U.S. patent application number 13/013376 was filed with the patent office on 2011-08-11 for composition for forming p-type diffusion layer, method for forming p-type diffusion layer, and method for producing photovoltaic cell.
This patent application is currently assigned to HITACHI CHEMICAL COMPANY, LTD.. Invention is credited to Shuuichirou Adachi, Mitsunori Iwamuro, YOUICHI MACHII, Takeshi Nojiri, Kaoru Okaniwa, Masato Yoshida.
Application Number | 20110195540 13/013376 |
Document ID | / |
Family ID | 44354037 |
Filed Date | 2011-08-11 |
United States Patent
Application |
20110195540 |
Kind Code |
A1 |
MACHII; YOUICHI ; et
al. |
August 11, 2011 |
COMPOSITION FOR FORMING P-TYPE DIFFUSION LAYER, METHOD FOR FORMING
P-TYPE DIFFUSION LAYER, AND METHOD FOR PRODUCING PHOTOVOLTAIC
CELL
Abstract
The composition for forming a p-type diffusion layer in
accordance with the present invention contains an acceptor
element-containing glass powder and a dispersion medium. A p-type
diffusion layer and a photovoltaic cell having a p-type diffusion
layer are prepared by applying the composition for forming a p-type
diffusion layer, followed by a thermal diffusion treatment.
Inventors: |
MACHII; YOUICHI;
(Tsukuba-shi, JP) ; Yoshida; Masato; (Tsukuba-shi,
JP) ; Nojiri; Takeshi; (Tsukuba-shi, JP) ;
Okaniwa; Kaoru; (Tsukuba-shi, JP) ; Iwamuro;
Mitsunori; (Tsukuba-shi, JP) ; Adachi;
Shuuichirou; (Tsukuba-shi, JP) |
Assignee: |
HITACHI CHEMICAL COMPANY,
LTD.
|
Family ID: |
44354037 |
Appl. No.: |
13/013376 |
Filed: |
January 25, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61301652 |
Feb 5, 2010 |
|
|
|
Current U.S.
Class: |
438/72 ; 252/500;
252/512; 252/519.51; 252/521.3; 257/E21.144; 257/E31.119; 438/558;
438/57 |
Current CPC
Class: |
H01L 31/022425 20130101;
Y02P 70/50 20151101; Y02P 70/521 20151101; H01L 31/1804 20130101;
H01L 31/1864 20130101; Y02E 10/547 20130101; H01L 21/2255 20130101;
H01L 21/2225 20130101 |
Class at
Publication: |
438/72 ; 438/558;
438/57; 252/500; 252/512; 252/521.3; 252/519.51; 257/E21.144;
257/E31.119 |
International
Class: |
H01L 31/18 20060101
H01L031/18; H01L 21/225 20060101 H01L021/225; H01B 1/00 20060101
H01B001/00; H01B 1/02 20060101 H01B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 13, 2011 |
JP |
2011-005312 |
Claims
1. A composition for forming a p-type diffusion layer, comprising
an acceptor element-containing glass powder and a dispersion
medium.
2. The composition for forming a p-type diffusion layer according
to claim 1, wherein the acceptor element is at least one selected
from boron (B), aluminum (Al) and gallium (Ga).
3. The composition for forming a p-type diffusion layer according
to claim 1, wherein the acceptor element-containing glass powder
contains: at least one acceptor element-containing material
selected from B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3;
and at least one glass component material selected from SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3.
4. A method for forming a p-type diffusion layer, including:
applying, on a semiconductor substrate, the composition for forming
a p-type diffusion layer of claim 1; and conducting a thermal
diffusion treatment.
5. A paste composition for forming a p-type diffusion region in a
semiconductor substrate, comprising a dispersion of acceptor
element-containing glass particles in a spreadable paste
medium.
6. A method for producing a photovoltaic cell, including: applying,
on a semiconductor substrate, the composition for forming a p-type
diffusion layer of claim 1; subjecting the substrate to a thermal
diffusion treatment to form a p-type diffusion layer; and forming
an electrode on the p-type diffusion layer.
7. The method for producing a photovoltaic cell according to claim
6, comprising the steps of applying the composition for forming an
p-type diffusion layer to the silicon substrate, optionally through
an n-type diffusion layer, and heat treatment to form a glass layer
and an p.sup.+-type diffusion layer beneath the glass layer.
8. The method for producing a photovoltaic cell according to claim
6, comprising the following steps: (x) removing the damaged surface
layer from a crystalline silicon substrate; (xi) etching the
crystalline silicon substrate to form a textured front surface
structure; (xii) forming an n-type diffusion layer around the
silicon substrate in a mixed gas atmosphere of phosphorus
oxychloride, nitrogen and oxygen, and removing the n-type diffusion
layer from the side faces by side etching; (xiii) applying the
composition for forming an p-type diffusion layer to the n-type
diffusion layer on the rear surface of the silicon substrate, and
after optional drying to remove solvent present in the composition,
heat treatment, preferably at a temperature of 600 to 1200.degree.
C., to form a glass layer and an p.sup.+-type diffusion layer
beneath the glass layer; (xiv) removing the glass layer by etching;
(xv) forming an antireflective film over the n-type diffusion layer
on the front surface; (xvi) forming surface electrode on the
antireflective film; (xvii) forming rear surface electrode on the
p.sup.+-type diffusion layer; and (xviii) sintering to establish
electrical connection between the surface electrode and the silicon
substrate.
9. The method for producing a photovoltaic cell according to claim
6 comprising the following steps: (xii) removing the damaged
surface layer from a crystalline silicon substrate; (xiii) etching
the crystalline silicon substrate to form a textured surface
structure; (xiv) applying a composition comprising a donor-element
containing glass powder and a dispersion medium on the textured
front surface; (xv) applying the composition for forming an p-type
diffusion layer to the rear surface of the silicon substrate; (xvi)
optional drying to remove solvent present in the compositions
applied to the surfaces of the silicon substrate; (xvii) heat
treatment, preferably at a temperature of 600 to 1200.degree. C.,
to form a glass layer and an n-type diffusion layer beneath the
glass layer on the front surface, and a glass layer and an
p.sup.+-type diffusion layer beneath the glass layer on the rear
surface; (xviii) removing the glass layers by etching; (xix)
forming an antireflective film over the n-type diffusion layer on
the front surface; (xx) forming surface electrode on the
antireflective film; (xxi) forming rear surface electrode on the
p.sup.+-type diffusion layer on the rear surface; and (xxii)
sintering to establish electrical connection between the surface
electrode and the silicon substrate.
10. A method for forming a p-type diffusion region in a
semiconductor, comprising the steps of: 1) coating a portion of a
semiconductor substrate with a layer of a composition comprising a
dispersion of acceptor element-containing glass particles in a
dispersion medium; and 2) heating the coated semiconductor
substrate to a temperature sufficient to cause acceptor element
diffusion from the glass into the semiconductor substrate so as to
form an p-type diffusion region in the semiconductor substrate.
