FIELD OF THE INVENTION
The present subject matter relates to the development of a single side etcher, more
particularly to a single side etcher using the methodology of air curtain, in order to
protect the front side of the silicon wafer from acid/alkali etching.
BACKGROUND
In current photovoltaic manufacturing industry, to reduce cost of material and attain
mechanical flexibility, thinner Si wafers are being used. Thicker wafers as compared
to thinner one, can absorb most of incident light spectrum from sun. Wafer thinning
leads to an increase of the ratio of the wafer surface to volume and therefore, both front
and rear surface passivation is essential for obtaining low surface recombination
velocities.
Due to the current demands of thin and ultra-thin solar cells in the PV industry, the
need for advanced light trapping structures becomes more critical. Good light trapping
mechanisms enhance light confinement and thereby light absorption within solar cell.
Different methods can be used for achieving this. First step is reflectance reduction of
sunlight falling on cell. Moreover, particular care should be paid to the rear side of the
cell where the introduction of a reflecting surface can produce an optical path length
enhancement over a wide wavelength spectrum. Rightly combining the front side
texturing and the rear side polishing, it is possible to enhance this path length up to 50
times the device thickness indicating that light bounces back and forth within the cell
many times performing a light confinement. To this purpose Bragg reflector formed
using thin film technology is one of the most promising approach to the back side
reflector.
During diffusion, full wafer is exposed to the dopant source, including the rear of the
solar cell and edges. This creates a current path from the front junction to the rear of

the device, effectively shunting the solar cell. Therefore, after diffusion, an edge
isolation process is required to remove the unwanted diffusion around the edges of the
solar cell, and electrically isolate the front and rear surfaces. This can be done through
Plasma etching, Laser etching or wet chemical etching. In latter process, the doped
wafers are etched using acidic /alkaline solution in a single-side etch tool. This method
ensures the complete removal of the rear diffusion and edges, without the risk of
damage (ion damage) from a plasma etching process. For this reason, because of the
in-line nature of single side etching tools which enables high throughput and low
breakage risk, the wet etching process is the most common method used in production
for edge isolation.
US20080041526A1 titled “Single-sided etching” relates to a method and apparatus for
single side etching. It consists of a vacuum chamber, a perforated belt positioned
against vacuum chamber, and an etch chamber positioned on an opposing side of
perforated belt relative to vacuum chamber. The etch chamber has an opening through
which an etchant is released. The vacuum chamber is configured to create a pressure
differential which protect the back side of wafer from the etchant. The back side of the
wafer is disposed against the perforated belt and is secured by the differential pressure.
On the other hand, the front side of wafer is exposed to the released etchant. The
disadvantage of the prior art disclosed is that maintaining the negative differential
pressure is highly cumbersome and is prone to failure. A minimum leak may suck the
etchant and damage the back side of the wafer.
IN201731010247 titled “A single side etcher for lab use” discloses silicon wafer
comprising a tank, a chemically inert chuck adapted to hold a silicon wafer to be
etched with the help of vacuum, said chuck being connected to a venture vacuum unit
by means of flexible tubing to enable free movement of the chuck, said chuck being
adapted to dip into an acid mixture contained in said tank, said venture vacuum unit
including a compressed air input and a compressed air output and releasable connected

via channel means to the outlet of the chuck by a suction tube. But herein the method
of holding silicon wafer with vacuum is prone to issues. Many a time, the wafer does
not perfectly seal with chuck and hence the surface may get damaged.
OBJECTS OF THE INVENTION
It is therefore a principal object of this invention is to provide a concept and a method
for removal of rear side junction of the wafer without etching the surface of the front
face.
It is another object of the present invention to propose and implement the concept of
the design of air curtain method in order to perfectly etch the rear side of the silicon
wafer such that the front surface of the wafer is not damaged.
It is yet another object of the present invention to propose a methodology for etching
of rear side junction of the wafer such that the proposed method can be used for edge
isolation and texturing of silicon wafer required for high efficiency solar cell
fabrication.
It is yet another object of the present invention to propose a methodology for etching
of rear side junction of the wafer such that the proposed method can be used both in
the acidic and alkaline medium.
It is another very important object of the present invention to provide a concept of the
methodology for removal of rear side junction of the wafer based on air curtain method
which is extremely simple and cost effective as well.
It is yet another very important object of the present invention is to provide a
methodology for removal of rear side junction of the wafer based on air curtain method
such that the system is portable in nature.
These and other objects and advantages of the present subject matter will be apparent
to a person skilled in the art after consideration of the following detailed description

