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Published October 6, 1997 | Published
Journal Article Open

Ion mass effect in plasma-induced charging

Abstract

Simulations of charging and profile evolution during etching of high aspect ratio polysilicon gates in typical high-density plasmas containing heavy ions (e.g., BCl3 + , Cl2 + ), predict a reduction in charging and notching when lighter ions (e.g., He + ) are added. The reduction occurs because of the influence of the ion mass on the ratio R of the ion sheath transit time to the rf period, which determines the spread in the ion energy distribution at the wafer. The effect is most pronounced when R <= 0.1–0.2 for light ions and, simultaneously, R >= 0.6 for heavy ions; then, more light ions arrive at the patterned structure with low energies, where they help decrease localized charging. When the rf bias frequency is reduced so that R <= 0.3 for all ions, the effect disappears.

Additional Information

© 1997 American Institute of Physics. (Received 20 June 1997; accepted 30 July 1997) This work was supported by a National Science Foundation-Career Award and a Camille Dreyfus Teacher-Scholar Award to KPG. An Applied Materials Scholarship in partial support of GSH is gratefully acknowledged.

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