U.S. patent application number 12/938733 was filed with the patent office on 2012-03-15 for plasma texturing reaction apparatus.
This patent application is currently assigned to Semi-Materials Co., Ltd.. Invention is credited to Gi-Hong Kim, Kun- Joo Park.
Application Number | 20120061022 12/938733 |
Document ID | / |
Family ID | 44999640 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120061022 |
Kind Code |
A1 |
Park; Kun- Joo ; et
al. |
March 15, 2012 |
PLASMA TEXTURING REACTION APPARATUS
Abstract
A plasma texturing reaction apparatus includes a chamber
including a dielectric window and a chamber body and receiving a
solar cell wafer to be textured, and a polygonal induction coil
provided at an outer upper portion of the dielectric window to
generate a magnetic field for generating plasma, a high frequency
low power supply unit that supplies a cathode of the chamber with
high frequency power corresponding to process conditions, and a
high frequency source power supply unit that supplies the polygonal
induction coil with high frequency power.
Inventors: |
Park; Kun- Joo; (Yongin-si,
KR) ; Kim; Gi-Hong; (Daegu-si, KR) |
Assignee: |
Semi-Materials Co., Ltd.
Seongnam-si
KR
|
Family ID: |
44999640 |
Appl. No.: |
12/938733 |
Filed: |
November 3, 2010 |
Current U.S.
Class: |
156/345.38 |
Current CPC
Class: |
H01J 37/32165 20130101;
H01J 37/3211 20130101 |
Class at
Publication: |
156/345.38 |
International
Class: |
C23F 1/08 20060101
C23F001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 13, 2010 |
KR |
10-2010-0089338 |
Claims
1. A plasma texturing reaction apparatus comprising: a chamber
including a dielectric window and a chamber body and receiving a
solar cell wafer to be textured; a polygonal induction coil
provided at an outer upper portion of the dielectric window to
generate a magnetic field for generating plasma; a high frequency
low power supply unit that supplies a cathode of the chamber with
high frequency power corresponding to process conditions; and a
high frequency source power supply unit that supplies the polygonal
induction coil with high frequency power.
2. The plasma texturing reaction apparatus according to claim 1,
wherein the polygon is at least a rectangle.
3. The plasma texturing reaction apparatus according to claim 1,
wherein the induction coil includes an induction coil having a
radial structure.
4. The plasma texturing reaction apparatus according to claim 1,
wherein the induction coil includes an induction coil having a
structure in which induction coils of a plurality of groups are
connected in parallel to one another.
5. The plasma texturing reaction apparatus according to claim 1,
wherein the induction coil includes an induction coil having a
batch type structure in which a plurality of induction coils are
arranged in a matrix format to generate a magnetic field with
respect to corresponding solar cell wafers.
6. The plasma texturing reaction apparatus according to claim 1,
wherein the induction coil includes an induction coil having a
batch type structure in which a plurality of induction coils are
arranged in a horizontal direction and a plurality of induction
coils are arranged in a vertical direction below or above the
plurality of induction coils arranged in the horizontal
direction.
7. The plasma texturing reaction apparatus according to claim 1,
wherein the induction coil includes an induction coil having a
structure in which at least one induction coil having a same shape
or different shapes is sequentially provided inside a single
induction coil.
8. The plasma texturing reaction apparatus according to claim 7,
wherein the single induction coil or the at least one induction
coil provided inside the single induction coil includes a polygonal
induction coil or a cylindrical induction coil.
9. The plasma texturing reaction apparatus according to claim 7 or
8, wherein the single induction coil or the at least one induction
coil provided inside the single induction coil independently
adjusts high frequency power radiated under a control of a high
frequency power distributor to allow ion density of a corresponding
area to be uniformly adjusted at a desired degree.
10. The plasma texturing reaction apparatus according to claim 1,
wherein the high frequency low power supply unit includes a
plurality of high frequency power generators and a plurality of
high frequency matching sections to adjust intensity and density of
ion energy and radical concentration.
11. The plasma texturing reaction apparatus according to claim 10,
wherein the plurality of high frequency power generators generate
high frequency power with a same frequency or different
frequencies.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plasma texturing
technology for a solar cell, and more particularly, to a plasma
texturing reaction apparatus which can improve the manufacturing
efficiency and quality of a solar cell by increasing the density
and uniformity of plasma ions and appropriately controlling ion
energy when conducting plasma texturing through dry etching on a
solar cell wafer to increase a light absorption amount of available
light to the inside of the solar cell by reducing a light
reflection amount on the surface of the solar cell.
[0003] 2. Description of the Related Art
[0004] A solar cell is a photoelectric element which converts light
energy into electrical energy. The solar cell is considered as a
clean energy source which can overcome problems such as
environmental pollution, high fuel cost, etc. caused by the use of
fossil fuel energy.
