U.S. patent application number 12/473342 was filed with the patent office on 2010-12-02 for devices containing silver compositions deposited by micro-deposition direct writing silver conductor lines.
This patent application is currently assigned to E. I. DU PONT DE NEMOURS AND COMPANY. Invention is credited to Roberto Irizarry, Patricia J. Olliver, Haixin Yang.
Application Number | 20100301479 12/473342 |
Document ID | / |
Family ID | 43219295 |
Filed Date | 2010-12-02 |
United States Patent
Application |
20100301479 |
Kind Code |
A1 |
Yang; Haixin ; et
al. |
December 2, 2010 |
DEVICES CONTAINING SILVER COMPOSITIONS DEPOSITED BY
MICRO-DEPOSITION DIRECT WRITING SILVER CONDUCTOR LINES
Abstract
Embodiments of the invention relate to a silicon semiconductor
device, and a conductive thick film composition for use in a solar
cell device.
Inventors: |
Yang; Haixin; (Chapel Hill,
NC) ; Irizarry; Roberto; (Raleigh, NC) ;
Olliver; Patricia J.; (Raleigh, NC) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Assignee: |
E. I. DU PONT DE NEMOURS AND
COMPANY
Wilmington
DE
|
Family ID: |
43219295 |
Appl. No.: |
12/473342 |
Filed: |
May 28, 2009 |
Current U.S.
Class: |
257/746 ;
136/256; 257/E21.159; 257/E23.01; 438/660 |
Current CPC
Class: |
Y02E 10/50 20130101;
B22F 1/0074 20130101; H01B 1/22 20130101; C09D 11/52 20130101; H01L
2924/01025 20130101; H01L 24/05 20130101; H01L 2924/01019 20130101;
H01L 2924/12043 20130101; H01L 2924/12043 20130101; H01L 2924/01078
20130101; H01L 31/022425 20130101; H01L 24/03 20130101; H01L
2924/00 20130101; H01L 2924/01079 20130101 |
Class at
Publication: |
257/746 ;
438/660; 136/256; 257/E23.01; 257/E21.159 |
International
Class: |
H01L 23/48 20060101
H01L023/48; H01L 21/283 20060101 H01L021/283; H01L 31/0224 20060101
H01L031/0224 |
Claims
1. A semiconductor device made by the method comprising the steps
of: (a) providing a semiconductor substrate, one or more insulating
films, and the thick film composition; (b) applying the insulating
film to the semiconductor substrate, (c) applying the thick film
composition to the insulating film on the semiconductor substrate,
and (d) firing the semiconductor, insulating film and thick film
composition, wherein the thick film composition comprises: (i) one
or more conductive materials; (ii) one or more inorganic binders;
and (iii) organic vehicle, wherein 1 to 15% of the inorganic
components are submicron particles.
2. A semiconductor device comprising an electrode, wherein the
electrode, prior to firing, comprises a composition comprising: (a)
one or more conductive materials; (b) one or more inorganic
binders; and (c) organic vehicle, wherein 1 to 15% of the inorganic
components are submicron particles.
3. The device of claim 2, wherein 85 to 99% of the inorganic
components have a d50 of 1.5 to 10 microns.
4. The device of claim 2, wherein the one or more conductive
materials comprise silver.
5. The device of claim 4, wherein the submicron particles comprise
silver.
6. The device of claim 2, wherein the submicron particles have a
d50 of 0.1 to 1 microns.
7. The device of claim 2, wherein the submicron particles have a
d50 of 0.1 to 0.6 microns.
8. The device of claim 2, wherein the inorganic components have a
bimodal size distribution.
9. The device of claim 2, wherein the thick film composition
further comprises one or more additives.
10. The device of claim 9, wherein the one or more additives
comprise components selected from the group consisting of: (a) a
metal wherein said metal is selected from Zn, Pb, Bi, Gd, Ce, Zr,
Ti, Mn, Sn, Ru, Co, Fe, Cu, and Cr; (b) a metal oxide of one or
more of the metals selected from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn,
Sn, Ru, Co, Fe, Cu and Cr; (c) any compounds that can generate the
metal oxides of (b) upon firing; and (d) mixtures thereof.
11. The device of claim 10, wherein the one or more inorganic
additives comprises ZnO.
