U.S. patent application number 12/466981 was filed with the patent office on 2010-07-08 for nozzle-based, vapor-phase, plume delivery structure for use in production of thin-film deposition layer.
This patent application is currently assigned to University of Delaware. Invention is credited to Robert W. Birkmire, Erten Eser, Gregory M. Hanket, T.W. Fraser Russell.
Application Number | 20100173440 12/466981 |
Document ID | / |
Family ID | 37863910 |
Filed Date | 2010-07-08 |
United States Patent
Application |
20100173440 |
Kind Code |
A1 |
Birkmire; Robert W. ; et
al. |
July 8, 2010 |
Nozzle-Based, Vapor-Phase, Plume Delivery Structure for Use in
Production of Thin-Film Deposition Layer
Abstract
A physical vapor deposition effusion method comprising
translating a strip material through a physical vapor deposition
zone in a deposition chamber and providing first and second
substantially closed vessels located serially along the processing
path in the same deposition chamber, each vessel emitting different
source materials to produce overlapping plumes and having an array
of vapor delivery nozzles distributed uniformly across the vessel
along the width of the zone, and configured to expel overlapping
plumes to create a fog having a substantially uniform composition
across the width and a varying composition across the length of the
zone. Also, an elongate vapor deposition effusion vessel having an
elongate lid including plural nozzles spaced from each other along
its elongate axis, and a continuous heating element in the lid
encircling the plural nozzles, the heating element having
electrical contacts connected to an electrical source on the same
side of the vessel.
Inventors: |
Birkmire; Robert W.;
(Newark, DE) ; Hanket; Gregory M.; (Newark,
DE) ; Russell; T.W. Fraser; (Newark, DE) ;
Eser; Erten; (Newark, DE) |
Correspondence
Address: |
RATNERPRESTIA
P.O. BOX 1596
WILMINGTON
DE
19899
US
|
Assignee: |
University of Delaware
Newark
DE
|
Family ID: |
37863910 |
Appl. No.: |
12/466981 |
Filed: |
May 15, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12263025 |
Oct 31, 2008 |
|
|
|
12466981 |
|
|
|
|
11725975 |
Mar 19, 2007 |
|
|
|
12263025 |
|
|
|
|
09613951 |
Jul 11, 2000 |
7194197 |
|
|
11725975 |
|
|
|
|
09527542 |
Mar 16, 2000 |
6310281 |
|
|
09613951 |
|
|
|
|
09527316 |
Mar 16, 2000 |
6372538 |
|
|
09527542 |
|
|
|
|
Current U.S.
Class: |
438/57 ; 118/724;
257/E31.001 |
Current CPC
Class: |
C23C 14/243 20130101;
H01L 21/02631 20130101; Y02E 10/541 20130101; H01L 21/02554
20130101; C23C 14/548 20130101; Y02P 70/521 20151101; C23C 14/562
20130101; Y02P 70/50 20151101; C23C 14/0623 20130101; H01L 31/0749
20130101; H01L 21/02568 20130101; C23C 14/24 20130101; C23C 14/0021
20130101 |
Class at
Publication: |
438/57 ; 118/724;
257/E31.001 |
International
Class: |
H01L 31/18 20060101
H01L031/18 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] This invention was made with Government support under
Agreement No. MDA972-95-3-0036 awarded by DARPA. The Government has
certain rights in the invention.
Claims
1. A physical vapor deposition effusion method, comprising:
translating a strip material through a physical vapor deposition
zone and along a processing path in a deposition chamber, each of
the strip material and the physical vapor deposition zone having a
width oriented perpendicular to the processing path and a length
oriented parallel to the processing path; and providing multiple
substantially closed vessels located serially along the processing
path in the same deposition chamber, each vessel containing a
heated quantity of a different source material, concurrently
emitting the different source materials from the multiple vessels
to produce overlapping plumes of the different source materials in
the physical vapor deposition zone in the same deposition chamber,
each vessel including an array of vapor delivery nozzles
distributed uniformly across the vessel in a direction
corresponding to the width of the physical vapor deposition zone
and configured to expel overlapping plumes of source material, so
that a fog of source materials is created and deposited on the
strip material in the deposition zone, the fog having a
substantially uniform composition across the width of the physical
vapor deposition zone and a varying composition across the length
of the physical vapor deposition zone.
2. A vapor deposition effusion vessel comprising an elongate vessel
having a pair of elongate side walls and an elongate axis oriented
generally parallel to the elongate side walls, the vessel having a
heating element and an elongate lid including plural nozzles spaced
from each other along the elongate axis.
3. The vapor deposition effusion vessel of claim 2, wherein the
vessel has a base, the side walls being joined to the base, and a
pair of end walls joined to the base and side walls.
4. The vapor deposition effusion vessel of claim 2, wherein the
heating element is controllable to maintain the lid and nozzles at
temperatures higher then the temperature of molten material
contained within the vessel.
5. The vapor deposition effusion vessel of claim 3, wherein the
heating element is controllable to maintain the lid and nozzles at
temperatures higher then the temperature of molten material
contained within the vessel.
6. The vapor deposition effusion vessel of claim 2, wherein the
nozzles are integrally formed into the lid.
7. The vapor deposition effusion vessel of claim 3, wherein the
nozzles are integrally formed into the lid.
8. The vapor deposition effusion vessel of claim 4, wherein the
nozzles are integrally formed into the lid.
9. The vapor deposition effusion vessel of claim 5, wherein the
nozzles are integrally formed into the lid.
10. The vapor effusion vessel of claim 2, wherein the vessel is
rectangular.
11. The vapor effusion vessel of claim 3, wherein the vessel is
rectangular.
12. The vapor effusion vessel of claim 4, wherein the vessel is
rectangular.
13. The vapor effusion vessel of claim 5, wherein the vessel is
rectangular.
14. The vapor effusion vessel of claim 6, wherein the vessel is
rectangular.
15. The vapor effusion vessel of claim 7, wherein the vessel is
rectangular.
16. The vapor effusion vessel of claim 8, wherein the vessel is
rectangular.
17. The vapor effusion vessel of claim 9, wherein the vessel is
rectangular.
18. The method of claim 1, wherein each vessel comprises a
rectangular vessel having a base, a pair of elongate side walls
joined to the base, and a pair of end walls joined to the base and
side walls, the vessel having an elongate axis oriented parallel to
the elongate side walls, the vessel having a lid including plural
nozzles integrally formed into the lid and spaced from each other
along the elongate axis.
19. The method of claim 18, wherein the vessel comprises a heating
element, the method comprising controlling the heating element to
maintain the lid and nozzles at temperatures higher then the
temperature of molten source material contained within the
vessel.
20. The method of claim 1, wherein the vessel comprises a heating
element, the method comprising controlling the heating element to
maintain the lid and nozzles at temperatures higher then the
temperature of molten source material contained within the vessel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
12/263,025 (pending), filed Oct. 31, 2008, which is continuation of
U.S. patent application Ser. No. 11/725,975 (pending), filed Mar.
19, 2007, and a continuation of U.S. patent application Ser. Nos.
12/154,548, 12/154,549, and 12/154,550 (all pending), filed May 22,
2008, all of which are continuations of U.S. patent application
Ser. No. 09/613,951 filed Jul. 11, 2000, now U.S. Pat. No.
7,194,197 ("the '197 patent"). The '197 patent is a continuation of
U.S. patent application Ser. No. 09/527,542, filed on Mar. 16,
2000, now U.S. Pat. No. 6,310,281, and a continuation of U.S.
patent application Ser. No. 09/527,316, filed Mar. 16, 2000, now
U.S. Pat. No. 6,372,538. All of the aforementioned are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0003] The invention disclosed herein relates to the field of
thin-film deposition, in general to controlled evaporation of
single component elements to create complex multi-element
films.
BACKGROUND OF THE INVENTION
[0004] Looking briefly at the background of the invention,
thin-film deposition is typically accomplished by two basic
methods: (1) physical vapor deposition (PVD) or (2) chemical vapor
deposition (CVD). Although there are several subsets of the above
techniques, generically all thin films (micron to submicron) are
deposited by one of the two methods. This invention particularly
relates to PVD processes and more particularly to the PVD field of
evaporation. In PVD based processes, atoms are removed from a
source material by some physical technique that adds energy to the
system causing atoms to be removed. Examples of PVD techniques
include sputtering, resistive evaporation, and electron-beam
evaporation. In sputtering, the atoms of the source material are
removed by the physical act of colliding argon atoms with the
source material. The evaporation technique entails removing atoms
from the source material by adding heat until the source material
atoms are more stable in a gaseous state than in the liquid or
solid state. Sputtering and evaporation are well known PVD
processes for which several excellent references are available.
(Vossen, Maissel and Glanc).
[0005] Generally, sputtering can be characterized as a
well-controlled, well-engineered process. Sputtering cathodes,
power supplies, and source material targets are available from
several vendors. Sputtering has been successfully applied in
several thin-film applications including deposition of impermeable
films on food packaging, low emissivity (low-e) coatings on
residential and commercial plate glass, and decorative coatings.
Control of sputtered film uniformity has been engineered into the
cathode structure. Negative aspects of sputtering including the
high cost of the sputtering systems, that the source (target)
utilization is generally poor (20 to 40%), and that there are
temporal limitations in creating multi-component films (i.e., more
that three elements). More specifically, to sputter multi-component
films, individual layers are usually deposited followed by a heat
treatment cycle to react the components together, which may require
considerable time.
[0006] Although generally more difficult to control than
sputtering, evaporation, is also used in commercial industrial
applications. Evaporation is typically used when the specific film
thickness uniformity and composition are not critical. Key
advantages of evaporation are the low cost of pellets or wire
source materials, the low cost of power supplies and crucibles (as
compared to sputtering), and the potential for high source
utilization (>50%). However, to achieve a uniform film thickness
using evaporation requires multiple evaporation sources. As a
result, evaporation is less prevalent for films requiring precise
thickness or composition uniformity. However, application of
evaporation to complex multi-component films that contain one or
more highly reactive species has proved problematic due to the
relative consistent rate control and thickness uniformity
issues.
[0007] As noted above, complex multi-element films are difficult to
produce using currently available techniques of sputtering or
evaporation. The invention described herein provides a new class of
evaporation principles and associated evaporation sources resulting
in the creation of uniform, well controlled multi-element thin
films.
[0008] The explicative example uncovered in this invention is
deposition of complex 4 or 5 element direct bandgap semiconductors
used for photovoltaics.
[0009] Looking briefly at the background for the field of
photovoltaics generally relates to the development of multi-layer
materials that convert sunlight directly into DC electrical power.
In the United States, photovoltaic (PV) devices are popularly known
as solar cells--which are typically configured as a cooperating
sandwich of p- and n-type semiconductors, wherein the n-type
semiconductor material (on one "side" of the sandwich) exhibits an
excess of electrons, and the p-type semiconductor material (on the
other "side" of the sandwich) exhibits an excess of holes. Such a
structure, when appropriately located electrical contacts are
included, forms a working PV cell. Sunlight incident on PV cells is
absorbed in the p-type semiconductor creating electron/hole pairs.
By way of a natural internal electric field created by sandwiching
p- and n-type semiconductors, electrons created in the p-type
material flow to the n-type material where they are collected,
resulting in a DC current flow between the opposite sides of the
structure when the same is employed within an appropriate, closed
electrical circuit. As a standalone device, conventional solar
cells do not have a sufficient voltage required to power most
applications. As a result, conventional solar cells are arranged
into PV modules by connecting the front of one cell to the back of
another, thereby adding the voltages of the individual cells
together. Typically a large number of cells, on the order to 36 to
50 are required to be connected in series to achieve a nominal
usable voltage of 12 to 18 V.
[0010] Although commercial use and interest in thin-film
photovoltaics has increased dramatically over the past five years,
commercial wide-scale use of thin film PVs for bulk power
generation historically has been limited due to PV's low
performance and high cost. In recent years, however, performance
has been less of a limiting factor as dramatic improvements in PV
module efficiency have been achieved with both crystalline silicon
and thin-film photovoltaics. The laboratory scale efficiency of
crystalline silicon is approaching 20%. Modules ranging from 10 to
14% are currently commercially available from several vendors.
Similarly, laboratory scale efficiencies of above 10% have been
achieved with thin-film PV devices of copper indium diselenide,
cadmium telluride, and amorphous silicon. The efficiency of a thin
film copper-indium-gallium-diselenide (CIGS) PV device is now
approaching 19%. Additionally, several companies have achieved
thin-film large area module efficiencies ranging from 8 to 12%.
