Profile evolution during polysilicon gate etching has been investigated with low-pressure high-density Cl2/HBr/O2 plasma chemistries. Etching was performed in electron cyclotron resonance Cl2/HBr/O2 plasmas as a function of HBr percentage in a Cl2/HBr mixture, using oxide-masked poly-Si gate structures. The linewidth was nominally 0.18 μm, and the spacing between the two neighboring poly-Si lines was varied in the range ∼0.2–10 μm. In addition, the macroscopic open space of the oxide-masked sample was also varied over a wide range from ≈28% to ≈76%. As the HBr percentage in Cl2/HBr is increased from 0 to 100%, the linewidth shift ΔL 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 ∼80%. In Cl2/O2 plasmas without HBr addition, ΔL was almost independent of the microscopic and macroscopic poly-Si open spaces although its value was relatively large; on the contrary, in HBr/O2 plasmas, ΔL increased with an increase of microscopic line spacing and/or the macroscopic open space of the sample. Comparisons of the etched profiles obtained in Cl2/HBr/O2 plasmas with numerical profile simulations indicate that the strongly tapered sidewalls observed at high HBr percentages (≳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 ∼O(0.1). On the other hand, the relatively large ΔL obtained in Cl2/O2 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.