U.S. patent application number 14/625649 was filed with the patent office on 2015-06-18 for method and system of providing dopant concentration control in different layers of a semiconductor device.
The applicant listed for this patent is First Solar, Inc.. Invention is credited to Arnold Allenic, John Barden, Feng Liao, Xilin Peng, Rick C. Powell, Kenneth M. Ring, Gang Xiong.
Application Number | 20150171258 14/625649 |
Document ID | / |
Family ID | 47595100 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150171258 |
Kind Code |
A1 |
Allenic; Arnold ; et
al. |
June 18, 2015 |
METHOD AND SYSTEM OF PROVIDING DOPANT CONCENTRATION CONTROL IN
DIFFERENT LAYERS OF A SEMICONDUCTOR DEVICE
Abstract
A method and system for controlling the amount of a second
material incorporated into a first material by controlling the
amount of a third material which can interact with the second
material.
Inventors: |
Allenic; Arnold; (San Jose,
CA) ; Barden; John; (Ottawa Hills, OH) ; Liao;
Feng; (Perrysburg, OH) ; Peng; Xilin;
(Bloomington, MN) ; Powell; Rick C.; (Ann Arbor,
MI) ; Ring; Kenneth M.; (Waterville, OH) ;
Xiong; Gang; (Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
First Solar, Inc. |
Perrysburg |
OH |
US |
|
|
Family ID: |
47595100 |
Appl. No.: |
14/625649 |
Filed: |
February 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13739183 |
Jan 11, 2013 |
9006020 |
|
|
14625649 |
|
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|
61585708 |
Jan 12, 2012 |
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Current U.S.
Class: |
118/722 ;
204/298.02 |
Current CPC
Class: |
H01L 31/073 20130101;
Y02E 10/543 20130101; H01L 21/02568 20130101; C23C 16/455 20130101;
C23C 16/402 20130101; H01J 37/3476 20130101; C23C 16/28 20130101;
H01L 21/0262 20130101; C23C 16/52 20130101; H01L 21/02573 20130101;
C23C 16/4488 20130101; H01J 2237/332 20130101; C23C 16/407
20130101; H01L 31/02963 20130101; C23C 16/483 20130101; H01L 31/18
20130101; C23C 16/40 20130101; H01L 21/02551 20130101 |
International
Class: |
H01L 31/18 20060101
H01L031/18; C23C 16/455 20060101 C23C016/455; H01J 37/34 20060101
H01J037/34; C23C 16/48 20060101 C23C016/48; C23C 16/448 20060101
C23C016/448; C23C 16/28 20060101 C23C016/28; C23C 16/52 20060101
C23C016/52; C23C 16/40 20060101 C23C016/40 |
Claims
1-26. (canceled)
27. A system comprising: a first chamber configured to house a
deposition material which includes a dopant; a second chamber in
fluid communication with said first chamber for depositing a vapor
which includes said deposition material and said dopant onto a
substrate; a first reactant inlet in fluid communication with at
least one of said first and second chambers for receiving a
reacting agent which reacts with said deposition material and
dopant and affects the amount of dopant deposited with said
deposition material on said substrate; and a first controller in
fluid communication with said first reactant inlet for adjusting
fluid flow through said first reactant inlet to control the amount
of dopant incorporated in the deposition material which is
deposited on the substrate.
28. The system of claim 27, wherein said first reactant inlet is in
fluid communication with said second chamber, and wherein said
reacting agent reacts with said deposition material and dopant in
said second chamber.
29. The system of claim 28, wherein said second chamber houses said
first chamber.
30. The system of claim 27, wherein said first reactant inlet is in
fluid communication with said first chamber, and wherein said
reacting agent reacts with said deposition material and dopant in
said first chamber.
31. The system of claim 30, further comprising: a second reactant
inlet in fluid communication with said second chamber; and a second
controller in fluid communication with said second reactant inlet
for adjusting fluid flow through said second reactant inlet to
control the amount of said dopant incorporated in said deposition
material which is deposited on said substrate.
