U.S. patent application number 10/709035 was filed with the patent office on 2005-01-27 for [method of fabricating polysilicon film].
Invention is credited to Chang, Mao-Yi.
Application Number | 20050020034 10/709035 |
Document ID | / |
Family ID | 34076415 |
Filed Date | 2005-01-27 |
United States Patent
Application |
20050020034 |
Kind Code |
A1 |
Chang, Mao-Yi |
January 27, 2005 |
[METHOD OF FABRICATING POLYSILICON FILM]
Abstract
A method of fabricating polycrystalline silicon layer of TFT is
provided. The method includes sequentially forming an insulating
layer, a first amorphous silicon layer, and a cap layer on a
substrate. A laser annealing is performed to transform the first
amorphous silicon layer to a first polycrystalline silicon layer,
wherein at least one hole is formed in the amorphous silicon layer
during the laser annealing process. Thereafter, the cap layer is
removed. A portion of the insulating layer exposed within the hole
is removed to form a second opening. A second amorphous silicon
layer is formed over the first polycrystalline silicon layer
filling the second opening. Finally a second annealing is performed
to transform the second amorphous silicon layer to a second
polycrystalline silicon layer.
Inventors: |
Chang, Mao-Yi; (Hsinchu
County, TW) |
Correspondence
Address: |
JIANQ CHYUN INTELLECTUAL PROPERTY OFFICE
7 FLOOR-1, NO. 100
ROOSEVELT ROAD, SECTION 2
TAIPEI
100
TW
|
Family ID: |
34076415 |
Appl. No.: |
10/709035 |
Filed: |
April 8, 2004 |
Current U.S.
Class: |
438/478 ;
257/E21.133; 257/E21.134; 257/E21.347; 257/E21.412 |
Current CPC
Class: |
H01L 21/02595 20130101;
H01L 27/1285 20130101; H01L 21/02532 20130101; H01L 21/02686
20130101; H01L 21/268 20130101; H01L 21/2022 20130101; H01L 29/6675
20130101; H01L 21/2026 20130101 |
Class at
Publication: |
438/478 |
International
Class: |
H01L 021/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 24, 2003 |
TW |
92120193 |
Claims
1. A method of fabricating a polysilicon film, comprising:
providing a substrate; forming an insulating layer, a first
amorphous silicon layer and a cap layer over the substrate;
performing a first annealing to transform the first amorphous
silicon layer into a first polysilicon layer with at least a hole;
removing the cap layer; removing a portion of the insulating layer
within the hole to form a first opening within the insulating
layer, wherein the hole and the first opening constitute a second
opening; forming a second amorphous silicon layer over the first
polysilicon layer and filling the second opening, wherein a recess
is formed over a portion of the second amorphous silicon layer over
the second opening; and performing a second annealing and forming a
second polysilicon layer by partially fusing the second amorphous
silicon layer and the first polysilicon layer, and taking an
unfused portion of the second amorphous silicon layer as seeds for
crystallization.
2. The method of fabricating a polysilicon film as recited in claim
1, wherein the cap layer comprises silicon dioxide.
3. The method of fabricating a polysilicon film as recited in claim
1, wherein the step of performing the first annealing comprises
performing an excimer laser annealing process.
4. The method of fabricating a polysilicon film as recited in claim
1, wherein the step of removing the portion of the insulating layer
within the hole comprises performing a wet etching using a solution
containing hydrofluoric acid.
5. The method of fabricating a polysilicon film as recited in claim
1, wherein the step of performing the second annealing comprises
performing an excimer laser annealing process.
6. The method of fabricating a polysilicon film as recited in claim
1, wherein a width of the second opening is smaller than one
micron.
7. A method of fabricating a polysilicon film, comprising:
providing a substrate; forming an insulating layer, a first
amorphous silicon layer, and a cap layer over the substrate;
performing a first annealing to transform the first amorphous
silicon layer into a first polysilicon layer with at least a hole;
removing the cap layer; removing a portion of the insulating layer
within the hole to form a first opening within the insulating
layer, wherein the hole and the first opening constitute a second
opening; forming a dielectric layer over the first polysilicon
layer and filling the second opening, wherein a recess is formed
over a portion of the dielectric layer above the second opening;
forming a second amorphous silicon layer over the dielectric layer;
and performing a second annealing and transforming the second
amorphous silicon layer into a second polysilicon layer by taking a
portion of the second amorphous silicon layer within the recess as
seeds for crystallization.
