Coating apparatus – Gas or vapor deposition – Running length work
Reexamination Certificate
1999-12-03
2001-11-06
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
Running length work
C118S7230AN, C118S7230MW
Reexamination Certificate
active
06312524
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a plasma CVD apparatus which are used for preparation of, for example, magnetic recording media and other functional thin films, and more particularly to a continuous plasma CVD apparatus and a continuous plasma CVD method which are suitable for forming, at high speed, a broad and uniform CVD thin film of high quality and free from defects.
In the wide variety of the fields of thin film magnetic recording media and various functional media produced using insulation films such as of polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyaramid and polyimide, it is attempted to further provide on these continuous substrates a plasma CVD film such as a protective film, lubricating film or moistureproof film.
When CVD film formation is carried out on such continuous flexible substrates, mass-production becomes possible and sharp reduction of cost can be expected, and for further improvement in productivity, technique of broad film formation at high speed is important.
The most important requirement for the increase of film forming speed is to produce molecular species such as active ions and radical molecules at a high density by supplying a large quantity of energy to plasma and to effectively introduce them into the substrate. Furthermore, in order to obtain films of high quality, a necessary kinetic energy must be given to the ions introduced into the substrate and for this purpose, a bias voltage is applied to the plasma exciting portion and/or substrate side to perform acceleration of ions. On the other hand, when a large quantity of energy is applied to plasma in this way, energy of the plasma naturally migrates to the substrate to heat the substrate. If the substrate is heated, the film forming speed considerably decreases, causing deterioration of film quality and distortion and breakage of the substrate.
In the case of the substrates having electrical conductivity such as those of thin film magnetic recording media and various functional films, furthermore, ionic current flows through the conductive film whereby the substrates are subjected to further heating due to Joule's heat. It is well known that especially when ion introduction amount is increased for increasing film forming speed and, moreover, ion acceleration voltage is increased for the improvement of film quality, the substrates are considerably damaged.
Furthermore, for increasing the productivity, broadening of the width of substrate is necessary together with increase in film forming speed. An important requirement which governs the width of film is uniformity of plasma density and ion acceleration bias voltage. If the plasma density and the bias voltage are ununiform, film thickness and film quality greatly vary in the width direction.
High-speed formation of broad plasma CVD films is very difficult as mentioned above, and especially when a substrate which has electrical conductivity in at least a part thereof and generates Joule's heat upon passing a current is used, the high-speed formation of broad plasma CVD films becomes more difficult and a breakthrough is required.
Many factors for occurrence of heating of substrate are considered, but main factors are heat generation caused by the striking energy of accelerated ions introduced into the substrate and heat generation caused by Joule's heat of ionic current. Among them, the heat generation caused by the striking energy cannot be avoided because the striking energy is necessary for obtaining a film of high quality. On the other hand, the Joule's heat due to ionic current is unnecessary and depends on the method of bias application for acceleration of ions. How to inhibit the heating by ionic current is the most important point for realization of a stable high-speed process.
Next, results of comparative investigation of conventional examples will be explained.
FIG. 28
schematically illustrates the construction of a plasma CVD apparatus which employs ion acceleration method by DC bias as one of conventional examples.
In
FIG. 28
, the numeral
131
indicates a substrate comprising, for example, a flexible synthetic resin film,
132
indicates a unwind roller for continuously feeding the substrate
131
,
133
indicates a DC source connected to the unwind roller
132
,
134
indicates an intermediate roller guiding the substrate
131
,
135
indicates a rotating drum,
136
indicates a plasma tube,
137
indicates a high-frequency coil wound around the plasma tube
136
,
138
indicates a high-frequency electric source which applies a high frequency to the high-frequency coil
137
,
139
indicates an anode provided in the plasma tube
136
,
140
indicates a DC source connected to the anode
139
,
141
indicates a gas inlet formed at the plasma tube
136
, and
142
indicates a wind roller which takes up the substrate
131
.
According to the method which comprises exciting plasma by the high-frequency coil
137
wound around the plasma tube
136
and applying a bias voltage to the substrate
131
having electrical conductivity by the DC source
133
, an ionic current flows through the conductive part of the substrate
131
as shown by arrow
143
.
Furthermore, as shown in
FIG. 28
, in the case of the method of applying a bias voltage from the anode
139
opposite to the side of the substrate
131
with the plasma intervening therebetween, a path for liberating ions from the substrate
131
must be provided in order to prevent the substrate
131
from charging with ion, and an ionic current similarly flows in the direction of arrow
143
.
As mentioned above, except for the case of electric resistance of the substrate being very small or very large, when an ionic current flows through the substrate having electric conductivity, a large quantity of Joule's heat is generated by the ionic current to cause decrease in film forming speed and damage of the substrate.
In order to diminish the heating of substrate caused by the ionic current, there was proposed a means according to which one or a plurality of potential rollers are provided on a film of a cooled rotating drum to localize the ionic current onto only the cooled rotating drum and further to divide the current as shown in FIG. 29 (JP-B-7-105037).
In
FIG. 29
,
151
indicates a substrate comprising a synthetic resin film or the like,
152
indicates a unwind roller for continuously feeding the substrate
151
,
153
indicates an intermediate roller for guiding the substrate
151
,
154
indicates a rotating drum,
155
indicates a plurality of plasma tubes,
156
indicates a high-frequency coil wound around each of the plasma tubes
155
,
157
indicates an anode provided in each of the plasma tube
155
,
158
indicates a DC source connected to the anode
157
,
159
indicates a gas inlet pipe connected to each of the plasma tubes
155
,
160
indicates a wind roller which takes up the substrate
151
, and
161
indicates a potential roller for applying a bias voltage.
According to the apparatus shown in
FIG. 29
, the total quantity of ionic current is the same as in the apparatus shown in
FIG. 28 and a
sharp reduction of heat which flows into the substrate
151
cannot be attained. Thus, the method of applying a bias voltage using a DC source (same as the method of applying a low-frequency bias which can be regarded to be a direct current as for plasma even though it is alternating current) cannot still solve the defect that the film forming speed is limited by ionic current in the method of film formation with a large ion introduction amount.
In order to increase cooling efficiency of substrate, there is proposed a means of enhancing the close contact between the substrate and the rotating drum utilizing the electrostatic adsorption by applying a high DC voltage between the substrate and the rotating drum.
In this DC biasing method, since the substrate
151
moves, the voltage of potential roller
161
must be adjusted by passing electricity through a slip ring or rotary joint
Asano Michio
Kubota Takashi
Kusada Hideo
Mizumura Tetsuo
Ogawa Yoichi
Alejandro Luz L.
Birch & Stewart Kolasch & Birch, LLP
Hitachi Maxell Ltd.
Mills Gregory
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