[0005] Recently, research has been actively conducted to improve
the photoelectric conversion efficiency of a solar cell. As a way
of improving the photoelectric conversion efficiency of a solar
cell, wet chemical texturing is conducted on a solar cell wafer so
as to decrease a light reflection amount on the surface of a solar
cell and increase a light absorption amount of available light to
the inside of the solar cell. By this fact, pyramid shapes with a
size of 4.about.10 .mu.m are formed on the surface of the solar
cell wafer.
[0006] In the case where surface texturing is conducted through wet
chemical etching as described above, both surfaces of the solar
cell wafer are etched. Generally, while it is required that the
solar cell wafer have a thickness of no less than 200 .mu.m, if the
surface texturing through wet chemical etching is conducted for an
ultrathin wafer (a solar cell wafer with a thickness of no greater
than 200 .mu.m), the breakage of the wafer may be caused as both
surfaces of the wafer are etched. As a consequence, it is difficult
to apply the surface texturing to an ultrathin wafer.
[0007] For this reason, plasma texturing has been spotlighted as an
alternative of the wet chemical texturing.
[0008] As well known in the art, plasma is called a fourth material
state and is a gas that has become partially ionized. Such plasma
has conductivity by particles which are electrically neutral but
positively and negatively charged, and is sensitive to an
electromagnetic field. In this regard, a technology of controlling
an electromagnetic field applied to the plasma may be applied to a
solar cell texturing process.
[0009] A plasma reaction apparatus may be classified into a
solenoid type plasma reaction apparatus, a planar type plasma
reaction apparatus and a dome type plasma reaction apparatus
according to an antenna and a dielectric window. According to the
solenoid type plasma reaction apparatus, since an inductance value
is relatively high and a sputtering problem due to a high voltage
occurs, efficiency may be reduced. According to the planar type
plasma reaction apparatus, since the distance between a plasma
source and a wafer is short, it may be difficult to independently
adjust ion energy reaching the surface of the wafer. According to
the dome type plasma reaction apparatus, since the area of a
substrate is increased, it may be difficult to ensure a uniform
etching rate.
[0010] Furthermore, a conventional planar inductively coupled
plasma system includes a cylindrical induction coil in
consideration that a semiconductor wafer has a circular shape.
However, since a solar cell wafer has a rectangular or square
shape, when using the conventional plasma reaction apparatus, it
may be difficult to ensure a uniform etching rate across the
wafer.
SUMMARY OF THE INVENTION
[0011] Accordingly, the present invention has been made in an
effort to solve the problems occurring in the related art, and an
object of the present invention is to increase the density and
uniformity of plasma ions and appropriately control ion energy by
using a square induction coil when conducting plasma texturing
through dry etching on a solar cell wafer.
[0012] In order to achieve the above object, according to one
aspect of the present invention, there is provided a plasma
texturing reaction apparatus including: a chamber including a
dielectric window and a chamber body and receiving a solar cell
wafer to be textured; a polygonal induction coil provided at an
outer upper portion of the dielectric window to generate a magnetic
field for generating plasma; a high frequency low power supply unit
that supplies a cathode of the chamber with high frequency power
corresponding to process conditions; and a high frequency source
power supply unit that supplies the polygonal induction coil with
high frequency power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above objects, and other features and advantages of the
present invention will become more apparent after a reading of the
following detailed description taken in conjunction with the
drawings, in which:
[0014] FIG. 1 is a block diagram illustrating a plasma texturing
reaction apparatus in accordance with an embodiment of the present
invention;
[0015] FIG. 2 is a schematic view illustrating an induction coil
manufactured in a polygonal shape in accordance with an embodiment
of the present invention;
[0016] FIG. 3 is a plan view illustrating an induction coil in
accordance with another embodiment of the present invention;
[0017] FIG. 4 is a schematic view illustrating an induction coil in
accordance with another embodiment of the present invention;
[0018] FIG. 5 to FIGS. 7A to 7D are plan views illustrating an
induction coil in accordance with another embodiment of the present
invention;
[0019] FIG. 8 is a diagram illustrating a high frequency low power
supply unit in accordance with another embodiment of the present
invention;
[0020] FIG. 9 is a graph illustrating an experimental result for
reflectivity of a solar cell wafer in the case of using a plasma
texturing reaction apparatus in accordance with an embodiment of
the present invention; and
[0021] FIG. 10 is a graph illustrating an experimental result for
uniformity of a solar cell wafer in the case of using a plasma
texturing reaction apparatus in accordance with an embodiment of
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] Reference will now be made in greater detail to a preferred
embodiment of the present invention, an example of which is
illustrated in the accompanying drawings.
