FIELD OF INVENTION

This invention is related to provide a shallow depth PTFE trays for processing large area Si wafers.
BACKGROUND OF THE INVENTION
Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Number of chemical processes are required for making efficient Si solar cells. For production processes, large volume tanks are available where large area (6" x 6') thin (180 microns) Si wafers can be dipped easily. For many chemical processes strong alkalis, strong acids are used including HF. The use of acids does not permit the use of metal containers and use of HF debars the use of even glass containers. The only material which can be used safely for all the acids and alkalis within a temperature range of -20°C to 150°C is Polytetrafluoroethylene (PTFE) commonly known as Teflon. For conducting experiments in a laboratory, the acid concentration needs to be varied frequently therefore acids are frequently replaced. For dipping the large area Si wafers vertically, at least a few liters of acid mixture is required for each experiment. Disposal of such large quantities is not environment friendly. In view of this problem, a new design of tray has been conceived where minimal quality (~ 300 cc) of acid mixture is required and the Si wafer can be dipped easily for several different experiments.
PRIOR ART
While searching with appropriate keywords, most of the patents were found on method of fabrication of solar cells and on method of chemical treatment of the silicon solar cells.


The invention at Ref. # 1 relates to a releasing apparatus for separating a semiconductor substrate from a template by using an enclosed pressure chamber having at least one gas inlet and at least one gas outlet. It uses top and bottom vacuum chuck for securing a released semiconductor substrate and template respectively or vice versa. A gap between the attached semiconductor substrate and semiconductor template and the top vacuum chuck allowing gas flowing through the gap to generate lifting forces on the attached semiconductor substrate and semiconductor template.
In the invention at Ref. # 2, deals with a silicon base material which is used as an anode, platinum is used as cathode and an electrolyte solution is arranged between the anode and the cathode, anodic oxidation is performed in constant current mode under the conditions where porous formation mode and electrolytic polishing mode coexist. The cathode is fitted in the anode with silicon elution and processes such as hole making, cutting, single-side pressing are performed.
One or more drawbacks of conventional systems and process for a method for improving yield strength of a workpiece and an apparatus are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are part of the claimed disclosure.

OBJECTS OF THE INVENTION:
It is therefore an object of the invention is to design a PTFE tray for conducting chemical processing of large area Si wafers by using minimal quantity of acid mixture.
Another object of the invention is to design a PTFE tray for conducting chemical treatment trials, where the height of the tray has been kept low so that the thin wafers can be removed from the tray after the experiment very easily using a PTFE tweezers.
SUMMARY OF THE INVENTION
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects embodiments, and features will become apparent by reference to the drawings and the following detailed description.
A new design of tray has been developed which has a very low depth. The tray has four very fine cylindrical pins (2). These pins (2) have been carved out of the PTFE block so that there are no crevices for the chemicals to get trapped. These pins (2) keep the delicate Si wafer elevated slightly above the bottom surface which helps easy removal of Si wafer using tweezer. The edges of the tray are kept slanting at 45 degree angle to allow easy insertion of tweezer and absence of sharp corners for easy removal of chemicals.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
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, the left-most digit(s) of 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 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 shallow depth PTFE trays for processing large area Si wafers in accordance to the present invention.
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.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.
It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and 10 embodiments may be combined to form a further embodiment of the disclosure.
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.
As used in the description herein and throughout the claims that follow, the meaning of “a”, “an” and “the” includes plural reference unless &e context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in”' includes “in” and “on” unless the context clearly dictates otherwise.
The terms "comprise", “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, apparatus or device.
These and other advantages of the present subject matter would be described in greater detail with reference to the following figures. It should be noted that the description merely illustrates the principles of the present subject matter. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described herein, embody the principles of the present subject matter and are included within its scope.
A new design of tray has been developed which has a very low depth. The tray has four very fine cylindrical pins (2). These pins (2) have been carved out of the PTFE block so that there are no crevices for the chemicals to get trapped. These pins (2) keep the delicate Si wafer elevated slightly above the bottom surface which helps easy removal of Si wafer using tweezer. The edges of the tray are kept slanting at 45 degree angle to allow easy insertion of tweezer and absence of sharp corners for easy removal of chemicals.