These recent improvements in efficiency have greatly reduced
performance concerns leaving cost as the primary deterrent
preventing wide-scale commercial application of PV modules for
electricity generation.
[0011] Thin-film photovoltaics, namely amorphous silicon, cadmium
telluride, and copper-indium-diselenide (CIS), offer reduced cost
by employing deposition techniques widely used in the thin-film
industry for protective, decorative, and functional coatings.
Common examples of low cost commercial thin-film products include
water permeable coatings on polymer-based food packaging,
decorative coatings on architectural glass, low emissivity thermal
control coatings on residential and commercial glass, and scratch
and anti-reflective coatings on eyewear.
[0012] Of all thin film PV compositions, CIGS has demonstrated the
greatest potential for high performance and low cost. More
specifically, CIGS has achieved the highest laboratory efficiency
(18.8% by NREL), is stable, has low toxicity, and is truly
thin-film (requiring less than two microns layer thickness). These
characteristics allow for the large-scale low cost manufacturing of
CIGS PVs thereby enabling the penetration by thin-film PVs into
bulk power generation markets.
SUMMARY OF THE INVENTION
[0013] The overall efforts that surround the developments that are
specifically addressed in this document have introduced a
significant collection of innovations that apply to improved
low-cost, large-scale manufacturing to the field of photovoltaics
and thin films. Generally speaking, several key areas of these
innovations include: (1) a general fabrication procedure, including
a preferably roll-to-roll-type, process-chamber-segregated,
"continuous-motion", method for producing such a structure; (2) a
special multi-material vapor-deposition environment which is
created to implement an important co-evaporation, layer-deposition
procedure performed in and part of the method just mentioned; (3) a
structural system uniquely focused on creating a vapor environment
generally like that just referred to; (4) an organization of method
steps involved in the generation of such a vapor environment; (5) a
unique, vapor-creating, materials-distributing system, which
includes specially designed heated crucibles with carefully
arranged, spatially distributed, localized and generally
point-like, heated-nozzle sources of different metallic vapors, and
a special multi-fingered, comb-like, vapor-delivering manifold
structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a simplified schematic elevation generally
illustrating process steps and stages employed for creating a
photovoltaic (PV) module.
[0015] FIG. 2 is a fragmentary, plan view, taken generally in the
direction of arrow 2-2 in FIG. 1, showing a piece of a roll of long
and thin strip material employed in the disclosed system, with this
piece being illustrated as containing portions of three
boundary-defined, PV cells still resident in the strip
material.
[0016] FIG. 3 is a further-enlarged, fragmentary, simplified cross
section, taken generally along the line 3-3 in FIG. 1, illustrating
one form of a multiple-layer construction that makes up a
photovoltaic device.
[0017] FIG. 4 illustrates an alternative photovoltaic device layer
construction.
[0018] FIG. 5 is a simplified, schematic side elevation
illustrating roll-to-roll, Mo-deposition, strip processing that
takes place within one of the several, separated chambers that are
employed in the production of a PV device constructed in accordance
with the disclosed system.
[0019] FIG. 6 is a simplified, schematic side elevation
illustrating a chamber wherein one format of
copper-indium-gallium-diselenide (CIGS) or copper-indium-diselenide
(CIS) roll-to-roll strip processing occurs according to the
disclosed embodiment, with this one format involving movement of
strip material past three vapor-plume-creating stations.
[0020] FIG. 7 is a schematic, perspective and partially-fragmented
view of a deposition zone R which exists in the chamber pictured in
FIG. 6.
[0021] FIG. 8 is a schematic section view taken generally along the
line 8-8 in FIG. 7.
[0022] FIG. 9 is a fragmentary plan view generally along the line
9-9 in FIG. 6.
[0023] FIG. 10 is a fragmentary schematic perspective view of a
vapor-deposition zone R wherein certain vapor-creating and
vapor-presence phenomena exist and take place within the chamber
illustrated in FIGS. 6, 7 and 8.
[0024] FIG. 11 illustrates two or three roll-to-roll
chamber-processing steps. Specifically, FIG. 11 can be viewed as
illustrating (a) a step of applying a layer of cadmium-sulfide
(CdS), (b) a step, when employed, of applying a layer of
intrinsic-zinc-oxide (i-ZnO), and (c) a step of applying a
conductive-oxide layer, such as a zinc-oxide:aluminum (ZnO:Al)
layer. This single-view, "multiple-purpose" drawing figure is
employed in the interest of simplifying the overall collection of
drawings.
[0025] FIG. 12 presents a schematic side elevation view of an
alternative chamber wherein another format of CIGS or CIS
roll-to-roll strip processing occurs according to another
embodiment of the present invention, with this other format
involving movement of strip expanses past five vapor-creating
stations.
[0026] FIG. 13 is a schematic, perspective view of the chamber of
FIG. 12.
[0027] FIG. 14 is a schematic sectional view taken generally along
the line 14-14 in FIG. 13.
[0028] FIG. 15 schematically illustrates the basic component
elements (including the selenium delivery elements) of a
nozzle-based vapor-delivery apparatus according to the disclosed
system, with this apparatus being shown isolated and removed from
the chamber of FIG. 6.
[0029] FIG. 16 is a fragmentary plan viewed of an upper left
portion of the chamber of FIG. 9.
[0030] FIG. 17 is a fragmentary plan view illustrating portions of
one of the nozzle-bearing crucibles pictured in FIGS. 6-16 employed
for the delivery of copper, gallium and indium vapors.
[0031] FIG. 18 is an end elevation taken from the bottom side of
FIG. 17, also with certain regions broken away to show inside
details.
[0032] FIG. 19 is an enlarged, fragmentary cross section taken
generally along the line 19-19 in FIG. 17, showing details of a
vapor-plume-generating nozzle in the crucible pictured in FIGS. 9
and 16-18.
[0033] FIG. 20 is an enlarged, fragmentary cross-section taken
generally along the line 20-20 in FIG. 16, showing an outlet port
or nozzle in a sparger tube, or finger, which forms part of a
comb-like manifold structure that functions to deliver selenium
vapor in the disclosed embodiment.
[0034] FIG. 21 is a fragmentary cross section taken generally along
the line 21-21 in FIG. 16.
[0035] FIG. 22 is a graph picturing, generally, the ratio of copper
to gallium-plus-indium at different locations along the length of
deposition zone R. The left side of FIG. 22 relates to the entry
end of zone R.
[0036] FIG. 23 is a graph illustrating, generally, the ratio of
gallium to gallium-plus-indium at different points along the length
of zone R, with this graph picturing, at its left-hand side,
conditions at the entry end of zone R.
[0037] FIGS. 24, 25 and 26 present graphs that relate the effusion
rates (in grams per hour) as a function of molten-material
temperature for copper, gallium and indium, respectively.
[0038] FIGS. 27, 28 and 29 in a simplified schematic manner,
illustrate several alternative ways in which deposition fog that is
produced by employing the vapor-plume apparatus of the present
system can be "delivered" (in a directional sense) for creating a
thin-film layer on a surface in a strip of reception material.
[0039] FIG. 30 is a fragmentary plan view illustrating portions of
the vapor-delivery system in the chamber of FIGS. 12-14.
[0040] FIG. 31 pictorially illustrates flow of a vapor through an
orifice.
[0041] FIG. 32 depicts the molecular beam profile from an effusion
source.
[0042] FIG. 33 illustrates the parameters of equation 14.
[0043] FIG. 34 illustrates transverse thickness profiles for two
and three orifice systems.
[0044] FIG. 35 illustrates the instantaneous flux of copper gallium
and indium as a strip passes through the deposition zone.
[0045] FIG. 36 illustrates the instantaneous ratio of Cu/(In+Ga) as
the strip passes through the deposition zone.
[0046] FIG. 37 illustrates the instantaneous ratio of Ga/(In+Ga) as
the strip passes through the deposition zone.
[0047] FIG. 38 illustrates the cumulative ratio of Cu/(In+Ga) as
the strip passes through the deposition zone.
[0048] FIG. 39 illustrates the cumulative ratio of Ga/(In+Ga) as
the strip passes through the deposition zone.
[0049] FIG. 40 illustrates the instantaneous flux of constituents
as the strip passes through the deposition zone.
DETAILED DESCRIPTION OF THE INVENTION
[0050] FIG. 1 illustrates the steps involved preferably in making a
new kind of photovoltaic (PV) module in a roll-to-roll,
continuous-motion process in accordance with the present invention.
Those skilled in the art should understand that, while
roll-to-roll, continuous motion processing is employed in the
described embodiment, non-roll-to-roll procedures could be used
effectively in certain applications.
[0051] FIG. 1 shows two rolls 10, 12, at the left and right,
respectively, which symbolize the several roll-to-roll,
continuous-motion processing stages employed in the manufacturing
of this new kind of PV module. Roll 10 represents a pay-out roll,
and roll 12, a take-up roll. It should be understood that rolls 10,
12 are representative of the different pay-out and take-up rolls
that are employed in different isolated processing chambers. Thus,
there are typically multiple pay-out and take-up rolls used during
the overall process.
[0052] A stretched-out, flat portion of an elongate strip of thin,
flexible, substrate material 14 is shown extending between rolls
10, 12. This substrate strip has different amounts of applied
(deposited) PV-cell layer structure at different positions between
the rolls. The strip has opposite end winds that are distributed as
turns on pay-out roll 10 and take-up roll 12. The direction of
travel of the strip material during processing is indicated
generally by arrow 16. Curved arrows 18, 20 indicate, symbolically,
the related, associated directions of rotation of rolls 10, 12
about axes 10a, 12a, respectively, which are generally normal to
the plane of FIG. 1.
[0053] Reference herein to the substrate strip material 14 should
be understood to be reference to a strip of material whose overall
structural character changes as the material travels, in accordance
with processing steps, between rolls 10 and 12. Through the
processing steps, layers of various components that go into the
fabrication of the type of PV-module are added.
[0054] Nine separate individual processing chambers 22, 24, 26 23,
25, 27, 28, 30, 29 are illustrated as rectangular blocks in FIG. 1.
The various layers of materials that are used to form a PV module
according to this invention are applied or modified in these
chambers. The relative sizes of these blocks as pictured in FIG. 1
are not important. It should be noted that the steps represented by
some of the processing chambers are optional in some applications.
For instance, the intrinsic-zinc-oxide (i-ZnO) layer created in
chamber 28 may be omitted.
[0055] Processing begins with a bare starter roll, or strip, of
elongate thin-film, flexible substrate material, preferably
polyimide (PI), which is supplied from pay-out roll 10. This
uncoated material might typically have a width of about 33-cm, a
thickness of about 0.005-cm, and a length of up to about
300-meters. The width, thickness and length dimensions are, of
course, matters of choice, depending on the ultimate intended
application for finished PV modules. One PI material suitable for
use in the disclosed system is Upilex S, a material currently
available commercially from KISCO in Santa Clara, Calif.
[0056] PI is a suitable supporting substrate because it (1) can be
made very thin, and thus can offer good flexibility, and (2) can
tolerate relatively high-temperature environments without
sustaining damage. PI material also is quite widely commercially
available, and is relatively inexpensive. Of course other materials
having similar physical properties, such as any high-temperature
polymer, or a thin metal such as stainless steel, titanium, covar,
invar, tantalum, brass or niobium etc, can also be used with
appropriate process modifications.
[0057] A fragment of such a starter strip of PI is illustrated
generally on edge at 32, immediately above roll 10. PI fragment 32
advances to the right in FIG. 1 through the several processing
environments represented in this figure, and is referred to
throughout the discussion of this figure with the same reference
numeral 32.
[0058] A stress-compliant metal interlayer, preferably
nickel-vanadium (Ni--V), chosen to have intermediate thermal
expansion characteristics between the PI and a subsequently-applied
molybdenum (Mo) layers can be optionally utilized as the first
layer deposited onto the PI. This step is not illustrated in FIG.
1, but can either be accomplished in a chamber similar in
construction to chamber 22 or within a separate processing zone in
chamber 22.
[0059] Within chamber 22, and in a manner that will be more fully
discussed shortly, two layers of Mo, each containing entrained
oxygen, and each possessing a certain level of intentionally
created, desired, internal compressive stress, are formed on the
opposite sides, or faces, of PI strip 32. These two layers are
shown on the opposite faces (top and bottom in FIG. 1) of fragment
32 at 34, 36 above chamber 22. Layer 34 forms a back contact layer
for the PV module of the present invention. In the case of a
stainless steel substrate strip, the Mo back contact layer would
normally be replaced with a chromium/molybdenum (Cr/Mo)
bilayer.
[0060] Material emerging from Mo-processing in chamber 22 is ready
for introduction into chamber 24, wherein it is exposed to a unique
vapor deposition environment created in accordance with the current
invention to create an absorber layer.