32. The system of claim 27, wherein said reacting agent comprises
an oxidizing agent.
33. The system of claim 32, wherein said oxidizing agent comprises
oxygen gas.
34. The system of claim 32, wherein said oxidizing agent comprises
water vapor.
35. The system of claim 27, wherein said dopant comprises
silicon.
36. The system of claim 27, wherein said dopant comprises
germanium.
37. The system of claim 35, wherein said deposited material has a
silicon concentration in the range of about 0.0001% to about
5%.
38. The system of claim 27, wherein said deposition material
comprises one of copper-indium-gallium-diselenide (CIGS), cadmium
sulfide, cadmium telluride, cadmium selenide, zinc telluride, zinc
sulfide, zinc selenide, and any pseudo-binary or ternary compounds
thereof.
39. The system of claim 27, wherein said deposition comprises one
of vapor transport deposition, close-space sublimation, sputtering,
pulse laser deposition, and chemical vapor deposition.
40. A system comprising: a first chamber configured to house a
deposition material which includes a dopant; a second chamber in
fluid communication with said first chamber for depositing a vapor
which includes said deposition material and said dopant onto a
substrate; a first reactant inlet in fluid communication with at
least one of said first and second chambers for receiving a
reacting agent which reacts with said deposition material and
dopant and affects the amount of dopant deposited with said
deposition material on said substrate; and a first controller in
fluid communication with said first reactant inlet for adjusting
fluid flow through said first reactant inlet to control the amount
of dopant incorporated in the deposition material which is
deposited on the substrate, wherein said reacting agent comprises
an oxidizing agent.
41. The system of claim 40, wherein said oxidizing agent comprises
oxygen gas.
42. The system of claim 40, wherein said oxidizing agent comprises
water vapor.
43. The system of claim 40, further comprising: a second reactant
inlet in fluid communication with said second chamber; and a second
controller in fluid communication with said second reactant inlet
for adjusting fluid flow through said second reactant inlet to
control the amount of said dopant incorporated in said deposition
material which is deposited on said substrate.
44. The system of claim 40, wherein said deposited material has a
silicon concentration in the range of about 0.0001% to about
5%.
45. The system of claim 40, wherein said deposition comprises at
least one of vapor transport deposition, close-space sublimation,
sputtering, pulse laser deposition, and chemical vapor
deposition.
46. A system comprising: a first chamber configured to house a
deposition material which includes a dopant; a second chamber in
fluid communication with said first chamber for depositing a vapor
which includes said deposition material and said dopant onto a
substrate; a first reactant inlet in fluid communication with at
least one of said first and second chambers for receiving a
reacting agent which reacts with said deposition material and
dopant and affects the amount of dopant deposited with said
deposition material on said substrate; and a first controller in
fluid communication with said first reactant inlet for adjusting
fluid flow through said first reactant inlet to control the amount
of dopant incorporated in the deposition material which is
deposited on the substrate, wherein said reacting agent reacting
with said deposition material and said dopant comprises at least
one chemical reaction selected from the group consisting of:
SiTex(g)+O2(g).fwdarw.SiO2(s)+x/2Te2(g);
SiSx(g)+O2(g).fwdarw.SiO2(s)+xS(g);
SiSx(g)+O2(g).fwdarw.SiO2(s)+SO2(g); and
SiSex(g)+O2(g).fwdarw.SiO2(s)+x/2Se2(g).
Description
CLAIM OF PRIORITY
[0001] This application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Patent Application Ser. No.
61/585,708 filed on Jan. 12, 2012, which is hereby incorporated by
reference in its entirety.
TECHNICAL FIELD
[0002] Disclosed embodiments relate generally to semiconductor
devices, and more particularly, to a system and method of providing
dopant concentration control in different layers of a photovoltaic
device.
