FIELD OF THE INVENTION
The present invention relates to wafer carriers for manufacturing hereto junction
solar cells. More particularly, the present invention relates to an improved wafer
carrier with adjustable wafer holder jig for uniform deposition in vacuum system.
BACKGROUND OF THE INVENTION
For manufacturing of hetero junction solar cells, layers of a-Si and ITO are to be
deposited on silicon wafers through a mask in high vacuum conditions. For
various applications in vacuum deposition, a plurality of holding jigs are used.
Some of the jigs used are only to support the sample while others are used to
prevent deposition on certain areas. The wafer holding jig has to be such that a
uniform deposition takes place on the silicon wafer in vacuum. If the layer is
deposited from the bottom then a lip has to be formed on the jig to hold the
wafer. If the lip width is more, then it covers more area on the wafer and
deposition takes place on lesser area which results in lower power output from a
cell. On the other hand, if the lip width is less, then due to variation in size of the
wafer, some wafers with smaller dimension shall have some of the edges
exposed to the deposition. So to resolve this problem a wafer carrier with
adjustable wafer holder jig is desirable so that wafers of variable sizes can be
accommodated with minimum shadow area loss.
In one of the embodiment (US Patent: 5042423, aug1991), a tapered wafer
carrier has been used. The purpose of the taper is to prevent the wafer from
thermal stress in case of heating during a vacuum processing.

In other embodiment (US application US 2002/0021981A1), a tapered lip is used
to support the wafer from mechanical stress during transport and processing.
While in another embodiment (WO2011.109348A2 step2011), a wafer carrier
handling jig has been proposed.
In none of the cited prior patents, the edge shadowing problem has been
addressed. As the silicon wafers normally do have variations in their dimensions
due to manufacturing from different sources, it is important to maximize the
active are of a solar cell i.e. to reduce the shaded area at the edges.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved wafer carrier
with adjustable wafer holder jig for uniform deposition in vacuum system, which
eliminates the disadvantages of the prior art
Another object of the invention is to propose an improved wafer carrier with
adjustable wafer holder jig for uniform deposition in vacuum system, which is
enabled to move two of its arms to accommodate size variation of the wafers.
A further object of the invention is to propose an improved wafer carrier with
adjustable wafer holder jig for uniform deposition in vacuum system, which inter
alia decreases shadow-loss area and thereby increase current generation by the
solar cell.

SUMMARY OF THE INVENTION
Accordingly, there is provided an improved wafer carrier with adjustable wafer
holder jig for uniform deposition in vacuum system, comprising : a steel body (1)
having a plurality of fixed corners (4); at least two fixed arms (2) configured on a
first side of the body (1) perpendicular to each other for holding at least one
wafer in a slot for deposit ion of thin film layers; at least two movable arms (5)
provided on a second side of the body (1) being perpendicular to each other and
enabled to freely move in slot (6) corresponding to the size of the wafer; a lip (3)
projecting upwardly around the periphery of the body (1); a control means (7)
moves in tapered slot controlling the movement of a first movable arm (5),
similar control means moves in tapered slot (8) controlling the movement of
second movable arm (5) . The two movable arms can be moved in a way such
that size variations in different wafers can be neutralized to increase active area
of deposition. The size of the wafer used in the invention for hetero junction cell
process is 125±0.5mm. pseudo square with corners of a circular arc with a
diameter of 165±1mm. For fixed edges to prevent shorting on the sides with
1mm tolerance, a carrier with 2 mm lip is required i.e. 4mm coverage area on
the sides. This results in a large shadow loss. So to reduce the shadow loss and
to maintain the uniformity of the deposited layer, an innovated wafer carrier with
adjustable holder jig is provided. In the adjustable carrier, the lip is reduced to
lmm so the shadow area decreases.
A prior art wafer carrier is with an inner dimension of 123 mm and an outer
dimension of 127 mm, the lip is of 2mm and the shadow loss is 4 mm wide on
sides. As shown in figure 1, the total shadow loss area is around 12 cm2. Due to
this shadow loss, the current generated in the cell reduces due to reduced light
capturing area.

According to the present invention, the two sides of the wafer holding jig are
adjustable and can be moved manually as shown in figure 2. This arrangement
helps in reducing the lip size to 1mm and to neutralize the variation in the size of
wafers. So an active area of around 6 cm2 is increased over the prior art design.
This improved wafer holding jig increases the current generated from the cell
and finally the power output from the cell.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 Shows a prior art wafer carrier for holding silicon wafers in a
vacuum system for deposition of thin films.
Figure 2 Shows an improved wafer carrier with adjustable holder jig
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
A wafer carrier with adjustable wafer holder jig for uniform deposition in vacuum
as shown in figure 2, includes a stainless steel body (1) at least two fixed arms
(2) for wafer holding a lip (3) projecting upwardly around the periphery a
plurality of fixed corners (4), and at least two movable arms (5) free to move
depending on size of the wafers accommodated in a slot (6). The movement of
the movable arms are controlled by a knob (7) within a tapered movable slot (8).

WE CLAIM :
1. An improved wafer carrier with adjustable wafer holder jig for uniform
deposition in vacuum system, comprising:
a steel body (1) having a plurality of fixed corners (4);
at least two fixed arms (2) configured on a first side of the body (1)
perpendicular to each other for holding at least one wafer in a slot for
deposition of thin film layers;
at least two movable arms (5) provided on a second side of the body (1)
being perpendicular to each other and enabled to freely move in slot (6)
corresponding to the size of the wafer;
a lip (3) projecting upwardly around the periphery of the body (1);
a control means (7) moves in tapered slot controlling the movement of a
first movable arm (5), similar control means moves in tapered slot (8)
controlling the movement of second movable arm (5) . The two movable
arms can be moved in a way such that size variations in different wafers
can be neutralized to increase active area of deposition.
2. The improved wafer carrier as claimed in claim 1, wherein the wafer jig is
formed of stainless steel.
3. The improved wafer carrier as claimed in claim 1, wherein the wafer jig is
made of aluminium.
4. The improved wafer carrier as claimed in claim 1, wherein the wafer jig is
made of carbon fibre body.

5. The improved wafer carrier as claimed in claim 1, wherein wafers of
125mm to 156mm pseudo square size with tolerances in wafer dimensions
upto 2mm can be deposited with uniform thin film layer in a vacuum
system.

ABSTRACT

The invention relates to an improved wafer carrier with adjustable wafer
holder jig for uniform deposition in vacuum system, comprising : a steel
body (1) having a plurality of fixed corners (4); at least two fixed arms (2)
configured on a first side of the body (1) perpendicular to each other for
holding at least one wafer in a slot for deposit ion of thin film layers; at
least two movable arms (5) provided on a second side of the body (1)
being perpendicular to each other and enabled to freely move in slot (6)
corresponding to the size of the wafer; a lip (3) projecting upwardly
around the periphery of the body (1); a control means (7) moves in
tapered slot controlling the movement of a first movable arm (5), similar
control means moves in tapered slot (8) controlling the movement of
second movable arm (5). The two movable arms can be moved in a way
such that size variations in different wafers can be neutralized to increase
active area of deposition.