid and liquid in the film and where a
fraction of the film is molten throughout its thickness in an
irradiated region; positioning the film relative to the laser beam
in preparation for at least partially pre-crystallizing a first
region of said plurality of spaced-apart regions; directing the
laser beam onto a moving at least partially reflective optical
element in the path of the laser beam, the moving optical element
redirecting the beam so as to scan a first portion of the first
region with the beam in a first direction at a first velocity,
wherein the first velocity is selected such that the beam
irradiates and forms the mixture of solid and liquid in the first
portion of the first region, wherein said first portion of the
first region upon cooling forms crystalline grains having
predominantly the same crystallographic orientation in at least a
single direction; and crystallizing at least the first portion of
the first region using laser-induced melting.
[0011] Some embodiments include one or more of the following
features. The laser beam is continuous-wave. Further comprising
re-positioning the film relative to the laser beam in preparation
for at least partially pre-crystallizing a second region of the
plurality of spaced-apart regions; and moving the optical element
so as to scan a first portion of the second region with the laser
beam in the first direction at the first velocity, wherein the
first portion of the second region upon cooling forms crystalline
grains having predominantly the same crystallographic orientation
in said at least a single direction. Said first velocity is further
selected such that heat generated by the beam substantially does
not damage the substrate. The moving optical element comprises a
rotating disk that comprising a plurality of facets that reflect
said laser beam onto the film. The first velocity is at least about
0.5 m/s. The first velocity is at least about 1 m/s.
[0012] The method of claim 1, further comprising, after redirecting
the beam with the moving optical element so as to scan the first
portion of the first region, translating the film relative to the
laser beam in a second direction so as to scan a second portion of
the first region with the laser beam in the first direction at the
first velocity, wherein the second portion of the first region upon
cooling forms crystalline grains having predominantly the same
crystallographic orientation in said at least a single direction.
The second portion of the first region partially overlaps the first
portion of the first region. Continuously translating the film in
the second direction with a second velocity selected to provide a
pre-determined amount of overlap between the first and second
portions of the first region. Continuously translating the film in
the second direction with a second velocity for a period of time
selected to sequentially irradiate and a plurality of portions of
the first region, wherein each of said plurality of portions upon
cooling forms crystalline grains having predominantly the same
crystallographic orientation in said at least a single direction.
Said crystallographic orientation in said at least a single
direction is substantially normal to the surface of the film. Said
crystallographic orientation in said at least a single direction is
a <100> orientation. Crystallizing at least the first portion
of the first region comprises performing uniform sequential lateral
crystallization. The uniform sequential lateral crystallization
comprises line-scan sequential lateral crystallization.
Crystallizing at least the first portion of the first region
comprises performing Dot sequential lateral crystallization.
Crystallizing at least the first portion of the first region
comprises performing controlled super-lateral growth
crystallization. Crystallizing at least the first portion of the
first region comprises forming crystals having a pre-determined
crystallographic orientation suitable for a channel region of a
driver TFT. Further comprising fabricating at least one thin film
transistor in at least one of the first and second regions. Further
comprising fabricating a plurality of thin film transistors in at
least the first and second regions. Defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a device of
circuit intended to be later fabricated in that region. Defining
the plurality of spaced-apart regions comprises defining a width
for each spaced-apart region that is at least as large as a width
of a thin film transistor intended to be later fabricated in that
region. The spaced-apart regions are separated by amorphous film.
The film comprises at least one of a conductor and a semiconductor.
The film comprises silicon. The substrate comprises glass. Shaping
said laser beam using focusing optics.
[0013] Some embodiments provide a system for processing a film, the
system comprising a laser source providing a laser beam having a
fluence that is selected to form a mixture of solid and liquid in
the film and where a fraction of the film is molten throughout its
thickness in an irradiated region; a movable at least partially
reflective optical element in the path of the laser beam capable of
controllably redirecting the path of the laser beam; a stage for
supporting the film and capable of translation in at least a first
direction; and memory for storing a set of instructions, the
instructions comprising defining a plurality of spaced-apart
regions to be pre-crystallized within the film, the film being
disposed on a substrate and capable of laser-induced melting;
positioning the film relative to the laser beam in preparation for
at least partially pre-crystallizing a first region of said
plurality of spaced-apart regions; moving the movable optical
element so as to scan a first portion of the first region with the
beam in the first direction at a first velocity, wherein the first
velocity is selected such that the beam forms a mixture of solid
and liquid in the film and where a fraction of the film is molten
throughout its thickness in the first portion of the first region,
wherein said first portion of the first region upon cooling forms
crystalline grains having predominantly the same crystallographic
orientation in at least a single direction.
