U.S. patent application number 14/685764 was filed with the patent office on 2015-08-06 for semiconductor device, in particular a solar cell.
The applicant listed for this patent is Q-CELLS SE. Invention is credited to Gijs DINGEMANS, Peter ENGELHART, Wilhelmus Mathijs Marie KESSELS, Robert SEGUIN.
Application Number | 20150221788 14/685764 |
Document ID | / |
Family ID | 44645275 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150221788 |
Kind Code |
A1 |
ENGELHART; Peter ; et
al. |
August 6, 2015 |
Semiconductor Device, In Particular A Solar Cell
Abstract
A semiconductor device, in particular a solar cell, comprises a
semiconductor substrate having a semiconductor substrate surface
and a passivation composed of at least one passivation layer which
surface-passivates the semiconductor substrate surface, wherein the
passivation layer comprises a compound composed of aluminium oxide,
aluminium nitride or aluminium oxynitride and at least one further
element.
Inventors: |
ENGELHART; Peter; (Hameln,
DE) ; SEGUIN; Robert; (Berlin, DE) ; KESSELS;
Wilhelmus Mathijs Marie; (Tilburg, NL) ; DINGEMANS;
Gijs; (Tilburg, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Q-CELLS SE |
Bitterfeld-Wolfen |
|
DE |
|
|
Family ID: |
44645275 |
Appl. No.: |
14/685764 |
Filed: |
April 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13118673 |
May 31, 2011 |
9029690 |
|
|
14685764 |
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Current U.S.
Class: |
136/256 |
Current CPC
Class: |
Y02E 10/52 20130101;
H01L 31/02167 20130101; H01L 31/02168 20130101; H01L 31/055
20130101 |
International
Class: |
H01L 31/0216 20060101
H01L031/0216 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2010 |
DE |
10 2010 017155.7 |
Claims
1. A solar cell, comprising a semiconductor substrate having a
semiconductor substrate surface and a passivation composed of at
least one passivation layer which surface passivates the
semiconductor substrate surface, wherein: the passivation layer
consists essentially of a compound containing a compound according
to a formula of Al.sub.xM.sub.mO.sub.y or Al.sub.xM.sub.m, where M
is nitrogen, m being greater than 0, with M present in the
passivation layer in a stoichiometrically significant amount.
2. The solar cell according to claim 1, wherein the passivation
layer is arranged directly on the semiconductor substrate
surface.
3. The solar cell according to claim 1, wherein the passivation
further comprises one or more further passivation layers arranged
between the passivation layer and the semiconductor substrate
surface.
4. The solar cell according to claim 3, wherein at least one
further passivation layer is arranged on a side of the passivation
layer which is remote from the semiconductor substrate surface.
5. The solar cell according to claim 3, wherein the passivation is
comprised of an alternating layer sequence composed of the
passivation layer and a further passivation layer.
6. The solar cell according to claim 1, wherein the passivation
layer is deposited by atomic layer deposition.
7. The solar cell according to claim 1, wherein the passivation
layer is an antireflection layer.
8. The solar cell according to claim 1 wherein the passivation
layer is a reflection layer.
9. The solar cell of claim 1 further comprising an antireflection
layer, the passivation layer being a part thereof.
10. The solar cell of claim 1 further comprising a reflection
layer, the passivation layer being a part thereof.
11. The solar cell of claim 1 wherein a density of M in the
passivation layer is at least 1 atomic percent
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/118,673, filed 31 May 2011 which claimed
priority in German Patent application no. 10 2010 017155.7, filed
31 May 2010, the contents of these documents incorporated herein by
reference.
TECHNICAL FIELD
[0002] The invention relates to a semiconductor device, in
particular a solar cell.
BACKGROUND
[0003] One of the limiting factors for the efficiency of
semiconductor components and devices is the recombination of charge
carriers at semiconductor surfaces which have surface states that
promote the recombination activity. This problem is of importance
particularly in solar cells. This is because in this case the
recombined charge carriers are no longer available for generating
current. In order to reduce recombinations, the semiconductor
surface has to be passivated by decreasing the recombination
activity of charge carriers by means of surface states.
