Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – On insulating substrate or layer
Reexamination Certificate
1999-09-30
2002-10-15
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
On insulating substrate or layer
C257S059000
Reexamination Certificate
active
06465285
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an a-Si TFT liquid crystal device, a liquid crystal display panel and a method of manufacturing them.
2. Description of Related Art
A conventional method for manufacturing an a-Si TFT liquid crystal display panel will now be described with regard to one liquid crystal device portion. As shown in FIGS.
15
(
a
) and
15
(
b
), a gate electrode
4
is first formed into a predetermined shape on a glass substrate
2
by a general technique. Then, as shown in
FIG. 16
, a gate insulating film
6
, a channel layer
8
and a SiN
x
film
10
serving as an etching stopper layer are successively stacked on the entire surface of the glass substrate
2
. As shown in FIGS.
17
(
a
),
17
(
b
) and
17
(
c
), after coating a resist on the SiN
x
film
10
, the glass substrate
2
is exposed to light from its back surface side by using the gate electrode
4
in the predetermined shape as a light shielding mask, and is subsequently subjected to stepper exposure from its front surface side by using a reticle, and then the resist is developed. Thereafter, the SiN
x
film
10
other than a portion working as an etching stopper (channel protecting film)
14
is etched with diluted hydrofluoric acid, and then the resist is removed.
It is noted that the etching stopper
14
can be basically formed through a single exposing step in which the glass substrate
2
is subjected to the stepper exposure from its front surface side by using a reticle. In this conventional manufacturing method, however, the etching stopper
14
is formed through a two-stage exposing step: a stage of exposing the substrate
2
to light from its back surface side and a stage of exposing the substrate
2
to light from its front surface side. This is because, when the etching stopper
14
is formed through a single-stage exposing step in which the glass substrate
2
is exposed to light from its front surface side, the alignment with the gate electrode
4
tends to be shifted and cannot be stabilized. In contrast, if the gate electrode
4
is effectively used in the two-stage exposing step, the etching stopper
14
can be disposed at the center of the gate electrode
4
in a self-alignment manner. This results in providing a source electrode
26
and a drain electrode
28
symmetrically about the gate electrode
4
, and also in reducing overlap areas between the gate electrode
4
and the drain electrode
28
and between the gate electrode
4
and the source electrode
26
. Thus, the two-stage exposure can improve a transistor characteristic.
However, in manufacturing a liquid crystal display panel, there are a large number of complicated manufacturing steps, and in addition, each steps requires time-consuming work. Therefore, reduction in the number of processes not only improves the productivity but also reduces the manufacturing cost of a liquid crystal display panel in which the process cost accounts for a large proportion.
After being developed, the resist used for forming the etching stopper
14
has a size of approximately 20×10 &mgr;m per pixel, and such rectangular resists are arranged side by side over the entire surface of an array substrate. Since the area of each resist is thus small, its adhesion to the underlying nitride film (i.e., the SiN
x
film) is low, and hence, the resist is apt to be easily peeled off. When the resist is peeled off, the etching stopper
14
cannot be properly formed, which leads to a transistor failure.
When the etching stopper layer
10
is etched with diluted hydrofluoric acid, the layer
10
is generally over-etched so as not to leave an insufficiently etched portion. However, excessive over-etching makes the side surface of the etching stopper
14
be inclined inward at the foot thereof, resulting in the formation of a “concave”
15
, which is hidden in a top view as shown in FIG.
17
(
c
). When films and/or foreign matter to be deposited in subsequent steps are attached to the concave
15
, they cannot be removed through cleaning and etching. As a result, as shown in
FIG. 18
, a leakage current flows between the source electrode
26
and the drain electrode
28
formed on the etching stopper
14
, which leads to a leakage failure of the transistor.
SUMMARY OF THE INVENTION
As the result of researches to remove the above disadvantages, the present inventors have eventually found the present invention. An object of the present invention is to reduce the number of steps, especially the number of exposing steps in manufacture of a liquid crystal device, so as to improve the productivity and reduce the manufacturing cost.
Another object of the present invention is to prevent a failure of a transistor related to an etching stopper portion, so as to improve the yield and the quality of a liquid crystal display panel.
The liquid crystal device of the present invention comprises an etching stopper whose two pairs of opposite side surfaces are inclined at different angles. Specifically, the two pairs of opposite side surfaces of the etching stopper of the liquid crystal device are respectively etched in different steps, and hence, they are generally inclined at different angles.
Alternatively, the liquid crystal device of the present invention comprises an etching stopper, one of opposite side surfaces of which is at substantially right angles to the substrate or tapers away from the substrate. When a side surface extending along current flow is oppositely tapered, a leakage current can be caused owing to a remaining impurity and the like. Therefore, such a side surface is desired to be at right angles or normally tapered. On the other hand, when a side surface extending perpendicularly to the current flow (namely, a side surface covered with a source electrode and a drain electrode) is oppositely tapered and is not controlled, the overlap area between the gate electrode and the source (or drain) electrode can be varied, resulting in varying the parasitic capacitance of each device. Accordingly, such a side surface is preferably controlled to be at right angles or to be normally tapered. The side surface extending perpendicularly to the current flow can be also formed into a normally tapered shape through wet etching in the present invention because the covering area of the etching stopper can be large so as to reduce the over-etching amount attained when the etching is almost completed.
In the liquid crystal device of the present invention, at least one side surface of an etching stopper extending perpendicularly to current flow, namely, at least one side surface not covered with the source electrode or the drain electrode, is at substantially right angles to the substrate or tapers away from the substrate. Accordingly, no attachment such as an insufficiently etched film and an impurity remains on the etching stopper portion, resulting in preventing a leakage current from flowing between the source electrode and the drain electrode.
Alternatively, the method of manufacturing a liquid crystal display panel of the present invention comprises at least a step of simultaneously etching an etching stopper and a source/drain layer. This manufacturing method makes it possible to eliminate a concave of the etching stopper, which is formed in the channel width direction as a result of excessive over-etching, and hence, a leakage current can be prevented from flowing between the source electrode and the drain electrode.
Moreover, in the alternative method of manufacturing a liquid crystal display panel according to the present invention, a gate insulating film, a channel layer and an etching stopper layer are formed on a transparent substrate bearing a gate electrode, and the substrate is exposed to light from its back surface side by using the gate electrode as a light shielding mask by a photography technique. Then, the resist is developed, and the etching stopper layer is etched, and thereby an etching stopper is formed. This manufacturing method makes it possible to form the etching stopper through an o
Machida Masahiko
Tokuhiro Osamu
Ueda Hiroyuki
LandOfFree
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