[0061] In chamber 24, a multi-element crystalline absorber layer 38
is formed on Mo layer 34 by a unique multi-source co-evaporation
technique. Preferably, layer 38 is p-type semiconductor in the form
of copper-indium-gallium-diselenide (CIGS), or its readily
acceptable counterpart, copper-indium-diselenide (CIS). For
purposes of simplicity, the following discussion will generally
utilize CIS or CIGS to refer to CIS with or without metal alloys
such as gallium, aluminum, boron, or sulfur. These different
compositions, among others, can be used essentially interchangeably
as an absorber layer in various embodiments of the invention
depending on the particular properties desired in the final
product.
[0062] As a direct consequence of the particular co-deposition
events that take place in the unique fog environment that exists in
chamber 24, layer 38 has a consistent multi-element-compositional
make-up and uniform thickness throughout. This applies both
longitudinally over the length of the substrate and side-to-side
across the substrate. Next, adhesion of the CIGS layer to the
receiving surface of the pre Mo layer is excellent. The adhesion
occurs with (a) no appreciable fabrication-caused damage to the Mo
layer, and (b) formation of a proper-constituent content,
single-crystalline structure in the CIGS layer. Lastly, these
benefits are achieved using a relatively simple,
single-deposition-chamber operation.
[0063] The configuration of the stack of layers after emergence of
the substrate from chamber 24 is shown above chamber 24. Note that
in this fragmentary edge view, only the most recently added layer
(38) is designated with a layer reference numeral, along with PI
designator 32. This labeling approach is used throughout the
remainder of the description provided herein for FIG. 1.
[0064] In chamber 26, a window or buffer layer in the form of
cadmium-sulfide (CdS) is applied as a layer 40 extending over the
CIGS or CIS layer that was formed in chamber 24. The CdS layer is
preferably applied in a non-wet manner by radio-frequency (RF)
sputtering. This results in an overall multiple-layer structure
such as pictured generally above chamber 26.
[0065] After deposition of the Mo, CIGS, and CdS, the strip
proceeds through a sequence of operations, 23, 25, 27 designed to
first divide, then subsequently, serially connect adjacent
`divided` areas. The first operation is to scribe through all
deposited layers exposing bare, uncoated PI. This first scribe
functionally divides the elongate strip of deposited layers into
plural individual segments and thereby isolates each segment
electrically. These segments are held together by the PI, which
remains intact. The scribing technique used is a matter of choice,
with the preferred method herein accomplished using a high power
density laser.
[0066] Directly adjacent to the first scribe operation, a second
selective scribe is conducted removing the CdS and CIGS layers but
leaving the Mo intact in the as-deposited conditions. This
selective scribe forms a via, or channel, that will be later filled
in with a conductive oxide.
[0067] To prevent the conductive oxide in the top contact layer
from `filling in` the first scribe, Mo/CIGS/CdS, and in effect
reconnecting adjacent divided Mo regions, the scribe must be filled
in with an insulator. Preferably, this is accomplished with a UV
curable ink deposited in operation 27 with a commercially adapted
ink jet dispense head that is coincident with the high power
density laser.
[0068] If the optional, electrically insulating,
intrinsic-zinc-oxide (i-ZnO) layer is employed, this is prepared in
processing chamber 28 to create a layer arrangement such as that
pictured above chamber 28. In this layer arrangement, the i-ZnO
layer is shown at 42, overlying the CdS layer.
[0069] A top contact layer in the form of a transparent,
conductive-oxide overlayer 44, such as ITO or ZnO:Al layer, is
formed in processing chamber 30, either directly upon CdS layer 40
in no i-ZnO layer is used, or directly on i-ZnO layer 42 where it
is present. The resulting composite layer structure is indicated
generally above chamber 30 in FIG. 1.
[0070] Where an insulating i-ZnO layer, such as layer 42, is
created, the resulting overall layer structure includes what is
referred to later herein as a sandwich substructure, indicated
generally by arrows 46 in FIG. 1. Substructure 46 includes the
i-ZnO layer sandwiched between the CdS layer and the
zinc-oxide:aluminum (ZnO:Al) layer. Thus, where such a sandwich
substructure is employed, a contiguous protective intermediary
layer (i-ZnO) is provided interposed between the CIGS/CIS layer and
the top contact layer 44.
[0071] FIG. 3 illustrates a PV-cell structure 47, such as produced
from the process outlined in FIG. 1. It should be noted that the
layer thicknesses are not drawn to scale. The specific layer
arrangement which makes up device 47 includes, a stress
neutralizing back side coating, a PI substrate 32, a stress
compliant-intermediate coefficient of thermal expansion (CTE)
Ni-alloy layer, oxygen-entraining and internally-compressed Mo
layers 34, 36, CIGS or CIS layer 38, CdS layer 40, i-ZnO layer 42,
and overlying, transparent conductive-oxide, ZnO:Al layer 44. This
is a device wherein the option to employ i-ZnO has been elected.
The sandwich substructure 46 mentioned earlier, which includes this
i-ZnO layer, is identified with a bracket which bears reference
numeral 46 in FIG. 3.
[0072] FIG. 4 illustrates the upper-layer portion of another
PV-cell structure 49. Cell structure 49 differs from cell structure
47 by not containing an i-ZnO layer. Thus, in device 49,
conductive-oxide layer 44 lies directly on and in contact with CdS
layer 40. Those skilled in the art will recognize, and be familiar
with, the particular kinds of applications or situations wherein a
CdS layer alone can be utilized without the intermediary i-ZnO
layer.
[0073] The product of the above-described process is a series of
long narrow cells of active PV material monolithically
interconnected along their edges such that the top of a cell
becomes electrically connected to the bottom of the next cell. The
result is a chain of cells electrically connected in series to
generated a desired cumulative voltage for a given product
application. The resulting plurality of edge-to-edge series
interconnected, thin-film, flexible PV cells, are schematically
depicted in FIG. 2 as 50, 51 and 52. These three cells are
separated by lines that represent scribes 41, 45 and 47. Scribe 41
is overcoated with the ink jet deposited, UV curable ink. Each of
these cells has "plan" or "footprint" dimensions of about 33-cm by
about 0.4 to 1-cm, most preferably in the range 0.5 to 0.6-cm.
Representative scribes 41, 45, 47 are about 50 microns wide and
extend the entire cell length of 33-cm. The inkjet deposited
insulator, 43, overlying scribe 41 has dimensions of about 50 to
200-microns wide, with the optimum dimension of about 80 to
125-microns, and extends the entire cell width of 33-cm. It should
be noted that each of cells 50, 51, 52 in FIG. 2 includes the
optional i-ZnO layer. The previously described layers in the
module--PI substrate 32, Mo back contact layers 34 and 36, CIS
absorber layer 38, CdS buffer layer 40, i-ZnO insulating layer 42,
and ZnO:Al top contact layer 44--are illustrated as separated by
the six cutaway lines in FIG. 2.
[0074] Monolithic integration creates a large building block,
referred to as a submodule used to create a final module with
desired voltage and current for the expected application. Building
block size may be 30.times.30-cm, but is, of course, a matter of
choice depending on the starting strip material size and the
anticipated end-use of the product. At appropriate points in time
during the overall processing procedure which has just been
generally outlined in the `monolithic interconnection` discussion,
the functional electrical circuitry which is required in the
end-product PV module structure is prepared. This circuitry
establishes the needed electrical interconnects between adjacent
submodules. The specific monolithic interconnection patterning
configuration employed, and the technique(s) for creating such a
configuration, are matters of choice, and are well known to those
versed in the art.
[0075] FIGS. 5-8 and 10-14 each pictures schematically one of the
processing chambers described generally above. It should be noted
that the chamber pictured in FIG. 11 is readable to illustrate two
or three of the processing steps performed in the practice of this
invention, depending upon whether the optional i-ZnO layer is
created. The enclosures forming the processing chambers are
conventional in construction.
[0076] The short open arrows employed in FIGS. 5, 6, 11 and 12
represent various conventional hardware components that are
involved in the introduction of substances and control parameters
employed within the environment of the respective associated
chamber. For instance, the arrow for chamber 22 represents the
various conduits, valves, nozzles and controllers that are
conventionally used to introduce the gas/vapor constituents
utilized in chamber 22. Pay-out/take-up, roll-to-roll transport
systems are also depicted schematically in these figures. The
details of these systems are not illustrated, inasmuch as such
details can take any one of a large number of different forms that
are well known to those skilled in the relevant arts. Thus,
appropriate guide rollers, tensioners, stationary guides, and other
devices that would make up the construction, typically, of a
suitable roll-to-roll transport system, are omitted from the
drawing figures, and are not discussed herein in any detail.
[0077] Also pictured within the chamber-representing blocks shown
in FIGS. 5-7 and 11, as well as in FIGS. 8, 13 and 14, are certain
other schematically-represented, process-implementing components
that play defined roles in the specific activities that take place
within the respective associated chambers, as will be described
below. Unprocessed strip material which pays out from roll 58 is
initially heated to a temperature within the range of about 100 to
about 500.degree. C., and preferably to about 300.degree. C.
Heating drives unwanted moisture (water) out of the PI material in
preparation for uniform back contact deposition. Heating is
performed in a heating arena 63 sized in relation to strip
transport speed to assure proper pre-Mo-deposition drying of the PI
strip material. Heat is supplied in the heating arena by a pair of
elongate, resistive, heating filaments, such as heating elements
made available from the Omega Corporation, or from Watlow of
Cleveland, Ohio. The elements are serpentine structures embedded in
metal plates on the order of about 15-cm to about 150-cm in length,
and most preferably about 60-cm long. Thus, at a web speed of
approximately 30-cm per minute, each point on the PI strip material
remains within the heating arena 63 for approximately two minutes.
Commonly employed alternate processes such as direct current plasma
treating may also be used to remove unwanted water from the
polymeric strip material prior to back contact deposition.
[0078] Driving out moisture contained in the "starter" PI material
and carefully monitoring and controlling the input of water vapor
facilitates precise control over the process of entraining
oxygen.
[0079] Processing proceeds with the back contact sputter deposited
on the dried web in chamber 22. Two options exist, (1) first
depositing the stress compliant layer in a separate chamber
virtually identical to the chamber 22 or directly in line with the
Mo deposition in chamber 22, or (2) depositing the Mo directly on
the PI web. In either case, Mo is deposited on both sides of the PI
strip and contains the oxygen entrapment.
[0080] Whether processing the Ni-based stress compliant layer or
the Mo within chamber 22, a pay-out roll 58 of PI strip material,
such as that identified earlier, feeds a downstream take-up roll
60, with a long reach or length 62 of this material extending
between these two rolls. With a PI material having dimensions like
those described above, the initial diameter of roll 58 is typically
about 25-cm. Preferably, the long flat strip 62 which extends
between rolls 58, 60 is maintained at a tension in the range of
about 0.1- to about 10-kg, and preferably within the somewhat
smaller range of about 1.0- to about 5.0-kg. Most particularly, a
strip tension in this chamber of approximately 2.0-kg is suitable.
The linear transport speed of the material within chamber 22 is
generally between about 1-cm-per-minute and about 5 m-per-minute. A
transport speed of about 30-cm-per-minute is typical. Transport
speed, of course, can be varied as a matter of technical
choice.
[0081] The environment within chamber 22 during processing is
typically maintained at a controlled vacuum, ultimately, of
approximately between 1.0 and 15 millitorr, but preferable
2-milli-Torr. Preferably, the interior of chamber 22 is evacuated
initially to a pressure on the order of about 1.0.times.10.sup.-6
Ton, whereupon argon gas is introduced until the pressure in the
chamber rises to approximately the 2-milli-Torr level mentioned
above. This pressure level is then maintained to within about plus
or minus 0.5-milli-Torr, and preferably to within about plus or
minus 0.1-milli-Torr. 10.sup.3
[0082] After heat treating processing begins by transporting the
dried polyimide material through chamber 22. Ni--V alloy has proven
to be suitable for the metal interlayer. However any stress
compliant metal, with a coefficient of thermal expansion (CTE)
intermediate to that of the flexible substrate and the back
electrical contact could be employed. Preferred materials are
nickel based alloys that have enough alloying element to render the
Ni non-magnetic but retain the Ni stress compliance, intermediate
CTE, low bulk resistivity, and doesn't react with the overlying Mo.
Examples include nickel alloyed with 0 to 10 weight percent
vanadium, nickel alloyed with 0 to 15 weight percent molybdenum,
and Ni alloyed with 0 to 7 weight percent chromium. Additionally,
alternative metals that have the characteristic of intermediate CTE
and low resistivity could be used. Examples include copper and
copper alloys including brass, niobium, chromium, tantalum, and
titanium.