BACKGROUND
[0003] Photovoltaic devices such as photovoltaic modules or cells
can include a plurality of layers of materials deposited on a
substrate using various deposition systems and techniques. Some of
the layers may have to be doped at times to enhance their
electrical properties and characteristics. However, the actual
amount of dopant used to dope the layers is very critical. For
example, a certain amount of dopant concentration may enhance the
electrical properties of a layer while another concentration of the
dopant may severely decrease those electrical properties. Hence, a
need exists for a method and system for controlling dopant
concentration in a layer of material of a photovoltaic device.
DESCRIPTION OF DRAWINGS
[0004] FIG. 1 is a schematic of a photovoltaic device having
multiple layers.
[0005] FIG. 2 is a schematic of a deposition system providing for
dopant material concentration control according to a first
embodiment.
[0006] FIG. 3 is a schematic of a deposition system providing for
dopant material concentration control according to a second
embodiment.
[0007] FIG. 4 is a schematic of a deposition system providing for
dopant material concentration control according to a third
embodiment.
DETAILED DESCRIPTION
[0008] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments that may be
practiced. These embodiments are described in sufficient detail to
enable those skilled in the art to make and use them, and it is to
be understood that structural, logical, or procedural changes may
be made to the specific embodiments disclosed without departing
from the spirit and scope of the invention.
[0009] Embodiments described herein provide a system and method of
controlling concentration of a second material (dopant material,
e.g., silicon) in manufacturing a photovoltaic device. The method
and system control an amount of dopant material which dopes a first
material for deposition (e.g., cadmium telluride) by having a third
material (or reacting agent, e.g., an oxidizing agent such as
oxygen or water vapor) react with the dopant material. The dopant
material may include silicon, germanium or other dopant material.
In the following description, control of a silicon dopant used to
dope thin film semiconductor layers, e.g., cadmium sulfide and
cadmium telluride, of a photovoltaic device will be described.
However, the methods and systems described herein may be used more
generally to provide dopant control for any suitable deposited
layer or film on a substrate.
[0010] Referring to FIG. 1, by way of example, a photovoltaic
device 10 can be formed by sandwiching a plurality of sequentially
formed layers of materials between two support/protection layers
(substrate 110 and back support layer 180 both of which may be made
of glass). In construction, barrier layer 114 may be deposited on
substrate 110. Upon the barrier layer 114, transparent conductive
oxide (TCO) layer 115, buffer layer 116, semiconductor window layer
150, semiconductor absorber layer 160, back contact layer 170 and
back support 180 may be sequentially deposited.
[0011] In some instances, barrier layer 114, TCO layer 115 and
buffer layer 116 may be formed separately and deposited as a stack
of layers upon substrate 110. For this reason, barrier layer 114,
TCO layer 115 and buffer layer 116 are often referred to as a TCO
stack labeled herein TCO stack 120.
[0012] Barrier layer 114 is used to protect semiconductor layers
150 and 160 from potential contaminants that may be generated by
substrate 110 during construction as well as while the device is in
operation. TCO layer 115 and back contact layer 170 are used as
electrodes to provide power generated by the photovoltaic device to
externally connected electrical devices. Buffer layer 116 is used
to lessen any ill effects that irregularities developed during the
deposition of semiconductor layers 150 and 160 may have on the
device.
[0013] Semiconductor 150 and 160 facilitate the conversion of light
to electricity. Specifically, window semiconductor 150 is an n-type
semiconductor layer while absorber semiconductor layer 160 is a
p-type semiconductor layer. The interface between the two
semiconductors forms a p-n junction where conversion of light to
electricity occurs.
[0014] It has been found desirable to incorporate dopants in
semiconductor window layer 150 and absorber layer 160. For example,
the incorporation of silicon as a dopant into cadmium sulfide (the
material used to form semiconductor window layer 150 in this
example) and cadmium telluride (the material used to form
semiconductor absorber layer 160) is found to promote better growth
of the cadmium telluride on the cadmium sulfide by improving their
crystalline structures (i.e., arrangement of atoms and/or molecules
in the materials). Tests have revealed that a silicon concentration
in the range of about 0.0001% to about 5% in the cadmium telluride
layer 160 and the cadmium sulfide layer 150 increases both light
transmission through the cadmium sulfide layer 150 and photon
absorbance by the cadmium telluride layer 160. Therefore, it is
desirable to control the concentration of silicon dopant within the
semiconductor layers 150, 160 such that the semiconductor layers
150 and 160 in the resulting photovoltaic device have the correct
amount of dopant concentration.