[0014] Some embodiments include one or more of the following
features. The laser beam is continuous-wave. Re-positioning the
film relative to the laser beam in preparation for at least
partially re-crystallizing a second region of the plurality of
spaced-apart regions; and moving the movable optical element so as
to scan a first portion of the second region with the beam in the
first direction at the first velocity, wherein the first portion of
the second region upon cooling forms crystalline grains having
predominantly the same crystallographic orientation in said at
least a single direction. The first velocity is further selected
such that heat generated by the beam substantially does not damage
the substrate. The movable optical element comprises a disk
comprising a plurality of facets that at least partially reflect
said laser beam onto the film. The first velocity is at least about
0.5 m/s. The first velocity is at least about 1 m/s. The memory
further includes instructions to, after moving the movable optical
element so as to scan the first portion of the first region,
translate the film relative to the laser beam in a second direction
so as to scan a second portion of the first region with the laser
beam in the first direction at the first velocity, wherein the
second portion of the first region upon cooling forms crystalline
grains having predominantly the same crystallographic orientation
in said at least a single direction. The memory further includes
instructions to partially overlap the first and second portions of
the first region. The memory further includes instructions to
continuously translate the film in the second direction with a
second velocity selected to provide a pre-determined amount of
overlap between the first and second portions of the first region.
The memory further includes instructions to continuously translate
the film in the second direction with the second velocity for a
period of time selected to sequentially irradiate and partially
melt a plurality of portions of the first region, wherein each of
said plurality of portions upon cooling forms crystalline grains
having predominantly the same crystallographic orientation in said
at least a single direction. The memory further includes
instructions to perform uniform sequential lateral crystallization
in at least the first region. The memory further includes
instructions for defining a width for each spaced-apart region that
is at least as large as a device or circuit intended to be later
fabricated in that region. The memory further includes instructions
for defining a width for each spaced-apart region that is at least
as large as a width of a thin film transistor intended to be later
fabricated in that region. The film comprises at least one of a
conductor and a semiconductor. The film comprises silicon. The
substrate comprises glass. Further comprising laser optics to shape
said laser beam.
[0015] Some embodiments provide a thin film, the thin film
comprising columns of pre-crystallized film positioned and sized so
that rows and columns of TFTs can later be fabricated in said
columns of pre-crystallized film, said columns of pre-crystallized
film comprising crystalline grains having predominantly the same
crystallographic orientation in at least a single direction; and
columns of untreated film between said columns of pre crystallized
film.
[0016] Some embodiments include one or more of the following
features. Said crystallographic orientation in said at least a
single direction is substantially normal to the surface of the
film. Said crystallographic orientation in said at least a single
direction is a <100> orientation. The columns of untreated
film comprise amorphous film.
[0017] Some embodiments provide a method of processing a film, the
method comprising defining at least one region within the film, the
film being disposed on a substrate and capable of laser-induced
melting; generating a laser beam having a fluence that is selected
to form a mixture of solid and liquid in the film and where a
fraction of the film is molten throughout its thickness in an
irradiated region; directing the laser beam onto a moving optical
element that is at least partially reflective, said moving optical
element directing the laser beam across a first portion of the
first region in a first direction at a first velocity; moving the
film relative to the laser beam in a second direction and at a
second velocity to displace the film along the second direction
during laser irradiation of the first portion while moving the
optical element, wherein said first portion of the first region
upon cooling forms crystalline grains having predominantly the same
crystallographic orientation in at least a single direction,
wherein the first velocity is selected such that the beam
irradiates and forms a mixture of solids and liquid in the first
portion of the film; and repeating the steps of moving the optical
element and moving the film at least once to crystallize the first
region.
[0018] Some embodiments include one or more of the following
features. The laser beam is continuous-wave. Further comprising
re-positioning the film relative to the laser beam in preparation
for at least partially pre-crystallizing a second region of the
plurality of spaced-apart regions; and moving the optical element
so as to scan a first portion of the second region with the laser
beam in the first direction at the first velocity, wherein the
first portion of the second region upon cooling forms crystalline
grains having predominantly the same crystallographic orientation
in said at least a single direction. Said first velocity is further
selected to avoid heat generation by the beam that damages the
substrate. Directing the moving optical element comprises rotating
a disk that comprises a plurality of facets that reflect said laser
beam onto the film. The first velocity is at least about 0.5 m/s.
The first velocity is at least about 1 m/s. The steps of moving the
optical element and moving the film provide first and second
portions of the first region having predominantly the same
crystallographic orientation and the second portion of the first
region partially overlaps the first portion of the first region.
Continuously translating the film in the second direction with a
second velocity selected to provide a pre-determined amount of
overlap between the first and second portions of the first region.
Continuously translating the film in the second direction with a
second velocity for a period of time selected to sequentially
irradiate and partially melt a plurality of portions of the first
region, wherein each of said plurality of portions upon cooling
forms crystalline grains having predominantly the same
crystallographic orientation in said at least a single direction.