[0083] In each of stations 64, 66, the Ni alloy source employed for
the stress compliant layer sputter-deposition preferably takes the
form of a 99.95% sintered Ni with 7 weight percent vanadium block,
for example, which is commercially available from Pure Tech Inc.,
Carmel, N.Y. For this Ni-7V source material the sputtering cathodes
are suitably (and conventionally) operated at power levels ranging
from 1 to 10 kW each, with a 4.0-kW each being most preferable.
[0084] Processing further proceeds with the formation/deposition of
the two previously discussed Mo layers on opposing faces of the PI
web. The Mo layers are formed by a Mo-deposition plasma generated
inside the chamber 22 (FIG. 5). In each of stations 64, 66, the Mo
source employed for Mo sputter-deposition preferably takes the form
of a 99.95% pure vacuum arc cast Mo block, for example, one which
is commercially available from Climax Specialty Metals of
Cleveland, Ohio. For this Mo source material the sputtering
cathodes are suitably (and conventionally) operated at power levels
ranging from 1 to 10 kW each, with 4.0-kW each being most
preferable.
[0085] In each of sputtering stations 64, 66, the spacing between
the strip material and the Mo source material is arranged to be
about 1- to about 20-cm, and most preferably about 10-cm. These
spacing considerations play an important role in ensuring that the
local deposition regions defined between the substrate and the Mo
source material are especially suited to promote the introduction
of appropriate compressive stress into the forming Mo layers.
Within these regions, the pressure of argon gas increases and
decreases, respectively, as the distance between the substrate and
the sources decreases and increases. The preferable spacing
distances and the chamber pressures stated above assure a condition
in chamber 22 which causes the activity of argon atoms to promote a
slight, but desirable, level of internal compressive stress in each
of the two, forming Mo layers. It is believed that this compressive
stress comes into being as a result of the fact that argon atoms
"hammer" and effectively "ball-peen" the forming Mo layers. As
described in more detail below, the internal compressive stress
tends to counteract the tension imparted in the Mo layers that
would otherwise occur as the strip is heated and the PI expands
during the CIGS processing described later.
[0086] It is important to note that the use of conventional
sputtering techniques for depositing a Mo layer on a PI substrate
can result in a Composite structure that is insufficiently ductile.
That is, normal sputtering techniques will typically result in a Mo
layer which is brittle, and which is therefore a likely candidate
for fracturing and failure during subsequent processing steps.
[0087] We have found, as at least one component of the present
invention, that a solution to this problem involves the addition of
the mentioned entrained oxygen to the Mo layers. It is believed
that the oxygen introduced into chamber 22 according to the present
invention occupies the interstitial site of the BCC unit cell.
Oxygen present at interstitial sites creates a higher level of
internal compressive stress. Because the coefficient of thermal
expansion of the PI is much greater that of the Mo, the high level
of compressive stress is necessary to ensure the Mo remains in
compression during heating in the CIGS chamber. If the Mo is not
subject to enough compression, the thermal expansion mismatch
between the PI and Mo would cause the Mo to transition into tension
in the CIGS chamber and create cracking within the Mo. The
introduced oxygen contributes to the act of creating internal
compressive stress in the Mo layers. As a consequence, the Mo
layers become more tolerant to bending and more resistant to
cracking.
[0088] Thus, two principles are applied here to increase the
compressive stress within the Mo: (1) the combination of low
sputtering pressure and short target-to-substrate spacing creates
reflected neutral argon peening which imparts and intrinsic high
state of compression in the Mo film; and (2) the addition of oxygen
to create a higher level of internal compressive stress in the
Mo.
[0089] Under static vacuum conditions, i.e., while maintaining a
closely controlled vacuum on the order of about 10 milli-Torr,
within chamber 22, an oxygen/argon environmental condition develops
with (as mentioned earlier) an optimum molar ratio of argon atoms
to oxygen molecule on the order of between about 5-to-1 and about
50-to-1. Most preferably, this ratio is about 20-to-1. That is, for
every 20-argon-atoms present within the chamber, approximately
1-oxygen-molecule exists; for every 15-argon-atoms within the
chamber, there is approximately 1-oxygen-atom. With the
environmental parameters established as above stated within chamber
22, the two, desired, oxygen-entraining Mo layers result with an
appropriate level, in each layer, of compressive stress.
[0090] The resulting thickness of Mo layers 34, 36 can be monitored
in any appropriate conventional manner as, for example, in an
indirect manner by employing a standard Quartz Crystal Monitor
(QCM) which can be configured to measure the rate of sputtering
(rate of build-up) of sputtered materials in terms of
angstroms-per-second, in situ. A suitable standard QCM is available
from Liebold Inficom of Syracuse, N.Y. An end result thickness for
this layer which has been found to be entirely satisfactory is
about 0.5-micrometers, resulting in a layer sheet resistance of
about 0.75-ohms-per-square.
[0091] Regardless of the precise physical mechanism(s) by which the
presences of oxygen and argon cause these elements to assert
themselves on, and in relation to, the formation of Mo layers 34,
36, important end results are: (a) that each of these layers bonds
strongly to its associated PI strip face; and (b) that these layers
are able to tolerate temperature changes that occur in subsequent
processing without suffering temperature-induced cracking and
fracturing. Additionally, layers 34, 36, disposed as they are on
the opposite faces of the PI strip material, mechanically "balance"
one another to inhibit product curling, or "bending out of plane."
Such bending could be a problem and/or an inconvenience if only a
single Mo layer were used. By way of example, the induced internal
compression in a single Mo layer would be sufficient to curl the
substrate to the diameter of a pencil without the balancing effect
of the opposite layer.
[0092] Oxygen is preferably made available for entrainment into the
Mo layers by controlled, variable-rate introduction of heated (for
anti-condensation purposes) water vapor into chamber 22. Although
there are several techniques available to those skilled in the art
of sputtering, specifically, we have found that a vapor source mass
flow controller as supplied by MKS Instruments of Boulder, Colo. is
suitable mechanism for the introduction of the water vapor. Typical
water flow rate is 0.1 to 10 sccm with a preferable range of 1.5 to
2.5 sccm. By maintaining in chamber 22 a molar ratio in the range
of about 5:1 to about 50:1 for argon-to-oxygen atoms, appropriate
entrainment of oxygen is attained, although values outside this
range may give adequate results as well. Where, instead of using
introduced water vapor, gaseous oxygen is employed according to a
practice of the present invention, such oxygen is preferably
delivered into chamber 22 from an external supply tank typically at
approximately 10-cm.sup.3-per-minute. Argon gas from an external
supply tank is fed into chamber 22 preferably at a rate of about
200-cm.sup.3-per-minute.
[0093] The heated and dried PI substrate is passed through first
and second Mo sputtering stations, shown generally at 64, 66,
respectively. It is within these two stations that oxygen is
introduced to the forming Mo layers and argon acts with such added
oxygen, to create a level of internal compressive stress within the
Mo layers. The creation of this compressive stress is discussed in
more detail above. In station 64, what can be thought of as the
"back side" of the substrate (the upper side of stretch 62 in FIG.
5) is sputter-coated with Mo to create a layer like
previously-mentioned layer 36. In station 66, the opposite (lower)
side of the substrate is also so coated, here to create a PV-active
Mo layer, like previously mentioned layer 34.
[0094] When the entire strip of material has finished its
processing transport within chamber 22, and has been collected on
take-up roll 60, the latter is removed from chamber 22, and placed
in chamber 24 (see now FIGS. 6-8, 10 and 12-14) to become the
operative pay-out roll in that chamber. The strip material feeds in
the direction of arrow 16 from pay-out roll 60 to a downstream
take-up roll 68 in chamber 24. As the strip material moves through
chamber 24, the absorber CIGS or CIS layer 38 is formed on Mo layer
34. A transport-guide structure (not shown) is employed between
rolls 60, 68 in chamber 24 to support and guide the strip. The
short, open arrow which appears at the left side of the block
representation of chamber 24 in FIG. 6 symbolizes the hardware
provided for the delivery of appropriate constituent substances to
chamber 24.
[0095] It is within chamber 24, and specifically within a
deposition zone R, that the unique molten-liquid-to-vapor
co-evaporation process mentioned above for establishing a CIGS or a
CIS layer is performed. FIGS. 6-8 and 10 illustrate schematically a
configuration for, and certain environmental conditions within, the
inside of chamber 24. Chamber 24 is designed specifically for the
creation (according to one way of practicing this stage of the
present invention) of a CIGS (rather than a CIS) layer.
Accordingly, pictured as small blocks and tiny circles (FIG. 6
only) distributed along the bottom of chamber 24, are structures,
designated 70, 72, 74, 76, 78, 79, 81, which function to generate
vapors of copper (70), gallium (72) indium (74) and selenium (76,
78, 79, 81) for deposition. Structures 70-81 form the bulk of the
vapor-deposition-creating system 83 of the present invention. One
of the features that distinguishes this embodiment is that the
vapor deposition environment created in Zone R is a continuum of
evaporant fluxes as opposed a step-wise processes. Within Zone R,
fluxes are held constant and by translation over the sources the
receiving elongate substrate encounters a varying flux of material
specifically designed to achieve optimum performance in the CIGS
layer.
[0096] Blocks 70, 72, 74, which relate specifically to the
vapor-delivery of copper, gallium and indium, respectively,
represent heated effusion sources for generating plumes of vapor
derived from these three materials. Each of these three effusion
source includes: (1) an outer thermal control shield; (2) a boat,
reservoir, or crucible containing the associated molten copper,
gallium, or indium; (3) a lid that covers the associated case and
reservoir, and that contains three vapor-ejection nozzles per
crucible which assist in creating vapor plumes; and (4) a specially
designed and placed heater located near the nozzles. Each such
effusion source preferably comprises an elongate rectangular body
disposed with its long axis oriented substantially orthogonally
relative to the direction of strip-material travel in chamber
24.
[0097] Directing attention now particularly to FIGS. 16-19, along
with FIG. 9, a description now immediately follows which explains
the constructions of effusion sources 70, 72, 74 in more detail.
Each of these effusion sources is substantially the same in
construction. Accordingly, description now proceeds with reference
made specifically (where appropriate) only to effusion source 70.
At the onset of this description of effusion sources construction,
we should note that other specific effusion sources configurations,
with more or less than four principal parts, could be used if
desired. The effusion source construction parameters set forth and
referred to herein, should amply guide those skilled in the art
toward the making and using of other, alternative effusion sources
structures.
[0098] A thermal control shield is disposed external to the
crucible and forms part of the effusion source. The shielding
consists of two elements, (1) an outer shell, and (2) multiple
layers of thermally insulating materials. Function of the outer
shell is to restrict motion and hold in place the multilayer
insulation. The shell can be constructed as either a four wall lid
with a top that slides onto the crucible and shielding or as an
four wall rectangular box with a bottom that the shielding and
crucible insert into.
[0099] Suitable materials for the shell is limited to materials
that can tolerate the high temperature vacuum environment in the
presence of hot metal gases of copper, indium, and gallium, as well
as the reactive selenium. Successfully employed materials for the
shell have included graphite, boron nitride, tantalum sheet,
molybdenum sheet, tungsten sheet, rhenium sheet, and titanium
sheet. Additional acceptable shell materials include the
before-mentioned materials coated with a protective ceramic film
such as pyrolitic boron nitride, alumina, and titanium diboride.
The material should be chosen to provide sufficient thermal
insulation and stability in the reaction zone. A particularly
suitable material is a graphite shell.
[0100] Each of effusion source shells 100 has a length dimension
herein of about 45-cm, a width dimension (measured along the long
axis of chamber 24) of about 7-cm, and a height dimension of about
7-cm. Length and width can be either proportionally or
non-proportionally scaled to match the ZONE R and substrate with
dimensions, and are matters of choice. From longitudinal
centerline-to-centerline of adjacent effusion sources, a preferred
distance is about 8.9-cm. Similar to the effusion source size the
centerline-to-centerline spacing can be adjusted to the ZONE R
dimensions and to the substrate width and are matters of choice.
However, from a "plan view" perspective of the effusion source
nozzle organization, this structure is generally centered with
respect to the footprint of ZONE R.
[0101] Moving closer to the crucible is a multi-layer insulation
that shields the high temperature sources operating at 1000 to
1700.degree. C. from other items in ZONE R, including the walls
that define ZONE R. Among other things the most important function
of the shielding is three-fold, (1) to reduce the electrical power
requirements necessary to maintain the source at the elevated
temperature for extended time periods, and (2) to minimize
radiative thermal load and subsequent heating of the surround
components in zone R, and (3) eliminate thermal `cross talk`
between adjacent sources operating at substantially different
temperatures.
