Profile evolution during polysilicon gate etching with low-pressure high-density Cl2/HBr/O2 plasma chemistries

Profile evolution during polysilicon Sate etching has been investigated with low-pressure high-density Cl-2/HBr/O-2 plasma chemistries. Etching was performed in electron cyclotron resonance Cl-2/HBr/O-2 plasmas as a function of HBr percentage in a Cl-2/HBr mixture, using oxide-masked poly-Si gate structures. The linewidth was nominally 0.18 mum, and the spacing between the two neighboring poly-Si lines was varied in the range similar to0.2-10 mum. In addition, the macroscopic open space of the oxide-masked sample was also varied over a wide range from approximate to 28% to approximate to 76%. As the HBr percentage in Cl-2/HBr is increased from 0 to 100%, the linewidth shift DeltaL of poly-Si relative to the mask width (or the degree of sidewall tapering of poly-Si lines) first decreased linearly, passed through a minimum, and then increased considerably at above similar to 80%. In Cl-2/O-2 plasmas without HBr addition, DeltaL was almost independent of the microscopic and macroscopic poly-Si open spaces although its value was relatively large; on the contrary, in HBr/O-2 plasmas, BL increased with an increase of microscopic line spacing and/or the macroscopic open space of the sample. Comparisons of the etched profiles obtained in Cl-2/HBr/O-2 plasmas with numerical profile simulations indicate that the strongly tapered sidewalls observed at high HBr percentages (greater than or equal to 80%) result from the simultaneous etch inhibitor deposition onto sidewalls during etching; moreover, such inhibitors are predicted to come from the plasma with a large sticking probability of similar toO(0.1). On the other hand, the relatively large DeltaL obtained in Cl-2/O-2 plasmas is considered to be due to intrinsic sidewall tapering, rather than inhibitor deposition arriving from the plasma or redeposition of etch products desorbed from the surface in microstructures. Such intrinsic tapering is discussed in terms of the angular dependence of the Si etch yield. (C) 2001 American Vacuum Society.