U.S. patent application number 12/019110 was filed with the patent office on 2008-08-07 for apparatus and method of temperature conrol during cleaving processes of thick film materials.
This patent application is currently assigned to Silicon Genesis Corporation. Invention is credited to Francois J. Henley.
Application Number | 20080188011 12/019110 |
Document ID | / |
Family ID | 39676507 |
Filed Date | 2008-08-07 |
United States Patent
Application |
20080188011 |
Kind Code |
A1 |
Henley; Francois J. |
August 7, 2008 |
APPARATUS AND METHOD OF TEMPERATURE CONROL DURING CLEAVING
PROCESSES OF THICK FILM MATERIALS
Abstract
An apparatus for temperature control of manufacture of thick
film materials includes a stage comprising a planar surface for
supporting a bulk material to be implanted and subsequently
cleaved. The bulk material has a surface region, a side region, and
a bottom region which provides a volume of material and defines a
length between the bottom region and the surface region. The
apparatus further includes a mechanical clamp device adapted to
engage the bottom region to the planar surface of the stage such
that the bulk material is in physical contact with the planar
surface for thermal energy to transfer through an interface region
between the bulk material and the stage while the surface region is
substantially exposed. Additionally, the apparatus includes a
sensor device configured to measure a temperature value of the
surface region and generate an input data. The apparatus further
includes an implant device configured to perform implantation of a
plurality of particles through one or more portions of the surface
region of the bulk material and a controller configured to receive
and process the input data to increase and/or decrease the
temperature value of the surface region through at least the
interface region between the planar surface of the stage and the
bottom region of the bulk material.
Inventors: |
Henley; Francois J.; (Aptos,
CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
Silicon Genesis Corporation
Aptos
CA
|
Family ID: |
39676507 |
Appl. No.: |
12/019110 |
Filed: |
January 24, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60886912 |
Jan 26, 2007 |
|
|
|
Current U.S.
Class: |
438/5 ;
219/121.6; 219/121.72; 250/492.21; 257/E21.347; 257/E21.528;
257/E21.568; 361/234 |
Current CPC
Class: |
H01J 37/20 20130101;
B28D 1/221 20130101; H01J 2237/2005 20130101; H01L 2924/0002
20130101; H01L 21/76254 20130101; H01L 2924/0002 20130101; H01J
2237/2007 20130101; H01L 22/26 20130101; H01J 2237/31701 20130101;
H01L 2924/00 20130101; B28D 5/00 20130101; H01J 2237/2001
20130101 |
Class at
Publication: |
438/5 ; 361/234;
250/492.21; 219/121.6; 219/121.72; 257/E21.347 |
International
Class: |
H01L 21/268 20060101
H01L021/268; H01L 21/687 20060101 H01L021/687; G21K 5/00 20060101
G21K005/00; B23K 26/38 20060101 B23K026/38 |
Claims
1. An apparatus for temperature control of manufacture of thick
film materials, the apparatus comprising: a stage comprising a
planar surface for supporting a bulk material to be implanted, the
bulk material having a surface region, a side region, and a bottom
region, the side region, bottom region, and the surface region
providing a volume of material, the volume of material having a
length defined between the bottom region and the surface region; a
mechanical clamp device adapted to engage the bottom region of the
bulk material to the planar surface of the stage such that the bulk
material is in physical contact with the planar surface for thermal
energy to transfer through an interface region between the bulk
material and the planar surface of the stage while the surface
region of the bulk material is substantially exposed; a sensor
device configured to measure a temperature value of the surface
region, the sensor device being adapted to generate an input data;
an implant device configured to perform implantation of a plurality
of particles through one or more portions of the surface region of
the bulk material; and a controller configured to receive the input
data and process the input data to increase and/or decrease the
temperature value of the surface region of the bulk material
through at least the interface region between the planar surface of
the stage and the bottom region of the bulk material.
2. The apparatus of claim 1 wherein the mechanical clamp device is
configured to engage one or more grooves on the side region of the
bulk material for clamping the bulk material on the planar surface
of the stage, wherein the one or more grooves are present in one of
a side of an adapter plate or in a homogenous portion of the bulk
material.
3. The apparatus of claim 2 wherein the one or more grooves on the
side region may be connected to surround the side region or may be
three or more isolated grooves on the side region with proper
locations for stable clamping.
4. The apparatus of claim 2 wherein the one or more grooves for
clamping the bulk material are located within 30% of the length of
the bulk material from the bottom region allowing the 70% bulk
material from the surface region to be cleaved without interference
with said grooves.
5. The apparatus of claim 1 wherein the surface region of the bulk
material comprises a planarized surface to facilitate the implant
process.
6. The apparatus of claim 1 wherein the bottom region of the bulk
material comprises a planarized surface for engaging with the
planar surface of the stage.
7. The apparatus of claim 1 wherein the interface region formed as
the bulk material engaged with the stage by the mechanical clamp
device comprises a cavity with a height enclosed by a close-looped
seal between at least part of the bottom region of the bulk
material and part of the planar surface of the stage.
8. The apparatus of claim 7 wherein the close-looped seal is
located near the edge vicinity of the bottom region of the bulk
material.
9. The apparatus of claim 7 wherein the cavity height may range
from 3 microns to 200 microns.
10. The apparatus of claim 7 wherein the planar surface of the
stage within the cavity comprises one or more gas passageways
connected to a gas supply/pump assembly.
11. The apparatus of claim 10 wherein the one or more gas
passageways allow a gas filled into the cavity with an adjustable
pressure.
12. The apparatus of claim 11 wherein the gas may be helium or
hydrogen.
13. The apparatus of claim 11 wherein the gas may be argon or
nitrogen.
14. The apparatus of claim 11 wherein the adjustable pressure may
be gauged from 1 Torr to 300 Torr.
15. The apparatus of claim 11 wherein the gas may be supplied at
cryogenic or room temperature, or being heated.
16. The apparatus of claim 1 wherein the stage is a dielectric
chuck configured to provide electrostatic force to attract the bulk
material.
17. The apparatus of claim 1 wherein the planar surface of the
stage comprises an area and a shape substantially the same as the
bottom region of the bulk material.
18. The apparatus of claim 1 wherein the stage further comprises a
fluid cooling and heating unit attached to its bottom.
19. The apparatus of claim 1 wherein the stage further comprises an
inductive heater to heat the bulk material.
20. The apparatus of claim 1 wherein the stage is mounted on a tray
that allows scanning of the implant beam across the tray.
21. The apparatus of claim 1 wherein the bulk material to be
cleaved comprises at least one of single crystalline silicon or
germanium ingot, polycrystalline silicon tile, multi-crystalline
silicon tile, or compound semiconductor ingot or tile.
22. The apparatus of claim 1 wherein the sensor device comprises
one or more temperature sensors, a position sensor, a pressure
sensor, and a surface roughness sensor.
23. The apparatus of claim 22 wherein the sensor device is capable
of updating the input data about the temperature value of the
surface region and the length of the bulk material after removing
each of the one or more free-standing thick films by the cleaving
process.
24. The apparatus of claim 22 wherein the sensor device further is
capable of measuring the surface roughness after each cleaving
process to determine whether the post-cleaving surface region of
the bulk material is smooth enough for next implant process,
otherwise, to perform certain surface smoothening process.
25. The apparatus of claim 24 wherein the surface smoothening
process comprises at least one of surface re-lapping,
ion-sputtering, etching, depositing a smooth layer, and in-situ
annealing processes.
26. The apparatus of claim 1 wherein the implant device comprises a
linear accelerator, the linear accelerator comprising one or more
radio frequency quadrupole (RFQ) elements and one or more drift
tube linear accelerator (DTL) elements or a combination RFQ and DTL
elements.
27. The apparatus of claim 26 wherein the linear accelerator may
accelerate ionic particles to an energy ranging from 1 MeV to 5 MeV
to form a particle beam for performing a cleaving process.
28. The apparatus of claim 26 wherein the linear accelerator
further comprises a beam expander located at an exit aperture, the
beam expander capable of expanding a beam size of the particle beam
up to 50 cm or further comprising beam scanner device.
29. The apparatus of claim 28 wherein the ionic particles comprise
hydrogen species.
30. The apparatus of claim 28 wherein the ionic particles comprise
deuterium species.
31. The apparatus of claim 1 wherein the implant device is at least
configured to: introduce a first plurality of particles at a first
temperature to form a defect region within a vicinity of a cleave
region; and introduce a second plurality of particles at a second
temperature into the defect region to increase a stress level from
a first value to a second value.
32. The apparatus of claim 31 wherein the first temperature ranges
from about -100 Degree Celsius to about 250 Degree Celsius.
33. The apparatus of claim 31 wherein the second temperature is
greater than about 250 Degree Celsius and no greater than 550
Degrees Celsius.
34. The apparatus of claim 31 wherein the implant device is
configured to further perform a treatment process after introducing
the first plurality of particles and before introducing the second
plurality of particles, the treatment process comprising a thermal
process provided at a third temperature of 400 Degree Celsius or
higher to render the defect region to be close to the cleave region
and stabilize the defect region.
35. The apparatus of claim 31 wherein the implant device is
configured to further perform a cleave process after introducing
the second plurality of particles, the cleave process comprising
annealing the cleave region and removing a free-standing film from
the bulk material at the cleave region.
36. The apparatus of claim 35 wherein each of the one or more
free-standing thick films cleaved from the bulk material ranges
from 15 microns to 200 micron in thickness.
37. The apparatus of claim 1 wherein the controller comprises a
control electronics capable of performing multiple control tasks
and process operations managed by a computer system by running a
plurality of corresponding control codes.
38. The apparatus of claim 37 wherein the controller may be
configured to execute a first control code for the operation of an
implant device including at least adjustments of duty factor,
particle power level, beam profile, and dose rate, or be configured
to execute a first code for operation of the implant including at
least adjustments of a power level, beam profile, scanning speed, a
pattern, and dose rate for a scanning process.
39. The apparatus of claim 37 wherein the controller may be
configured to execute a second control code for commanding the
mechanical clamp device to handle the bulk material such that
substantial volume from the surface region of the bulk material can
be processed without physical interference by the clamp device
and/or commanding the sensor device to monitor the state of the
bulk material during process.
40. The apparatus of claim 37 wherein the controller is further
configured to execute a third control code for temperature control
of bulk material during process by balancing a cooling of the stage
assisted with a gas-layer interface and the heating from the
implant particle and one or more external radiant heat sources.
41. The apparatus of claim 40 wherein the one or more external
radiant heat sources comprise a plurality of two-dimensionally
distributed flash lamps, each flash lamp being independently
operated by the controller to tune at least one of pulse rate and
intensity.
42. The apparatus of claim 40 wherein the one or more external
radiant heat sources located above the surface region of the bulk
material include one or more sources with slowly varying thermal
power flux rate to heat the surface region of the bulk material
with a less than 20.degree. C. surface-to-bottom temperature
difference.
43. The apparatus of claim 40 wherein the one or more external
radiant heat sources located above the surface region of the bulk
material include one or more sources with rapidly varying thermal
power flux rate to heat the surface region of the bulk material
faster than a thermal conduction time constant for the surface
region.
44. The apparatus of claim 43 wherein the source with rapidly
varying thermal power flux rate is a pulsed laser.
45. The apparatus of claim 44 wherein the pulsed laser is a YAG or
YLF Q-switched laser.
46. An apparatus of mounting a bulk material for manufacture of one
or more thick films, the apparatus comprising: a stage comprising a
planar surface for supporting the bulk material, the bulk material
having a planarized surface region, a planarized end region, and a
side region having a length from the surface region to the end
region; and a mechanical clamp device adapted to engage the
planarized end region of the bulk material with the planar surface
of the stage such that the surface region and at least 70% length
of the side region from the surface region is substantially exposed
and can be cleaved for manufacture of one or more thick films
without interference of the clamp device.
47. The apparatus of claim 46 wherein the engaged planar surface of
the stage and the bottom region of the bulk material forms an
interface region comprising a cavity with a height enclosed by a
close-looped gas-tight seal located around the edge of the bottom
region.
48. The apparatus of claim 47 wherein the planar surface of the
stage within the cavity comprises a plurality of gas passageways
connected to a gas supply/pump assembly.
49. The apparatus of claim 48 wherein the plurality of gas
passageways allow a gas filled into the cavity with an adjustable
pressure.
50. The apparatus of claim 49 wherein the gas may be helium,
hydrogen, argon, or nitrogen.
51. The apparatus of claim 49 wherein the adjustable pressure may
be gauged from 1 Torr to 300 Torr.
52. The apparatus of claim 49 wherein the gas may be supplied at
cryogenic or room temperature, or being heated.
53. The apparatus of claim 46 wherein the close-looped seal
comprises an O-ring or metal flange that substantially resemble to
the shape of the bottom region of the bulk material including
essentially symmetric polygonal or circular shape.
54. The apparatus of claim 46 wherein the stage is a dielectric
chuck configured to provide electrostatic force to attract the bulk
material.
55. The apparatus of claim 46 wherein the stage further comprises a
fluid cooling and heating unit attached to its bottom.
56. The apparatus of claim 46 wherein the stage further comprises
an inductive heater to heat the bulk material.
57. The apparatus of claim 46 wherein the mechanical clamp device
is part of a robot capable of performing removable clamping.
58. The apparatus of claim 46 wherein the mechanical clamp device
is adapted to removably clamp the bulk material on the stage by
utilizing one or more grooves on the side region or one or more
holding means on the bottom region of the bulk material.
59. A method for temperature control during a process of cleaving a
plurality of free-standing thick films from a bulk material, the
method comprising: providing a bulk material for cleaving, the bulk
material having a surface region, a bottom region, a side region
having a length from the surface region to the bottom region;
clamping the bulk material using a mechanical clamp device adapted
to engage the bottom region of the bulk material through a seal
with a planar surface of a stage to form a cavity with a height
between the bottom region and the planar surface, the planar
surface comprising a plurality of gas passageways allowing a gas
filled in the cavity with adjustable pressure; sensing the state of
the bulk material to generate an input data, the input data
comprising temperature information at the surface region and the
bottom region and the length of the bulk material between the
surface region and the bottom region; maintaining the temperature
of the surface region by processing at least the input data and
executing a control scheme utilizing at least one or more of;
particle bombardment to heat the surface region; radiation to heat
the surface region; and gas-assisted conduction between the bottom
region and the stage.
60. The method of claim 59 wherein the stage further comprises
inductive heating of the bulk material in the control scheme.
