U.S. patent application number 12/361020 was filed with the patent office on 2009-05-21 for method for producing semi-conducting devices and devices obtained with this method.
This patent application is currently assigned to OERLIKON TRADING AG, TRUEBBACH. Invention is credited to Juliette Ballutaud, Cedric Bucher, Christoph Hollenstein, Alan Howling, Ulrich Kroll, Markus Poppeller, Jacques Schmitt.
Application Number | 20090127673 12/361020 |
Document ID | / |
Family ID | 32180507 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090127673 |
Kind Code |
A1 |
Kroll; Ulrich ; et
al. |
May 21, 2009 |
METHOD FOR PRODUCING SEMI-CONDUCTING DEVICES AND DEVICES OBTAINED
WITH THIS METHOD
Abstract
A semi-conducting device has at least one layer doped with a
doping agent and a layer of another type deposited on the doped
layer in a single reaction chamber. An operation for avoiding the
contamination of the other layer by the doping agent separates the
steps of depositing each of the layers.
Inventors: |
Kroll; Ulrich; (Corcelles,
CH) ; Bucher; Cedric; (Montet-Cudrefin, CH) ;
Schmitt; Jacques; (Va Ville Du Bois, FR) ; Poppeller;
Markus; (Feldkirch, AT) ; Hollenstein; Christoph;
(Lutry, CH) ; Ballutaud; Juliette; (Lausanne,
CH) ; Howling; Alan; (Cugy, CH) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET, SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
OERLIKON TRADING AG,
TRUEBBACH
Truebbach
CH
|
Family ID: |
32180507 |
Appl. No.: |
12/361020 |
Filed: |
January 28, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11947245 |
Nov 29, 2007 |
7504279 |
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12361020 |
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|
10691102 |
Oct 22, 2003 |
7344909 |
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11947245 |
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60421171 |
Oct 25, 2002 |
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60439764 |
Jan 13, 2003 |
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60476670 |
Jun 6, 2003 |
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Current U.S.
Class: |
257/656 ;
257/E29.336 |
Current CPC
Class: |
H01L 21/02664 20130101;
Y02P 70/521 20151101; H01L 31/1804 20130101; Y02E 10/548 20130101;
Y02P 70/50 20151101; H01L 21/02491 20130101; H01L 31/202 20130101;
H01L 21/0242 20130101; H01L 21/02529 20130101; H01L 21/02579
20130101; Y02E 10/547 20130101; H01L 31/075 20130101; H01L 21/2205
20130101; H01L 31/0288 20130101; H01L 21/0262 20130101 |
Class at
Publication: |
257/656 ;
257/E29.336 |
International
Class: |
H01L 29/868 20060101
H01L029/868 |
Claims
1. A semi-conducting device comprising at least a layer doped with
a doping agent and a layer of another type deposited on said doped
layer, wherein the interface between said layers contains traces of
oxygen as a result of a treatment for avoiding the contamination of
said another layer by the doping agent.
2. The semi-conducting device of claim 1, wherein the content of
oxygen is higher than 10.sup.19 atomscm.sup.-3.
3. A semi-conducting device comprising at least a layer doped with
a doping agent and a layer of another type deposited on said doped
layer, wherein the interface between said layers contains traces of
nitrogen as a result of a treatment for avoiding the contamination
of said another layer by the doping agent.
4. The semi-conducting device of claim 3, wherein the content of
nitrogen is higher than 10.sup.19 atomscm.sup.-3.
5. The semi-conducting device of claim 1, wherein said treatment
comprises dosing a reaction chamber where said doped layer and
other layer are deposited, intermediate deposition of the
respective layers, with a vapour or gas comprising water, methanol,
isopropanol or another alcohol without plasma.
6. The semi-conducting device of claim 3, wherein said treatment
comprises dosing a reaction chamber where said doped layer and
other layer are deposited, intermediate deposition of the
respective layers, with a vapour or gas comprising ammonia,
hydrazine or volatile organic amines without plasma.
7. The semi-conducting device of claim 5, wherein said dosing is
performed at around 0.05 to 100 mbar and between 100 and
350.degree. C. for less than 10 minutes.
8. The semi-conducting device of claim 6, wherein said dosing is
performed at around 0.05 to 100 mbar and between 100 and
350.degree. C. for less than 10 minutes.
9. The semi-conducting device of claim 1, wherein the doped layer
is a p-doped layer.
