Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-03-25
2001-11-20
Paladini, Albert W. (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S250000, C251S315040, C251S315040, C438S688000
Reexamination Certificate
active
06320138
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a substrate which has wiring electrically connected to a semiconductor element and showing excellent characteristics, and in particular to a substrate with wiring which has an excellent anti-hillock characteristic, an excellent anti-pinhole characteristic and a low resistance, and is suitable for use in, for example, an active matrix type liquid crystal display device.
There is an active matrix type liquid crystal display device which has, for example, wiring including a scanning line
1
and a data line
2
, etc., a pixel electrode
3
, and a thin film transistor
4
as a switching element located in the vicinity of each intersection of the scanning line
1
and the data line
2
, as is shown in FIG.
10
. The thin film transistor
4
has a gate electrode G connected to the scanning line
1
, a drain electrode D connected to the data line
2
, and a source electrode S connected to the pixel electrode
3
.
FIG. 11
shows a cross section of part of the thin film transistor
4
of FIG.
10
. The scanning line
1
including the gate electrode G (see
FIG. 10
) is formed on a predetermined portion of a glass substrate
11
, an anode oxide film
12
is formed on the surface of the scanning line
1
, and a gate insulating film
13
is formed on the overall surfaces of the lines and the substrate. A semiconductor thin film
14
made of amorphous silicon is formed on that portion of the gate insulating film
13
which corresponds to the gate electrode G. A blocking layer
15
is formed on a center portion of the semiconductor thin film
14
. Ohmic contact layers
16
and
17
made of n
+
-conductivity silicon are formed on upper opposite side portions of the semiconductor thin film
14
and the blocking layer
15
. The drain electrode D and the source electrode S are formed on the ohmic contact layers
16
and
17
, respectively. These electrodes D and S and the data line
2
may be formed simultaneously. The pixel electrode
3
is formed on a predetermined upper portion of the gate insulating film
13
such that it is connected to the source electrode S. A passivation film
18
is formed on the overall upper surface of the resultant structure, except for on the surface of the predetermined portion of the pixel electrode
3
.
It is known that an Al (Aluminum) alloy which contains a high-melting-point metal such as Ti (Titanium) is used as the material of the wiring forming the scanning line
1
with the gate electrode G (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 4-130776). In this case, the high-melting-point metal Ti is contained in Al in order to suppress the occurrence of hillocks, which may well be formed during a heating treatment performed later since Al itself does not have a sufficient thermal resistance. The anti-hillock characteristic is considered to, for example, reduce the breakdown voltage of the gate insulating film
13
on the scanning line
1
including the gate electrode G. If the Ti concentration of the Al—Ti alloy thin film is reduced to lower its specific resistance, occurrence of any hillock and pinhole cannot be suppressed. If, on the other hand, the concentration of Ti is increased, the above drawback can be countered but the specific resistance of the alloy thin film increases. This alloy thin film is not preferable as an electrode or wiring.
BRIEF SUMMARY OF THE INVENTION
It is the object of the invention to provide a wiring substrate with a conductor which can reduce the specific resistance of the substrate to a value equal to or less than the case of using the Al—Ti alloy thin film, and also can suppress the occurrence of hillocks or pinholes.
The inventors of the present invention made various experiments to test the Al—Ti alloy thin film in detail. The experiment's results and our opinion thereon will now be described.
First, the dependency of the specific resistance of the Al—Ti alloy thin film upon the concentration of Ti was tested, and test results as shown in
FIG. 5
were obtained. In
FIG. 5
, the ordinate indicates the specific resistance of the alloy thin film, the abscissa the concentration (atomic %) of Ti, the solid line the specific resistance of an Al—Ti alloy thin film formed, by sputtering or deposition, on a glass substrate which is kept at a room temperature, and the broken line, the one-dot chain line and the two-dot chain line the specific resistances of Al—Ti alloy thin films after heating of the Al—Ti alloy thin film formed at the room temperature, at temperatures of 250° C., 300° C. and 350° C., respectively. As is evident from
FIG. 5
, in all the Al—Ti alloy thin films, the higher the concentration of Ti, the higher the specific resistance. Further, the higher the heat treatment temperature, the lower the specific resistance. Thus, it was confirmed from the experiments that the lower the Ti concentration, the lower the specific resistance of the Al—Ti alloy thin film, and that the higher the heat treatment temperature, the lower the specific resistance.
Moreover, the anti-hillock characteristic of each of the Al—Ti alloy thin films was tested, and test results as shown in
FIG. 6
were obtained. In
FIG. 6
, the ordinate indicates the temperature at which a hillock or hillocks occur. More specifically, the hillock occurrence temperature means a heat treatment temperature at which any hillock with a height of 0.5-1 &mgr;m or more can be observed using an electron microscope with a magnification of about 100 (hereinafter, the hillock occurrence temperature means the same). As is evident from
FIG. 6
, the occurrence of a hillock can be suppressed if the heat treatment temperature is 250° C. and the Ti concentration is 3 atm % or more. In light of the anti-hillock characteristic, it is desirable to set the Ti concentration at 3 atm % or more through the overall process of forming the wiring substrate, when a heat treatment is performed at about 250° C. at highest in the process. In the case of a heat treatment temperature of 250° C. indicated by the broken line in
FIG. 5
, however, the specific resistance is about 18 &mgr;&OHgr;cm or more if the Ti concentration is 3 atm % or more. In other words, when the anti-hillock characteristic is considered, it is not preferable to set the Ti concentration at 3 atm % or less, which means that the specific resistance of the wiring (the scanning line
1
including the gate electrode G) cannot be set at about 18 &mgr;&OHgr;cm or less. On the other hand, more and more reduction of the resistance of wiring has recently been requested with the development of refining techniques, the increase of the numerical aperture, etc. in the field of liquid crystal display devices. To meet the request, attention has been paid to an Al alloy containing a rare earth metal such as Nd, which has an excellent anti-hillock characteristic and a low specific resistance of about 10 &mgr;&OHgr;cm or less (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-45555).
However, the inventors of the present invention made experiments using an Al—Nd alloy thin film, and obtained the following results. First, the dependency of the specific resistance of the Al—Nd alloy thin film upon the Nd (Neodymium) concentration was tested, and test results as shown in
FIG. 7
were obtained. In
FIG. 7
, the ordinate indicates the specific resistance of the alloy thin film, and the abscissa the Nd concentration. Further, the solid line indicates the specific resistance, with respect to the Nd concentration, of an Al—Nd alloy thin film formed, by sputtering or deposition, on a glass substrate which is kept at a room temperature, and the broken line, the one-dot chain line and the two-dot chain line the specific resistances of Al—Nd alloy thin films after heating of the Al—Nd alloy thin film formed at the room temperature, at temperatures of 250° C., 300° C. and 350° C., respectively. As is evident from
FIG. 7
, in all the Al—Nd alloy thin films, the higher the concentration of Nd, the higher the specific resistance. Further, when the Nd concentration is,
Kamiya Kenji
Shiota Junji
Casio Computer Co. Ltd.
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Paladini Albert W.
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