(A) study on the influence of microwave propagation mode upon the power absorption and uniformity in ECR plasma

Abstract

Electron Cyclotron Resonance(ECR) plasma system was developed which can be used for deposition and etching without substrate heating and plasma damages. In this system, half of a rotary joint is used to couple rectangular waveguide to the circular waveguide, allowing us an easy mode selection between $TE_{11}$ and $TM_{01}$. So microwave can propagate in $TE_{11}$ or $TM_{01}$ mode selectively using waveguide coupler as proved by model experiment. And the linearity of magnetic field is also shown. We explained the mechanisms of ECR plasma reactors such as microwave propagation in the plasma, power absorption and losses, and plasma in the divergent magnetic field. We suggest a new way to characterize the turning point magnetic field from the simple measurement of the plasma density in the plasma stream. And from this, it is possible to guess the mechanism of microwave power absorption. ECR plasma was characterized by the Langmuir probe in the plasma stream. Electron temperature of about $5 \sim 8 eV$ and plasma density of $0.5 \sim 2 \times 10^{11} cm^{-3}$ are measured. To see the power absorption characteristics in the ECR plasma, we compared the profiles of the ion saturation current density, the plasma densities and the turning point magnetic fields of $TE_{11}$ and $TM_}01}$ mode. And it is thought that microwave is absorbed by ECR for $TE_{11}$ mode regardless of the magnetic field profile. Whereas for $TM_{01}$ mode, microwave is absorbed primarily by ECR if the peak magnetic field is less than 1000 Gauss. But as the peak magnetic field increases, the absorption of electric field parallel to magnetic field by Landau damping, becomes dominant. Moreover, the plasma density for $TE_{11}$ mode propagation, is higher than that of $TM_{01}$ mode propagation by about two times, but uniformity is worse by two times. The uniformity of plasma SiNx and low temperature plasma thermal $SiO_2$ films are compared for $TE_{11}$ and $TM_{01}$ mode. The results show that $...