61. The method of claim 59 wherein the bulk material comprises at
least one of single crystalline silicon or germanium ingot,
polycrystalline silicon tile, multi-crystalline silicon tile, and
compound semiconductor ingot or tile.
62. The method of claim 59 wherein the bulk material is
preprocessed to planarize the surface region for facilitating the
cleaving process.
63. The method of claim 59 wherein the clamping of the bulk
material by the mechanical clamp device is performed such that the
surface region and at least 70% of the bulk material from the
surface region are substantially exposed for cleaving thick films
without interference of the clamp device.
64. The method of claim 63 wherein the mechanical clamp is a part
of a robot capable of performing removable clamping.
65. The method of claim 63 wherein the mechanical clamp also
electrically connects to the bulk material to heat the bulk
material through Joule heating.
66. The method of claim 63 wherein the seal is gas-tight and
secured enough to sustain gas pressure up to 300 Torr in the
cavity.
67. The method of claim 66 wherein the seal comprises an O-ring or
a dielectric flange or a metal flange.
68. The method of claim 66 wherein the gas supplied in the cavity
comprises at least one gas of hydrogen, helium, argon, or
nitrogen.
69. The method of claim 66 wherein the gas supplied in the cavity
can be a cryogenic gas, room temperature gas, or a heated gas.
70. The method of claim 59 wherein the planar surface of the stage
comprises an area and shape substantially the same as the bottom
region of the bulk material.
71. The method of claim 70 wherein the stage is an electrostatic
chuck capable of generating electrostatic force to attract the bulk
material.
72. The method of claim 70 wherein the stage further comprises a
fluid temperature control unit attached to its bottom.
73. The method of claim 72 wherein the fluid temperature control
unit utilizes a liquid or gas for cooling or heating the bulk
material through the stage.
74. The apparatus of claim 59 wherein the stage and the mechanical
clamp device are both mounted on a tray that allows X-Y two
dimensional move.
75. The method of claim 59 wherein sensing the state of the bulk
material comprising using a plurality of sensors including
temperature sensor, position sensor, pressure sensor, and/or
surface roughness probe.
76. The method of claim 75 wherein the temperature sensor comprises
one or more optical pyrometers or thermocouples performing
temperature measurement.
77. The method of claim 75 wherein the position sensor is capable
of tracking the length of the bulk material after each
free-standing thick film being removed from the bulk material by
the progressive cleaving process.
78. The method of claim 75 wherein the surface roughness probe is
capable of performing in-situ measurement of a roughness value of
the surface region after cleaving each free-standing thick film
from the bulk material.
79. The method of claim 78 wherein the cleaving process may
continue, if the roughness parameter meets a pre-set criterion;
otherwise, the cleaving process is paused for repairing the surface
region.
80. The method of claim 79 wherein the surface region of the bulk
material is repaired at least by one process of ion particle
bombardment, etching, or depositing a smooth layer on the surface
region.
81. The method of claim 59 wherein the utilizing radiation to heat
the surface region comprising using an external radiant heat source
located above the surface region.
82. The method of claim 81 wherein the radiant heat source
comprises a plurality of flash lamps with a controlled power
supply, pulse rate, and spatial distribution.
83. The method of claim 81 wherein the external radiant heat source
comprises one or more sources with slowly varying thermal power
flux rate to heat the surface region of the bulk material with a
less than 20.degree. C. surface-to-bottom temperature
difference.
84. The method of claim 81 wherein the external radiant heat source
comprises one or more sources with rapidly varying thermal power
flux rate to heat the surface region of the bulk material faster
than a thermal conduction time constant for the surface region.
85. The method of claim 84 wherein the source with rapidly varying
thermal power flux rate is a pulsed laser.
86. The method of claim 85 wherein the pulsed laser is a YAG or YLF
Q-switched laser.
87. The method of claim 59 wherein the utilizing particle
bombardment to heat the surface region comprising using a power
flux from an ionic particle beam generated by an implant
device.
88. The method of claim 87 wherein the power flux from an ionic
particle beam can be adjusted by changing a duty factor of the
implant device.
89. The method of claim 88 wherein the duty factor can be adjusted
by an electromagnetic scanning device.
90. The method of claim 59 wherein the utilizing the gas-assisted
conduction between the bottom region and the stage to cool the
bottom region comprising adjusting the gas pressure in the cavity
to control the thermal power transfer.
91. The method of claim 59 wherein the cavity height may range from
3 microns to 200 microns
92. The method of claim 59 wherein the cleaving process to
progressively remove one or more free-standing thick films from the
bulk material comprising introducing a first plurality of particles
to form a defect region within a vicinity of a cleave region at a
first temperature and introducing a second plurality of particles
into the defect region at a second temperature to cause an increase
of stress of the cleave region from a first value to a second
value.
93. The method of claim 92 wherein the first plurality of particles
comprises at least one species of hydrogen, deuterium, or
helium.
94. The method of claim 93 wherein the first plurality of particles
are provided at a dose of 8.times.10.sup.16 per cm.sup.2 and
less.
95. The method of claim 92 wherein the second plurality of
particles comprises at least one species of hydrogen, deuterium, or
helium.
96. The method of claim 92 wherein the second plurality of
particles are provided at a dose of 5.times.10.sup.16 per cm.sup.2
and less.
97. The method of claim 92 wherein the introducing of the plurality
of particles is provided using a linear accelerator process, the
linear accelerator process comprising using a plurality of radio
frequency quadrupole (RFQ) elements and a plurality of drift tube
linear accelerator (DTL) elements or a combination of both to
confine and accelerate said particles.
98. The method of claim 97 wherein the plurality of particles are
provided in an energy ranging from 1 MeV to 5 MeV.
99. The method of claim 92 further comprising a treatment process
after introducing the first plurality of particles and before
introducing the second plurality of particles, the treatment
process comprising a thermal process provided at a temperature of
400 Degree Celsius or higher to render the defect region to be
close to the cleave region and stabilize the defect region.
100. The method of claim 92 wherein the first temperature ranges
from about -100 Degree Celsius to about 250 Degree Celsius.
101. The method of claim 92 wherein the first temperature is less
than about 250 Degree Celsius.
102. The method of claim 92 wherein the second temperature is
greater than about 250 Degree Celsius and no greater than 550
Degrees Celsius.
103. The method of claim 59 wherein the cleaving process to
progressively remove one or more free-standing thick films from the
bulk material further comprising repeatedly producing a plurality
of free-standing thick films of the bulk material with a thickness
greater than about 15 microns and less than 200 microns.
104. The method of claim 103 wherein the cleaving process is a
thermal cleaving process to remove the film.
105. The method of claim 103 wherein the cleaving process is a
controlled cleaving process (CCP) utilizing vertical thermal
gradient to remove the film.
106. The method of claim 105 wherein the vertical thermal gradient
is made using one or more of a group comprising a pulsed laser
system, a pulsed flash lamp, a pulsed ion beam, convection heat
transfer generated, and conduction heat transfer generated.
107. The method of claim 103 wherein the cleaving process is a
controlled cleaving process (CCP) utilizing horizontal
temperature/strain gradient to remove the film.
108. The method of claim 59 wherein the cleaving process to
progressively remove one or more free-standing thick films from the
bulk material further comprising using implant dose gradients to
cause the cleaving preferentially starting at the higher dose.
109. The method of claim 108 wherein the ion implant source may
also be used to create a patterned implant having a high dose
region configured to initiate cleaving alone or upon exposure to
additional energy.
110. The method of claim 59 wherein the cleaving process to
progressively remove one or more free-standing thick films from the
bulk material further comprising performing surface treatment on
the free-standing thick film to remove surface cracks and reduce
the surface roughness of the remaining bulk material.
111. The method of claim 59 wherein the particle bombardment
creates a patterned implant having portions of sufficiently high
dose to initiate cleaving alone or upon application of thermal
energy.
112. The method of claim 59 wherein the mechanical clamp engages a
groove in a homogenous portion of the bulk material, or engages a
groove in an adapter plate in contact with the homogenous
portion.
113. A method for processing semiconductor materials for thick film
transfer, the method comprising: providing a bulk semiconductor
material onto a planar surface of a stage, the bulk semiconductor
material having a surface region, a side region, and a bottom
region, the side region, bottom region, and the surface region
providing a volume of material, the volume of material having a
length defined between the bottom region and the surface region,
the bottom region coupled to the planar surface; securing the bulk
semiconductor material using a mechanical clamp device adapted to
engage the bottom surface of the bulk material to the planar
surface of the stage such that the bulk material is in physical
contact with the planar surface to cause thermal energy to transfer
between the bulk material and the planar surface of the stage while
the surface region of the bulk material is substantially exposed;
and processing the surface region of the bulk material while the
surface region is substantially exposed and maintained on the
planar surface of the stage with the mechanical clamp device.
114. A method for progressively cleaving free-standing films from a
bulk material, the method comprising: securing the bulk material on
a stage using a mechanical clamp device, the bulk material having a
surface region, a side region, and a bottom region, the surface
region being continuous with the side region and oriented at an
angle of about 90 Degrees from the side region to define a volume,
the mechanical clamp device being adapted to couple with the bottom
region and/or the side region of the bulk material so that the
bottom region is firmly engaged with the stage; maintaining the
surface region substantially free from any physical interference in
a direction normal to the surface region; processing at least the
surface region while the surface region is substantially free from
any physical interference from the processing of the surface
region; and selectively maintaining a temperature of the surface
region during the processing of the surface region.
115. The method of claim 114 wherein bulk material comprises at
least one of single crystalline silicon or germanium ingot,
polycrystalline silicon tile, multi-crystalline silicon tile, or
compound semiconductor ingot or tile.
116. The method of claim 114 wherein the stage comprises a planar
surface for firmly engaging the bottom region of the bulk material
through a seal between the planar surface and the bottom
region.
117. The method of claim 116 wherein the seal is a close-looped
gas-tight seal capable of forming a gas-filled cavity between the
stage and the bottom region.
118. The method of claim 116 wherein the planar surface of the
stage comprises a plurality of gas passageways connected to a gas
supply assembly in the stage.
119. The method of claim 116 wherein the stage is an electrostatic
chuck capable of generating electrostatic force to attract the bulk
material.
120. The method of claim 114 wherein the mechanical clamp device
are engaged with the bulk material through one or arms at location
at least below 30% length of the side region from the bottom region
or at the bottom region.
121. The method claim 120 wherein the one or more arms have smooth
surfaces adapted to the shape of the bulk material.
122. The method of claim 114 wherein the stage and the mechanical
clamp device are both mounted on a tray that allows X-Y two
dimensional move parallel to the stage.
123. The method of claim 114 wherein maintaining the surface region
substantially free from any physical interference in a direction
normal to the surface region comprising exposing 100% area of the
surface region including all edges for processing.
124. The method of claim 114 wherein processing at least the
surface region while the surface region is substantially free from
any physical interference from the processing of the surface region
further comprising an implant process by introducing a plurality of
particles to form a defect region within a vicinity of a cleave
region with a desired depth underneath the surface region.
125. The method of claim 124 wherein processing at least the
surface region while the surface region is substantially free from
any physical interference from the processing of the surface region
further comprising performing thermal treatment and controlled
cleaving to remove a first film from the cleave region out of the
bulk material.
126. The method of claim 125 wherein processing at least the
surface region while the surface region is substantially free from
any physical interference from the processing of the surface region
further comprising repeating the implant process and cleave process
to remove a second or more films out of at least 70% volume of the
bulk material without any physical interference.
127. The method of claim 114 wherein selectively maintaining a
temperature of the surface region during the processing of the
surface region comprising maintaining a temperature at either the
surface region, at the overlying film above the cleave region, or
at the both.
128. The method of claim 114 wherein selectively maintaining a
temperature of the surface region during the processing of the
surface region comprising increasing the temperature of the surface
region by utilizing at least one of radiation from implant ionic
particles, one or more external radiant source including CW source
or pulsed heat source, Joule heat passed from the clamp device, or
decreasing the temperature by cooling the bottom region of the bulk
material via gas-assisted conduction from the bottom region to the
stage.
129. A system for processing bulk materials, the system including a
mechanical clamp device adapted to secure a bulk material on a
stage, the bulk material having a surface region, a side region,
and a bottom region, the surface region being continuous with the
side region and oriented at an angle of about 90 Degrees from the
side region to define a volume, the mechanical clamp device being
adapted to couple with the bottom region and/or the side region of
the bulk material so that the bottom region is firmly engaged with
the stage, while the surface region is maintained substantially
free from any physical interference in a direction normal to the
surface region, the system including one or more computer readable
memories, the computer readable memories including: one or more
codes directed to initiating a program to process at least the
surface region while the surface region is substantially free from
any physical interference from the processing of the surface
region; and one or more codes directed to selectively maintaining a
temperature of the surface region during the processing of the
surface region.
130. The apparatus of claim 26 wherein the linear accelerator
comprises a DC linear accelerator.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The instant nonprovisional patent application claims
priority to U.S. Provisional Patent Application No. 60/886,912,
filed Jan. 26, 2007, and which is incorporated by reference in its
entirety herein for all purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to techniques
including methods and apparatuses for manufacturing materials. More
particularly, the present methods and apparatuses include a
temperature control for cleaving free-standing thick films from
material in bulk form, such as a silicon ingot. Such free-standing
thick films are useful as a photovoltaic material such as a solar
cell. But, it will be recognized that embodiments in accordance
with the present invention have a wider range of applicability; it
can also be applied to other types of applications such as for
three-dimensional packaging of integrated semiconductor devices,
photonic devices, piezoelectronic devices, flat panel displays,
microelectromechanical systems ("MEMS"), nano-technology
structures, sensors, actuators, integrated circuits, semiconductor
substrate manufacturing, biological and biomedical devices, and the
like.
[0003] From the beginning of time, human beings have relied upon
the sun to derive almost all useful forms of energy. Such energy
comes from petroleum, radiant, wood, and various forms of thermal
energy. As merely an example, human beings have relied heavily upon
petroleum sources such as coal and gas for much of their needs.
Unfortunately, such petroleum sources have become depleted and have
lead to other problems. As a replacement, in part, solar energy has
been proposed to reduce our reliance on petroleum sources. As
merely an example, solar energy can be derived from "solar cells"
commonly made of silicon.
[0004] The silicon solar cell generates electrical power when
exposed to solar radiation from the sun. The radiation interacts
with atoms of the silicon and forms electrons and holes that
migrate to p-doped and n-doped regions in the silicon body and
create voltage differentials and an electric current between the
doped regions. Depending upon the application, solar cells have
been integrated with concentrating elements to improve efficiency.
