U.S. patent application number 14/294141 was filed with the patent office on 2014-09-18 for methods and apparatuses for roll-on coating.
This patent application is currently assigned to Dynamic Micro Systems, Semiconductor Equipment GmbH. The applicant listed for this patent is Dynamic Micro Systems, Semiconductor Equipment GmbH. Invention is credited to Lutz Rebstock, Klaus Conrad Wolke.
Application Number | 20140259498 14/294141 |
Document ID | / |
Family ID | 46965099 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140259498 |
Kind Code |
A1 |
Rebstock; Lutz ; et
al. |
September 18, 2014 |
Methods and apparatuses for roll-on coating
Abstract
Methods and apparatuses for a deposition system are provided to
deposit a thin coating layer on flat substrates, such as
semiconductors or panels. In an embodiment, liquid supplied rollers
accepting liquid media provide liquid chemicals to the substrates
for coating the substrates. The liquid delivery system can control
the flow and the pressure of the liquid to achieve optimum process
condition with minimum excess waste. In another embodiment, rollers
with non-uniform distribution of liquid media provide a non-uniform
thickness profile on the substrates, which can be used to
compensate for the non-uniformity of subsequent processes.
Inventors: |
Rebstock; Lutz; (Gaienhofen,
DE) ; Wolke; Klaus Conrad; (Althengstett,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dynamic Micro Systems, Semiconductor Equipment GmbH |
Radolfzell |
|
DE |
|
|
Assignee: |
Dynamic Micro Systems,
Semiconductor Equipment GmbH
Radolfzell
DE
|
Family ID: |
46965099 |
Appl. No.: |
14/294141 |
Filed: |
June 2, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13081508 |
Apr 7, 2011 |
|
|
|
14294141 |
|
|
|
|
Current U.S.
Class: |
15/230 |
Current CPC
Class: |
B05C 1/025 20130101;
Y02E 10/543 20130101; Y02P 70/521 20151101; Y02P 70/50 20151101;
B05C 1/10 20130101; B05D 2252/00 20130101; B05D 1/28 20130101; H01L
31/1828 20130101; B05C 1/0808 20130101; Y02E 10/547 20130101; H01L
31/068 20130101; B05C 9/04 20130101; H01L 31/1804 20130101; B05D
2252/10 20130101 |
Class at
Publication: |
15/230 |
International
Class: |
B05C 1/08 20060101
B05C001/08 |
Claims
1. A roller comprising: an elongated rod, wherein the elongated rod
is configured for accepting a fluid at an end of the elongated rod,
wherein the elongated rod configured to transfer the fluid from the
end of the rod to at least a first portion of an outer surface of
the elongated rod; and a layer covering at least a second portion
of the outer surface of the elongated rod for receiving the fluid
at the outer surface of the elongated rod, wherein the elongated
rod is operable to produce a coating layer on a substrate surface,
wherein the coating layer is non-uniform in thickness in a
direction along a length of the elongated rod.
2. A roller as in claim 1 wherein the elongated rod is configured
to transfer a non-uniform amount of fluid along the elongated
direction.
3. A roller as in claim 1 wherein the elongated rod comprises a
hollow cylindrical shape with perforation holes at a portion of the
cylindrical surface, wherein the perforation holes are distributed
non uniformly in a direction along a length of the elongated
rod.
4. A roller as in claim 1 wherein the perforation holes are larger
at end portions of the elongated rod.
5. A roller as in claim 1 wherein the perforation holes are larger
at a middle portion of the elongated rod.
6. A roller as in claim 1 further comprising: one or more tubes
comprising perforation holes, wherein the one or more tubes are
embedded in the elongated rod along the elongated direction of the
rod, wherein the perforation holes are distributed non uniformly in
a direction along a length of the elongated rod.
7. A roller as in claim 1 wherein the rod is concave along the
elongated direction.
8. A roller as in claim 1 wherein the rod is convex along the
elongated direction.
9. A roller as in claim 1 wherein the layer is thicker at a middle
portion of the elongated rod.
10. A roller as in claim 1 wherein the layer is thinner at a middle
portion of the elongated rod.
11. A roller as in claim 1 wherein the layer is porous, wherein the
porous layer has a non-uniform pore size or pore density along the
elongated direction of the rod.
12. A roller comprising: an elongated rod, wherein the elongated
rod is configured for accepting a fluid at an end of the elongated
rod, wherein the elongated rod configured to transfer the fluid
from the end of the rod to at least a first portion of an outer
surface of the elongated rod; and a layer covering at least a
second portion of the outer surface of the elongated rod for
receiving the fluid at the outer surface of the elongated rod,
wherein the elongated rod or the layer is convex or concave in a
direction along a length of the elongated rod.
13. A roller as in claim 12 wherein the concave or convex elongated
rod is configured to transfer a non-uniform amount of fluid along
the elongated direction.
14. A roller as in claim 12 wherein the layer is thicker at a
middle portion of the elongated rod.
15. A roller as in claim 12 wherein the layer is thinner at a
middle portion of the elongated rod.
16. A roller as in claim 12 wherein the layer is porous, wherein
the porous layer has a non-uniform thickness along the elongated
direction of the rod.
17. A roller comprising: an elongated rod, wherein the elongated
rod is configured for accepting a fluid at an end of the elongated
rod, wherein the elongated rod configured to transfer the fluid
from the end of the rod to at least a first portion of an outer
surface of the elongated rod; and a layer covering at least a
second portion of the outer surface of the elongated rod for
receiving the fluid at the outer surface of the elongated rod,
wherein the elongated rod comprises a hollow cylindrical shape with
perforation holes at a portion of the cylindrical surface, wherein
the perforation holes are distributed non uniformly in a direction
along a length of the elongated rod.
18. A roller as in claim 17 wherein the non uniformly distributed
perforation holes elongated rod is configured to transfer a
non-uniform amount of fluid along the elongated direction.
19. A roller as in claim 17 wherein the layer is non uniform along
the elongated direction of the rod.
20. A roller as in claim 17 wherein the layer is porous, wherein
the porous layer has a non-uniform thickness along the elongated
direction of the rod.
Description
[0001] This application is related to co-pending application
"Methods and apparatuses for roll-on coating", of the same
inventors.
[0002] This application is a continuation of and claims priority
from U.S. patent application Ser. No. 13/081,506, filed on Apr. 7,
2011, which is now U.S. Pat. No. 8,739,728, entitled "Methods and
apparatuses for roll-on coating", which is incorporated herein by
reference.