10. The semi-conducting device of claim 1, wherein the doped layer
is a n-doped layer.
11. The semi-conducting device of claim 3, wherein the doped layer
is a p-doped layer.
12. The semi-conducting device of claim 3, wherein the doped layer
is a n-doped layer.
13. The semi-conducting device of claim 1, further comprising a
buffer layer intermediate said doped layer and said other
layer.
14. The semi-conducting device of claim 3, further comprising a
buffer layer intermediate said doped layer and said other
layer.
15. The semi-conducting device of claim 5, wherein said dosing is
followed by the deposition of a buffer layer on said doped
layer.
16. The semi-conducting device of claim 6, wherein said dosing is
followed by the deposition of a buffer layer on said doped
layer.
17. The semi-conducting device of claim 5, wherein said dosing is
followed by said reaction chamber pumping at high vacuum between
100 and 350.degree. C. for less than 5 minutes.
18. The semi-conducting device of claim 5, wherein said dosing is
followed by said reaction chamber pumping at high vacuum between
100 and 350.degree. C. for less than 5 minutes.
19. The semi-conducting device of claim 1, said doped layer being a
plasma-deposited doped layer.
20. The semi-conducting device of claim 3, said doped layer being a
plasma-deposited doped layer.
21. The semi-conducting device of claim 6, wherein said doping
agent comprises trimethylboron.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates in general to the domain of
semiconductor films based on silicon technology. It concerns, more
particularly, a method for producing silicon junctions, doped or
not, which can be used, for example, in solar cells. It also
concerns any other semi-conducting devices obtained by such a
method.
[0002] Amorphous or microcrystalline silicon solar cells are made
of multilayer systems where semiconducting material with certain
electronical and physical properties is deposited, layer by layer,
on a substrate.
[0003] The n-layers and p-layers are doped with other elements to
achieve desired properties, such as electrical conductivity. More
precisely: [0004] p-doped layers have a surplus of positive charge
carriers, [0005] n-doped layers have a surplus of negative charge
carriers, and [0006] i layers are intrinsic.
[0007] Generally, boron is used as the doping agent of the p-layers
and phosphor as the doping agent of the n-layers.
[0008] Silicon solar cells manufacturers use either single-chamber
or multi-chamber reactors to produce commercial photovoltaic (PV)
modules. Plasma deposition of silicon solar cells in a
single-chamber reactor leads to considerable simplifications and
reduced costs as compared to multi-chamber processes.
[0009] However, in a single chamber deposition process of a p-i-n
solar cell, for example, the subsequent deposition of the i-layer
on the p-layer may cause boron recycling from the reactor walls and
from the deposited p-layer. As a result, boron will contaminate the
i-layer at the critical p-i interface and thereby weaken the
strength of the electrical field in the i-layer close to p-i
interface. This provokes a less efficient carrier separation just
in this zone and leads to a reduced collection efficiency in the
solar cell and thereby to a deterioration of the cell
performance.
[0010] For that reason, most silicon p-i-n solar cells modules are,
at present, deposited using multi-chamber reactors. Boron
cross-contamination by recycling is avoided by simply depositing
the p-layer and the i-layer in different chambers. However, the
higher investment in multi-chamber systems equipment becomes a
drawback particularly in the field of solar cells where costs are a
major issue.
[0011] Similar problems exist with n-i-p solar cells in which
phosphor used to dope the n-layer contaminates the i-layer at the
critical n-i interface.
[0012] Thus, an interesting solution would be to combine a low
cost-single chamber reactor with a process scheme able to suppress
the boron or phosphor cross-contamination.
[0013] Different treatments have been tested with encouraging
results, but they still leave open the question of the
light-induced degradation of these solar cells, they use expensive
gases, they have long treatment durations or are incompatible with
large area deposition in industrial reactors.
SUMMARY OF THE INVENTION
[0014] The object of the present invention is to provide a method
for producing semiconductors with a particular application in solar
cells, avoiding cross-contamination by doping agents and exempt of
disadvantages above mentioned.
[0015] More precisely, in order to achieve these goals, the
invention concerns a method for producing a semi-conducting device
comprising at least a layer doped with a doping agent and a layer
of another type deposited on said doped layer in a single reaction
chamber. The deposition steps of said layers are separated by an
operation for avoiding the contamination by the doping agent of
said another layer.