[0023] FIG. 1 is a block diagram illustrating a plasma texturing
reaction apparatus in accordance with an embodiment of the present
invention. Referring to FIG. 1, the plasma texturing reaction
apparatus includes a chamber 103, a polygonal induction coil 104, a
high frequency low power supply unit 108, and a high frequency
source power supply unit 111. The chamber 103 includes a dielectric
window 103A and a chamber body 103B and receives a solar cell wafer
102 to be textured. The polygonal induction coil 104 is provided at
an outer upper portion of the dielectric window 103A to generate a
magnetic field for generating plasma. The high frequency low power
supply unit 108 supplies a cathode 101 of the chamber 103 with high
frequency power corresponding to process conditions. The high
frequency source power supply unit 111 supplies the induction coil
104 with high frequency power. Reference numeral 105 denotes a
process model.
[0024] The high frequency power generated by a high frequency power
generator 106 of the high frequency low power supply unit 108 is
supplied to the cathode 101, on which the solar cell wafer 102 to
be textured is loaded, through a high frequency matching section
107. Thus, the cathode 101 is maintained in a negative potential
state, and the intensity of ion energy and ion density are
determined.
[0025] Simultaneously to this, the high frequency power generated
by a high frequency power generator 109 of the high frequency
source power supply unit 111 is supplied to the induction coil 104,
which is installed above the solar cell wafer 102, through a high
frequency matching section 110. The induction coil 104 is not
limited to a specific type induction coil. The embodiment of the
present invention employs an ICP (Inductively Coupled Plasma)
induction coil.
[0026] Thus, a longitudinal magnetic field is formed around the
induction coil 104 by a high frequency current supplied to the
induction coil 104. As a transverse electric field is formed in the
plasma by the magnetic field, electrons are accelerated. The
accelerated electrons obtain energy from the electromagnetic field
by passing through a skin depth, are introduced into the plasma,
and collide with accelerated particles, so that gas introduced into
the chamber 103 is ionized, resulting in the generation of high
density plasma.
[0027] The induction coil 104 has a polygonal (e.g., a rectangular
or a square) shape in order to ensure a uniform etching rate across
the solar cell wafer 102 having a rectangular shape.
[0028] FIG. 2 is a schematic view illustrating the induction coil
manufactured in the above shape in accordance with the embodiment
of the present invention, which illustrates an example of a
structure in which a coil is wound three times in a rectangular
shape. The induction coil 104 illustrated in FIG. 1 is a section
taken along line A-A' which is drawn in the induction coil 104
illustrated in FIG. 2.
[0029] FIG. 3 is a plan view illustrating the induction coil in
accordance with another embodiment of the present invention, which
illustrates a structure in which a coli is wound in a radial
direction in order to increase uniformity.
[0030] FIG. 4 is a schematic view illustrating the induction coil
in accordance with another embodiment of the present invention,
which illustrates a structure of a multiple induction coil in order
to achieve the uniformity of ion energy and ion density. The
multiple induction coil has a structure in which induction coils
401A and 401B having the same shape (e.g., a rectangle) of two
groups are connected in parallel to each other. The directions of
currents flowing through the induction coils 401A and 401B of the
two groups are the same. The number of the groups is not limited to
two. For example, the number of the groups may increase as is
required.
[0031] According to an experimental result, for example, when the
ratio of a distance `r` between right and left windings in the
induction coil 401A and an interval `d` between the induction coils
401A and 401B of the two groups is 1, the uniformity of an etching
rate is the highest. The distance and the interval in the induction
coils 401A and 401B of the two groups may be the same or different
from each other.
[0032] However, it is difficult to install the solar cell wafer 102
to be textured between the induction coils 401A and 401B of the two
groups. In this regard, as illustrated in FIG. 1, the solar cell
wafer 102 is loaded on the cathode 101 in the chamber 103 and the
multiple induction coil manufactured as illustrated in FIG. 4 is
installed above the solar cell wafer 102. Herein, it is preferred
to achieve the uniformity of ion density and energy distribution by
appropriately adjusting the interval `d` between the induction
coils 401A and 401B of the two groups.
[0033] FIG. 5 is a plan view illustrating the induction coil in
accordance with another embodiment of the present invention, which
illustrates a batch type structure designed such that a plurality
of solar cell wafers can be textured at a time. Since a plurality
of induction coils 501 arranged in a matrix format independently
generate a magnetic field as described above with respect to the
solar cell wafers 102 arranged on the cathode 101, texturing can be
simultaneously conducted.
[0034] FIG. 6 is a plan view illustrating the induction coil in
accordance with another embodiment of the present invention, which
illustrates a batch type structure designed such that a plurality
of solar cell wafers can be textured at a time. The batch type
induction coil includes a plurality of coils 601 arranged in the
horizontal direction and a plurality of coils 602 arranged in the
vertical direction below or above the coils 601. The interval `d`
between the right and left coils and the height `h` (not shown)
between the upper and lower coils are adjusted, so that ion density
and ion energy of each wafer can be individually controlled and the
plurality of solar cell wafers can be textured at a time.