As shown in figure 1, a new design of tray has been developed which has a very low depth (15 mm). The tray has four very fine dome shaped cylindrical pins (2) of 2 sq mm area with a height of 2mm. These pins (2) have been carved out of the PTFE block so that there are no crevices for the chemicals to get trapped. These pins (2) do not allow the Si wafer to sit full flat on the bottom of the tray which can result in wafer getting stuck to the bottom of the tray due to vacuum. The pins (2) keep the wafer about 2mm above the bottom of the tray. The size of the pins (2) has been kept very small and they have a dome shape of the top to minimize surface contact with the Si wafer thereby minimizing damage to the
Wafer surface. This will result in availability of full bottom surface of the Si wafer for chemical reaction. The inside edges of the tray are kept slanted at 45 degree angle. This ensures that lesser quantity of chemicals to be used for each experiment and also ensures easy insertion of tweezer below the Si wafer for removal from the tank after the reaction time is over. For improving uniformity, the tray is equipped with two handles (1), one each on opposite sides so that the tray can be shaken during the experiment to ensure rigorous uniform reaction. The slanted sides of the tray also ensure that here are no sharp edges and the remaining chemicals can be removed effectively by purging the tray with water. The actual dimensions are given in the attached drawing.
Direction of usage:
The required chemicals or mixture of chemicals need to be prepared in a beaker and transferred to the PTFE tray, As the Si wafers are very thin (180 Microns) total solution required will be very small in quantity (-400 cc). The solution needs to heated or cooled to desired temperature and then poured into the PTFE tray with all safety precautions such as safety goggles, gloves and protective clothing. The Full size Si wafer can be placed in the tray and dipped with the help of PTFE rod for required length of time and can be removed using PTFE tweezer and washed with copious amount of water in a beaker.

Key Features:
1. A simple design of PTFE tray which is easy-to-use for carrying out chemical processes in a laboratory for large area Si (6” x 6”) wafers with thickness 180 microns.
2. The special design requires minimal amount of chemicals to be used (<400cc).
3. Use of PTFE allows use of all organic/ inorganic acids safely within a
temperature range of -50°C to 150°C.
4. Small pins (2) at the bottom of the tray keep the delicate wafer elevated a few mm above the bottom of the tray allowing easy insertion of the PTFE tweezer for removal of wafer.
5. The pins (2) at the bottom do not allow the Si wafer to get stuck to the bottom of the tray due to vacuum and both sides of the wafer are available for proper chemical treatment.
6. The dome shape of the top of the pins (2) ensures minimal contact of pins (2) with the Si wafer and damage is minimized.

8. The tray is equipped with two handles (1), one each on opposite sides so that the tray can be shaken during the experiment to ensure rigorous uniform reaction.
9. The slanted sides of the tray ensure easy and effective removal of chemical during cleaning cycle of tray with water.
Each of the appended claims defines a separate invention, which for infringement purposes is “reorganized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
Groupings of alterative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be

referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted form, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
With respect to the use of substantially plural and/or singular terms herein, those having skill in the art can translate form the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It still be understood by takes 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 claim may contain usage of the introductory phrases “at least one” and “one or more” to introduce claims 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 claims includes the introductory phrases “one or more” or “at least one” and indefinite articles such a “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 article 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 recitation,” without other modifiers, typically mean at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of the 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 A, B and C etc. 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”.
The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known related art or later developed deigns and materials should be employed. Those in the art can choose suitable manufacturing and design details.
The technology used herein is for the expose of describing embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternative thereof, may be combined into other systems or application. Various presently unforeseen or unanticipated alternatives, modification, variation, or improvements therein.

WE CLAIM:
1. A modified PTFE tray for large silicon wafers, the tray comprising four numbers dome shaped cylindrical pins (2) to position the wafer at an elevation, a pair of side handles (1) to hold the tray; in which the tray height may be 15mm.
2. The PTFE tray as claimed in claim 1, in which the pins (2) forms a gap between inner base of the tray and the silicon wafer.
3. The PTFE tray as claimed in claim 1, in which the inner sides of the tray are sloping inwards to allow easy cleaning process.
4. A modified PTFE tray for large silicon wafers, the tray, as substantially described and illustrated herein with reference to the accompanying drawings.