12. The device of claim 5, wherein the submicron particles further
comprise ZnO and an inorganic binder.
13. The device of claim 2, further comprising an insulating film
and a semiconductor substrate.
14. A solar cell comprising the semiconductor device of claim
2.
15. The device of claim 13, wherein the insulating film comprises
one or more components selected from: titanium oxide, silicon
nitride, SiNx:H, silicon oxide, and silicon oxide/titanium oxide.
Description
FIELD OF THE INVENTION
[0001] Embodiments of the invention relate to a silicon
semiconductor device, and a conductive thick film composition for
use in a solar cell device.
TECHNICAL BACKGROUND OF THE INVENTION
[0002] A conventional solar cell structure with a p-type base has a
negative electrode that may be on the front-side (also termed
sun-side or illuminated side) of the cell and a positive electrode
that may be on the opposite side. Radiation of an appropriate
wavelength falling on a p-n junction of a semiconductor body serves
as a source of external energy to generate hole-electron pairs in
that body. Because of the potential difference which exists at a
p-n junction, holes and electrons move across the junction in
opposite directions and thereby give rise to flow of an electric
current that is capable of delivering power to an external circuit.
Most solar cells are in the form of a silicon wafer that has been
metallized, i.e., provided with metal contacts that are
electrically conductive.
[0003] There is a need for compositions, structures (for example,
semiconductor, solar cell or photodiode structures), and
semiconductor devices (for example, semiconductor, solar cell or
photodiode devices) which have improved electrical performance, and
methods of making.
SUMMARY OF THE INVENTION
[0004] An embodiment of the invention relates to composition
including: (a) one or more conductive materials; (b) one or more
inorganic binders; and (c) organic vehicle, wherein 1 to 15% of the
inorganic components are submicron particles. In an embodiment, 85
to 99% of the inorganic components may have a d50 of 1.5 to 10
microns. In an embodiment, one or more conductive materials may
include silver. In an embodiment, a portion of the silver contains
submicron particles. In an embodiment, the submicron particles have
a d50 of 0.1 to 1 microns. In an embodiment, the submicron
particles have a d50 of 0.1 to 0.6 microns. In an embodiment, the
particles have a bimodal size distribution.
[0005] The composition may include one or more additives selected
from the group consisting of: (a) a metal wherein said metal is
selected from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu,
and Cr; (b) a metal oxide of one or more of the metals selected
from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (c)
any compounds that can generate the metal oxides of (b) upon
firing; and (d) mixtures thereof. In an embodiment, the additives
may include ZnO, or a compound that forms ZnO upon firing. In an
embodiment, the ZnO and/or inorganic binder may include submicron
particles. The ZnO may be 2 to 10 wt % of the total composition.
The glass frit may be 1 to 6 wt % of the total composition. The
conductive material may include Ag. The Ag may be 90 to 99 wt % of
the solids in the composition. In an embodiment, the inorganic
components may be 70 to 95 wt % of the total composition.
[0006] A further embodiment relates to a method of manufacturing a
semiconductor device including the steps of: (a) providing a
semiconductor substrate, one or more insulating films, and the
thick film composition described herein; (b) applying the
insulating film to the semiconductor substrate; (c) applying the
thick film composition to the insulating film on the semiconductor
substrate, and (d) firing the semiconductor, insulating film and
thick film composition. In an aspect, the insulating film may
include one or more components selected from: titanium oxide,
silicon nitride, SiNx:H, silicon oxide, and silicon oxide/titanium
oxide.
[0007] A further embodiment relates to a semiconductor device made
by the methods described herein. An aspect relates to a
semiconductor device including an electrode, wherein the electrode,
prior to firing, includes the composition described herein. An
embodiment relates to a solar cell including the semiconductor
device.
[0008] An embodiment relates to a semiconductor device including a
semiconductor substrate, an insulating film, and a front-side
electrode, wherein the front-side electrode comprises one or more
components selected from the group consisting of zinc-silicate,
willemite, and bismuth silicates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a process flow diagram illustrating the
fabrication of a semiconductor device.
[0010] Reference numerals shown in FIG. 1 are explained below.
