FIELD OF INVENTION
The present invention relates to a carrier for horizontal chemical etching of ZnO thin film deposited on glass/sapphire/quartz substrate for surface texturing for developing a-Si:H solar cells. More particularly, the invention relates to a carrier designed for consistent and uniform surface texturing by wet chemicals process of deposited ZnO thin film on glass substrate.
BACKGROUND OF THE INVENTION
ZnO films deposited by sputtering, need to be textured in chemicals consistently all over deposited films at a time. This is required for making them suitable as TCO for a-Si:H solar cells. Thin film solar cells need to be developed on textured glass to obtain higher efficiencies (7%) than that is achievable for thin film solar cells on flat glass substrates. This is a junction device and chemical texturing of ZnO deposited as conducting layer on glass for developing amorphous silicon (a-Si:H) thin film solar cell requires careful and severe processing. The time taken for texturing is also very small making the whole process very critical. Carriers available for holding the substrates vertically are not suitable in our case. The reason for it is the contact angle or predominantly contact time between the deposited film and chemical changes as we

dip the substrate into the solution or remove it from the solution. Change in time of dipping leads to uneven texturing of the thin TCO film, which may be critical to achieve anticipated properties in the end product.
In patent no. US 5403401 A of Substrate carrier a flat substrate carrier comprising a machined main surface such that the surface of the substrate carrier opposite to the main surface has been subjected to the mechanical stresses at the two surfaces substantially compensate each other. The objective of this invention is to provide a flat substrate carrier which will remain flat also after coating has been applied which doesn't suffice our requirements.
Patent no. WO 2014007664 A1 claims the method provides a complete destroying of the data carrier together with the data recorded thereon, and thus eliminates any possibility of re-reading the data at a later time. The invention is to a digest a reaction in a reactor containing hydrochloric acid and (V) nitrate of one or more alkali metals, alkaline earth metals, rare earth metals and ammonium; or nitric (V) acid and chloride of one or more alkali metals, alkaline earth metals, rare earth metals and ammonium. We have no requirement for magnetic material.

In the above patents horizontal etching is done for coating on substrate to adjust the mechanical stress on the carrier and removal of magnetic data recorder respectively. These doesn't serve or requirement of uniform horizontal, quick etching in batch method.
In patent no. US20130199608 A1 and EP2381482 A1 surface treatment to nano-scale level of the TCO layer is done by employing laser irradiation increases haze. Laser scribing is an expensive method and dry method which will add up to the device cost. Searches on net has not revealed any similar design.
Inconsistent texturing of the top conducting layer will decrease the mobility of carriers in the succeeding layers. This will add resistance in subsequent layers decreasing the efficiency of the solar cell. Because of the specific requirement of the process, the carrier has been so made where care has been taken to hold the substrate horizontally without touching hardly any active surface of the film. The carrier has been so premeditated that the active area gets thoroughly exposed to chemical.
As per our prerequisite texturing of ZnO thin film sputtered both on plain and textured glass. This is required for making a-Si:H thin film solar cells.

OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a carrier for horizontal chemical etching of ZnO thin film deposited on glass/sapphire/quartz substrate for surface texturing for developing a-Si:H solar cells, which is capable of horizontal chemical etching of thin film deposited on the glass substrate.
Another object of the invention is to propose a carrier for horizontal chemical etching of ZnO thin film deposited on glass/sapphire/quartz substrate for surface texturing for developing a-Si:H solar cells, which is able to etch in nano-scale in chemicals rapidly and homogeneously thin films deposited by any of various methods.
An yet another object of the invention is to propose a carrier for horizontal chemical etching of ZnO thin film deposited on glass/sapphire/quartz substrate for surface texturing for developing a-Si:H solar cells, which can undertake a chemical cleaning processes for the substrate like glass, quartz, sapphire etc. for a precise size of 104 Sq.m and below specific thickness (2.99m).
A further object of the invention is to propose a carrier for horizontal chemical etching of ZnO thin film deposited on glass/sapphire/quartz substrate for surface

texturing for developing a-Si:H solar cells, which is capable of polishing or nano texturing of deposited thin films either on one side or on both the sides of the substrate.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 : Shows the carrier with carrier holder, glasses and slots for placing
the glasses and locking pin and legs of carrier.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
A horizontal substrate carrier (c) comprised of chemical inert substrates Teflon. The substrate is so designed that films deposited on top surface or bottom surface or all sides can be etched chemically. Any substrate of specified size can be cleaned, polished or textured easily. The main surface of the holding grooves or slots (3) of the carrier (c) have been machined. Machining was done with a view to hold the substrates (2) from dropping down and uniform chemical treatment. The surface preparation of deposited films followed by uniform chemical etching plays vital role for excellent light scattering at the interface. It effectively increases light trapping in thin film by prolonging its path through the intrinsic a-Si:H layer and thereby increasing the probability of absorption.

