Dual excitation reactive ion etcher for low energy plasma processing

The influence of the excitation frequency in the parallel plate cathode-coupling equipment has been investigated and it was found that the self-bias voltage of the cathode becomes a logarithmic function of the excitation frequency in two distinct regions. By selecting appropriate excitation frequencies in a dual excitation system, the study found that the plasma density can be controlled by varying the plasma generating rf power without affecting the dc potential of the electrodes. The effect of the plasma generating rf power on plasma density was determined by monitoring the optical emission spectrum, ion current collected at dc biased electrode, and the SiO2 etching rate when the substrate was rf biased to −50 V. Also, the low ion energy etching of Si and SiO2 was demonstrated in CF4 and SiF4 plasmas utilizing the dual excitation system. Then, applied to the plasma cleaning of the fluorocarbon layer subsequent to CF4/H2 plasma etching, i.e., a typical gas combination used for SiO2 etching. SiF4 plasma cleaning as well as H2 plasma were effective in removal of organic contamination of the silicon.