Particle Transport in Etching Chamber Influenced by Coulomb Force

Particle transport under Coulomb force during plasma on and off periods was studied in a plasma of mixed gases of Ar, O₂, and N₂ generated by a microwave electron cyclotron resonance plasma etching system. The relationship between the number of particles attached to the wafer and the wafer potential was studied, where the wafer potential was supplied by radio frequency (RF) and direct current biases during the plasma on and off periods, respectively. During plasma on periods, the particle counts decreased when a self-bias voltage on the wafer was large in the negative by increasing RF bias power. During plasma off periods, the particle counts decreased when the wafer potential was positive. These results show that particles charge negatively during plasma on periods and particles charge positively during plasma off periods. In this paper, it is found that controlling particle transport with the Coulomb force from the wafer potential is effective for particle attachment prevention.