Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material
Reexamination Certificate
2000-03-29
2001-11-13
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
Reexamination Certificate
active
06316343
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a transparent conductive film on a substrate of a color filter for liquid crystal displays and a transparent conductive film formed by the method.
2. Prior Art
Oxide indium films with addition of tin (hereinafter referred to “ITO films”) are generally used as excellent transparent conductive films (transparent electrode films) formed on substrates of color filters for liquid crystal displays.
Conventionally known methods for forming such ITO films include a vacuum evaporation method, spattering method, and RF (radio frequency) ion-plating method.
Transparent conductive films for color liquid crystal displays are required to be thin for high resolution and high light transmittance, and also required to have a low specific resistance and high uniformity for increased size and increased response speed.
In forming an ITO film on a surface of a transparent glass plate or a transparent resin plate as a substrate of a color filter for a color liquid crystal display using any of the above methods, in order to avoid thermal deterioration of the color filter which is usually formed of an organic resin such as an epoxy resin or an acrylic resin with a pigment or a dye mixed therein, the formation of the ITO film is carried out with the temperature of the substrate being set to 250° C. or less at or below which the deterioration of the resin forming the color filter does not occur. As a consequence of the low temperature of the substrate, the reaction of indium and oxygen on the substrate and crystallization of a film to be formed are not effected to a sufficient degree, resulting in formation of a film with a small crystal grain size and many defects, i.e. pores. The ITO film thus formed has many defects or pores which capture the carriers, and consequently the film has a reduced carrier electron density and hence an increased specific resistance.
To overcome the above disadvantage, there has been proposed an apparatus which forms an ITO film using an ion plating method. An example of this apparatus is shown in FIG.
1
. In the figure, a vacuum vessel
1
inside which a vacuum chamber
1
a
is defined has a mounting opening
2
formed in a side wall thereof, at which a guide part
3
is mounted on the vacuum vessel
1
. Mounted on the guide part
3
is an arc discharge plasma gun
4
such as a pressure gradient type plasma gun, which serves as discharge plasma generating means constituting a cathode. Further provided on the guide part
3
is a steering coil
5
for guiding a plasma beam. The plasma gun
4
includes a first intermediate electrode
6
and a second intermediate electrode
7
which are concentrically arranged for the convergence of the plasma beam.
The plasma gun
4
further includes an insulating tube
8
, the interior of which communicates with a passage defined by the first and second intermediate electrodes
6
,
7
. Arranged inside the insulating tube
8
is a Mo cylinder
9
formed of molybdenum (Mo), inside which is arranged a Ta pipe
10
formed of tantalum (Ta), with a space between the cylinder
9
and the pipe
10
being partitioned by an annular plate
11
formed of LaB
6
(lanthanum hexaboronite). Mounted on ends of the insulating tube
8
, Mo cylinder
9
and Ta pipe
10
is a conductive plate
12
which has a carrier gas inlet opening
13
formed therein, through which an Ar gas as a carrier gas is introduced and passes through the Ta pipe
10
.
At an upper location within the vacuum chamber
1
a
, a substrate
14
as an object to be processed is supported by a conveyer device
15
. At a lower location within the vacuum chamber
1
a
, a hearth
17
which accommodates a permanent magnet
24
is arranged in opposed relation to the substrate
14
to serve as a main anode. An evaporation material
18
formed of indium oxide with addition of tin is received in the hearth
17
. A magnet case
20
accommodating a permanent magnet
19
is arranged around the hearth
17
via an insulating material, not shown. The permanent
19
and the magnet case
20
constitute an auxiliary anode for correcting the plasma beam direction.
A negative electrode side of a variable voltage power supply
21
is connected to the conductive plate
12
. A positive electrode side of the variable voltage power supply
21
is connected to the first intermediate electrode
6
through a resistor R
1
, as well as to the second intermediate electrode
7
through a resistor R
2
. The positive electrode side of the power supply
21
is also connected to the hearth
17
, and grounded through a resistor R
3
.
A gas inlet opening
22
and a gas discharge opening
23
are formed in another side wall of the vacuum vessel
1
. The gas inlet opening
22
introduces a carrier gas formed of a mixture of argon and oxygen or oxygen. The gas discharge opening
23
discharges the carrier gas within the vacuum chamber
1
a
to the outside.
With the above construction of the conventional ion plating apparatus, when the carrier gas is introduced through the gas inlet opening
22
, a discharge occurs between the first intermediate electrode
6
and the Mo cylinder
9
so that a plasma beam
30
is generated. The plasma beam
30
is guided by the steering coil
5
and the permanent magnet
19
within the magnet case
20
to reach the hearth
17
forming the anode and the magnet case
20
. Accordingly, the evaporation material
18
received in the hearth
17
is Joule-heated by the plasma beam
30
to evaporate. Particles of the evaporated material
18
are ionized while passing the plasma beam
30
and attached to a surface of the substrate
14
that is opposed to the hearth
17
to form a thin film (ITO film) thereon.
FIG. 2
is a vertical sectional view showing details of the substrate
14
with the ITO film formed on the surface thereof. As shown in the figure, a color filter
14
b
for a color liquid display is formed on a transparent glass plate
14
a
, and a protective film
14
c
formed of an organic resin such as an acrylic resin is formed on the color filter
14
b
. The color filter
14
b
is formed of an organic resin such as an acrylic resin with a pigment and a dye mixed therein.
In forming an ITO film which is a transparent conductive film using the conventional ion plating apparatus constructed as above, when the evaporation material
18
is heated by the plasma beam
30
to evaporate, particles of the evaporated material
18
are ionized while passing the plasma beam
30
and attached to the substrate
14
to form a thin film on the surface thereof. Since these particles of the evaporated material
18
are indium atoms, positively ionized indium particles attached to the substrate
14
react with an O
2
component of the carrier gas introduced into the vacuum chamber
1
a
through the gas inlet opening
22
to form the ITO film
14
d
on the surface of the substrate
14
. On this occasion, a vertical magnetic field is formed by the permanent magnet
19
and the magnet case
20
so that the plasma density increases to increase the temperature of electrons, which promotes the reaction of indium and O
2
component of the carrier gas and crystallization thereof. Consequently, the formed ITO film has a sufficient carrier electron density and hence a reduced specific resistance. That is, an ITO film having a specific resistance of 150 &mgr;&OHgr;·cm or less can be obtained.
According to the conventional ion plating apparatus, however, the discharge voltage of the plasma beam
30
that reaches the hearth
17
is so high that positive ions generated when particles of the evaporated material
18
pass the plasma beam
30
are accelerated to a higher degree than required. Consequently, the accelerated particles are implanted into the ITO film being formed on the surface of the substrate
14
at too high a speed, to form defects or pores in the ITO film, resulting in increased film compressive stress (increased internal compressive stress of the ITO film). For example, an ITO film formed at 250° C. or less ha
Aoki Yuichi
Chikugo Ryoji
Mineo Motohisa
Wada Syunji
Yagawa Hiroshi
Hoang Quoc
Nelms David
Nippon Sheet Glass Co. Ltd.
Rossi & Associates
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