Method to prevent an ITO from opening

Details Method to prevent an ITO from opening Method to prevent an ITO from opening

2001-05-02

2002-12-17

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S030000, C438S149000, C438S158000, C438S609000

Reexamination Certificate

active

06495440

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method of fabricating a liquid crystal display (LCD). In particular, the present invention relates to a method of forming an opening-free ITO (indium tin oxide).
2. Description of the Related Art
ITO is generally used as electrode or contact layer in LCD technology. When the ITO is deposited, in order to prevent the ITO from becoming poly-ITO, thereby rendering the etching of the ITO incomplete and resulting in an ITO to ITO short, the thickness of the ITO is controlled at 400 &mgr;m or thereabouts. However, the thin ITO has a distinct disadvantage. The thin ITO crosses the second metal layer (about 3000 &mgr;m), whose taper easily causes opening. If the second metal layer is a tri-layered metal layer, it easily comes across under cutting, inducing the ITO to open.
FIG. 1
depicts the ITO with an opening according to the prior art. A first metal layer (not shown) used as a gate is formed on a substrate
10
. A gate insulating layer
14
is formed thereon.
A second metal layer
16
, the tri-layered metal layer of Mo(
16
a
)/Al(
16
b
)/Mo(
16
c
), is formed on the gate insulating layer
14
. An insulating layer
18
, used as passivation layer, is formed thereon. Then an ITO layer
20
with a thickness of 400-500 &mgr;m is deposited on the insulating layer
18
. When etching the metal layer
16
, a Mo/Al/Mo tri-layered structure, the Al layer
16
b
has under cutting (labeled as
22
), causing the insulating layer
18
to produce tear-drops, or recesses,
24
. This occurs because the material of the middle Al layer
16
b
is different from the other two layers
16
a
and
16
c
. Moreover, the ITO layer
20
is so thin that it easily opens at the tear-drops
24
, therefore affecting the electrical properties of the whole structure.
Additional prior art, intended as a solution, is shown in FIG.
2
. The second metal layer
36
corresponding to the edge of the ITO layer
40
is designed in a twisting pattern to enlarge the circumference in the area to enhance the effectiveness of the contact area of the ITO layer
40
. However, actual opening is not completely prevented. Hence, prior art cannot thoroughly resolve the opening of the ITO layer
40
.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method to prevent the ITO from opening at the tapered edge of the underlayer.
To achieve the above-mentioned object, a method to prevent an ITO from opening, comprising the following steps is provided. A dummy material layer with tapered edges is formed on a substrate. A first insulating layer is formed on the dummy material layer. A metal layer is formed on the first insulating layer, one edge of the metal layer corresponding to one of the tapered edges of the dummy material layer and the other tapered edge situated away from the edge of the metal layer. A second insulating layer is formed on the metal layer. An ITO layer without opening around the edge of the metal layer is formed on the second insulating layer.
According to the embodiment of the present invention, the dummy material layer is metal and the thickness of the ITO layer is between 400 &mgr;m and 500 &mgr;m. Moreover, a gate can be formed with the dummy material layer, that is, both the gate and the dummy material layer belong to the first metal layer.
If the above-mentioned method is used to form a bottom gate structure, an etching stop layer, made of silicon nitride, is formed substantially corresponding to the dummy material layer on the gate insulating layer.


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