taking into consideration with accompanied drawings in which preferred embodiments
of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
This summary is provided to introduce concepts related to a method of removal of the
rear side junction of the wafer without damaging the front surface. This invention
relates to design of a lab scale tool for single side etching of silicon wafer. The setup
consists of a chemically inert tank and wafer carrier. The subject wafer is held in
position through adjustable carrier. Air curtain is formed along with periphery of wafer
through slits designed on chuck. The etchant chemical is prevented to entering from
edges of wafer though regulated positive air pressure.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be considered for
limiting of its scope, for the invention may admit to other equally effective
embodiments. The detailed description is described with reference to the
accompanying figures. In the figures, a reference number identifies the figure in which
the reference number first appears. The same numbers are used throughout the figures
to reference like features and components. Some embodiments of system or methods
or structure in accordance with embodiments of the present subject matter are now
described, by way of example, and with reference to the accompanying figures, in
which
Figure 1 illustrates the top view of the wafer carrier (9)
Figure 2 depicts the carrier (9) showing pins (2) for holding the wafer
Figure 3 illustrates the schematic of the passage for air distribution (4)
Figure 4 depicts the front view of the single side etcher
Figure 5 illustrates the side view showing air knives (6) of the single side etcher

Figure 6 depicts the complete assembly of the single side etcher
Figure 7 depicts the enclosure for exhaust (7) for the chemical tank (8) of the single
side etcher
The figures depict embodiments of the present subject matter for the purposes of
illustration only. A person skilled in the art will easily recognize from the following
description that alternative embodiments of the structures and methods illustrated
herein may be employed without departing from the principles of the disclosure
described herein.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING
DRAWINGS
While the embodiments of the disclosure are subject to various modifications and
alternative forms, specific embodiment thereof have been shown by way of example in
the figures and will be described below. It should be understood, however, that it is not
intended to limit the disclosure to the particular forms disclosed, but on the contrary,
the disclosure is to cover all modifications, equivalents, and alternative falling within
the scope of the disclosure.
The terms “comprises”, “comprising”, or any other variations thereof used in the
disclosure, are intended to cover a non-exclusive inclusion, such that a device, system,
assembly that comprises a list of components does not include only those components
but may include other components not expressly listed or inherent to such system, or
assembly, or device. In other words, one or more elements in a system or device
proceeded by “comprises… a” does not, without more constraints, preclude the
existence of other elements or additional elements in the system or device.

Fig 1 illustrates the top view of the wafer carrier used for removal of junction of the
rear side surface of wafer by means of etching. In an embodiment, the wafer carrier
used for the purpose is four legged designed specifically to hold the material with the
plurality of four points. In another embodiment, each leg of the plurality of the legs of
carrier stand consists of a plurality of holding points. The plurality of holding points
are arranged at equal height on each legs of the plurality of the carrier legs.
Fig 2 depicts that the plurality is to conveniently hold on the wafer on each leg of the
plurality of carrier (9) legs. It is further disclosed in the present invention that the
height of the plurality of the carrier (9) legs is adjustable by means of a screw (1)
provided at the top of the leg. Moreover, the holding edge present at each leg of the
carrier (9) stand in designed in a pointed manner so as to ensure minimum contact area
between the surface and the wafer.
The customized arrangement of the plurality of the carrier (9) legs and the holding
points as illustrated in Fig 1 and Fig 2 ensures that the front surface of the wafer is not
exposed to the etchant by any means.
Fig 3 illustrates the distribution of the air knives (6) on all the four points of the carrier
(9) stand. In an embodiment, a plurality of air knives (6) are arranged in the form of a
plurality of triangular slits and are present at the plurality of all the sides of the plurality
of bottom faces of the carrier (9) stand. In an embodiment, these plurality of slits are
joined together at the plurality of all the ends and titled at a specific angle with the
plurality of the bottom face of the carrier (9) stand. In an embodiment, such customized
arrangement of the slits are performed in order to maintain the outward flow of the air.
Further, in an embodiment, the plurality of the slits are connected with the single source
of air supply by means of the plurality of the holes (3).
Fig 4 depicts the front view of the single side etcher containing an inlet for compressed
dry air (CDA). In an embodiment, the CDA passes through the plurality of holes (as

