Prediction of a radial variation of plasma structure and ion distributions in the wafer interface in two-frequency capacitively coupled plasma

Two-frequency capacitively coupled plasmas (2f-CCP) are widely used as one of the powerful tools for SiO₂ etching. We numerically performed the design of SiO₂ etching by using VicAddress. Radial variation of plasma structure and ion distributions having a direct influence on etching were investigated in a 2f-CCP in CF₄(5%)/Ar, which consists both of a power source [very high frequency (VHF) 100 MHz] for high-density plasma production and a bias source (1 MHz) for the acceleration of ions toward the wafer. Degradation of the radial uniformity was observed near the wafer edge due to the distortion of surface potential mainly caused by the nonuniformity of electron flux at a wafer. Furthermore, we proposed a way of reducing the charge build-up inside the micro trench with the aid of negative charge injection by using a pulsed operation of VHF power source, especially at the low pressure condition.