Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-02-11
2003-01-21
Nguyen, Tuan H. (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S072000, C257S059000
Reexamination Certificate
active
06509614
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a structure of a thin film transistor (TFT) and its forming process, and more particularly to a structure of a thin film transistor-liquid crystal display (TFT-LCD) and its forming process.
BACKGROUND OF THE INVENTION
Nowadays, for maturely developing structures of thin film transistor-liquid crystal displays (TFT-LCD), a tri-layer structure of a TFT-LCD becomes the main steam. Compared to a back channel etch (BCE) structure of a TFT-LCD of the last generation, a tri-layer structure additionally includes a top nitride over the semiconductor layer as an etch stopper so that the etching step for defining source/drain and channel regions can be well controlled. Accordingly, the thickness of the active layer can be made to be thinner in the tri-layer structure than in the BCE structure, which is advantageous for the stability of resulting devices and the performance in mass production. However, the provision of the additional etch stopper layer needs an additional masking step, thereby making the process for forming a tri-layer structure relatively complicated.
As for the tri-layer structure of a TFT-LCD, a conventional forming process with six masking steps is illustrated as follows with reference to FIGS.
1
A~
1
G which are cross-sectional views of intermediate structures at different stages. The conventional forming process includes steps of:
i) forming a first conductive layer (made of chromium, tungsten molybdenum, tantalum, aluminum, or copper) on an insulating substrate
10
, and using a first mask and photolithography procedure to etch the first conductive layer for defining a gate electrode
11
, as shown in
FIG. 1A
;
ii) forming a tri-layer structure (usually formed of silicon nitride layer-intrinsic amorphous silicon layer-silicon nitride layer) including a gate insulation layer
121
, a semiconductor layer
122
and an etch stopper layer
123
, and a photoresist layer
124
on the resulting structure of
FIG. 1A
, as shown in FIG.
1
B.
iii) using a second mask and photolithography procedure to etch the etch stopper layer
123
for defining an etch stopper
13
, as shown in
FIG. 1C
;
iv) using a third mask and photolithography procedure to etch the semiconductor layer
122
for defining a channel region
14
, as shown in
FIG. 1D
;
v) forming a doped semiconductor layer (usually made of amorphous silicon) and a data and connection lines layer (usually made of a chromium/aluminum or a molybdenum/aluminum/molybdenum composite metal layers) on the resulting structure of
FIG. 1D
, and using a fourth mask and photolithography procedure to etch the doped semiconductor layer and the data and connection lines layer for defining a source/drain region
15
and a data and connection lines region
16
, as shown in
FIG. 1E
;
vi) forming a passivation layer
17
(usually made of silicon nitride) on the resulting structure of
FIG. 1E
, and using a fifth mask and photolithography procedure to etch the passivation layer for defining tape automated bonding (TAB) openings (not shown), and a contact window
18
, as shown in
FIG. 1F
; and
vii) forming a transparent electrode layer (usually made of indium tin oxide) on the resulting structure of
FIG. 1F
, and using a sixth mask and photolithography procedure to etch the transparent electrode layer for defining a pixel electrode
19
, as shown in FIG.
1
G.
However, the conventional process for forming the tri-layer structure of a TFT-LCD with six masking steps is too complicated.
As known, the number of mask and photolithography procedures directly affects not only the production cost but also the manufacturing time. Moreover, for each mask and photolithography procedure, the risks of misalignment and particulate contamination may be involved so as to affect the production yield. Therefore, the major object of the present invention is to solve the drawbacks of prior art, and further provide a forming process with reduced mask and photolithography procedures.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process for forming a TFT-LCD with reduced mask and photolithography procedures.
It is another object of the present invention to provide a structure of a TFT-LCD with reduced mask and photolithography procedures.
In accordance with an aspect of the present invention, the process for forming a TFT-LCD includes steps of: providing an insulating substrate; forming a transparent electrode layer, a first conductive layer and a first photoresist layer on the insulating substrate; using a first mask and photolithography procedure to etch the transparent electrode layer and the first conductive layer for defining a transparent electrode and a gate electrode, and removing the first photoresist layer; forming an insulation layer, a semiconductor layer, an etch stopper layer and a second photoresist layer on the insulating substrate and the gate electrode, and using a second mask and photolithography procedure to etch the etch stopper layer and the semiconductor layer for defining an etch stopper and a channel region; forming a doped semiconductor layer and a data and connection lines layer, removing the second photoresist layer, and forming a third photoresist layer above the insulating substrate; using a third mask and photolithography procedure to etch the data and connection lines layer, the doped semiconductor layer and the insulation layer for defining a data and connection lines region, a source/drain region and a gate insulating region; forming a second conductive layer above the insulating substrate, and removing the third photoresist layer for defining a conductive region; and forming a passivation layer and a fourth photoresist layer above the insulating substrate, using a fourth mask and photolithography procedure to etch the passivation layer, the conductive region and the gate electrode for defining a passivation region and a pixel electrode, and removing the fourth photoresist layer.
Preferably, the insulating substrate is made of a light-transmitting material.
Preferably, the light-transmitting material is glass.
Preferably, the conductive layer is made of chromium, molybdenum, tantalum, tantalum molybdenum, tungsten molybdenum, aluminum, aluminum silicon, copper or the mixture thereof.
Preferably, the insulation layer is made of silicon nitride, silicon oxide, silicon oxynitride, tantalum oxide, aluminum oxide or the mixture thereof.
Preferably, the etch stopper layer is made of silicon nitride, silicon oxide or silicon oxynitride.
Preferably, the semiconductor layer is made of intrinsic amorphous silicon, micro-crystalline silicon or polysilicon.
Preferably, the doped semiconductor layer is made of highly doped amorphous silicon, highly doped micro-crystalline silicon or highly doped polysilicon.
Preferably, the transparent electrode layer is made of indium tin oxide or indium lead oxide.
Preferably, the data and connection lines layer is made of a chromium/aluminum or a molybdenum/aluminum/molybdenum composite metal layers.
Preferably, the passivation layer is made of silicon nitride or silicon oxynitride.
According to the process for forming a TFT-LCD described above, a process for forming a storage capacitor is performed simultaneously, which includes steps of: using the first mask and photolithography procedure to etch the transparent electrode layer and the first conductive layer for defining a lower electrode of the storage capacitor; using the third mask and photolithography procedure to etch the data and connection lines layer, the doped semiconductor layer and the insulation layer for defining an upper electrode and an insulating region of the storage capacitor; and using the fourth mask and photolithography procedure to etch the passivation layer, the conductive region and the gate electrode for defining a passivation region of the storage capacitor.
Preferably, the storage capacitor is made of metal-insulator-metal or metal-insulator-silicon.
According to the process for forming a TFT-LCD described above, a process for forming
Hannstar Display Corp.
Nguyen Tuan H.
Volpe and Koenig P.C.
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