Said crystallographic orientation in said at least a single
direction is substantially normal to the surface of the film. Said
crystallographic orientation in said at least a single direction is
a <100> orientation. Further comprising subjecting the film
to a subsequent sequential lateral crystallization process to
generate location controlled grains having wherein crystallizing at
least the first portion of the first region comprises performing
uniform sequential lateral crystallization. The uniform sequential
lateral crystallization comprises line-scan sequential lateral
crystallization. Crystallizing at least the first portion of the
first region comprises performing Dot sequential lateral
crystallization. Crystallizing at least the first portion of the
first region comprises performing controlled super-lateral growth
crystallization. Crystallizing at least the first portion of the
first region comprises forming crystals having a pre-determined
crystallographic orientation suitable for a channel region of a
driver TFT. Further comprising fabricating at least one thin film
transistor in at least one of the first and second regions. Further
comprising fabricating a plurality of thin film transistors in at
least the first and second regions. Defining the plurality of
spaced-apart regions comprises defining a width for each
spaced-apart region that is at least as large as a device or
circuit intended to be later fabricated in that region. Defining
the plurality of spaced-apart regions comprises defining a width
for each spaced-apart region that is at least as large as a width
of a thin film transistor intended to be later fabricated in that
region. The spaced-apart regions are separated by amorphous film.
The film comprises at least one of a conductor and a semiconductor.
The film comprises silicon. The substrate comprises glass. Shaping
said laser beam using focusing optics.
DESCRIPTION OF THE DRAWINGS
[0019] In the drawing:
[0020] FIG. 1 illustrates a thin film with regions pre-crystallized
with high throughput pre-crystallization according to some
embodiments.
[0021] FIG. 2 illustratively displays a method for the high
throughput pre-crystallization of a thin film and optional
subsequent TFT fabrication according to some embodiments.
[0022] FIG. 3 is a schematic diagram of an apparatus for high
throughput pre-crystallization of a thin film according to some
embodiments.
[0023] FIG. 4A-4B illustrates the pre-crystallization of a TFT
region using a high throughput pre-crystallization apparatus
according to some embodiments.
[0024] FIG. 5 is a schematic diagram of an apparatus for sequential
lateral crystallization of a semiconductor film according to some
embodiments.
[0025] FIG. 6A illustrates crystalline microstructures formed by
excimer laser annealing.
[0026] FIGS. 6B-6D illustrate crystalline microstructures formed by
sequential lateral crystallization.
[0027] FIGS. 7A-7D illustrate schematically processes involved in
and microstructures formed by sequential lateral crystallization
according to some embodiments.
DETAILED DESCRIPTION
[0028] Systems and methods described herein provide
pre-crystallized thin films having controlled crystallographic
texture. The textured films contain grains having predominantly the
same crystallographic orientation in at least a single
crystallographic orientation. The thin films are suitable for
further processing with SLS or other lateral growth processes, as
discussed in greater detail below. In SLS, the crystal orientation
of lateral growth during SLS depends on the orientation of the
material at the boundary of the irradiated region. By
pre-crystallizing the film before performing SLS, the crystals that
laterally grow during SLS adopt the crystalline orientation
generated during pre-crystallization, and thus grow with an
improved crystalline orientation relative to crystal grains grown
without pre-crystallization. The pre-crystallized and laterally
crystallized film can then be processed to form TFTs, and
ultimately be used as a display device.
[0029] When a polycrystalline material is used to fabricate devices
having TFTs, the total resistance to carrier transport within the
TFT channel is affected by the combination of barriers that a
carrier has to cross as it travels under the influence of a given
potential. Within a material processed by SLS, a carrier crosses
many more grain boundaries if it travels perpendicularly to the
long grain axes of the polycrystalline material, and thus
experiences a higher resistance, than if it travels parallel to the
long grain axes. Thus, in general, the performance of TFT devices
fabricated on SLS-processed polycrystalline films depends on the
microstructure of the film in the channel, relative to the film's
long grain axes. However, SLS is not able to fully define the
crystallographic texture of those grains, because they grow
epitaxially from existing grains that do not themselves necessarily
have a well-defined crystallographic texture.
[0030] Pre-crystallizing a thin film can improve the crystal
alignment, e.g., texture, obtained during subsequent lateral
crystallization processes, and can allow separate control and
optimization of the texture and the microstructure of the film.
Pre-crystallizing the film generates a textured film having crystal
grains with predominantly the same crystallographic orientation in
at least one direction. For example, if one crystallographic axis
of most crystallites in a thin polycrystalline film points
preferentially in a given direction, the film is referred to as
having a one-axial texture. For many embodiments described herein,
the preferential direction of the one-axial texture is a direction
normal to the surface of the crystallites. Thus, "texture" refers
to a one-axial surface texture of the grains as used herein. In
some embodiments, the crystallites have a (100) texture. The degree
of texture can vary depending on the particular application. For
example, a high degree of texture can improve the performance of
thin film transistor (TFT) being used for a driver circuit, but not
provide as significant a benefit to a TFT that is used for a switch
circuit.
