U.S. patent application number 14/311388 was filed with the patent office on 2014-10-09 for apparatus and method for producing solar cells.
The applicant listed for this patent is TSMC SOLAR LTD.. Invention is credited to Ying-Chen CHAO, Kuo-Jui HSIAO, Edward TENG, Chih-Jen YANG.
Application Number | 20140302634 14/311388 |
Document ID | / |
Family ID | 48868423 |
Filed Date | 2014-10-09 |
United States Patent
Application |
20140302634 |
Kind Code |
A1 |
TENG; Edward ; et
al. |
October 9, 2014 |
APPARATUS AND METHOD FOR PRODUCING SOLAR CELLS
Abstract
A method and apparatus for forming a solar cell. The apparatus
includes a housing defining a vacuum chamber and a rotatable
substrate apparatus configured to hold a plurality of substrates on
a plurality of surfaces. A first sputtering source is configured to
deposit a plurality of absorber layer atoms of a first type over at
least a portion of a surface of each one of the plurality of
substrates. An evaporation source is configured to deposit a
plurality of absorber layer atoms of a second type over at least a
portion of the surface of each one of the plurality of
substrates.
Inventors: |
TENG; Edward; (Sunnyvale,
CA) ; CHAO; Ying-Chen; (Hsinchu City, TW) ;
YANG; Chih-Jen; (Taichung City, TW) ; HSIAO;
Kuo-Jui; (Taichung City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TSMC SOLAR LTD. |
Taichung City |
|
TW |
|
|
Family ID: |
48868423 |
Appl. No.: |
14/311388 |
Filed: |
June 23, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13486079 |
Jun 1, 2012 |
8785235 |
|
|
14311388 |
|
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61597608 |
Feb 10, 2012 |
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Current U.S.
Class: |
438/95 ;
204/298.25; 204/298.28 |
Current CPC
Class: |
C23C 14/24 20130101;
H01L 31/18 20130101; H01L 31/0326 20130101; H01L 21/02104 20130101;
C23C 14/3464 20130101; Y02E 10/541 20130101; C23C 14/505 20130101;
Y02P 70/521 20151101; H01L 21/67011 20130101; H01L 21/28194
20130101; H01L 31/0322 20130101; H01L 21/02631 20130101; H01L
21/67155 20130101; C23C 14/185 20130101; Y02P 70/50 20151101; C23C
14/0623 20130101 |
Class at
Publication: |
438/95 ;
204/298.28; 204/298.25 |
International
Class: |
H01L 31/18 20060101
H01L031/18; H01L 21/67 20060101 H01L021/67; H01L 21/02 20060101
H01L021/02; H01L 31/032 20060101 H01L031/032 |
Claims
1. An apparatus for forming a solar cell, comprising: a housing
defining a vacuum chamber; a rotatable substrate apparatus
configured to hold a plurality of substrates on a plurality of
surfaces; a first sputtering source configured to deposit a
plurality of absorber layer atoms of a first type over at least a
portion of a surface of each one of the plurality of substrates;
and an evaporation source configured to deposit a plurality of
absorber layer atoms of a second type over at least a portion of
the surface of each one of the plurality of substrates.
2. The apparatus of claim 1, wherein each of the plurality of
surfaces is disposed facing an interior surface of the vacuum
chamber.
3. The apparatus of claim 1, further comprising: a first isolation
source configured to isolate the evaporation source from the first
sputtering source.
4. The apparatus of claim 3,wherein the first isolation source
comprises one or more of an isolation pump.
5. The apparatus of claim 3, wherein the first isolation source
comprises: a vacuum pump disposed within a first subchamber of the
vacuum chamber-to maintain the pressure in the first subchamber
lower than the pressure in the vacuum chamber outside of the first
subchamber.
6. The apparatus of claim 1, wherein the evaporation source is
disposed in the first subchamber.
7. The apparatus of claim 1, further comprising: a heater apparatus
configured to heat the plurality of substrates, wherein the heater
apparatus has a shape that is substantially conformal with the
shape of the substrate apparatus.
8. The apparatus of claim 1, further comprising: a second
sputtering source configured to deposit a plurality of absorber
layer atoms of a third type over at least a portion of the surface
of each one of the plurality of substrates.
9. The apparatus of claim 1, further comprising: an isolation
baffle disposed about the evaporation source.
10. The apparatus of claim 8, further comprising: a first isolation
pump disposed between the evaporation source and the second
sputtering source; and wherein the first isolation source is
disposed between the evaporation source and the first sputtering
source.
11. The apparatus of claim 8, wherein the first type comprises
copper, the second type comprises selenium and the third type
comprises indium.
12. The apparatus of claim 11, wherein the first sputtering source
is configured to deposit a plurality of absorber layer atoms of a
first type and a fourth type over at least a portion of the surface
of each one of the plurality of substrates, and wherein the fourth
type is gallium.
13. The apparatus of claim 1, wherein each of the plurality of
surfaces of the substrate apparatus are disposed at a predetermined
tilt angle relative to an interior surface of the vacuum
chamber.
14. A method of forming a solar cell, comprising: disposing a
plurality of substrates about a plurality of surfaces of a
substrate apparatus that is operatively coupled to rotate within a
vacuum chamber; rotating the substrate apparatus; forming an
absorber monolayer over a surface of each one of the plurality of
substrates, the step of forming comprising: depositing a plurality
of absorber layer atoms of a first type over at least a portion of
the surface of each one of the plurality of substrates; depositing
a plurality of absorber layer atoms of a second type over at least
a portion of the surface; depositing a plurality of absorber layer
atoms of a third type deposit over at least a portion of the
surface of each one of the plurality of substrates; and reacting
the plurality of absorber layer atoms of the first and third types
with the plurality of absorber layer atoms of the second type to
form the absorber monolayer.
15. The method of claim 14, wherein the absorber layer atoms of the
first type are deposited using a first sputtering source, the
absorber layer atoms of the second type are deposited using an
evaporation source, and the absorber layer atoms of the third type
are deposited using a second sputtering source.
16. The method of claim 15, further comprising: evacuating absorber
layer atoms of the second type from the vacuum chamber to prevent
contamination of the first and second sputtering sources using a
first isolation pump.
