Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
2002-05-06
2003-05-06
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C438S149000, C438S160000
Reexamination Certificate
active
06558992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a method to fabricate a flat panel display with thin film transistors. In particular, the present invention relates to a liquid crystal display (hereinafter LCD) formed using the light from the back of a substrate for exposure to simplify the fabricating process.
2. Description of the Related Art
The conventional active matrix LCD comprises a plurality of pixel electrodes and switching devices, for example, thin film transistors (hereinafter TFT). The pixels are defined by connected gate lines and data lines. Each pixel comprises a storage capacitor and a pixel electrode connected to the switching devices.
The conventional fabricating process of the TFT of LCD comprises the following steps. First, in
FIG. 1A
, a first metal film is formed on a transparent substrate
40
. Next, a first mask pattern is used to form the gate metal line
42
on the first metal film. Next, in
FIG. 1B
, an insulating layer
44
a
is formed on the substrate
40
. Next, an amorphous silicon layer
44
b
is formed on the insulating layer
44
a
. Next, an n-type doped layer
44
c
is formed on the amorphous silicon layer
44
b
. Next, a conductor layer
46
is formed on the n-type doped layer
44
c
. Next, a photoresist layer
48
is formed on the conductor layer
46
. Next, in
FIG. 1C
, patterns are defined by performing exposure with a second mask and a photo etching process. This step forms an island structure
52
composed of the amorphous silicon layer
44
b
, the n-type doped layer
44
c
, and the conductor layer
46
using the photoresist layer
48
a
on the gate metal line
42
. Next, in
FIG. 1D
, the n-type doped layer
44
c
and the conductor layer
46
on the gate metal line
42
are removed by performing exposure with a third mask and photo etching process to form a channel
53
, the drain electrode
54
and a source electrode
56
. Next, a protecting thin-film and a second photoresist layer are formed. In
FIG. 1E
, a protecting layer
58
is formed by performing exposure with a fourth mask and photo etching process. The protecting layer
58
covers the drain electrode
54
, the source electrode
56
, the amorphous silicon layer
44
b
, and the insulating layer
44
a
. The protecting layer
58
further comprises a plurality of openings (
58
a
,
58
b
). The drain opening
58
a
is on the drain electrode
54
, and the source opening
58
b
is on the source electrode
56
. Finally, in
FIG. 1F
, the pixel electrode comprises a drain pixel electrode
62
and a source pixel electrode
64
. The drain pixel electrode
62
contacts the drain electrode
54
through the drain opening
58
a
and the source pixel electrode
64
contacts the source electrode
56
through the source opening
58
b.
However, the conventional process requires five performances of photo etching process. The cost and efficiency can be greatly improved if the steps of the photo etching process can be reduced to four.
SUMMARY OF THE INVENTION
To achieve the above-mentioned object, the method to fabricate thin film transistors of a flat panel display comprises the following steps. First, a gate metal line is formed on the substrate. Next, an insulating layer, a semiconductor layer, a doped silicon layer, and a signal metal line are formed on the substrate and the gate metal line. Next, the doped silicon layer and the signal metal line are defined to form a drain electrode and a source electrode, then a channel between the drain electrode and the source electrode is defined. Next, a photoresist layer is formed on the semiconductor layer, the drain electrode, the source electrode, and the channel. Next, the photoresist layer is exposed by the light from the bottom of the substrate, and then the exposed photoresist layer is removed. Then, the semiconductor layer is removed using the remaining photoresist layer as a mask to form an island structure containing the semiconductor layer, the doped silicon layer, the drain electrode, and the source electrode. Next, the photoresist layer is removed and a protecting layer is formed on the insulating layer, the drain electrode, the source electrode, and the semiconductor layer. The protecting layercomprises an opening on the drain electrode or source electrode. Finally, a pixel electrodeis formed on the protecting layer, wherein the pixel electrode contacts the drain electrode through the opening.
Further, the method to fabricate thin film transistors of a flat panel display comprises the following steps. First, a gate metal line is formed on the transistor region of the substrate. Next, an insulating layer, a semiconductor layer, a doped silicon layer, and a signal metal line are formed on the gate metal line. Next, the doped silicon layer and the signal metal line are defined to form a drain electrode and a source electrode, and a channel is defined between the drain electrode and the source electrode. Next, a photoresist layer is formed on the semiconductor layer, the drain electrode, the source electrode, and the channel. Next, the photoresist layer is exposed by the light from the bottom of the substrate, then the exposed photoresist layer is removed. Next, the semiconductor layer is removed using the remaining photoresist layer as a mask to form an island structure containing the semiconductor layer, the doped silicon layer, the drain electrode, and the source electrode. Next, the photoresist layer is removed, and a pixel electrode is formed on the insulating layer and the drain electrode, wherein the pixel electrode covers the drain electrode. Finally, a protecting layer is formed on the drain pixel electrode and the insulating layer.
The characteristic of the present invention is that the method to fabricate the TFT of a flat panel display includes four photo etching processes and a single back-exposure step. The gate is formed by the first photo etching process. The source and the drain are formed by the second photo etching process. Next, the exposure is performed from the back of the substrate to form an island structure. Then, a protecting layer is formed by the third photo etching process. Finally, the pixel electrode is formed by the fourth photo etching process.
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Au Optronics Corp.
Kennedy Jennifer M.
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