[0016] Advantageously, the operation comprises a dosing of the
reaction chamber with a compound able to react with the doping
agent.
[0017] According to a first embodiment, the contamination avoiding
operation comprises a dosing of the reaction chamber with a vapour
or gas comprising water, methanol, isopropanol or another
alcohol.
[0018] According to a second embodiment, the contamination avoiding
operation comprises a dosing of the react-on chamber with a vapour
or gas comprising ammonia, hydrazine or volatile organic
amines.
[0019] The invention also concerns a semi-conducting device
comprising at least a layer doped with a doping agent and a layer
of another type deposited on said doped layer. The interface
between said layers contains traces of oxygen or of nitrogen as a
result of a treatment for avoiding the contamination of said
another layer by the doping agent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Other characteristics of the invention will be shown in the
description below, made with regard to the attached drawing,
where:
[0021] FIG. 1 shows the reactor used for the implementation of the
method, and
[0022] FIG. 2 illustrates the effect of the doping agent
contamination avoiding operation.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The following description is particularly related, as an
example, to the production of a boron doped p-i-n junction, i.e. a
semiconductor device comprising respective p, 1 and n layers
successively deposited on a suitable substrate providing the base
of a solar cell.
[0024] The three layers are deposited in a manner well known by a
person skilled in the art but, according to the invention, the
method comprises an important supplementary step.
[0025] FIG. 1 shows the reactor used to produce such a
semi-conducting device. Basically, it comprises: [0026] a vacuum
chamber 10 connected to a vacuum circuit 11, [0027] a hot wall
inner chamber 12 disposed inside the vacuum chamber 10, [0028] a
radio-frequency-powered electrode 13 placed inside the inner
chamber 12, and [0029] a showerhead 14 incorporated within the
electrode 13 and connected to different gas feeding lines to
introduce appropriate reacting products.
[0030] A substrate 15, for example a glass/TCO substrate of the
type Asahi U, based on SnO.sub.2:F (glass coated with fluorine
doped SnO2), is being arranged in the inner chamber 12.
[0031] The above described installation is preferably adapted from
the industrial KAI.TM.-S reactor of Unaxis Displays in order to
constitute a Plasma Enhanced Chemical Vapour Deposition (PECVD)
system. The typical dimensions of the inner chamber 12 are 50 cm
width.times.60 cm length.times.2.5 cm height.
[0032] For the initial p-layer deposition on substrate 15, the
reacting gas introduced in the reactor through the showerhead 14
are, typically: [0033] to form the p-layer: silane, methane and
hydrogen, and [0034] to dope the layer with boron: trimethylboron
(TMB).
[0035] TMB is particularly well suited, instead of diborane
(commonly used) because it has a superior thermal stability in the
hot reactor and is reported to cause less contamination.
[0036] To perform the deposition of the p-layer, the plasma
excitation frequency used is e.g. 40.68 MHz, the temperature is
200.degree. C., while the pressure is kept at 0.3 mbar, and the
power RF is applied at a level of 60 W.
[0037] Many experiments have suggested that boron introduced in the
reactor is not simply present in a gaseous state which could be
easily pumped out, but might be physisorbed on the internal reactor
surfaces and desorb very slowly after a pumping period.
[0038] Therefore, according to a first embodiment of the invention,
after the deposition of the p-layer and before the deposition of
the i-layer, the internal surfaces of the reactor and the substrate
also are dosed with a vapour or a gas comprising water, methanol or
isopropanol or another alcohol.
[0039] More precisely, in this example, the dosing product is
stored in a separate bottle 21 connected, via a valve 22, to the
vacuum chamber 10, which is kept at low pressure condition. When
the valve 22 is opened, the dosing product starts boiling in the
bottle 21 because of the low pressure inside and vapour flushes
into the chamber 10. Of-course, the RF electrode 13 is off. The
operation is performed between 100 and 350.degree. C., typically at
200.degree. C. and during less than 10 minutes, typically 2 minutes
and at 0.05 to 100 mbar. The flow of water vapour has to be
sufficient. For example, 90 mbarsec is a good value. If methanol or
isopropanol is used, the flow is generally higher.
[0040] After the dosing operation, a short pumping period of less
than 5 minutes, typically around 3 minutes, under similar
conditions but without any dosing gas addition, is advantageously
respected before the deposition of the i-layer.