17. The method of claim 14, wherein the first type comprises
copper, the second type comprises selenium and the third type
comprises indium.
18. An apparatus for forming a solar cell, comprising: a housing
defining a vacuum chamber; a rotatable substrate apparatus
configured to hold a plurality of substrates on a plurality of
surfaces; a first sputtering source configured to deposit a
plurality of absorber layer atoms of a first type over at least a
portion of the surface of each one of the plurality of substrates;
an evaporation source disposed in a first subchamber of the vacuum
chamber and configured to deposit a plurality of absorber layer
atoms of a second type over at least a portion of the surface of
each one of the plurality of substrates; and a second sputtering
source configured to deposit a plurality of absorber layer atoms of
a third type over at least a portion of the surface of each one of
the plurality of substrates.
19. The apparatus of claim 18, further comprising: a third
sputtering source disposed in a first subchamber of the vacuum
chamber and configured to deposit a buffer layer over the surface
of each one of the plurality of substrates.
20. The apparatus of claim 18, further comprising: an evacuation
source configured to evacuate atoms from the vacuum chamber to
prevent contamination of the first and second sputtering sources.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of and claims
priority to U.S. patent application Ser. No. 13/486,079, filed on
Jun. 1, 2012, which claims priority to, U.S. Provisional Patent
Application Ser. No. 61/597,608 filed on Feb. 10, 2012, the
entirety of which are herein incorporated by reference.
FIELD
[0002] The present disclosure relates generally to the field of
photovoltaics, and more specifically to an apparatus and method for
producing solar cells.
BACKGROUND
[0003] Copper indium gallium diselenide (CIGS) is a commonly used
absorber layer in thin film solar cells. CIGS thin film solar cells
have achieved excellent conversion efficiency (>20%) in
laboratory environments. Most conventional CIGS deposition is done
by one of two techniques: co-evaporation or selenization.
Co-evaporation involves simultaneously evaporating copper, indium,
gallium and selenium. The different melting points of the four
elements makes controlling the formation of a stoichiometric
compound on a large substrate very difficult. Additionally, film
adhesion is very poor when using co-evaporation. Selenization
involves a two-step process. First, a copper, gallium, and indium
precursor is sputtered on to a substrate. Second, selenization
occurs by reacting the precursor with toxic H2Se/H2S at 500.degree.
Celsius or above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Various aspects of the present disclosure will be or become
apparent to one with skill in the art by reference to the following
detailed description when considered in connection with the
accompanying exemplary non-limiting embodiments.
[0005] FIG. 1 is a schematic diagram illustrating a top view of an
example of a solar cell forming apparatus according to embodiments
of the present disclosure.
[0006] FIG. 2 is a schematic diagram illustrating a top view of an
example of a solar cell forming apparatus according to some
embodiments.
[0007] FIG. 3 is a schematic diagram illustrating a top view of an
example of a solar cell forming apparatus according to some
embodiments.
[0008] FIG. 4 is a schematic diagram illustrating a top view of an
example of a solar cell forming apparatus according to some
embodiments.
[0009] FIG. 5 is a schematic diagram illustrating a side view of an
example of a solar cell forming apparatus with a substrate
apparatus having a substantially vertical loading surface according
to embodiments of the present disclosure.
[0010] FIG. 6 is a schematic diagram illustrating a side view of an
example of a solar cell forming apparatus with a substrate
apparatus having a tilted loading surface according to some
embodiments.
[0011] FIG. 7 illustrates a perspective view of an example of an
isolation baffle according to embodiments of the present
disclosure.
[0012] FIG. 8 is a flow chart illustrating a method of forming a
solar cell absorber layer on the substrate according to embodiments
of the present disclosure.
[0013] FIG. 9 is a flow chart illustrating a step of forming an
absorber monolayer of a method of forming a solar cell according to
embodiments of the present disclosure.
[0014] FIG. 10 is a flow chart illustrating a step of forming an
absorber monolayer of a method of forming a solar cell according to
embodiments of the present disclosure.
[0015] FIGS. 11A, 11B, 11C, 11D, 11E, and 11F illustrate a
sectional view of a deposition of an absorber layer over a
substrate according to embodiments of the present disclosure.
[0016] FIG. 12 is a graph illustrating an Auger Electron
Spectroscopy (AES) depth profile analysis of an example absorber
layer according to embodiments of the present disclosure.
DETAILED DESCRIPTION OF THE EXAMPLES
[0017] With reference to the Figures, where like elements have been
given like numerical designations to facilitate an understanding of
the drawings, the various embodiments of a multi-gate semiconductor
device and methods of forming the same are described. The figures
are not drawn to scale.
[0018] The following description is provided as an enabling
teaching of a representative set of examples. Many changes can be
made to the embodiments described herein while still obtaining
beneficial results. Some of the desired benefits discussed below
can be obtained by selecting some of the features or steps
discussed herein without utilizing other features or steps.
Accordingly, many modifications and adaptations, as well as subsets
of the features and steps described herein are possible and may
even be desirable in certain circumstances. Thus, the following
description is provided as illustrative and is not limiting.
[0019] This description of illustrative embodiments is intended to
be read in connection with the accompanying drawings, which are to
be considered part of the entire written description. In the
description of embodiments disclosed herein, any reference to
direction or orientation is merely intended for convenience of
description and is not intended in any way to limit the scope of
the present disclosure. Relative terms such as "lower," "upper,"
"horizontal," "vertical,", "above," "below," "up," "down," "top"
and "bottom" as well as derivative thereof (e.g., "horizontally,"
"downwardly," "upwardly," etc.) should be construed to refer to the
orientation as then described or as shown in the drawing under
discussion. These relative terms are for convenience of description
only and do not require that the apparatus be constructed or
operated in a particular orientation. Terms such as "attached,"
"affixed," "connected" and "interconnected," refer to a
relationship wherein structures are secured or attached to one
another either directly or indirectly through intervening
structures, as well as both movable or rigid attachments or
relationships, unless expressly described otherwise. The term
"adjacent" as used herein to describe the relationship between
structures/components includes both direct contact between the
respective structures/components referenced and the presence of
other intervening structures/components between respective
structures/components.
