FIELD OF INVENTION
The present invention relates to development of a jig for protecting the bending
of glass sheet during transparent conductive oxide film deposition inside a hot
furnace.
BACKGROUND OF THE INVENTION
The transparent conductive oxide (TCO) coated glasses are used as the substrate
for producing large area thin film solar cells. TCO is the first thin film to be
deposited at a high temperature of about 570°C in a roll bound conveyorised
furnace on glass substrate of about 3-4 mm thick. TCO coated layer consists of a
silicon dioxide layer and a tin oxide layer. The rate of deposition is very high
(~0.6 micron/min/sq ft) and at the time of the production, glasses of full length
of more than 3' have to be loaded into the preheated furnace one after the other
continuously. The glasses are pre-cleaned in water in an on-line washer at room
temperature and loaded onto an ss belt of the furnace. The profile of the furnace
is such that the glasses do not break due to thermal shock. The glasses travel
through gradually increasing temperature zones inside the furnace for a duration

of 15 minutes. The highest temperature is ~570°C. The glasses pass through
under the injectors wherein process gases are sprayed downward in the form of
vapors. The gap between the glass and the injectors is about 3-4 mm. These
vapors cool the top surface of the glass. As only top surface is cooled, the glass
bend upwards due to unequal contraction of the top and bottom surface of the
glass and the leading edge of the glass plates is raised by more than 5 mm. The
glass has to move forward to the injector for the deposition of tin oxide layer. As
the gap between the second injector and the glass surface is also 3-4 mm, and
cannot be changed as it has been optimized to get the best properties of the
TCO layer, the glass would get stuck in the second injector and the deposition
process comes to a halt. To overcome this problem of bending of glass plates, an
innovative technique has been invented. A special type of jig of ss sheet has
been designed. While loading the glass plates into the furnace after initial
cleaning, the trailing edge of a first glass plate is locked with the leading edge of
the following second glass plate with the help of the ss jig. The shape of the jig
has been specially designed so that it is easy to slip-on to the glass while loading
it. The ss jig shadows only a very small area (40 mm X 10 mm) on the corner
edge of the glass and is not affected by the high temperature of the furnace.
When the glass plates reach below the first injector, it tries to bend up due to
differential heating of the top and bottom surface of the glass. As the edge of

this glass is locked with the trialing edge of the preceding glass plate with the
help of ss jig, the glass does not bend up and the glass moves below the next
injector without any problem. When the glass comes out from the furnace, these
jigs are removed manually and stored for next loading of glasses.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a development of a
jig for protecting the bending of glass sheet during TCO film deposition inside a
hot furnace which eliminates the disadvantages of existing state of art.
Another object of the present invention is to propose a development of a jig for
protecting the bending of glass sheet during TCO film deposition inside a hot
furnace which increases the productivity.
A further object of the present invention is to propose a development of a jig for
protecting the bending of glass sheet during TCO film deposition inside a hot
furnace which is capable for easy handling.
A still further object of the present invention is to propose a development of a jig
for protecting the bending of glass sheet during TCO film deposition inside a hot
furnace which can be used in a repeated cycles of operation without deforming.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.l - shows a schematic diagram of glass plate loaded into the TCO furnace
without ss jigs, bend after crossing first injector.
Fig.2 - shows a schematic diagram of enlarged view of ss jig for 3 mm thick
glass according to the invention.
Fig.3 - shows a schematic diagram of two glass plates locked with the help of ss
jig according to invention.
Fig.4 - shows a schematic diagram of glass plates mounted with a jig are
conveyed into the TCO furnace without bend after crossing first injector.
DETAILED DECSRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
As s.hown in fig.2, a c-shaped configured jig made of stainless steel sheets
having a thickness of 0.5 mm. The length and width of upper and lower member
of Y shaped jig arc 40-50 mm and 10 mm and length of connecting vertical
small member of c-shaped jig 3.0 mm. The internal gap between the mid point
of two arms of c-shaped jig is in the range of 2.5-3.0 mm and internal gap
between the edge of two arms of c-shaped jig is in the range of 3.2 mm to 3.3
mm at the open end.