[0041] As a result of the above dosing operation, the boron which
was physisorbed on all the internal surfaces of the reactor and of
the substrate is transformed into stable chemical compounds unable
to desorb. A contamination of the layer which will be later
deposited on the p-layer is thus avoided.
[0042] After this treatment, the i-layer, then the n-layer are
deposited in the same reactor. The conditions described above for
the p-layer deposition are reused with appropriate reacting gases,
as known by a person skilled in the art.
[0043] As an example, the reacting gases used for the deposition of
the i-layer are a mix of 75% of silane and 25% of hydrogen, whereas
the reacting gases used for the deposition of the n-layer are
silane, hydrogen and phosphine.
[0044] The evaluation of the base level boron contamination of the
i-layers can be made by Secondary Ion Mass Spectroscopy (SIMS) in
order to trace the boron concentration depth profile across the p-i
interface.
[0045] To illustrate the efficiency of the above-described dosing
treatment, FIG. 2 shows, as an example, the boron SIMS profile
(depth X from surface in Angstroms versus boron concentration Y in
atomscm.sup.-3) of a p-i-p-i sandwich structure deposited on a c-Si
wafer. Both p-doped portions 17 and 18 are normally deposited.
[0046] A first i-layer 19 is deposited on the p-layer 17 without
performing any additional treatment. The base level contamination
of boron measured in the i-layer 19 is about 10.sup.18
atomscm.sup.-3.
[0047] A second i-layer 20 is deposited on the p-layer 18 portion
after the dosing treatment as described above. The base level
contamination of boron measured in the i-layer 20 is reduced to
about 10.sup.17 atomscm.sup.-3, which represents an improvement of
one order of magnitude.
[0048] The boron contamination in the i-layer of a solar p-i-n cell
treated according to the invention can also be indirectly detected
by performing voltage dependent quantum efficiencies measurements
as well as monitoring the global cell performance especially the
fill factor of the solar cell. The results are substantially the
same as those obtained with cells deposited in multi-chamber
reactors.
[0049] Furthermore, an oxygen peak can be observed with a SIMS
analysis at the treated p-i interface, meaning that the above
described treatment has been used. Typically, the amount of oxygen
in the peak is higher than 10.sup.19 atomscm.sup.3.
[0050] According to a second embodiment of the invention, after the
deposition of the p-layer and before the deposition of the i-layer,
the internal surfaces of the reactor are dosed with a vapour or gas
comprising ammonia, hydrazine or volatile organic amines. This
dosing operation is performed at low pressure conditions (0.05 to
100 mbar), between 100 and 350.degree. C., typically at around
200.degree. C. and during less than 10 minutes, typically around to
2 minutes. The flow of gas has to be sufficient. For example, 90
mbarsec is a good value for ammonia. After the dosing operation, a
short pumping period of less than 5 minutes is also respected
before the deposition of the i-layer.
[0051] A nitrogen peak can be observed with a SIMS analysis at the
treated n-i interface, meaning that such a treatment has been used.
Typically, the amount of nitrogen is higher than 10.sup.19
atomscm.sup.-3.
[0052] For both embodiments of the invention, it may be useful to
depose on the p-layer, after the above described treatments, a
hydrogen-diluted buffer layer. This layer is obtained by PECVD of a
mix of 10% silane and 90% hydrogen. The plasma excitation frequency
used is 40.68 MHz, the temperature is 200.degree. C., while the
pressure is kept at 0.5 mbar, and the power RF is applied at a
level of 60 W. Such a layer alone has usually already a beneficial
effect on the boron cross contamination in the i-layer.
[0053] The method of the invention, according to both described
embodiments, offers the advantage to eliminate the boron
contamination while working with a single reactor. There is neither
wasted pumping time nor loss of time due to transfer of the
substrate out of the reactor for a cleaning step nor loss of time
for reheating of the substrate which cooled down during the
transfer. Moreover, apart from simpler and faster processes the
single chamber approach bears the potential of considerably
simplified deposition systems as compared to multi-chamber systems.
It has to be noted that such methods allow to produce a complete
solar cell in only 30 minutes.
[0054] A person skilled in the art can easily adapt the above
described treatments to a n-i-p solar cell in order to avoid
phosphor cross-contamination after the deposition of n-doped
layer.
[0055] Needless to say that the invention can also be applied to a
any junction based on a p-doped or n-doped layer. The dosing can
also be performed by injecting the dosing compound directly in the
gas feeding line.
* * * * *