8. The method of fabricating a polysilicon film as recited in claim
7, wherein the cap layer comprises silicon dioxide.
9. The method of fabricating a polysilicon film as recited in claim
7, wherein the step of performing the first annealing process
comprises an excimer laser annealing process.
10. The method of fabricating a polysilicon film as recited in
claim 7, wherein the step of removing the portion of the insulating
layer within the hole comprises performing a wet etching using a
solution containing hydrofluoric acid.
11. The method of fabricating a polysilicon film as recited in
claim 7, wherein the step of performing the second annealing
comprises performing an excimer laser annealing process.
12. The method of fabricating a polysilicon film as recited in
claim 7, wherein the dielectric layer comprises silicon
dioxide.
13. The method of fabricating a polysilicon film as recited in
claim 7, wherein a width of the second opening is smaller than one
micron.
14. A method of fabricating a polysilicon film, comprising:
providing a substrate; forming an insulating layer, a first
amorphous silicon layer and a cap layer over the substrate;
performing a first annealing to transform the first amorphous
silicon layer into a first polysilicon layer with at least a first
hole; removing the cap layer; removing a portion of the insulating
layer within the first hole to form a first opening within the
insulating layer, wherein the first hole and the first opening
constitute a second opening; forming a dielectric layer over the
first polysilicon layer and filling the second opening, wherein the
dielectric layer surrounds a second hole within the second opening;
forming a second amorphous silicon layer over the dielectric layer;
and performing a second annealing and transforming the second
amorphous silicon layer into a second polysilicon player, wherein a
portion of the second amorphous silicon layer over the second hole
is subjected to a higher temperature than other portion of the
second amorphous silicon layer relative to the second hole.
15. The method of fabricating a polysilicon film as recited in
claim 14, wherein the cap layer comprises silicon dioxide.
16. The method of fabricating a polysilicon film as recited in
claim 14, wherein the step of performing the first annealing
comprises performing an excimer laser annealing process.
17. The method of fabricating a polysilicon film as recited in
claim 14, wherein the step of removing the portion of the
insulating layer within the first hole comprises performing a wet
etching using a solution containing hydrofluoric acid.
18. The method of fabricating a polysilicon film as recited in
claim 14, wherein the step of performing the second annealing
comprises performing an excimer laser annealing.
19. The method of fabricating a polysilicon film as recited in
claim 14, wherein the dielectric layer comprises silicon
dioxide.
20. The method of fabricating a polysilicon film as recited in
claim 14, wherein a width of the second opening is smaller than one
micron.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of Taiwan
application serial no. 92120193, filed Jul. 24, 2003.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a method of fabricating Thin Film
Transistor Liquid Crystal Display (TFT-LCD), and more particularly,
relates to a method of fabricating a polysilicon film of TFT array
in a TFT-LCD thereof.
[0004] 2. Description of the Related Art
[0005] An ordinary active TFT LCD array is generally categorized
into polysilicon TFT and amorphous silicon TFT based materials used
for making the TFT LCD, where a polysilicon (poly-Si) TFT being
capable of integrating driving circuit thus provides a higher
opening rate and lower fabrication cost than a corresponding
amorphous silicon (a-Si) TFT. Another reason that polysilicon TFT
technology is greatly promoted is that poly-Si TFT significantly
reduces device feature size so that high image resolution can be
achieved. In order to mass-produce polysilicon TFT-LCD, three
primary conditions are low temperature (about 450 to 550.degree.
C.) process, low-temperature filming technology for high quality
gate-insulator layer, and broad ion-implantation.
[0006] In view of the cost of a glass substrate, low temperature
thin film process is adopted where Solid Phase Crystallization
(SPC) is introduced thereby, yet the active temperature not only
tends to be relatively higher than expected, which is around
600.degree. C., but also causes degraded crystallization. Thus
Excimer Laser Crystallization (ELC) or Excimer Laser Annealing
(ELA) process that is applied to the foregoing low-temperature TFT
process is developed, wherein an a-Si thin film is fused by laser
scanning and is crystallized to poly-Si thin film.
