The etching of polysilicon by low energy Cl-2+HBr plasma beam was studied, and the etching yield as a function of composition, ion impingement energy and ion incident angle was measured. The etching yield by HBr plasma beam is slightly lower than Cl, plasma beam. The angular dependence of etching yield by both Cl-2 and HBr beam strongly suggests the mechanism of ion induced chemical etching, with highest etching yield at normal incident angle. For Cl, beam, the etching yield almost keeps constant until the off-normal incident angle of ions increased to 45, while for HBr beam, the etching yield starts dropping even with small off-normal angle. The angular dependence of etching yield by Cl-2+HBr plasma at different composition exhibits similar trend as pure HBr. Using x-ray photoelectron spectroscopy, the coverage of Cl and Br on polysilicon surfaces after etching in Cl-2+HBr plasmas was measured. The Cl coverage after etching with pure Cl-2 plasma beam is about 1.4 times higher than the Br coverage after etching with pure HBr plasma beam, due to the larger size of Br atom. The instantaneous sputtering yields of polysilicon by Ar+ ions after Cl-2 and HBr plasma etching are similar, indicating that the lower Br coverage is not responsible for the lower etching rate in HBr plasma. The effect of the angular dependent etching yield difference between Cl-2 and HBr on feature profile evolution, as identified with Monte Carlo simulation, might contribute to the more anisotropic etching in HBr plasma. 2002 American Vacuum Society.