11. A use of an acceptor element-containing glass powder for
forming a p-type diffusion layer on a semiconductor substrate.
12. The use according to claim 11, wherein the acceptor element is
at least one selected from boron (B), aluminum (Al) and gallium
(Ga).
13. The use according to claim 11, wherein the acceptor
element-containing glass powder contains: at least one acceptor
element-containing material selected from B.sub.2O.sub.3,
Al.sub.2O.sub.3 and Ga.sub.2O.sub.3; and at least one glass
component material selected from SiO.sub.2, K.sub.2O, Na.sub.2O,
Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5,
SnO, ZrO.sub.2 and MoO.sub.3.
14. The use according to claim 11, wherein the acceptor
element-containing glass powder is used in the form of a
composition, which further comprises a dispersion medium.
15. The use according to claim 14, wherein the dispersion medium
comprises a binder and a solvent.
16. The use according to claim 15, wherein the binder is a
cellulose derivative, in particular ethylcellulose, and/or the
solvent is an ester.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. 119(e) form
Provisional U.S. Patent Application No. 61/301,652, filed Feb. 5,
2010, and Japanese Patent Application No. 2011-005312 filed Jan.
13, 2011, the disclosure of which is incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a composition for forming a
p-type diffusion layer of a photovoltaic cell, a method for forming
a p-type diffusion layer, a method for producing a photovoltaic
cell, a paste composition, and a use of the composition. More
specifically, the present invention relates to a technique for
forming a p-type diffusion layer, which enables reduction in
internal stress of silicon substrate serving as a semiconductor
substrate, whereby damage to a crystal grain boundary can be
suppressed and increase in crystal defects and warpage can be
suppressed.
[0004] 2. Description of the Related Art
[0005] A related art procedure of a silicon photovoltaic cell is
described hereinbelow.
[0006] First, in order to realize high efficiency by promoting
optical confinement effects, a p-type silicon substrate having a
texture structure formed thereon is prepared, and subsequently
subjected to a treatment at a temperature of from 800 to
900.degree. C. for several tens of minutes under a mixed gas
atmosphere of phosphorus oxychloride (POCl.sub.3), nitrogen and
oxygen, thereby uniformly forming an n-type diffusion layer.
According to this related art method, since diffusion of phosphorus
is carried out using a mixed gas, the n-type diffusion layer is
formed not only on the surface, but also on the side face and the
rear surface. For these reasons, there has been a need for a side
etching process to remove the n-type diffusion layer of the side
face. Further, the n-type diffusion layer of the rear surface needs
to be converted into a p.sup.+-type diffusion layer, and
correspondingly an aluminum paste is applied to the n-type
diffusion layer of the rear surface and then sintered to achieve
conversion of the n-type diffusion layer into the p.sup.+-type
diffusion layer and also formation of ohmic contact at the same
time.
[0007] However, aluminum paste has low conductivity, and therefore,
it is generally necessary to form a thick aluminum layer of about
10 to 20 .mu.m after sintering on the entire rear surface in order
to reduce the sheet resistance. Further, the coefficient of thermal
expansion of aluminum is considerably different from the
coefficient of thermal expansion of silicon, and therefore, such a
difference results in generation of large internal stress in the
silicon substrate during the sintering and cooling processes, which
contributes to damage to a crystal grain boundary, increase in the
crystal defects, and the warpage.
[0008] In order to solve this problem, there has been a method to
reduce the thickness of the rear surface electrode by decreasing
the amount of a paste composition to be coated. However, when the
coating amount of the paste composition is decreased, the amount of
aluminum diffused from a surface of a p-type silicon substrate into
an internal portion is insufficient. As a result, a desirable BSF
(Back Surface Field) effect (an effect in which collection
efficiency of generated carriers is increased due to the presence
of a p.sup.+-type layer) is not achieved, resulting in the problem
of a decrease in properties of a photovoltaic cell.
[0009] For these reasons, for example, there has been proposed a
paste composition including an aluminum powder, an organic vehicle,
and an inorganic compound powder whose coefficient of the thermal
expansion is lower than that of aluminum, and whose at least one of
melting temperature, softening temperature and decomposition
temperature is lower than the melting temperature of aluminum (for
example, Japanese Patent Application Laid-Open (JP-A) No.
2003-223813)
SUMMARY OF THE INVENTION
[0010] A first embodiment according to the present invention is a
composition for forming a p-type diffusion layer, including an
acceptor element-containing glass powder and a dispersion
medium.
[0011] A second embodiment of the present invention is a method for
forming a p-type diffusion layer, including:
[0012] applying, on a semiconductor substrate, the composition for
forming a p-type diffusion layer of the first embodiment; and
[0013] conducting a thermal diffusion treatment.
[0014] A third embodiment of the present invention is a method for
producing a photovoltaic cell, including:
[0015] applying, on a semiconductor substrate, the composition for
forming a p-type diffusion layer of any one of the first
embodiment;
[0016] subjecting the substrate to a thermal diffusion treatment to
form an p-type diffusion layer; and
[0017] forming an electrode on the p-type diffusion layer.
[0018] A fourth embodiment of the present invention is a paste
composition for forming an p-type diffusion region in a
semiconductor substrate, comprising a dispersion of acceptor
element-containing glass particles in a spreadable paste
medium.
[0019] A fifth embodiment of the present invention is a method for
forming an p-type diffusion region in a semiconductor, comprising
the steps of:
[0020] 1) coating a portion of a semiconductor substrate with a
layer of a composition comprising a dispersion of acceptor
element-containing glass particles in a dispersion medium; and
[0021] 2) heating the coated semiconductor substrate to a
temperature sufficient to cause acceptor element diffusion from the
glass into the semiconductor substrate so as to form an p-type
diffusion region in the semiconductor substrate.
[0022] A sixth embodiment of the present invention is a use of an
acceptor element-containing glass powder for forming a p-type
diffusion layer on a semiconductor substrate.
[0023] The present invention enables the formation of a p-type
diffusion layer without causing internal stress in a silicon
substrate and warpage of the substrate during the process of
producing a photovoltaic cell using a silicon substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The invention includes the following embodiments. [0025]
<1> A composition for forming a p-type diffusion layer,
comprising an acceptor element-containing glass powder and a
dispersion medium. [0026] <2> The composition for forming a
p-type diffusion layer according to <1>, in which the
acceptor element is at least one selected from boron (B), aluminum
(Al) and gallium (Ga). [0027] <3> The composition for forming
a p-type diffusion layer according to <1>, in which the
acceptor element-containing glass powder contains:
[0028] at least one acceptor element-containing material selected
from B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3; and
[0029] at least one glass component material selected from
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3. [0030]
<4> A method for forming a p-type diffusion layer,
including:
[0031] applying, on a semiconductor substrate, the composition for
forming a p-type diffusion layer of <1>; and
[0032] conducting a thermal diffusion treatment. [0033] <5> A
paste composition for forming a p-type diffusion region in a
semiconductor substrate, comprising a dispersion of acceptor
element-containing glass particles in a spreadable paste medium.
