Semiconductor device manufacturing: process – Making passive device – Resistor
Reexamination Certificate
2000-12-12
2002-06-18
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Making passive device
Resistor
C438S151000, C438S165000, C438S257000, C438S586000, C438S724000
Reexamination Certificate
active
06406969
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 1999-59601, filed on Dec. 21, 1999, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin film transistors and to liquid crystal display (LCD) devices.
2. Discussion of the Related Art
In general, a LCD includes upper and lower substrates and an interposed liquid crystal layer. The upper substrate includes a color filter and a common electrode, while the lower substrate includes an array of switching elements and a pixel electrode. The liquid crystal layer is comprised of optically anisotropic liquid crystal molecules that arrange according to the state of the switching element.
The lower substrate is often referred to as an array substrate. That substrate is manufactured using various processes such as deposition, photolithography, and etching. Manufacturing the lower substrate involves repeating those processes several times. Of the various processes, the principles of the present invention most directly relate to photolithography. Therefore, photolithography will be explained in more detail.
FIG. 1
is a photolithography flow chart, and
FIGS. 2A
to
2
D are cross-sectional views illustrating a typical photolithography process. In general, photolithography includes deposition, (light) exposure, and development.
First, as shown in
FIG. 2A
, a thin film
11
is deposited on a glass substrate
10
. Referring now to ST
100
of
FIG. 1
, after the deposition of the thin film
11
the glass substrate
10
is pre-baked to remove humidity on the substrate's surface. This enhances adhesion between the glass substrate
10
and a subsequently deposited photoresist
13
. Thereafter, the photoresist
13
is uniformly coated on the thin film
11
using spin-coating. Then, a soft-bake process that evaporates solvents remaining in the photoresist
13
is performed. This hardens the photoresist
13
. The result is as illustrated in
FIG. 2
a.
ST
200
of
FIG. 1
is carried out by placing the glass substrate
10
in a light exposure device and aligning the glass substrate with a photomask. This is shown in
FIG. 2B
, which shows a mask
15
. The glass substrate
10
then undergoes light exposure for a predetermined period of time. Beneficially, the light exposure uses ultra-violet (UV) radiation. Due to the light exposure and the mask
15
, the portion of the photoresist
13
that is not protected by the mask
15
is polymerized.
After polymerization, ST
300
of
FIG. 1
is performed as illustrated by FIG.
2
C. Depending on the particular process being used, either the exposed portion or the non-exposed portion of the photoresist
13
is selectively removed by a developer. The result is a photoresist pattern
13
. To enhance the adhesion of the photoresist pattern
13
to the thin film
11
the glass substrate
10
is hard-baked by performing a heat-treatment at a predetermined temperature.
After the hard-bake, ST
400
(etch) of
FIG. 1
is performed as shown in FIG.
2
D. Using either a dry or a wet etch process, the thin film
11
is selectively removed with the photoresist
13
acting as a mask. The result is a thin film pattern
11
a
. In other words, a portion of the thin film
11
that is not covered with the photoresist pattern
13
is removed.
After the etch, ST
500
(strip) of
FIG. 1
is performed, also as illustrated in FIG.
2
D. The photoresist
13
on the thin film pattern
11
a
is removed using a chemical stripper. After stripping, a cleaning process is carried out, beneficially one that uses distilled water. Since the stripper tends to stick to and solidify on the surface of the substrate
10
, the substrate is first immersed in an isopropyl alcohol solution ((CH
3
)
2
CHOH) to prevent stripper solidification. Then, the substrate
10
is cleaned using distilled water.
The structure of a conventional array substrate that is manufactured using the foregoing photolithography process is explained below.
FIG. 3
is a plan view illustrating an array substrate of a conventional LCD device. As shown in
FIG. 3
, gate lines
19
are arranged in a transverse direction, and data lines
21
are arranged in a longitudinal direction. Pixel electrodes P are formed at a region defined by the gate and data lines
19
and
21
. Thin film transistors (TFTs) are formed at a crossing portion of the gate and data lines
19
and
21
. A storage capacitor C is formed adjacent the gate line
19
. A portion of the gate line
19
is used as a first electrode of the storage capacitor C, and a portion of the pixel electrode P is used a second electrode. Alternatively, a separate capacitor electrode can be formed and used instead of the portion of the gate line
19
.
Each TFT includes a gate electrode
23
, an active layer
29
, a source electrode
25
, and a drain electrode
27
that is spaced apart from the source electrode. The end portion of the active layer
29
is overlapped by the source and drain electrodes
25
and
27
.
Each of the foregoing components is formed by photolithography. As the ends of the active layer
29
is overlapped by the source and drain electrodes
25
and
27
, the surface of the active layer
29
must be completely clean to prevent problems. Therefore, as described above, the array substrate is immersed in the isopropyl alcohol solution after removing the photoresist using the stripper solution.
However, the isopropyl alcohol solution adversely affects an insulating layer that is beneficially located under the active layer
29
. In addition, the isopropyl alcohol solution is relatively costly. Therefore, an improved method of manufacturing a thin film transistor array substrate would be beneficial.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method of manufacturing a thin film transistor array substrate that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
To overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing a thin film transistor array substrate that includes an effective method of cleaning an active layer of a thin film transistor.
Another object of the present invention is to provide a method of manufacturing a thin film transistor array substrate that includes a low cost process of cleaning an active layer of a thin film transistor.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from that description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve the above objects, the principles of the present invention provide a method of manufacturing a thin film transistor array substrate that includes forming a gate electrode on a substrate, and then sequentially forming a first insulating layer, a pure semiconductor layer and a doped semiconductor layer that cover the gate electrode. A photoresist layer is then coated on the doped semiconductor layer. The photoresist layer is then exposed and developed to form a photoresist pattern. The pure semiconductor layer and the doped semiconductor layer are then etched to form an active layer and an ohmic contact layer by using the photoresist pattern as a mask. The photoresist pattern is then removed using a stripper. The array substrate is then immersed into a thin alkali-based solution. The array substrate is then cleaned using distilled water. Spaced apart source and drain electrodes are then formed on the ohmic contact layer.
The method further includes forming a second insulating layer over the array substrate, and then forming a pixel electrode on the second insulating layer such that the pixel electrode contacts the drain electrode.
Beneficially, the alkali-based solution
Huh Soon-Ku
Kim Hye-Young
Anya Igwe U.
Everhart Caridad
LG. Philips LCD Co. Ltd.
Long Aldridge & Norman LLP
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