[0102] Within a vacuum where the key thermal transport mechanism is
radiation (as opposed to convection or conduction), effective
shielding consists of several layers, preferably with a low
emissivity. Generally, the CIGS effusion source shielding should
offer, (1) thermal stability at temperatures from 1000 to
1700.degree. C., (2) stable and consistent thermal properties, (3)
stability in vacuum in the presence of gaseous metals and selenium,
and (4) stable when in contact with the shell, crucible, and lid
materials. Successfully employed materials for the effusion source
shielding have included graphite felt, graphite foil, ceramic felt,
boron nitride sheet, tantalum sheet, molybdenum sheet, tungsten
sheet, rhenium sheet, and titanium sheet all of which are
commercially available from several vendors. The selected material
should provide thermal insulation and stability in the reaction
zone and multiple layers of graphite felt and graphite foil have
proven particularly suitable. Three felt layers 101 and nine foil
layers 103 in a alternating sequence starting at the crucible of
felt, three foils, felt, three foils, felt, three foils provides a
suitable specific configuration.
[0103] Inserted in a somewhat nested condition within the walls of
case 100, and formed of pyrolitic boron nitride coated graphite, is
an elongate boat, reservoir, or crucible, 102 which is generally
rectangular in form, and which includes a base 102a, a pair of
elongate side walls 102b, 102c which join with base 102a, and a
pair of end walls 102d, 102e which join with the reservoir base and
side walls. Although pyrolitic boron nitride coated graphite is the
crucible material of choice, several materials are suitable for the
crucible including metals of tantalum, molybdenum, and tungsten,
several forms of uncoated graphite, and other thermally and vacuum
stable ceramics such as alumina, sintered boron nitride and
titanium diboride. Additionally, the crucible can be formed from a
combination of the above-mentioned materials coated with a
thermally stable coating, CTE matched to the crucible material,
such as pyrolitic boron nitride, alumina, and titanium diboride. As
can be seen especially in FIG. 17, end walls 102d, 102e, as such
appear in this figure, have thicknesses, of about 0.125-inches,
with side walls 102b, 102c having a somewhat smaller thickness of
about 0.1-inches. Base 102a has a thickness of about 0.1-inches.
End walls 102d, 102e each has a pocket-like void space (only one
being shown), such as void space 102f in wall 102e, which void
space is somewhat planar, with the plane of this void space being
substantially normal to the plane of FIG. 17 The role of the pocket
is to improve the temperature uniformity of the molten metal within
the crucible. The pocket improves thermal uniformity by reducing
the thermal transport by conduction to the end of the crucible
where heat is radiated to the shielding. Formed in base 102a, and
opening to the outside surface of end wall 102e, are two
laterally-spaced elongate bores (no reference numbers shown) which
receive two elongate temperature-monitoring thermocouples such as
thermocouples 104, 106 pictured at the lower side of FIG. 18.
[0104] The lower end of crucible 102 in FIG. 17 essentially
occupies the previously-mentioned open end of case 100, through
which open end the reservoir can be inserted and removed relative
to what can be thought of as the inside volumetric space provided
in case 100. This reservoir includes an elongate central deep well
102g that receives and contains molten copper--such molten copper
being indicated at 108 in FIG. 18.
[0105] Fitting snugly within the upper portions of
previously-mentioned crucible walls 102a, 102b, 102c, 102d is an
elongate lid 110 formed of graphite. The wall thickness of the
material making up lid 110 is about 0.1-inches. Suitably formed in
the upper part of lid 110, i.e., in that part in the lid that faces
the viewer in FIG. 17, and which is near the top of FIG. 18, are
the three previously mentioned, spaced vapor-delivery nozzles, such
as nozzle 112 pictured in FIGS. 17 and 18. The nozzles are
essentially unitary with lid 110. In the preferred embodiment, the
nozzles are integrally machined into the lid and are formed of
graphite, however, nozzles constructed of sintered boron nitride,
pyrolitic boron nitride coated graphite, and many refractory metals
such as molybdenum, tantalum, and tungsten have been constructed.
Nozzles formed of materials different from the machined lid are
inserted into matching holes in the graphite lid.
[0106] The nozzles lie in a common vertical plane which
substantially contains the long axis of vessel 70, with the central
nozzle being substantially centered relative to the opposite ends
of the lid, and the two end nozzles having their axial centerlines
each spaced from that of the central nozzle by about 15.0-cm.
Nozzle spacing can be adjusted based on the source-to-substrate
spacing using methodologies described later in this disclosure. In
brief summary, as the source-to-substrate space increases, the
nozzles spacing increases, and conversely, as the
source-to-substrate spacing decreases, the inter-nozzle spacing
increases. Typical inter-nozzle spacing range from about 1 to 20
cm. The discharge tips of the nozzles lie preferably in a common
plane, which plane substantially parallels the plane of the path
followed by the expanse of strip material passing through zone R.
This nozzle-tip plane is spaced from (above) the
substrate-transport plane in chamber 24 from 10 to 25-cm but most
often at about 18-cm.
[0107] Nozzle 112 (typical of all of the crucible nozzles) is shown
in an enlarged and more detailed manner in FIG. 19. Here, one can
see that this nozzle includes an outlet port 114 which is generally
cylindrical with a wall 115, and which possesses an axial length
(the vertical dimension of port 114 in FIG. 19) of about 0.95-cm,
and a diameter, pictured as the horizontal dimension of the port in
FIG. 19, also of about 0.95-cm. The discharge openings in the
nozzles each preferably has a diameter within the range of about
0.25-cm to about 2.5-cm, and a depth, measured normal to the plane
of FIG. 17, which preferably lies in the same range. The diameter
and depth dimensions are preferably about equal.
[0108] Extending appropriately into lid 110 from the upper end
thereof in FIG. 17, and through previously mentioned bores, are
two, elongate, conventional electrically-energized heating elements
114, 116, respectively. These heating elements, which are formed
preferably of pyrolithic graphite lie in appropriate slots machined
in the graphite lid. Several refractory metals such as tantalum,
molybdenum, and tungsten have also been successfully used as the
effusion source heater(s). As a result of the heater location, the
respective lids and nozzles in each of crucibles 70, 72, 74 remain
and operate at temperatures which are higher than the temperatures
of the associated molten materials within the crucible.
[0109] The entire effusion source arrangement with the exterior
shell, shielding, and spaced exposed nozzles, produces proper
deposition of the CIGS materials, while at the same time protecting
the strip material from overheating, and substantially eliminates
undesired condensation of metal vapor liberated from the boats in
the regions of the openings of the nozzles. The traveling strip
material, while directly exposed to the individual heated nozzles,
is shielded from direct exposure to the molten source materials.
While two elements are shown herein, more or less in number could
be used. For example, a single, generally U-shaped heating element
having two long runs leading to a reverse bend within the crucible
could be employed. U-shaped is the preferred method because it
allows the heater to be rigidly mounted to the electrical energy
source on one end, allowing the other end to freely move as a
result of thermal expansion, in affect, representing a roadway
bridge. Hard mounting the electrical source on both ends would
likely cause excessive deformation of the heating element due to
thermal expansion, leading to premature failure.
[0110] FIG. 10, in dashed lines, shows representative plumes 70a,
72a which emanate from effusion sources 70, 72, respectively, as if
to form, nominally, what we sometimes refer to as a vapor-tufted
environment, such as was generally mentioned earlier. Use of the
word "tufted" herein is made simply to evoke visualization of how a
co-mingled deposition-vapor fog comes into being in chamber 24. The
copper, gallium and indium vapor plumes that exist during CIGS
deposition in chamber 24 are thought to be a vector quantity in the
shape of the form sin.sup.2.theta. as shown in FIG. 32. Effusion
from a single orifice source is essentially the sum of two
processes. The first of these is the evaporation of the source
material, the second is the flow of the vapor through the orifice
as pictorially shown in FIG. 31. Each of these processes provides a
"resistance" to the effusion of the source material. Evaporation of
the source materials will be described later.
[0111] The theory of low-pressure gas flow though an orifice is
well understood and can be predicted to within 5 or 10%. Within a
vacuum there are two regimes in which low pressure gas flow occurs:
(1) the free molecular and (2) transitional flow regimes. In
qualitative terms, the free molecular regime describes gas flow in
which gas phase collisions are rare enough that only molecule-wall
collisions are significant. Transitional flow describes a situation
where molecule-molecule collisions occur frequently enough to
affect the flow behavior, but do not occur frequently enough to be
described accurately by the full viscous flow model as would be
used at near atmospheric pressure.
[0112] The determination of the applicable flow regime is achieved
by calculating the Knudsen number:
Kn = .lamda. .GAMMA. ( eqn . 1 ) ##EQU00001##
[0113] where .lamda. is the mean free path and .GAMMA. is the
orifice radius. If Kn>1, the system is in the free molecular
regime and the mass flow rate is described by the following
equation:
F eff = .GAMMA. 2 K ( M 2 .pi. RT ) 1 / 2 ( p 1 - p 2 ) ( eqn . 2 )
##EQU00002##
where F is the mass flow rate through the orifice, M is the
molecular weight of the gas molecules, R is the ideal gas constant,
T is the temperature, and p.sub.1 and p.sub.2 are the pressures on
either side of the orifice. K is an empirically determined constant
which is a function of the aspect ratio (L/.GAMMA.where L is the
orifice length) of the orifice. For L/.GAMMA.<1.5, K is given
by
K = 1 1 + 0.5 L .GAMMA. ( eqn . 3 ) ##EQU00003##
For L/.GAMMA.>1.5,
[0114] K = 1 + 0.4 ( L .GAMMA. ) 1 + 0.95 ( L .GAMMA. ) + 0.15 ( L
.GAMMA. ) 2 ( eqn . 4 ) ##EQU00004##
[0115] In the case of 0.01<Kn<1, there are two equations
which must be solved for both F and p':
F eff = .pi. .GAMMA. 2 C ( M 2 .pi. RT ) 1 / 2 ( p 1 - p ' ) ( eqn
. 5 ) F eff = .pi..GAMMA. 4 16 .mu. L ( p '2 - p 2 2 ) ( 1 + 4 ( 2
f d - 1 ) .lamda. .GAMMA. ) ( M RT ) ( eqn . 6 ) ##EQU00005##
where .mu. is the viscosity, f.sub.d is the fraction of molecules
diffusely reflected from the walls (0.85<f<1), and C is a
constant (C=20).
[0116] After determining the mass flow rate, F.sub.eff, through the
orifice it becomes necessary to describe the flux intensity profile
of the effusing beam, that is, to determine f=f(r, .theta.), where
f is the flux, r is the distance from the effusion orifice, and
.theta. is the azimuthal angle.
[0117] An equation describing the flux as a function of .theta. and
the rate of effusion is obtained by setting the rate of effusion
equal to the integral of the flux over a hemispherical area.
Assuming that the flux can be approximated by f=a cos.sup.n
.theta.:
F eff = .intg. 0 .pi. 2 .intg. 0 2 .pi. a cos n .theta. ( r 2 sin
.theta. ) .differential. .xi. .differential. .theta. ( eqn . 7 )
##EQU00006##
After solving for a in eqn. 7,
f = F eff ( n + 1 ) 2 .pi. r 2 cos n .theta. ( eqn . 8 )
##EQU00007##
Although the a priori prediction of a value for n is not completely
well defined, a safe approximation for both transitional flow
regimes and free molecular regimes of L/D=1 is n=2. The molecular
beam profile is depicted in FIG. 32.
[0118] Effusion rate from a given nozzle is a function of vapor
pressure within the inside of the associated crucible, and that
this pressure is a function of the temperature of the molten
material inside the reservoir in that crucible. Thus, for a
particular, selected nozzle size, the effusion rate to be expected
is essentially a function of the temperature within the
crucible.
[0119] Predicting the rates of effusion of the copper, gallium, and
indium sources is a straightforward solution of the equations
above. The temperature-vapor pressure data of the three elements
are easily found in literature and can be approximated by:
Cu: log
P.sub.Cu.sup.sat=-19.818+2.0643.times.10.sup.-2.times.T-5.2119.t-
imes.10.sup.-6.times.T.sup.2 (eqn. 9)
Ga: log
P.sub.Ga.sup.sat=-17.2982+2.0829.times.10.sup.-2.times.T-6.0.tim-
es.10.sup.-6.times.T.sup.2 (eqn. 10)
In: log
P.sub.In.sup.sat=-16.238+2.1427.times.10.sup.-2.times.T-6.7885.t-
imes.10.sup.-6.times.T.sup.2 (eqn. 11)
where pressure is in ton and temperature is in .degree. C.