As an example, solar radiation accumulates and focuses using
concentrating elements that direct such radiation to one or more
portions of active photovoltaic materials. Although effective,
these solar cells still have many limitations.
[0005] As merely an example, solar cells rely upon starting
materials such as silicon. Such silicon is often made using either
polysilicon and/or single crystal silicon materials. These
materials are often difficult to manufacture. Polysilicon cells are
often formed by manufacturing polysilicon plates. While these
polysilicon plates may be formed in a cost effective manner, they
do not exhibit the highest possible efficiency in capturing solar
energy and converting the captured solar energy into usable
electrical power. By contrast, single crystal silicon (c-Si)
exhibits suitable properties for high grade solar cells. Such
single crystal silicon is, however, expensive to manufacture and
difficult to use for solar applications in an efficient and cost
effective manner. In particular, techniques for manufacturing
single crystal silicon substrates for incorporation into solar
cells involves the separation of single crystal silicon thick films
from a single crystal silicon ingot originally grown.
[0006] From the above, it is seen that improved techniques for the
manufacture of free-standing thick films for integrated circuit
device applications including solar cells, are desirable.
BRIEF SUMMARY OF THE INVENTION
[0007] Embodiments in accordance with the present invention relate
generally to techniques including methods and apparatuses for
temperature control during cleaving free-standing thick films from
material in bulk form, such as a silicon ingot. Such free-standing
thick films are useful as a photovoltaic material such as a solar
cell. But, it will be recognized that the invention has a wider
range of applicability; it can also be applied to other types of
applications such as for three-dimensional packaging of integrated
semiconductor devices, photonic devices, piezoelectronic devices,
flat panel displays, microelectromechanical systems ("MEMS"),
nano-technology structures, sensors, actuators, integrated
circuits, semiconductor substrate manufacturing, biological and
biomedical devices, and the like.
[0008] A free-standing thick film of semiconductor material having
a thickness of 15 .mu.m or greater, may be cleaved from a bulk
material utilizing implantation of an ionic species at a desired
surface temperature. In an embodiment, the cleaving involves
removably holding the bulk material through a seal on a temperature
controlled stage using a mechanical clamp device, then implanting
particles such as ions at a first, lower temperature to create a
cleave region, and then implanting particles such as ions at a
second, higher temperature to enhance stress in the cleave region.
In another embodiment, the seal between the temperature controlled
stage and the bottom of the bulk material creates a thin cavity
capable of filling a gas with adjustable pressure. In yet another
embodiment, by adjusting the gas pressure in the thin cavity the
heat transfer from the surface to bottom of the bulk material and
further the surface temperature for implanting are controlled. In
certain embodiments, the bottom of the bulk material is glued (e.g.
using thermally conductive glue or thermally conductive epoxies) to
a thermal and mechanical adapter plate which can facilitate the
mounting and handling of the bulk material. Depending upon the
particular embodiment, the adapter plate can be slightly larger
than, smaller than, or the same size in cross section as, the bulk
material. In accordance with certain embodiments, the adapter plate
can be reused on other bulk substrates. The resulting cleaved
free-standing thick films of semiconductor material such as single
crystal silicon, are particularly suited for use in the collection
of solar energy.
[0009] In a specific embodiment, the invention provides an
apparatus for temperature control of manufacture of thick film
materials. The apparatus includes a stage comprising a planar
surface for supporting a bulk material to be implanted. The bulk
material includes a surface region, a side region, and a bottom
region. The side region, bottom region, and the surface region
provide a volume of material which has a length defined between the
bottom region and the surface region. The apparatus further
includes a mechanical clamp device adapted to engage the bottom
region of the bulk material to the planar surface of the stage such
that the bulk material is in physical contact with the planar
surface for thermal energy to transfer through an interface region
between the bulk material and the planar surface of the stage while
the surface region of the bulk material is substantially exposed.
Additionally, the apparatus includes a sensor device configured to
measure a temperature value of the surface region. The sensor
device is adapted to generate an input data. Moreover, the
apparatus includes an implant device configured to perform
implantation of a plurality of particles through one or more
portions of the surface region of the bulk material. Furthermore,
the apparatus includes a controller configured to receive the input
data and process the input data to increase and/or decrease the
temperature value of the surface region of the bulk material
through at least the interface region between the planar surface of
the stage and the bottom region of the bulk material.
[0010] In another specific embodiment, the invention provides an
apparatus of mounting a bulk material for manufacture of one or
more thick films. The apparatus includes a stage comprising a
planar surface for supporting the bulk material. The bulk material
includes a planarized surface region, a planarized end region, and
a side region having a length from the surface region to the end
region. The apparatus further includes a mechanical clamp device
adapted to engage the planarized end region of the bulk material
with the planar surface of the stage such that the surface region
and at least 70% length of the side region from the surface region
is substantially exposed and can be cleaved for manufacture of one
or more thick films without interference of the clamp device.
[0011] In yet another specific embodiment, the invention provides a
method for temperature control during a process of cleaving a
plurality of free-standing thick films from a bulk material. The
method includes providing a bulk material for cleaving. The bulk
material includes a surface region, a bottom region, a side region
having a length from the surface region to the bottom region.
Additionally, the method includes clamping the bulk material using
a mechanical clamp device adapted to engage the bottom region of
the bulk material through a seal with a planar surface of a stage
to form a cavity with a height between the bottom region and the
planar surface. The planar surface includes a plurality of gas
passageways allowing a gas filled in the cavity with adjustable
pressure. The method further includes sensing the state of the bulk
material to generate an input data. The input data includes
temperature information at the surface region and the bottom region
and the length of the bulk material between the surface region and
the bottom region. Moreover, the method includes maintaining the
temperature of the surface region by processing at least the input
data and executing a control scheme utilizing at least one or more
of particle bombardment to heat the surface region, radiation to
heat the surface region and gas-assisted conduction between the
bottom region and the stage.
[0012] In still another specific embodiment, the invention provides
a method for processing semiconductor materials for thick film
transfer. The method includes providing a bulk semiconductor
material onto a planar surface of a stage. The bulk semiconductor
material includes a surface region, a side region, and a bottom
region. The side region, bottom region, and the surface region
provide a volume of material which has a length defined between the
bottom region and the surface region. The bottom region couples to
the planar surface of the stage. Additionally, the method includes
securing the bulk semiconductor material using a mechanical clamp
device adapted to engage the bottom surface of the bulk material to
the planar surface of the stage such that the bulk material is in
physical contact with the planar surface to cause thermal energy to
transfer between the bulk material and the planar surface of the
stage while the surface region of the bulk material is
substantially exposed. Moreover, the method includes processing the
surface region of the bulk material while the surface region is
substantially exposed and maintained on the planar surface of the
stage with the mechanical clamp device.
[0013] In still yet another embodiment, the invention provides a
method for progressively cleaving free-standing films from a bulk
material. The method includes securing the bulk material on a stage
using a mechanical clamp device. The bulk material has a surface
region, a side region, and a bottom region. The surface region is
continuous with the side region and oriented at an angle of about
90 Degrees from the side region to define a volume. The mechanical
clamp device is adapted to couple with the bottom region and/or the
side region of the bulk material so that the bottom region is
firmly engaged with the stage. Additionally, the method includes
maintaining the surface region substantially free from any physical
interference in a direction normal to the surface region. The
method further includes processing at least the surface region
while the surface region is substantially free from any physical
interference from the processing of the surface region. Moreover,
the method includes selectively maintaining a temperature of the
surface region during the processing of the surface region.
[0014] According to certain embodiments, the bottom region of the
bulk material opposite to the surface region, can be contacted
thermally and mechanically through an adapter or interface plate.
The bulk material could be secured to such an adapter plate using
glue or other techniques, with an opposing face of the plate
mounted onto the temperature controlled stage. Particular
embodiments of the adapter plate can also allow for clamp mounting.
In such an embodiment, the adapter plate with clamp mounting
eliminates the requirement to clamp the bulk material directly, and
improves utilization of the bulk material by allowing the bulk
material to be cleaved closer to the bottom region.
[0015] Use of an adapter plate according to embodiments of the
present invention could also desirably relax the planarization
tolerances of the bulk material bottom region and thus reduce
costs. For example, under certain conditions the bottom of the
ingot can be slightly uneven. However, this unevenness can be
offset by the attachment between the adapter and susceptor. In
particular, the adapter can have pins or seats to help align the
ingot to it.
[0016] In a specific embodiment, the side of the adapter plate in
contact with the bulk material, can have a recessed region
configured to receive a part of a sealing member. Such a sealing
member can be an o-ring made, for example, of a suitable material
(e.g., Kalrez.TM. by DuPont Performance Elastomers L.L.C.), which
is disposed within a vicinity of an edge region of the adapter
plate. In a particular embodiment, glue can be applied within an
interior region of the edge region, while the o-ring seals and
maintains the glue material within the interior region.
[0017] According to specific embodiments, electrical conductivity
can be provided between the adapter plate and the bulk material.
Seating pins or other types of connection devices can be spatially
disposed within the interior region defined within an o-ring, or
within an interior region of a specific embodiment of a chuck
lacking an o-ring. Such seating pins can electrically and
mechanically couple the bulk material with the adapter.
[0018] Numerous benefits may be achieved over pre-existing
techniques using embodiments of the present invention. In
particular, embodiments of the present invention use a cost
effective linear accelerator device and method for providing a high
energy implant process for layer transfer techniques. Such linear
accelerator device may include, but is not limited to, a drift tube
technique, a Radio Frequency Quadrupole, commonly called RFQ, or
combinations of these, (for example, a RFQ combined with a Drift
Tube Linac or a RFI (RF-Focused Interdigital) Linear Accelerator),
DC accelerators, and other suitable techniques. An example of a
linear accelerator can be found in U.S. Provisional Application No.
60/864,584 commonly assigned, and hereby incorporated by reference
for all purposes. In a preferred embodiment, the present method and
device forms a thickness of transferable material defined by a
cleave plane in a donor substrate. The thickness of transferable
material may be further processed to provide a high quality
semiconductor material for application such as photovoltaic
devices, 3D MEMS or integrated circuits, IC packaging,
semiconductor devices, any combination of these, and others. In a
preferred embodiment, the present method provides for single
crystal silicon for highly efficient photovoltaic cells among
others. In a preferred embodiment, the present method and structure
use a low initial dose of energetic particles, which allows the
process to be cost effective and efficient. Additionally, the
present method and structure allow for fabrication of large area
substrates. It will be found that this invention can be applied to
make thin silicon material plates of the desired form factor (for
example, 50 .mu.m-200 .mu.m thickness with a area size from 15
cm.times.15 cm to upwards of 1 m.times.1 m or more for polysilicon
plates). In an alternative preferred embodiment, embodiments
according to the present invention may provide for a seed layer
that can further provide for layering of a hetero-structure
epitaxial process. The hetero-structure epitaxial process can be
used to form thin multi-junction photovoltaic cells, among others.
Merely as an example, GaAs and GaInP layers may be deposited
heteroepitaxially onto a germanium seed layer, which is a
transferred layer formed using an implant process according to an
embodiment of the present invention. In a specific embodiment, the
present method can be applied successively to cleaving multiple
slices from a single ingot, e.g., silicon boule. That is, the
method can be repeated to successively cleave slices (similar to
cutting slices of bread from a baked loaf) according to a specific
embodiment. In a preferred embodiment, the present invention
provides a clamping and/or holding device and related method for
securing a bulk silicon ingot for mechanical and thermal purposes.
Of course, there can be other variations, modifications, and
alternatives.
[0019] These and other benefits may be described throughout the
present specification and more particularly below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 shows a simplified view of an apparatus for
temperature control of manufacture of thick film materials in
accordance with an embodiment of the present invention.
[0021] FIG. 1A shows a simplified view of a controller included in
the apparatus of FIG. 1 in accordance with an embodiment of the
present invention.
[0022] FIG. 1B shows a more detailed diagram of subsystems in the
computer system included in the controller of FIG. 1A in accordance
with an embodiment of the present invention.
[0023] FIG. 2A shows a simplified cross section view of a bulk
material being held on a stage by a mechanical clamp device via
grooves the side region according to an embodiment of the present
invention.
[0024] FIG. 2B shows a simplified top view of a bulk material with
circular cross section shape being clamped by a mechanical clamp
device according to an embodiment of the present invention.
[0025] FIG. 2C shows a simplified top view of a bulk material with
hexagon cross section shape being clamped by a mechanical clamp
device according to another embodiment of the present
invention.
[0026] FIG. 2D shows a simplified cross section view of a bulk
material being clamped by a mechanical clamp device via a lock
structure at the bottom region according to another embodiment of
the present invention.
[0027] FIG. 2E shows a simplified cross section view of a bulk
material being held on a stage by a mechanical clamp device direct
at side region without a groove according to an embodiment of the
present invention.
[0028] FIG. 2F shows a simplified top view of the bulk material of
FIG. 2E being clamped by a mechanical clamp device direct at side
region without a groove according to an embodiment of the present
invention.
[0029] FIG. 3 shows a simplified view of the bottom region of a
bulk material with a close-looped groove according to an embodiment
of the present invention.
[0030] FIG. 4 shows a simplified cross section view of a bulk
material being held by a clamp on a stage with a sealed cavity
filled with gas between the bottom of the bulk material and the
stage in accordance with an embodiment of the present
invention.
[0031] FIG. 5 shows a simplified flow chart illustrating a method
of temperature control during implantation and cleaving process
according to an embodiment of the present invention.
[0032] FIG. 6-11 are simplified diagrams illustrating a method of
cleaving a free-standing film from a bulk material under
temperature control according to an embodiment of the present
invention.
[0033] FIG. 12 shows a simplified view of a plurality of
free-standing thick films being removed from a bulk material in
accordance with an embodiment of the present invention.
[0034] FIGS. 13A-E show various approaches to securing a bulk
material to a temperature control stage taken by embodiments of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] The present invention relates generally to techniques
including methods and apparatuses for manufacturing materials. More
particularly, the present methods and apparatuses include a
temperature control for cleaving free-standing thick films from
material in bulk form, such as a silicon ingot. Such free-standing
thick films are useful as a photovoltaic material such as a solar
cell. But, it will be recognized that embodiments in accordance
with the present invention have a wider range of applicability; it
can also be applied to other types of applications such as for
three-dimensional packaging of integrated semiconductor devices,
photonic devices, piezoelectronic devices, flat panel displays,
microelectromechanical systems ("MEMS"), nano-technology
structures, sensors, actuators, integrated circuits, semiconductor
substrate manufacturing, biological and biomedical devices, and the
like.
