Lissajous Electron Plasma (LEP) Generation for Dry Etching

A new concept for plasma generation which enhances plasma density at low pressures through the use of a high-frequency rotating electric field is introduced. A 50-MHz electric power was applied to three electrodes which are positioned with a triangular symmetry. A phase shift of 120° between the electrodes brought about uniform and high plasma density at a pressure of 1 Pa. The nonuniformity of Ar gas plasma generated was within 10% over a 6” wafer using a tuned Langmuir probe electron density measurement. Polysilicon etchings were made by both SF6/O2 and Cl2/O2 plasmas. The achieved polysilicon etch-rate was over 200 nm/min for both kinds of plasmas at an electric power of 90 W along with a 13.56 MHz RF bias power of 30 W applied to the substrate. High etch-rate selectivity between polysilicon and oxide of 45 for SF6/O2 and 152 for Cl2/O2 was realized. A very low etch-rate nonuniformity of 1.5% was attained for Cl2/O2.