Negative Ion Formation in SiO₂ Etching Using a Pulsed Inductively Coupled Plasma

The formation of negative ions in conjunction with their effect on SiO 2 etching characteristics has been investigated within a CF 4 /Ar pulsed-power inductively coupled plasma. Electron energy distribution function in the pulsed plasma shows a narrow distribution compared with the CW mode. The average electron energy and electron density decrease greatly with decreasing duty ratio, which indicates that the high-energy electrons can be cooled effectively during afterglow time. By means of threshold ionization mass spectrometry, radical densities including CF x ( x =1 to 3) and F are measured as a function of duty ratio and also correlated with the average energy and density of electrons. For negative ions, two major peaks, F - and CF 3 - , are formed predominantly through the electron attachment reactions during afterglow time. The possible mechanisms for the negative ion formation are proposed in the pulsed plasma. Additionally, the SiO 2 etch rate decreases nearly linearly with decreasing duty ratio and microtrenching is suppressed by the reduction of charge accumulation on the sidewalls in the pulsed plasma.