[0020] As used herein, use of a singular article such as "a," "an"
and "the" is not intended to exclude pluralities of the article's
object unless the context clearly and unambiguously dictates
otherwise.
[0021] Improved apparatus and processes for manufacturing thin film
solar cells are provided. The inventors have observed that by
combining evaporation and sputtering processes into an apparatus
and/or method of manufacturing thin film solar cells, an improved
mixing of absorber layer atoms may be obtained with an easily
scalable volume production. The inventors have determined that
including an isolation source in the apparatus, and using an
isolation source in performing the method, can isolate and separate
evaporation and sputtering processes, minimize sputtering source
contamination and provide a safer and more efficient process for
manufacturing thin film solar cells.
[0022] FIG. 1 is a schematic diagram illustrating a top view of an
example of a solar cell forming apparatus 100 according to
embodiments of the present disclosure. As shown, a solar cell
forming apparatus 100 includes a housing 105 defining a vacuum
chamber. In various embodiments, the housing 105 may be shaped as a
polygon. For example, as shown in the illustrated embodiment, the
housing 105 may be octagonally shaped. In various embodiments, the
housing 105 has one or more removable doors built on one or more
sides of the vacuum chamber. The housing 105 may be composed of
stainless steel or other metals and alloys used for drum coater
housings. For example, the housing 105 can define a single vacuum
chamber having a height of approximately 2.4 m (2.3 m to 2.5 m)
with a length and width of approximately 9.8 m (9.7 m to 9.9
m).
[0023] In some embodiments, the solar cell forming apparatus 100
includes a rotatable substrate apparatus 120 configured to hold a
plurality of substrates 130 on a plurality of surfaces 122 where
each of the plurality of surfaces 122 are disposed facing an
interior surface of the vacuum chamber. In some embodiments, each
one of the plurality of substrates 130 include a suitable material
such as, for example, glass. In other embodiments, one or more of
the plurality of substrates 130 include a flexible material. In
some embodiments, the flexible material includes stainless steel.
In other embodiments, the flexible material includes plastic. In
various embodiments, the rotatable substrate apparatus 120 is
shaped as a polygon. For example, in the illustrated embodiment, a
plurality of substrates 130 are held on a plurality of surfaces 122
in a substantially octagonal shaped rotatable substrate apparatus
120. In other embodiments, for example, the substrate apparatus 120
may be rectangular shaped. Any suitable shape can be used for the
rotatable substrate apparatus 120.
[0024] As shown in FIG. 1, the substrate apparatus 120 is rotatable
about an axis in the vacuum chamber. FIG. 1 illustrates a clockwise
direction of rotation for the rotatable substrate apparatus 120. In
some embodiments, substrate apparatus 120 is configured to rotate
in a counter-clockwise direction. In various embodiments, the
rotatable substrate apparatus 120 is operatively coupled to a drive
shaft, a motor, or other mechanism that actuates rotation from a
surface of the vacuum chamber. In some embodiments, substrate
apparatus 120 is rotated at a speed, for example, between
approximately 5 and 100 RPM (e.g. 3 and 105 RPM). In various
embodiments, a speed of rotation of the rotatable substrate
apparatus 120 is selected to minimize excessive deposition of
absorption components on the plurality of substrates 130. In some
embodiments, the substrate apparatus rotates at a speed of
approximately 80 RPM (e.g. 75-85 RPM). In some embodiments, the
apparatus 100 includes a rotatable drum 110 disposed within the
vacuum chamber and coupled to a first surface of the vacuum
chamber. As illustrated in FIG. 1, the rotatable drum 110 can be
disposed within the vacuum chamber. In the illustrated embodiment,
the rotatable drum 110 is operatively coupled to the substrate
apparatus 120. As shown, the rotatable drum 110 has a shape that is
substantially conformal with the shape of the substrate apparatus
120. However, the rotatable drum can have any suitable shape.
[0025] In various embodiments, the apparatus 100 includes a first
sputtering source 135 configured to deposit a plurality of absorber
layer atoms of a first type over at least a portion of a surface of
each one of the plurality of substrates 130. As shown in the
illustrated embodiment, the first sputtering source 135 can be
disposed within a vacuum chamber between the substrate apparatus
120 and the housing. The first sputtering source 135 can be coupled
to a surface of the vacuum chamber. The first sputtering source 135
can be, for example, a magnetron, an ion beam source, a RF
generator, or any suitable sputtering source configured to deposit
a plurality of absorber layer atoms of a first type over at least a
portion of a surface of each one of the plurality of substrates
130. In some embodiments, the first sputtering source 135 includes
at least one of a plurality of sputtering targets 137. The first
sputtering source 135 can utilize a sputtering gas. In some
embodiments, sputtering is performed with an argon gas. Other
possible sputtering gases include krypton, xenon, neon, and
similarly inert gases.
[0026] As shown in FIG. 1, apparatus 100 can include a first
sputtering source 135 disposed within the vacuum chamber and
configured to deposit a plurality of absorber layer atoms of a
first type over at least a portion of a surface of each one of the
plurality of substrates 130 and a second sputtering source 135
disposed within the vacuum chamber and opposite the first
sputtering source and configured to deposit a plurality of absorber
layer atoms of a second type over at least a portion of a surface
of each one of the plurality of substrates 130. In other
embodiments, the first sputtering source 135 and the second
sputtering source 135 are disposed adjacent to each other within
the vacuum chamber. In some embodiments, the first and second
sputtering sources 135 can each include at least one of a plurality
of sputtering targets 137.