[0007] Providing process temperature lower than 450.degree. C. in
ELC and providing higher electron mobility and lower current
leakage than SPC in forming an amorphous silicon thin film, a less
expensive glass substrate is introduced so as to reduce fabrication
cost whereas better TFT device characteristic is obtained
thereby.
[0008] Referring to FIG. 1A, a substrate 100 is provided. A first
insulating layer 102 is formed on the substrate 100. Next, a
photolithography etching is performed to form a first opening 104
in the first insulating layer 102. In the sub-micron technology,
the photolithography technology is not applicable to the present
micro TFT field, because the threshold feature of the first opening
104 using photolithography technique is about 1 micrometer, which
is relatively large compared to the threshold crystal feature size
for TFT thin film.
[0009] Attempts to resolve the issue is illustrated with reference
to FIG. 1B. A second insulating layer 106 is further formed over
the first insulating layer 102 and the first opening 104. The
deposition of the second insulating layer 106 further shrinks the
first opening 104 to a second opening 108 to satisfy the feature
size requirement for polysilicon TFT crystallization.
[0010] Referring to FIG. 1C, an a-Si layer 110 is formed over the
second insulating layer 106. Next, fuse and liquefy the a-Si layer
110 by an Excimer Laser 112.
[0011] Finally, referring to FIG. 1D, the fused liquefied silicon
undergoes crystallization from the second opening 108 to transform
the a-Si layer 110 into a poly-Si layer 114, which is suitable for
forming source/drain and channel of a TFT therein.
[0012] However, problems in the foregoing process do exist, as
described below.
[0013] The forming of the first opening 104 in the foregoing
process requires a mask process and an additional deposition step
of forming the second insulating layer 106 adjusting to the size of
the first opening 104, and therefore not only complication but also
lowers throughput results.
[0014] Moreover, the scheme of depositing the second insulating
layer 106 for adjusting to the size of the second opening 108
requires precise control of the process conditions, thus narrowing
the processing tolerance window.
SUMMARY OF INVENTION
[0015] According to foregoing issues, one object of the present
invention is to provide a method of fabricating a poly-Si thin
film, wherein the steps of complicated photolithography exposure,
extra deposition procedure, etc. can be excluded, and an opening
with proper deep sub-micron dimensions can be formed.
[0016] Another object of the present invention is to provide a
method of fabricating a poly-Si film, wherein an opening having a
size sufficient for poly-Si thin film crystallization can be formed
without precise control of process conditions, and thereby
increasing the process window allowing greater process condition
tolerance.
[0017] The present invention provides a method of fabricating a
poly-Si layer, wherein a substrate is provided, an insulating
layer, a first a-Si layer, and a cap layer are sequentially formed
over the substrate. A first laser annealing is performed for
transforming the first a-Si layer into a first poly-Si layer having
at least one hole. Next, the cap layer is removed, and then a
portion of the insulating layer within the hole is removed to form
a first opening in the insulating layer, and the first opening and
the insulating layer form a second opening. Subsequently, a second
a-Si layer is formed over the first a-Si layer and the second
opening, wherein the second a-Si layer has a recess over the second
opening. Finally, the resulting structure is subjected to a second
laser annealing, wherein an unfused portion of the second a-Si
layer at a bottom of the second opening serves as a seed for
crystal growth during the crystallization, thus the second a-Si
layer is transformed into a second poly-Si layer.
[0018] The present invention provides another method of fabricating
a poly-Si thin film. A substrate is provided. An insulating layer,
a first a-Si layer, and a cap layer are sequentially formed over
the substrate. A first laser annealing is performed to transform
the first a-Si layer into a first poly-Si layer having at least a
first hole. Afterwards, the cap layer is removed, removing a
portion of the insulating layer exposed within the first hole to
form a first opening in the insulating layer, and the first hole
and the first opening define a second opening. Then a dielectric
layer is formed over the first poly-Si layer and the second
opening, and a second a-Si layer is formed over the dielectric
layer, wherein the second a-Si layer has a recess over the second
opening. Finally, the resulting structure is subjected to a second
annealing, wherein a portion of the second a-Si layer within the
recess serves as the seed for crystal growth during the
crystallization, so that the second a-Si layer is transformed into
a second poly-Si layer.