[0031] One method that can be used to pre-crystallize a film is
known as mixed-phase zone-melt recrystallization (ZMR), which, in
some embodiments, uses a continuous wave (CW) laser beam to
partially melt a silicon film and thus produce a film having a
desired texture, e.g., (100) texture. In ZMR, irradiation causes
some parts of the film to completely melt while others remain
unmelted, forming a "transition region" which exists as a result of
a significant increase in reflectivity of Si upon melting (a
semiconductor-metal transition). Crystal grains having (100)
texture form in this transition region. For further details, see
U.S. Patent Publication No. 2006/0102901, entitled "Systems and
Methods for Creating Crystallographic-Orientation Controlled
poly-Silicon Films," the entire contents of which are incorporated
herein by reference. The texture of a pre-crystallized film can be
further improved by scanning the film multiple times, as preferably
oriented grains get enlarged at the expense of less preferably
oriented grains. For further details, see U.S. Provisional Patent
Application No. 60/707,587, the entire contents of which are
incorporated herein by reference. For further general details on
ZMR, see M. W. Geis et al., "Zone-Melting recrystallization of Si
films with a movable-strip-heater oven," J. Electro-Chem. Soc. 129,
2812 (1982), the entire contents of which are incorporated herein
by reference.
[0032] However, pre-crystallizing an entire panel to get (100)
large-grain material can be time consuming, as typical CW laser
sources have limited power. Additionally, pre-crystallizing a
silicon film with a CW laser can significantly heat the film and
underlying substrate due to the continuous radiation. For glass
substrates, sufficient heat can be generated to cause the substrate
to warp or actually melt and damage the substrate. In general, a
glass substrate benefits from a scan velocity of at least about 1
m/s in order to avoid damage. However, as substrate sizes increase,
this velocity becomes increasingly difficult to achieve; for
example, current panel sizes in so-called low-temperature
polycrystalline silicon (LTPS) technology, commonly used for mobile
(small-display) applications, are up to .about.720 mm.times.930 mm
(which can be divided into 4 or more devices) or larger. Currently
available stage technology typically limits scan velocities to a
few cm/s or a few 10's of cm/s, as is used in normal SLS processes.
Thus, conventional pre-crystallization using a CW laser is not
readily applied to large substrates. Although heat-resistant
substrates can be used, they are more costly and are less
attractive for large-area electronic applications.
[0033] The pre-crystallization systems and methods described herein
allow the film to be scanned at high scan velocities, which helps
to prevent heat damage to the underlying substrate. The systems can
use conventional (e.g., relatively slow) handling stages to move
large substrates, and at the same time can provide scan velocities
of about 1 m/s, or even higher. Specifically, a handling stage
moves the film and substrate at a typical scan velocity in one
direction, while moving optics scan a laser beam across the film at
a much higher velocity in a different, e.g., perpendicular,
direction. The motions of the stage and laser beam are coordinated
so that defined regions of the film are pre-crystallized, and other
regions are left untreated. This increases the effective scanning
velocity of the film above a threshold at which the substrate would
be damaged, and greatly improves the efficiency of
pre-crystallizing the film.
[0034] The systems and methods also are capable of reducing the
overall time to process the film. Specifically, the film is
pre-crystallized in regions of the film where devices that benefit
from controlled crystallographic texture, e.g., regions that
contain the most demanding circuitry, will be fabricated. In some
embodiments, these regions are on the periphery of a display, where
the integration TFTs will be fabricated. Regions of the film where
such devices will not be located, or devices not requiring
controlled crystallographic texture, are not pre-crystallized. In
some embodiments, the speed with which panels are pre-crystallized
are approximately matched to the throughput rate of SLS systems and
methods, with which the pre-crystallization systems and methods can
be incorporated.
[0035] FIG. 1 illustrates an embodiment of a silicon film 300 that
is pre-crystallized in defined regions, and left untreated in other
regions. The defined regions can be selected for a variety of
reasons, such as that devices benefiting from improved crystalline
texture will eventually be fabricated there. In some embodiments,
the defined regions correspond to TFT channels. The film includes
areas of pre-crystallized silicon 325, and areas of untreated
silicon 310. The areas are positioned and sized so that rows and
columns of TFTs can optionally be subsequently fabricated within
the areas of pre-crystallized silicon 325, e.g., with SLS and other
processing steps. The untreated regions 310 can be uncrystallized
silicon, e.g., amorphous silicon, or can be, e.g., polycrystalline
silicon.