[0027] In various embodiments, a first sputtering source 135 is
configured to deposit a plurality of absorber layer atoms of a
first type (e.g. copper (Cu)) over at least a portion of a surface
of each one of the plurality of substrates 130 and a second
sputtering source 135 is configured to deposit absorber layer atoms
of a second type (e.g. indium (In)) over at least a portion of a
surface of each one of the plurality of substrates 130. In some
embodiments, the first sputtering source 135 is configured to
deposit a plurality of absorber layer atoms of a first type (e.g.
copper (Cu)) and a third type (e.g. gallium (Ga)) over at least a
portion of a surface of each one of the plurality of substrates
130. In some embodiments, a first sputtering source 135 includes
one or more copper--gallium sputtering targets 137 and a second
sputtering source 135 includes one or more indium sputtering
targets 137. For example, a first sputtering source 135 can include
two copper--gallium sputtering targets and a second sputtering
source 135 can include two indium sputtering targets. In some
embodiments, a copper--gallium sputtering target 137 includes a
material of approximately 70 to 80% (e.g. 69.5 to 80.5%) copper and
approximately 20 to 30% (e.g. 19.5 to 30.5%) gallium. In various
embodiments, the solar cell forming apparatus 100 has a first
copper--gallium sputtering target 137 at a first copper: gallium
concentration and a second copper--gallium sputtering target 137 at
a second copper: gallium concentration for grade composition
sputtering. For example, a first copper--gallium sputtering target
can include a material of 65% copper and 35% gallium to control
monolayer deposition to a first gradient gallium concentration and
a second copper--gallium sputtering target can include a material
of 85% copper and 15% gallium to control monolayer deposition to a
second gradient gallium concentration. The plurality of sputtering
targets 137 can be any suitable size. For example, the plurality of
sputtering targets 137 can be approximately 15 cm wide (e.g. 14-16
cm) and approximately 1.9 m tall (e.g. 1-8-2.0 m).
[0028] In some embodiments, a sputtering source 135 that is
configured to deposit a plurality of absorber layer atoms of indium
over at least a portion of the surface of each one of the plurality
of substrates 130 can be doped with sodium (Na). For example, an
indium sputtering target 137 of a sputtering source 135 can be
doped with sodium (Na) elements. The inventors have determined that
doping an indium sputtering target 137 with sodium may minimize the
need for depositing an alkali-silicate layer in the solar cell.
This improvement may result in lower manufacturing costs for the
solar cell as sodium is directly introduced to the absorber layer.
In some embodiments, a sputtering source 135 is a sodium-doped
copper source having between approximately two and ten percent
sodium (e.g. 1.95 to 10.1 percent sodium). In various embodiments,
an indium sputtering source 135 can be doped with other alkali
elements such as, for example, potassium. In other embodiments,
apparatus 100 can include multiple copper--gallium sputtering
sources 135 and multiple sodium doped indium sputtering sources
135. For example, the solar cell forming apparatus can have a 65:35
copper--gallium sputtering source 135 and an 85:15 copper--gallium
sputtering source 135 for grade composition sputtering.
[0029] In various embodiments, apparatus 100 includes an
evaporation source 140 configured to deposit a plurality of
absorber layer atoms of a fourth type over at least a portion of
the surface of each one of the plurality of substrates 130. In
various embodiments, the fourth type is non-toxic elemental
selenium. The fourth type can include any suitable evaporation
source material. In some embodiments, evaporation source 140 is
configured to produce a vapor of an evaporation source material of
the fourth type. In various embodiments, the vapor can condense
upon the one or more substrates 130. For example, the evaporation
source 140 can be an evaporation boat, crucible, filament coil,
electron beam evaporation source, or any suitable evaporation
source 140. In some embodiments, the evaporation source 140 is
disposed in a first subchamber of the vacuum chamber 110. In
various embodiments, the vapor of the fourth type evaporation
source material can be ionized, for example using an ionization
discharger, prior to condensation over the substrate to increase
reactivity. In the illustrated embodiment, a first and second
sputtering source 135 are disposed on opposing sides of the vacuum
chamber and substantially equidistant from evaporation source 140
about the perimeter of the vacuum chamber.
[0030] In various embodiments, apparatus 100 includes a first
isolation source configured to isolate an evaporation source 140
from a first sputtering source 135. The first isolation source can
be configured to prevent fourth type material from evaporation
source 140 from contaminating the first sputtering source 135. In
the illustrated embodiment, the first isolation source is an
isolation pump 152, such as, for example, a vacuum pump. In other
embodiments, the apparatus 100 can include a plurality of isolation
pumps 152. In various embodiments, the isolation source can include
a combination of an isolation pump 152 and an isolation subchamber
(not shown).
[0031] In some embodiments, the first isolation pump can include a
vacuum pump 152 disposed within a first subchamber of the vacuum
chamber to maintain the pressure in the first subchamber lower than
the pressure in the vacuum chamber outside of the first subchamber.
For example, the first isolation pump 152 can be disposed within a
first subchamber of the vacuum chamber housing the evaporation
source 140 to maintain the pressure in the first subchamber lower
than the pressure in the vacuum chamber outside of the first
subchamber and to isolate the evaporation source 140 from the first
sputtering source. In various embodiments, the isolation source 152
can be an evacuation source 152 such as, for example, a vacuum pump
152 configured to evacuate atoms from the vacuum chamber to prevent
contamination of a sputtering source 135. For example, isolation
source 152 can be a vacuum pump 152 disposed within a first
subchamber of the vacuum chamber housing the evaporation source 140
and configured to evacuate evaporation source material atoms to
prevent contamination of a sputtering source 135. In various
embodiments, isolation source 152 can be a vacuum pump disposed
along a perimeter surface of the vacuum chamber and configured to
evacuate atoms (e.g. evaporation source material atoms) from the
vacuum chamber to prevent contamination of sputtering source
135.
[0032] In embodiments including a plurality of sputtering sources
135 and/or a plurality of evaporation sources 140, apparatus 100
can include a plurality of isolation sources to isolate each of the
evaporation sources from each of the sputtering sources 135. For
example, in embodiments having first and second sputtering sources
135 disposed on opposing sides of a vacuum chamber and an
evaporation source 140 disposed there between on a perimeter
surface of the vacuum chamber, apparatus 100 can include a first
isolation pump 152 disposed between the first sputtering source 135
and evaporation source 140 and a second isolation pump 152 disposed
between the second sputtering source 135 and evaporation source
140. In the illustrated embodiment, apparatus 100 includes an
isolation pump 152 disposed between evaporation source 140 and one
of the two sputtering sources 135.
[0033] The solar cell forming apparatus 100 can include one or more
heaters 117 to heat the plurality of substrates 130 disposed on a
plurality of surfaces 122 of the rotatable substrate apparatus 120.
