Diagnostics and control of radio-frequency glow discharge

Abstract

The diagnostics of 13.56 MHz planar radio-frequency (rf) plasma were carried out using spatially resolved optical emission spectroscopy between the parallel electrodes. Plasma sheath thickness d evaluated from the optical emission profiles depends on gas pressure P, and a relationship of Pnd=const. was obtained for CH4, CF4, and O2 plasmas with n≥1/3, and for He and Ar plasmas with n≥1/2. The etching rate and the etching profile of silicon in CF4 plasma were also examined as a function of gas pressure. A novel technique for controlling rf plasmas using the optical sheath thickness and maximum optical emission intensity is presented. This technique was applied to dry etching of silicon in CF4 plasma. When this novel control technique was used, the deviation in the etched depth for a constant etching time became smaller than that obtained using conventional power control methods.