The glasses (2,3) are pre-cleaned in water in an online washer at room
temperature and loaded into an ss belt (6) of the furnace (8). The profile and
belt speed of the furnace (8) is such that the glasses (9) do not break due to
thermal shock. The glass (9) moves forward inside the furnace (8) and reaches a
zone which is preheated to 570°C and it takes about 15 minutes time to cross
over. The glass moves under a first injector (4) (injector 1) where process gases
spray downward in the form of vapor. The gap between the top surface of glass
and mouth of the injector is 3-4 mm. The vapor ejecting out from the injector
1(4) cools the upper surface of the glass. As the top surface of the glass is
cooled faster than the bottom one, the glass tries to bend upward at the edge
point due to unequal contraction of the top and bottom surface of the glass.
The leading edge of the glass plate is raised by more than 5 mm. Immediately
after a minutes the glass has to go under a second injector 2(5) for the
deposition of tin oxide film at the same temperature. The gap between this
injector and the glass is also 3-4 mm and cannot be changed as it has been
optimized to get the best properties of the TCO layer. The glass cannot pass and
gets struck at the second injector (5) and deposition process comes to a halt.
To overcome this practical problem of bending of glass plate, a new jig has been
developed as shown infig.2, while loading the glass plates into the furnace after

cleaning, the leading corner edge of glass plate (2) is locked with a trailing
corner edge of follower glass plate (3) with the help of a ss jig (1) as shown in
fig.3. The shape of the jig is such that it is very easy to slip it to the glass edge
while loading on the furnace belt (6) without touching the glass surface. The ss
jig shadows only a very small area (40 mm X 10 mm) on the edge of the glass
(2,3) and is not affected by the high temperature of the furnace. As 10 mm
border of the glass edge is supposed to be free from any deposition. Shadow of
the jig does not affect the solar cell performance. When the glass plate (6)
(fig.4) reaches below the first injector (4) it tries to bend up due to differential
cooling of the top and bottom surface of the glass. As the edge of this plate (3)
is locked with the trailing edge of the front glass (2) with the help of ss jig (1),
the glass does not bend up and the glass moves below the second injector (5)
without any problem (fig.4). The shape of the jig is such that it grips each sheet
20 mm lengthwise and does not allow it to bend i.e. vertical movement is
restricted. The grip of the jig is kept sufficiently loose so as to allow same
movement of the glass in the horizontal plane so as to accommodate the thermal
expansion/contraction of glass sheets during heating/cooling cycle. After
processing is over the glass enters into the cooling zone and come out of the
furnace at 150°C-160°C. The jigs are easily removed manually and taken to the
station for further use.

WE CLAIM
1. A newly developed jig for projecting the bending of glass sheet during
TCO film deposition inside a hot furnace comprising:
- 'c' shaped configured article made of stainless steel sheet having a
open gap between the upper long member and lower long member
of 'c' shaped at one side through which the jig can grip and release
a glass plate smoothly
characterised in that the grip of the jig is kept sufficiently loose
fittings to allow a movement of glass in horizontal plane so as to
accommodate the thermal expansion/contraction of glass during
heating that in turn preventing the bending of glass sheet.
2. The jig as claimed in claim 1 wherein the length and width of the upper
and lower long member of 'c' shaped are 40-50 mm and 10 mm and the
length of vertical connecting member is 3.0-3.5 mm.
3. The jig as claimed in claim 1 wherein an internal gap between the mid
point of upper and lower member is 3.0 mm and 3.0 mm to 3.5 mm at the
edges of upper and lower member towards open end.

4. The jig as claimed in claim 1 wherein the thickness of ss sheet is 0.5-1
mm.

The present invention relates to a newly developed jig for projecting the bending of glass sheet during TCO film deposition inside a hot furnace comprising 'c' shaped configured article made of stainless steel sheet having a open gap between the upper long member and lower long member of 'c' shaped at one side through which the jig can grip and release a glass plate smoothly characterised in that the grip of the jig is kept sufficiently loose fittings to allow a movement of glass in horizontal plane so as to accommodate the thermal expansion/contraction of glass during heating that in turn preventing the bending of glass sheet.