In the illustrated embodiment, a plurality of heaters are disposed
in a heater apparatus 115 to heat the plurality of substrates. As
shown in FIG. 1, heater apparatus 115 can have a shape that is
substantially conformal with the shape of the substrate apparatus.
In the illustrated embodiment, the plurality of heaters 117 are
shown positioned in a substantially octagonal shape arrangement
within a heating apparatus 115.
[0034] However, the heater apparatus 115 can have any suitable
shape. In various embodiments, the heater apparatus 115 is disposed
to maintain a substantially uniform distance about the perimeter of
the substrate apparatus 120. In the illustrated embodiment, heater
apparatus 115 is disposed about an interior surface of the
rotatable substrate apparatus 120. In some embodiments, the heater
apparatus 115 can be disposed about an interior surface of a
rotatable drum 110. A power source of the heater apparatus 115 can
extend through a surface of the rotatable drum 110. In various
embodiments, the substrate apparatus 120 is rotatable around the
heater apparatus 115. In some embodiments, the heater apparatus 115
is disposed about an exterior surface of a rotatable drum 110. In
some embodiments, the heater apparatus 115 can be coupled to a
surface of the vacuum chamber. The heater apparatus 115 can be
rotatable. In other embodiments, the heater apparatus 115 is
configured to not rotate. The one or more heaters 117 can include,
but are not limited to, infrared heaters, halogen bulb heaters,
resistive heaters, or any suitable heater for heating a substrate
130 during a deposition process. In some embodiments, the heater
apparatus 115 can heat a substrate to a temperature between
approximately 300 and 550 degrees Celsius (e.g. 295 and 555 degrees
Celsius).
[0035] As shown in FIG. 1, apparatus 100 can include an isolation
baffle 170 disposed about the evaporation source 140. Isolation
baffle 170 can be configured to direct a vapor of an evaporation
source material to a particular portion of a surface of the
plurality of substrates 130. Isolation baffle 170 can be configured
to direct a vapor of an evaporation source material away from a
sputtering source 135. Apparatus 100 can include an isolation
baffle 170 in addition to one or more isolation sources to minimize
evaporation source material 122 contamination of one or more
sputtering sources 135. The isolation baffle 170 can be composed of
a material such as, for example, stainless steel or other similar
metals and metal alloys. In some embodiments, the isolation baffle
170 is disposable. In other embodiments, the isolation baffle 170
is cleanable.
[0036] In some embodiments, apparatus 100 can include one or more
in-situ monitoring devices 160 to monitor process parameters such
as temperature, chamber pressure, film thickness, or any suitable
process parameter. In various embodiments, apparatus 100, can
include a load lock chamber 182 and/or an unload lock chamber 184.
In embodiments of the present disclosure, apparatus 100 can include
a buffer subchamber 155 (e.g. a buffer layer deposition subchamber)
configured in-situ in apparatus 100 with a vacuum break. In some
embodiments, a buffer layer deposition subchamber 155 configured
in-situ in apparatus 100 with a vacuum break includes a sputtering
source (not shown) including one or more sputtering targets (not
shown). In various embodiments, apparatus 100 includes a sputtering
source (not shown) disposed in a subchamber of the vacuum chamber
and configured to deposit a buffer layer over a surface of each one
of the plurality of substrates 130 in substrate apparatus 130. In
various embodiments, apparatus 100 includes an isolation source to
isolate the buffer layer sputtering source from an evaporation
source and/or an absorber monolayer sputtering source. The buffer
layer material can include, for example, non-toxic ZnS--O or
CdS.
[0037] The apparatus 100 of FIG. 1 can also be used to form solar
cells of different absorber films, for example, a
copper-zinc-tin-sulfur-selenium (CZTSS) absorber film. In some
embodiments, a number of CZTSS absorber layer are formed in
apparatus 100 by further providing tin, copper, zinc, or
copper/zinc targets. as targets 137. The evaporation source 140 may
use sulfur, selenium or both sulfur and selenium as source
material. Additionally, another evaporation source 140 may be used
to separately provide selenium and sulfur source material.
[0038] With reference now to FIG. 2, a schematic diagram
illustrating a top view of an example of a CIGS solar cell forming
apparatus 200 according to embodiments of the present disclosure is
provided. In various embodiments, apparatus 200 can include a
housing 205 defining a vacuum chamber, a rotatable substrate
apparatus 220 configured to hold a plurality of substrates 230 on a
plurality of surfaces 222, a first sputtering source 235 configured
to deposit a plurality of absorber layer atoms of a first type over
at least a portion of a surface of each of the plurality of
substrates 230, an evaporation source 240 configured to deposit a
plurality of absorber layer atoms of a second type over at least a
portion of the surface of each of the plurality of substrates 230,
a first isolation source 252 configured to isolate the evaporation
source 240 from the first sputtering source 235, a second
sputtering source 235 configured to deposit a plurality of absorber
layer atoms of a third type over at least a portion of the surface
of each of the plurality of substrates 230, and a second isolation
source configured to isolate the evaporation source 240 from the
second sputtering source 235.
[0039] In the illustrated embodiment, apparatus 200 includes a
rotatable drum 210, a heater apparatus 215 including a plurality of
heaters 217, an isolation baffle 270, a load lock chamber 282, an
unload lock chamber 284, a monitoring device 260, and sputtering
targets 237 in each of the first and second sputtering sources 235,
as described above for FIG. 2. In various embodiments, apparatus
200 includes a buffer layer deposition source 265. In the
illustrated embodiment, buffer layer deposition source 265 is
disposed along an interior perimeter surface of housing 205. In
some embodiments, buffer layer deposition source 265 can be
disposed in a subchamber of the vacuum chamber. In various
embodiments, buffer layer sputtering source 265 is configured to
deposit a n-type buffer layer, such as for example, a cadmium
sulfide(CdS) buffer layer, or a ZnS--O buffer layer, over the
absorber layer. The buffer layer can include any suitable buffer
layer material.