BACKGROUND
[0003] In photovoltaic devices, electrical energy is converted from
light via the photoelectric effect and resulting charges are
collected via pn junctions in semiconductor substrates for current
generation. PN junctions can be formed by means of diffusing
dopants into the bulk semiconductor material. The diffusion process
can occur from a dopant vapor ambient, for example, phosphine or
POCl.sub.3, or from solid source releasing dopant vapor. Another
process can employ a dopant layer coated on the substrate, which,
upon heating or firing, causes the dopant to diffuse from the
dopant layer into the substrate. Another important process in solar
cell fabrication is thin film deposition, such as the coating of
passivation or absorber layer.
[0004] In-line fabrication processes, such as in-line doping
diffusion or in-line thin film deposition, are preferred processes
for minimizing cost and toxicity. For example, in a typical in-line
diffusion process, the substrate is coated with a dopant containing
layer and subsequently, the dopants from the dopant layer are
diffused into the substrate in a furnace. The coating of the dopant
source can be accomplished by spraying, dipping, spin-on, or
condensation of a dopant-containing chemical, in liquid or gaseous
form, with or without solvent, and with or without carrier gas.
Such systems can be difficult to control with respect to uniformity
and doping levels, particularly on textured surfaces. Also these
processes often require significant excess chemicals, driving up
the cost of production.
SUMMARY
[0005] The present invention relates to methods and apparatuses for
coating substrates, such as coating thin films or dopant layers on
single crystalline or multicrystalline silicon substrates. In an
embodiment, the present invention discloses a roll-on coating
process for coating a layer on the substrate surfaces, for example,
a passivation or absorber layer, or a dopant layer in which the
dopants are then diffuse into the substrate after a high
temperature anneal, forming a pn junction for solar cells.
[0006] In an embodiment, the present invention discloses a system
for roll-on coating a substrate, comprising at least a roller
accepting a fluid flow and then migrating the fluid to the roller
surface. Upon contacting a substrate surface, the fluid on the
roller's surface is transferred to the substrate surface, forming a
coating layer. The fluid can comprise active chemicals in a
solution mixture, which is subsequently dried to form a solid thin
film layer on the substrate. The fluid can comprise a dopant
chemical, which is continuously supplied to the roller for coating
a plurality of substrate surfaces by rolling contact. The dopant
chemical can contain boron, arsenic or phosphorus chemical in a
solution or mixture form.
[0007] In an embodiment, the present invention discloses a fluid
supplying roller, comprising a cylindrical structure spanning
across a large substrate or a number of smaller substrates. The
substrates can be positioned above the roller, under the roller, or
sandwiched between two rollers, and moved relative to a rotation of
the roller. The fluid supplying roller can be configured to accept
a fluid flow at one end of the roller and to supply fluid at the
roller's surface. The roller can be hollow or can have inner
channels for guiding the fluid along the length of the roller. The
surface of the roller can have a plurality of holes distributed
along the length of the roller's core and connected with the inner
channels for transferring the fluid to the outer surface of the
roller. In one embodiment, the roller can further comprise a soft
porous layer covering the outer surface of the roller, which is
wetted with the fluid at the roller's surface, for example, the
fluid coming from the holes distributed along the length of the
roller's core. Upon contacting a substrate, the wetted porous layer
can transfer the fluid to the substrate surface, effectively
coating the substrate surface with layer of the fluid. In an
embodiment, the fluid supplied roller is configured for delivering
a uniform coating across the substrate surface, for example, by a
uniform distribution of the holes along the length of the roller's
core, or by a uniform pore density of the porous layer along the
length of the roller. In another embodiment, the roller is
configured to tailor the delivery of the fluid, effectively
providing different coating thickness at different portions of the
substrates, for example, by a non-uniform distribution of holes or
a non-uniform pore density of the porous layer. This thickness
non-uniformity can be used to compensate for subsequent process
non-uniformity, for example, the non-uniformity of the anneal
temperature in a diffusion furnace during the dopant drive-in
process.
[0008] In an embodiment, temperature control devices such as
heaters or coolers can be provided for heating or cooling the
fluid, either at the fluid reservoir, at the fluid delivery lines,
and/or at the fluid within the roller. In addition, heaters/coolers
can be provided to heat/cool the roller and/or to heat/cool the
substrates, for example, in the coating process.
[0009] In an embodiment, the present invention discloses an in-line
coating system, comprising a plurality of rotating fluid supplied
rollers for coating a substrate. The fluid supplied roller can be
positioned above the substrate for coating the top surface of the
substrate. The wetted roller can be positioned under the substrate
for coating the bottom surface of the substrate. Two rollers can
sandwich the substrate to coat the top and bottom surfaces of the
substrate simultaneously. The rotating rollers can double as a
transporting mechanism, continuously moving a plurality of
substrates from an input to an output stage of the in-line coating
system. The in-line coating system can further comprise means of
controllably reducing the amount of dopant or carrier fluid on the
substrates, such as additional liquid absorbing intrinsically dry
rollers.
[0010] In an embodiment, the in-line coating system further
comprises additional coating mechanisms, such as spraying nozzles
for delivering additional fluid onto the substrate surfaces.
Further the in-line coating system can comprise additional roller
wetting mechanisms, such as providing an outer belt to deliver
fluid to the outer surface of the roller, or providing a
fluid-filled pan for mounting the roller.
[0011] In an embodiment, the present invention discloses an
integrated in-line processing system, comprising an in-line coating
system for coating a dopant layer on the substrates feeding an
in-line furnace anneal system for driving the dopant into the
substrates from the surface coating layer. The coating system and
the furnace anneal system can be disposed next to each other, or
can be separated, for example, by a transport line. The system may
also consist of a pre-conditioning step prior to processing such as
ozone treatment or chemical oxidation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIGS. 1A-1B illustrate exemplary process flows according to
embodiments of the present invention.
[0013] FIGS. 2A-2B illustrate exemplary schematics of the basic
coating method and apparatus concept according to an embodiment of
the present invention.
[0014] FIGS. 3A-3E illustrate various configurations for the roller
according to an embodiment of the present invention.
[0015] FIGS. 4A-4D illustrate other roller configurations according
to an embodiment of the present invention.
[0016] FIGS. 5A-5C illustrate exemplary coating processes according
to an embodiment of the present invention.
[0017] FIGS. 6A-6D illustrate exemplary rollers for uniform
deposition according to an embodiment of the present invention.
[0018] FIGS. 7A-7I illustrate exemplary rollers for non-uniform
deposition according to an embodiment of the present invention.
[0019] FIGS. 8A-8D illustrate exemplary configurations for heaters
according to an embodiment of the present invention.