[0036] Although the areas of untreated and pre-crystallized silicon
are illustrated to have approximately the same width, the area
widths and relative spacing can vary, depending on the desired area
of the display and the width of the integration regions. For
example, the integration regions can be only several mm wide for a
display that can have a diagonal of several inches. In this case,
the pre-crystallized silicon columns 325 can be fabricated to be
substantially narrower than the untreated areas 310. This will
further improve the efficiency with which the film can be
processed, because large regions of the film will not need to be
pre-crystallized. In general, the width of the pre-crystallized
regions needs only to be long enough to cover the area for
integration circuits.
[0037] FIG. 2 illustratively displays a method 400 for the high
throughput pre-crystallization, and optional subsequent processing
of a semiconductor film to form TFTs, according to certain
embodiments. First, the regions to be pre-crystallized are defined
(410). The defined regions optionally correspond to areas in which
TFT circuits will be fabricated, as described above. The area
widths and spacings are selected according to the requirements of
the device that will eventually be fabricated using the film.
[0038] Then, the film is pre-crystallized in the defined regions
(420). In some embodiments, this is done with a continuous wave
(CW) laser as described in greater detail below. The laser
partially melts the film, which crystallizes to have a desired
texture. The textured film contains grains having predominantly the
same crystallographic orientation in at least a single direction.
However, the grains are randomly located on the film surface, and
are of no particular size.
[0039] Then, the film is optionally laterally crystallized (430).
In many embodiments, this is done with SLS processes, for example
as described in greater detail below. For further details and other
SLS processes, see U.S. Pat. Nos. 6,322,625, 6,368,945, 6,555,449,
and 6,573,531, the entire contents of which are incorporated herein
by reference.
[0040] Then, TFTs are optionally fabricated within the defined
regions (440). This can be done with silicon island formation, in
which the film is etched to remove excess silicon except where the
TFTs are to be fabricated. Then, the remaining "islands" are
processed using techniques known in the art to form active TFTs,
including source and drain contact regions as illustrated in FIG.
6A.
[0041] Note that in general, even if defined regions of a given
film are pre-crystallized and the remaining regions left untreated,
the SLS process need not be performed solely within the
pre-crystallized regions. For example, the entire film, or portions
thereof, can be laterally crystallized with SLS. Then, TFTs can be
fabricated at desired locations within the laterally crystallized
regions of the film, such that some or all of the TFTs are
fabricated within the regions that were originally
pre-crystallized. Determining which steps to perform on a given
region of the film depends on the performance requirements of the
finished device.
[0042] FIG. 3 schematically illustrates an embodiment of a system
that can be used for precrystallizing a thin film. The system
includes a rotating disk with a plurality of facets, each of which
is at least partially reflective for the laser beam wavelength. The
laser beam is directed at the rotating disk, which is arranged such
that the facets redirects the laser beam so that it irradiates the
film. As the disk rotates, it causes the laser beam to scan the
surface of the film, thus pre-crystallizing successive portions of
the film. As the disk continues to rotate, each new facet that
reflects the laser beam effectively "re-sets" the position of the
beam relative to the film in the direction of rotation, bringing
the laser beam back to its starting point on the film in that
direction. At the same time, the film is translated in another
direction, e.g., perpendicular to the scan direction, so that as
the disk continues to rotate, new facets reflect the laser beam
onto successive portions of the film that are displaced from each
other in the second direction. Thus, an entire region of the thin
film can be pre-crystallized.
[0043] As illustrated in FIG. 3, pre-crystallization system 500
that can be used to pre-crystallize a thin film 515 within defined
region 520. A laser (not shown), e.g., an 18 W, 2.omega.
Nd:YV0.sub.4 Verdi laser from Coherent Inc., generates a CW laser
beam 540. One or more optics (also not shown) shape laser beam 540
so that it forms a thin line beam. In some embodiments, the beam
has a length of between about 1-15 mm, a width of between about
5-50 .mu.m, and a fluence of between about 10-150 W/mm of beam
length. Note, however, that the beam may have any desired length,
and in some cases may be a "line beam" having a very high length to
width aspect ratio (e.g., about 50-10.sup.5), and may even extend
for the full length of the panel being irradiated. In this case,
the film need not be scanned in the second direction, because the
entire length of a given region will be irradiated at once. In some
embodiments, the beam has approximately uniform energy along the
long axis, although in other embodiments the beam will have other
energy profiles such as Gaussian or sinusoidal. In some
embodiments, the beam along the short axis has a "top hat" energy
profile, i.e., having substantially equal energy across the short
axis profile of the beam, and in other embodiments, the beam has a
tightly focused Gaussian profile along the short axis. Other energy
profiles, and other beam sizes, are possible and can be selected
according to the performance requirements of the finished device.