[0034] <6> A method for producing a photovoltaic cell,
including:
[0035] applying, on a semiconductor substrate, the composition for
forming a p-type diffusion layer of <1>;
[0036] subjecting the substrate to a thermal diffusion treatment to
form a p-type diffusion layer; and
[0037] forming an electrode on the p-type diffusion layer. [0038]
<7> The method for producing a photovoltaic cell according to
<6>, comprising the steps of applying the composition for
forming an p-type diffusion layer to the silicon substrate,
optionally through an n-type diffusion layer, and heat treatment to
form a glass layer and an p.sup.+-type diffusion layer beneath the
glass layer. [0039] <8> The method for producing a
photovoltaic cell according to <6>, comprising the following
steps: [0040] (i) removing the damaged surface layer from a
crystalline silicon substrate; [0041] (ii) etching the crystalline
silicon substrate to form a textured front surface structure;
[0042] (iii) forming an n-type diffusion layer around the silicon
substrate in a mixed gas atmosphere of phosphorus oxychloride,
nitrogen and oxygen, and removing the n-type diffusion layer from
the side faces by side etching; [0043] (iv) applying the
composition for forming an p-type diffusion layer to the n-type
diffusion layer on the rear surface of the silicon substrate, and
after optional drying to remove solvent present in the composition,
heat treatment, preferably at a temperature of 600 to 1200.degree.
C., to form a glass layer and an p.sup.+-type diffusion layer
beneath the glass layer; [0044] (v) removing the glass layer by
etching; [0045] (vi) forming an antireflective film over the n-type
diffusion layer on the front surface; [0046] (vii) forming surface
electrode on the antireflective film; [0047] (viii) forming rear
surface electrode on the p.sup.+-type diffusion layer; and [0048]
(ix) sintering to establish electrical connection between the
surface electrode and the silicon substrate. [0049] <9> The
method for producing a photovoltaic cell according to <6>
comprising the following steps: [0050] removing the damaged surface
layer from a crystalline silicon substrate; [0051] (ii) etching the
crystalline silicon substrate to form a textured surface structure;
[0052] (iii) applying a composition comprising a donor-element
containing glass powder and a dispersion medium on the textured
front surface; [0053] (iv) applying the composition for forming an
p-type diffusion layer to the rear surface of the silicon
substrate; [0054] (v) optional drying to remove solvent present in
the compositions applied to the surfaces of the silicon substrate;
[0055] (vi) heat treatment, preferably at a temperature of 600 to
1200.degree. C., to form a glass layer and an n-type diffusion
layer beneath the glass layer on the front surface, and a glass
layer and an p.sup.+-type diffusion layer beneath the glass layer
on the rear surface; [0056] (vii) removing the glass layers by
etching; [0057] (viii) forming an antireflective film over the
n-type diffusion layer on the front surface; [0058] (ix) forming
surface electrode on the antireflective film; [0059] (x) forming
rear surface electrode on the p.sup.+-type diffusion layer on the
rear surface; and [0060] (xi) sintering to establish electrical
connection between the surface electrode and the silicon substrate.
[0061] <10> A method for forming a p-type diffusion region in
a semiconductor, comprising the steps of:
[0062] 1) coating a portion of a semiconductor substrate with a
layer of a composition comprising a dispersion of acceptor
element-containing glass particles in a dispersion medium; and
[0063] 2) heating the coated semiconductor substrate to a
temperature sufficient to cause acceptor element diffusion from the
glass into the semiconductor substrate so as to form an p-type
diffusion region in the semiconductor substrate. [0064] <11>
A use of an acceptor element-containing glass powder for forming a
p-type diffusion layer on a semiconductor substrate. [0065]
<12> The use according to <11>, in which the acceptor
element is at least one selected from boron (B), aluminum (Al) and
gallium (Ga). [0066] <13> The use according to <11>, in
which the acceptor element-containing glass powder contains:
[0067] at least one acceptor element-containing material selected
from B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3; and
[0068] at least one glass component material selected from
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3. [0069]
<14> The use according to <11>, in which the acceptor
element-containing glass powder is used in the form of a
composition, which further comprises a dispersion medium. [0070]
<15> The use according to <14>, in which the dispersion
medium comprises a binder and a solvent. [0071] <16> The use
according to <15>, in which the binder is a cellulose
derivative, in particular ethylcellulose, and/or the solvent is an
ester.
[0072] The present invention enables the formation of a p-type
diffusion layer without causing an internal stress in a silicon
substrate and warpage of the substrate during the process of
producing a photovoltaic cell using a silicon substrate.
[0073] First, a composition for forming a p-type diffusion layer in
accordance with the present invention will be described, and then a
method for forming a p-type diffusion layer and a method for
producing a photovoltaic cell, using the composition for forming a
p-type diffusion layer, will be described.
[0074] In the present specification, the term "process" denotes not
only independent processes but also processes that cannot be
clearly distinguished from other processes as long as a purpose is
accomplished by the process.
[0075] Furthermore, in the present specification, "from . . . to .
. ." denotes a range including each of the minimum value and the
maximum value of the values described in this expression.
[0076] The composition for forming a p-type diffusion layer in
accordance with the present invention includes at least an acceptor
element-containing glass powder (hereinafter, often referred to
simply as "glass powder") and a dispersion medium, and may further
contain other additives as necessary, taking into consideration
coatability or the like.
[0077] As used herein, the term "composition for forming a p-type
diffusion layer" refers to a material which contains an acceptor
element-containing glass powder and is capable of forming a p-type
diffusion layer through thermal diffusion of the acceptor element
after application of the material to a silicon substrate. The use
of the composition including the acceptor element-containing glass
powderfor forming a p-type diffusion layer, in which the acceptor
element is included in the glass powder, ensures that a process of
forming a p.sup.+-type diffusion layer and a process of forming
ohmic contact are separated, whereby the options for the electrode
material for forming ohmic contact are expanded, and the options
for the structure of the electrode are also expanded. For example,
when a low resistance material like Ag is applied to an electrode,
an electrode having a thin film thickness and low resistance can be
achieved. Further, there is no need to form an electrode on the
whole surface, and therefore, the electrode may be partially formed
such as a comb-shaped electrode. As mentioned above, due to forming
a thin or partial electrode such a comb-shaped electrode, it is
possible to form a p-type diffusion layer, while suppressing an
internal stress in a silicon substrate and warpage of the
substrate.