[0015] Precise silicon dopant concentration control during
deposition of semiconductor layers 150, 160 using current vapor
transport deposition (VTD) systems and methods is difficult.
Examples of current VTD systems can be found in U.S. Pat. Nos.
5,945,163, 5,945,165, 6,037,241, and 7,780,787, all assigned to
First Solar, Inc. A VTD system may use a powder delivery unit, a
powder vaporizer and vapor distributor, and a vacuum deposition
unit. VTD powder vaporizers are designed to vaporize or sublimate
raw material powder into a gaseous form. In conventional powder
vaporizers, raw material powder combined with a carrier gas is
injected into a permeable heated cylinder from a powder delivery
unit. The material is vaporized in the cylinders and the vaporized
material diffuses through the permeable walls of the vaporizer into
the distributor. The distributor collects and directs the flow of
vaporized raw material for deposition as a thin film layer on a
substrate. The distributor typically surrounds the vaporizer
cylinder and directs collected vapors toward openings which face
toward a substrate.
[0016] Controlling dopant concentration using current VTD systems
and methods may be difficult for several reasons. First, most of
the silicon dopant-containing materials are in a solid phase (e.g.,
powder form). For example, for cadmium telluride and cadmium
sulfide deposition, respective raw material powders containing
cadmium telluride and silicon and cadmium sulfide and silicon are
used. Adjusting the powder composition balance of a semiconductor
material-dopant powder mixture requires time-consuming and costly
VTD system shutdowns. For example, if the semiconductor layer 150
or 160 has a silicon concentration outside the range of about
0.0001% to about 5%, the VTD system shutdowns may be required to
adjust the silicon concentration in the semiconductor
material-dopant powder mixture, which slows processing time. An
increase in system shutdowns results in an undesirable increase in
raw material and production costs.
[0017] Second, although some silicon-containing gas phase dopant
materials such as silane (SiH.sub.4) can be used instead of a
powder, their applications typically require special chemical
handling procedures, equipment, and safety pre-cautions, due to
high-toxicity and inflammability. SiH.sub.4 is highly inflammable
and could cause an explosion if not properly stored and handled, as
described in Asia Industrial Gases Association (AIGA), "Storage And
Handling Of Silane And Silane Mixtures," AIGA 052/08.
[0018] Moreover, at high temperatures of between about 450.degree.
C. and about 800.degree. C., which occur during cadmium telluride
and cadmium sulfide deposition, silicon integral to various
components of deposition vessels, such as a heaters, ceramics, or
process vessels, may be liberated and react with the gas phase
deposition material. For example, deposition of silicon-doped
cadmium telluride may involve depositing a gaseous mixture of
SiTe.sub.x, cadmium and tellurium onto a substrate. At such
temperatures, the silicon present within deposition vessels can
react with tellurium to form excess SiTe.sub.x, which may be
incorporated into the cadmium telluride layer. Likewise, deposition
of silicon-doped cadmium sulfide may involve depositing a gaseous
mixture of SiS.sub.x, cadmium and sulfide onto a substrate. At high
temperatures, the silicon present within or on deposition vessels
can react with sulfur to produce unwanted SiS.sub.x which may be
incorporated into the cadmium sulfide layer. Therefore, the silicon
present within deposition vessels may increase expected dopant
concentrations in the deposited material and impair photovoltaic
device performance, for example silicon concentrations of greater
than about 5% in a deposited cadmium telluride or cadmium sulfide
material layer.