[0019] The present invention provides another method of fabricating
a poly-Si thin film. A substrate is provided. An insulating layer,
a first a-Si layer, and a cap layer are formed sequentially over
the substrate. Thereafter the resulting structure is subjected to a
first annealing wherein the first a-Si layer is transformed into a
first poly-Si layer having at least a first hole. Next, the cap
layer is removed, and then a portion of the insulating layer
exposed within the first hole is removed to form a first opening in
the insulating layer, and the first hole and the first opening form
a second opening. Then a dielectric layer having a second hole is
formed over the first poly-Si layer and the second opening, wherein
the second hole is formed within the second opening. Next, a second
a-Si layer is formed over the dielectric layer. Finally, the
resulting structure is subjected to a second laser annealing. A
portion of the second a-Si layer over the second hole is subjected
to a higher temperature than other portion of the second a-Si layer
relative to the second hole, and crystallization lasts longer, so
that the second a-Si layer is transformed into a second poly-Si
layer.
[0020] According to the foregoing description, it is noted that a
proper deep sub-micron hole in the insulating layer is formed by
sequentially forming an insulating layer, a a-Si layer and a cap
layer over the substrate and then performing a laser annealing
process without performing any photolithography and etching.
Accordingly, process steps such as light exposure, photolithography
and additional deposition as described above for forming an opening
having a deep sub-micron feature can be effectively excluded. Thus,
the throughput can also be effectively increased.
[0021] Moreover, the method of the present invention can be
implemented without precisely controlling the process conditions by
forming the cap layer, the a-Si layer, the insulating layer or
laser annealing process. Thus the method of the present invention
has a broader process tolerance compared to the conventional
process described above.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIGS. 1A to 1D show the cross sectional views illustrating
the progression of the process according to a conventional method
of fabricating a polysilicon (poly-Si) thin film.
[0023] FIGS. 2A to 2E show the cross sectional viewsillustrating
the progression of the process of a method of fabricating a poly-Si
thin film according to a first embodiment of the present
invention.
[0024] FIGS. 3A to 3F show the cross sectional viewsillustrating
the progression of the process of a method of fabricating a poly-Si
thin film according to a second embodiment of the present
invention.
[0025] FIGS. 4A to 4F show the cross sectional viewsillustrating
the progression of the process of a method of fabricating a poly-Si
thin film according to a third embodiment of the present
invention.
DETAILED DESCRIPTION
[0026] First Embodiment
[0027] Referring to FIGS. 2A to 2E, show the cross sectional
viewsillustrating the progression of the process of a method of
fabricating a polysilicon (poly-Si) thin film according to the
first embodiment of the present invention.
[0028] Referring to FIG. 2A, a substrate 200 is provided, wherein
the material of the substrate 200 includes a silicon wafer, a glass
substrate or a plastic substrate, for example. An insulating layer
202 is formed over the substrate 200, wherein the insulating layer
202 includes silicon dioxidecan be formed by performing a
conventional deposition process such as Low Pressure Chemical Vapor
Deposition (LPVCD), Plasma Enhanced Chemical Vapor Deposition
(PECVD) or sputtering. Thereafter a first a-Si layer 204, which can
be formed by performing a conventional process such as LPVCD, PECVD
or sputtering, is formed over the insulating layer 202. Further, a
cap layer 206 is formed over the first a-Si layer 204, wherein the
material of the cap layer 206 includes a silicon dioxide, for
example, wherein the cap layer 206 may be formed by performing a
conventional deposition process such as LPCVD, PECVD, or
sputtering. Afterwards, the resulting structure is subjected to a
first laser annealing 208, for example, an excimer laser may be
used to perform the first laser annealing 208, so as to fuse the
first a-Si layer 204. The energy density of the excimer laser is
about 50 to 500 mJ/cm.sup.2.
[0029] Referring to FIG. 2B, a first poly-Si layer 210 is formed
transformed from the first a-Si layer 204 through crystallization.
In addition, a plurality of holes are randomly formed in the first
poly-Si layer 210, however, in the FIG. 2B, only one hole 212 is
shown for illustration purpose.
[0030] According to the foregoing procedures, the reasons why the
hole 212 is formed in the first poly-Si layer 210 is not exactly
known but it is most likely due to a cohesion force of poly-Si
being stronger than an adhesion force between the cap layer and the
first poly-Si layer 210. The first poly-Si layer 210 shrinks
inwardly to form the holes 212 as the first a-Si layer 204 is
transformed into the first poly-Si layer 210. Additionally, each of
the holes 212 has the feature of a proper deep sub-micron dimension
for back-end crystallization.
