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

Abstract

The formation of negative ions in conjunction with their effect on SiO2 etching characteristics has been investigated within a CF4/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 CFx (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 CF3-, 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 SiO2 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.