[0040] In the illustrated embodiment, the first and second
isolation sources include first and second isolation pumps 252,
such as vacuum pumps 252, configured to respectively isolate the
first and second sputtering sources 235 from the evaporation source
240. In some embodiments (not shown), one or more of the isolation
pumps 252 is configured to maintain the pressure in an evaporator
source 240 sub-chamber (not shown) lower than the pressure in the
vacuum chamber. The isolation pumps 252 can be configured to
evacuate second type absorber layer atoms from evaporation source
240 from the vacuum chamber, prevent diffusion of the second type
absorber layer atoms into the sputtering targets 237, and prevent
the second type absorber layer atoms from contaminating the two
sputtering sources 235. In some embodiments, apparatus 200 can
include an loading/unloading substrate chamber 255 and
post-treatment chamber 280. In various embodiments, post-treatment
chamber 280 can be configured for post treatment of the CIGS cell
such as, for example, cooling the CIGS cell.
[0041] Referring now to FIG. 3, a schematic diagram illustrating a
top view of an example of a solar cell forming apparatus 300
according to embodiments of the present disclosure is provided. In
the illustrated embodiment, apparatus 300 includes a housing 305
defining a vacuum chamber, a rotatable drum 310, a heater apparatus
315 including a plurality of heaters 317, a rotatable substrate
apparatus holding a plurality of substrates 330, a plurality of
sputtering sources 335, a plurality of sputtering targets 337, an
evaporation source 340, an isolation baffle 370, a load lock
chamber 382, an unload lock chamber 384, and a buffer subchamber
355 as described above for FIGS. 1 and 2. In the illustrated
embodiment, the rotatable drum 310, heater apparatus 315, and
housing 305 are substantially shaped as a decagon. As shown in FIG.
3, apparatus 300 can include two evaporation sources 340. In the
illustrated embodiment, four isolation pumps 352 are provided and
configured to isolate evaporation sources 340, sputtering sources
335 and buffer subchamber 355. In various embodiments, isolation
pumps 352 are configured to minimize evaporation source type
absorber layer atom contamination on the two sputtering sources 335
and in buffer subchamber 355. Referring now to FIG. 4, apparatus
400 includes one sputtering source 435, one evaporation source 440,
and buffer subchamber 455. In the illustrated embodiment, two
isolation pumps 452 are provided in apparatus 400 and configured to
isolate sputtering source 435, evaporation source 440, and buffer
subchamber 455, and to minimize evaporation source type absorber
layer atom contamination on the sputtering sources 435 and in
buffer subchamber 455. In some embodiments, buffer subchamber 455
can be configured for buffer layer deposition such as, for example,
by sputtering.
[0042] With reference to FIG. 5, a schematic diagram illustrating a
side view of an example of a solar cell forming apparatus 500 with
a rotatable substrate apparatus 520 having a substantially vertical
loading surface according to embodiments of the present disclosure.
In the illustrated embodiment, the rotatable substrate apparatus
520 is configured to hold a plurality of substrates 530 on a
plurality of surfaces where each of the plurality of surfaces are
substantially vertical and are disposed facing an interior surface
of the vacuum chamber. The sputtering source 537 is disposed within
the vacuum chamber. In various embodiments, a heater apparatus 515
including a plurality of heaters 517 is provided. As shown, the
heater apparatus 515 can be coupled to a bottom surface of the
housing 505 such that it is configured not to rotate. In the
illustrated embodiment, the plurality of heaters are disposed along
an interior surface of the rotatable substrate apparatus 520 and
are disposed substantially vertically to substantially conform with
the disposition of the plurality of surfaces of the substrate
apparatus 520.
[0043] Referring now to FIG. 6, in other embodiments, the rotatable
substrate apparatus 620 can be configured to hold a plurality of
substrates 630 on a plurality of surfaces where each of the
plurality of surfaces are disposed at a predetermined tilt angle
relative to vertical such as, for example, relative to the interior
surface of the vacuum chamber. In some embodiments, the
predetermined tilt angle is between approximately 1 and 5 degrees
of tilt (e.g. 0.8 degrees and 5.2 degrees of tilt). For example,
the plurality of surfaces of substrate apparatus 620 can be tilted
at a predetermined tilt angle of 2 degrees relative to the interior
surface of the vacuum chamber. In another example, the plurality of
surfaces of substrate apparatus 620 can be tilted at a
predetermined tilt angle of 0.5 degrees relative to the interior
surface of the vacuum chamber. In various embodiments, the
plurality of heaters 617 in the heater apparatus 615, and/or
sputtering targets 637 in sputtering sources 635 can also be tilted
at the predetermined tilt angle to substantially conform with the
disposition of the plurality of surfaces of the substrate apparatus
620. In other embodiments, the plurality of surfaces of substrate
apparatus 620 can be tilted at a predetermined tilt angle while the
plurality of heaters 617 in the heater apparatus 615, and/or
sputtering targets 637 in sputtering sources 635 remain
substantially vertical.
[0044] Referring now to FIG. 7, a perspective view of an example of
an isolation baffle 770 is provided. In various embodiments, the
shape of isolation baffle 770 is configured to substantially
conform with the shape of rotatable substrate apparatus 720. In the
illustrated embodiment, isolation baffle 770 has a shape that is
configured to substantially conform with the octagonal shape of the
rotatable substrate apparatus 720. Isolation baffle 770 can extend
to an evaporation shield 740, which has a port. The evaporation
source (not shown) is disposed to direct a vapor of a material from
evaporation source to a particular portion of a surface of the
plurality of substrates held in substrate apparatus 720. The
evaporation shield 740 can have a port and extended to the
isolation baffle 770 is disposed to direct a vapor of a material
from an evaporation source (not shown) away from a sputtering
source. FIG. 7 illustrates diffusion of a material from an
evaporation source (not shown) into a port of evaporation shield
740. As shown, the port can be rectangular in shape. However, the
port can be any suitable shape. A slot can be provided in the port
and blade of isolation baffle 770 to permit passage of absorber
layer atoms from the evaporation source to at least a portion of a
surface of each of the substrates held in substrate apparatus
720.
[0045] FIG. 8 is a flow chart illustrating a method 800 of forming
a solar cell according to embodiments of the present disclosure. At
block 810, a plurality of substrates (e.g. 130) are disposed about
a plurality of surfaces (e.g. 122) of a substrate apparatus
(e.g.
