Pulsed plasma processing for reduction of profile distortion induced by charge buildup in electron cyclotron resonance plasma

The distortion of etched profiles was investigated in pulse-modulated Cl-2 and HCl plasmas using optical emission spectroscopy. Notch depth reduction was observed in both gases with repeated pulsing of the plasma. This reduction strongly depends on the off-time length. According to optical emission analysis, attenuation in the off-period was quite different in Cl-2 and HCl plasmas; it was 2 times faster in HCl plasma. This is explained by higher ambipolar diffusion of protons existing in HCl plasma. The damping process of plasma greatly influences the notch characteristics. In the case of HCl plasma, no aspect-ratio dependence of notching was observed. This indicates that accumulated charges on every pattern area were neutralized by exposure to repeated pulses of plasma.