[0036] As used herein, the term "bulk material" can refer to a
predominantly homogenous piece of single crystal or polycrystalline
material standing alone, for example a single crystal silicon boule
or a portion thereof. Alternatively, for purposes of the instant
patent application the term "bulk material" can also refer to the
predominantly homogenous single crystal or polycrystalline material
in conjunction with one or more additional elements, for example
the various adapter plate embodiments described below, as well as
any o-rings or other elements employed to secure such an adapter
plate to the predominantly homogenous single crystal or
polycrystalline material.
[0037] A free-standing thick film of semiconductor material having
a thickness of 15 .mu.m or greater, may be cleaved from a bulk
material utilizing implantation of an ion ionic species at MeV
energy level. In one embodiment, the cleaving involves implanting
ions at a first, lower temperature to create a cleave region, and
then implanting ions at a second, higher temperature to enhance
stress in the cleave region. Cleaving the bulk material in this
manner substantially reduces the amount of semiconductor material
that is conventionally lost to the kerf of a blade or wire cut. The
resulting cleaved free-standing thick film of semiconductor
material, such as single crystal silicon, is particularly suited
for the collection of solar energy.
[0038] For purposes of the following disclosure, a "free-standing
thick film" is defined as a film of material that can maintain its
structural integrity (i.e. not crumble or break apart), without
being in contact with a supporting member such as a handle or
transfer substrate and/or requiring mechanical support from the
supporting member. Typically, thin films (for example silicon films
having a thickness of 5-10 .mu.m and thinner) are unable to be
handled without breaking. Conventionally, such thin films are
manipulated using a supporting structure, which may also be needed
to create the thin film in the first place. Handling of thicker
films (e.g. silicon films having a thickness of 15-50 .mu.m) may be
facilitated by the use of a support, but such a support is not
mandatory. Accordingly embodiments of the present invention relate
the fabrication of free-standing thick films of silicon having a
thickness of greater than 15 .mu.m.
[0039] In order to ensure the free-standing thick films with
thickness up to 150 .mu.m being successfully removed by a
controlled cleaving process from a cleave region created by ion
implantation, a well controlled temperature of the bulk material
may be desirable according to a specific embodiment. Particularly
the optimum temperature control can be achieved by balancing one or
more heat sources and/or sinks of thermal power during the
implantation and cleaving process. Further details of the
temperature control can be found throughout the present
specification and more particularly below.
[0040] Most of the thermal power management involved is CW
(steady-state) thermal power according to a specific embodiment.
The CW power flux sources and/or sinks can be one or more of the
following (i) a temperature-controlled stage with a planar surface
appropriately engaged with the bulk material through a high thermal
conductivity backside contact, i.e., heating or cooling through a
gas-layer interface region; (ii) an IR heating source by forcing a
current to flow through the bulk material volume (such as
electromagnetic inductive heating source); and (iii) floodlight or
other appropriate CW radiant source for heating the surface from
above, and any combinations of the above. Of course, someone of
ordinary skill in the art would recognize other variations,
modifications, and alternatives.
[0041] In a specific embodiment, the purpose of these CW sources or
sinks will be to set the desired range of the treatment zone of the
bulk material, defined as the cleave region and the silicon layer
overlying the cleave region, as accurately and quickly as possible.
These thermal sources or sinks can be controlled through surface
and bulk temperature measurement via electronic controller to
achieve the desired overall thermal profile for the treatment zone.
Of course, someone of ordinary skill in the art would recognize
other variations, modifications, and alternatives.
[0042] An additional thermal power source is the implant
irradiation itself according to a specific embodiment. A
conventional implant device may deliver 50-100 kW of beam power to
the surface under irradiation. This is a substantial additional
heating source during the cleave region formation by implantation.
The cleave region essentially includes relatively concentrated
defect networks around a cleave plane located near the End-Of-Range
(EOR) of the implanted high energy ionic particles high energy
ionic particles where the kinetic energy of the implanted particles
is partially transferred to thermal energy. This thermal source can
be a scanned CW or pulsed thermal source and can be partially
controlled by adjusting the duty factor of the implant device and
the scanning speed and spatial characteristics of the particle
beam. Beam expansion can occur by rapid electromagnetic scanning
but can also occur through drift of the beam over a distance where
the beam will naturally expand to the desired beam diameter and
beam flux spatial distribution.
[0043] If the power flux is low enough, slow scanning (or even no
scanning) of the expanded beam can occur without surface
overheating. With a smaller beam diameter such as 5 cm for example
(which is useful for generating patterned implant dose profiles
within each tile), the power flux can be as high as 5-10
kw/cm.sup.2 and may require magnetic or electrostatic fast scanning
to avoid surface overheating. Implant radiation can be combined
with other forms of energy according to a specific embodiment.
[0044] Furthermore, the surface can also be treated through a
pulsed thermal power flux in a specific embodiment. Pulsed power is
defined here as a thermal pulse delivered within a thermal time
constant depending on particular material and film thickness to be
cleaved. For example, for a typical silicon treatment zone, the
time constant is estimated to be 20-50 .mu.sec. Longer thermal
pulses are quasi-CW and would be combined as a CW source mentioned
above. The pulsed power flux sources may include flash lamps and
pulsed laser sources with energies deposited within 30-50 .mu.sec.
The thermal pulses delivered by these sources can instantaneously
heat the treatment zone up to and past the melting point of the
bulk material if desired.
[0045] The effect contemplated by this treatment is to add shear
stresses onto the cleave region under formation to lower its cleave
energies. More specifically, because the thermal conductivity
within an implant EOR is significantly degraded, a temperature
difference is generated across the cleave plane. The temperature
differential causes a CTE (coefficient of thermal expansion)
mismatch between the materials across the cleave plane and a
corresponding shear stress. The shear stress adds to internal
stress present due to the way of holding the bulk material on the
stage and other stress such as silicon displacement stresses.
[0046] The stresses are in-plane stresses (along the X-Y surface of
the cleave plane) and if the cleave plane is heated, the stresses
are compressive in-plane stresses. These in turn produce
out-of-plane tensile stresses in an amount proportional to the
in-plane stress multiplied by the Poisson Ratio (about 0.27 for
silicon). This stress value can be quantified by the following
relation:
.sigma.=E.alpha..DELTA.T
where .sigma. is the stress across the cleave region, E is Young's
Modulus, .alpha. is the coefficient of thermal expansion and
.DELTA.T is the temperature difference across the cleave plane.
Assuming a thermal power flux density of P.sub.a in Watts/cm.sup.2,
the following relationship holds:
P.sub.a=.kappa..sub.cr.DELTA.T/t.sub.cr
where .kappa..sub.cr is the effective thermal conductivity of the
cleave region and t.sub.cr is the thickness of the cleave region.
The stress across the film can be further expressed as following
equation:
.sigma.=(E.alpha.t.sub.crP.sub.a.beta.)/.kappa..sub.bulk
where .beta. is the conductivity reduction factor for the cleave
region relative to the bulk material. Therefore, the stress value
is driven by the power flux P.sub.a and increases with a reduced
thermal conductivity in terms of a factor .beta. which depends on
the amount of implant EOR damage. For example, if the bulk material
is a Silicon ingot, .beta. may be as large as 100.
[0047] The treatment by using the pulsed power flux to increase
shear stress may effectively lower the implant dose required to
facilitate the cleaving process and simultaneously help anneal bulk
radiation defects. Of course, there can be other variations,
modifications, and alternatives.
[0048] FIG. 1 shows a simplified diagram of an apparatus of
temperature control for manufacture of the thick film materials in
accordance with an embodiment of the present invention. This figure
is merely an example, which should not unduly limit the scope of
the claims. One of ordinary skill in the art would recognize many
variations, alternatives, and modifications. As shown in FIG. 1,
apparatus 100 for temperature control includes a stage 120, a
mechanical clamp device 130, an implant device 140, a sensor device
150, and a controller 160. The stage 120 with a planar surface 122
is used to support the bulk material 110 to be cleaved. The bulk
material 110 to be implanted and cleaved can be characterized by a
surface region 112 including the treatment zone consisting of the
cleave plane 115 and the overlying film of undetached silicon
material 113, a side region 117, a bottom region 118, a length 111
defined from the surface region 112 to the bottom region 118. More
details about the bulk material for processing will be described
later.
[0049] As shown in FIG. 1 in one embodiment, the planar surface 122
of the stage 120 is engaged with the bottom region 118 of the bulk
material 110, utilizing a mechanical clamp device 130. The clamping
by the mechanical clamp device 130 is removably applied in such a
way that the surface region 112 as well as the side region 117 with
at least 70% of the length 111 (from the surface region) of the
bulk material are substantially exposed and ready to be cleaved for
manufacture of one or more free-standing thick films. For example,
optional clamping mechanisms according to certain embodiments are
illustrated in FIGS. 2A-2F. In one embodiment, both the stage 120
and the mechanical clamp device 130 may be mounted on a tray 170
that is two-dimensionally movable in a plane parallel to the planar
surface 122 of the stage. In another embodiment, the stage 120 is
used for temperature control of the bulk material as one of the CW
power flux source or sink. By heating or cooling the engaged bottom
region 118 of the bulk material via a high thermal conductivity
gas-layer interface region between the bottom region of the bulk
material and the planar surface of the stage, the stage 120 is
capable of changing the thermal flux 148 from the surface region
112 during the cleaving process. Alternatively, an inductive Joule
heating source can be applied in the apparatus 100 by forcing a
current through the bulk material 110 volume via the mechanical
clamp device 130.
[0050] Referring to the FIG. 1, the implant device 140 is used to
form a cleave region 115 by introducing ionic particles in MeV
energy level with a certain power flux 145 to the surface region
112 of the bulk material. The implant device 140, due to the power
flux 145 from particle bombardment on the surface region, also can
be used for temperature control by adjusting the duty factor of the
implant device 140 to tune the particle power flux. In one
embodiment, one or more CW thermal sources 141 such as floodlight
located above the surface region can be used to provide additional
controllable radiant heat flux 146. In another embodiment, one or
more pulsed power flux source 142 can also be used to provide
pulsed thermal flux towards the surface region 112 or specifically
to the cleave region (from the side region) to add shear stress to
facilitate cleaving.
[0051] The sensor device 150 comprises a plurality of sensors
including temperature sensor, position sensor, pressure sensor, and
surface roughness probe. At a given time point when the bulk
material 110 is held on to the stage 120 and during the
implantation processes., the sensor device 150 is capable of
collecting all sensor data related to the state of the bulk
material 110 at that time point. The sensor data recorded by the
sensor device will be delivered to the controller 160 and be used
as an input data for executing a feedback/feedforward control
scheme to determine a control routine to change and maintain the
temperature of the bulk material to an recipe value for
implantation and subsequent cleaving process.
[0052] FIG. 1A is a simplified diagram of a controller 160 that is
used to oversee and perform operation of the apparatus 100 of FIG.
1 as well as processing of information according to an embodiment
of the present invention. This diagram is merely an example, which
should not unduly limit the scope of the claims herein. One of
ordinary skill in the art would recognize many other modifications,
alternatives, and variations. As shown, the controller 160 includes
control electronics 162 which links a computer system 170.
[0053] In a specific embodiment, the controller 160 uses the
control electronics 162 to execute plurality of control functions.
For example, the control electronics 162 includes multiple
electronic boards or function cards. Each of those boards may be
respectively adapted to couple the stage 120 to perform temperature
control function, to couple the mechanical clamp device 130 to
clamp or unclamp the bulk material 110, to couple the implant
device 140 for implantation process, to couple external heat source
(such as CW source 141 and pulsed source 142) for both temperature
control and assisting the cleave process, and to couple the sensor
device 150 to receive the information related to current state of
the bulk material and generate an input data packet for the
computer system 170.
[0054] In another specific embodiment, the computer system 170 may
be a Pentium.TM. class based computer, running Windows.TM. NT
operating system by Microsoft Corporation. However, the computer
system is easily adapted to other operating systems and
architectures by those of ordinary skill in the art without
departing from the scope of the present invention. FIG. 1B is a
more detailed diagram of hardware elements in the computer system
170 of FIG. 1A according to an embodiment of the present invention.
This diagram is merely an example, which should not unduly limit
the scope of the claims herein. As shown, the computer system 170
is configured to receive the input sensor data via an I/O
controller 171, to process the data in a plurality of control codes
165, 166, 167, running in a central processor 173, and to send the
output control commands/instructions back to the control
electronics via I/O controller 171. Each of the plurality of
control codes is specifically designed for certain control
functions in the apparatus 100. For example, the control code 165
running in the computer system 170 may be a program for controlling
the operation of the implant device to deliver certain high-energy
ionic particle beams towards the surface region of the bulk
material. In another example, the control code 166 may be a program
to generating a sample handling procedure to be performed by the
mechanical clamp device or a sample monitoring scheme to be
executed by the sensor device. In yet another example, the control
code 167 may be a program capable of generating output commands for
cooling of the stage, adding Joule heat through the clamp, and/or
heating the surface by the external heat sources etc. Of course,
one of ordinary skill in the art would recognize many other
modifications, alternatives, and variations.
[0055] In specific embodiments, all the hardware elements or
subsystems of the computer system 170 are interconnected via a
system bus 175. For example, subsystems such as a printer 174,
keyboard 178, fixed disk 179, monitor 176, which is coupled to
display adapter 176A, and others are shown. Peripherals and
input/output (I/O) devices, which couple to I/O controller 171, can
be connected to the computer system by any number of means known in
the art, such as serial port 177. For example, serial port 177 can
be used to connect the computer system to an external interface 180
such as a modem, which in turn connects to a wide area network such
as the Internet, a mouse input device, or a scanner. The
interconnection via system bus 175 allows central processor 173 to
communicate with each subsystem and to control the execution of
instructions from system memory 172 or the fixed disk 179, as well
as the exchange of information between subsystems. Other
arrangements of subsystems and interconnections are readily
achievable by those of ordinary skill in the art. System memory,
and the fixed disk are examples of tangible media for storage of
computer programs, other types of tangible media include floppy
disks, removable hard disks, optical storage media such as CD-ROMS
and bar codes, and semiconductor memories such as flash memory,
read-only-memories (ROM), and battery backed memory.
