Active solid-state devices (e.g. – transistors – solid-state diode – Non-single crystal – or recrystallized – semiconductor... – Field effect device in non-single crystal – or...
Reexamination Certificate
2000-03-13
2003-09-02
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Non-single crystal, or recrystallized, semiconductor...
Field effect device in non-single crystal, or...
C257S048000, C257S057000, C257S059000, C257S072000, C349S042000, C349S043000, C349S054000, C349S139000, C349S140000
Reexamination Certificate
active
06614053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an active matrix substrate on which transistors are formed, an electrooptical device using this active matrix substrate, and a method of producing the active matrix substrate. More particularly, the present invention relates to a technique of forming a film quality evaluation region for evaluating films used to form transistors.
2. Description of Related Art
A representative active matrix substrate on which transistors and signal lines are formed is one for use in a liquid crystal display (electrooptical device). Some active matrix substrates of this type include a driving circuit disposed thereon. In this case, a plurality of scanning lines and data lines are disposed on an insulating substrate, and furthermore, a plurality of pixels are disposed in the form of an array at intersections of the scanning lines and data lines. Each pixel includes a pixel electrode and a pixel switching thin film transistor (hereafter referred to as a TFT) connected to a scanning line and a data line. On the insulating substrate, in an area outside an image display area, there are disposed a data line driving circuit for supplying an image signal to the respective data lines and a scanning line driving circuit for supplying a scanning signal to the respective scanning lines. These driving circuits are formed of a plurality of TFTs.
Of these TFTs, each TFT for switching a pixel includes, as shown in FIGS.
5
(A) and
5
(B), a gate electrode
3
a
formed simultaneously with the scanning lines, source regions
1
f
and
1
d
electrically connected via a first contact hole
4
a
formed in a first interlayer insulating film
4
to a source electrode
6
a
which is a part of a data line
30
, drain regions
1
g
and
1
e
electrically connected via a second contact hole
4
a
formed in the first interlayer insulating film
4
to a drain electrode
6
a
which is formed of an aluminum film, or the like, simultaneously with the data lines
30
. A second interlayer insulating film
7
is formed in a layer above the first interlayer insulating film
4
. A third contact hole
8
a
is formed in this second interlayer insulating film
7
, and a pixel electrode
9
a
is electrically connected to the drain electrode
6
d
via the third contact hole
8
a
. The structure described above is also employed for TFTs used to form the driving circuits.
In the active matrix substrate, when various elements, such as the TFT
50
have been formed using a semiconductor process, various characteristics are tested. If the active matrix substrate fails this test, various analyses are performed and the result is fed back. For example, analyses are performed in terms of the impurity concentrations of the source and drain regions and crystallinity of the channel region
1
a
. Conventionally, such an analysis is performed as follows. First, the surface of the sample, on which the TFTs
50
for switching pixels or used in the driving circuits, is lustered so as to successively remove the second interlayer insulating film
7
, the first interlayer insulating film
4
, the gate electrode
3
a
, and the gate insulating film
2
, until the channel
1
a
or the source/drain region is exposed. Thereafter, elemental analysis by way of SIMS (secondary ion mass spectrometory) or X-ray analysis is performed.
In the conventional method of analyzing the source/drain region or the channel region
1
a
, a long time is needed to remove the second interlayer insulating film
7
, the first interlayer insulating film
4
, the gate electrode
3
a
, and the gate insulating film
2
. Although the thickness of a film to be analyzed is as small as 50 nm to 100 nm, it is required to remove an interlayer insulating film having a thickness as large as 1 &mgr;m. To analyze the channel region
1
a
, it is required to remove the gate electrode
3
a
with a thickness of 400 nm. Another problem is that high-accuracy analysis is difficult because the channel region
1
a
of the TFT
50
which is finally exposed after performing long-time lustering has a small area of at most 100 &mgr;m square.
SUMMARY OF THE INVENTION
In view of the above, the present invention to provides an active matrix substrate which allows the film quality of a transistor, such as a TFT, to be evaluated easily and accurately, and also provides an electrooptical device using such an active matrix substrate.
The present invention also provides a method of producing an active matrix substrate having a film quality evaluation region which is formed through substantially the same process as that through which a film of a transistor is formed, without needing an additional process, thereby making it possible to accurately evaluate film quality.
According to the present invention, as described above, there is provided a film quality evaluation region in which a semiconductor film for film quality evaluation is formed of the same layer as the semiconductor film used to form a transistor. Alternatively, a semiconductor film for film quality evaluation and a gate insulating film for film quality evaluation are formed using the same layers as a channel region and a gate insulating film, respectively, of a transistor, whereby the film quality evaluation, such as elemental analysis or crystallinity analysis, of the semiconductor film forming the channel region or the source/drain region of the transistor or an impurity distribution at an interface between the gate insulating film and the channel region, can be performed by analyzing the film quality evaluation region.
In the analysis using the film quality evaluation region, unlike the analysis performed directly upon the transistor, it is possible to immediately start the analysis without having to remove the interlayer insulating film and the gate electrode, because the film quality region is exposed through the opening formed through the interlayer insulating film which is formed in the evaluation region simultaneously with the interlayer insulating film in the transistor region. This makes it possible to easily evaluate the film quality in a short time. The film quality evaluation region can be formed over a large area without influencing the characteristics of the transistor. The large film quality evaluation region allows high-accuracy analysis for various items.
According to an aspect of the present invention, to achieve the above objects, there is provided an active matrix substrate that may include a transistor and a signal line both formed on a substrate. The active matrix substrate may further include a film quality evaluation region including a semiconductor film for film quality evaluation, the semiconductor film for film quality evaluation being formed of the same layer as a semiconductor film used to form the transistor, the film quality evaluation region being disposed at one or more locations on the substrate at which neither the transistor nor the signal line is formed. In the following description, a MIS (metal insulator semiconductor) transistor is employed as the transistor. Note that the MIS transistor is not limited to those whose gate is formed of a metal, but those whose gate is formed of a conductive silicon or any other similar material.
In this active matrix substrate according to the present invention, it is desirable that the semiconductor film for film quality evaluation be exposed through an opening formed in an interlayer insulating film in the evaluation region, the interlayer insulating film in the evaluation region being formed of the same layer as an interlayer insulating film formed above the transistor.
In this active matrix substrate according to the present invention, because the semiconductor film for film quality evaluation is formed in the film quality evaluation region using the same layer as the semiconductor film used to form the transistor, analysis, such as elemental analysis or crystallinity analysis, of the semiconductor film forming the channel region and the source/drain region of the transistor can be performed by ana
Flynn Nathan J.
Oliff & Berridg,e PLC
Sefer Ahmed N.
Seiko Epson Corporation
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