Electric heating – Metal heating – By arc
Reexamination Certificate
2000-02-11
2001-07-31
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121400, C219S121520, C156S345420, C118S7230MW, C204S298150
Reexamination Certificate
active
06268582
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The invention relates to an electron cyclotron resonance plasma chemical vapor deposition apparatus (hereinafter referred to as ECR plasma CVD apparatus) suitable for forming a protective membrane or layer for, for example a magnetic disc of a hard disc recording apparatus.
It has been known that a fine and uniform protective membrane, i.e. film or layer, can be obtained through combined use of an ECR plasma CVD technique and an RF base plate bias system, and the technique has been used for forming a protective membrane in a post process in manufacturing a magnetic head. In case a magnetic disc for a hard disc recording device is formed of an aluminum disc, the RF base plate bias system is employed in the ECR plasma CVD apparatus in its post process, as well, so that a high quality protective membrane or layer can be formed. In this case, in order to form the membranes on both surfaces of a base plate or substrate at the same time regardless of a shape of a base plate holder, i.e. claws, it is suitable to adopt a system where a pulse-superposed DC bias is applied to the base plate.
However, in the conventional ECR plasma CVD apparatus having the bias application system, there has been a problem that the membrane can not be formed on a non-conductive glass base plate. In other words, in the recent magnetic disc market, since a higher density is required, glass is used as the base plate material. However, the glass base plate can not cope with this situation.
More specifically, since the glass base plate is non-conductive, DC bias can not be applied thereto. Further, in case of a base plate holder having a craw structure used for preventing damage or contamination which may occur on the base plate surface, since a bias distribution greatly depends on the claw structure of the base plate holder, a uniform membrane or layer is not obtained. Thus, the RF bias can not be employed either. It is considered that the bias need not be applied to the base plate at all, but the obtained membrane is not a fine membrane, so that it is not suitable as the protective membrane.
The present invention has been made in view of the above problems of the conventional ECR plasma CVD apparatus, and an object of the invention is to provide an ECR plasma CVD apparatus, wherein a uniform membrane can be formed on a non-conductive base plate or substrate, such as a glass base plate.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To attain the above objects, an ECR plasma CVD apparatus of the invention is formed of a cavity having an electromagnetic coil therearound, into which a microwave is introduced, for producing ECR plasma; a vacuum chamber connected to the cavity for taking out the plasma therein from the cavity; a base plate holder for holding a base plate or substrate; an electrode plate disposed in the vacuum chamber on a side opposite to the cavity and arranged parallel to the base plate with a predetermined space therebetween; and a high frequency current applying device for applying a high frequency current to the electrode plate.
The base plate holder may be located in a state such that an electric potential is not applied to the base plate in the vacuum chamber.
The electrode plate is disposed on a back surface side of the base plate, i.e. on the side opposite to the cavity for producing the ECR plasma, parallel to the base plate with a predetermined space between the base plate and the electrode plate in the vacuum chamber. On the other hand, the base plate is held in a state where the electric potential is not applied in the vacuum chamber, i.e the base plate is electrically floated. Therefore, in case a high frequency current is applied to the electrode plate, the high frequency current is also applied to the base plate through an electrostatic coupling between the electrode plate and the base plate. Thus, a high frequency bias can be applied to the base plate without contacting.
On the other hand, the base plate holder may be connected to a resistance so that the base plate in the vacuum chamber is grounded through the resistance. In this case, the base plate in the vacuum chamber is held in a predetermined electric potential. Therefore, in case a high frequency current is applied to the electrode plate, the high frequency current is also applied to the base plate through an electrostatic coupling between the electrode plate and the base plate. Since the base plate holder is grounded through the resistance, ions entering into the base plate escape to the ground, so that the base is prevented from being charged up.
In the invention, since the electrode plate and the base plate are disposed parallel to each other with the predetermined space therebetween, uniform high frequency bias can be applied on the surface of the base plate to thereby form a uniform CVD membrane or layer on the surface of the base plate. Since the high frequency bias is applied to the base plate without contacting, the back surface of the base plate is not scratched or damaged. Therefore, when the back surface of the base plate is arranged to face the cavity and the CVD membrane forming is carried out, good CVD membranes can be obtained on both surfaces of the base plate.
REFERENCES:
patent: 5476182 (1995-12-01), Ishizuka et al.
patent: 5976327 (1999-11-01), Tanaka
patent: 6056848 (2000-05-01), Daviet
Akita Noritaka
Ishii Satoko
Kanesaka & Takeuchi
Paschall Mark
Shimadzu Corporation
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