[0020] FIGS. 9A-9C illustrate exemplary configurations for liquid
coating according to an embodiment of the present invention.
[0021] FIGS. 10A-10C illustrate exemplary configurations of liquid
media distributions in an in-line deposition system according to an
embodiment of the present invention.
[0022] FIGS. 11A-11C illustrate an exemplary coating process
according to an embodiment of the present invention.
[0023] FIGS. 12A-12C illustrate an exemplary doping process
according to an embodiment of the present invention.
[0024] FIGS. 13A-13C illustrate exemplary flowcharts of liquid
deposition according to an embodiment of the present invention.
[0025] FIGS. 14A-14B illustrate exemplary flowcharts for liquid
deposition controls according to an embodiment of the present
invention.
[0026] FIGS. 15A-15B illustrate exemplary flowcharts for different
liquid deposition processes according to an embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] The present invention relates to methods and systems for
uniform deposition of materials on a flat substrate, such as
photovoltaic substrates, for creation of thin layers by a roll-on
technology. The thin layers can be any layer deposited by a liquid
material. For example, the thin layers can comprise Phosphorus or
Boron, deposited on a semiconductor layer for emitter formation
after subsequent treatments. The thin layers can also be absorber
layers, for example CdS or ZnS, in thin film photovoltaic
processing.
[0028] The present invention further pertains to the manufacture of
photovoltaic cells, such as in crystalline solar cell
manufacturing, including improved dopant coating processes and
systems for producing photovoltaic emitter junctions by dopant
diffusion. The substrate is preferably single crystal or
multicrystalline (or polycrystalline) substrate, but other
semiconductor substrate can also be utilized. The present invention
can provide high performance junctions for cost reduction and
efficiency improvement in photovoltaic cells and related devices.
In an embodiment, the substrate is first exposed to a
fluid-containing surface comprising dopant material, such as
phosphorus, arsenic, or boron compounds, such as phosphoric acid
(H.sub.3PO.sub.4). The exposure will form a dopant coating on the
substrate surface. Afterward, the dopant coating maybe subjected to
a high temperature ambient to diffuse the dopant into the substrate
or annealed in a furnace at high temperature, for example, between
600 and 1000 C.
[0029] In another embodiment, the present invention discloses a
deposition process by liquid roll-on technology, such as absorber
layers in thin film photovoltaic, including controlled heating of
the substrates for deposition of the layer constituents from the
coating fluid, for example by crystallization.
[0030] FIG. 1A illustrates an exemplary process flow according to
an embodiment of the present invention. A substrate 10 is provided,
which can comprise various layers, such as a semiconductor layer.
The substrate 10 is then exposed to a liquid coating process 15,
which forms a dropletless liquid coating layer 11 on the substrate
10. The layer 11 can be formed by contact with a fluid surface to
generate a liquid layer coated on the substrate, and then can be
dried in an elevated temperature ambient.
[0031] FIG. 1B illustrates another exemplary process flow according
to an embodiment of the present invention. A substrate 10 is
provided, which is preferably a semiconductor substrate, such as a
single crystal or multicrystalline silicon substrate.
Alternatively, the substrate can comprise a layer of semiconductor
material on a support substrate. The substrate material can also be
non-semiconductor, such as W, ITO or metallic mirror material. In
addition, other processes can be performed on the substrate 10
before exposing the substrate to the dopant ambient. For example,
an oxide passivation layer can be formed on the silicon substrate
to protect the substrate, or a hydrophilic layer can be coated on
the surface of the substrate 10 to improve the wettability of the
substrate surface. The passivation layer can further prevent high
concentration of dopant at the surface of the semiconductor
substrate. For example, at the interface of the dopant layer, a
high concentration of dopant can be formed after a high temperature
diffusion process, which might affect the quality and functionality
of the pn junction. Thus the passivation layer can protect the
semiconductor substrate from this high surface concentration. The
buffer layer can also act as an interface layer between the dopant
and the substrate, providing adhesion and surface preparation for
the coating of the dopant layer.
[0032] The substrate 10 is then exposed to a dopant coating process
15, which forms a dopant layer 11 on the substrate 10. The dopant
layer 11 is preferably a solid dopant source, comprising the
appropriate dopant for forming a pn junction with the semiconductor
substrate 10. The dopant layer 11 can be formed by contact with a
fluid surface to generate a liquid layer coated on the substrate,
and then dried in an elevated temperature ambient. The coating
process comprises a dopant precursor, such as phosphorus-containing
chemicals (phosphorus acid, phosphine), boron-containing chemicals,
or arsenic-containing chemicals. The dopant precursors can be
delivered in liquid or semi-liquid form, and with or without
solvent or carrier gas. Other dopant sources in liquid form can be
used, including solutions and mixtures.
[0033] In an embodiment, the dopant material is phosphorus, for
example, from phosphorus acid solution. For example, phosphorus
acid solution is applied to the core of the roller, which then
rolls on the substrate to form a phosphoric acid coating. An
exhaust or a hood, and a capture pan can be included to capture any
phosphorus acid not adhered to the substrate.
[0034] The substrate may then be dried 11* and annealed 16 in a
diffusion furnace, or the substrate may be directly annealed
without a dry step. The anneal temperature may be about 800 to 900
C to drive phosphorus into the substrate to form a doping layer
12.
[0035] In an embodiment, the present invention discloses a system
for coating a substrate, comprising a rotated roller with outer
surface wetted from a fluid supplied through an inner core. In an
embodiment, the present system comprises a plurality of rotated
soft porous rollers for liquid media deposition, wherein the
rollers is wetted with the liquid media supplied from one end of
the rollers. The rotated soft porous rollers can be used to
simultaneously transport the substrates, for example, in an in-line
conveyor mechanism.
[0036] An advantage of the invention includes the ability to
combine the transport of the substrates in an inline process system
with the deposition process. The substrates are fed through the
system in single or multiple parallel lanes by a sequence of
rotated rollers, which can be positioned on top and/or bottom of
the substrates. Rotating the rollers will move the substrates
linearly from the input of the in-line process system to the output
end. Liquid media is supplied to the rollers at one end, and
traveled through inner channels of the rollers to wet the outer
surface. Liquid layers are then dispensed with ultrathin thickness
onto the substrates while moving through the equipment.