[0011] 10: p-type silicon substrate
[0012] 20: n-type diffusion layer
[0013] 30: silicon nitride film, titanium oxide film, or silicon
oxide film
[0014] 40: p+ layer (back surface field, BSF)
[0015] 60: aluminum paste formed on backside
[0016] 61: aluminum back electrode (obtained by firing back side
aluminum paste)
[0017] 70: silver or silver/aluminum paste formed on backside
[0018] 71: silver or silver/aluminum back electrode (obtained by
firing back side silver paste)
[0019] 500: silver paste formed on front side according to the
invention
[0020] 501: silver front electrode according to the invention
(formed by firing front side silver paste)
DETAILED DESCRIPTION OF THE INVENTION
[0021] There is a need for improved solar cells with increased
efficiency. There is a need for conductive compositions suitable
for the formation of narrow conductor lines with increased height.
An aspect of the invention relates to compositions containing
submicron particles. The compositions may be thick film
compositions. These compositions may be used to form solar cell
electrodes. The electrodes may be on the front-side of a solar
cell. In an embodiment, the electrode lines may be narrow and have
increased height.
[0022] As used herein, "thick film composition" refers to a
composition which, upon firing on a substrate, has a thickness of 1
to 100 microns. The thick film compositions may contain a
conductive material, a glass composition, and organic vehicle. The
thick film composition may include additional components. As used
herein, the additional components are termed "additives".
[0023] The compositions described herein include one or more
electrically functional materials and one or more glass frits
dispersed in an organic medium. These compositions may be thick
film compositions. The compositions may also include one or more
additive(s). Exemplary additives may include metals, metal oxides
or any compounds that can generate these metal oxides during
firing.
[0024] In an embodiment, the electrically functional powders may be
conductive powders. In an embodiment, the composition(s), for
example conductive compositions, may be used in a semiconductor
device. In an aspect of this embodiment, the semiconductor device
may be a solar cell or a photodiode. In a further aspect of this
embodiment, the semiconductor device may be one of a broad range of
semiconductor devices. In an embodiment, the semiconductor device
may be a solar cell.
[0025] In an embodiment, the thick film compositions described
herein may be used in a solar cell. In an aspect of this
embodiment, the solar cell efficiency may be greater than 70% of
the reference solar cell. In a further embodiment, the solar cell
efficiency may be greater than 80% of the reference solar cell. The
solar cell efficiency may be greater than 90% of the reference
solar cell.
[0026] In an embodiment, the ratio of organic medium in the thick
film composition to the inorganic components in the dispersion may
be dependent on the method of applying the paste and the kind of
organic medium used, as determined by one of skill in the art. In
an embodiment, the dispersion may include 70-95 wt % of inorganic
components and 5-30 wt % of organic medium (vehicle) in order to
obtain good wetting.
[0027] In an embodiment, a portion of the inorganic components may
be submicron particles. In an aspect of this embodiment, the
submicron particles may have a d50 of 0.1 to 1 microns. In a
further aspect, the submicron particles may have a d50 of 0.1 to
0.8 microns. In a further aspect, the submicron particles may have
a d50 of 0.2 to 0.6 microns.
[0028] In an embodiment, the submicron particles may be 1 to 15 wt
% of the composition. In a further embodiment, the submicron
particles may be 2 to 10 wt % of the composition. In a further
embodiment, the submicron particles may be 3 to 6 wt % of the
composition.
[0029] In an embodiment, the submicron particles may include a
portion of the conductive material. In an aspect, 1 to 15 wt % of
the conductive material may be submicron particles. In a further
aspect, 2 to 10 wt % of the conductive material may be submicron
particles. In a further aspect, 3 to 6 wt % of the conductive
composition may be submicron particles.
[0030] In an embodiment, a portion of the composition may have a
d50 of 1.5 to 10 microns. In an aspect of this embodiment, 85 to 99
wt % of the inorganic components of the composition may have a d50
of 1.5 to 10 microns. In an aspect of this embodiment, a portion of
the composition may have a d50 of 2.0 to 7.0 microns. In an aspect
of this embodiment, a portion of the composition may have a d50 of
2.5 to 5.0 microns.
[0031] In a further aspect, the conductive material may include
silver. In an aspect, 50 to 100 wt % of the conductive material may
be silver. In a further aspect, 70 to 99 wt %, 70 to 98 wt %, or 80
to 95 wt % of the conductive material may be silver.