[0046] 120) that is operatively coupled to rotate within a vacuum
chamber. At block 820, the substrate apparatus 120 is rotated. At
block 830, an absorber monolayer is formed over a surface 122 of
each one of the plurality of substrates 130.
[0047] Referring now to FIG. 9, a flow chart illustrating details
of the step 830 (of FIG. 8) of forming the absorber monolayer of
the method 800 of forming a solar cell according to embodiments of
the present disclosure is provided. In various embodiments, at
block 832, a plurality of copper and gallium atoms are deposited
over at least a portion of the surface 122 of each one of the
plurality of substrates 130 using a first sputtering source (e.g.
135). At block 834, a plurality of selenium atoms are deposited
over at least a portion of the surface 122 of each one of the
plurality of substrates 130 using an evaporation source (e.g. 140).
At block 836, a plurality of indium atoms are deposited over at
least a portion of the surface 122 of each one of the plurality of
substrates 130 using a second sputtering source (e.g. 135). At
block 838, the plurality of copper, gallium, and indium atoms are
reacted with the plurality of selenium atoms to form the absorber
monolayer.
[0048] With reference to FIG. 10, a flow chart illustrating details
of the step 830 (of FIG. 8) of forming the absorber monolayer of
the method 800 of forming a solar cell according to some
embodiments of the present disclosure is provided. In some
embodiments, at block 832, a plurality of copper and gallium atoms
are deposited over at least a portion of the surface 122 of each
one of the plurality of substrates 130 using a first sputtering
source (e.g. 135). At block 834, a plurality of indium atoms are
deposited over at least a portion of the surface 122 of each one of
the plurality of substrates 130 using a second sputtering source
(e.g. 135). At block 836, a plurality of selenium atoms are
deposited over at least a portion of the surface 122 of each one of
the plurality of substrates 130 using an evaporation source (e.g.
140). At block 838, the plurality of copper, gallium, and indium
atoms are reacted with the plurality of selenium atoms to form the
absorber monolayer.
[0049] Adjusting a power source of a sputtering source (e.g. first
and/or second sputtering source 135) can control a sputtering rate
and a concentration of the sputtered copper, gallium, and/or indium
atoms deposited over the substrate 130. Similarly, adjusting a
power source of an evaporation source 140 can control an
evaporation rate and a concentration of the evaporated selenium
atoms deposited over the substrate 130. The speed and/or direction
of rotation of the substrate apparatus 120 also can affect the rate
and amount of sputtered copper, gallium, and/or indium atoms and
the amount of evaporated selenium atoms deposited over the
substrate 130. As described above, selecting the copper-gallium
concentration in one or more copper--gallium sputtering targets
(e.g. 137) of one or more sputtering sources (e.g. 135) can control
concentration of the sputtered copper and gallium atoms to a
desired gradient concentration. In various embodiments, one or more
of the power source of each sputtering source and each evaporation
source, the sputtering rate of each sputtering source, the
evaporation rate of each evaporation source is controlled to form a
predetermined composition of an absorber monolayer. In various
embodiments, the formed absorber monolayer includes a composition
of 20 to 24% copper, 4 to 14% gallium, 10 to 24% indium and 49 to
53% selenium. In some embodiments, the composition is 23% copper,
9% gallium, 17% indium, 51% selenium. The inventors have discovered
that by using the methods and apparatus of forming the absorber
monolayer described herein, an increased efficiency and accuracy
for forming the absorber monolayer having the predetermined
composition can be achieved.
[0050] Referring again to FIG. 8, at block 840, the step of forming
the absorber monolayer 930 is repeated to form an absorber layer.
In various embodiments, each one of the formed monolayers of the
absorber layer include a composition of 20 to 24% copper, 4 to 14%
gallium, 10 to 24% indium and 49 to 53% selenium. The inventors
have determined that by using the methods and apparatus of forming
the absorber monolayer described herein, an increased efficiency
and accuracy for forming each one of the absorber monolayers in the
absorber layer at the predetermined composition can be achieved.
Thus, in various embodiments, each rotation of the substrate
apparatus (e.g. 120) results in the deposition of a plurality of
atoms of the absorber layer elements to achieve a desired gradient
composition. At block 850, a plurality of atoms are evacuated from
the vacuum chamber to prevent contamination of the first and second
sputtering sources. In various embodiments, a plurality of selenium
atoms are evacuated from the vacuum chamber using a first isolation
pump (e.g. 252) disposed between the evaporation source 140 and the
first sputtering source 135 and a second isolation pump (252)
disposed between the evaporation source 140 and the second
sputtering source 135. In various embodiments, a buffer layer is
deposited over the absorber layer of each one of the plurality of
substrates using a third sputtering source (e.g. 135) disposed in a
subchamber (e.g. 155) of the vacuum chamber. In other embodiments,
the absorber monolayers can comprise elements of other
semiconductor compounds, including, but not limited to, ClSe, CGSe,
CIS, CGS, CIGSe, CIGSeS, CZTS or any suitable compound to form an
absorber layer of a solar cell.
[0051] With reference now to FIGS. 11A-F, a sectional view of a
deposition of an absorber layer over a substrate is illustrated
according to embodiments of the present disclosure. A plurality of
absorber layer atoms can be deposited over the substrate 1130 as
described and shown in FIGS. 1-10. In the illustrated embodiment,
the plurality of absorber layer atoms are shown as being deposited
on a bottom electrode layer 1132 deposited on the substrate.
Referring now to FIG. 11A, a plurality of first type absorber layer
atoms 1141 such as, for example, indium atoms, can be deposited by
sputtering such as by a first sputtering source (e.g. 135) to
achieve a first concentration of indium atoms. Referring to FIG.
11B, a plurality of second type absorber layer atoms 1042 such as,
for example, selenium atoms, can be deposited by evaporating such
as by an evaporating source (e.g. 140) to achieve a second
concentration of selenium atoms. As shown in FIG. 11C, a plurality
of third type absorber layer atoms 1143, such as, for example,
copper atoms, or third type 1143 and fourth type 1144 absorber
layer atoms, such as, for example, copper and gallium atoms, can be
deposited by sputtering such as by a second sputtering source (e.g.
