Tri-layer process for forming TFT matrix of LCD with gate...

Details Tri-layer process for forming TFT matrix of LCD with gate... Tri-layer process for forming TFT matrix of LCD with gate...

2000-09-06

2002-09-10

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making field effect device having pair of active regions...

On insulating substrate or layer

C438S609000

Reexamination Certificate

active

06448117

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a process for forming a thin film transistor (TFT) matrix for a liquid crystal display (LCD), and more particularly to a simplified tri-layer process for forming the TFT matrix with reduced masking steps. A part of gate metal layer around pixel electrodes functions as a black matrix.
BACKGROUND OF THE INVENTION
For conventional manufacturing processes of a TFTLCD, a tri-layer process and a back channel etch (BCE) process are main streams for forming the TFT matrix. Compared to a BCE structure, a tri-layer structure additionally includes an top nitride over the semiconductor layer as an etch stopper so that the etching step for defining a source/drain and channel region 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 performance in mass production. However, the provision of the additional etch stopper layer needs an additional masking step, thereby making the tri-layer process relatively complicated.
Conventionally, six to nine masking steps are required for either a BCE process or a tri-layer process. After the formation of the TFT matrix, a step of providing a black matrix around each pixel electrode region is generally required to improve the performance of the LCD. The provision of the black matrix after the process, however, will have difficulty in alignment.
On the other hand, the count of photo-masking and lithography steps directly affects not only the production cost but also the manufacturing time. Moreover, for each photo-masking and lithography step, the risks of mis-alignment and contamination may be involved so as to affect the production yield. Therefore, many efforts have been made to improve the conventional processes to reduce masking steps.
For example, for a BCE structure, U.S. Pat. Nos. 5,346,833 and 5,478,766 issued to Wu and Park et al., respectively, disclose 3 and/or 4-mask processes for making a TFTLCD, which are incorporated herein for reference. By the way, it is to be noted that the 3-mask process for each of Wu and Park et al. does not include the step of forming and patterning of a passivation layer. If a passivation layer is required to assure of satisfactory reliability, the count of photo-masking and lithography steps should be four. Further, Wu and Park et al. use an ITO layer, which is integrally formed with the ITO pixel electrode, as the connection line between the TFT unit and the data line so that the area of the TFTLCD is limited due to the high resistivity of ITO.
As for the tri-layer structure, a conventional 6-mask process 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 process includes steps of:
i) applying a first conductive layer onto a glass substrate
10
, and using a first photo-masking and lithography procedure to pattern and etch the first conductive layer to form an active region
11
consisting of a scan line and a gate electrode of a TFT unit, as shown in
FIG. 1A
;
ii) sequentially forming tri-layers including an insulation layer
121
, a semiconductor layer
122
and an etch stopper layer
123
, and a photoresist
124
on the resulting structure of
FIG. 1A
, as shown in FIG.
1
B.
iii) using a second photo-masking and lithography procedure to pattern and etch the etch stopper layer
123
to form an etch stopper
13
which have a shape similar to the shape of the gate electrode, as shown in
FIG. 1C
;
iv) using a third photo-masking and lithography procedure to pattern and etch the semiconductor layer
122
to form a channel structure
14
, as shown in
FIG. 1D
;
v) sequentially applying a doped semiconductor layer and a second conductive layer on the resulting structure of
FIG. 1D
, and using a fourth photo-masking and lithography procedure to pattern and etch them to form source/drain regions
15
and data and connection lines
16
, as shown in
FIG. 1E
;
vi) applying a passivation layer
17
on the resulting structure of
FIG. 1E
, and using a fifth photo-masking and lithography procedure to pattern and etch the passivation layer
17
to create tape automated bonding (TAB) openings (not shown), and create a contact window
18
, as shown in
FIG. 1F
; and
vii) applying a transparent electrode layer on the resulting structure of
FIG. 1F
, and using a sixth photo-masking and lithography procedure to pattern and etch the transparent electrode layer to form a pixel electrode
19
, as shown in FIG.
1
G.
Six masking steps, however, are still too complicated.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a reduced mask process for forming a thin film transistor (TFT) matrix for a liquid crystal display (LCD), in which the count of photo-masking and lithography steps can be reduced to four.
Another object of the present invention is to provide a simplified process for forming a thin film transistor (TFT) matrix for a liquid crystal display (LCD), in which a part of gate metal layer around a pixel electrode functions as a black matrix.
A further object of the present invention is to provide a tri-layer process for forming a thin film transistor (TFT) matrix for a liquid crystal display (LCD), in which the connection line between a TFT unit and a data line has a relatively low resistivity compared to the ITO connection line so as to be suitable for a large-area TFTLCD.
According to a first aspect of the present invention, a process for forming a thin film transistor (TFT) matrix for a liquid crystal display (LCD) includes steps of providing a substrate made of an insulating material; successively forming a transparent conductive layer and a first conductive layer on a first side of the substrate, and using a first masking and patterning procedure to remove portions of the transparent conductive layer and the first conductive layer to define a pixel electrode area, a scan line and a gate electrode of a TFT unit; successively forming an insulation layer, a semiconductor layer, an etch stopper layer, and a photoresist layer on the first side of the substrate; providing an exposing source from a second side of the substrate opposite to the first side by using a remaining portion of the first conductive layer as shields to obtain an exposed area and an unexposed area; removing the photoresist, the etch stopper layer and the semiconductor layer of the exposed area so that the remaining portions of the etch stopper layer and the semiconductor layer in the unexposed area have a specific shape substantially identical to the shape of the remaining portion of the first conductive layer, by which a channel region is defined; using a second masking and patterning procedure to further remove portions of the etch stopper layer, the semiconductor layer and the insulation layer to form a contact via accessible to the first conductive layer; successively forming a doped semiconductor layer and a second conductive layer on the substrate, and using a third masking and patterning procedure to remove portions of the second conductive layer and the doped semiconductor layer to define data and connection lines and source/drain regions of the TFT unit; and forming a passivation layer on the substrate, and using a fourth masking and patterning procedure to remove portions of the passivation layer, the etching stopper layer, the semiconductor layer and the insulation layer in the pixel electrode area to expose the transparent conductive layer as a pixel electrode.
When the exposing source is a light radiation, the insulating material is a light-transmitting material such as glass.
Preferably, the first conductive layer and the second conductive layer are formed of chromium, molybdenum, tantalum molybdenum, tungsten molybdenum, tantalum, aluminum, aluminum silicide or copper. More preferably, a specific etching selectivity between the first conductive layer and the second conductive layer

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