Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-08-18
2002-12-17
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S187000, C349S192000, C216S023000, C216S072000
Reexamination Certificate
active
06496242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an etching end point detection window used in the fabrication of a liquid crystal display device to detect an etching end time accurately and a method of fabricating the etching end point detection window. Also, the present invention is directed to an etching end point detecting method for detecting an etching end time using the etching end point detection window.
2. Description of the Related Art
Generally, an active matrix type of liquid crystal display device displays a picture using a pixel (or picture element) matrix having pixels arranged at intersections between gate lines and data lines. Each pixel includes a liquid crystal cell controlling a transmitted light quantity in accordance with a voltage level of a data signal from the data line. Thin film transistors (TFTs) are installed at the intersections between the gate lines and the data lines to switch a data signal to be transmitted toward a liquid crystal cell in response to a scanning signal from the gate line.
Referring to
FIG. 1
, there is shown a TFT formed on a substrate
18
. Hereinafter, a method of fabricating the TFT will be described. First, a gate electrode
20
, made from Al or a metal film including Al or the like, is formed on the substrate
18
. The gate electrode
20
is integral with a gate line(not shown). On the substrate
18
and the gate electrode
20
, a gate insulating film
22
made of an inorganic film, such as SiN
x
, SiO
x
or the like, is provided.
A semiconductor layer
24
made from an amorphous Si, hereinafter referred to as a-Si, and an Ohmic contact layer
26
made from a-Si doped with N+ ions are sequentially deposited on the gate insulating film
22
. A source electrode
28
and a drain electrode
30
made from a metal such as Cr, etc. are provided on the Ohmic contact layer
26
and the gate insulating film
22
. The source electrode
28
is integral with a data line (not shown). The Ohmic contact layer
26
exposed through an opening between the source electrode
28
and the drain electrode
30
are removed by means of dry or wet etching. A protective film
32
made from SiN
x
or SiO
x
is deposited over the substrate
18
to cover the TFT. The protective film
32
has the same thickness on the substrate
18
and is deposited with an inorganic material.
In order to provide contact holes, a portion of the protective film
32
disposed on a pad of the drain electrode
30
, the data line and the gate line are etched out. At this time, a pixel electrode
34
made from indium tin oxide is electrically connected, via a contact hole through the protective film
32
, to the drain electrode
30
. Output lines of drive circuits are electrically connected, via contact holes defined by the protective film
32
, to the pads of the data line and the gate line, respectively.
As seen from the foregoing, etching is performed in forming the electrode pattern and the contact holes. And, because an etched area defined only by the pattern during the etching process is small, it is difficult to sense an etched depth accurately. Accordingly, as shown in
FIG. 2
, an end point detection (EDP) window
42
is provided at the outside of a display region
40
, that is, a non-display region
19
. A number of gate lines
2
and a number of data lines
3
are formed in a direction perpendicular to each other in the display region
40
. TFTs
10
are formed at intersections between the gate lines
2
and the data lines
3
. The non-display region
19
includes (1) the peripheral area of the display region
40
where pads
2
a
and
3
a
, formed at the ends of the gate lines
2
and the data lines
3
, respectively, are located, (2) the edge area of the substrate
18
, and (3) an area between the display regions
40
. After fabrication of the TFTs
10
is completed, the display region
40
and the pads
2
a
and
3
a
are cut along a line
41
in such a manner that the display region
40
includes the pads
2
a
and
3
a.
FIG.
3
A and
FIG. 3B
are sectional views taken along line III—III in
FIG. 2
for the purpose of explaining an etching process for defining a contact hole at a pad of a gate line. As shown, a photo-resist pattern
44
is formed on the substrate
18
so as to define a contact hole
21
a
on the pad
2
a
of the gate line. Specifically, an EPD window
42
and a real pattern window
43
are formed in the photo-resist pattern
44
through exposure and development. The gate insulating film
22
and the protective film
32
are disposed between the EDP window
42
and the substrate
18
. The pad
2
a
of the gate line, the gate insulating film
22
and the protective film
32
are disposed between the real pattern window
43
and the substrate
18
. The substrate
18
, patterned with the EDP window
42
and the real pattern window
43
, is mounted within an etching chamber so as to form the contact hole
21
a
to the pad
2
a
of the gate line. SF
6
gas is then injected into the etching chamber. At this time, an etchant including SF
6
gas contacts the protective film
32
through the EDP window
42
and the real pattern window
43
, and simultaneously begins to etch the protective film
32
.
The etchant and the protective film
32
react to produce a nonvolatile gas SiF
4
. After the protective film
32
within the real pattern window
43
is removed, the gate insulating film
22
is removed to expose the pad
2
a
of the gate line. Also, the protective film
32
and the gate insulating film
22
within the EDP window
42
are removed to expose the substrate
18
under the EDP window
42
. The concentration of SiF
4
gas dramatically decreases or is no longer generated once the pad
2
a
of the gate line and the substrate
18
are exposed. Accordingly, an operator can determine an etching end time by sensing a concentration difference in or generation of SiF
4
gas. Herein, the SiF
4
gas evacuated during etching is converted into a voltage signal so that an operator can easily perform the sensing operation.
A liquid crystal display has the advantages of small dimensions (e.g., being slim) and low power consumption. And, studies for improving the liquid crystal display device are ongoing to further reduce power consumption. Recently, a scheme for overlapping the pixel electrode
34
with the data line
3
has become a prevailing technique. In this technique, in order to reduce a parasitic capacitance between the data line
3
and the superimposed pixel electrode
34
, the protective film
32
, formed between the pixel electrode
34
and the data line
3
, is made from an organic substance with a low dielectric constant instead of an inorganic substance. For example, an organic material, such as Benzocyclobutene (BCB), is used as a material for the protective film
32
.
Generally, the organic substance is grown into a film by spin-coating and thus the surface of the film becomes even. In this case, as shown in
FIG. 4A
, an organic protective film
46
exposed by the EPD window
42
is thicker than the film exposed by the real pattern window
43
. Specifically, a relationship of a thickness t
1
of the organic protective film
46
under the EPD window
43
to a thickness t
2
of the organic protective film
46
under the real pattern window
43
is t
1
>t
2
. Thus, after etching the organic protective film
46
to expose the pad
2
a
of the gate line, a portion of the organic protective film
46
exposed by the EPD window
42
remains. As shown in
FIG. 4B
, a thickness of Dt remains once the pad
2
a
of the gate line is exposed. As a result, there is only a slight variation in the amount of evacuated SiF
4
gas once the pad
2
a
of the gate line is exposed, and it is difficult to determine an etching end point. Accordingly, as shown in
FIG. 4C
, the pad
2
a
of the gate line can become damaged from over-etching. Also the photoresist pattern
44
sticks onto the organic protective film
46
to cause a defect at the time of forming the pixel electrode
34
.
SUMMARY OF THE INVENTION
Accordingly,
Birch & Stewart Kolasch & Birch, LLP
Chowdhury Tarifur R
LG. Philips LCD Co. Ltd.
Sikes William L.
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