shown in Fig 3) (3) by means of this inlet (5). The inlet (5) is actually a regulated valve
and thus can control the flow of CDA through it.
Fig 5 depicts the side view of the air knives (6). The plurality of air knives (6), as
already mentioned are titled at an angle in order to maintain the outward flow of the
air.
Fig 6 depicts the detailed unit diagram of the system. The complete assembly of the
single side etcher as shown in the figure consists of the carrier (9) stand accompanied
with the set up for holding the wafer by means of the plurality of holding pins (2). In
an embodiment, the CDA follows into the system by means of a single inlet (5) but the
outward flow of the air is carried out by the plurality of the holes (3) present in the
system. In an embodiment, the system further consists of a square shaped chemical
bath used for heating of the etchant. It is further disclosed in the embodiment that the
chemical bath is made up of chemically inert material so as to permit the etching
process in both the acidic and alkaline medium.
Fig 7 depicts the presence of a conical enclosure acting as an exhaust (7) for the system
described in Fig 6. In an embodiment, the conical enclosure is equipped with air suction
capacity to remove the fumes of the chemical process carried out while etching the rear
side surface of the wafer. The enclosure typically drives out the fumes or the reactive
gas phases or the vapours of the etchant that might have been produced during the
process of etching of the wafer.
The present subject matter discusses about the use of a technique by means of which
not only the etching of the rear side junction of the wafer is possible, but also the front
surface of the wafer is not damaged by the etchant. The arrangement of etching setup
in the present subject matter consists of a carrier stand made up of a plurality of legs.
The carrier (9) stand is made up of a chemically inert material in order to prevent
contamination in the etching process. The plurality of the legs of the carrier (9) stand
further consists of a plurality of holding points in order to efficiently support the wafer.

The plurality of holding points are maintained at an equal height on the plurality of legs
of the carrier (9) stand and are provided with screw (1) at the top of the leg for
adjustment of the height. Therefore, the wafer can be placed at a flexible height in the
carrier (9) stand. The invention discloses the use of a chemical bath made up of a
chemically stable material. The chemical bath further consists of a plurality of levels
marked by its side and is provided with a heating arrangement in order to attain the
desired process temperature. An etchant is filled up to predefined level in the chemical
tank (8). In an embodiment, on attaining the desired temperature of the etchant, the
carrier (9) along with the wafer is placed in the chemical tank (8). A wide range of
temperature ranging from ambient temperature to 90 degrees Celsius can be achieved
in the developed system depending on the medium of etching. In an embodiment, acidic
etching is performed at a lower temperature ranging from 5- 15 degree Celsius,
whereas, the alkaline etching is performed at a considerably higher temperature range
of 65-85 degree Celsius. The subject matter further discloses the presence of a plurality
of air knives (6) in the form of triangular slits on plurality of all the sides of bottom
face of the etcher. The plurality of air knives (6) form a specific angle in order to
regulate the flow of air in the outward direction. The plurality of slits are connected
with a single source of air supply by means of a plurality of holes (3). The invention
further discloses the presence of a single valve that regulates the flow of compressed
dry air (CDA) within the system. Due to the supply of the CDA through a single inlet
(5) in the centre its further distribution in the outer lines by means of the plurality of
air knives (6), the floating wafer remains stable in the chemical by exerting a mild
downward force that is consequently balanced by the buoyant force produced as a result
of effervescence. Consequently, an air curtain is maintained that prevents the front of
the surface from etching. In the embodiment, the plurality of factors related to etching,
like the process temperature depends on desired operation for example, texturization,
edge isolation or polishing and the etching rate, on the other hand, is dependent
concentration of etchant, time and temperature.

It should be noted that the description and figures merely illustrate the principles of the
present subject matter. It should be appreciated by those skilled in the art that
conception and specific embodiment disclosed may be readily utilized as a basis for
modifying or designing other structures for carrying out the same purposes of the
present subject matter. It should also be appreciated by those skilled in the art that by
devising various arrangements that, although not explicitly described or shown herein,
embody the principles of the present subject matter and are included within its spirit
and scope. Furthermore, all examples recited herein are principally intended expressly
to be for pedagogical purposes to aid the reader in understanding the principles of the
present subject matter and the concepts contributed by the inventor(s) to furthering the
art and are to be construed as being without limitation to such specifically recited
examples and conditions. The novel features which are believed to be characteristic of
the present subject matter, both as to its organization and method of operation, together
with further objects and advantages will be better understood from the following
description when considered in connection with the accompanying figures.
Although embodiments for the present subject matter have been described in language
specific to package features, it is to be understood that the present subject matter is not
necessarily limited to the specific features described. Rather, the specific features and
methods are disclosed as embodiments for the present subject matter. Numerous
modifications and adaptations of the system/device of the present invention will be
apparent to those skilled in the art, and thus it is intended by the appended claims to
cover all such modifications and adaptations which fall within the scope of the present
subject matter.
It will be understood by those within the art that, in general, terms used herein, and
especially in the appended claims (e.g., bodies of the appended claims) are generally
intended as “open” terms (e.g., the term “including” should be interpreted as “including

