Active solid-state devices (e.g. – transistors – solid-state diode – With means to control surface effects – Insulating coating
Reexamination Certificate
2000-05-08
2001-06-26
Ngô, Ngân V. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
With means to control surface effects
Insulating coating
C257S059000, C257S072000, C257S350000, C257S642000, C257S643000
Reexamination Certificate
active
06252297
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an array substrate, liquid crystal display device and their manufacturing method. More specifically, the invention relates to an array substrate having an inter-layer insulating film thick enough to suppress cross talk or coupling capacitance between wiring lines, preventing step-off breakage of electrodes at contact holes, and having a sufficient reliability; a liquid crystal device using the array substrate; and their manufacturing method.
The demand for high integration has progressively become strong regarding liquid crystal display devices such as an active matrix type display device. That is, it is required to make a number of various electronic elements and wiring lines in an extremely limited space.
To meet the requirement, multi-layer technologies are being brought into use. They are methods for stacking semiconductor layers and wiring layers via inter-layer insulation films. Multi-layer technologies enable to stack electronic devices and wiring lines without increasing the device area. Moreover, by making contact holes in the inter-layer insulating films to electrically connect upper and lower layers, complex wiring can be readily realized within a limited device area.
FIG. 12
is a schematic cross-sectional view of an array substrate
130
of a liquid crystal display device made by the multi-layer technique. The array substrate
130
shown here includes a poly-silicon (poly-crystalline silicon) layer
136
formed on a glass substrate
132
via an under-coat layer
134
. A gate electrode
140
and an auxiliary capacity line
142
form a transistor and a capacitor. The source electrode
146
of the transistor is formed on an insulating film
144
. The pixel electrode
154
is connected to the contact electrode
148
of the transistor via a contact hole
150
a
formed in the insulating film
150
. A multi-layer technique is used in the layer under the source electrode
146
and the layer under the pixel electrode
154
.
However, when a metal electrode and a semiconductor layer are stacked via an inter-layer insulating film as shown in
FIG. 12
, so-called cross talk occurs and causes an interference between signals which cannot be neglected. Moreover, an electrode layer and a semiconductor layer confronting with each other via an insulating film form a capacitor, and produces a coupling capacitance which causes problems, such as decrease of the response speed of the device.
For example, in the array substrate
130
shown in
FIG. 12
, the source electrode
146
supplies different signals as a signal line to other transistors not shown. However, as shown in
FIG. 12
by the symbol A, the source electrode
146
and the pixel electrode
154
locally overlap via the inter-layer insulating film
150
, and cross-talk or coupling capacitance occur in the overlapping portion. This causes problems, such as increase of noise components in a video signal, decrease of the video display quality due to a slow-down of the driving speed, and so on.
Additionally, wiring layers and other conductive layers on and under an inter-layer insulating film are patterned in many cases. Therefore, as the number of stacked layers increases, the surface unevenness becomes prominent, and makes it more difficult to form a multi-layered structure.
In order to prevent these problems, namely, an increase in cross-talk, coupling capacitance and surface unevenness, the inter-layer insulating film must be thick. However, conventional inter-layer insulating films made of inorganic materials are subject to cracking or peeling when they are thicker than hundreds of nm, and are unsuitable for use as thick films. On the other hand, inter-layer insulating films made of organic materials can be stacked thick, but cannot promise a sufficient reliability due to their high moisture permeability.
Another problem contained in multi-layered structures s step-off breakage of conductive layers at contact holes. Namely, when a conductive layer is stacked on an inter-layer insulating film having a contact hole, the thickness of the conductive layer becomes thinner on the inner wall surface of the contact hole, and readily broken there. For example, in
FIG. 12
, step-off breakage of the pixel electrode
154
is liable to occur at a position of the contact hole
150
a
shown by the arrow B. Step-off breakage inevitably causes insufficient connection between conductive layers resulting in low-quality video images of a liquid crystal display device. Step-off breakage more often occurs as the inter-layer insulating film
150
becomes thicker.
To prevent step-off breakage, the pixel electrode
154
must be thick. In a liquid crystal display deice, however, the pixel electrode
154
is typically a transparent electrode, and it is difficult to increase the thickness of the pixel electrode
154
due to a restriction by materials or its manufacturing process. Additionally, a thick conductive layer usually promotes the surface unevenness, and makes it difficult to form a multi-layered structure.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a reliable array substrate having an inter-layer insulating film having a sufficient thickness and preventing step-off breakage of a conductive layer at a contact hole.
Another object of the invention is to provided a liquid crystal display device using such a reliable array substrate.
Another object of the invention is to provide a method for manufacturing the array substrate and the liquid crystal display device.
According to the invention, there is provided an array substrate comprising a first conductive layer stacked on a substrate; a first inter-layer insulating film having a first hole; and a second inter-layer insulating film having a second hole, in which the inner wall surface of the first hole is covered by the wall surface of the second hole substantially concentric with the first hole so that the first inter-layer insulating film is not exposed to the inner wall surface of the second hole. Thus, the entire inter-layer insulating film can be stacked thick enough to decrease cross talk and coupling capacitance between conductive layers, and step-off breakage of the second conductive layer can be prevented. Using the array substrate, a reliable liquid crystal display device can be realized.
The first inter-layer insulating film is made of an inorganic material, and the second inter-layer insulating film is made of an organic material, so as to form an entirely thick inter-layer insulating film having a contact hole with a moderately angled inner wall surface.
When the second hole has a tapered configuration at its opening end and entirely covers the material of the first inter-layer insulating film with the material of the second inter-layer insulating material in the hole, step-off breakage of the second conductive layer is effectively prevented.
The second hole is preferably shaped so that the steepest portion of its inner wall surface makes an angle not larger than 70 degrees relative to the base plane to form a gently sloping contact hole and to effectively prevent step-off breakage of the second conductive layer.
The shape of the second hole may be circular, rectangular or polygonal to provide a sufficient contact area in a fine sizing rule.
The second hole may have an opening end forming a curved plane to prevent step-off breakage there.
Especially when the curved plane has a radius of curvature not smaller than 1×10
−8
m and not larger than radium 1×10
−4
m, step-off breakage can be prevented more effectively.
The second inter-layer insulating film is preferably stacked thicker than the fist inter-layer insulating film to increase the distance between the first conductive layer and the second conductive layer large enough to prevent cross talk or coupling capacitance.
By using the first conductive layer as the output terminal of switching elements, making the first inter-layer insulating film of a material containing at least one of silicon nitride and silicon oxide,
Kemmochi Masato
Shoji Masato
Kabushiki Kaisha Toshiba
Ngo Ngan V.
Pillsbury & Winthrop LLP
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