(1) Field of the Invention
This invention relates to an induction coil for generating plasma, a plasma generator and a plasma generating method.
(2) Description of the Related Art
A plasma generator is provided as a plasma source (Inductive Plasma Source:IPS) to be used in a device for a semiconductor production or an etching, a surface treatment and vapor deposition using plasma. For example, the plasma generator comprises of a cylindrical chamber and an induction coil wound around the cylindrical chamber spirally. The other known plasma generators comprises of a planar spiral induction coil in the upper part of the chamber (cf. U.S. Pat. No. 4,948,458).
In such a plasma generator, processing gas is supplied in the chamber. In addition, when a high frequency (RF) electricity is supplied to the induction coil, the induction coil generates plasma in the chamber by circular eddy current.
There were following problems with the plasma generator using such induction coil. When a high frequency electricity is supplied to the induction coil, different electric potential is generated in each position on the coil due to the high frequency electricity along the induction coil. Then capacity characteristics electric current (capacitive current) is generated between each different positions of the electric potential. Such phenomenon causes heterogeneous electricity concentration in the chamber of the plasma generator.
FIG. 7 is a vertical section view showing an example of the conventional plasma generator.
The figure shows a cylindrical chamber 1 which generates plasma in itself, and an induction coil 2 which is wound up spirally in the cylindrical chamber 1. The induction coil 2 is shown with the sectional position only to simplify illustration. In addition, plasma processing space 3 and board support pedestal 4 in the space 3 are shown beneath the chamber 1.
Board support pedestal 4 supports a board 5 which is the object of the plasma processing. One end 2a of the both ends of the induction coil 2 is connected to high frequency power supply 6, and the other end 2b is connected to a ground. Then a potential difference occurs between these both ends 2a,2b, and capacitive current due to the positional relationship of both ends flows in the chamber 1 which is a plasma generating space.
The figure schematically shows general capacity characteristics current (the sum of a capacitive current flown from each position of the induction coil 2) generated in the chamber 1 as D.
The capacitive current generated as mentioned above causes inhomogeneity of the electric field in the chamber, and further causes inhomogeneity (non-uniformity) of the plasma generated in the chamber.