[0056] Although the above has been illustrated in terms of specific
hardware features, it would be recognized that many variations,
alternatives, and modifications can exist. For example, any of the
hardware features can be further combined, or even separated. The
features can also be implemented, in part, through software or a
combination of hardware and software. The hardware and software can
be further integrated or less integrated depending upon the
application. Further details of the functionality of the present
invention can be outlined below according to the Figures.
[0057] FIGS. 2A and 2B show simplified views of a bulk material
being held on a stage by a mechanical clamp device via grooves the
side region according to an embodiment of the present invention.
These figures are merely examples, which should not unduly limit
the scope of the claims. One of ordinary skill in the art would
recognize many variations, alternatives, and modifications. The
bulk material 110A may be pre-processed, in addition to have a
surface region planarized for facilitating implantation, to have
one or more grooves on the side region configured to receive the
mechanical clamp device so that the bulk material can be securely
held on the stage 120A. FIG. 2A shows a simplified side view of a
groove surrounding the peripheral side region and two clamping arms
of the mechanical clamp device adapted to the grooves to clamp the
bulk material. FIG. 2B shows a simplified top view of the same bulk
material as shown in FIG. 2A being clamped, assuming that the bulk
material has a circular cross-sectional shape.
[0058] In accordance with an embodiment of the present invention,
the bulk material 110A may be prepared to have a desired length
from the surface region to the bottom region. As shown in FIG. 2A,
in a specific embodiment, the positions of the bulk material 110A
being clamped by the mechanical clamp device 131 are located (on
the side region) near the bottom region so that at least 70% part
of the bulk material, including the surface region and the side
region in at least 70% of length from the surface region, is
substantially exposed for processing without the interference of
the mechanical clamp device. The length of the bulk material,
depending on the material type, may be pre-determined based on the
capability of handling the thermal mass and heat transfer by a
particular apparatus 100. The length of the bulk material also
determines, depending on the film thickness, how many free-standing
films can be yielded from cleaving the bulk material.
[0059] For example, the bulk material 110A may be a single crystal
silicon ingot that exhibits an original length of 5 cm and has
lateral dimensions of 15 cm.times.15 cm (with a weight of about 3
kg). In one embodiment, cleavage of about 70% of the length of such
an ingot, utilizing techniques according to embodiments of the
present invention, may produce 350 free-standing single crystal
silicon films, each having a thickness of 100 .mu.m. As 1 m.sup.2
represents about 45 tile surfaces with an area of 15 cm.times.15
cm, about 7.8 m.sup.2 surface area of silicon can be produced from
70% of such a 5 cm thick ingot. In another embodiment, cleavage of
about 70% of the length of such an ingot may produce 1750
free-standing single crystal silicon films having a thickness of 20
.mu.m. In this embodiment about 39 m.sup.2 of silicon can be
produced from 70% of a 5 cm thick ingot. The remaining 30% of the
ingot not cleaved to form single crystal silicon, can be returned
to the melt as highly purified starting material to produce a fresh
ingot for cleaving.
[0060] In a specific embodiment, the bulk material 110A can be a
single crystal silicon ingot, a polysilicon cast wafer, tile, or
substrate, a silicon germanium wafer, a germanium wafer, a
substrate of group III/V materials, group II/VI materials, gallium
nitride, silicon carbide or the like. In a specific embodiment, the
bulk material can be a photosensitive material. The single-crystal
silicon can be either from solar, semiconductor or metallic grade
purity levels, depending upon tradeoffs sought between factors such
as efficiency, cost, and post-processing such as impurity
gettering.
[0061] Any of the single-crystal material can be cut to specific
orientations that offer advantages such as ease of cleaving,
preferred device operation or the like. For example, silicon solar
cells can be cut to have predominantly (100), (110), or (111)
surface orientation to yield free-standing substrates of this type.
Of course, starting material having orientation faces which are
intentionally mis-cut from the major crystal orientation can be
also prepared. Of course there can be other variations,
modifications, and alternatives.
[0062] In accordance with an embodiment of the present invention,
the bulk material 110 may be prepared to have a plurality of cross
sectional shapes based on the manufacture setup and material type.
Accordingly, the clamping setup or mechanism can be varied or
modified, provided that the surface region and majority of the side
region of the bulk material can be processed without interference
of the mechanical clamp device and the remaining bulk material can
be released from the clamp device after certain cleaving process
ends. For example, two arc shaped clamping arms located in opposite
sides are shown in FIG. 2B for the circular cross section shape. In
another embodiment, a single arc arm with longer length may be used
for the removable clamping. In yet another embodiment, three or
more arc arms with shorter length and alternative locations may be
used for the removable clamping. FIG. 2C shows a simplified top
view of a bulk material 110B with a hexagon cross section shape
being removably clamped by three rectangular shaped clamping arms
132 adapted to the three notches 103 on the side region. FIG. 2D
shows a simplified side view of a bulk material 110C being held on
a stage 120B by a mechanical clamp device 133 via a lock structure
104 from the bottom region. The clamping arm 133 may be used as a
key-like structure. The clamp arm 133 can be inserted into the lock
structure built in the bottom region of the bulk material 110C,
then rotated certain degree to a position to hold or lock the bulk
material 110C securely. Of course there can be other variations,
modifications, and alternatives.
[0063] Still in accordance with an embodiment of the present
invention, as shown in FIGS. 2E and 2F, the bulk material 110D such
as silicon ingot in its natural form without any preprocessed
grooves or notches can be clamped by two or more C-shaped
mechanical clamp devices 134 and fixed on top of a stage 120C. The
clamping positions are located near the lower half (for example, at
less than 30% of the length measured from the bottom region) of the
side region. In one embodiment, this clamping position allows that
100% of the surface region of the bulk material 110D is exposed and
available for process without physical interference from the clamp
device. Specifically, 100% utilization of the surface region for
thick film cleaving out of the silicon ingot for photovoltaic
device is one of advantages provided by the present invention.
Additionally, in another embodiment, the clamping mechanism is
aimed to allow the cleave process can be performed progressively to
remove the thick films one by one from major portion of volume (for
example, at least 70%) of the bulk material. In yet another
embodiment, the clamping mechanism is using friction force to hold
the bulk material 110D on the stage 120C. The thermal expansion
coefficient for the mechanical clamp device may be bigger than that
of the bulk material so that when the bulk material is processed at
an elevated temperature or certain heat flux is passed through the
clamp towards the bulk material the thermal expansion causes the
clamping even tighter. In yet another embodiment, the clamp arms
are adapted to match the shape of the bulk material to be clamped
and have no sharp protrusion on surfaces so that the clamping
engagement with the bulk material does not cause cracking on the
side region due to strong clamping force applied.
[0064] In accordance with an embodiment of the present invention,
the bulk material may be pre-processed to have a planarized surface
region where the implant process will start with and a smooth
bottom region where the stage may engage with. As shown in FIG. 3,
the bulk material may be additionally processed to have a
close-looped groove 114 located in the smooth bottom region 118. As
an example, the bulk material is assumed to have a square cross
section shape. In one embodiment, the groove 114 is also in
substantially square shape and located along the vicinity of the
edge of the bottom region 118. In another embodiment, the groove
114 is capable of receiving a adapted gas-tight seal as the bottom
region 118 of the bulk material 110E is engaged with the planar
surface of the stage (assisted with the mechanical clamp device).
The gas-tight seal and the two engaged planar surfaces between the
bottom region of the bulk material 110E and the stage creates a
cavity that can be filled with a layer of gas. The layer of gas,
depending on the pressure, can greatly increase the thermal
conductivity between the bottom region of the bulk and the stage.
In yet another embodiment, once a certain gas-supply assembly is
built in the stage this gas-assisted conduction effectively turns
the stage, that is used to support the bulk material by engaging
its bottom region, into a temperature controlled stage.
[0065] FIG. 4 shows a simplified cross section view of a bulk
material being clamped on a temperature controlled stage in
accordance with an embodiment of the present invention. This figure
is merely an example, which should not unduly limit the scope of
the claims. One of ordinary skill in the art would recognize many
variations, alternatives, and modifications. As shown in FIG. 4 the
bulk material 110 is clamped with its bottom region 118 being held
on to the surface 121 of the stage 120 with a gas-tight seal 122
inserted between the bottom region 118 and the surface 121 of the
stage 120. The gas-tight seal 122 adapted to the first groove 114
in the bottom region 118 creates a cavity 124 with the bottom
region 118 and the surface 121 of the stage 120 respectively as its
top and bottom boundaries. The stage 120 further includes a
plurality of gas passageways 126 on the surface 121 within the
cavity 124 enclosed by the gas-tight seal 122. The plurality of gas
passageways 126 are connected within the body of stage 120 through
a gas supply assembly (not shown) having a gas inlet 128 and a gas
outlet 129 so that a gas 127 with a certain pressure can fill in
the cavity 124.
[0066] In one embodiment, the gas-tight seal 122 can securely
maintain high pressure in the cavity 124 up to 20 Torr for a 6-inch
silicon wafer or up to 300 Torr for a thick silicon ingot or tile
with a weight of about 3 kg. Outside the cavity, the bulk material
may be located in a vacuum system under a pressure around
5.times.10.sup.-7 Torr. In one example, the gas-tight seal 122 may
be an O-ring. In another example, the gas-tight seal 122 may be a
flange made of dielectric material or metal material. The gas 127
may be a cryogenic gas or a room temperature gas or a heated gas.
In one example, the gas 127 may be at least one gas of helium,
hydrogen, argon, or nitrogen.
[0067] In one embodiment, a mechanical clamp device 130 adapted to
the second groove 116 in the side region of the bulk material is
applied to clamp the bulk material 110 on the surface 121 of the
stage 120. In another embodiment, the clamp device 130 may comprise
a metal body with designed strength to securely hold the bulk
material with certain weight plus the upward force due a pressure
difference between the surface region with a vacuum environment and
the bottom region under the backpressure within the cavity. For
example, a 200 Torr cooling gas backpressure in the cavity 124 used
while the bulk material in undergoing implantation within a vacuum
environment would produce about 135 lbs of force. Clamp device 130
would therefore have to hold the bulk material against such upward
forces.
[0068] In certain embodiment, the stage 120 is a electrostatic
chuck containing a dielectric body embedded with a metal plate
electrode. By applying a voltage between the metal plate electrode
and the bulk material 110, an electrostatic force may be generated
to attract the bulk material 110 on the stage 120. In one
embodiment, when smaller backpressures up to about 25 Torr is
gauged in the cavity 124, the mechanical clamp device 130 may be
eliminated and replaced if such an electrostatic chuck is used.
Alternatively, both the clamp device 130 and a stage with
electrostatic chucking can be used. Additionally, both the
mechanical clamp device 130 and the stage 120 are mounted on a tray
base 190. The tray base itself is capable of moving
two-dimensionally in a X-Y plane that is parallel to the planar
surface 121. Of course there can be other variations,
modifications, and alternatives.
[0069] In another embodiment, the clamp device 130 can also be used
as an electric contact means to add IR heating to the bulk material
110 according to an embodiment of the invention. An electric source
138 develops a joule heating due to a current I passing the bulk
material. The heating level is equal to I.sup.2R where R is the
resistance of the material based on its resistivity, material
dimensions and contact geometry.
[0070] Adjustment of the pressure of the gas 127, through the gas
supply assembly (not shown) built in the stage 120, can result in
temperature control in the apparatus 100. Gas molecules bounce
between the bottom region 118 and the planar surface 121 of the
stage, transferring energy between the surfaces. For certain bulk
material, stage dielectric material, and gas type, a gas surface
accommodation coefficient is about fixed. For a fixed height of
cavity 124 the higher the gas pressure the higher the thermal
conductivity or better energy transfer between surfaces 118 and
121. For a cavity height less than 10 microns, the gas mean free
path typically still may be larger than the cavity height even with
the high gas pressure, for example 200 Torr. Therefore, on average
the gas molecules may travel between the surfaces 118 and 121
without collision so that energy is not returned to the surface
that it came from, making the most efficient heat transfer between
surfaces 118 and 121. When the gas pressure is reduced with a
controlled rate, the heat transfer is lowered under control and
further the temperature at the surface region 112 can be changed
with control.
[0071] Adjustment of the temperature of the gas supplied further
can result in the temperature control. In one example, the gas 127
can be pre-cooled to cryogenic temperature for accelerated cooling,
providing a downward heat transfer 148 from the surface region to
the bottom region of the bulk material. Alternatively, the gas 127
can be pre-heated to either slow down the cooling or even form an
upward heating flux 148 towards the surface region from the stage.
Essentially, the stage 120 including the gas-layer interface region
can be used as a steady state temperature control device with CW
power flux control for the bulk material. The temperature control
can be provided during an implanting process and/or other like
process.
[0072] In another embodiment, the gas-assisted conduction is
limited by a surface accommodation coefficient that depends on the
physical properties of bottom region of the bulk material and the
stage surface. The surface accommodation coefficient is 1 when the
gas molecules have complete randomizing speed within the cavity,
and when molecules bounce off elastically without energy transfer
between the boundaries of the cavity. In one example, a typical
value of this coefficient is about 0.3 for silicon surface and a
stage surface made of dielectric material.
[0073] The desired thermal conductivity is depended on the heat
capacity or thermal mass of the bulk material that is being
handled. With a relatively heavy bulk material and a thin cavity
height between the stage and the bottom region of the bulk
material, high pressure of a light gas such as He or H.sub.2 could
be best choice for achieving high thermal conductivity.
Additionally, adjusting the gas pressure could be a very effective
way to control the heat transfer between two solid surfaces. For
example, for a silicon ingot about 5 cm thick, a thermal
conductivity up to 4.times.10.sup.4 Wm.sup.-2K.sup.-1 may be
achieved using a thin cavity of a few microns in height and a gas
pressure up to 300 Torr. This high thermal conductivity achieved
with a relatively high backpressure can only be maintained if the
bulk material is of sufficient mechanical rigidity against
potential upward bending. For the 5 cm thick ingot materials
described in some embodiments (and even after thinning to a final
thickness of 1.5 cm after repeated film detachments), this
requirement is met.
[0074] In the above examples, the bottom of the bulk material could
also be coupled to the temperature controlled face through an
adapter plate to which it is permanently or temporarily fixed. As
described in more detail below, the adapter plate would allow the
mechanical and thermal coupling from the bulk to the heat transfer
plate. Of course, there can be other variations, modifications, and
alternatives.
