The present invention provides a method of defining polysilicon patterns. The method forms a polysilicon layer on a substrate, and a patterned mask on the polysilicon layer. Then, a first etching process is performed to remove a portion of the polysilicon layer not covered by the mask, thus forming a plurality of cavities in the polysilicon layer. A strip process is performed to strip the mask utilizing gases excluding O.sub.2. Finally, a second etching process is performed to remove a portion of the polysilicon layer, thus extending the plurality of cavities down to a surface of the substrate.