The overall beam power, as well as the size of the beam, is
selected to provide a sufficient energy density to partially melt
the film 515 so that it recrystallizes with the desired amount of
texture. One of skill in the art would be able to readily select
appropriate lasers and optics to achieve a desired beam profile,
wavelength, and energy. Note that the laser beam need not be CW,
but can also have any suitable temporal profile, for example
sufficiently long pulses to partially melt the irradiated regions,
or have a relatively high repetition rate ("quasi-CW").
[0044] The laser beam is directed towards a rotating disk 560
having a plurality of at least partially reflective surfaces or
facets 580. Reflective facets 580 of disk 560 are positioned
relative to film 575 so as to direct laser beam 540 towards the
film surface. Specifically facets 580 are arranged so as to
redirect laser beam 540 so that it irradiates film 515 within
defined region 520. Where the laser beam irradiates region 520, it
partially melts the film, which crystallizes upon cooling as
described in greater detail in U.S. Patent Publication No.
2006/0102901. Disk 560 rotates about axis 570. This rotation moves
facets 580 relative to laser beam 540, so that they behave as a
moving mirror for the laser beam, and guide the beam in a line
across the substrate. The movement of facets 580 move laser beam
540 rapidly relative to film 515 in the (-y) direction. The
relative velocity v.sub.scan of the beam relative to the film 515
in the (-y) direction is determined by the speed of rotation of
disk 560. The velocity of the beam imparted by the disk is
substantially higher than could be generated by moving the
substrate with typical mechanical stage. At the same time, stage
518 moves film 515 in the (+x) direction with a velocity
v.sub.stage, perpendicular to the direction of beam motion. Thus,
the total beam velocity relative to a given point of the film can
be substantially higher than normally achievable using stage 518
alone. Furthermore the irradiation pattern of the film surface is
defined by the state scanning speed and direction as well as the
facet size and rotation rate of the disk, as well as the distance
between the disk and the film.
[0045] While FIG. 3 shows faceted disk 560 with eight facets 580,
this number of facets is meant to be illustrative only. In general,
other ways of deflecting the beam in order to provide high velocity
scanning are contemplated, for example, a single movable mirror.
Or, for example, other numbers of facets can be used, according to
the desired processing speed and size of pre-crystallized regions
520.
[0046] FIG. 4A illustrates a detailed view of the path of laser
beam 540 relative to the substrate 610. As disk 560 rotates, a
first facet 580 reflects beam 540 so that it first irradiates
substrate 610 at a first edge 621 of the defined film region 620 to
be pre-crystallized, starting a "first scan" of the region. Disk
560 continues to rotate the given facet 580, so that the beam moves
across film region 620 in the (-y) direction with a velocity
v.sub.scan. At the same time, stage 518 moves substrate 610 in the
(+x) direction with a velocity v.sub.stage resulting in a diagonal
crystallization path. Wherever beam 540 irradiates defined film
region 620, it partially melts the film, which upon cooling
recrystallizes with texture as described above. Thus, as can be
seen in FIG. 6A, the width w.sub.scan of a particular scanned
region is defined by the length of the laser beam in that region,
and the edge of the scanned region follows a "diagonal" path
relative to the substrate, defined by v.sub.scan and v.sub.stage,
as described in greater detail below.
[0047] As disk 560 continues to rotate, the first facet 580
eventually rotates far enough that it no longer reflects beam 540.
When this happens, the beam stops irradiating the defined region
620 at second edge 622 which coincides with the other edge defining
the preselected region 620. With continued rotation of disk 560,
the laser beam 540 is directed onto a second facet 580. Second
facet 580 redirects laser beam 540 so that it irradiates substrate
610 at a first edge 621 of the defined film region 620, starting a
"second scan" of the region. At the beginning of the second scan,
the stage has moved the substrate 610 by a predetermined distance
(based on stage velocity) in the (+x) direction relative to where
it was at the beginning of the first scan. This yields an offset in
the (+x) between the edge of the first scan and the edge of the
second scan that is determined by stage speed v.sub.stage. This
offset can be chosen to provide a desired amount of overlap between
the first and second scans. As mentioned above, pre-crystallizing a
film multiple times can enlarge the size of preferably oriented
grains, so it may be desirable to use a relatively small offset to
provide a large amount of overlap between the first and second
scanned areas.
[0048] As disk 560 continues to rotate, second facet 580 moves the
beam 540 across region 620 in the (-y) direction, and stage 518
moves substrate 610 in the (+x) direction. Eventually the second
facet 580 moves out of the path of beam 540, and a third facet 580
reflects the beam 540 to irradiate region 620, again offset in the
(+x) direction by an amount determined by speed v.sub.stage. In
this way, as disk 560 continues to rotate and stage 518 moves the
substrate 610, defined film region 620 is substantially
pre-crystallized, while other regions of substrate 610 are not
pre-crystallized and remain, e.g., amorphous silicon. After
completing the pre-crystallization of region 620, the stage moves
the substrate 610 in the (-x) and (+y) or (-y) direction, so that a
new region can be pre-crystallized as described above.