[0078] Accordingly, when the composition for forming a p-type
diffusion layer in accordance with the present invention is
employed, internal stress in a silicon substrate and warpage of the
substrate, which occur in the conventionally widely used method,
namely a method in which an aluminum paste is applied to the n-type
diffusion layer and then sintered to convert the n-type diffusion
layer into the p.sup.+-type diffusion layer and also to form ohmic
contact at the same time, are suppressed.
[0079] Furthermore, since the acceptor element included in the
glass powder is hardly vaporized during sintering, formation of the
p-type diffusion layer in areas other than a desired area due to
vaporization of the acceptor element is suppressed.
[0080] The acceptor element-containing glass powder in accordance
with the present invention will be described in more detail.
[0081] As used herein, the term "acceptor element" refers to an
element which is capable of forming a p-type diffusion layer by
doping thereof on a silicon substrate. As the acceptor element,
elements of Group XIII of the periodic table can be used. Examples
of the acceptor element include B (boron), aluminum (Al) and
gallium (Ga).
[0082] Examples of the acceptor element-containing material which
is used for introducing the acceptor element into the glass powder
include B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3. At
least one selected from B.sub.2O.sub.3, Al.sub.2O.sub.3 and
Ga.sub.2O.sub.3 is preferably used.
[0083] Further, the melting temperature, softening point,
glass-transition point, chemical durability and the like of the
acceptor element-containing glass powder can be controlled by
adjusting the component ratio, if necessary. Further, the glass
powder preferably contains the below-mentioned glass omponent
material.
[0084] Examples of the glass component material include SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, WO.sub.3, MoO.sub.3, MnO,
La.sub.2O.sub.3, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, Y.sub.2O.sub.3,
TiO.sub.2, GeO.sub.2, TeO.sub.2, and Lu.sub.2O.sub.3. At least one
selected from SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO,
CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, and
MoO.sub.3 is preferably used.
[0085] Specific examples of the acceptor element-containing glass
powder include those including both the acceptor element-containing
material and the glass component material such as, for example,
B.sub.2O.sub.3 based glass which includes B.sub.2O.sub.3 as the
acceptor element such as B.sub.2O.sub.3--SiO.sub.2 (the acceptor
element-containing material and the glass component material are
listed in this order, and are listed in the same order below) based
glass, B.sub.2O.sub.3--ZnO based glass, B.sub.2O.sub.3--PbO based
glass, single B.sub.2O.sub.3 based glass; Al.sub.2O.sub.3 based
glass which includes Al.sub.2O.sub.3 as the acceptor element such
as Al.sub.2O.sub.3--SiO.sub.2 based glass; and Ga.sub.2O.sub.3
based glass which includes Ga.sub.2O.sub.3 as the acceptor element
such as Ga.sub.2O.sub.3--SiO.sub.2 based glass.
[0086] The acceptor element-containing glass powder may include two
or more acceptor element-containing materials such as
Al.sub.2O.sub.3--B.sub.2O.sub.3, Ga.sub.2O.sub.3--B.sub.2O.sub.3 or
the like.
[0087] Although composite glasses containing one or two components
are illustrated in the above, composite glass containing three or
more components, such as B.sub.2O.sub.3--SiO.sub.2--Na.sub.2O, may
also be possible.
[0088] The content of the glass component material in the glass
powder is preferably appropriately set taking into consideration
the melting temperature, the softening point, the glass-transition
point, and chemical durability. Generally, the content of the glass
component material is preferably from 0.1% by mass to 95% by mass,
and more preferably from 0.5% by mass to 90% by mass.
[0089] The softening point of the glass powder is preferably in the
range of from 200.degree. C. to 1000.degree. C., and more
preferably from 300.degree. C. to 900.degree. C., from the
viewpoint of diffusivity during the diffusion treatment, and
dripping.
[0090] The shape of the glass powder includes a substantially
spherical shape, a flat shape, a block shape, a plate shape, a
scale-like shape, and the like. From the viewpoint of coating
property and uniform dispersion property, it is preferably a
spherical shape, a flat shape, or a plate shape.
[0091] The particle diameter of the glass powder is preferably 50
.mu.m or less. When a glass powder having a particle diameter of 50
.mu.m or less is used, a smooth coated film can be easily obtained.
Further, the particle diameter of the glass powder is more
preferably 10 .mu.m or less. The lower limit of the particle
diameter is not particularly limited, and preferably 0.01 .mu.m or
more.
[0092] The particle diameter of the glass powder means the average
particle diameter, and may be measured by laser diffraction
particle size analyzer.
[0093] The acceptor element-containing glass powder is prepared
according to the following procedure.
[0094] First, raw materials are weighed and filled in a crucible.
The crucible may be made of platinum, platinum-rhodium, iridium,
alumina, quartz, carbon, or the like, which is appropriately
selected taking into consideration the melting temperature,
atmosphere, reactivity with melted materials, and the like.
[0095] Next, the raw materials are heated to a temperature
corresponding to the glass composition in an electric furnace,
thereby preparing a solution. At this time, stirring is preferably
applied such that the solution becomes homogenous.
[0096] Subsequently, the solution is allowed to flow on a zirconia
or carbon plate or the like to result in vitrification of the
solution.
[0097] Finally, the glass is pulverized into a powder. The
pulverization can be carried out by using a known method such as
jet mill, bead mill or ball mill.
[0098] The content of the acceptor element-containing glass powder
in the composition for forming a p-type diffusion layer is
determined taking into consideration coatability, diffusivity of
acceptor elements, and the like. Generally, the content of the
glass powder in the composition for forming a p-type diffusion
layer is preferably from 0.1% by mass to 95% by mass, more
preferably from 1% by mass to 90% by mass, still more preferably
from 1.5% by mass to 85% by mass, and furthermore preferably from
2% by mass to 80% by mass.
[0099] Hereinafter, a dispersion medium will be described.
[0100] The dispersion medium is a medium which disperses the glass
powder in the composition. Specifically, a binder, a solvent or the
like is employed as the dispersion medium.
[0101] For example, the binder may be appropriately selected from
a, polyvinyl alcohol, polyacrylamides, polyvinyl amides, polyvinyl
pyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide
alkyl sulfonic acid, cellulose derivatives such as cellulose
ethers, carboxymethylcellulose, hydroxyethylcellulose,
ethylcellulose, gelatin, starch and starch derivatives, sodium
alginates, xanthane, guar and guar derivatives, scleroglucan,
tragacanth or dextrin derivatives, (meth)acrylic acid resins,
(meth)acrylic acid ester resins (for example, alkyl (meth)acrylate
resins, dimethlaminoethyl (meth)acrylate resins, or the like),
butadiene resins, styrene resins, copolymers thereof, siloxane
resins and the like. These compounds may be used individually or in
a combination of two or more thereof.
[0102] The molecular weight of the binder is not particularly
limited and is preferably appropriately adjusted taking into
consideration a desired viscosity of the composition.
[0103] Examples of the solvent include ketone solvents such as
acetone, methylethylketone, methyl-n-propylketone,
methyl-iso-propylketone, methyl-n-butylketone,
methyl-iso-butylketone, methyl-n-pentylketone,
methyl-n-hexylketone, diethylketone, dipropylketone,
di-iso-butylketone, trimethylnonanone, cyclohexanone,
cyclopentanone, methylcyclohexanone, 2,4-pentanedione,
acetonylacetone, .gamma.-butyrolactone, and .gamma.-valerolactone;
ether solvents such as diethyl ether, methyl ethyl ether,
methyl-n-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyl
tetrahydrofuran, dioxane, dimethyl dioxane, ethylene glycol
dimethyl ether, ethylene glycol diethyl ether, ethylene glycol
di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol
dimethyl ether, diethylene glycol diethyl ether, diethylene glycol
methyl ethyl ether, diethylene glycol methyl-n-propyl ether,
diethylene glycol methyl-n-butyl ether, diethylene glycol
di-n-propyl ether, diethylene glycol di-n-butyl ether, diethylene
glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether,
triethylene glycol diethyl ether, triethylene glycol methyl ethyl
ether, triethylene glycol methyl-n-butyl ether, triethylene glycol
di-n-butyl ether, triethylene glycol methyl-n-hexyl ether,
tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl
ether, tetradiethylene glycol methyl ethyl ether, tetraethylene
glycol methyl-n-butyl ether, diethylene glycol di-n-butyl ether,
tetraethylene glycol methyl-n-hexyl ether, tetraethylene glycol
di-n-butyl ether, propylene glycol dimethyl ether, propylene glycol
diethyl ether, propylene glycol di-n-propyl ether, propylene glycol
dibutyl ether, dipropylene glycol dimethyl ether, dipropylene
glycol diethyl ether, dipropylene glycol methylethyl ether,
dipropylene glycol methyl-n-butyl ether, dipropylene glycol
di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene
glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether,
tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl
ether, tripropylene glycol methyl-n-butyl ether, tripropylene
glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether,
tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl
ether, tetradipropylene glycol methylethyl ether, tetrapropylene
glycol methyl-n-butyl ether, dipropylene glycol di-n-butyl ether,
tetrapropylene glycol methyl-n-hexyl ether, and tetrapropylene
glycol di-n-butyl ether; ester solvents such as methyl acetate,
ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate,
i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl
acetate, 3-methoxybutyl acetate, methyl pentyl acetate, 2-ethyl
butyl acetate, 2-ethyl hexyl acetate, 2-(2-butoxyethoxy)ethyl
acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl
acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate,
diethylene glycol monomethyl ether acetate, diethylene glycol
monoethyl ether acetate, diethylene glycol mono-n-butyl ether
acetate, dipropylene glycol monomethyl ether acetate, dipropylene
glycol monoethyl ether acetate, glycol diacetate, methoxy triglycol
acetate, ethyl propionate, n-butyl propionate, i-amyl propionate,
diethyl oxalate, and di-n-butyl oxalate; ether acetate solvents
such as ethylene glycol methyl ether propionate, ethylene glycol
ethyl ether propionate, ethylene glycol methyl ether acetate,
ethylene glycol ethyl ether acetate, diethylene glycol methyl ether
acetate, diethylene glycol ethyl ether acetate, diethylene
glycol-n-butyl ether acetate, propylene glycol methyl ether
acetate, propylene glycol ethyl ether acetate, propylene glycol
propyl ether acetate, dipropylene glycol methyl ether acetate, and
dipropylene glycol ethyl ether acetate; aprotic solvents such as
acetonitrile, N-methyl pyrrolidinone, N-ethyl pyrrolidinone,
N-propyl pyrrolidinone, N-butyl pyrrolidinone, N-hexyl
pyrrolidinone, N-cyclohexyl pyrrolidinone, N,N-dimethyl formamide,
N,N-dimethyl acetamide, N,N-dimethyl sulfoxide; alcohol solvents
such as methanol, ethanol, n-propanol, i-propanol, n-butanol,
i-butanol, sec-butanol, t-butanol, n-pentanol, i-pentanol,
2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxy butanol,
n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol,
sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl
alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol,
sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol,
cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol,
1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol,
dipropylene glycol, triethylene glycol, and tripropylene glycol;
glycol monoether solvents such as ethylene glycol methyl ether,
ethylene glycol ethyl ether, ethylene glycol monophenyl ether,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol mono-n-butyl ether, diethylene glycol
mono-n-hexyl ether, ethoxy triglycol, tetraethylene glycol
mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene
glycol monomethyl ether, dipropylene glycol monoethyl ether, and
tripropylene glycol monomethyl ether; ester solvents such as methyl
lactate, ethyl lactate, n-butyl lactate, and n-amyl lactate;
terpene solvents such as .alpha.-terpinene, .alpha.-terpinenol,
myrcene, allo-ocimene, imonene, dipentene, .alpha.-dipentene,
.beta.-dipentene, terpinenol, carvone, ocimene and phellandrene;
water, and the like. These materials may be used individually or in
a combination of two or more thereof.
[0104] The composition and content of the dispersion medium in the
composition for forming a p-type diffusion layer is determined
taking into consideration coatability and acceptor
concentration.
[0105] Hereinafter, the method for producing a p-type diffusion
layer and a photovoltaic cell in accordance with the present
invention will be described.
[0106] First, an alkaline solution is applied to silicon substrate
which is a p-type semiconductor substrate, thereby removing the
damaged layer, and a texture structure is obtained by etching.
[0107] Specifically, the damaged layer of the silicon surface,
which is caused at the time of being sliced from an ingot, is
removed by using 20% by mass of caustic soda. Then, a texture
structure is formed by etching with a mixture of 1% by mass of
caustic soda and 10% by mass of isopropyl alcohol. The photovoltaic
cell achieves high efficiency through the formation of a texture
structure on a light-receiving side (surface) to promote optical
confinement effects.
[0108] Next, an n-type diffusion layer is uniformly formed by
subjected to a treatment at a temperature of from 800 to
900.degree. C. for several tens of minutes under a mixed gas
atmosphere of phosphorus oxychloride (POCl.sub.3), nitrogen and
oxygen. At this time, according to the method using phosphorus
oxychloride, since phosphorus is diffused bilaterally, the n-type
diffusion layer is formed not only on the surface, but also on the
side face and the rear surface. For these reasons, there has been a
need for a side etching process to remove the n-type diffusion
layer of the side face.
[0109] Further, the composition for forming a p-type diffusion
layer is applied on the n-type diffusion layer formed on the rear
surface, i.e., non-light receiving surface. In the present
invention, although there is no limit to the application method,
for example, a printing method, a spinning method, brush
application, a spray method, a doctor blade method, a roll coater
method, an inkjet method or the like can be used.
[0110] The coating amount of the composition for forming a p-type
diffusion layer is not particularly limited, and for example, may
be from 0.01 g/m.sup.2 to 100 g/m.sup.2, and preferably from 0.1
g/m.sup.2 to 10 g/m.sup.2 as an amount of the glass powder.
[0111] Further, depending on the composition of the composition for
forming a p-type diffusion layer, a drying process for
volatilization of the solvent contained in the composition may be
required after the application thereof, if necessary. In this case,
the drying is carried out at a temperature of from 80 to
300.degree. C., for 1 to 10 minutes when using a hot plate, or for
10 to 30 minutes when using a dryer or the like. Since these drying
conditions are dependent on the solvent composition of the
composition for forming a p-type diffusion layer, the present
invention is not particularly limited to the above-stated
conditions.
[0112] The semiconductor substrate, to which the composition for
forming a p-type diffusion layer was applied, is subjected to a
heat treatment at a temperature of from 600 to 1200.degree. C. This
heat treatment results in diffusion of an acceptor element into the
semiconductor substrate, thereby forming an p.sup.+-type diffusion
layer. The heat treatment can be carried out using a known
continuous furnace, batch furnace, or the like.
[0113] As a glass layer made of phosphoric acid glass or the like
is formed on the surface of the p.sup.+-type diffusion layer, the
phosphoric acid glass is removed by etching. The etching can be
carried out by using a known method, including a method of dipping
a subject in an acid such as hydrofluoric acid, a method of dipping
a subject in an alkali such as caustic soda, or the like.
[0114] In the conventional production method, an aluminum paste is
applied to the rear surface and then sintered, thereby converting
the n-type diffusion layer into the p.sup.+-type diffusion layer
and also forming an ohmic contact at the same time. However, since
a aluminum paste has low conductivity, in order to reduce a sheet
resistance, it is generally necessary to form a thick aluminum
layer of about 10 to 20 .mu.m after sintering on the entire rear
surface. Furthermore, the coefficient of thermal expansion of
aluminum is considerably different from the coefficient of thermal
expansion of silicon, and therefore, such a difference results in
generation of large internal stress in the silicon substrate during
the sintering and cooling processes, which contributes to warpage
of the silicon substrate.
[0115] The internal stress leads to the problem of damage to a
crystal grain boundary resulting in an increase in power loss. The
warpage makes a photovoltaic cell prone to damage during conveying
of the cell in a module process or during connecting to a copper
line which is referred to as a tub line. Recently, owing to
improvement in slicing techniques, the thickness of the silicon
substrate continues to be mode thinner, whereby the cell is more
readily cracked.
[0116] However, according to the production method of the present
invention, an n-type diffusion layer is converted into a
p.sup.+-type diffusion layer with a composition for forming a
p-type diffusion layer, and then an electrode is made on the
p.sup.+-layer as another process. Accordingly, the material used
for an electrode of the rear surface is not limited to aluminum.
For example, Ag (silver), Cu (copper) or the like may also be used,
so the thickness of the electrode of the rear surface can be
further reduced as compared to the related art, and in addition,
there is no need to form an electrode on the whole rear surface. As
a result, it is possible to inhibit the generation of internal
stress in the silicon substrate and warpage in sintering and
cooling processes.
[0117] An antireflective film is formed over the n-type diffusion
layer. The antireflective film is formed by using a known
technique. For example, when the antireflective film is a silicon
nitride film, the antireflective film is formed by a plasma CVD
method using a mixed gas of SiH.sub.4 and NH.sub.3 as a raw
material. In this case, hydrogen diffuses into crystals, and an
orbit which does not contribute to bonding of silicon atoms, that
is, a dangling bond binds to hydrogen, which inactivates a defect
(hydrogen passivation).
[0118] More specifically, the antireflective film is formed under
the conditions of a mixed gas NH.sub.3/SiH.sub.4 flow ratio of from
0.05 to 1.0, a reaction chamber pressure of from 0.1 to 2 Torr, a
film-forming temperature of from 300 to 550.degree. C., and a
plasma discharge frequency of 100 kHz or higher.
[0119] A metal paste for a surface electrode is printed and applied
on the antireflective film of the surface (light-receiving side) by
a screen printing method, followed by drying to form a surface
electrode. The metal paste for a surface electrode contains metal
particles and glass particles as essential components, and
optionally a resin binder, other additives, and the like.
[0120] Then, a rear surface electrode is also formed on
p.sup.+-type diffusion layer. As described hereinbefore, the
constitutive material and forming method of the rear surface
electrode are not particularly limited in the present invention.
For example, the rear surface electrode may also be formed by
applying the rear surface electrode paste containing a metal such
as aluminum, silver or copper, followed by drying. In this case, a
portion of the rear surface may also be provided with a silver
paste for forming a silver electrode, for connection between cells
in the module process.
[0121] Electrodes are sintered to complete a photovoltaic cell.
When the sintering is carried out at a temperature of from 600 to
900.degree. C. for several seconds to several minutes, the surface
side undergoes melting of the antireflective film which is an
insulating film, due to the glass particles contained in the
electrode-forming metal paste, and the silicon surface is also
partially melted, by which metal particles (for example, silver
particles) in the paste form a contact with the silicon substrate,
followed by solidification. In this manner, electrical conduction
is made between the formed surface electrode and the silicon
substrate. This type of process is called fire-through.
[0122] Hereinafter, the shape of the surface electrode is
described. The surface electrode is made up of a bus bar electrode
and a finger electrode intersecting the bus bar electrode.
[0123] The surface electrode can be formed, for example, by the
above-stated screen printing of a metal paste, or plating of
electrode materials, deposition of electrode materials by electron
beam heating under high vacuum, or the like. The surface electrode
made up of the bus bar electrode and the finger electrode is well
known since it is typically used as an electrode of the
light-receiving surface side, and a known method for the formation
of the bus bar electrode and the fmger electrode of the
light-receiving surface side can be applied.
[0124] In the above methods for producing a p-type diffusion layer
and a photovoltaic cell, in order to form an n-type diffusion layer
on a silicon serving as a p-type semiconductor substrate, a mixed
gas of phosphorus oxychloride (POCl.sub.3), nitrogen and oxygen is
used. However, a composition for forming an n-type diffusion layer
may be used to form the n-type diffusion layer. The composition for
forming an n-type diffusion layer contains an element of Group XV
of the periodic table such as phosphorous (P), antimony (Sb) or the
like as a donor element.