[0037] FIGS. 2A and 2B illustrate an exemplary schematic of basic
equipment concept according to an embodiment of the present
invention. The media are supplied 24 through the inner core of the
soft porous rollers 21 and 22 which due to their material behavior
are wetted uniformly. The dispense of media onto the substrate 26
is controlled independently by liquid flow and liquid concentration
as well as the contact pressure due to the spacing between the top
rollers 21 and the bottom rollers 22 in a way to deposit a thin
uniform film on the top and bottom surfaces of the substrate 26
with minimum surplus media. In rotating the rollers 21 and 22, the
substrates are transported from one end of the equipment to the
other end of the equipment, in addition to gaining a coating of
liquid supplied from the rollers' wet surfaces.
[0038] In an embodiment, the porous rollers comprise a rigid hollow
core surrounded by a layer of porous material such as a sponge
material. The rigid core preferably has adequate stiffness and
horizontal flatness across the deposition area of the substrates to
ensure uniform deposition of the coating layer. The core material
can be metal, alloys, carbon, glass, ceramic, or plastic such as
PVC, PP or fluorocarbons.
[0039] The porous material can be polymer or polymer foams or
sponge, such as PVA, Poly urethane and poly olefin, or can be any
materials with pores to allow the liquid media to pass through. In
addition, the porous material can be a soft material, which can
help in relaxing the requirement of the horizontal flatness of the
rigid core.
[0040] FIGS. 3A-3C illustrate various configurations for the roller
according to an embodiment of the present invention. FIG. 3A shows
a roller 31 having inlet 34 at one end of the roller to accept a
fluid media, which is distributed 35 to the outer surfaces of the
roller. When contacting substrate 36, the fluid media is
transferred to the contacting surface, forming a liquid layer 34*.
The roller 31 can rotate for better spreading the fluid on the
substrate surface. A coupler 39 can be coupled between the rotating
roller 31 (or the inlet 34) and the stationary fluid entrance 38.
The coupler 39 can comprise rotatable seal, or a twistable
connection to accommodate the rotating roller.
[0041] The roller 31B can comprise a soft porous layer 35B at the
outer surface of the roller for ease of fluid transfer between the
roller and the substrate (FIG. 3B). The outer surface of the roller
31C can be covered with a solid layer 35C, preferably a soft layer
for improve contact tolerance. The fluid then forms a layer at the
outer surface of the roller, which can be transferred by contact to
the substrate surface (FIG. 3C).
[0042] FIGS. 3D-3E illustrate various exemplary configurations for
a rotatable coupler between a rotating roller and a fixed liquid
delivery line. In FIG. 3D, o-ring or liquid bearing 39D is disposed
at an extreme end of the roller 31D, coupling a fixed line 38D with
the rotating roller 31D. In FIG. 3E, o-ring or liquid bearing 39E
is disposed at a cylindrical surface near a vicinity end of the
roller 31E, coupling a fixed line 38E with the rotating roller 31E.
Other rotatable coupler can be used, for connecting a rotating
roller with a fixed liquid delivery line.
[0043] FIGS. 4A-4D illustrate other roller configurations according
to an embodiment of the present invention. FIG. 4A shows roller 41
comprising a porous layer 45 covering a solid core with trenches 42
that can hold small diameter tubing (PFA, PVDF, PP) 43. Liquid
media 44 enters the small tubing 43 and transfers to the porous
layer 45 through perforations in the tubing 43. Diameter and
spacing of the perforation holes of the tubing 43, together with
the pore density of the porous layer 45, can be varied to optimize
uniformity and media flow. FIG. 4B shows roller 41 having outer
cover layer 46 with trenches 47. Liquid media 44 enters the
trenches 47 and transfers to the porous layer 45 through
perforations in the trenches 47. FIG. 4C shows hollow roller 41
having inner layer 48 with trenches 49. Liquid media 44 enters the
trenches 49 and transfers to the porous layer 45 through
perforations in the trenches 49. FIG. 4D shows hollow roller 41
having perforation 52 in the roller walls 51. Liquid media 44
enters the hollow roller and transfers to the porous layer 45
through perforations 52.
[0044] FIGS. 5A-5C illustrate exemplary coating processes according
to an embodiment of the present invention. FIG. 5A shows the roller
61 accepting liquid media 64 and distributed to porous layer 65.
During direct contact with substrate 66, the liquid media is
transferred to the substrate surface, forming layer 64*. The roller
61 rotates to provide an even coating, and at the same time, moving
the substrate forward. FIGS. 5B and 5C show roller 61 in indirect
contact with substrate 66, through intermediate rollers 62, 62A and
62B.
[0045] Uniformity of the coating layers can be controlled by
adjusting the liquid media available at the surfaces of the
rollers. In general, an even distribution of the liquid media along
the length of the roller can create a uniform coating on the
substrates along the direction perpendicular to the path of travel.
Using multiple rollers, the uniformity along the direction of
travel can be further improved.
[0046] FIGS. 6A-6D illustrate exemplary rollers for uniform
deposition according to an embodiment of the present invention.
FIG. 6A shows roller 71A with uniform distribution of perforation
holes 73 along the length of the roller. When the liquid media 74
enters the roller 71A at one end (e.g., at the extreme end, or at a
vicinity of the extreme end), the uniform distribution of
perforation holes can enable a uniform distribution of liquid media
on the substrate surfaces. The perforation holes are shown also
with uniform distribution along the circumference of the roller,
other configurations can be equally effective, such as multiple
perforated tubing. FIG. 6B shows roller 71B comprising porous layer
77 having uniform distribution of pore sizes or pore densities 78
along the length of the porous layer 77. Porous layer 77 can be a
foam or sponge material, with the pores 78 characterized by the
pore size or pore density. Porous layer 77 can be a liquid
permeable layer, having uniform permeability along the length of
the roller. Having a uniform distribution of liquid media, the
coating layer 70 on a large substrate 76 can be uniform across the
width of the substrate (FIG. 6C), or the coating 70* can be uniform
and similar for multiple substrates 76* disposed along the length
of the roller.
[0047] FIGS. 7A-7G illustrate exemplary rollers for non-uniform
deposition according to an embodiment of the present invention.
FIG. 7A shows roller 71C with different distributions of
perforation holes 72 and 73A/73B along the length of the roller.
With larger holes 73A/73B at the edges of the roller, as compared
to smaller holes 72 in the middle, more liquid can be transferred
to the substrates at the edges, creating thicker coating at the
edges. Practically any desired distribution of coating thickness
can be achieved with appropriate distribution of perforation holes
72/73A/73B. In another configuration, FIG. 7B shows roller 71D
comprising porous layer 77D having non-uniform distribution of pore
sizes or pore densities 79/78A/78B along the length of the porous
layer 77D. Similarly, the porous 77D can generate any desirable
distribution of coating thickness, such as a distribution 75 on
substrate 76 (FIG. 7C), or thicker coating 75** on outer-edge
substrates 76** as compared to thinner coating 75* on inner
substrates 76* (FIG. 7D).