[0075] Referring back to FIG. 1, another component of the apparatus
100 is the implant device 140. The implant device 140 may be an
independently operated linear accelerator that is capable of
producing ionic particles with high energy, for example 2 MeV or
higher. The linear accelerator may include but is not limited to a
plurality of radio frequency quadrupole (RFQ) elements and/or a
plurality of drift tube linear accelerator (DTL) units and/or the
combination of both. These elements may extract an ion beam from a
microwave ECR ion source then confine and accelerate the ions to a
final desired energy level. The ionic species may comprise
hydrogen, deuterium, or helium species. The particle beam current
can be up to 20 mA and beam size can expanded to nearly 50 cm by a
beam expander (not shown) mounted at the exit aperture of the
implant device 140.
[0076] Of course, one of skilled in the art would recognize many
alternatives, variations, and modifications of the configuration of
the implant device. For example, such implant device has been made
recently available by the use of radio-frequency quadrupole linear
accelerator (RFQ-Linac) or Drift-Tube Linac (DTL) available from
companies such as Accsys Technology Inc. of Pleasanton, Calif., or
RF-Focused Interdigitated (RFI) technology from Linac Systems, LLC
of Albuquerque, N. Mex. 87109, and others.
[0077] Referred again to the FIG. 1, apparatus 100 utilizes the
implant device 140 to introduce a beam of ionic particles in MeV
level to the surface region 112 of the bulk material 110. This
implantation of ionic particles into the bulk material, in
accordance with embodiments of the present invention, may enable a
cleaving process to form free-standing films. The energies depend,
in part, upon the implantation species and conditions. Effectively
for certain energy level of the particle beam, the particles can
reach down to a certain end-of-range (EOR) depth beneath the
surface region 112 and add stress or reduce fracture energy along a
plane at about the EOR depth. These particles reduce a fracture
energy level of the bulk material around EOR depth to form a cleave
region 115 or cleave plane. This allows for a controlled cleave
along the formed cleave region to remove the overlaid film 113 from
the bulk material 110.
[0078] In accordance with embodiments of the present invention, ion
implantation can occur under conditions such that the energy state
of the bulk material at all internal locations is insufficient to
initiate a non-reversible fracture (i.e., separation or cleaving)
in the bulk material. It should be noted, however, that
implantation does generally cause a certain amount of defects
(e.g., micro-detects) in the bulk material that can typically be at
least partially repaired by subsequent heat treatment, e.g.,
thermal annealing or rapid thermal annealing.
[0079] An associated result of the ion implantation may be a
temperature increase of the bulk material around the surface region
and beneath due to the power flux 145 of impinging ion particles.
The output beam from the implant device 140 in apparatus 100 may be
on the order of a few millimeters in diameter. The implantation
application may require the beam diameter to be expanded to the
order of a few hundred millimeters or more in order to keep the
power flux impinging on the target surface from becoming too large
and possibly overheating or damaging the target surface. For a
particular particle beam profile (with certain beam current and
beam size), the temperature rise due to the particle power flux 145
could be also limited by setting a proper duty factor (e.g., 0% is
off, 50% is half power, and 100% is full power) for the implant
device 140. In another embodiment, the moving tray 170 allows the
beam to scan with a certain rate across the surface region 112 so
that the ion beam heating by the flux 145 is time-averaged.
Alternatively, beam scanning alone or in conjunction with movement
of the tray, would allow the beam to be moved across the surface of
the target surface and also allow time-averaging of the beam
flux.
[0080] Both the ion implantation and the associated temperature
rise may be rate limited thermal processes that can be utilized for
the temperature control during the implant and in-situ implant
annealing processes. For example, the apparatus 100 described
earlier may be able to control the ion implantation results in
terms of both the dosage and the substrate temperature rise, to
achieve a desired cleaving plane appropriate for removing
free-standing films from the bulk material.
[0081] Referring again to FIG. 1, the apparatus 100 uses a sensor
device 150 to collect data related to current conditions about the
bulk material. Particularly, the sensor device 150 uses a plurality
of sensors to measure or monitor surface properties of the bulk
material 110, including at least the temperature values at both the
surface region 112 and the bottom region 118 as well as the surface
roughness of the surface region 112. The measurement and monitoring
may be continuous and dynamic during the implant process. The
sensor device 150 may be capable of dynamically generating a set of
input data for any particular process time point.
[0082] The sensor device 150 may include at least five different
types of sensors. A first type are temperature sensors, which may
be placed near the surface region 112 and bottom region 118, and
are capable of measuring the temperatures at the surface region and
the bottom region of the bulk material 110. Temperature sensors may
be used as direct input data for the controller 160 to execute
programmed temperature control routines. Additional temperature
sensors may be placed at the gas inlet 128 to measure the
temperature of supplied gas 127. More temperature sensors may be
needed for measuring temperature at the second groove 116 to
provide input for thermal or electrical conduction through the
clamp device 130. In one example, the temperature sensors can
include contact type such as thermocouples. In another example,
non-contact type temperature sensors such as optical pyrometers may
be used.
[0083] A second type of sensor is the pressure sensor, which may be
placed within the cavity 124 near the bottom region 118 to measure
the pressure of supplied gas 127 therein. The pressure sensor may
sense the pressure of supplied gas that guides the temperature
change of the bottom region 118 using gas-assisted conduction. Such
a pressure sensor, for example a pressure gauge, should be operable
for a wide pressure range or multiple gauges can be used to achieve
the desired pressure measurement range.
[0084] The third type of sensor may be capable of tracking the
weight of the bulk material 110 after each thick film has been
detached by the cleaving processes. The weight of the bulk material
corresponds to a specific heat capacity and thermal resistance,
which in turn determines a thermal time constant useful for
optimizing the temperature control using the temperature controlled
stage 120. Alternative or in conjunction with a weight sensor, a
position sensor or "tile-counter" may be used, which monitors the
surface level change or the current length 111 of the bulk
material, measured from a current surface region 112 to the bottom
region 118, after each progressive cleaving processes.
[0085] A fourth type of sensor is the surface roughness or defect
inspection sensor that provides information of the surface
condition after each cleaving process. Based on this input data the
apparatus 100 is able to determine whether the ingot or tile
surface needs to be relapped, polished or repaired. In an
embodiment, this type of sensor may be able to measure planarity
differences or particle spikes that were caused by certain cleave
failures. This information allows the apparatus 100 to
self-diagnose its ability to continue in full production and
ensures the general quality of the resulting free-standing thick
films.
[0086] A fifth type of sensor may include an acoustic or optical
sensor to capture pre-cleave information of the treatment zone so
that how the cleaving power flux is inducing the onset of
microcracks propagating along the cleave plane, can be monitored.
Additionally, the acoustic emission detected by the sensor, which
is transient elastic waves within a material due to localized
stress release, can be used to throttle the laser pulse energies up
or down during the cleaving process. Such an acoustic sensor works
in the ultrasonic regime, typically within the range between 100
kHz and 1 MHz, but may be down to 1 kHz or up to 100 MHz. Typical
acoustic sensor includes a transducer based on electric,
electronic, electromechanical, or electromagnetic mechanisms.
Alternatively, use of an optical sensor would sense optical changes
in the cleave plane prior or during cleaving to control the onset
and propagation of the cleave process according to a specific
embodiment. Depending upon the embodiment, sensing can occur using
combinations of any of these techniques and others.
[0087] Referring again to FIG. 1, the apparatus 100 further
includes an controller 160 which can be configured to receive and
process the input data generated by the sensor device 150. The
controller 160 also couples to and commands the implant device 140
and the temperature controlled stage 120 to dynamically control the
temperature of the bulk material 110 during the progressive implant
processes useful to produce a plurality of free-standing thick
films. In one embodiment, the controller 160 is configured to
execute a dynamic feedback/feedforward control scheme to determine
the best operation routine. In this control scheme an input data
related to current conditions of the bulk material including
surface temperature, bottom temperature, bulk material weight (or
length), surface roughness, and etc. is processed. Based on a
pre-determined recipe for implantation, in-situ annealing, and/or
subsequent cleaving at any specific time point, the controller
calculates an optimized control routine as an output wherein the
operation instructions are given to adjust duty factor of the
implant device 140 and/or to change the bottom temperature using
the stage 120 by adjusting the backpressure and temperature of the
supplied gas 127 in the cavity 124.
[0088] Additionally, in one example, the controller 160 may be also
coupled to one or more external floodlight heating source 141 above
the surface region to provide extra CW power flux 146 towards the
treatment zone of the bulk material under processing. In another
example, one or more pulsed thermal sources 142 located above the
surface region may be further applied to supply power flux 147 for
annealing or increase surface temperature with rapid ramping rate.
In one embodiment, the pulsed thermal sources 142 can help develop
an efficient cleave region 115 through the introduction of an
energy pulse 149 locally within a thermal time constant of the
treatment zone, roughly 50 microseconds for a 100 .mu.m thick
free-standing film production process. One example of a pulsed
thermal source is a YAG laser pulse system delivering about 0.1-50
joules of energy per cm.sup.2 with a characteristic pulse width of
a few nanoseconds to tens of nanoseconds or more. The fundamental
1.06 .mu.m YAG line would deposit most of the laser thermal energy
within 100 .mu.m required for this application. The cleave region
is expected to efficiently absorb the residual infrared (IR)
radiation reaching there for that the local EOR damage increases
the silicon IR absorption coefficient. The instantaneous
temperature difference across the lower thermal conductivity EOR
region produces a shear stress that can further reduce cleave
energies or even initiate cleave processes.
[0089] As another example, if the laser light is to be mostly
absorbed within the EOR damage in the cleave region (where the
light can impinge onto the cleave region along all angles from the
peripheral side region of the bulk material), the laser pulse
energy will generate a high level of stress after irradiation until
thermal relaxation to the surrounding material. The relaxation time
constant of the cleave region will be on the order of 25
nanoseconds to 20 microseconds or more depending on the implant
energy (which determines the cleave region thickness) and the
effective thermal conductivity of the cleave region. In accordance
with certain embodiments of this invention, heating of the surface
region includes heating of either the EOR cleave region, the
overlying film to be cleaved, or both.
[0090] In yet another example, extra cooling may be contributed by
attaching a water cooling system (not shown) at the bottom of the
stage 120 and by attaching independent heat sink to the mechanical
clamps 130 to enhance conduction. More descriptions of a method of
temperature control during the cleaving processes for removing
free-standing thick films from bulk material will be seen in the
specification below.
[0091] FIG. 5 shows a simplified flow chart illustrating a method
of temperature control during cleaving processes for progressively
removing free-standing films from a bulk material according to an
embodiment of the present invention. This figure is merely an
example, which should not unduly limit the scope of the claims. One
of ordinary skill in the art would recognize many variations,
alternatives, and modifications. The method 200 includes the
following processes:
[0092] 1. Process 210 for preparing a bulk material;
[0093] 2. Process 220 for collecting sensor data related to current
state of the bulk material;
[0094] 3. Process 230 for processing sensor data to determine
control routine and temperature set point;
[0095] 4. Process 240 for executing control routine to reach the
set point;
[0096] 5. Process 250 for performing implant and in-situ annealing
processes at the set point;
[0097] 6. Process 260 for performing cleaving processes (if within
system 100);
[0098] 7. Process 270 for checking length of remaining bulk
material, if less than 30% end process; if not, proceed to next
process; and
[0099] 8. Process 280 for checking surface roughness of bulk
material; if meets criterion set back to process 220 and onwards;
otherwise, set back to process 210 and onwards.
[0100] The above sequence of processes provides a method according
to an embodiment of the present invention. Other alternatives can
also be provided where processes are added, one or more processes
are removed, or one or more processes are provided in a different
sequence without departing from the scope of the claims herein.
Further details of the present invention can be found throughout
the present specification and more particularly below.
[0101] Referring to the FIG. 5, the method 200 first includes a
process step 210 to preparing bulk material for cleaving to produce
free-standing film. In accordance with certain embodiments, the
bulk material may comprise a semiconductor material such as single
crystal silicon, present as grown in the form of a bulk ingot. In
another embodiment, the bulk material may be a large tile of
polycrystalline silicon. In a specific embodiment, the ingot
materials and/or polycrystalline tiles may have a pre-processed
body with a length and a substantially circular or polygonal
cross-section shape. The length of the bulk materials can be
predetermined to facilitate temperature controlled cleaving. For a
bulk material with uniform density, the length is equivalent to its
weight. For example, for crystalline silicon ingot, preferred
length is about 5 cm with a weight about 3 kg.
[0102] In another specific embodiment, preparing the bulk material
for cleaving includes using a variety of planarization processes to
smoothen both the surface region for producing quality device-ready
films and the bottom region for holding onto a stage. In yet
another specific embodiment, preparing the bulk material includes
using a modified high dose energetic ionic particle implant
process, for example the high energy particles generated by the
implant device 140 in the apparatus 100, to collapse the surface
roughness to a lower level. In certain embodiments, preparing the
bulk material also includes lightly etching the surface and/or
depositing a thin smooth layer to reduce the surface roughness. In
certain other embodiments, preparing the bulk material further
includes incorporating the device manufacture processes to deposit
coatings/films such as optical coupling layers, transparent
conductive oxides, and light trapping layers on the surface region
before the cleaving process. For subsequent cleaving, the surface
conditions will be rechecked each time a film is removed from the
bulk material to determine if the surface needs treatment that may
lead to different options for next process step.
[0103] The first process step 210 of the method 200 to prepare the
bulk materials further includes making a first groove on the bottom
region of the bulk material. In a specific embodiment, the first
groove can be a close-looped one which is located near the edge of
the polygonal bottom. The first groove is designed to fit a
gas-tight seal for creating an gas-layer interface when the
smoothened bottom region of the bulk material is engaged with the
planar surface of the stage. Additionally in one embodiment, the
process 210 further includes making a second groove on the
peripheral side region of the bulk material at a pre-determined
position. The position of the second groove typically may be set
below 30% of the length of the bulk material measured from the
bottom so that, at the next step, a mechanical clamp device adapted
to the groove can properly clamp the bulk material from the side
region without interfering the implant or cleaving process
progressively performed up to 70% of the bulk material from the
surface region. In one example, the second groove may be a single
groove surrounding the peripheral side. In another example, there
may be a group of grooves located at various positions around the
bulk material. In another embodiment, the process 210 may include
making a lock structure at the bottom region for, at the next step,
a mechanical clamp device having a key structure to securely lock
the bulk material on the stage from the bottom.
