Concentric Spread Plasma Source.

A new microwave plasma source termed "concentric spread plasma (CSP)" is presented. By mounting an inner conductor of the coaxial waveguide perpendicular to and directly on a quartz plate, the CSP source can generate a disk-shaped plasma (electron density >3.8×1017 m-3) with high stability below the quartz plate that faces the wafers, regardless of the process conditions. One of the notable features of the CSP source is the concentric expansion of the plasma with increasing microwave power. The CSP is generated by the following mechanism (process): (1) the plasma itself becomes a part of the waveguide for microwave, (2) the microwaves are transmitted concentrically in the quartz plate from its center toward its outer circumference, and (3) the CSP is generated by Joule heating caused by the surface current of the microwave flowing in the plasma. In short, the plasma is self-guided.