[0120] FIGS. 24-26, graphically picture the respective effusion
rates of copper, gallium and indium that we have observed with
respect to nozzles constructed in accordance with the descriptive
information given above. These graphs relate to effusion rate
(grams-per-hour for different molten-material temperatures) with
respect to the activity of a single nozzle. In particular, FIGS.
24-26 illustrate the effusion rate of copper, gallium, and indium
as a function of temperature for an orifice 0.9525-cm in diameter
and 0.9525-cm in length. The copper, indium, and gallium sources
all operate in the free molecular flow regime. It is also
noteworthy that the evaporation process in these cases is
responsible for <5% of the resistance of the total effusion
process. That is, the orifice geometry is the overwhelming factor
in determining rate of effusion.
[0121] Further application of the above principals reveals that the
vapor flux incident at the deposition surface presented in chamber
24 is, essentially, a function of the temperature within a selected
crucible, the distance between that crucible and the intended
deposition surface, and the angle between a point on the substrate
and the effusion source nozzle. Accordingly, it will be apparent
that, for a fixed distance being decided upon to exist between the
crucibles and the traveling strip material in chamber 24 traveling
at a constant speed, the amount of metal vapor (collectively)
incident at the deposition surface of the traveling strip material
is essentially a function of the temperature of the molten
materials within the crucibles.
[0122] Thus, it should be very apparent, that, by carefully
controlling the temperatures of the molten materials within
crucibles 70, 72, 74, and by maintaining substantially constant the
transport or travel speed of the strip material in chamber 24, the
rate at which metal vapor from each crucible is applied to the
appropriate deposition surface of the traveling strip material can
be controlled readily to produce uniform thin-layer deposition
thickness along the length of such material.
[0123] In accordance with a preferred embodiment of the system of
the present invention, the molten temperature of copper within
crucible 70 is suitably maintained in the range of about
1400.degree. C. to about 1700.degree. C., and most preferably at a
temperature of about 1565.degree. C. (.+-.about 1.degree. C.). The
temperature of the molten gallium within crucible 72 is suitably
maintained within the range of about 1000.degree. C. to about
1350.degree. C., and most preferably at about 1225.degree. C.
(.+-.about 1.degree. C.). Finally, the temperature of the molten
indium within crucible 74 is most appropriately (according to what
we have learned in our practice of use of this invention)
maintained in the range of about 950.degree. C. to about
1300.degree. C., and most preferably at about 1205.degree. C.
(.+-.about 1.degree. C.). The temperature of molten selenium in
reservoir 85b is preferably maintained in the range of about
275.degree. C. to about 500.degree. C., and most preferably to
about 415.degree. C. (.+-.about 10.degree. C.). Although these
temperatures are in the preferred range for the disclosed sources
with 0.95-cm orifices, the rate restricting nozzle principals
outlined herein indicated that as the orifice size increases, the
temperature would decrease to achieve a constant rate, or
alternatively, as the orifice decreases, the temperature would
increase to achieve a constant rate.
[0124] It should be noted that, although the effusion rate (and
hence the flux) of selenium vapor is quite sensitive to changes in
temperature in the body of molten selenium in reservoir 85b,
changes in selenium flux over time do not appreciably affect the
formation of the end-result CIGS/CIS layer because the chamber is
already essentially saturated with selenium.
[0125] By carefully controlling the vapor effusion rates from the
nozzles in crucibles 70, 72, 74, and from those in the sparger
tubes, for example by proper dimensioning of the respective
collections of nozzles, and further by carefully controlling the
temperatures of the molten metals within the reservoirs in the
crucibles and in the selenium delivery structures, and thereby
effectively controlling the pressures within these crucibles and
the "selenium structures", the desired effusion characteristics of
the generated vapor plumes may also be carefully controlled.
Coupling to these considerations, the further considerations of (1)
selecting an appropriate number of nozzles for each vapor-delivery
crucible and sparger tube, (2) appropriately positioning the
nozzles in the lids of the respective crucibles and in the sparger
tubes, and (3) carefully arranging the overall disposition layout
of the crucibles and sparger tubes, an optimum aggregate
multiple-plume configuration can be obtained.
[0126] The particular positionings and sizings of the nozzles
present in chamber 24 as described herein, with each of the nozzles
having substantially the same configuration as each other nozzle,
produces a preferred arrangement in chamber 24 for the deposition
of our desired CIGS/CIS layer. From a reading of plume geometry
principles described herein, coupled with a careful review of the
specific design considerations so far described herein for the
layouts of the crucibles and their nozzles, those skilled in the
art will see that careful selection of the size and number of
orifices for each such kind of crucible can produce substantially
any desired, and substantially transversely uniform, vapor flux
across the width of a deposition surface, which uniformity will
result in a substantially uniform layer thickness throughout the
resulting deposited thin-film layer.
[0127] The flux seen at a surface is a function of both the
intensity of the incident flux and angle of incidence. As the angle
of incidence, .PHI. here defined as the angle between the surface
normal vector and flux vector), increases, the deposition flux seen
by the surface decreases as the cosine of the angle of
incidence.
J.sub.dep=f cos .PHI. (eqn. 12)
Combining equations 11 and 12, we obtain an expression for the
deposition flux at a point on a surface due to a single source:
f dep = F eff ( n + 1 ) 2 .pi. r 2 cos n .theta. cos .PHI. ( eqn .
13 ) ##EQU00008##
[0128] If the centerline of the source orifice is parallel to the
surface normal vector (i.e. the source is not tilted--See FIG. 33),
eqn. 13 reduces to
f dep = F eff ( n + 1 ) 2 .pi. r 2 cos n + 1 .theta. ( eqn . 14 )
##EQU00009##
Knowing the molecular weight, MW, and density .rho., of the
material being deposited, the rate of growth,
.delta.(thickness/time) at a point on the substrate surface is
written as:
.delta. = F eff ( n + 1 ) 2 .pi. r 2 cos n + 1 .theta. .times. MW
.rho. ( eqn . 15 ) ##EQU00010##
By applying the equations outlined above, the cumulative flux
distribution of several nozzles within a single source can be
determined, and subsequently the nozzle spacing can be determined
as discussed early in the document during the detailed disclosure
of the effusion source dimensions. FIG. 34 graphically pictures the
respective effect of overlapping plumes for two and three nozzles
within a 15-cm span of a single effusion source. This graph shows
the optimum nozzle spacing is approximately 15-cm as disclosed
earlier.
[0129] Further regarding these nozzles/discharge openings, under
certain circumstances, it may be desirable to construct and employ,
for one or more of the several deposition materials, discharge
orifices which have different discharge diameters or shapes. In
other words, a given vessel or boat for a particular deposition
material may have associated with it plural orifices with different
discharge diameters or shapes. Orifice discharge diameter plays an
important role, inter alia, in defining certain aspects (for
example, vapor-discharge volume per unit of time) of its associated
discharge vapor plume.
[0130] Those skilled in the art will recognize, accordingly, that
certain aspects of discharge behavior can be adjusted to suit
particular needs and circumstances through suitable adjustments
made in nozzle characteristics. In addition, it is possible to have
the effusion sources supply materials in a downward, lateral or
oblique orientation to the substrate, as shown in FIGS. 27-29.
[0131] It should be noted that, although the disclosed embodiment
utilizes separate chambers, it is also possible to combine two or
more of the processing steps into a single chamber. However,
separate chamber processing offers a number of advantages. The
layers of CIGS (Mo, CIGS, CdS, i-ZnO, and ITO) consist of several
very mobile atoms when in a gaseous form in a vacuum where the mean
free path is long, especially selenium, sulfur, cadmium, zinc, and
tin. This mobility is primarily related to high vapor pressures
even at moderate temperatures. Cross-contamination of one element
in another processing zone can dramatically alter (negatively) the
properties of the layer. In in-line glass lines, several isolation
lock chambers are used to prevent cross contamination. An
individuated plate of glass is moved into the lock from the
upstream deposition zone while a valve isolates the lock from the
downstream processing zone. Once the plate is fully in the zone,
the valve is closed between the lock and the upstream zone, the
vacuum environment is stabilized to the downstream zone, and then
the valve to the downstream zone is opened. The lock chambers
usually also contain special provisions to preferentially pump
constituents (i.e., Se, water) that reside in the processing zones
on either side of the lock chamber. This approach is not
technically practical with a fully continuous roll to roll process,
especially one in which only the backside of the web is contacted
with rollers. It is done in some instances when applying hard
coatings to flexible substrates but these systems usually contain
nip rolls or thin membranes that drag on the coated side of the
substrate to create a seal (i.e., the back of the strip is sealed
with a roller and the front is sealed with a roller or dragging
membrane. However, it is preferable not to contact both sides of
the web.
[0132] Separate chambers are also beneficial because of the
substantial differences in environment between separate zones,
i.e., Mo is typically done at .about.1.5 mtorr with argon and
water, CIGS is typically done at 0.001 mtorr with no argon or
water, CdS is typically done at 2 mtorr with just argon. With a
combined chamber, a lock is used to stabilize the environment
before the valves separating the zones from the lock is opened. For
example, as the lock chamber is brought to the pressure of the Mo
zone, the valve separating the Mo zone from the lock is opened.
Bringing the two zones to the same pressure is important to prevent
a pressure surge in the Mo zone. The valve between Mo and the lock
is closed, the lock is pumped to the pressure of the CIGS
processing chamber, and then the valve between the lock and the
CIGS zone is opened. Such an arrangement adds considerable
unnecessary complexity to the system.
[0133] Another advantage of separate chamber processing is that
downtime for unscheduled maintenance for repair does not take down
the entire plant. This is particularly important where there are
several chambers installed for each layer because even if one CIGS
is down, for example, the entire plant is not down. In addition,
scheduled downtime for source replenishment does not require
stopping an entire line. It is also easier to scale the processing
to the desired production rate because the chambers can be
independently sized, i.e., not all chambers have to run at the same
rate. For example, a single Mo chamber may be able to process web
fast enough for four CIGS chambers, two CdS chambers and two ITO
chambers. Similarly, additional chambers can be added more
easily.
[0134] Chamber 24 is preferably maintained at a pressure of about
5.times.10.sup.-5-Torr. Tension within the straight part of the
transported moving strip (between rolls 60, 68) is held typically
to within a range of about 0.5- to about 20-kg, and most preferably
to within a range of about 3- to about 4-kgs. Linear transport
speed lies preferably within the range of about 15-cm-per-minute to
about 2-meters-per-minute, and most preferably about
30-cm-per-minute.
[0135] As strip material travels in chamber 24, from left-to-right
as indicated by arrow 16, the developing CIGS layer increases
generally quite linearly in thickness, from zero at the entrance
end of deposition zone R, to (preferably) within the range of about
1- to about 3-micrometers, and most preferably to about 1.7 to
2.0-micrometers, at the downstream, exit end of this zone.
[0136] Zone R (the fog-containing zone) is illustrated in FIG. 10
as a freestanding rectangular block. Zone R has a length Z herein
(FIGS. 6, 7, 9 and 10) of about 10- to about 250-cm, and most
preferably about 80-cm, a width W (FIGS. 6, 7, 9 and 10) of about
90-cm, and a height H (FIGS. 6, 7 and 10) of about 25-cm. All Zone
R dimensions are matters of choice and are somewhat a function of
the substrate strip width and the effusion source size, and as
mentioned before effusion source design and construction techniques
outlined in this patent can be universally applied to very small
strip widths and effusion source sizes, (i.e., 2.5-cm wide
substrate strip and 5-cm wide sources) to very large reaction zones
and substrate strip widths (1.5-m wide substrate strip and 2-m wide
effusion sources). The fog in zone R is effective, as strip
material passes through the zone, to create an extremely
uniform-thickness, controlled-content, multi-element CIGS layer,
such as previously mentioned layer 38.
[0137] Referring to FIG. 6, circles 76, 78, 79, 81 represent end
views of plural, laterally spaced, generally parallel elongate
sparger tubes (or fingers) that form part of a comb-like, single
manifold (see also FIG. 9) that supplies, to the deposition
environment within chamber 24, a relatively evenly volumetrically
dispersed selenium vapor. Each sparger tube has a length of about
30-inches and a diameter of 0.25-in, and adjacent pairs of these
tubes are characterized by a tube-to-tube spacing of about 8.9-cm.