[0031] Referring to FIG. 2C, the cap layer 206 is removed by
performing a wet etching or an anisotropic dry etching. Thereafter,
a portion of the insulating layer 202 exposed within the hole 212
is removed to form a first opening 214, wherein the step of
removing the portion of the insulating layer 202 exposed within the
first opening 214 can be carried out by performing a wet etching,
for example. The width of the first opening 214 is smaller than
about 0.5 micron for further crystallization. The hole 212 and the
first opening 214 form a second opening 216.
[0032] Referring to FIG. 2D, a second a-Si layer 218 is formed over
the first poly-Si layer 210 and the second opening 216, wherein the
second a-Si layer 218 is deposited by performing LPCVD, PECVD, or
sputtering, for example, wherein the second a-Si layer 218 includes
a recess 220 neighboring with the second opening 216. The resulting
structure is subjected to a second laser annealing 222, for
example, using an excimer laser to irradiate the second a-Si layer
218 with an energy density of about 50 to 500 mJ/cm.sup.2 so as to
fuse the second a-Si layer 218 and the first poly-Si layer 210.
According to the second opening 216, an unfused portion of the
second a-Si layer 218 serves as a seed for crystallization, wherein
the unfused portion of the second a-Si layer 218 is at the bottom
of the second opening 216.
[0033] Finally, referring to FIG. 2E, a second poly-Si layer 224 is
transformed from a fused portion of the second a-Si layer 218 and
the first poly-Si layer 210 crystal growing in a lateral direction
226.
[0034] Second Embodiment
[0035] Referring to the FIGS. 3A to 3F, show the cross sectional
viewsillustrating the progression of the process of a method of
fabricating a poly-Si film according to a second embodiment of the
present invention.
[0036] Referring to FIG. 3A, a substrate 300 is provided, wherein
the material of the substrate 300 includes, for example, a silicon
wafer, a glass or a plastic. An insulating layer 302 is formed over
the substrate 300, wherein the material of the insulating layer 302
includes, for example, a silicon dioxide, and the insulating layer
302 can be formed by, for example, performing a conventional
deposition process such as a LPVCD, a PECVD or a sputtering.
Thereafter, a first a-Si layer 304 is formed over the insulating
layer 302, by performing, for example, a LPCVD, PECVD or sputtering
process.
[0037] Further, a cap layer 306 is formed over the first a-Si layer
304, wherein the material of the cap layer 306 includestemptemp,
for example, silicon dioxide, and the cap layer 306 can be formed
by, for example, performing a conventional deposition process such
as LPCVD, PECVD or sputtering. The resulting structure is then
subjected to a first laser annealing 308, for example, performing
an excimer laser annealing to fuse the first a-Si layer 304. The
energy density of the excimer laser is about 50 to 500
mJ/cm.sup.2.
[0038] Referring to FIG. 3B, a first poly-Si layer 310 is formed
transformed from the first a-Si layer 304 through the fusion and
crystallization. Moreover, as described in the first embodiment, as
the first a-Si layer 304 is transformed to the first poly-Si layer
310, a plurality of holes 312 are randomly formed in the first
poly-Si layer 310, however only a single hole 312 is shown in FIG.
3B for illustration purpose.
[0039] Referring to FIG. 3C, the cap layer 306 is removed, wherein
the step of removing the cap layer 306 is accomplished by, for
example, performing a wet etching using hydrofluoric acid or an
anisotropic dry etching. Thereafter, a portion of the insulating
layer 302 exposed within the hole 312 is removed to form a first
opening 314, wherein the portion of the insulating layer 302
exposed within the first opening 314 can be removed by, for
example, performing a wet etching. The first opening 314 has a
width smaller than about 0.5 micron for further crystallization.
The hole 312 and the first opening 314 constitute a second opening
316.
[0040] Referring to FIG. 3D, a dielectric layer 317 is formed over
the first poly-Si layer 310 and the second opening 316, wherein the
dielectric layer 317 can be formed by, for example, performing a
conventional process such as either LPCVD, PECVD or sputtering,
wherein the dielectric layer 317 includes a recess 320 neighboring
with the second opening 316.