[0004] For the passivation of semiconductor surfaces, at the
present time aluminium oxide is used diversely (Al.sub.2O.sub.3 or
AlO.sub.x, which very generally is taken to mean any suitable
stoichiometric composition of aluminium and oxygen). Aluminium
oxide has a high negative surface charge density and, if applied to
the semiconductor surface indirectly by way of an intermediate
layer or directly, can displace charge carriers from the
semiconductor surface into the semiconductor volume. On account of
this field-effect-passivating effect, the semiconductor surface is
effectively passivated.
[0005] Such passivation layers composed of aluminium oxide have the
disadvantage, however, that they are not resistant to specific
production processes, particularly in the production of solar
cells, for example to wet-chemical cleaning or etching processes.
Therefore, they have to be protected by means of additional
covering layers. This leads to higher production costs and longer
production times.
[0006] Furthermore, particularly in the case of solar cells, not
only is it necessary to take account of the electrical properties
of the layer sequences, but it is also necessary for the optical
properties of the individual layers to be coordinated with one
another. However, if only aluminium oxide is used as material of
the passivation layer, then the design of the solar cell is fixed
to a specific refractive index (namely approximately 1.6).
SUMMARY OF THE INVENTION
[0007] Therefore, it is an object of the invention to provide a
semiconductor device, in particular a solar cell, which can be
produced with lower expenditure in respect of costs and time and
has an effective passivation that is simultaneously resistant to
production process steps.
[0008] The object is achieved according to the invention by means
of a semiconductor device, in particular solar cell, comprising a
semiconductor substrate having a semiconductor substrate surface
and a passivation composed of at least one passivation layer which
surface-passivates the semiconductor substrate surface, wherein the
passivation layer comprises a compound composed of aluminium oxide,
aluminium nitride or aluminium oxynitride and at least one further
element. Advantageous developments of the invention are discussed
further below.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The semiconductor device is preferably a solar cell, in
which an improved surface passivation of the semiconductor
substrate surface leads to a more efficient conversion of incident
light into electric current. However, a good surface passivation
can also be of importance in other areas of semiconductor
technology. The surface passivation described here can be employed
in the case of solar cells on the front side, that is to say on the
light incidence side of the solar cell, on the rear side, that is
to say on the light-remote side of the solar cell, or on both
sides. The semiconductor substrate is advantageously formed from
silicon. The semiconductor substrate can comprise a semiconductor
wafer.
[0010] The invention is based on the insight that, by means of the
addition of additional elements to an aluminium oxide compound of a
passivation layer, the chemical, electrical and/or optical
properties thereof can be optimized. This holds true both with
regard to the surface passivation and with regard to further
functional tasks which can be performed by the passivation layer on
the semiconductor device during and/or after its production.
[0011] For this purpose, a compound containing aluminium oxide,
aluminium nitride or aluminium oxynitride and at least one further
element which is not aluminium is used as material for the
passivation layer. The chemical formula for such a material can
generally be noted as Al.sub.xM.sub.mO.sub.y,
Al.sub.xM.sub.mN.sub.z or Al.sub.xM.sub.mO.sub.yN.sub.z, a desired
stoichiometric ratio being obtained by a suitable choice of x, y, z
and, if appropriate, m. In this case, M denotes the further
element. In the last case, Al.sub.xM.sub.mO.sub.yN.sub.z, if M
denotes a further metal element, the refractive index of the
material can be set for example by a suitable choice of the
stoichiometric ratio, to be precise from approximately 1.6 for z=0
up to approximately 2.0 for y=0.
[0012] By means of the addition of the further element, therefore,
the refractive index of the passivation layer can be altered in
order to be able to additionally use the passivation on the
semiconductor device for optical functions, in particular by means
of targeted influencing of its reflection and/or absorption
behaviour. The refractive index values mentioned in the present
case relate to measurements in the visible light spectrum.