Length and spacing of the sparger tubes are, similar to the
effusion sources, material of choice based on the substrate strip
width and the effusion source size. Again principals outlined in
this disclosure are applicable regardless of scale. Each tube, as
illustrated herein, has three linearly spaced and distributed
outlet orifices or vapor-ejection nozzles that are spaced from one
another by about 15-cm. The diameter of each such sparger-tube
orifice is about 0.1-cm. The "collection" of sparger-tube orifices
(from a plan point of view) is substantially centered on Z.times.W
footprint of zone R, and these orifice's discharge (upper) ends lie
generally in a common plane which substantially parallels the
strip-material transport plane at a distance of about 17.8-cm.
[0138] Four such sparger tubes are employed in the chamber
structure now being described, with each sparger tube being
equipped three vapor-ejection nozzles, such as representative
nozzle 76a in sparger tube 76 (see particularly FIGS. 9, 16 and
20). Nozzle 76a has a diameter herein of about 0.100-cm (the
nozzle's vertical dimension in FIG. 20), and an axial length of
about 0.71-cm (its horizontal dimension in FIG. 20). Significantly,
the delivered selenium vapor, which resides essentially at the
saturation point within chamber 24, is derived from a single pool,
site, or reservoir 85b (shown in FIGS. 9 and 15) of molten
selenium.
[0139] These tubes are preferably made of stainless steel, but can
be constructed of any material that is stable at high temperature,
in vacuum in the presence of selenium and metal vapors. The tubes
are located generally as shown in positions effectively bracketing
opposite (left and right) sides in FIGS. 6 and 9 of each of blocks
70, 72, 74. This special selenium-vapor distribution system is
preferable to prior art systems, which typically employ a plurality
of spaced molten pools of selenium. Heat which functions to trigger
and to sustain appropriate downstream vapor-distribution operation
of this selenium-delivery system is derived from the close
proximities of the sparger tubes and the heated crucibles in
structures 70, 72, 74. In other words, radiant heat from these
crucibles plays an important role in the delivery of selenium.
[0140] It should be noted that crucibles of structures 70, 72, 74,
sparger tubes 76, 78, 79, 81, and the respective nozzles associated
with these structures, are collectively substantially centered on
the footprint of zone R (its W and Z dimensions). Preferably, the
width W of zone R is somewhat greater than the width of the
traveling strip material, and laterally, the width dimension of the
strip material is substantially centered on width W. Consequently,
the lateral boundaries, or edges, of the strip material are
completely within zone R, and as strip material passes through the
zone, it is treated to a generally bilaterally symmetrical
engagement with the vapor components being deposited. The bilateral
symmetry just mentioned is such symmetry viewed relative to the
long axis 24a of chamber 24. See FIG. 9.
[0141] In general terms, and as is pictured schematically by the
three downwardly-curving dashed lines in FIG. 6 that represent
billowing plumes (such as previously mentioned plumes 70a, 72a) of
copper, gallium and indium, created within chamber 24, generally in
the previously mentioned deposition region, or zone, R, is a
special co-evaporation fog (mentioned earlier) which is formed from
these several effusion plumes (copper, gallium and indium), and
from the selenium vapor (the sparger tubes) mentioned above.
[0142] At substantially each longitudinal point or transverse slice
along zone R, and as a result of the nozzle spacing determined
earlier, the fog therein is effectively uniform across the width of
the zone, i.e., along the direction transverse to the direction of
strip-material travel. As a result, each point along every line
extending across the width of the strip material (perpendicular to
the direction of material travel) advantageously is subject to
approximately the same material-specific flux from each
material-specific boat at any particular instant.
[0143] As the strip of Mo-coated substrate material travels in
chamber 24 through the vapor deposition zone, each point on that
material first passes directly over the copper source, thereafter
over the gallium source, thereafter over the indium source, and
throughout, over the selenium sources (the sparger tubes). With
this arrangement, and recognizing that selenium vapor is
distributed rather evenly throughout zone R, each point on the
moving strip material first encounters a continuum co-evaporation
environment which is substantially copper-rich, but which also
contains lesser amounts of gallium and indium vapor. As a
particular point on the strip travels through the fog, it next
encounters a region, in the comingled, aggregate fog, which is
substantially gallium-rich, but which also contains copper and
indium vapor. Each point on the strip thereafter encounters a
region in zone R that is substantially indium-rich, but which
contains lesser concentrations of gallium vapor and copper vapor.
Significantly and preferably, this transition from copper-rich,
through gallium-rich and finally to an indium-rich vapor occurs in
a setting wherein the specific, individual fluxes from molten
copper, gallium, indium, and selenium sources are maintained
substantially constant as a function of time. In the process of the
invention now being described, it is the travel of the strip
material through zone R that causes each point on that material to
experience the aforementioned, longitudinally-spatially-changing
vapor (fog) sub-environments. By maintaining the effusion rate from
each boat substantially constant over time, and by moving the strip
material at a substantially constant rate of speed, the
contribution to the CIGS layer attributable to each of the molten
metal sources may be precisely controlled along the length of the
deposition zone. Using similar equations applied to determine the
optimum nozzle spacing within a source, as the strip transitions
through the zone, at any instantaneous point in time, the
instantaneous flux at the strip and the cumulative composition of
the CIGS film deposited on the strip can be determined. The strip
will have a incident flux of each of the elements that is a strong
function of the position of the strip in the zone. The incident
flux at any instantaneous time can be plotted as the strip
transfers through the zone. FIG. 35 shows the instantaneous flux as
a function of position as the web transfers through Zone R for the
copper, gallium and indium sources. This figure shows that the
strip first encounters a large copper flux, but also a flux from
the gallium and indium. As the strip continues, the gallium, and
then the indium fluxes become dominant.
[0144] In a similar fashion, the cumulative composition of copper,
gallium, and indium can be calculated for the strip as it
transitions through the zone, as graphically shown in FIGS. 36 and
37. As was mentioned above, the respective vapor effusion rates of
copper, gallium and indium from the crucibles/boats in structures
70, 72, 74, respectively, are controlled in such a fashion that the
entrance end of zone R is copper-rich, the middle region of this
zone is gallium-rich, and the exit end of the zone is indium-rich.
In particular, we have found that, by establishing appropriate
effusion rates for copper, gallium and indium: (a), within the
entrance end of zone R, the ratio (Cu)/(Ga+In) is generally about
3.4, and the ratio (Ga)/(Ga+In) is generally about 0.46; (b),
within the middle region of zone Z, the ratio (Cu)/(Ga+In) is
generally about 1.9, and the ratio (Ga)/(Ga+In) is generally about
0.43; and (c), within the exit end of zone Z, the ratio
(Cu)/(Ga+In) is generally between 0.8 and 0.92, most preferably,
about 0.88, and the ratio (Ga)/(Ga+In) is between generally between
0.25 and 0.3, most preferably 0.275.
[0145] The CIGS layer created with either chamber organization
(FIGS. 6 and 12) has an internal make-up or composition of
approximately 23.5 atomic percent copper, 19.5 atomic percent
indium, 7 atomic percent gallium, and 50 atomic percent selenium.
The key difference is the CIGS formed in the chamber of FIG. 12
better tolerates mechanical stresses imparted on the film as a
consequence of fabricating the unique flexible photovoltaic device
disclosed herein.
[0146] As described above, the copper, gallium, and indium effusion
sources each include a shielded, insulatively enclosed, heated
subchamber or crucible wherein source material is heated to a
molten condition, and from which subchamber vapor-phase metal
readily exits through the nozzle openings to become part of the
deposition fog. As a result, the vessels may be placed fairly close
to one another and fairly close to the path of the traveling strip
material. This allows precise control over the distribution
geometry of the respective plumes emanating from each respective
effusion source and, therefore, effective control over the
aggregate fog resulting from the comingling of the plumes from all
three effusion sources. In addition, by so establishing thermal
insulation and isolation, the effusion sources may be placed close
enough to the path of strip travel to maximize (as suggested above)
the effectiveness of material deposition without causing
overheating of the reception strip material.
[0147] During co-evaporation in chamber 24, and in accordance with
practice of this invention, special attention is directed toward
the production and maintenance of the effective deposition
temperature, also called herein the local processing temperature,
of the strip-material surface upon which deposition occurs. To
assure proper interlayer integrity and adhesion between Mo and CIGS
and to assure proper formation of an ultimately well-functioning,
clearly defined and established polycrystalline CIGS layer, it is
preferable that the local spot or region which is currently
receiving deposition treatment be held at between 300 and
650.degree. C., preferably below 450.degree. for the polyamide
substrate and at 550.degree. for substrates capable of higher
temperatures such as stainless steel, titanium, and glass.
[0148] From all of the above discussion relating to nozzle
placement, population and sizing, it is apparent that there is
substantial room to vary any one of more of these parameters to
achieve a deposition fog environment of a specific desired
character. Thus, while we have found preferable for the specific
process described in this document to have three nozzles present in
each of crucibles 70, 72, 74, and with each nozzle in each crucible
being substantially the same in construction (sizing, etc.), these
particular choices could be changed. For example, one could choose
to use more or less than three nozzles per crucible. One, also,
could choose to use different numbers of nozzles with respect to
different crucibles. The nozzles themselves, (either with regard to
an inter-crucible way of thinking about things, or with regard to
an intra-crucible way of thinking about things), could have
different respective axial lengths and diameters.
[0149] For the purpose of describing one preferred way of creating
a CIGS layer herein, chamber 24 is illustrated and specifically
discussed as including (in addition to the structure provided for
delivering selenium vapor) just the three vapor-delivery blocks 70,
72, 74. However, a very useful alternative approach employable in
practicing this invention employs a multitude of such blocks
distributed within chamber 24. Use of this alternative allows
unique control of the CIGS through thickness composition that can
alter, positively or negatively, the performance of the resultant
CIGS thin film photovoltaic material.
[0150] Several source orders have been investigated to achieve the
optimum composition. An alternative construction for chamber 24 is
illustrated in FIGS. 12-14. The primary distinction, relative to
the first-described chamber-24 construction, is the use of five
rather than three elongate, heated, vapor-delivery effusion sources
86, 88, 90, 92 and 94 (generally like previously discussed effusion
sources 70, 72, 74). It should be noted that a space with no vapor
source is provided between second and third effusion sources. The
nozzles (three each) in the central vessel 90 delivers copper
vapor; those in effusion sources 86 and 92 delivery gallium vapor;
and those in vessels 88 and 94 deliver indium vapor. An additional
modification includes a final gallium deposition employed after the
final indium in FIGS. 12-14, more will be said about this
alternative possibility later--a special alternative which can be
thought of as possessing "longitudinal vapor (material)-delivery
symmetry".
[0151] Thus, each point on the surface of a strip passing through
this version of chamber 24 encounters, in sequence: a
gallium/indium-rich region, a copper-rich region, and finally,
another indium/gallium-rich region. This "encounter" experience can
be thought of as involving a kind of longitudinal
material-deposition symmetry within zone R. Similar to the three
source example, instantaneous flux of a point on the strip can be
plotted as a function of position in Zone R, as graphically shown
in FIGS. 38 and 39. As was mentioned above, the respective vapor
effusion rates of the five effusion sources 86, 88, 90, 92 and 94,
respectively, are controlled in such a fashion that the entrance
end of zone R is indium-gallium, the middle region of this zone is
copper-rich, and the exit end of the zone is gallium-indium-rich,
as graphically illustrated in FIG. 40. In particular, we have found
that, by establishing appropriate effusion rates for all sources:
(a), within the entrance end of zone R, the ratio (Cu)/(Ga+In) is
generally about 0.0, and the ratio (Ga)/(Ga+In) is generally about
0.35; (b), within the middle region of zone Z above the copper
source, the ratio (Cu)/(Ga+In) is generally about 1.1, and the
ratio (Ga)/(Ga+In) is generally about 0.2; and (c), within the exit
end of zone Z, the ratio (Cu)/(Ga+In) is generally between 0.8 and
0.92, most preferably, about 0.88, and the ratio (Ga)/(Ga+In) is
between generally between 0.25 and 0.3, most preferably 0.275.
[0152] In accordance with a preferred embodiment of the system of
the present invention, the molten temperature of gallium within
crucible 86 is suitably maintained in the range of about
1000.degree. C. to about 1350.degree. C., and most preferably at a
temperature of about 1120.degree. C. (.+-.about 1.degree. C.). The
temperature of the molten indium within crucible 84 is suitably
maintained within the range of about 950.degree. C. to about
1300.degree. C., and most preferably at about 1130.degree. C.
