Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-10-02
2003-09-16
Whitehead, Jr., Carl (Department: 2813)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S042000, C349S043000
Reexamination Certificate
active
06621545
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a thin film transistor (TFT) panel for a liquid crystal display (LCD) by photolithography and a photolithography method for fabricating thin films, especially to a method to reduce the number of photolithography steps in manufacturing a TFT panel for an LCD.
DESCRIPTION OF THE RELATED ART
An LCD (liquid crystal display) is one of the most popular FPDs (flat panel displays). The LCD has two panels having two kinds of electrodes for generating electric fields and a liquid crystal layer interposed therebetween. The transmittance of incident light is controlled by the intensity of the electric field applied to the liquid crystal layer.
The field-generating electrodes may be formed at each of the panels, or at one of the panel. The panel having at least one kind of the electrodes has switching elements such as thin film transistors.
In general, a TFT (thin film transistor) array panel of an LCD includes a plurality of pixel electrodes and TFTs controlling the signals supplied to the pixel electrodes. The TFT array panel is manufactured by photolithography using a plurality of photomasks, and it goes through five or six photolithography steps to complete the TFT array panel. The high costs and long time that the photolithography process bears makes it desirable to reduce the number of the photolithography steps.
Several manufacturing methods of LCDs using only four photolithography steps are suggested such as in Korean Patent Application No. 1995-189 ('189). The corresponding U.S. patent is U.S. Pat. No. 5,818,551. In the meantime, since an LCD actually requires wires for transmitting electric signals to the TFTs and wire pads for receiving the signals from outside, the full process to complete a TFT array panel requires the step of forming the pads. However, '189 does not disclose how to form the pads.
Other conventional method of manufacturing a TFT array panel using four photolithography steps is disclosed in “A TFT Manufactured by 4 Masks Process with New Photolithography (Chang Wook Han et al., Proceedings of The 18th International Display Research Conference Asia Display 98, pp. 1109-1112, 1998. 9.28-10.1).
Meanwhile, a storage capacitor for sustaining the voltage applied to a pixel is generally provided in the TFT array panel, and the storage capacitor includes a storage electrode and a portion of a pixel electrode as well as a passivation layer interposed therebetween. The storage electrode is made of the same layer as a gate wire, and the portion of the pixel electrode is formed on the passivation layer. The storage electrode is covered with a gate insulating layer, a semiconductor layer and a passivation layer, and most portion of the pixel electrode is formed directly on the substrate in Han et al., Therefore, the pixel electrode should step up the triple layers of the gate insulating layer, the semiconductor layer and the passivation layer, in order to overlap the storage electrode. It may cause a disconnection of the pixel electrode near the high step-up area.
In the meantime, as shown in '189, the conventional photolithography process uses a photoresist (PR) layer. The conventional photoresist layer is exposed to light through a photomask and divided into two sections, one exposed to the light and the other not exposed. The development of the photoresist layer forms the PR pattern having a uniform thickness with the PR layer exposed to the light removed. Accordingly, the etched thickness of the layers under the PR pattern is also uniform. However, Han et al. uses a photomask having a grid, which lowers the amount of light reaching the portion of a positive PR layer thereunder, to form a PR pattern having thinner portions than the other portions. The different thickness of the PR pattern produces the different etching depth of the underlying layers.
Therefore, Han et al. has a problem in forming the grid throughout a wide region, and it is hard to make the etching depth uniform under the grid region, even though the grid is formed throughout the wide region.
U.S. Pat. Nos. 4,231,811, 5,618,643, and 4,415,262 and Japanese patent publication No. 61-181130, etc., which disclose similar methods as Han et al., have the same problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to suggest a novel method for manufacturing thin films using photolithography.
It is another object of the present invention to simplify the manufacturing method of a TFT array panel for an LCD, thereby reducing the manufacturing cost and increasing the productivity.
It is another object of the present invention to etch thin films to a different uniform depths depending on the position, at the same time.
These and other objects are provided, according to the present invention, by forming a contact hole for a gate pad along with at least one other layer.
According to the present invention, a gate wire including a plurality of gate lines, gate electrodes and gate pads, is formed on a substrate having a display area and a peripheral area. A gate insulating layer pattern is formed thereon. A semiconductor pattern is formed on the gate insulating layer, and a ohmic contact pattern is formed on the semiconductor pattern. Then, a data wire including data lines, source and drain electrodes located on the display area, and data pads located on the peripheral area is formed thereon. A passivation layer for channel is formed and a plurality of pixel electrodes connected to the drain electrodes are formed. At this time, the gate insulating layer pattern is formed along with at least one other layer through a photolithography process using a photoresist pattern of which thickness is varying according to location.
It is preferable that the photoresist pattern has a first portion located at the position corresponding to the gate pad, a second portion which is thicker than the first portion and located in the display area, and a third portion which is thicker than the second portion.
The photoresist pattern is formed on the passivation layer. The gate insulating layer pattern, the semiconductor layer pattern and the passivation layer pattern are formed by etching the passivation layer and the semiconductor layer under the first portion of the photoresist pattern, and the second portion of the photoresist pattern at the same time. Then, the second portion of the photoresist pattern to expose the passivation layer thereunder is removed by an ashing process, etching the passivation layer and the gate insulating layer to expose the semiconductor layer under the first portion and to form a first contact hole exposing the gate pad under the first portion by using the photoresist pattern as an etch mask, and removing the semiconductor layer under the second portion by using the photoresist pattern as an etch mask.
At this time, a second contact hole exposing the data pad may be formed in the step of etching passivation layer and the semiconductor layer under the first portion or forming the first contact hole. A third contact hole exposing the drain electrode may be formed in the step of forming the first contact hole or etching the passivation layer and the semiconductor layer under the first portion. The etching step of the passivation layer and the semiconductor layer may be performed by a dry etch of using SF
6
+O
2
or SF
6
+HCl as an etch gas, and the ashing process may be performed by using N
2
+O
2
or O
2
+Ar gas. The semiconductor layer may be made of amorphous silicon, and the first contact hole may be formed by using one of such gases as SF
6
+O
2
, SF
6
+N
2
, CF
4
+O
2
and CF
4
+CHF
3
+O
2
, which have a high etch selectivity between the passivation layer and the semiconductor layer. The semiconductor layer may be removed by a dry etch using Cl
6
+O
2
or SF
6
+HCl+Ar+O
2
as an etch gas. A redundant gate pad and a redundant data pad respectively covering the gate pad and the data pad is formed while forming the pixel
Baek Bum-Ki
Park Woon-Yong
Jr. Carl Whitehead
McGuireWoods LLP
Samsung Electronics Co,. Ltd.
Schillinger Laura M
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