but not limited to,” the term “having” should be interpreted as “having at least,” the
term “includes” should be interpreted as “includes but is not limited to,” etc.). It will
be further understood by those within the art that if a specific number of an introduced
claim recitation is intended, such an intent will be explicitly recited in the claim, and
in the absence of such recitation no such intent is present. For example, as an aid to
understanding, the following appended claims may contain usage of the introductory
phrases “at least one” and “one or more” to introduce claim recitations. However, the
use of such phrases should not be construed to imply that the introduction of a claim
recitation by the indefinite articles “a” or “an” limits any particular claim containing
such introduced claim recitation to inventions containing only one such recitation, even
when the same claim includes the introductory phrases “one or more” or “at least one”
and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be
interpreted to mean “at least one” or “one or more”); the same holds true for the use of
definite articles used to introduce claim recitations. In addition, even if a specific
number of an introduced claim recitation is explicitly recited, those skilled in the art
will recognize that such recitation should typically be interpreted to mean at least the
recited number (e.g., the bare recitation of “two recitations,” without other modifiers,
typically means at least two recitations, or two or more recitations). Furthermore, in
those instances where a convention analogous to “at least one of A, B, and C, etc.” is
used, in general such a construction is intended in the sense one having skill in the art
would understand the convention (e.g., “a system having at least one of A, B, and C”
would include but not be limited to systems that have A alone, B alone, C alone, A and
B together, A and C together, B and C together, and/or A, B, and C together, etc.). In
those instances where a convention analogous to “at least one of A, B, or C, etc.” is
used, in general such a construction is intended in the sense one having skill in the art
would understand the convention (e.g., “a system having at least one of A, B, or C”
would include but not be limited to systems that have A alone, B alone, C alone, A and
B together, A and C together, B and C together, and/or A, B, and C together, etc.). It
will be further understood by those within the art that virtually any disjunctive word

and/or phrase presenting two or more alternative terms, whether in the description,
claims, or drawings, should be understood to contemplate the possibilities of including
one of the terms, either of the terms, or both terms. For example, the phrase “A or B”
will be understood to include the possibilities of “A” or “B” or “A and B.”
It will be further appreciated that functions or structures of a plurality of components
or steps may be combined into a single component or step, or the functions or structures
of one-step or component may be split among plural steps or components. The present
invention contemplates all of these combinations. Unless stated otherwise, dimensions
and geometries of the various structures depicted herein are not intended to be
restrictive of the invention, and other dimensions or geometries are possible. In
addition, while a feature of the present invention may have been described in the
context of only one of the illustrated embodiments, such feature may be combined with
one or more other features of other embodiments, for any given application. It will also
be appreciated from the above that the fabrication of the unique structures herein and
the operation thereof also constitute methods in accordance with the present invention.
The present invention also encompasses intermediate and end products resulting from
the practice of the methods herein. The use of “comprising” or “including” also
contemplates embodiments that “consist essentially of” or “consist of” the recited
feature.
Although embodiments for the present subject matter have been described in language
specific to structural features, it is to be understood that the present subject matter is
not necessarily limited to the specific features described. Rather, the specific features
and methods are disclosed as embodiments for the present subject matter. Numerous
modifications and adaptations of the system/component of the present invention will
be apparent to those skilled in the art, and thus it is intended by the appended claims to
cover all such modifications and adaptations which fall within the scope of the present
subject matter.

We Claim:
1. A single side etcher for etching the rear side of a wafer comprising:
a carrier (9) stand configured to hold the wafer to be etched wherein a
plurality of holding points are present at each leg of a plurality of the legs of
the carrier (9) stand wherein a plurality of holding pins (2) act as the holding
points;
a plurality of interconnected holes (3) wherein a compressed dry air (CDA)
circulates throughout the single side etcher;
a plurality of air knives (6) configured on bottom surface of the etcher; and
a chemical tank (8) connected to the carrier (9) stand wherein an exhaust (7)
is connected in order to drive out fumes and vapors generated as a result of
effervescence.
2. The single side etcher as claimed in Claim 1, wherein the carrier (9) stand is
made up of a chemically inert material.
3. The single side etcher as claimed in Claim 1, wherein the height of the plurality
of the legs of the carrier (9) stand are adjustable by a screw (1) such that the
wafer to be etched is configurable at a flexible height in the carrier (9) stand.
4. The single side etcher as claimed in Claim 1, wherein a plurality of holding
points of the carrier (9) stand are present at the same height.
5. The single side etcher as claimed in Claim 1, wherein the air knives (6) are
configured in the form of triangular slits and further make an angle in order to
maintain the outward flow of air.

6. The single side etcher as claimed in Claim 1, wherein the CDA enters through
a regulated single inlet (5) and passes out through the plurality of interconnected
holes (3) thus forming an air curtain.
7. The single side etcher as claimed in Claim 1, wherein the chemical tank (8) is
made up of a chemically stable material and wherein further the temperature of
the chemical tank (8) can be varied in the range of 5 to 90 degree Celsius.
8. The single side etcher as claimed in Claim 1, wherein etching can be performed
at both acidic and alkaline mediums.