135) to achieve a third concentration or a third concentration and
fourth concentration. In various embodiments, the plurality of
third type absorber layer atoms 1143 can include sodium doped
copper atoms.
[0052] As shown in FIG. 11D, the plurality of absorber layer atoms
(1141, 1142, 1143, 1144) can react in a monolayer reaction. In
various embodiments, the monolayer reaction can form an absorber
monolayer 1146 over the substrate. In various embodiments, the
absorber monolayer 1146 is a CIGS monolayer. The monolayer reaction
results in better uniformity and a more consistent and desired
bandgap in the absorber layer. The inventors have determined that
the sequential method of forming the absorber monolayer described
herein results in a more accurate and improved process to achieve
the desired monolayer composition. In some embodiments, ionizing a
plurality of the second absorption components such as, for example,
selenium, can increase the reaction rate. As shown in FIGS.
11A-11F, this process forms an absorber layer at a predetermined
stoichiometric composition in a more accurate and more efficient
manner.
[0053] In various embodiments, the formed absorber layer has a
graded energy band gap. The absorber layer can be configured to
substantially absorb the energy of a plurality of wavelengths of
incoming light. In various embodiments, an absorber monolayer
(1146, 1147, 1148, etc.) can be approximately 10 .ANG. or 1 nm
thick. As shown in FIG. 11E, more of the plurality of absorption
components can be deposited over the absorber monolayer 1146 using
the same process (11A-11D) to react in another monolayer reaction
to form another absorber monolayer. An aggregate of all of the
absorber monolayers can form the absorber layer 1150 as shown in
FIG. 11F. In various embodiments, the absorber layer 1150 is a
polycrystalline CIGS layer. The step of forming the absorber
monolayers monolayer (1146, 1147, 1148, etc.) can be repeated until
a predetermined thickness of the absorber layer 1150 is achieved.
In some embodiments, the predetermined thickness can be
approximately 1500 nm (1490-1510 nm.) In other embodiments, the
predetermined thickness can be approximately 1200 nm (1190-1210
nm.) In various embodiments, a buffer layer (not shown) can be
formed over the absorber layer.
[0054] FIG. 12 illustrates a graph of an Auger Electron
Spectroscopy (AES) depth profile analysis of an example of an
absorber layer formed according to some embodiments. As shown in
FIG. 12, the absorber layer has a gradient composition that is
substantially consistent across different depths of the absorber
layer. An X-axis of the AES depth profile analysis is an etching
time in seconds. A left side Y-axis of the AES depth profile
analysis is an atomic composition of the plurality of absorber
layer elements. As shown in FIG. 12, the atomic composition of
copper and selenium remained substantially constant across
different depths of the absorber layer. FIG. 12 also shows
decreasing amounts of indium, consistent with the increasing
amounts of gallium, across different depths of the absorber layer.
The right side Y-axis of the AES depth profile analysis is the
atomic composition ratio of gallium to indium plus gallium. FIG. 12
shows the atomic composition ratio of gallium to indium plus
gallium can be controlled with double gradient throughout the
absorber layer.
[0055] Throughout the description and drawings, example embodiments
are given with reference to specific configurations. It will be
appreciated by those of ordinary skill in the art that the present
disclosure can be embodied in other specific forms. Those of
ordinary skill in the art would be able to practice such other
embodiments without undue experimentation. The scope of the present
disclosure, for the purpose of the present patent document, is not
limited merely to the specific example embodiments or alternatives
of the foregoing description.
[0056] As shown by the various configurations and embodiments
illustrated in FIGS. 1-12 various improved CIGS films have been
described.
[0057] According to some embodiments, an apparatus for forming a
solar cell is provided. The apparatus includes a housing defining a
vacuum chamber, a rotatable substrate apparatus configured to hold
a plurality of substrates on a plurality of surfaces, a first
sputtering source configured to deposit a plurality of absorber
layer atoms of a first type over at least a portion of a surface of
each one of the plurality of substrates, and an evaporation source
configured to deposit a plurality of absorber layer atoms of a
second type over at least a portion of the surface of each one of
the plurality of substrates.
[0058] According to various embodiments, a method of forming a
solar cell is provided. The method includes disposing a plurality
of substrates about a plurality of surfaces of a substrate
apparatus that is operatively coupled to rotate within a vacuum
chamber, rotating the substrate apparatus, and forming an absorber
monolayer over a surface of each one of the plurality of
substrates. The step of forming includes depositing a plurality of
absorber layer atoms of a second type over at least a portion of
the surface of each one of the plurality of substrates, depositing
a plurality of absorber layer atoms of a second type over at least
a portion of the surface, depositing a plurality of absorber layer
atoms of a third type over at least a portion of the surface of
each one of the plurality of substrates, and reacting the plurality
of absorber layer atoms of the first and third types with the
plurality of absorber layer atoms of the second type to form the
absorber monolayer.
[0059] According to some embodiments, an apparatus for forming a
solar cell is provided. The apparatus includes a housing defining a
vacuum chamber, a rotatable substrate apparatus configured to hold
a plurality of substrates on a plurality of surfaces, a first
sputtering source configured to deposit a plurality of absorber
layer atoms of a first type over at least a portion of the surface
of each one of the plurality of substrates, an evaporation source
disposed in a first subchamber of the vacuum chamber and configured
to deposit a plurality of absorber layer atoms of a second type
over at least a portion of the surface of each one of the plurality
of substrates, and a second sputtering source configured to deposit
a plurality of absorber layer atoms of a third type over at least a
portion of the surface of each one of the plurality of
substrates.
[0060] While various embodiments have been described, it is to be
understood that the embodiments described are illustrative only and
that the scope of the subject matter is to be accorded a full range
of equivalents, many variations and modifications naturally
occurring to those of skill in the art from a perusal hereof.
[0061] Furthermore, the above examples are illustrative only and
are not intended to limit the scope of the disclosure as defined by
the appended claims. Various modifications and variations can be
made in the methods of the present subject matter without departing
from the spirit and scope of the disclosure. Thus, it is intended
that the claims cover the variations and modifications that can be
made by those of ordinary skill in the art.
* * * * *