[0013] It should be pointed out that the further element can be a
compound partner with respect to aluminium oxide, aluminium nitride
or aluminium oxynitride only when the further element is contained
stoichiometrically significantly in the passivation layer. In other
words, natural contaminations with the further element which
inevitably occur during the production process are not involved in
this case. Expediently, the density of the further element in the
material of the passivation layer is at least 1 atomic percent (at
%). Preferably, the further element in the material of the
passivation layer has a density of at least approximately 2 at %, 5
at %, 8 at %, 10 at %, 15 at % or 20 at %.
[0014] One preferred embodiment provides for the compound of the
passivation layer to comprise nitrogen, carbon, phosphorus, boron
and/or fluorine as a further element. A higher stability, in
particular chemical stability, can possibly be expected when
nitrogen is added or aluminium oxynitride (Al.sub.xO.sub.yN.sub.z)
is used for the production of the passivation layer. This effect is
already known when nitrogen is added to silicon oxide layers.
[0015] While the refractive index of the passivation layer is
increased by the addition of nitrogen, it is reduced by means of
the addition of fluorine. Aluminium fluoride has, for example, a
refractive index of approximately 1.4. Moreover, the chemical
resistance of the passivation layer can be increased by means of
doping by boron or phosphorus. Furthermore, a passivation layer
doped in this way can serve as a source for selectively doping an
underlying semiconductor layer, for example by means of laser
doping.
[0016] Further properties of the passivation layer can be
influenced by means of the incorporation of carbon into the
aluminium oxide. For example, the carbon concentration can be
manipulated in a targeted manner by means of the setting of the
semiconductor substrate temperature during a deposition of the
passivation layer. A lower temperature leads to a higher carbon
concentration in the passivation layer. The carbon concentration in
the passivation layer can alternatively or cumulatively be
influenced by means of the use of a carbon dioxide plasma.
[0017] One advantageous development provides for the compound of
the passivation layer to comprise a metal as a further element. In
particular, one expedient configuration provides for the compound
of the passivation layer to comprise a rare earth metal as a
further element.
[0018] By way of example, the effect of up-conversion can be used
by means of the admixture of a suitable amount of optically active
elements such as erbium ions (Er3+), for example. In this case,
from two long-wave photons which cannot be absorbed by the solar
cell, one short-wave photon is generated, which is then available
for obtaining current by absorption in the semiconductor.
Generally, by means of the admixture of erbium, ytterbium or
terbium in the form of atoms or ions, the spectral conversion
(up-conversion, down-conversion or shift) can be improved and, at
the same time, a high surface passivation of the semiconductor
substrate surface can be guaranteed.
[0019] Moreover, there are indications that the crystallization
temperature is increased by the incorporation of a small amount of
erbium into aluminium oxide. It is assumed that this effect is also
manifested for other elements. Generally, an increased thermal
stability can be derived therefrom on account of the
crystallization. This is of importance particularly in the
metallization of solar cells, if the solar cell is in this case
subjected to a thermal treatment, also called firing step.
[0020] It is preferably provided that the passivation layer is
arranged directly on the semiconductor substrate surface. In other
words, in this embodiment, there is no further layer situated
between passivation layer and semiconductor substrate surface. In
all the embodiments described here, the semiconductor substrate
surface can have differently doped regions, for example in order to
form base and emitter regions in the semiconductor substrate.
[0021] One expedient embodiment provides for the passivation to
comprise one or more further passivation layers arranged between
the passivation layer and the semiconductor substrate surface. By
way of example, a chemically passivating further passivation layer
can be applied directly to the semiconductor substrate surface.
This further passivation layer can be produced by means of
oxidation of the semiconductor substrate surface or advantageously
by means of a deposition process.
[0022] One advantageous configuration provides for the passivation
to comprise at least one further passivation layer arranged on a
side of the passivation layer which is remote from the
semiconductor substrate surface.
[0023] One preferred development provides for the passivation to
comprise an alternating layer sequence composed of the passivation
layer and a further passivation layer. In this case, the layer
sequence preferably comprises between 2 and 1000 passivation
layers, preferably at least 10 or at least 100 passivation layers.
Examples thereof form a layer sequence composed of titanium oxide
and aluminium oxide
(TiO.sub.2/AlO.sub.x/TiO.sub.2/AlO.sub.x/TiO.sub.2/AlO.sub.x . . .