[0019] In a first embodiment, a method and system control an amount
of a dopant material with which to dope a material for deposition,
e.g., cadmium telluride, by having an oxidizing agent, such as, for
example, oxygen or water vapor, react with the dopant material in a
second chamber which houses a first chamber. A second embodiment is
similar to the method and system of the first embodiment except
that the dopant material may react with the oxidizing agent in the
first chamber.
[0020] FIG. 2 illustrates a first embodiment of a deposition system
15 for controlling the amount of dopant material with which to dope
a cadmium telluride layer deposited on a substrate 5. Note that in
this particular case, substrate 5 will already have cadmium sulfide
layer 150 and TCO stack 120 deposited thereon. In this exemplary
embodiment, oxygen is used as a reacting agent to control the
amount of the silicon dopant during the deposition of the cadmium
telluride layer.
[0021] Referring to FIG. 2, deposition system 15 may include a
first chamber 112 which is housed in a second chamber 101. The
first chamber 112 is in vapor (or fluid) communication with the
second chamber 101. First chamber 112 may include any vapor
transport deposition system known in the art. Silicon dopant may be
incorporated into the deposited materials in any suitable manner,
including, for example, by mixing silicon powder into the powder of
the material to be deposited, as described below. A deposition zone
within the second chamber 101 proximate to one or more openings 139
in the first chamber 112 is configured to receive substrate 5.
Substrate 5 is received and positioned inside second chamber 101
such that it receives vapor output from first chamber 112 through
one or more openings 139.
[0022] Chamber 112 contains a cadmium telluride semiconductor
material powder and a silicon dopant powder combined as a
silicon-cadmium telluride powder mixture. The mixture is vaporized
and reacts to form a gaseous mixture of SiTe.sub.x, cadmium and
tellurium. The gaseous mixture exits the chamber 112 through
openings 139 and enters into the second chamber 101. There, as
shown in the chemical reaction below, the SiTe.sub.x gas reacts
with oxygen (O.sub.2) to yield solid-phase silicon dioxide
(SiO.sub.2) and tellurium (x/2Te.sub.2): [0023]
SiTe.sub.x(g)+O.sub.2(g).fwdarw.SiO.sub.2(s)+x/2Te.sub.2(g)
[0024] The resulting solid phase SiO.sub.2 which is formed will be
deposited in the second chamber 101 as opposed to being a vapor
phase material which can be deposited onto the substrate 5.
[0025] Generally, in a 0.1 mol cadmium telluride, 0.00015 mol
silicon, and 0.0001 mol oxygen gas mixture, it is desirable to use
0.00005 mol silicon (0.05% concentration in cadmium telluride) to
dope the cadmium telluride deposited on the substrate 5. The
remaining 0.0001 mol silicon can be converted into silicon dioxide
through the above reaction. Therefore, it is necessary to control
the amount of silicon dioxide generated by limiting the amount of
oxygen in the system. By adjusting the oxygen ratio in the second
chamber 101 during material growth, silicon doping concentration
can be controlled. Thus, in system 15 of FIG. 2, oxygen as a
reacting agent is effectively used to isolate any unused silicon
dopant, so that it is not incorporated into the deposited cadmium
telluride film or at the very least is incorporated to such a low
extent as to not adversely impact performance of the photovoltaic
device.
[0026] If first chamber 112 is positioned above the substrate 5 and
the gaseous mixture of SiTe.sub.x, cadmium and tellurium flows
downwardly toward the substrate 5 from first chamber 112, some
SiO.sub.2 may inadvertently deposit on the substrate 5. In FIG. 2,
to ensure that SiO.sub.2 is not deposited on the substrate 5, first
chamber 112 is positioned below substrate 5. In this configuration,
the gaseous mixture of SiTe.sub.x, cadmium and tellurium flows
upwardly from first chamber 112 through one or more openings 139
toward bottom surface 4 of substrate 5. The heavier solid phase
SiO.sub.2 will aggregate and condense faster than vapor phase
material such as SiTe.sub.x and CdTe. Hence, the heavier solid
phase SiO.sub.2 produced as a result of the reaction between
SiTe.sub.x and O.sub.2 will settle on portions 138 of exterior wall
137 of the first chamber 112 before reaching the substrate 5. Note
that, a constant flow of the gaseous mixture of SiTe.sub.x, cadmium
and tellurium from first chamber 112 (illustrated by the arrow in
FIG. 2) will partially block solid phase SiO.sub.2 from falling
through one or more openings 139 and settling inside first chamber
112.