Topographically uniform textured film is required for the method. In an industrial process, it is required to texture a number of substrates at a time. The jig as disclosed in the present invention has been designed and made use for this purpose.
There is a special requirement for nano chemical etching of ZnO thin films deposited on the glass for developing a-Si:H thin film solar cells. Uniform surface preparation by chemical etching within few seconds of deposited films on any substrate is a challenge. Nano textured surface leads to excellent light scattering at the interface of two consecutive films. Accordingly a carrier for industrial use has been designed optimally. A carrier (c) with a special design has been made for this purpose. This design takes care of two contradicting requirements. On one hand, the substrate (2) needs to be held firmly in the jig but with a minimum area of contact so at that the chemicals reach all the surfaces without nay hindrance. For this, the slots (5) in the carrier have been kept sufficiently wide so as to allow easy passage of chemicals to all the parts of the film deposited on the substrate. The slot width and height is such that film doesn’t get damaged and the chemical flow adequately to all parts of the films deposited on the glass. The depth of the slots (3) has been kept such that it allows sufficient movement for the substrates (2) and still does not allow the glass to slip out of the slot. The carrier is made of Teflon to withstand acids/ alkalis. Schematic of the design is shown in Fig. 1. with all the specifications. It can be seen that there is a

provision for holding the substrate at only three points and substrates are accessible to the liquid etchant. The glass substrates are fragile and placed horizontally with a certain gap between them in order to have free passage for the gases generated for exothermic reaction between films and chemicals. During the chemical reaction between films and chemicals some gases may generate which shouldn't harm the nano-texturing of the films on substrate placed in adjacent groove. After identifying the exact requirement of the process, the carrier has been so made that it should have enough space to escape the reactive gases. The carrier has been used successfully and ZnO thin film deposited on glass have been etched using these carriers with almost 100% yield.
The carrier (c) as shown in Fig. 1 is constructed with an aim of uniform texturing of any substrate of 10 x 10 Sq.cm size. The carrier (c) is made of a material which is non-reactive to chemicals at elevated or low or room temperature, like Teflon. Handle
(1) of the carrier is also made of Teflon. The carrier can hold ten nos. of 104 Sq.cm substrates. There are twelve slots (3) in the carrier (c) for holding the glass substrates
(2) for texturing. The width of each slot (3) is 3mm. This is designed as per our requirement of fixed size and width of the samples to be textured. Any sample having width less than 3mm of fixed size can be safely mounted for any chemical treatment required for cleaning, texturing etc. At the top of the carrier (6), there is a holder (1)

fixed to it for holding while the carrier (c) is dipped into acidic or alkaline solution. It is an inverted U-shaped handle (1) which has made the handling of the carrier easy and effortless. The carrier is basically consisted of three pillars or legs (5) having slots (3) for holding the substrate and restrict fall to substrate from the carrier. There are 12 Nos. slots (2) provided in the pillars (5). In this carrier, substrate (2) of particular length and width are mounted. The size of the slot is 3 mm. This is designed as per requirement of fixed size and width of the samples to be texturised. Any sample having width less than 3 mm of fixed size is safely mounted for cleaning and texturing. Each slot (3) holds the substrate (2) at sufficient gap to allow the liquid to enter all the corner of the substrate (2). The slots (3) have some allowed space so that chemical etching of deposited films is done consistently. It enables sufficient free flow of chemicals for uniform etching from all sides. The slots (3) at three locations are made slightly wider than the glass thickness so that the liquid can evenly reach the substrate at all points. There is a setter (6) in the middle to set the carrier (c) accordingly and providing support to the structure. The legs (5) are of 5 cm thick to support the structure with total load when placed inside or out of liquid tank. Two conflicting requirements are fulfilled by the design of slot and thickness of the pillar which is 5 cm by providing lowest contact area for affluence flow of liquid all over the substrate (2). Maximum width is provided to restrict the fall of substrate from the carrier. There is a fixed lock pin (4) at the mounting side of the carrier (c) so that plates do not fall. The

lock pins are of width 1 cm and height 50 cm which is totally removable. This meets two requirements. One is easy stacking another a lock to restrict the fall of substrate (2) from the carrier (c). Therefore, it is open from one side from which the substrate is heaped. Lock pin (4) is stranded in semicircular made slits at the base and top of carrier structure.

WE CLAIM
1. A carrier (C) for horizontal chemical etching of ZnO thin film deposited on
glass/sapphire/quartz substrate for surface texturing for developing a-Si:H solar cells, the said carrier comprising;
an upper structure (7) and a lower structure (8) for holding pillars/legs (5) the carrier;
a plurality of pillars/legs (5) fixed to the upper (7) and lower (8) structures;
a plurality of slots (3) disposed in the said pillars (5) for holding glass substrates for texturing;
at least one setter (6) disposed for setting the carrier (C) and providing support to the structure;
at least one removable locking pin (4) disposed in the carrier emerging out from the top support (7) to the bottom support (8) for restricting the fall of the substrate (2) from the carrier;
a u-shaped holder (1) fixed to the top support (7) for carrying the carrier as well as for restricting the slippage of the substrate from the carrier; characterized in that, the slots (3) are disposed to hold the substrate at sufficient gap and made to provide lowest contact area for affluence flow of liquid all over the substrate and are made

slightly wider than the glass substrate thickness so that liquid evenly reaches the substrate at all points for better etching of film.
2. The carrier as claimed in claim 1, wherein twelve slots are provided in the said carrier, each slot is of 3mm width.
3. The carrier as claimed in claim 1, wherein the said carrier is made of material like Teflon which can withstand acids and alkalis.
4. The carrier as claimed in claim 1, wherein batch production is carried out in the said carrier when the substrates are retained in the carrier horizontally.
5. The carrier as claimed in claim 1, wherein the lock pins (4) are of 1 cm width and 50 cm height.