) or a layer sequence composed of silicon oxide and aluminium oxide
(SiO.sub.2/AlO.sub.x/SiO.sub.2/AlO.sub.x/SiO.sub.2/AlO.sub.x . . .
). Each of the passivation layers from which the passivation is
formed is preferably a monolayer composed of the respective
material, a larger number of monolayers per passivation layer also
being possible, for example 5, 10 or more monolayers.
[0024] Since the individual partial layers/monolayers can have
different visible, optical and/or electrical properties from the
bulk material, such a multilayer stack does not behave like a layer
stack composed of two bulk materials. Furthermore, the optical
property of the multilayer system changes with very thin individual
layers. Thus, it is known, for example, that with alternating
layers composed of aluminium oxide and titanium oxide it is
possible to produce a so-called nano-laminate, in which, by means
of the layer thickness ratio between the two partial layers, the
total or global refractive index of the laminate can be set in a
continuously variable manner between 1.6 (refractive index of
aluminium oxide) and 2.4 (refractive index of titanium
dioxide).
[0025] In order to produce the passivation layers described here by
means of deposition processes, the different elements can be added
to the starting substances during deposition. Both chemical and
physical vapour deposition methods are suitable for the deposition,
which methods can preferably proceed in a plasma-enhanced fashion.
Wet-chemical deposition methods may also be used.
[0026] It is advantageously provided that the passivation layer is
a layer deposited by atomic layer deposition. To put it another
way, the passivation layer is applied, during production, by means
of atomic layer deposition (ALD), which, if appropriate, is
plasma-enhanced. In this case, the incorporation of further
elements can be performed in a targeted manner by said elements
being directed cyclically to the starting substances or plasma
gases in the deposition reactor. The cyclic deposition additionally
allows a gradual change in layer properties such as refractive
index, for example, perpendicularly to the layer surface. This is
advantageous, for example, for an optical adaptation on the light
incidence side of a solar cell. Moreover, by means of a gradual
alteration of process parameters, the process speed can be
optimized since the density of the passivation layer can change in
this case, which influences the deposition rate.
[0027] One preferred configuration provides for the passivation
layer to be designed as an antireflection layer, as a reflection
layer or as part of such a layer. The passivation layer can also
perform other functions, in particular including functions during
the production of the semiconductor device. It can act for example
as an etching, texture and/or diffusion barrier.
[0028] The result of a process of depositing a passivation layer
composed of aluminium oxynitride (Al.sub.xO.sub.yN.sub.z) is
described below as an exemplary embodiment. A plasma-enhanced
atomic layer deposition method was used, with a plasma power of
approximately 150 W and a chamber pressure of approximately 170
mtorr, wherein the substrate was kept at a temperature of
200.degree. C. Trimethylaluminium (TMA) with a dose time of 20 ms
was used as aluminium precursor. Argon was introduced into the
reaction chamber with a gas volumetric flow rate of 20 standard
cubic centimetres per minute (sccm). The deposition time was 3.5
seconds. Of these parameters, three deposition processes each with
different gas concentrations for nitrogen (N.sub.2) and oxygen
(O.sub.2) were carried out, as a result of which the layers thus
formed have different refractive indices and growth rates.
[0029] At gas volumetric flow rates of 10 sccm for N.sub.2 and 40
sccm for O.sub.2, this gave rise to an aluminium oxynitride layer
at a growth rate of approximately GPC=0.36 nm (GPC: growth per
cycle), with a refractive index of approximately n=1.57.
[0030] At gas volumetric flow rates of 25 sccm for N.sub.2 and for
25 sccm for O.sub.2, this gave rise to an aluminium oxynitride
layer at a growth rate of approximately GPC=0.33 nm with a
refractive index of approximately n=1.59.
[0031] At gas volumetric flow rates of 40 sccm for N.sub.2 and for
10 sccm for O.sub.2, this gave rise to an aluminium oxynitride
layer at a growth rate of approximately GPC=0.29 nm with a
refractive index of approximately n=1.63.
[0032] Layers formed without the addition of oxygen only had a
growth rate of approximately GPC=0.06 nm.
* * * * *