Glass frits
[0032] In an aspect of the invention, the composition includes
glass frit compositions. Glass frit compositions useful in the
present invention will readily recognized by one of skill in the
art. Glass frit compositions useful in compositions used to make
front-side solar cell electrodes may be used, for example.
Exemplary glass frit compositions include lead borosilicate
glasses. In an embodiment, glass frits compositions useful in the
present invention may include 20-24 wt % SiO.sub.2, 0.2-0.8 wt %
Al.sub.2O.sub.3, 40-60 wt % PbO, and 5-8 wt % B.sub.2O.sub.3. In an
embodiment, the glass frit composition may optionally also include
3-7 wt % TiO.sub.2. In an embodiment, the glass frit composition
may optionally also include one or more fluorine-containing
components, including but not limited to: salts of fluorine,
fluorides, metal oxyfluoride compounds, and the like. Such
fluorine-containing components include, but are not limited to
PbF.sub.2, BiF.sub.3, AlF.sub.3, NaF, LiF, KF, CsF, ZrF.sub.4,
TiF.sub.4 and/or ZnF.sub.2. In an embodiment, the glass frit
composition may include 8-13 wt % PbF.sub.2.
[0033] In a further aspect of this embodiment, thick film
composition may include electrically functional powders and
glass-ceramic frits dispersed in an organic medium. In an
embodiment, these thick film conductor composition(s) may be used
in a semiconductor device. In an aspect of this embodiment, the
semiconductor device may be a solar cell or a photodiode.
Conductive Materials
[0034] In an embodiment, the thick film composition may include a
functional phase that imparts appropriate electrically functional
properties to the composition. In an embodiment, the electrically
functional powder may be a conductive powder. In an embodiment the
electrically functional phase may include conductive materials
(also termed conductive particles, herein). The conductive
particles may include conductive powders, conductive flakes, or a
mixture thereof, for example.
[0035] In an embodiment, the conductive particles may include Ag.
In a further embodiment, the conductive particles may include
silver (Ag) and aluminum (Al). In a further embodiment, the
conductive particles may, for example, include one or more of the
following: Cu, Au, Ag, Pd, Pt, Al, Ag--Pd, Pt--Au, etc. In an
embodiment, the conductive particles may include one or more of the
following: (1) Al, Cu, Au, Ag, Pd and Pt; (2) alloy of Al, Cu, Au,
Ag, Pd and Pt; and (3) mixtures thereof.
[0036] In an embodiment, the functional phase of the composition
may include coated or uncoated silver particles which are
electrically conductive. In an embodiment in which silver particles
are coated, they are at least partially coated with a surfactant.
In an embodiment, the surfactant may include one or more of the
following non-limiting surfactants: stearic acid, palmitic acid, a
salt of stearate, a salt of palmitate, lauric acid, palmitic acid,
oleic acid, stearic acid, capric acid, myristic acid and linoleic
acid, and mixtures thereof. The counter ion may be, but is not
limited to, hydrogen, ammonium, sodium, potassium and mixtures
thereof.
[0037] In an embodiment, the silver may be 60 to 90 wt % of the
paste composition. In a further embodiment, the silver may be 70 to
85 wt % of the paste composition. In a further embodiment, the
silver may be 75 to 85 wt % of the paste composition. In a further
embodiment, the silver may be 78 to 82 wt % of the paste
composition.
[0038] In an embodiment, the silver may be 90 to 99 wt % of the
solids in the composition (i.e., excluding the organic vehicle). In
a further embodiment, the silver may be 92 to 97 wt % of the solids
in the composition. In a further embodiment, the silver may be 93
to 95 wt % of the solids in the composition.
[0039] As used herein, "particle size" is intended to mean "average
particle size"; "average particle size" means the 50% volume
distribution size. Volume distribution size may be determined by a
number of methods understood by one of skill in the art, including
but not limited to LASER diffraction and dispersion method using a
Microtrac particle size analyzer.
[0040] In an embodiment, a portion of the conductive materials may
be submicron particles. In an aspect of this embodiment, the
submicron particles may have a d50 of 0.1 to 1 microns. In a
further aspect, the submicron particles may have a d50 of 0.1 to
0.8 microns. In a further aspect, the submicron particles may have
a d50 of 0.2 to 0.6 microns.