[0027] Referring again to FIG. 2, the second chamber 101 may
comprise an outlet 130 and a first reactant inlet 140a. The
concentration of oxygen in the second chamber 101 is adjusted via
mass flow controller 123a. Outlet 130 may comprise or be in fluid
communication with a vacuum pump system configured to evacuate
second chamber 101 of gases, including oxygen, contained
therein.
[0028] First mass flow controller 123a may be adjusted manually or
automatically by a computer system and may be connected to a system
or network, and may be adjusted as needed to ensure that the proper
amount of oxygen is being used in the deposition process.
[0029] As is well known in chemistry, the reaction of SiTe.sub.x
and oxygen in the second chamber 101 may also be controlled by
adjusting the system's temperature and/or pressure. In such
instance, the temperature of the system 15 may be anywhere from
about 20.degree. C. to about 1500.degree. C. Altering the
temperature can induce an equilibrium shift of the chemical
reaction
SiTe.sub.x(g)+O.sub.2(g).fwdarw.SiO.sub.2(s)+x/2Te.sub.2(g). It may
also change the sticking coefficient of SiTe.sub.x on the substrate
5, that is, the ratio of the number of SiTe.sub.x molecules that
adsorb, or stick to the deposited cadmium telluride, to the total
number of SiTe.sub.x molecules that contact the deposited cadmium
telluride, which can alter the silicon concentration in the
deposited cadmium telluride.
[0030] The oxygen partial pressure in the second chamber 101 may be
adjusted through the use of first reactant inlet 140a and outlet
130, as described above. Oxygen may be injected into the system 15
at any suitable pressure that provides for the desired silicon
dopant concentration in the cadmium telluride material deposited on
substrate 5. For example, oxygen may be injected into the system 15
at a pressure of more than about 1 ton, more than about 3 ton, more
than about 5 ton, less than about 20 ton, less than about 15 ton,
less than about 10 torr, or less than about 7 torr.
[0031] FIG. 3 illustrates a second embodiment of a deposition
system 20. This system is similar to the one in FIG. 2, except that
the reacting agent, e.g., oxygen, is injected directly into first
chamber 112 where the powder mixture of cadmium telluride
semiconductor material, silicon dopant and silicon-cadmium
telluride is vaporized.
[0032] Consequently, the oxygen reacts with the SiTe.sub.x vapor
inside first chamber 112 rather than in second chamber 101 as in
FIG. 2. Similar to the system in FIG. 2, however, the amount of
SiTe.sub.x vapor that can be transported from the first chamber 112
to substrate 5 in the second chamber 301 is limited by the amount
of oxygen in first chamber 112.
[0033] FIG. 4 illustrates a third embodiment of a deposition system
25 that is similar to system 15 in FIG. 3. In FIG. 4, additional
reacting agents may flow into the second chamber 301 through one or
more second reactant inlets 140b, which may be regulated by a
second mass flow controller 123b. Additional reacting agents may be
the same as, or different than, the reacting agent that flows
through the first reactant inlet 140a.
[0034] Although the first chamber 112 is positioned below substrate
5 in FIG. 2-4, this is not limiting. First chamber may be
positioned above substrate 5 or in any other location suitable for
depositing material onto substrate 5 and controlling the dopant
concentration in such material.
