The effect of etching gases on notching and charging in high-density plasma

A comparison of notching of metal etching in Cl-2/BCl3 and HCl plasma was carried out using a transformer coupled plasma (TCP) etcher. We observed that notches can be reduced by eliminating BCl3 from the gases for overetching. Furthermore, the HCl overetch process provides notch-flee profiles with high selectivities. The reduction in the sidewall attack by heavy ions (e.g., BCl2+ or BCl3+) and the scavenging of excess Cl radicals by H radicals are considered to be possible causes for the reduced notching in the HCl process. The neutralization of the negatively charged upper photoresist sidewalls by H+ ions is also thought to be the cause for the reduction in the electron shading damage and notching.