The effects of excess phosphorous on plasma etching of polycrystalline silicon were studied by SEM and TEM. The phosphorous levels were altered by the time duration of POCl3 deposition, by the presence or absence of a phosphosilicate glass layer during high temperature treatments, and by using either an N2 or O2 drive-in anneal thereby causing the snow plow effect of oxidation to locally increase the phosphorous levels. Wherever the phosphorous levels were highest (at the poly-Si free surface or at grain boundaries), the extent of plasma etching was greatest. This etching effect was found to cause poly-Si line edge roughening. © 1981, The Electrochemical Society, Inc. All rights reserved.