[0048] FIGS. 7E-7I illustrate exemplary roller profiles according
to an embodiment of the present invention. In FIG. 7E, the roller
comprises a cylindrical core 161A and a porous layer 167A covering
the outer surface of the core 161A. The core 161A and the porous
layer 167A have uniform profiles, e.g., straight cylinder for the
core 161A and equal thickness for the porous layer 167A. Profile
distribution of the liquid can be accomplished through the
distribution of perforation holes in the core 161A or through the
pore density of the porous layer 167A along the length of the
roller.
[0049] In FIG. 7F, the roller comprises a cylindrical core 161B
having a concave inward surface, together with a mated porous layer
167B having thicker layer at the middle than at the ends. The
structure of the complete roller (e.g., including core 171B and
porous layer 176B) preferably forms a straight cylindrical surface,
in order to rollingly contact the substrate. In this configuration,
coating thickness can be varied along the length of the roller. For
example, for high compression, the end portions are squeezed much
more than the middle portion, resulting in more liquid coating at
the end portions. For light compression, more fluid is stored in
the middle portion (due to thicker porous layer), and can result in
more fluid at the middle portion. In FIG. 7G, the roller comprises
a cylindrical core 161C having a concave outward surface (or
convex), together with a mated porous layer 167C having thinner
layer at the middle than at the ends.
[0050] In FIG. 7H, the roller comprises a cylindrical core 161D
having a straight surface, together with a concave inward porous
layer 167D having thinner layer at the middle than at the ends. In
this configuration, with flat substrates, the end portions are
compressed more than the middle portion, resulting in more fluid
coating at the ends. In FIG. 7I, the roller comprises a cylindrical
core 161E having a straight surface, together with a concave
outward porous layer 167E having thicker layer at the middle than
at the ends. These configurations are exemplary. Other
configurations can be used to achieve a desired thickness profile
of coating (uniform or non-uniform) along the length of the roller.
For example, the rollers may have diameter variations.
[0051] In an embodiment, the non-uniform profile of the thickness
across the doper is designed to compensate for the non-uniform
profile of a subsequent process. An example is the dopant diffusion
process. After coating the substrates with a dopant layer, the
substrates are annealed in a furnace to drive the dopant into the
substrates. For in-line processing, after dopant coating, the
substrates will move into an inline furnace with the same
arrangements (rows) as they have been in the doper. It is costly to
make the temperature in the furnace perfectly uniform in the
direction perpendicular to the path of the substrates. For example,
the temperature can be higher at the center than at the edge due to
the boundary heat loss. This temperature difference can result in
different substrate qualities according to their locations inside
the furnace, for example, more dopant can be diffused to the
substrates at the center than at the edges of the furnace.
[0052] The present rollers having core design with multiple types
of perforations to apply a non-uniform coating layer on the
substrates can compensate for this temperature difference to
generate a homogeneous quality of the substrates after the furnace.
For example, more chemical can be applied to the substrates at the
edges of the doper, resulting in a thicker layer of coating, as
compared to the substrates at the center of the doper. Thicker
coating layers contain more dopant, which can be used to compensate
for the lower temperature in the anneal furnace. Thus substrates
positioned at the edges and at the center of the in-line conveyor
(which is used to move the substrates from one location to another
location) can have similar dopant concentration regardless of the
temperature profile in the anneal furnace. Further, the coating
layers can be removed after the anneal process, and thus the
substrates remain uniform in surface topology.
[0053] In an embodiment, the present system comprises one or more
temperature control devices, such as heaters or coolers, to provide
thermal energy to the substrates or to the chemicals. Some
chemicals may require high temperature (e.g., higher than room
temperature) before a successful coating, thus heaters can be used
to heat the chemicals to a desired temperature. Some chemicals may
require low temperature (e.g., temperature lower than room
temperature) for coating or for preserving the chemicals, thus
coolers can be used to chill the chemicals to a desired
temperature. For example, the heaters/coolers can be disposed at
the chemical reservoir, at the liquid delivery line, or at the
rollers to heat or cool the chemicals directly. In addition, or
alternatively, the heaters/coolers can also be disposed at or near
the rollers to heat/cool the rollers' surfaces, thus heating or
cooling the chemicals when they reach the rollers' surfaces.
[0054] Heating or cooling can also be directed to the substrates.
For example for deposition of emulgated solid salts to form
absorber layers like CdS and ZnS in thin film solar cell
manufacturing, the chemicals is heated after deposition, to
accelerate the reactions of the chemicals, to dry the liquid
chemicals, or to anneal the coating layers. The heaters can be
disposed at or near the substrates to heat the substrates' surface,
including IR or UV lamps disposed on top and/or bottom of the
substrates, or between the rollers. In addition, both heaters and
coolers can be used. For example, in deposition of absorber layers,
the chemicals are preferably cooled, e.g., by coolers disposed at
or near the chemical reservoir or delivery line, to around or below
room temperature to preserve the life time of the chemicals. The
chemicals are then heated, e.g., by IR heating the substrates,
after deposited on the substrates to form the absorber layers.
[0055] FIGS. 8A-8D illustrate exemplary configurations for
temperature control devices according to an embodiment of the
present invention. FIG. 8A shows a roller 77 having foam or
solidified foam 71 covering a large portion of the outer surface. A
liquid media 74 is delivered to the inside of the roller 77 to be
transferred to the foam 71. A temperature control device such as
heater or cooler 82 can be disposed in the vicinity of the chemical
delivery line, such as wrapping around the piping line, to
heat/cool the chemicals to a desirable temperature. A heater/cooler
81 can be disposed in the vicinity of the roller outer surface,
such as attaching to an exposed end of the roller, or disposed
along the roller 77 under the foam layer 71. A heater/cooler 83 can
be disposed inside the roller 77 to heat/cool the roller or to
heat/cool the chemical reaching the roller. Any combinations of
heaters and coolers can be used.
[0056] FIG. 8B shows heater/cooler 84 disposed inside the roller
77, such as attached to the inner surface of a hollow roller. FIG.
8C shows heater/cooler 85 disposed in the middle of the roller 77,
heating/cooling the roller and the chemicals in the chemical
pockets 86. FIG. 8D shows heaters 87 disposed near the rollers to
heat the substrate 96 with shielding 88 to direct thermal energy to
the substrate 96. Heaters 87 can be disposed between consecutive
rollers, at the top of the substrates, at the bottom of the
substrates, or both.