[0125] In the method using a composition for forming an n-type
diffusion layer in order to form the n-type diffusion layer, first,
the composition for forming an n-type diffusion layer is applied on
a front surface of the p-type semiconductor substrate which is a
light receiving surface, the composition for forming an p-type
diffusion layer is applied on a rear surface, and then a thermal
treatment is carried out at 600 to 1200.degree. C. This thermal
treatment results in diffusion of the donor element into the front
surface of the p-type semiconductor substrate to form an n-type
diffusion layer, and in diffusion of an acceptor element into the
rear surface of the p-type semiconductor substrate to form a
p.sup.+-type diffusion layer. Aside from these processes, a
photovoltaic cell is produced according to the same processes as in
the method described above. The composition for forming an n-type
diffusion layer referred to above preferably comprises a donor
element-containing glass powder and a dispersion medium. The donor
element is preferably selected from phosphorus (P) and/or antimony
(Sb), and the description provided in this specification for the
dispersion medium of the composition according to the present
invention likewise applies to the dispersion medium of the above
composition for forming an n-type diffusion layer.
[0126] The invention further includes the following embodiments.
[0127] (1) A paste composition for forming an p-type diffusion
region in a semiconductor substrate, containing a dispersion of
acceptor element-containing glass particles in a spreadable paste
medium. [0128] (2) The composition of (1), in which the glass
particles contain a acceptor element selected from the group
consisting of B (boron), aluminum (Al) and gallium (Ga). [0129] (3)
The composition of (1), in which the glass particles have a glass
composition containing:
[0130] at least one acceptor element-containing material selected
from B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3; and
[0131] at least one glass component material selected from
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3. [0132]
(4) The composition of (3), in which the glass composition contains
from about 0.1% to about 95%, by mass, of the glass-forming
compound. [0133] (5) The composition of (4), in which the glass
composition contains from about 0.5% to about 90%, by mass, of the
glass-forming compound. [0134] (6) The composition of (3), in which
the glass composition contains not more than about 50%, by mass, of
V.sub.2O.sub.5. [0135] (7) The composition of (6), in which the
glass composition contains from about 1% to about 50%, by mass, of
V.sub.2O.sub.5. [0136] (8) The composition of (7), in which the
glass composition contains from about 3% to about 40%, by mass, of
V.sub.2O.sub.5. [0137] (9) The composition of (3), in which the
glass composition is substantially devoid of v.sub.2O.sub.5. [0138]
(10) The composition of (1), in which the glass particles have a
softening temperature in a range from about 200.degree. C. to about
1000.degree. C. [0139] (11) The composition of (1), in which the
glass particles have a softening temperature in a range from about
300.degree. C. to about 900.degree. C. [0140] (12) The composition
of (1), in which the glass particles have a particle diameter not
greater than about 100 micrometers. [0141] (13) The composition of
(1), in which the glass particles have a particle diameter not
greater than about 50 micrometers. [0142] (14) The composition of
(1), in which spreadable paste medium comprises a binder and a
solvent for the binder. [0143] (15) The composition of (14), in
which the binder comprises at least one natural or synthetic
organic polymer. [0144] (16) The composition of (14), in which the
binder comprises ethylcellulose. [0145] (17) The composition of
(14), in which the solvent is a solvent volatile in a temperature
range from about 80.degree. C. to about 300.degree. C. [0146] (18)
The composition of (1), in which the glass particles constitute
from about 0.1%, by mass, to about 95%, by mass, of the paste
composition. [0147] (19) The composition of (1), in which the glass
particles constitute from about 1%, by mass, to about 90%, by mass,
of the paste composition. [0148] (20) The composition of (1),
further including particles of a metal capable of promoting
crystallization of the glass. [0149] (21) The composition of (20),
in which the metal is selected from the group consisting of silver,
silicon, copper, iron, zinc, and manganese. [0150] (22) The
composition of (20), in which the metal is selected from the group
consisting of silver, silicon, and zinc. [0151] (23) A method for
forming an p-type diffusion region in a semiconductor, containing
the steps of:
[0152] 1) coating a portion of a semiconductor substrate with a
layer of a composition containing a dispersion of acceptor
element-containing glass particles in a dispersion medium, and
[0153] 2) heating the coated semiconductor substrate to a
temperature sufficient to cause acceptor element diffusion from the
glass into the semiconductor substrate so as to form an p-type
diffusion region in the semiconductor substrate. [0154] (24) The
method of (23), in which the layer of the composition is dried
before step 2). [0155] (25) The method of (24), in which the drying
is conducted at a temperature in a range of about 80.degree. C. to
about 300.degree. C. [0156] (26) The method of (23), in which the
heating in step 2) is conducted at a temperature in a range of
about 600.degree. C. to about 1200.degree. C. [0157] (27) The
method of (23), in which the heating in step 2) is conducted for a
period of time in a range from about one minute to about 60
minutes. [0158] (28) The method of (27), in which the heating in
step 2) is conducted for a period of time in a range from about 2
minutes to about 30 minutes. [0159] (29) The method of (23), in
which the semiconductor substrate is silicon. [0160] (30) The
method of (23), in which a glass layer formed on the surface of the
semiconductor substrate in step 2) is subsequently removed. [0161]
(31) The method of (30), in which the glass layer formed on the
surface of the semiconductor substrate in step 2) is removed by
etching. [0162] (32) The method of (23), in which the glass
particles contain a acceptor element selected from the group
consisting of B (boron), aluminum (Al) and gallium (Ga). [0163]
(33) The method of (23), in which the glass particles have a glass
composition containing:
[0164] at least one acceptor element-containing material selected
from B.sub.2O.sub.3, Al.sub.2O.sub.3 and Ga.sub.2O.sub.3; and
[0165] at least one glass component material selected from
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3. [0166]
(34) The method of (33), in which the glass composition contains
from about 0.1% to about 95%, by mass, of the glass-forming
compound. [0167] (35) The method of (34), in which the glass
composition contains from about 0.5% to about 90%, by mass, of the
glass-forming compound. [0168] (36) The method of (33), in which
the glass composition contains not more than about 50%, by mass, of
V.sub.2O.sub.5. [0169] (37) The method of (36), in which the glass
composition contains from about 1% to about 50%, by mass, of
V.sub.2O.sub.5. [0170] (38) The method of (37), in which the glass
composition contains from about 3% to about 40%, by mass, of
V.sub.2O.sub.5. [0171] (39) The method of (33), in which the glass
composition is substantially devoid of V.sub.2O.sub.5. [0172] (40)
The method of (23), in which the glass particles have a softening
temperature in a range from about 200.degree. C. to about
1000.degree. C. [0173] (41) The method of (23), in which the glass
particles have a softening temperature in a range from about
300.degree. C. to about 900.degree. C. [0174] (42) The method of
(23), in which the glass particles have a particle diameter not
greater than about 100 micrometers. [0175] (43) The method of (23),
in which the glass particles have a particle diameter not greater
than about 50 micrometers. [0176] (44) The method of (23), in which
the spreadable paste medium comprises a binder and a solvent for
the binder. [0177] (45) The method of (44), in which the binder
comprises at least one natural or synthetic organic polymer. [0178]
(46) The method of (44), in which the binder comprises
ethylcellulose. [0179] (47) The method of (44), in which the
solvent is a solvent volatile in a temperature range from about
80.degree. C. to about 300.degree. C. [0180] (48) The method of
(23), in which the glass particles constitute from about 0.1%, by
mass, to about 95%, by mass, of the paste composition. [0181] (49)
The method of (23), in which the glass particles constitute from
about 1%, by mass, to about 90%, by mass, of the paste composition.