(.+-.. about 1.degree. C.). The temperature of the molten copper
within crucible 86 is suitably maintained within the range of about
1350.degree. C. to about 1700.degree. C., and most preferably at
about 1496.degree. C. (+about 1.degree. C.). The temperature of the
molten gallium within crucible 88 is suitably maintained within the
range of about 1000.degree. C. to about 1350.degree. C., and most
preferably at about 1130.degree. C. (.+-.about 1.degree. C.).
Finally, the temperature of the molten indium within crucible 94 is
most appropriately (according to what we have learned in our
practice of use of this invention) maintained in the range of about
950.degree. C. to about 1300.degree. C., and most preferably at
about 1055.degree. C. (.+-.about 1.degree. C.). The temperature of
molten selenium in reservoir 85b is preferably maintained in the
range of about 275.degree. C. to about 500.degree. C., and most
preferably to about 415.degree. C. (+about 0.degree. C.). As stated
before, although these temperatures are in the preferred range for
the disclosed sources with 0.95-cm orifices, the rate restricting
nozzle principals outlined herein indicated that as the orifice
increases, the temperature would decrease to achieve a constant
rate, or alternatively, as the orifice decreases, the temperature
would increase to achieve a constant rate.
[0153] This sequential exposure to the initial copper-poor
material, followed by copper-rich material as the strip passes over
the central copper source, and then transition back to a slightly
copper-poor CIGS composition, results in a CIGS film with a good
combination of adhesion to the underlying Mo layer and high
conversion efficiency. Variations of the sequence between the
gallium and indium sources on both sides of the centrally located
copper have also been employed successfully.
[0154] Essentially all other environmental and operational
conditions and parameters within chamber 24, as pictured in FIGS.
12-14, as well as all temperatures, spacing and other dimensions,
match substantially those counterpart characteristics present in
the first-discussed version of chamber 24. The chief apparent
difference resides in the distributed order and pattern in and by
which the positional-content-variable constituents of the
deposition fog are encountered by regions on the traveling strip
material. CIGS/CIS deposition by way of an arrangement such as that
pictured in FIGS. 12-14, offers somewhat different opportunities
for deposition delivery control than does the arrangement shown in
FIGS. 6-10.
[0155] Differentiating reasons for choosing to employ, for example,
one or the other of these two illustrated arrangements are outlined
below. For the three source arrangement, principal advantages
include simplified control of three sources, ensuring the copper
rich stage which is an important factor in achieving high
efficiency, however, controlling adhesion of the CIGS deposited by
the three source technique to substrates with a large coefficient
of thermal expansion mismatch with the absorber is difficult.
Additionally, the three source arrangement is more likely to lead
to through thickness composition variations that may limit the
photovoltaic device performance Principal advantages of the five
source arrangement are improved adhesion, even with substrates with
a large CTE mismatch to CIGS, and greater ability to tailor the
through thickness composition to enhance the photovoltaic device
performance. The key challenge with the five source arrangement is
controlling the relative fluxes of indium and gallium on either
side of the centrally located copper source. We further recognize
that other considerations might well dictate a preference for
selecting and implementing an altogether different distributed
vapor-plume layout, and these other kinds of approach can certainly
be determined easily by those skilled in the art in view of the
present disclosure.
[0156] Typically, the exposed surface of a deposited CIS or CIGS
layer will have a quite irregular, three-dimensional surface
topography, with such topography being characterized by many
randomly distributed peaks and valleys. The character of this
surface is the primary determinant of the desirability of utilizing
an i-ZnO layer immediately underneath the final, conductive ZnO:Al
layer. It is important that the CdS layer completely separates the
CIS layer from the top contact layer. Therefore, where the CdS
layer alone provides adequate separation, no supplemental
insulating layer is necessary. However, where the CdS layer does
not sufficiently cover the CIS layer, the i-ZnO layer can provide
such separation. As was mentioned earlier, the present invention
avoids the necessity of using a CdS wet-dipping technique--favoring
instead, and preferably, the application of the CdS layer by way of
RF-sputtering. However, the resulting CdS layer is thinner and less
certain to completely isolate the two layers it lies between. This
issue is more significant where a typical, prior art, wet-dipping
technique for applying a layer of CdS is not used. With
RF-sputtering preference, it is generally desirable, at least in
certain instances, to include such an i-ZnO intermediary layer.
Determination, of course, about whether to include, or not to
include, this layer is dependent on the particular application and
is a matter of design choice.
[0157] The chamber-representing blocks 26, 28 and 30 illustrated in
FIG. 11 can be viewed, as has been mentioned, as illustrating the
steps, and the equipment employed therefor, involved in creating
(a) the mentioned CdS layer, (b) the mentioned optional i-ZnO
layer, and (c) the final conductive-oxide ZnO:Al overlayer.
[0158] The short open arrow at the left side of FIG. 11 represents
input parameters and equipment related to the deposition
environment which exists within the processing chamber drawn in
FIG. 11. The particulars of such input parameters are specifically
related to the specific task to be performed in a chamber like the
one drawn in FIG. 11--i.e., CdS deposition, i-ZnO deposition, and
ZnO:Al deposition.
[0159] Viewing FIG. 11 first of all as an illustration relating to
CdS deposition, and with the chamber representation for this
purpose being numbered 26, appropriate equipment is provided in and
for this chamber to implement a roll-to-roll procedure for the
formation, on the previously formed CIGS layer, of a CdS layer. In
the practice of the present invention, the CdS layer is created
efficiently, inexpensively and safely in chamber 26 by way of
RF-sputtering. Preferably, such sputtering is used to create a CdS
layer with a thickness generally in the range of about 300- to
about 2500-Angstroms. Most preferably, in a case where an
intermediary i-ZnO layer is employed, the CdS layer has a thickness
of about 600-Angstroms. In a situation where such an intermediary
layer is not used, the CdS layer may have a thickness of about
1200-Angstroms. This sputtering approach to the building of the CdS
layer is effective at creating substantially full-surface coverage
of the underlying CIGS layer--i.e., dealing with the many typical
peaks and valleys mentioned earlier which exist on the exposed
surface of the CIGS layer. It should be noted that low frequency
alternating current, or AC, sputtering could also be employed to
deposit the CdS layer.
[0160] RF-sputtering of the CdS layer employs an appropriate CdS
target, and this sputtering takes place preferably at an RF
frequency of 13.5-MHz. The power level employed for sputtering is
chosen to coordinate layer-formation activity with a selected strip
linear transport speed to achieve the desired CdS layer thickness.
An appropriate transport speed lies in the range of about
1.0-cm-per-minute to about 2-meters-per-minute, and a transport
speed of about 30-cm-per-minute is particularly suitable. Within
this strip transport speed, appropriate RF power ranges between 100
and 1200 watts, most appropriately at 300 watts.
[0161] Following CdS-layer formation, the take-up roll 60 from
chamber 26 which now contains a layer structure including CdS is
transferred to another isolated processing chamber 28 of FIG. 11,
wherein the optional intermediary i-ZnO layer is created. This
layer is established utilizing a DC sputtering technique to achieve
a final layer thickness preferably in the range of about 100- to
about 1000-Angstroms, and most preferably about 400-Angstroms.
[0162] Referring now specifically to the making of this i-ZnO
layer, oxide targets employed for this purpose are typically
sintered during manufacture, and during such sintering, these
targets often lose some of their elemental oxygen, thus rendering
the target substoichiometric. This loss of oxygen and concomitant
substoichiometric condition renders the target slightly conductive,
as opposed to a stoichiometric zinc oxide target which would be
nonconductive.
[0163] Recognizing the fact that, where an i-ZnO sublayer is to be
created it should end up as a very poorly conductive layer, we
nevertheless preferably choose to employ substoichiometric
zinc-oxide as a "starter" material because such material especially
facilitates the use of the preferred DC sputtering technique, as
opposed to an RF sputtering technique. In this context, the use of
such a substoichiometric (e.g., oxygen-deficient) zinc-oxide target
tends to suppress and even eliminate the usual positive charge
buildup which tends to occur on the surface of more conventional,
stoichiometric targets during DC sputtering. In the present
invention, the substoichiometric starter target is compensated for
by, for example, providing a supply of oxygen into the chamber-28
sputtering environment. In particular, an appropriate external
supply tank containing compressed oxygen can be used to furnish and
support a controlled bleed of oxygen into chamber 28. By providing
oxygen into such a sputtering environment, the substoichiometric
zinc-oxide target effectively applies an appropriate conductivity
intrinsic-zinc-oxide layer to the traveling strip material,
notwithstanding the target's nominal, oxygen-deficient,
substoichiometric starter character. It should be noted that RF or
low frequency alternating current, or AC, sputtering could also be
employed to deposit the i-ZnO layer using stoichiometric ZnO
targets.
[0164] The last PV-operative layer to be created according to the
practice of the present invention is the overlying conductive-oxide
layer, herein ZnO:Al. This is done in chamber 30 (the third
point-of-view for FIG. 11) under appropriate internal environmental
conditions which are effective to create a final ZnO:Al layer with
a thickness in the range of about 2000- to about 15,000-Angstroms,
and most preferably within the somewhat narrower range of about
10,000- to about 12,000 Angstroms.
[0165] The next steps comprise the methodology for monolithically
integrating individual PV cells on the elongated strip from above
into a PV module.
[0166] Following completion of the i-ZnO deposition or
alternatively, CdS deposition where the optional i-ZnO layer is not
utilized, the roll is transferred to the laser isolation equipment.
The laser is utilized to selectively remove material (e.g. CIGS or
CIS, CdS, intrinsic ZnO, and Mo) through the Mo layer to the PI,
thereby electrically isolating adjacent cells. In the present
embodiment, the beam of laser light moves while the substrate is
stationary, but other options can presumably be as effective. For
this step the laser presently moves relative to the substrate at
12-inches per second.
[0167] Using the same equipment, a dielectric layer, which utilizes
a UV curable insulating polymer, is concurrently applied by ink-jet
printing methods over the laser-scribed area, and within seconds is
cured by a directed, intense UV source. The UV curable material was
chosen such that it can be cured rapidly after application and such
that it can be applied over a width less than 400 micrometers and
preferably less than 125 micrometers but greater than 60
micrometers. The orifice diameter of the ink-jet applicator is
between 100 micrometers and 300 micrometers with a preferred
diameter of approximately 100 to 150 micrometers. The thickness of
the resulting layer is approximately 60 micrometers, however this
specific dimension is not considered critical. The more significant
properties for this UV curable insulating material are its adhesion
to the CdS, the i-ZnO, if utilized, the CIGS or CIS, and the Mo,
its viscosity, its slump, its rate of cure, and its surface
characteristics since it must allow for good over-layer adhesion by
the conductive oxide. Various combinations of these critical
parameters will result in satisfactory performance.
[0168] Again using the same laser equipment, a second laser cut is
utilized for the selective removal of material (e.g. CIGS or CIS,
CdS, intrinsic ZnO) to provide access to the Mo layer. This access
is necessary to allow the next layer, the conductive-oxide
overlayer, to bridge from the top of one cell to the back electrode
(Mo) of the adjacent cell. For this step the laser presently moves
relative to the substrate at 30-cm per second. The conductive-oxide
overlayer is deposited as described earlier. A third laser cut is
utilized for a selective removal of conductive-oxide overlayer
material, thereby isolating individual cells and completing the
monolithic interconnection of previously-individual adjacent
cells.
[0169] Assuming that proper thin-film "patterning" has been
performed to result in monolithically interconnected PV modules,
then protective overcoatings, if any such coatings are desired, are
then produced in a conventional manner, and electrical contact
structures, which are required to tap the electrical output power
that can be generated by each such module, are appropriately
established--again, utilizing conventional and well-known
techniques for such activity.
[0170] It is believed that the disclosure set forth above
encompasses multiple distinct inventions with independent utility.
While each of these inventions has been disclosed in its preferred
form, the specific embodiments thereof as disclosed and illustrated
herein are not to be considered in a limiting sense as numerous
variations are possible. The subject matter of the inventions
includes all novel and non-obvious combinations and subcombinations
of the various elements, features, functions and/or properties
disclosed herein. No single feature, function, element or property
of the disclosed embodiments is essential to all of the disclosed
inventions. Similarly, where the claims recite "a" or "a first"
element or the equivalent thereof, such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements.
[0171] It is believed that the following claims particularly point
out certain combinations and subcombinations that are directed to
one of the disclosed inventions and are novel and non-obvious.
Inventions embodied in other combinations and subcombinations of
features, functions, elements and/or properties may be claimed
through amendment of the present claims or presentation of new
claims in this or a related application. Such amended or new
claims, whether they are directed to a different invention or
directed to the same invention, whether different, broader,
narrower or equal in scope to the original claims, are also
regarded as included within the subject matter of the inventions of
the present disclosure.
* * * * *