Effect of SF6 and CI2 plasma on bottom rounding of silicon trench

Abstract

The trench formation is important process in isolation of circuits in submicron devices. The sharp bottom corners in trench can cause undue stress during subsequent furnace cycle and may become the cause for dislocation formations. Dislocations cause leakage in devices and yield loss. Isotropic profiles of trench may cause problems in filling of oxide in trench. Bottom rounding of trench is desirable for stress reduction and leakage reduction. In this paper SF6 and C12 plasma along with other process parameters are explored to obtain bottom corner rounding. It was found that SF6 and C12 plasma etching was able to produce bottom corner rounding in all cases where as conventional C12 and HBR and other similar anisotropic etch processes produced sharp bottom corners. Etch rate and hardmask removal rate was compared with new process and was found to be comparable to conventional HBR and C12 chemistry. Defects formation related to trench chemistry was also compared using metrology equipment like KLA2132. Etch rate and bottom rounding was also compared with respect to radial and circuit density dependence. Scanning Electron Microscopy method was used to obtain all related trench profiles.