[0057] In an embodiment, the present invention discloses an in-line
deposition system comprising rollers accepting a liquid flow to the
inside of the rollers and distributing the liquid to the outer
surfaces. The liquid media is protected by the delivery lines, and
the only liquid exposed to the environment is the liquid adhered to
the roller surfaces. This minimum exposure can improve safety for
the deposition system, especially for hazardous liquids such as
phosphorous acid or boron trifluoride.
[0058] The deposition coating with the present rollers can be
performed on both sides of the substrate, or can be applied to only
one side. In addition, other types of coating can be included. The
substrates can be transported with an in-line transport, such as
any type of conveyor or ceramic rollers, to the liquid rollers to
be coated, and then to an outlet in-line transport to subsequent
processes such as an anneal furnace. Other components can be
implemented, for example, exhaust and isolation to prevent
hazardous gas from escaping, temperature isolation to provide wall
safety, carrier gas and curtain gas for atmospheric isolation and
purging, substrate conditioning before removal from the process
chamber, such as a drying environment, and spray cleaning system
for system cleaning.
[0059] FIGS. 9A-9C illustrate exemplary configurations for liquid
coating according to an embodiment of the present invention. FIG.
9A shows a substrate 96 sandwiched between two rotating rollers 91A
and 91B. The rollers accept a liquid media 94A and 94B, entering
the rollers from one end, and distributing to the rollers' surface.
Foam or solidified foam layers 95A and 95B cover the outer surfaces
of the rollers, and receive the liquid media from the roller
surfaces to be transferred to the substrate 96. With rollers at the
top and bottom of the substrate, both sides of the substrate can be
coated simultaneously. In addition, the rollers can move the
substrate forward, thus acting as transport rollers.
[0060] The liquid media flowing to the rollers 91A/91B can be
controlled to perform a desired coating on the substrate 96 with
minimum excess waste. In addition, the separation of the rollers
can be controlled to exert appropriate contact pressure to the
substrate 96 to minimize the wasted liquid. For example, a spring
can be positioned on top roller 91A to provide a desired pressure
to the substrate 96. The multiple independent control mechanisms
can eliminate or minimize the excess fluid on the substrate
surfaces, such as providing a uniform coating without any liquid
droplets. The bottom roller 91B can be fixed around the axis of
rotation, and rotated to coat the bottom surface of the substrate,
together with forward substrate movement. Optionally, pan 99 can be
used to capture any residue liquid.
[0061] FIG. 9B shows a roller 91A disposed at top of substrate 96
to deposit a coating layer on the top surface. The bottom surface
can have no coating, or have a coating from another coating process
97A. The other coating process can be a liquid spray coating
comprising a nozzle delivering chemical media in aerosol or liquid
form and with or without carrier gas or solvent, or sponge rollers
dipped in liquid chemical media. In addition, the bottom surface
can be supported by roller 97B, which can be transport rollers or
non liquid-supplied rollers. The roller 97B can be used for
transporting the substrate forward, or for exerting contact
pressure between the liquid-supplied roller 91A and the substrate
96.
[0062] FIG. 9C shows a roller 91B disposed at bottom of substrate
96 to deposit a coating layer on the bottom surface. The top
surface can have no coating, or have a coating from another coating
process 98A. The bottom liquid roller 91A can be used as transport
roller for moving the substrates. In addition, roller 98B can be
provided on top of the substrate, which can be non liquid-supplied
rollers, and can serve to exert contact pressure between the
liquid-supplied roller 91B and the substrate 96.
[0063] In an embodiment, all rollers can accept the same liquid
media from a single reservoir and pumping system. Alternatively,
different rollers can accept different liquid media from multiple
reservoirs. Different chemicals can be deposited on top and bottom
surfaces. Different chemicals can be deposited on a same surface
for a coating mixture. Filling rollers, e.g., rollers without
accepting a liquid flow, can be included for other purposes, such
as improved media distribution. The liquid media can be all
distributed from a single reservoir, or can be individually
provided from multiple reservoirs. Flow distribution mechanisms can
be included, such as pumping mechanism, pressure controller, flow
controller and distribution manifold. Recirculating mechanism and
automatic refilling can also be included.
[0064] FIGS. 10A-10C illustrate exemplary configurations of liquid
media distributions in an in-line deposition system according to an
embodiment of the present invention. FIG. 10A shows substrates 103
moving by rolling conveyor rollers 101. Bottom liquid rollers 106
can replace conveyor rollers 101 to continue moving the substrates
forward, together with providing a liquid coating on the bottom
surfaces. Top liquid rollers are disposed with appropriate pressure
to deposit a top coating with minimum excess liquid residue.
[0065] The liquid media can be provided to the rollers from one or
more reservoirs. For example, a reservoir 104A containing chemical
liquid can provide liquid media to a pump 104B, which can push the
liquid media to the rollers 106. A pressure controller 104C and a
flow controller 104D can be added to regulate the pressure and flow
to the rollers. Manifold 104E serves to distribute the liquid media
to the rollers. Temperature controller 104F can provide heat or
cooling to the liquid media and/or the substrates. For simplicity,
the manifold is shown distributing the same liquid media with same
pressure and flow to the bottom rollers 106, but the invention is
not so restricted. Different configurations can be used, such as a
manifold distributing liquid media to all rollers, or different
delivery systems can be added to deliver different chemicals with
different pressures and different flows to different rollers.
[0066] The flow and pressure controllers can regulate the liquid
media that is to be provided to the substrate surfaces, which can
serve to optimize the coating process, such as minimizing the
excess liquid to the substrates, or regulating a desired coating to
the substrates with liquid media having different properties such
as higher or lower viscosity or higher or lower reaction rates with
the substrates. The present liquid delivery system can further
prevent reactions in the delivery lines, such as at the rollers or
at the liquid source. For example, the present liquid roller can be
used to deposit an absorber layer for solar cell device, with
crystallization occurring at the substrate surfaces instead of at
the roller surfaces. The multiple independent controllers of flow
rate, flow pressure, roller pressure, chemical temperature and
substrate temperature can provide an optimized coating on the
substrate surfaces, for example, a uniform coating layer with zero
or minimum liquid droplet or excess liquid waste.