[0041] Referring to FIG. 3E, a second a-Si layer 318 is formed over
the dielectric layer 317, wherein the second a-Si layer 318 is
formed by, for example, performing with a conventional deposition
process such as a LPCVD, a PECVD, or a sputtering process.
Thereafter, the resulting structure is subjected to a second laser
annealing 322 by performing, for example, an excimer laser
annealing, to irradiate the second a-Si layer 318. The energy
density of the excimer laser is about 50 to 500 mJ/cm.sup.2.
[0042] Finally, referring to FIG. 3F, a second poly-Si layer 324 is
formed transformed from a fused portion of the second a-Si layer
318 crystal growing in a lateral direction 326, wherein an unfused
portion of the second a-Si layer 318 neighboring with the recess
320 serves as a seed for crystallization.
[0043] Referring to the FIGS. 4A to 4F, show the cross-sectional
views illustrating the progression of the process of the method of
fabricating a poly-Si film according to a third embodiment of the
present invention.
[0044] Referring to FIG. 4A, a substrate 400 is provided, wherein
the material of the substrate 400 includes, for example, silicon
wafer, glass, or plastic. An insulating layer 402 is formed over
the substrate 400, wherein the material of the insulating layer 402
includes, for example, silicon dioxide, and wherein the insulating
layer 402 can be formed by performing conventional deposition
methods such as LPVCD, PECVD, or sputtering. Thereafter a first
a-Si 404 is formed over the insulating layer 402, which can be
formed by performing LPCVD, PECVD or sputtering method, for
example.
[0045] Next, a cap layer 406 is formed over the first a-Si layer
404, wherein the material of the cap layer 406 includes, for
example, silicon dioxide, and wherein the cap layer 406 can be
formed by performing conventional deposition methods such as LPCVD,
PECVD or sputtering method. Thereafter, the resulting structure is
subject to a first laser annealing 408 by performing, for example,
an excimer laser, so as to fuse the first a-Si layer 404. The
energy density of the excimer laser is about 50 to 500
mJ/cm.sup.2.
[0046] Referring to FIG. 4B, a first poly-Si layer 410 is formed
from the first a-Si layer 404 through fusion and crystallization.
Moreover, a plurality of first holes 412 are randomly formed in the
first poly-Si layer 410, however, in the FIG. 4B, only one first
hole 412 is shown for illustration purpose.
[0047] Further, referring to FIG. 4C, the cap layer 406 is removed,
wherein the method for removing the cap layer 406 is accomplished
by performing a wet etching using hydrofluoric acid or anisotropic
dry etching. Thereafter, a portion of the insulating layer 402
within the first hole 412 is removed to form a first opening 414,
wherein the portion of the insulating layer 402 is removed by
performing a wet etching, for example. The first opening 414 formed
by the foregoing method has a width smaller than about 0.5 micron
for further crystallization. The first opening 412 and the first
opening 414 constitute a second opening 416.
[0048] Next, referring to FIG. 4D, a dielectric layer 417 is formed
over the first poly-Si layer 410 and the second opening 416,
wherein the dielectric layer 417 can be formed by performing LPCVD,
PECVD or sputtering, for example. A second hole 420 is formed as an
air space in the dielectric layer 417, wherein the second hole 420
is neighboring with the second opening 416.
[0049] Furthermore, referring to FIG. 4E, a second a-Si layer 418
is formed over the dielectric layer 417, wherein the second a-Si
layer 418 is formed by performing LPCVD, PECVD or sputtering, for
example. Thereafter, the resulting structure is subjected to a
second laser annealing 422 by performing an excimer laser annealing
for example, to irradiate and fuse the second a-Si layer 418. The
energy density of the excimer laser is about 50 to 500
mJ/cm.sup.2.
[0050] Finally, referring to FIG. 4F, a second poly-Si layer 424 is
transformed from the second a-Si layer 418 through fusion and
crystallization. When the second laser annealing 422 is performed,
a portion of the second a-Si layer 418 over the second hole 420 is
subjected to a higher temperature than other portion of the second
a-Si player 418 relative to the second hole 420 because the thermal
conductivity is poor around the second hole 420. A lateral
crystallization progress from a region with lowest temperature (not
shown) along the direction 426 is performed, wherein the lateral
crystallization lasts longer around the second hole 420.
[0051] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention covers modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *