USO0H002207H
(19) United States (12) Statutory Invention Registration (10) Reg. No.: Bij ker
(43) Published: (57)
(54) ADDITIONAL POST-GLASS-REMOVAL PROCESSES FOR ENHANCED CELL EFFICIENCY IN THE PRODUCTION OF SOLAR CELLS
(76) Inventor:
US H2207 H Dec. 4, 2007
ABSTRACT
A method is provided for the production of solar cells from raW crystalline p-type silicon Wafer material. The surface
condition prior to SiNx deposition is improved by providing additional process steps following the phosphorous glass
Martin D. Bijker, BetuWehof 64, Helmond 5709 KR (NL)
removal and prior to the SiNx anti-re?ection coating depo sition. In one embodiment, the Wafer is submitted to a
(21) Appl. No.: 11/650,595
thermal anneal under oxygen atmosphere followed by a Wet-chemical oxide removal. The anneal reduces the surface
(22) Filed:
phosphorous concentration by diifusion, reduces lattice
(51)
Jan. 5, 2007
Int. Cl. H01L 21/336
defects in the emitter and oxidizes the silicon surface. In another embodiment, both a surface oxide is obtained and
(2006.01)
subsequently removed With Wet chemistry. This sequence alloWs for an integration of the phosphorous glass removal,
(52)
US. Cl. ..................................................... .. 438/287
the Wet-chemical oxidation, and the SiOx removal into a
(58)
Field of Classi?cation Search ..................... .. None
single machine.
See application ?le for complete search history. (56)
References Cited
2 Claims, 2 Drawing Sheets
U.S. PATENT DOCUMENTS 6,946,404 B2 *
9/2005
Bijker et a1. .............. .. 438/778
2/2004 Bijker et a1.
438/200
A statutory invention registration is not a patent. It has
2006/0231031 Al * 10/2006 Dings et a1.
. 118/723 R
the defensive attributes of a patent but does not have the enforceable attributes of a patent. No article or adver
2004/0029334 Al *
2006/0292891 A1 * 12/2006
Bijker et a1. .............. .. 438/778
tisement or the like may use the term patent, or any term
* cited by examiner
Primary ExamineriDaniel Pihulic (74) Attorney, Agent, or FirmiPillsbury Winthrop ShaW
suggestive of a patent, When referring to a statutory invention registration. For more speci?c information on the rights associated With a statutory invention registra
Pittman LLP
tion see 35 U.S.C. 157.
Wet-chemical saw-damage
Wet-chemical saw-damage
removal and surface texturization
removal and surface texturization
L
1 1 1 1
Deposition of phosphorous
Deposition of phosphorous
Precursor
Precursor
[
Wet-chemical SiOx removal
1
Deposition of SiNx anti-reflection coating
1
Screen printing
Screen printing
of metallization pastes
of metallimtion pastes
I Emitter diffusion
I phosphorous glass removal
I Emitter anneal and surface oxidation
I
I
1 1
1 1 1 1
L
l
[
I
I ablation
(a)
]
Wet-chemical phosphorous glass removal
I Wet chemical surface 1 oxidation Wet-chemical SiOx removal
I Deposition of SiNx anti-reflection coating
I
Firing of metallization pastes ] Cell edge isolation by laser
Emitter di?usion
Firing of metallization pastes ]
I
1
Cell edge isolation by laser ablation
(b)
U.S. Patent
Dec. 4, 2007
Sheet 1 of2
r
US H2207 H \
Wet-chemical saw-damage removal and surface texturization
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Deposition of phosphorous
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precursor
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Emitter diffusion
Wet-chemical
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Deposition of SiNx
anti-re?ection coating L
J
i Screen printing of metallization pastes
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[ Firing ofmetallization pastes ] r
Cell edge isolation by laser ablation
Figure l
(PRIOR ART)
U.S. Patent
r
Dec. 4, 2007
Sheet 2 of 2
Wet-chemical saw-damage
Wet-chemical saw-damage
removal and surface texturization
removal and surface texturization
L
Deposition of phosphorous
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Deposition of phosphorous ]
precursor
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Deposition of SiNx anti-re?ection coating J
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Deposition of SiNx anti-re?ection coating F
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US H2207 H
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of metallization pastes
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Cell edge isolation by laser k
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US H2207 H 1
2 (h) screen printing metalliZation pastes on the surface of
ADDITIONAL POST-GLASS-REMOVAL PROCESSES FOR ENHANCED CELL EFFICIENCY IN THE PRODUCTION OF SOLAR CELLS
the Wafer; (i) ?ring the metalliZation pastes formed on the surface of the Wafer; and
(j) laser ablating the Wafer, thereby isolating the emitters and collectors formed at the edges of the Wafer.
FIELD OF THE INVENTION
In a second embodiment of the invention, a process for
producing a solar cell from a silicon Wafer, comprising the
This invention relates to the process sequence in the
steps of: (a) removing any saW-damage on the Wafer by a Wet chemical etching process, thereby de?ning surface tex
production of solar cells from raW crystalline p-type silicon Wafer material. Process tests shoW that the cell e?iciencies obtained With
ture on the Wafer;
the current production lines can be improved signi?cantly by inserting one or more additional process steps.
(b) depositing a phosphorous containing precursor on the
BACKGROUND OF INVENTION
(c) placing the Wafer in a furnace, thereby initiating emitter di?fusion; (d) removing a phosphorous glass layer, formed on the
Wafer;
The process sequence of the existing production lines is shoWn in FIG. 1. The saW-damage and impurities present on
obtained. A phosphorous containing precursor is deposited
surface of the Wafer during the emitter diffusion step, by a Wet-chemical etching process; (e) oxidiZing the surface of the Wafer by a Wet-chemical
that serves as the phosphorous source during the emitter diffusion in a horizontal passage furnace. A phosphorous
(f) removing oxides from the Wafer by a Wet-chemical
the raW silicon Wafers are removed With a Wet etching.
Simultaneously With this process a de?ned surface texture is
20
process;
glass layer is formed during diffusion. This layer is removed With Wet etching prior to the deposition of a SiNx anti re?ection coating. Front- and back-side metalliZation is
25
realiZed by screen printing and ?ring of metalliZation pastes. Finally, laser ablation electrically isolates the emitter and collector at the edge of the Wafer. The cell ef?ciency obtained With the process sequence described in FIG. 1 is limited by the surface condition that is obtained after the phosphorous glass removal. The non ideal surface condition may originate from:
(a) an excessively large phosphorous concentration;
the Wafer; 30
and collectors formed at the edges of the Wafer. Other objects, features, and advantages of one or more embodiments of the present invention Will seem apparent 35
40
accompanying schematic draWings in Which corresponding reference symbols indicate corresponding parts, in Which FIG. 1 shoWs the process sequence of the existing pro 45
DETAILED DESCRIPTION 50
The surface condition prior to SiNx deposition is
comprising the steps of:
improved by providing additional process steps folloWing
(a) removing any saW-damage on the Wafer by a Wet
the phosphorous glass removal and prior to the SiNx anti re?ection coating deposition. FIG. 2 shoWs tWo sequence
chemical etching process, thereby de?ning surface tex ture on the Wafer; 55
Wafer; (c) placing the Wafer in a fumace, thereby initiating emitter diffusion; (d) removing a phosphorous glass layer, formed on the surface of the Wafer during the emitter diffusion step, by a Wet-chemical etching process; (e) thermally annealing the Wafer under an oxygen atmo
etching process; (g) depositing a SiNx anti-re?ection coating on the Wafer;
embodiments With additional process steps, in accordance With the invention. In the ?rst embodiment, as shoWn in FIG. 2(a), the Wafer is submitted to a thermal anneal under oxygen atmosphere folloWed by a Wet-chemical oxide removal. The anneal
60
reduces the surface phosphorous concentration by diffusion,
65
reduces lattice defects in the emitter and oxidiZes the silicon surface. In the second embodiment, as shoWn in FIG. 2(b), both a surface oxide is obtained and subsequently removed With Wet chemistry. This sequence alloWs for an integration of the
sphere; (f) removing oxides from the Wafer by a Wet-chemical
duction lines; and FIG. 2 shoWs tWo sequence embodiments With additional process steps, in accordance With the invention.
In a ?rst embodiment of the invention, a process is
(b) depositing a phosphorous containing precursor on the
Embodiments of the present invention Will noW be
disclosed, by Way of example only, With reference to the
SUMMARY OF THE INVENTION
provided for producing solar cells from a silicon Wafer,
from the folloWing detailed description, and accompanying draWings, and the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS
silicon). It is, therefore, an object of the present invention to provide an improved process sequence for the production of solar cells from raW crystalline p-type silicon Wafer material.
(i) ?ring the metalliZation pastes formed on the surface of the Wafer; and
(j) laser ablating the Wafer, thereby isolating the emitters
(b) residues left from the preceding processes that are not
removed by the standard Wet chemical glass removal; (c) segregation of impurities from the bulk to the surface during preceding processes that are not removed by the standard Wet chemical glass removal; and (d) nanometer-scale surface roughness (e. g. porous
etching process; (g) depositing a SiNx anti-re?ection coating on the Wafer; (h) screen printing metalliZation pastes on the surface of
phosphorous glass removal, the Wet-channel oxidation, and the SiOx removal into a single machine.
US H2207 H 4
3 A combination of the tWo sequences described above is also envisioned.
(j) laser ablating the Wafer, thereby isolating the emitters
While the speci?c embodiments of the present invention have been described above, it Will be appreciated that the invention may be practiced otherWise than described. The
2. A process for producing a solar cell from a silicon
and collectors formed at the edges of the Wafer.
Wafer, comprising the steps of: (a) removing any saW-damage on the Wafer by a Wet
description is not intended to limit the invention. What is claimed is: 1. A process for producing a solar cell from a silicon
chemical etching process, thereby de?ning surface tex ture on the Wafer;
(b) depositing a phosphorous containing precursor on the
Wafer, comprising the steps of:
Wafer;
(a) removing any saW-damage on the Wafer by a Wet
(c) placing the Wafer in a furnace, thereby initiating emitter di?fusion; (d) removing a phosphorous glass layer, formed on the
chemical etching process, thereby de?ning surface tex ture on the Water;
(b) depositing a phosphorous containing precursor on the
surface of the Wafer during the emitter diffusion step, by a Wet-chemical etching process; (e) oxidizing the surface of the Wafer by a Wet-chemical
Wafer; (c) placing the Wafer in a fumace, thereby initiating emitter diffusion; (d) removing a phosphorous glass layer, formed on the surface of the Wafer during the emitter diffusion step, by a Wet-chemical etching process; (e) thermally annealing the Wafer under an oxygen atmo
process;
(f) removing oxides from the Wafer by a Wet-chemical 20
sphere; (f) removing oxides from the Wafer by a Wet-chemical
etching process; (g) depositing a SiNx anti-re?ection coating on the Wafer; (h) screen printing metalliZation pastes on the surface of
the Wafer; (i) ?ring the metalliZation pastes formed on the surface of the Wafer; and
etching process; (g) depositing a SiNx anti-re?ection coating on the Wafer; (h) screen printing metalliZation pastes on the surface of
the Wafer; 25
(i) ?ring the metalliZation pastes formed on the surface of the Wafer; and
(j) laser ablating the Wafer, thereby isolating the emitters and collectors formed at the edges of the Wafer. *
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