[0041] In an embodiment, 1 to 15 wt % of the conductive material
may be submicron particles. In a further aspect, 2 to 10 wt % of
the conductive material may be submicron particles. In a further
aspect, 3 to 6 wt % of the conductive composition may be submicron
particles.
[0042] In an embodiment, a portion of the conductive materials may
have a d50 of 1.5 to 10 microns. In an aspect of this embodiment,
85 to 99 wt % of the conductive materials may have a d50 of 1.5 to
10 microns. In an aspect of this embodiment, a portion of the
conductive materials may have a d50 of 2.0 to 7.0 microns. In an
aspect of this embodiment, a portion of the conductive materials
may have a d50 of 2.5 to 5.0 microns.
Additives
[0043] In an embodiment, the thick film composition may include one
or more additives. In an embodiment, the additive may be selected
from one or more of the following: (a) a metal wherein said metal
is selected from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe,
Cu, and Cr; (b) a metal oxide of one or more of the metals selected
from Zn, Pb, Bi, Gd, Ce, Zr, Ti, Mn, Sn, Ru, Co, Fe, Cu and Cr; (c)
any compounds that can generate the metal oxides of (b) upon
firing; and (d) mixtures thereof.
[0044] In an embodiment, the additive may include a Zn-containing
additive. The Zn-containing additive may include one or more of the
following: (a) Zn, (b) metal oxides of Zn, (c) any compounds that
can generate metal oxides of Zn upon firing, and (d) mixtures
thereof. In an embodiment, the Zn-containing additive may include
Zn resinate.
[0045] In an embodiment, the Zn-containing additive may include
ZnO. In an embodiment, a portion of the ZnO may include submicron
particles.
[0046] In an embodiment, ZnO may be present in the composition in
the range of 2-10 wt % total composition. In an embodiment, the ZnO
may be present in the range of 3-7 wt % total composition. In a
further embodiment, the ZnO may be present in the range of 4-6 wt %
total composition.
Organic Medium
[0047] In an embodiment, the thick film compositions described
herein may include organic medium. The inorganic components may be
mixed with an organic medium, for example, by mechanical mixing to
form pastes. A wide variety of inert viscous materials can be used
as organic medium. In an embodiment, the organic medium may be one
in which the inorganic components are dispersible with an adequate
degree of stability. In an embodiment, the rheological properties
of the medium may lend certain application properties to the
composition, including: stable dispersion of solids, appropriate
viscosity and thixotropy for screen printing, appropriate
wettability of the substrate and the paste solids, a good drying
rate, and good firing properties. In an embodiment, the organic
vehicle used in the thick film composition may be a nonaqueous
inert liquid. The use of various organic vehicles, which may or may
not contain thickeners, stabilizers and/or other common additives,
is contemplated. The organic medium may be a solution of polymer(s)
in solvent(s). In an embodiment, the organic medium may also
include one or more components, such as surfactants. In an
embodiment, the polymer may be ethyl cellulose. Other exemplary
polymers include ethylhydroxyethyl cellulose, wood rosin, mixtures
of ethyl cellulose and phenolic resins, polymethacrylates of lower
alcohols, and monobutyl ether of ethylene glycol monoacetate, or
mixtures thereof. In an embodiment. the solvents useful in thick
film compositions described herein include ester alcohols and
terpenes such as alpha- or beta-terpineol or mixtures thereof with
other solvents such as kerosene, dibutylphthalate, butyl carbitol,
butyl carbitol acetate, hexylene glycol and high boiling alcohols
and alcohol esters. In a further embodiment, the organic medium may
include volatile liquids for promoting rapid hardening after
application on the substrate.
[0048] In an embodiment, the polymer may be present in the organic
medium in the range of 8 wt. % to 11 wt. % of the total
composition, for example. The thick film silver composition may be
adjusted to a predetermined, screen-printable viscosity with the
organic medium.
Fired Thick Film Compositions
[0049] In an embodiment, the organic medium may be removed during
the drying and firing of the semiconductor device. In an aspect,
the glass frit, Ag, and additives may be sintered during firing to
form an electrode. The fired electrode may include components,
compositions, and the like, resulting from the firing and sintering
process.