[0049] Although FIG. 4A shows a non-pre-crystallized area at the
bottom of defined film region 620, resulting from the "diagonal"
motion of the beam relative to the substrate, this area can be
pre-crystallized by simply starting the first scan below the edge
of the substrate. Alternately, the bottom of the substrate can be
trimmed, or TFTs simply not fabricated on that particular area.
[0050] As illustrated in FIG. 4B, the combination of beam velocity
v.sub.scan in the (-y) direction and stage velocity v.sub.stage in
the (+x) direction yields an effective scan velocity
v.sub.scan,eff. This velocity v.sub.scan,eff. is elected so that
the beam travels fast enough not to damage the substrate 610, but
slow enough to partially melt the defined film region 620 to the
desired degree.
[0051] Assuming that the beam 540 moves in only one direction
(although it can be bidirectional), and continuously irradiates the
film, the frequency of scanning f.sub.scan is given by:
f scan = v scan l scan ##EQU00001##
where v.sub.scan is the scan velocity, as described above, and
l.sub.scan is the length of the region to be scanned, i.e.,
they-dimension of the pre-treated area. As an example, for a scan
velocity v.sub.scan of 1 m/s and a scan length l.sub.scan of 4 mm,
the scan frequency will be 250 Hz.
[0052] For a certain number of scans per unit area n, the beam with
w.sub.scan follows from:
w scan = n v stage l scan ##EQU00002##
where v.sub.stage is the velocity of the stage. So, in addition to
the exemplary numbers above, if n=10 scans per unit area are
desired and the stage velocity v.sub.stage is approximately 20
cm/s, then the beam width w.sub.scan is approximately 8 mm.
[0053] In order to remain within the margins of the partial melting
regime, the scanning velocity is held to be substantially constant,
as opposed to following, for example, a sinusoid trace. In the
described embodiment, disk 560 rotates at a substantially constant
speed, which causes beam 540 to also move at a substantially
constant speed. Translation of the stage allows a new region to be
pre-crystallized.
[0054] In some embodiments, the semiconductor film is first
pre-crystallized in defined regions, and then laterally
crystallized everywhere. The pre-crystallized regions will have
more highly aligned crystals than the non-pre-crystallized regions,
although all the regions of the film will be laterally
crystallized. The regions that are both pre-crystallized and
laterally crystallized can be used to fabricate devices that are
particularly sensitive to microstructure, such as integration TFTs;
the non-pre-crystallized regions can be used to fabricate devices
that are less sensitive to microstructure, but still benefit from
lateral crystals, such as pixel TFTs. Pre-crystallizing the film
only in regions needing improved crystalline alignment can save
time and energy over pre-crystallizing the entire semiconductor
film.
[0055] In some embodiments, the semiconductor film is laterally
crystallized following pre-crystallization. One suitable protocol,
referred to herein as "uniform-grain sequential lateral
solidification," or "uniform SLS," may be used to prepare a uniform
crystalline film characterized by repeating columns of laterally
elongated crystals. Uniform crystal growth is described with
reference to FIGS. 7A-7D. The crystallization protocol involves
advancing the film by an amount greater than the characteristic
lateral growth length, e.g., .delta.>LGL, where .delta. is the
translation distance between pulses, and less than two times the
characteristic lateral growth length, e.g., .delta.<2 LGL. The
term "characteristic lateral growth length" (LGL) refers to the
characteristic distance the crystals grow when cooling. The LGL is
a function of the film composition, film thickness, the substrate
temperature, the laser pulse characteristics, the buffer layer
material, if any, and the optical configuration. For example, a
typical LGL for 50 nm thick silicon films is approximately 1-5
.mu.m or about 2.5 .mu.m. The actual growth may be limited by other
laterally growing fronts, e.g., where two fronts collide as
illustrated below.
[0056] Referring to FIG. 7A, a first irradiation is carried out on
a film with a narrow, e.g., less than two times the lateral growth
length, and elongated, e.g., greater than 10 mm and up to or
greater than 1000 mm, laser beam pulse having an energy density
sufficient to completely melt the film. As a result, the film
exposed to the laser beam (shown as region 400 in FIG. 7A), is
melted completely and then crystallized. In this case, grains grow
laterally from an interface 420 between the unirradiated region and
the melted region. As noted above, the grains grow epitaxially from
the solidus boundaries on either side of the melted region. Thus,
the laterally growing grains adopt the texture of the
pre-crystallized film, formed as described above. By selecting the
laser pulse width so that the molten zone width is less than about
two times the characteristic LGL, the grains growing from both
solid/melt interfaces collide with one another approximately at the
center of the melted region, e.g., at centerline 405, and the
lateral growth stops. The two melt fronts collide approximately at
the centerline 405 before the temperature of the melt becomes
sufficiently low to trigger nucleation.