[0067] The top and bottom rollers can accept different liquid media
for different coating material. FIG. 10B shows the top rollers 106
accepting a chemical solution and bottom rollers 102 accepting
another chemical solution. The top and bottom rollers can rotate at
a same speed or at different speeds. For example, for same liquid
media on top and bottom rollers, the top and bottom rollers can
rotate at a same speed for depositing a similar coating layer on
top and bottom surfaces of the substrates. For different liquid
media, the top and bottom rollers can rotate at appropriate speeds,
which can be the same or different from each other.
[0068] Additional rollers can be added. For example, one or more
dry rollers can be provided for better liquid media distribution.
The dry rollers can be disposed alternate to the liquid rollers, or
can be disposed at selected locations. The dry rollers can be
rollers without any wetting liquid, roller without accepting liquid
from the inside, or rollers with vacuum suction (instead of liquid
flowing) to dry the porous layer, or brush rollers.
[0069] Different rollers can be used on a same surface. FIG. 10C
shows alternate rollers 108 for top rollers 106 and alternate
rollers 109 for bottom rollers 102. The alternate rollers can
provide different chemical liquid for coating mixture. The
alternate rollers can be dry rollers.
[0070] In an embodiment, the present invention discloses deposition
processes using continuous liquid media supply. FIGS. 11A-11C
illustrate an exemplary deposition process according to an
embodiment of the present invention. In FIG. 11A, a substrate is
coated 110 with a liquid layer using liquid rollers and then
optionally underwent a layer conditioning process 111. The layer
conditioning process is optional, meaning it will serve to
conditioning the deposited layer only if needed. For example, some
processes require a liquid layer as deposited and thus no
conditioning process is needed. The conditioning process can be a
drying process, for example, by a heater or be a drying roller. The
drying process is optional, meaning an active drying process is not
necessary, for example, the deposition process can be air dried, or
the drying process can be embedded in subsequent process, for
example, in a subsequent annealing process.
[0071] FIG. 11B illustrates an exemplary configuration of separate
coating and drying, comprising separate coating station comprising
liquid rollers 116 and conditioning/drying station comprising
heater 114. When the transport rollers transfer the substrates 103
to the coating station, liquid rollers 116 deposit a liquid coating
on the substrates. As shown, the liquid rollers deposit coating
layers on both top and bottom, with similar rollers, but other
configurations can be used. After completing the coating layers,
the substrates are transported, by the same bottom liquid rollers
116, to the drying station to be dried by the thermal energy
provided by heaters 114. As shown, heaters 114 comprising IR
heaters disposed in parallel to the rollers for heating the
substrates as the substrates passing through, but other heating
configurations can be used, such as different orientations, or
different types of heaters.
[0072] FIG. 11C illustrates an exemplary configuration of
integrated deposition and drying. The coating station and the
drying station are integrated to a deposition station, where the
heaters 114 and the liquid rollers 116 are disposed next to each
other, so that the liquid coating from each roller 116 can be
heated immediately by the next heater 114. Other configurations can
be used, such as multiple heaters 114 after one liquid roller 116,
or one heater 114 after multiple liquid rollers 116.
[0073] FIGS. 12A-12C illustrate an exemplary deposition process
according to an embodiment of the present invention. In FIG. 12A, a
substrate is coated 120 with a dopant liquid layer using liquid
rollers, dried 121 to form a solid layer, and then annealed in a
furnace to drive the dopant under the substrate surface. The drying
process can be omitted, or can be embedded in the annealing
process. FIG. 12B illustrates an exemplary configuration of
coating, drying and annealing, comprising separate coating station
comprising liquid rollers 126 and drying station comprising heater
124. When the transport rollers 127 transfer the substrates 103 to
the coating station, liquid rollers 126 deposit a liquid coating on
the substrates. After completing the coating layers, the substrates
are transported, by the same bottom liquid rollers 126, to the
drying station to be dried by the thermal energy provided by
heaters 124. The substrates are then transferred to an anneal
furnace using heaters 125.
[0074] FIG. 12C illustrates an exemplary configuration of
integrated coating and drying. The coating station and the drying
station are integrated to a deposition station, where the heaters
124 and the liquid rollers 126 are disposed next to each other, so
that the liquid coating from each roller 126 can be heated
immediately by the next heater 124. After drying, the substrates
are annealed by the heaters 125. Alternatively, the drying step can
be skipped, or incorporated in the anneal process. For example, the
anneal process can include a pre-anneal step before a main anneal
step, and the drying process can be included in the pre-anneal
step.
[0075] In an embodiment, the present invention discloses methods
for depositing liquids on substrates, comprising using a roller
accepting liquid media at at least one end and migrating the liquid
to the outer surfaces for contact coating. The end of the roller
accepting the liquid media can be an extreme end, such as the end
surface of a cylindrical roller, or can be near the extreme end,
such as on the outer surface of the roller close to the end
surface. The roller has channels to bring the liquid media to the
outer surface of the roller, such as the circumference surface of a
cylindrical roller.
[0076] FIGS. 13A-13B illustrate exemplary flowcharts of liquid
deposition according to an embodiment of the present invention. In
FIG. 13A, operation 130 provides one or more substrates on a moving
platform, for example, a large flat panel substrate or multiple
semiconductor substrates placed in rows. The moving platform can be
an in-line conveyor, comprising means such as rollers to move the
substrates from one process station to another process station. The
moving platform can be an input station for an in-line coating
station, accepting substrates and transferring the substrates to
the coating zone. The substrate can be prepared before entering the
coating station, for example, by a surface cleaning process to
remove impurities or particulates, or by an oxidation process to
form an oxide layer. In certain cases, the native oxide on the
substrate might not be desirable, and thus a HF solution cleaning
might be performed to provide a clean surface. The substrate can be
transported to an enclosure, for example, by a substrate moving
mechanism, or the substrate can move continuously through the
enclosure, for example, by an in-line transport mechanism.
[0077] In operation 131, the substrates enter a coating zone
comprising a plurality of liquid rollers, some of which also acting
as transport rollers to move the substrates forward. Liquid media
is flowing to at least one end of the liquid rollers, where the
liquid media is transferred to the outer surface of the rollers.
Optional foam material covering the rollers can be used for
improving the coating process, such as reducing substrate damage
and improving distribution of liquid media on the substrates. The
rollers can have channels, such as hollow cylindrical tubes, or
grooves along the length of the rollers, to guide the liquid
media.
[0078] In operation 132, the rollers are rotating so that the
liquid media from the roller surfaces coats the substrate surfaces
by contact. In addition, the rotating transport rollers move the
substrates to the end of the coating zone. Means for improving the
coating layers can be included, such as dry rollers disposed after
the liquid rollers for better media distribution.