[0182] (50) The method of (23), further containing particles of a
metal capable of promoting crystallization of the glass. [0183]
(51) The method of (50), in which the metal is selected from the
group consisting of silver, silicon, copper, iron, zinc, and
manganese. [0184] (52) The method of (50), in which the metal is
selected from the group consisting of silver, silicon, and
zinc.
EXAMPLES
[0185] Hereinafter, Examples in accordance with the present
invention will be described in more detail, but the present
invention is not limited thereto. Unless specifically indicated,
the chemicals all used reagents. Unless specifically indicated, "%"
refers to "% by mass".
Example 1
[0186] 20 g of B.sub.2O.sub.3--SiO.sub.2--R.sub.2O (R: Na, K, Li)
based glass powder whose particle shape is substantially spherical,
average particle diameter is 4.9 .mu.m and softening point is
561.degree. C. (trade name: TMX-404, manufactured by Tokan Material
Technology Co., Ltd.), 0.5 g of ethylcellulose and 10 g of
2-(2-butoxyethoxy) ethyl acetate were mixed with an automatic
mortar kneading machine and made into a paste to prepare a
composition for forming a p-type diffusion layer.
[0187] The particle shape of the glass powder was judged by
observation with a scanning electron microscope (trade name:
TM-1000, manufactured by Hitachi High-Technologies Corporation).
The average diameter of the glass powder was calculated with a
laser diffraction particle size analyzer (measurement wave length:
632 nm, trade name: LS 13 320,manufactured by Beckman Coulter,
Inc.). The softening point of the glass powder was measured
according to a differential thermal analysis (DTA) curve with a
Thermo Gravimetry Differential Thermal Analyzer (trade name:
DTG-60H, manufactured by SHIMADZU CORPORATION).
[0188] Next, the prepared paste was applied to a p-type silicon
substrate surface having an n-type layer formed thereon by screen
printing, and dried on a hot plate at 150.degree. C. for 5 minutes.
Subsequently, a thermal diffusion treatment was carried out in an
electric furnace at 1000.degree. C. for 30 minutes. Then, in order
to remove the glass layer, the substrate was dipped in hydrofluoric
acid for 5 minutes, followed by washing with running water.
[0189] The surface at the side where the composition for forming a
p-type diffusion layer was applied exhibited sheet resistance of
190.OMEGA./.quadrature. and the formation of a p-type diffusion
layer through diffusion of B (boron).
[0190] The sheet resistance was measured by four probe method with
a low resistance meter (trade name: Loresta-EP MCP-T360,
manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
Example 2
[0191] A p-type diffusion layer was formed in the same manner as in
Example 1, except that the glass powder was changed to
B.sub.2O.sub.3--SiO.sub.2--RO (R: Mg, Ca, Sr, Ba) based glass
powder whose particle shape is spherical, average particle diameter
is 3.2 .mu.m and softening point is 815.degree. C. (trade name:
TMX-603, manufactured by Tokan Material Technology Co., Ltd.). The
surface at the side where the composition for forming a p-type
diffusion layer was applied exhibited sheet resistance of
35.OMEGA./.quadrature. and the formation of a p-type diffusion
layer through diffusion of B (boron).
Example 3
[0192] A p-type diffusion layer was formed in the same manner as in
Example 1, except that the glass powder was changed to
B.sub.2O.sub.3--SiO.sub.2--RO (R: Mg, Ca, Sr, Ba) based glass
powder whose particle shape is spherical, average particle diameter
is 5.1 .mu.m and softening point is 808.degree. C. (trade name:
TMX-403, manufactured by Tokan Material Technology Co., Ltd.). The
surface at the side where the composition for forming a p-type
diffusion layer was applied exhibited sheet resistance of
45.OMEGA./.quadrature. and the formation of a p-type diffusion
layer through diffusion of B (boron).
Example 4
[0193] 20 g of P.sub.2O.sub.5--ZnO.sub.2--R.sub.2O (R: Na, K, Li)
based glass powder whose particle shape is spherical, average
particle diameter is 3.1 .mu.m and softening point is 416.degree.
C. (trade name: TMX-203, manufactured by Tokan Material Technology
Co., Ltd.), 0.3 g of ethylcellulose and 7 g of 2-(2-butoxyethoxy)
ethyl acetate were mixed with an automatic mortar kneading machine
and made into a paste to prepare a composition for forming an
n-type diffusion layer. The prepared paste was applied to a p-type
silicon substrate surface.
[0194] Subsequently, 20 g of B.sub.2O.sub.3--SiO.sub.2--RO (R: Mg,
Ca, Sr, Ba) based glass powder (trade name: TMX-603, manufactured
by Tokan Material Technology Co., Ltd.), 0.5 g of ethylcellulose
and 10 g of 2-(2-butoxyethoxy) ethyl acetate were mixed and made
into a paste to prepare a composition for forming a p-type
diffusion layer. The prepared paste was applied by screen printing
to a p-type silicon substrate surface where a composition for
forming an n-type diffusion layer was not printed, and dried on a
hot plate at 150.degree. C. for 5 minutes.
[0195] Next, a thermal diffusion treatment was carried out in an
electric furnace at 1000.degree. C. for 10 minutes. Then, in order
to remove the glass layer, the substrate was dipped in hydrofluoric
acid for 5 minutes, followed by washing with running water.
[0196] The surface at the side where the composition for forming an
n-type diffusion layer was applied exhibited sheet resistance of
35.OMEGA./.quadrature. and the formation of an n-type diffusion
layer through diffusion of P (phosphorus). The surface at the side
where the composition for forming a p-type diffusion layer was
applied exhibited sheet resistance of 47.OMEGA./.quadrature. and
the formation of a p-type diffusion layer through diffusion of B
(boron).
[0197] The foregoing description of the embodiments of the present
invention has been provided for the purposes of illustration and
description. It is not intended to be exhaustive or to limit the
present invention to the precise forms disclosed. Obviously, many
modifications and variations will be apparent to practitioners
skilled in the art. The embodiments were chosen and described in
order to best explain the principles of the present invention and
its practical applications, thereby enabling others skilled in the
art to understand the present invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the present
invention be defined by the following claims and their
equivalents.
[0198] All publications, patent applications, and technical
standards mentioned in this specification are herein incorporated
by reference to the same extent as if each individual publication,
patent application, or technical standard was specifically and
individually indicated to be incorporated by reference.
* * * * *