[0050] In an aspect of this embodiment, the semiconductor device
may be a solar cell or a photodiode.
Method of Making a Semiconductor Device
[0051] An embodiment relates to methods of making a semiconductor
device. In an embodiment, the semiconductor device may be used in a
solar cell device. The semiconductor device may include a
front-side electrode, wherein, prior to firing, the front-side
(illuminated-side) electrode may include composition(s) described
herein.
[0052] In an embodiment, the method of making a semiconductor
device includes the steps of: (a) providing a semiconductor
substrate; (b) applying an insulating film to the semiconductor
substrate; (c) applying a composition described herein to the
insulating film; and (d) firing the device.
[0053] Exemplary semiconductor substrates useful in the methods and
devices described herein are recognized by one of skill in the art,
and include, but are not limited to: single-crystal silicon,
multicrystalline silicon, ribbon silicon, and the like. The
semiconductor substrate may be junction bearing. The semiconductor
substrate may be doped with phosphorus and boron to form a p/n
junction. Methods of doping semiconductor substrates are understood
by one of skill in the art.
[0054] The semiconductor substrates may vary in size
(length.times.width) and thickness, as recognized by one of skill
in the art. In a non-limiting example, the thickness of the
semiconductor substrate may be 50 to 500 microns; 100 to 300
microns; or 140 to 200 microns. In a non-limiting example, the
length and width of the semiconductor substrate may both equally be
100 to 250 mm; 125 to 200 mm; or 125 to 156 mm.
[0055] Exemplary insulating films useful in the methods and devices
described herein are recognized by one of skill in the art, and
include, but are not limited to: silicon nitride, silicon oxide,
titanium oxide, SiN.sub.x:H, hydrogenated amorphous silicon
nitride, and silicon oxide/titanium oxide film. The insulating film
may be formed by PECVD, CVD, and/or other techniques known to one
of skill in the art. In an embodiment in which the insulating film
is silicon nitride,the silicon nitride film may be formed by a
plasma enhanced chemical vapor deposition (PECVD), thermal CVD
process, or physical vapor deposition (PVD). In an embodiment in
which the insulating film is silicon oxide, the silicon oxide film
may be formed by thermal oxidation, thermal CVD, plasma CVD, or
PVD. The insulating film (or layer) may also be termed the
anti-reflective coating (ARC).
[0056] Compositions described herein may be applied to the
ARC-coated semiconductor substrate by a variety of methods known to
one of skill in the art, including, but not limited to,
screen-printing, ink-jet, coextrusion, syringe dispense, direct
writing, and aerosol ink jet. In an embodiment, compositions may be
applied to substrates using methods and devices described in US
patent application publication 2003/0100824, which is hereby
incorporated herein by reference. The composition may be applied in
a pattern. The composition may be applied in a predetermined shape
and at a predetermined position. In an embodiment, the composition
may be used to form both the conductive fingers and busbars of the
front-side electrode. In an embodiment, the width of the lines of
the conductive fingers may be 10 to 200 microns; 40 to 150 microns;
or 60 to 100 microns. In an embodiment, the width of the lines of
the conductive fingers may be 10 to 100 microns; 15 to 80 microns;
or 20 to 75 microns. In an embodiment, the thickness of the lines
of the conductive fingers may be 5 to 50 microns; 10 to 35 microns;
or 15 to 30 microns. In a further embodiment, the composition may
be used to form the conductive, Si contacting fingers.
[0057] The composition coated on the ARC-coated semiconductor
substrate may be dried as recognized by one of skill in the art,
for example, for 0.5 to 10 minutes, and then fired. In an
embodiment, volatile solvents and organics may be removed during
the drying process. Firing conditions will be recognized by one of
skill in the art. In exemplary, non-limiting, firing conditions the
silicon wafer substrate is heated to maximum temperature of between
600 and 900.degree. C. for a duration of 1 second to 2 minutes. In
an embodiment, the maximum silicon wafer temperature reached during
firing ranges from 650 to 800 C for a duration of 1 to 10 seconds.
In a further embodiment, the electrode formed from the conductive
thick film composition(s) may be fired in an atmosphere composed of
a mixed gas of oxygen and nitrogen. This firing process removes the
organic medium and sinters the glass frit with the Ag powder in the
conductive thick film composition. In a further embodiment, the
electrode formed from the conductive thick film composition(s) may
be fired above the organic medium removal temperature in an inert
atmosphere not containing oxygen. This firing process sinters or
melts base metal conductive materials such as copper in the thick
film composition.