[0035] FIGS. 7A to 7D are plan views illustrating the induction
coil in accordance with another embodiment of the present
invention, which illustrate a structure in which an induction coil
is additionally provided in the induction coil in order to achieve
uniformity of plasma ion density in consideration of the large
diameter (e.g., 300 mm, 450 mm) of the solar cell wafer.
[0036] FIG. 7A is an example in which a cylindrical induction coil
702 is additionally provided in a rectangular induction coil 701.
FIG. 7B is an example in which a rectangular induction coil 704 is
additionally provided in a rectangular induction coil 703. FIG. 7C
is an example in which a rectangular induction coil 706 is
additionally provided in a cylindrical induction coil 705. FIG. 7D
is an example in which a rectangular induction coil 708 is
additionally provided in a rectangular induction coil 707 and a
rectangular induction coil 709 is additionally provided in the
rectangular induction coil 708.
[0037] In the case of using the induction coil with such a
structure, high frequency power, which is supplied from the high
frequency source power supply unit 111 to the induction coil
provided at an outside, and high frequency power, which is supplied
from the high frequency source power supply unit 111 to the
induction coil provided at an inside, are independently adjusted
using a power distributor (not shown), so that ion density of a
corresponding area can be determined at a desired degree.
[0038] The present invention is not limited the embodiments
illustrated in FIGS. 7A to 7D. For example, it may be possible to
employ various embodiments in which one or more induction coils
having the same shape or different shapes are sequentially provided
inside a single induction coil.
[0039] FIG. 8 is a diagram illustrating the high frequency low
power supply unit 108 illustrated in FIG. 1 in accordance with
another embodiment of the present invention. Referring to FIG. 8,
the high frequency low power supply unit 108 includes a plurality
of high frequency power generators 106A to 106C and a plurality of
high frequency matching sections 107A to 107C, so that the
intensity and density of ion energy and radical concentration can
be adjusted.
[0040] In such a case, high frequency power supplied from the high
frequency power generators 106A to 106C can be suitably supplied
according to process conditions. For example, the high frequency
power generator 106A supplies power of a relatively low frequency
(2 MHz), the high frequency power generator 106B supplies power of
a relatively high frequency (12.56 MHz to 13.56 MHz), and the high
frequency power generator 106C supplies power of a higher frequency
(27 MHz to 30 MHz or 60 MHz).
[0041] The high frequency power generators 106A to 106C supply
power of a relatively low frequency in order to improve the
intensity of ion energy, and power of a relatively high frequency
in order to improve the density of the ion energy.
[0042] The high frequency power supplied from the high frequency
power generators 106A to 106C, and the high frequency power
supplied from the high frequency power generator 109 in a low
dissociation region or a high dissociation region are adjusted, so
that the intensity and density of ion energy and radical
concentration are adjusted. Consequently, a high etching rate, wide
uniformity and a process margin of the solar cell wafer 102 can be
ensured.
[0043] Among the plurality of high frequency power generators 106A
to 106C and the plurality of high frequency matching sections 107A
to 107C, desired high frequency power generators and high frequency
matching sections can be selectively used according to process
conditions.
[0044] FIG. 9 is a graph illustrating an experimental result for
reflectivity of the solar cell wafer in the case of using the
plasma texturing reaction apparatus in accordance with the
embodiment of the present invention. Referring to FIG. 9, as
compared with the case where light reflectivity of a bare wafer is
averagely 31.54% in a wavelength range of 300 nm to 800 nm, light
reflectivity of the solar cell wafer in accordance with the
embodiment of the present invention is reduced as the passage of
texturing time and is smaller than 1% at maximum.
[0045] FIG. 10 is a graph illustrating an experimental result for
uniformity of the solar cell wafer in the case of using the plasma
texturing reaction apparatus in accordance with the embodiment of
the present invention. Referring to FIG. 10, in the case of
conducting texturing using a general induction coil, the difference
of 1% or more occurs in uniformity of a center portion and an edge
portion. However, in the case of conducting texturing using the
induction coil in accordance with the embodiment of the present
invention, uniformity of a center portion and an edge portion is
smaller than 0.03%.
[0046] In accordance with the embodiments of the present invention,
a magnetic field is generated using a polygonal induction coil when
conducting texturing on the surface of ultrathin wafer through dry
etching in a process of manufacturing a solar cell, so that etching
uniformity is improved from the center portion to an outer
peripheral portion of the wafer, resulting in the reduction of
reflectivity of the solar cell. As a result, the photoelectric
conversion efficiency of the solar cell is improved.
[0047] Although a preferred embodiment of the present invention has
been described for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
the spirit of the invention as disclosed in the accompanying
claims.
* * * * *