Plasma Mode Trench Etching with Direct Hydrocarbon Injection

Abstract

AbstractPlanar plasma etching of silicon for fabrication of deep trenches has been studied using the method of factorial design.A highly anisotropic etching profile with a slight positive slope is obtained using SF6, C2C1F5, and CH4 in the low energy plasma etch mode.The anisotropy is attributed to the polymerization of CH4 molecules with the active species in the plasma.The polymer is removed preferentially in the vertical direction by energetic ions from the plasma, leaving the polymer layer on the side wall to inhibit lateral etching of silicon.Good uniformity across the wafer and smooth trench surfaces are obtained with this process.Trench depths of greater than 3μm with less than 0.24μm of undercut are observed.Etch rate measurements were made and found to be greater than 1000 angstroms/minute.Selectivity over the oxide mask is greater than 15:1.By using factorial design to statistically characterize this process, the effects of interactions between various process parameters are studied.Optimal etching conditions are obtained from the interaction terms for the process parameters.The ability to etch deep trenches with smooth surfaces, low damage, low linewidth degredation, and high selectivity make this process useful for many applications in VLSI devices.