[0104] The first process step 210 of the method 200 to prepare the
bulk materials further includes clamping the bulk material by a
mechanical clamp device using the second groove as a clamp groove.
In an alternative embodiment, the bulk material 110 can be securely
held by the mechanical clamp device from the bottom region via a
lock structure. In a specific embodiment, as shown in FIG. 4, the
bulk material 110 is clamped by a mechanical clamp device 130 and
is held on the stage 120 with the bottom region 118 coupled to the
planar surface 121 of the stage separated only by a gas-tight seal
122. The gas-tight seal 122 is configured to match the first groove
114 to connect the bottom region 118 and the stage surface 121 and
at the same time create a thin cavity 124 between them, with the
bottom region 118 of the bulk material and the planar surface 121
of the stage being the top and bottom boundaries respectively. The
gas-tight seal 122 is secure enough, assisted with the mechanical
clamp device, to hold a high-pressure difference inside/out the
thin cavity 124 formed thereof. In a specific embodiment, the
planar surface 121 of the stage 120 contains a plurality of gas
passageways 126 to allow a gas 127 filled in the cavity 124 with an
adjustable pressure. The gas typically is hydrogen or helium gas
supplied with an assembly built inside the stage 120 with an inlet
128 and an outlet 129. The gas 127 can be at cryogenic or room
temperature. Alternatively the gas can be heated.
[0105] Referring back to FIG. 5, once the bulk material is prepared
and held onto the stage surface, the process step 220 of the method
is performed. In this step, the data related to the current state
of the bulk materials are collected by one or more sensors operated
by a sensor device. For example, the sensor device is shown in FIG.
1 as sensor device 150.
[0106] In one embodiment, the one or more sensors operated by the
sensor device include temperature sensors for measuring temperature
at the surface region, T.sub.s, and the temperature at the bottom
region, T.sub.b. In another embodiment, the one or more sensors
also include a position sensor to track the bulk material history
during the cleaving processes by detecting the surface region
position of the bulk material which in turn provides the current
length or weight information of the bulk material. In yet another
embodiment, the one or more sensors include a pressure sensor to
indicate the pressure within the cavity between the bulk material
bottom region and the stage surface. Collecting the sensor data or
performing certain measurements are carried at any given time point
once the bulk material is prepared at process 210 and till the
final cleaving process is over (except certain cleaving process
criterion is not met that stop the process flow). The collected
sensor data can be sent and processed by a linked controller. For
example, the controller 160 is included within the apparatus 100 as
shown in FIG. 1.
[0107] The process step 230 of the method 200 is to use the
controller to process these sensor data as an input of a
temperature feedback/feedforward control scheme to change the
surface temperature of the bulk material to a desired process
(implantation and/or cleaving) temperature based on a process
recipe. At any specific time point, the recipe determines a set
point for the desired process temperature, T.sub.p, of the bulk
material at the surface region, more specifically within the
treatment zone. Then the input data from the sensors data at the
time point will be received and processed by the controller in the
feedback/feedforward control scheme to determine a best routine to
change the current temperature at the surface region, T.sub.s, to
the target set point, T.sub.p, and/or maintain at that temperature
as desired. The control routine is programmed to keep the control
loop stable to achieve the fastest or at least predetermined
heat/cool rates to reach to the process temperature in the most
efficient manner.
[0108] The process step 240 of the method 200 is then performed to
execute the selected control routine to reach the set point from a
given time point. In an embodiment, the control routine to change
temperature includes both heating and cooling operations utilizing
multiple radiation, convection, and conduction heat transfer paths.
For example, heating is required if the current temperature T.sub.s
is below the set point T.sub.p. In a specific embodiment, as shown
in the simplified diagram of FIG. 6, one or more external radiant
sources 302 such as floodlights can be used to heat the surface
region 301 of the bulk material 300 from above with a CW power flux
326. The controller may be linked to these external radiant sources
through a feedback loop to control the lamp current, on/off
frequency, and spatial contribution to heat the surface with
desired ramp rate and uniformity. External radiant sources may also
include pulsed thermal sources 303 such laser pulsing sources for
annealing and cleave region enhancement through pulsed power flux
327.
[0109] In another embodiment, part of the cleaving process involves
an ion implantation process utilizing high energy particles
generated by an implant device. Power flux 305 of the high-energy
particles bombarded on the surface region 301 tend to heat up the
latter. The controller may be linked to the implant device, for
example the implant device 140 in the apparatus 100, to control the
duty factor, on/off frequency of the operation as well as the beam
size and scanning speed of the particle beam to control the heating
during implantation.
[0110] In yet another embodiment, heat flow 306 can also come from
the bottom region 309 to the surface region 301 by thermal
conduction. The supporting stage 310 may be used to drive or
control the heat transfer by changing the bottom temperature. In
one example, the heat may be supplied through this path for a post
ion implantation annealing process at certain elevated surface
temperature.
[0111] In yet another embodiment, heat flow 306 can also come from
Joule heating, inductive heating or the like. One example is
I.sup.2R heating of the bulk material by passing an electric
current through the bulk material. In one example, the heat may be
supplied through this path for a post ion implantation annealing
process at certain elevated surface temperature.
[0112] In another specific embodiment of the present invention, the
stage may be used predominantly for cooling by lowering the bottom
temperature so that the heating of surface region during the
implantation or cleaving process can be compensated. In other
words, through the same path as shown in the simplified diagram of
FIG. 6, heat flow 307 is now flowing from the surface region 301 to
the bottom region 309. To efficiently lower the bottom temperature
T.sub.b, a cryogenic gas may be supplied into the cavity 315
between the bottom region and the cooled stage surface 311 enclosed
by the gas-tight seal 313. With a pressure as high as 300 Torr in
the thin cavity (e.g., of a few microns) the fast moving gas
molecules collide with the two surfaces can efficiently transfer
thermal energy from the bottom region 309 to the cold stage surface
311. By adjusting the gas pressure, the gas molecules mean free
path can be changed relative to the cavity height to optimize the
heat transfer.
[0113] In most cases, due to large thermal mass of the bulk
material the cooling control time constant by conduction through
the stage is slower than the heating by radiant source or particle
bombardment on the surface region since the EOR region will develop
a progressively lower thermal conductivity upon implant and certain
cleave plane formation anneals and thus this layer will be more
susceptible to surface heating. As the cleaving process continues
progressively, the bulk material length is reduced and so does its
cooling time constant. By utilizing the position sensor data that
tracks the changing length, the controller would be able to update
the time constant and adjust other control paths if necessary. Thus
an updated optimum control routine for the upcoming cleaving
process can be generated.
[0114] In one embodiment, as the bulk material is thinning, the gas
pressure within the cavity may be lowered to reduce the thermal
conductivity to slow down the cooling. In another embodiment, the
control scheme is design to accommodate all the rate processes to
keep the control loop stable and to achieve the fastest or at least
pre-determined heat/cool rates to get the desired process
temperature in a most efficient manner. For example, prior to
implant, if the target bulk material is cold but the recipe calls
for 300.degree. C., a hotter than 300.degree. C. setting may be
used to allow the implant bulk material to reach the 300.degree. C.
at the surface faster with the stage reducing the temperature
earlier than the point being reached, overdriving the temperature
to keep heat/cool cycles as fast as possible.
[0115] Referring back to FIG. 5, once the surface temperature
T.sub.s is reached to the set process temperature T.sub.p, the
process step 250 of the method 200 is performed to start the
implant process. In accordance with particular embodiments of this
present invention, as shown in the simplified diagram of FIG. 7,
the process 250 includes subjecting the surface region 401 of the
bulk material 400 to a first plurality of high-energy particles
405. In accordance with particular embodiments, high energy
particles 405 can be generated using the implant device which may
include a linear accelerator. In-situ anneals that incorporate a
sub-process of set point temperature treatments between implant
sub-steps and post implant anneals can also be made. As with all
other steps in FIG. 5, the steps 220 and 230 can be re-applied
numerous times within the succeeding steps 250 and 260. FIG. 5 is
therefore just an example of a first set point process and not to
be regarded as limiting. Of course there can be other variations,
modifications, and alternatives.
[0116] In a specific embodiment, as shown in the simplified diagram
of FIG. 8, the resulting implantation of the high energy particles
505 causes formation of a plurality of gettering sites or an
accumulation region within a cleave region 503. This cleave region
503 may be provided beneath the surface region 501 to define a
thickness 510 of the bulk material 500 that is to be detached as a
free-standing layer. Preferably, the first plurality of high-energy
particles provide an implant particle profile having a peak
concentration and a base spatially disposed within a depth of the
bulk material. Of course there can be other variations,
modifications, and alternatives.
[0117] In one embodiment, the cleave region is maintained at a
first temperature during the implantation, for example in a range
between about -100.degree. C. and 250.degree. C., which can be
provided directly or indirectly. In one embodiment, the temperature
can be controlled by the apparatus 100. In another embodiment, the
temperature may be controlled by performing process steps 220, 230,
and 240. Of course there can be other variations, modifications,
and alternatives.
[0118] Depending upon the application, according to particular
embodiments, smaller mass particles are generally selected to
decrease the energy requirement for implantation to a desired depth
in a material and to reduce a possibility of damage to the material
region. That is, smaller mass particles more easily travel through
the substrate material to the selected depth without substantially
damaging the material region that the particles traverse through.
For example, the smaller mass particles (or energetic particles)
can be almost any charged (e.g., positive or negative) and or
neutral atoms or molecules, or electrons, or the like. In a
specific embodiment, the particles can be neutral or charged
particles including ions such as ion species of hydrogen and its
isotopes, rare gas ions such as helium and its isotopes, and neon,
or others depending upon the embodiment. Alternatively, the
particles can be any combination of the above particles, and or
ions and or molecular species and or atomic species. The particles
can be derived from compounds such as gases, e.g., hydrogen gas,
water vapor, methane, and hydrogen compounds, and other light
atomic mass particles. The particles generally have sufficient
kinetic energy to penetrate through the surface to the selected
depth underneath the surface.
[0119] For example, using hydrogen as the implanted species, the
implantation process is performed using a specific set of
conditions. Doses of implanted hydrogen can ranges from about
1.times.10.sup.15 to about 1.times.10.sup.16 atoms/cm.sup.2, and
preferably the dose of implanted hydrogen is less than about
8.times.10.sup.16 atoms/cm.sup.2. The energy of hydrogen
implantation can range from about 0.5 MeV to about 5 MeV and
greater, for the formation of thick films useful for photovoltaic
applications. Implantation temperature ranges from about
-100.degree. C. to about 250.degree. C., and is preferably less
than about 400.degree. C. to avoid a possibility of hydrogen ions
diffusing out of the implanted silicon cleave region. The hydrogen
ions can be selectively introduced into the silicon wafer to the
selected depth at an accuracy of about .+-.0.03 to .+-.3 microns.
Of course, the type of ion used and process conditions depend upon
the application.
[0120] In a specific embodiment, a silicon film thickness ranges
from about 15 .mu.m to about 200 .mu.m may be formed using a proton
implant having an energy range of about 1 MeV to about 5 MeV. This
thickness range allows the detachment of a thickness of a
single-crystal silicon that can be used as a free-standing silicon
layer. Free-standing silicon layers having a thickness range of
15-200 .mu.m according to embodiments of the present invention may
be used to replace conventional wafer sawing, etching, or polishing
processes. Thus where a conventional separation technique would be
expected to result in a kerf loss of about 50% (kerf loss as being
defined as the material lost during the cutting and wafering
operations), techniques in accordance with embodiments of the
present invention result in virtually no kerf losses, resulting in
substantial cost savings and improvements in the efficiency of
material utilization.
[0121] In accordance with certain embodiments, implantation
energies higher than 5 MeV may be used. Such high energies of
implantation may be useful to fabricate free-standing layers as
substrates of alternative materials in the fabrication of
semiconductor devices. In the manufacture of solar cells, however,
a free-standing material thickness of 200 .mu.m or less is
generally desired.
[0122] Referring now to FIG. 9, embodiments of the method 200 in
accordance with the present invention may optionally perform a
thermal treatment process on the bulk material 600 to further form
the plurality of gettering sites within the cleave region 603. That
is, the thermal treatment process anneals out and/or quenches the
cleave region 603 to fix the plurality of first particles in place
in a defect network. The thermal treatment provides a fixed network
of defects that can act as efficient sites for gettering and
accumulating particles in a subsequent and/or concurrent
implantation process. In a specific embodiment, this process may be
utilize CW and/or pulsed radiation heat 605 from above the surface
region 601 and the heat conductance 607 from bottom to compensate
for achieving the desired heat treatment temperature. Joule or
inductive heating flow 608 can also be utilized. For example, the
temperature control is performed with the apparatus 100.
[0123] In a specific embodiment, the process 260 of the method 200
further includes subjecting the surface region of the bulk material
to a second plurality of high energy particles, as illustrated in
the simplified diagram of FIG. 9. The second plurality of high
energy particles 705 may be generated using an implant device, for
example the implant device 140 in apparatus 100 which may include a
linear accelerator. As shown, the method includes the second
plurality of high energy particles 705, which are provided in the
bulk material 700. The second plurality of high energy particles
705 are introduced into the cleave region 703, which increases a
stress level of the cleave region from a first stress level to a
second stress level. In a specific embodiment, the second stress
level is suitable for a subsequent cleaving process. In a
particular embodiment, the bulk material is maintained at a second
temperature, for example in a range between about 20.degree. C. and
500.degree. C., which is higher than the first temperature. For
example, the second temperature is controlled by the apparatus 100
and by performing processes 220, 230 and 240. Of course, the type
of ion used and process conditions depend upon the application.
[0124] Using hydrogen as the species implanted into bulk single
crystal silicon material in the second implantation step as an
example, the implantation process is performed using a specific set
of conditions. Implantation dose ranges from about
5.times.10.sup.15 to about 5.times.10.sup.16 atoms/cm.sup.2, and
preferably the dose is less than about 1-5.times.10.sup.17
atoms/cm.sup.2. Implantation energy ranges from about 1 MeV and
greater to about 5 MeV and greater for the formation of thick films
useful for photovoltaic applications. Implant dose rate can be
provided at about 500 microamperes to about 50 milliamperes and a
total dose rate can be calculated by integrating an implantation
rate over the expanded beam area. Implantation temperature ranges
from about 250 Degree Celsius to about 550 Degrees Celsius, and is
preferably greater than about 400 Degrees Celsius. The hydrogen
ions can be selectively introduced into the silicon wafer to the
selected depth at an accuracy of about .+-.0.03 to .+-.3 microns.