[0058] In an embodiment, during firing, the fired electrode
(preferably the fingers) may react with and penetrate the
insulating film, forming electrical contact with the silicon
substrate.
[0059] In a further embodiment, prior to firing, other conductive
and device enhancing materials are applied to the opposite type
region of the semiconductor device and cofired or sequentially
fired with the compositions described herein. The opposite type
region of the device is on the opposite side of the device. The
materials serve as electrical contacts, passivating layers, and
solderable tabbing areas.
[0060] In an embodiment, the opposite type region may be on the
non-illuminated (back) side of the device. In an aspect of this
embodiment, the back-side conductive material may contain aluminum.
Exemplary back-side aluminum-containing compositions and methods of
applying are described, for example, in US 2006/0272700, which is
hereby incorporated herein by reference.
[0061] In a further aspect, the solderable tabbing material may
contain aluminum and silver. Exemplary tabbing compositions
containing aluminum and silver are described, for example in US
2006/0231803, which is hereby incorporated herein by reference.
[0062] In a further embodiment the materials applied to the
opposite type region of the device are adjacent to the materials
described herein due to the p and n region being formed side by
side. Such devices place all metal contact materials on the non
illuminated (back) side of the device to maximize incident light on
the illuminated (front) side.
[0063] The semiconductor device may be manufactured by the
following method from a structural element composed of a
junction-bearing semiconductor substrate and a silicon nitride
insulating film formed on a main surface thereof. The method of
manufacture of a semiconductor device includes the steps of
applying (such as coating and printing) onto the insulating film,
in a predetermined shape and at a predetermined position, the
conductive thick film composition having the ability to penetrate
the insulating film, then firing so that the conductive thick film
composition melts and passes through the insulating film, effecting
electrical contact with the silicon substrate. The electrically
conductive thick film composition is a thick-film paste
composition, as described herein, which is made of a silver powder,
Zn-containing additive, a glass or glass powder mixture having a
softening point of 300 to 600.degree. C., dispersed in an organic
vehicle and optionally, additional metal/metal oxide
additive(s).
[0064] An embodiment of the invention relates to a semiconductor
device manufactured from the methods described herein. Devices
containing the compositions described herein may contain
zinc-silicates, as described above.
[0065] An embodiment of the invention relates to a semiconductor
device manufactured from the method described above.
[0066] Additional substrates, devices, methods of manufacture, and
the like, which may be utilized with the thick film compositions
described herein are described in US patent application publication
numbers US 2006/0231801, US 2006/0231804, and US 2006/0231800,
which are hereby incorporated herein by reference in their
entireties.
EXAMPLES
[0067] An organic medium was prepared by dissolving polymers in
organic solvent at about 100 C. Into the organic medium, other
ingredients were added, including silver powder, glass frits, zinc
oxide and other additives. The resulting mixture was dispersed by a
three roll-milling process, known in thick film paste manufacturing
industry. Compositions I, II, and III, shown in Table 1, were
formed.
[0068] Pastes from the compositions I and II were filtered through
a Roki 40L-SHP-200XS filter capsule before print. Composition III
was used without filtration.
[0069] Pastes were evaluated at room temperature by a 3D-450 Smart
Pump.TM. printer that is made by nScrypt Inc, using re-usable
ceramic pen tip of ID/OD 50/75 .mu.m. Pump pressure was between 10
psi and 100 psi. The printing speed was between 200 mm per second
and 300 mm per second. The gap between pen tip and substrate
surface is 150 .mu.m.
[0070] Groups of ten four inches long lines were printed, dried in
a box oven at 150 C for 20 minutes, and fired in a belt furnace at
850 C peak temperatures for 2 minutes.
TABLE-US-00001 TABLE I Summary of Silver Paste Compositions
Composition Composition Ingredient Composition I II III Silver
81.05 Powder I Silver 81.05 Powder II Silver 81.05 Powder III Glass
Frit I 2.5 Glass Frit II 2.5 Glass Frit III 2.5 Zinc Oxide 5.5 5.5
5.5 Organic 10.95 10.95 10.95 Medium * based on wt % of total
composition Silver powder I, a mixture of spherical and flake
shapes with size of D10 = 0.88, D50 = 4.60, D95 = 10.73 microns.