[0079] In optional operation 133, the coating layers are
conditioned, for example, drying by thermal energy such as IR lamps
or by other forms of energy excitation to the liquid coatings, or
by one or more dry rollers. The drying zone can be disposed after
the coating zone, for example, by disposing IR heaters after the
liquid rollers. Alternatively, the drying zone can be integrated
with the coating zone, for example, by disposing IR heaters
alternatedly with the liquid rollers.
[0080] Additional elements can be used in the deposition process.
For example, for deposition processes requiring hot chemicals,
heaters can be used to heat the liquid supplier before reaching the
substrates. For deposition processes requiring high temperature
substrates for activating chemical reactions, heaters can be used
to heat the substrates. In addition, temperature control devices
can be used to keep the chemicals in appropriate temperature, such
as cooling or heating.
[0081] FIG. 13B shows an exemplary process for depositing a layer.
Operation 130 provides one or more substrates on a moving platform.
In operation 135, the substrates are heated to a desired
temperature, such as a temperature to accelerate the reactions of
the chemicals deposited thereon, to evaporate the liquid carrier in
the chemicals, or to anneal the deposited layers. In operation 136,
the heated substrates receive a rolled-on deposition of a liquid
layer by a plurality of liquid rollers accepting liquid media from
at least one end of the rollers. For example, the liquid layer can
be an absorber layer in a solar cell device structure, with the
absorber chemicals comprising a suspension of small globules of
absorber elements in a liquid medium. The absorber chemicals can be
stored and delivered at room temperature or sub-room temperature to
prevent reaction and prolong the chemical life time. The cooled
chemicals are then deposited on hot substrates, using thermal
energy to activate a reaction, forming a thin film layer on the
substrates.
[0082] FIG. 13C shows an exemplary process for depositing a dopant
layer. Operation 130 provides one or more substrates on a moving
platform. In operation 137, the substrates receive a rolled-on
deposition of a dopant coating layer by a plurality of liquid
rollers accepting liquid media from at least one end of the
rollers. The dopant layers comprise a doping element, which reacts
with the substrates to form pn junctions.
[0083] In operation 138, the substrates enter a diffusion furnace
to drive the dopant to the substrates. The furnace can comprise a
plurality of heaters to heat the coating layers to a high
temperature, such as between 600 and 1000 C. The furnace can
comprise a pre-heating zone, acting to form a transition
temperature zone between the hot furnace zone and the room
temperature ambient. The pre-heating zone can also act as a drying
zone for drying the liquid coating layers.
[0084] In an embodiment, the present invention discloses
improvements to the roll-on coating process using liquid supplied
rollers. For example, pressing mechanisms can be included to apply
a desired pressure to the liquid rollers, enabling wet coating on
the substrates without or with minimum excess liquid. The liquid
media can be regulated to compensate for different liquid
properties, such as viscosity, evaporation property, density, or
reactivity, using active mechanism such as pumps and
controllers.
[0085] FIGS. 14A-14B illustrate exemplary flowcharts for liquid
deposition controls according to an embodiment of the present
invention. In FIG. 14A, the liquid media delivered to the
substrates is controlled to achieve a desired goal, such as
optimizing the coating and minimizing operation cost. Operation 140
provides one or more substrates on a moving platform. In operation
141, liquid media is flowing to at least one end of the liquid
rollers, where the liquid media is transferred to the outer surface
of the rollers for coating the substrates with the rollers rotated
to apply an even coating onto the substrate surfaces.
[0086] In operation 142, at least one of the liquid temperature,
the liquid flow rate, the fluid concentration, the fluid
temperature,and the liquid pressure are regulated to achieve a
desired coating layer on the substrate surfaces. Further, in the
case of coating using top and bottom rollers, the contact pressure
between the top and bottom rollers can be controlled to obtain
optimum coating conditions, such as having a desired coating,
minimizing excess fluid waste, or compensating for the variations
of liquid media properties. The multiple control mechanisms can
offer significant advantages, for example, enabling a deposition
process having zero or minimum droplets or excess fluid media,
allowing a uniform coating layer with reduced consumable chemicals.
The consistency of the fluid, and other fluid properties, such as
concentration or temperature, can be controlled to ensure
consistency and desired properties of the deposited layer.
[0087] In FIG. 14B, coating layers on the substrate surfaces are
controlled to compensate for a non-uniformity of subsequent
process. Operation 140 provides one or more substrates on a moving
platform. The substrates are exposed to a plurality of liquid
supplied rollers for rolling deposition a coating on the substrate
surfaces. Operation 145 controls the coating thickness uniformity
on the substrates to achieve a non-uniform thickness profile. The
coating can comprise a dopant layer that will be subjected to a
subsequent anneal process. The non-uniform thickness profile can be
used to compensate for the non-uniformity of other process, such as
a non-uniform temperature profile in the furnace of a subsequent
anneal. Operation 146 subjects the non-uniform substrates to a
non-uniform subsequent process that can be compensated by the
thickness non-uniformity. For example, the temperature can be
non-uniform in an anneal furnace, and the thickness of the
substrates can be used to compensate for this temperature
non-uniformity so that a uniform doping profile can be
achieved.
[0088] In an embodiment, the present invention discloses different
process conditions for achieving a desired coating using liquid
rollers. For example, top and bottom rollers can accept different
liquid media to enable coating different layers on the top and
bottom of the substrates. Different liquid media can be applied to
alternating rollers to enable mixing layers or laminate layers.
[0089] FIGS. 15A-15B illustrate exemplary flowcharts for different
liquid deposition processes according to an embodiment of the
present invention. In FIG. 15A, different coating layers can be
applied to the top and bottom surfaces of the substrates. Operation
150 provides one or more substrates on a moving platform. In
operation 151, first liquid media is applied to the top rollers and
second liquid media is applied to the bottom rollers. In operation
152, the rollers are rotated to deposit different coating layers on
the top and bottom of the substrates.
[0090] In FIG. 15B, mixed coating or laminate coating can be
applied to the substrates. Operation 150 provides one or more
substrates on a moving platform. In operation 155, first and second
liquid media are applied to alternate rollers. In addition, top and
bottom rollers can accept similar or different liquid media. In
operation 156, the rollers are rotated to deposit coating layers on
the substrates.
[0091] While the present invention has been described with respect
to a preferred mode thereof, it will be apparent that numerous
alterations and modifications will be apparent to those skilled in
the art without departing from the spirit of the invention. As in
all such obvious alterations and modifications, it is desired that
they be included within the purview of my invention, which is to be
limited only by the scope, including equivalents, of the following
appended claims.
* * * * *