In a specific embodiment, the temperature and dose are selected to
allow for efficient conversion of mono-atomic hydrogen to molecular
hydrogen within the cleave region, while there may be some
diffusion of mono-atomic hydrogen. Of course, the type of ion used
and process conditions depend upon the application.
[0125] Specific embodiments of the present method may use a
mass-selected high-energy implant approach, which has the
appropriate beam intensity. To be cost-effective, the implant beam
current should be on the order of a few tens of milliamps of
H.sup.+ or H.sup.- ion beam current. If the system can implant
sufficiently high energies, H.sub.2.sup.+ ions can also be
advantageously utilized for achieving higher dose rates. Such ion
implant apparatuses have been made recently available by the use of
radio-frequency quadrupole linear accelerator (RFQ-Linac) or
Drift-Tube Linac (DTL), or RF-Focused Interdigitated (RFI)
technology. These are available from companies such as Accsys
Technology Inc. of Pleasanton, Calif., Linac Systems, LLC of
Albuquerque, N. Mex. 87109, and others.
[0126] Optionally, specific embodiments of the process 250 of the
method 200 in accordance with the present invention further include
a thermal treatment process after the implanting process. One
particular embodiment uses a thermal process ranging from about 450
to about 600 Degrees Celsius for silicon material. In a preferred
embodiment, the thermal treatment can be performed by at least
partially performing temperature control processes 220, 230, and
240 of the method 200. Of course, there can be other variations,
modifications, and alternatives.
[0127] Referring back to FIG. 5, the cleaving processes can occur
within system 100 where once the surface temperature T.sub.s is
reached to the set process temperature T.sub.p, the process step
260 of the method 200 is performed to start the cleaving process.
Of course there can be other variations, modifications, and
alternatives.
[0128] A specific embodiment of a method in accordance with the
present invention includes a step of freeing the free-standing
layer using a cleaving process, while the free-standing layer is
free from a permanent overlying support member or the like, as
illustrated by FIG. 11. As shown, the free-standing layer 810 is
removed from the remaining bulk material 800. In a specific
embodiment, the step of freeing can be performed using a controlled
cleaving process. The controlled cleaving process provides a
selected energy within a portion of the cleave region. As merely an
example, the controlled cleaving process has been described in U.S.
Pat. No. 6,013,563 titled Controlled Cleaving Process, commonly
assigned to Silicon Genesis Corporation of San Jose, Calif., and
hereby incorporated by reference for all purposes. As shown, the
method in accordance with an embodiment of the present invention
frees the free-standing thickness of the layer from the bulk
material to completely remove the free-standing layer. Of course,
there can be other variations, alternatives, and modifications.
[0129] Certain embodiments of the present invention may employ one
or more patterned regions to facilitate initiation of a cleaving
action. Such approaches may include subjecting the surface region
of the semiconductor substrate to a first plurality of high energy
particles generated from a linear accelerator, to form a patterned
region of a plurality of gettering sites within a cleave region. In
one embodiment of a method according to the present invention, the
cleave region is provided beneath the surface region to defined a
thickness of material to be detached. The semiconductor substrate
is maintained at a first temperature. The method also includes
subjecting the semiconductor substrate to a treatment process,
e.g., thermal treatment. The method includes subjecting the surface
region of the semiconductor substrate to a second plurality of high
energy particles, which have been provided to increase a stress
level of the cleave region from a first stress level to a second
stress level. The method includes initiating the cleaving action at
a selected region of the patterned region to detach a portion of
the thickness of detachable material using a cleaving process and
freeing the thickness of detachable material using a cleaving
process.
[0130] Such a patterned implant sequence subjects the surface to a
dose variation, where the initiation area is usually developed
using a higher dose and/or thermal budget sequence. Propagation of
the cleaving action to complete the cleaving action can occur
using: (i) additional dosed regions to guide the propagating cleave
front, (ii) stress control to guide a depth that is cleaved, and/or
(iii) a natural crystallographic cleave plane. Some or most of the
area may be implanted at a lesser dose (or not implanted at all)
depending on the particular cleaving technique used. Such lower
dosed regions can help improve overall productivity of the
implantation system by reducing the total dose needed to detach
each film from the substrate.
[0131] According to a specific embodiment, generation of the
higher-dosed initiation area can be facilitated by the use of the
implantation beam itself to simultaneously increase the area dose,
while heating the region and preparing the region for localized
film detachment. The detachment can be accomplished in-situ during
the implantation beam process, or after implantation using a
separate thermal process step. Use of a sensor to measure and feed
back the state of the initiation region, may be helpful to allow
precise and controlled localized film detachment and avoid
overheating or damaging the layer immediately after cleaving has
occurred.
[0132] Specific embodiments of the present method can perform other
processes. For example, the method can place the free-standing
layer in contact with a support member, which is later processed.
Additionally or optionally, a method in accordance with an
embodiment of the present invention performs one or more processes
on the bulk material before subjecting the surface region to the
first plurality of high-energy particles. Depending upon the
particular embodiment, the processes can be for the formation of
photovoltaic cells, integrated circuits, optical devices, any
combination of these, and the like. Of course, there can be other
variations, modifications, and alternatives.
[0133] The thickness of the free-standing material may be varied
from 15 microns or less to 200 microns in accordance with the
embodiments of present invention. For example, cleavage of about
70% of the thickness of a silicon ingot utilizing techniques may
produces 350 free-standing single crystal silicon films, each
having a thickness of 100 um. As 1 m.sup.2 represents about 45 tile
surfaces having an area of 15 cm.times.15 cm, a total silicon
surface area of about 7.8 m.sup.2 can be produced from 70% of a 5
cm thick ingot. The thickness of the free-standing material is
further processed to provide a high quality semiconductor material
for application such as photovoltaic devices, 3D MEMS or integrated
circuits, IC packaging, semiconductor substrate manufacturing,
semiconductor devices, any combination of these, and others. One
embodiment of the present method provides for single crystal
silicon for highly efficient photovoltaic cells among others.
Certain embodiments use a low initial dose of energetic particles,
which allows the process to be cost effective and efficient.
[0134] Referring back to the FIG. 5, after each of the
free-standing film is freed from the bulk material the process 270
of the method 200 may be carried out, particularly for producing
one or more free-standing films in production mode. This process
includes reading the position sensor data to determine if the
remaining bulk material is less than 30% of original bulk material.
It also is translated to detect the length of the remaining bulk
material and compare with the stored original length. Once the
sensor reading indicates the length of remaining bulk material is
less than 30%. The controller can send signals to command ending
the process, followed by removing the remaining bulk material. The
remaining 30% of the bulk material not cleaved can be returned to
the melt as highly purified starting material to produce a fresh
bulk material for cleaving. If the position sensor reading
indicates that the remaining bulk material length is more than 30%,
the method 200 leads to the next process step with the remaining
bulk material. In another specific embodiment, the position sensor
may partially provide a new input data related to the thermal
capacity of the remaining bulk material. The new input data can be
processed to determine the updated control routine for the next
process step.
[0135] The next process step 280 of the method 200 includes
checking more sensor data related to the remaining bulk material,
which is also related to the application of the method to
manufacture one or more free-standing films in production mode. In
this process step, surface roughness of the surface region of the
remaining bulk material is inspected. The process 280 includes
utilizing one or more in-situ probes to measure the surface
roughness of the remaining bulk material. The measured surface
roughness parameter (or other properties including surface defects)
may be compared with predetermined criterion. In one embodiment, at
the process 280 the criterion may be met, indicating also the
quality of the cleaved film is acceptable and the remaining bulk
material may be capable of being applied with a new cleaving
process cycle. The process flow of the method 200 may be set back
to the process step 220, followed by the processes 230, 240, 250,
and 260 again.
[0136] In another embodiment, at the process 280 the criterion may
not be met, indicating that the surface after cleaving may need to
be repaired or the bulk material needs to be re-prepared. The
process flow now thus, at least partially, may be set back to the
process step 210 where a surface treatment for the remaining bulk
material may be applied. In one example, which may be relatively
high cost, the surface is performed a re-lapping and/or
re-polishing treatment, i.e., the process flow is fully reset to
process 210. In another example, a less cost process such as using
the ion beam with a increasing dose, or performing an etching of
the surface, or adding a thin smoothing layer by spin-on
deposition, etc. may be performed to collapse the surface roughness
until the criterion is met.
[0137] FIG. 12 shows a simplified schematic view of the formation
of a plurality of free-standing films out of a bulk material in
accordance with one embodiment of the present invention. Single
crystal silicon ingot 900 exhibits an original thickness of 5 cm
and has lateral dimensions of 15 cm.times.15 cm. As the density of
single crystal silicon is about 2.32 gm/cm.sup.3, the weight of
this bulk single crystal silicon material is
15.times.15.times.5.times.2.32=2.61 Kg. Thus, cleavage of about 70%
of the thickness of such ingot 900 utilizing techniques according
to embodiments of the present invention, produces 350 free-standing
single crystal silicon films 910, each having a thickness of 100
.mu.m. As 1 m.sup.2 represents about 45 tile surfaces having an
area of 15 cm.times.15 cm, a total silicon surface area of about
7.8 m.sup.2 can be produced from 70% of a 5 cm thick ingot. The
remaining 30% of the ingot not cleaved to form single crystal
silicon, can be returned to the melt as highly purified starting
material to produce a fresh ingot for cleaving.
[0138] In accordance with an alternative embodiment of the present
invention, a seed layer may further provide for layering of a
hetero-structure epitaxial process. The hetero-structure epitaxial
process can be used to form thin multi-junction photovoltaic cells,
among others. Merely as an example, GaAs and GaInP layers may be
deposited heteroepitaxially onto a germanium seed layer, which is a
free-standing layer formed using an implant process according to an
embodiment of the present invention.
[0139] While the above is a full description of the specific
embodiments, various modifications, alternative constructions, and
equivalents may be used. For example, while the preceding
embodiments above show the bulk material in direct contact with a
temperature control stage, this is not required by the present
invention. In accordance with alternative embodiments, a bottom
portion of the bulk material could be secured to an adapter or
interface plate intermediate between the bulk material and the
temperature control stage.
[0140] FIGS. 13A-E show various approaches to securing a bulk
material to a temperature control stage taken by embodiments of the
present invention. The embodiment of FIG. 13A is analogous to that
previously described, wherein the bottom portion of the bulk
material is secured in direct contact with an o-ring of a
temperature control chuck, utilizing a clamp engaging with a notch
in the side of the bulk material.
[0141] By contrast, the embodiment of FIG. 13B utilizes an adapter
plate 1320 that is secured a lower surface 1322a of a tile (bulk
material) 1322 utilizing a tile retaining glue 1326. In this
particular embodiment, the adapter plate is slightly smaller than
the surface area of the bottom of the tile, but this is not
required. In alternative embodiments, the adapter plate could be
the same size as, or even bigger than, the bottom surface of the
tile.
[0142] The particular embodiment of FIG. 13B also shows the adapter
plate having a notch 1328. This is also not required, and the
adapter plate need not have such a notch.
[0143] FIG. 13C shows the tile-adapter plate configuration of FIG.
13B, secured to a temperature controlled chuck. Specifically, the
adapter face opposite that in contact with the tile, is sealed
against an o-ring positioned in a recess of the temperature
controlled chuck. The temperature controlled chuck is configured to
expose a backside of the adapter to a cooling gas, thereby
controlling its temperature and a temperature of the tile in
contact therewith.
[0144] Depending on the environment of the adapter plate, different
adapter clamping can be used. For example, atmospheric applications
could allow the use of vacuum chucking. In the particular
embodiment of FIG. 13C, the adapter is maintained in contact with
the chuck through suction only, as no clamp is shown engaged with
the clamp groove of the adapter. In other embodiments, however, a
clamp could engage with the clamp groove of the adapter to ensure
secure contact between the adapter and temperature control stage.
In accordance with still other embodiments, the adapter plate could
be secured to the temperature control chuck utilizing an applied
vacuum or electrostatic forces.
[0145] FIG. 13D shows a simplified cross-sectional view of still
another configuration in accordance with the present invention,
wherein surface 1330a of adaptor plate 1330 facing the tile 1324,
includes a recess 1332 configured to receive an o-ring 1334. Recess
1332 is positioned inside edge region 1334, and encloses interior
region 1336. In this embodiment, recess 1332 serves not only to
hold the o-ring in place, but also serves to confine any spread of
the tile retaining glue within the interior region 1336, when the
tile and adapter plate are bonded together.
[0146] FIG. 13E shows the tile-adapter plate configuration of FIG.
13D, secured to a temperature controlled chuck. Specifically, the
face of the adapter opposite that which is in contact with the
tile, is sealed against an o-ring positioned in a recess of the
temperature controlled chuck. The temperature controlled chuck is
configured to expose a backside of the adapter to a cooling gas,
thereby controlling its temperature as well as a temperature of the
tile that is in contact with the adapter plate.
[0147] In the particular embodiment of FIG. 13E, the adapter is
maintained in contact with the chuck utilizing a clamp configured
to engage with the clamp groove that is located in the side of the
adapter plate. This is not required by the present invention,
however, and in alternative embodiments the adapter plate could be
secured to the temperature control chuck utilizing other
approaches, for example an applied vacuum or electrostatic
force.
[0148] Although the above has been described using a selected
sequence of steps, any combination of any elements of steps
described as well as others may be used. Additionally, certain
steps may be combined and/or eliminated depending upon the
embodiment. Furthermore, the particles of hydrogen can be replaced
using co-implantation of helium and hydrogen ions to allow for
formation of the cleave plane with a modified dose and/or cleaving
properties according to alternative embodiments. Another form of
co-implantation involves substituting deuterium instead of hydrogen
in one or more of the implant sub-steps. Deuteron implantation into
silicon at 1-10 MeV produces about 3 times more atomic
displacements and thus may be more efficient in forming the
plurality of gettering sites within the cleave region 603 in FIG.
9. Of course there can be other variations, modifications, and
alternatives. For example, the second accumulation implant can be
substituted by a hydrogenation or deuteration step where getter
region accumulation by hydrogen or deuterium occurs by a diffusion
process. Therefore, the above description and illustrations should
not be taken as limiting the scope of the present invention which
is defined by the appended claims.
[0149] It is also understood that the examples and embodiments
described herein are for illustrative purposes only and that
various modifications or changes in light thereof will be suggested
to persons skilled in the art and are to be included within the
spirit and purview of this application and scope of the appended
claims.
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