Silver powder II, a spherical shape powder, with size of D10 = 1.0,
D50 = 1.71, D95 = 4.41 microns and surface area of 0.44 m2/g.
Silver powder III, a spherical shape powder, with size of D10 =
0.26, D50 = 0.45, D95 = 1.67 microns, with solid of 99.5%. Its
surface area is 1.0 m2/g. Glass frit I, SiO.sub.2 23.0%,
Al.sub.2O.sub.3 0.4%, PbO 58.8% and B.sub.2O.sub.3 7.8%, based on
wt % of glass composition, with a size of D10 = 0.36, D50 = 0.61
and D95 = 1.44 microns. Glass frit II, SiO.sub.2 22.08%,
Al.sub.2O.sub.3 0.38%, PbO 46.68%, B.sub.2O.sub.3 6.79%, TiO.sub.2
5.86% and PbF.sub.2 10.72%, based on wt % of glass composition,
with size of D10 = 0.42, D50 = 0.77 and D90 = 1.96 microns. Glass
frit III, SiO.sub.2 22.08%, Al.sub.2O.sub.3 0.38%, PbO 46.68%,
B.sub.2O.sub.3 6.79%, TiO.sub.2 5.86% and PbF.sub.2 10.72%, based
on wt % of glass composition, with a size of D10 = 0.34, D50 = 0.50
and D95 = 0.89 microns. Zinc oxide, purchased from Aldrich
Chemicals.
Example I
[0071] Composition I was able to go through the 50/75 micron pen
tip under pump pressure less than 50 psi for less than a period of
5 minutes before the pen tip was clogged. The best resulting fired
lines were 83 microns wide and 13 microns tall.
Example II
[0072] Composition I was able to go through the 75/125 micron pen
tip under pump pressure less than 60 psi for less than a period of
30 minutes before the pen tip was clogged. The best resulting fired
lines were 100 microns wide and 12 microns tall.
Example III
[0073] Composition II was able to go through the 50/75 micron pen
tip under pump pressure ranging from 10 psi to 100 psi for a period
of at least 30 minutes before printing was stopped. The best
resulting fired lines were 89 microns wide and 19 microns tall.
Example IV
[0074] A blend of composition II and composition III with a weight
percentage ratio of 95.5 to 4.5 was able to go through the 50/75
micron pen tip under pump pressure ranging from 10 psi to 80 psi
for a period of at least 3 hours before printing was stopped. The
best resulting fired lines were 67 microns wide and 25 microns
tall.
Example V
[0075] Composition III could not be printed through a 50/75 micron
pen tip under a pump pressure larger than 30 psi. Under 30 psi,
printing lasted for less than 5 seconds before pen tip was
clogged.
Example VI
[0076] Composition III could be printed through a 75/125 micron pen
tip under a pump pressure larger than 60 psi. Under 60 psi,
printing lasted for less than 5 minutes before pen tip was
clogged.
Example VII
[0077] A series of blends of composition II and III with ratios
ranging from 90 to 10 to 10 to 90 by weight was prepared and
printed. Once the composition III was more than 30%, 50/75 micron
pen tip was clogged within 1 minute.
Example VIII
[0078] The efficiency of the above printed substrates are analyzed.
An exemplary efficiency test is provided below. It is predicted
that the efficiency of the solar cell from Example IV will be
greater than the efficiency of the solar cells from the other
Examples.
Test Procedure-Efficiency
[0079] The solar cells built according to the method described
herein are tested for conversion efficiency. An exemplary method of
testing efficiency is provided below.
[0080] In an embodiment, the solar cells built according to the
method described herein are placed in a commercial I-V tester for
measuring efficiencies (ST-1000). The Xe Arc lamp in the I-V tester
simulates the sunlight with a known intensity and irradiated the
front surface of the cell.
[0081] The tester uses a multi-point contact method to measure
current (I) and voltage (V) at approximately 400 load resistance
settings to determine the cell's I-V curve. Both fill factor (FF)
and efficiency (Eff) are calculated from the I-V curve.
* * * * *