[0057] Referring to FIG. 7B, after being displaced by a
predetermined distance o that is at least greater than about LGL
and less than at most two LGL, a second region of the substrate
400' is irradiated with a second laser beam pulse. The displacement
of the substrate, .delta., is related to the desired degree of
overlap of the laser beam pulse. As the displacement of the
substrate becomes longer, the degree of overlap becomes less. It is
advantageous and preferable to have the overlap degree of the laser
beam to be less than about 90% and more than about 10% of the LGL.
The overlap region is illustrated by brackets 430 and dashed line
435. The film region 400' exposed to the second laser beam
irradiation melts completely and crystallizes. In this case, the
grains grown by the first irradiation pulse serve as crystallizing
seeds for the lateral growth of the grains grown from the second
irradiation pulse. FIG. 7C illustrates a region 440 having crystals
that are laterally extended beyond a lateral growth length. Thus, a
column of elongated crystals are formed by two laser beam
irradiations on average. Because two irradiation pulses are all
that is required to form the column of laterally extended crystals,
the process is also referred to as a "two shot" process.
Irradiation continues across the substrate to create multiple
columns of laterally extended crystals. FIG. 7D illustrates the
microstructure of the substrate after multiple irradiations and
depicts several columns 440 of laterally extended crystals.
[0058] Thus, in uniform SLS, a film is irradiated and melted with a
low number of pulses, e.g., two. The crystals that form within the
melted regions preferably grow laterally and with a similar
orientation, and meet each other at a boundary within the
particular irradiated region of film. The width of the irradiation
pattern is preferably selected so that the crystals grow without
nucleation. In such instances, the grains are not significantly
elongated; however, they are of uniform size and orientation. For
further details on variations of uniform SLS processes, see U.S.
Pat. No. 6,573,531, the contents of which are incorporated herein
in their entirety by reference, and PCT Publication No. WO
20061107926, entitled "Line Scan Sequential Lateral Solidification
of Thin Films," the entire contents of which are incorporated
herein by reference. Other lateral crystallization methods that
provide relatively short elongations of crystal grains are also
suitable, for example so-called "Dot-SLS" methods as described in
U.S. Patent Publication number 2006/0102901, as well as controlled
super-lateral growth, or "C-SLG" methods, as described in PCT
Publication No. WO US03/25947, the entire contents of which are
incorporated herein by reference.
[0059] FIG. 5 illustrates an SLS system according to some
embodiments. A light source, for example, an excimer laser 710
generates a laser beam which then passes through a pulse duration
extender 720 and attenuator plates 725 prior to passing through
optical elements such as mirrors 730, 740, 760, telescope 735,
homogenizer 745, beam splitter 755, and lens 765. The laser beam
pulses are then passed through a mask 770, which may be on a
translation stage (not shown), and projection optics 795. The mask
can be a slit, which shapes the laser beam into a "line beam,"
although the system is capable of making more complex beam shapes
depending on the choice of mask. The projection optics reduce the
size of the laser beam and simultaneously increase the intensity of
the optical energy striking substrate 799 at a desired location.
The substrate 799 is provided on a precision x-y-z stage 800 that
can accurately position the substrate 799 under the beam and assist
in focusing or defocusing the image of the mask 770 produced by the
laser beam at the desired location on the substrate. As described
in U.S. Patent Publication No. 2006/0102901, the firing of the
laser can be coordinated with the motion of x-y-z stage 800 to
provide location-controlled firing of pulses.
[0060] Although the discussion above refers to the processing of
silicon thin films, many other kinds of thin films are compatible.
The thin film can be a semiconductor or a conductor, such as a
metal. Exemplary metals include aluminum, copper, nickel, titanium,
gold, and molybdenum. Exemplary semiconductor films include
conventional semiconductor materials, such as silicon, germanium,
and silicon-germanium. Additional layers situated beneath or above
the metal or semiconductor film are contemplated, for example,
silicon oxide, silicon nitride and/or mixtures of oxide, nitride,
or other materials that are suitable, for example, for use as a
thermal insulator to further protect the substrate from overheating
or as a diffusion barrier to prevent diffusion or impurities from
the substrate to the film. See, e.g., PCT Publication No. WO
2003/084688, for methods and systems for providing an aluminum thin
film with a controlled crystal orientation using pulsed laser
induced melting and nucleation-initiated crystallization.
[0061] In view of the wide variety of embodiments to which the
principles of the present invention can be applied, it should be
understood that the illustrated embodiments are illustrative only,
and should not be taken as limiting the scope of the present
invention.
* * * * *