[0035] The materials employed when the FIG. 2-4 embodiments are
used for cadmium telluride deposition are not limiting. Systems 15,
20, 25 may be used for deposition of other materials on a substrate
including a cadmium sulfide layer, in which a cadmium sulfide
semiconductor material powder and a silicon dopant powder can be
combined as a silicon-cadmium sulfide powder mixture and then
vaporized and reacted in first chamber 112 of FIGS. 2-4 to form a
gaseous mixture of SiS,, cadmium and sulfur. The gas phase dopant
(SiS.sub.x) concentration in the cadmium sulfide layer may be
controlled through its reaction with oxygen according to, but not
limited to, the following reactions: [0036]
SiS.sub.x(g)+O.sub.2(g).fwdarw.SiO.sub.2(s)+xS.sub.(g) [0037]
SiS.sub.x(g)+O.sub.2(g).fwdarw.SiO.sub.2(s)+SO.sub.2(g)
[0038] The disclosed embodiments may also be used to control dopant
levels in other material layers which may be used in photovoltaic
or other devices. For example, during manufacturing of a
photovoltaic device which includes a copper indium gallium selenide
(CIGS) semiconductor material layer, a reacting agent (e.g.,
oxygen) may be used to control the concentration of silicon dopant
in a CIGS material layer via the following exemplary reaction of
silicon and selenium: [0039]
SiSe.sub.x(g)+O.sub.2(g).fwdarw.SiO.sub.2(s)+x/2Se.sub.2(g)
[0040] The FIG. 2-4 embodiments may also be used for deposition of
other materials including a transition metal (Group 12) combined
with a chalcogenide (Group 18) such as cadmium selenide (CdSe),
zinc telluride (ZnTe), zinc selenide (ZnSe) or zinc sulfide (ZnS),
or suitable semiconductor alloys such as Cd.sub.xZn.sub.1-xTe or
CdTe.sub.xS.sub.1-x, and their pseudo-binary or ternary compounds.
Such deposition materials may include dopants such as silicon or
germanium. The embodiments may also be suitable to control dopants
used during deposition of other material layers on a substrate,
including, for example, silicon material layers such as amorphous
silicon (a-Si).
[0041] The FIG. 2-4 embodiments may also be used to control
incorporation and concentration of various dopants, including, for
example, group-IV elements such as silicon, germanium, and their
respective compounds. Such dopants may consist of any element or
compound having a higher chemical affinity (or reactivity) with the
reacting agent than with a base material being deposited.
[0042] A variety of reacting agents are available for use in the
FIG. 2-4 embodiments, for example, water vapor, nitrogen gas, argon
gas or other oxidizing agent, depending on the dopant being
controlled and materials with which the dopant may react. Oxidizing
agents may be in vapor or liquid phase.
[0043] In addition to being used in vapor transport deposition, the
methods and systems of the FIG. 2-4 embodiments may also be
suitable for various deposition methods and systems, including, for
example, close-space sublimation, sputtering, pulse laser
deposition, and chemical vapor deposition with appropriate
modification of systems.
[0044] The deposition systems discussed and depicted herein may be
part of a larger system for fabricating a photovoltaic device.
Prior to or after encountering deposition system 15, 20, 25 the
substrate may undergo various other deposition and/or processing
steps to form the various layers shown in FIG. 1, for example.
[0045] Also, each layer may in turn include more than one layer or
film. Additionally, each layer can cover all or a portion of the
device and/or all or a portion of the layer or substrate underlying
the layer. For example, a "layer" can include any amount of any
material that contacts all or a portion of a surface. It should be
noted and appreciated that any of the aforementioned layers may
include multiple layers, and that "on" or "onto" does not mean
"directly on," such that in some embodiments, one or more
additional layers may be positioned between the layers
depicted.
[0046] The embodiments described above are offered by way of
illustration and example. It should be understood that the examples
provided above may be altered in certain respects and still remain
within the scope of the claims. It should be appreciated that,
while the invention has been described with reference to the above
example embodiments, other embodiments are within the scope of the
claims. It should also be understood that the appended drawings are
not necessarily to scale, presenting a somewhat simplified
representation of various features and basic principles of the
invention.
* * * * *