Regimes of particle trapping in inductively coupled plasma processing reactors

Contamination of wafers by particles in plasma processing reactors is a continuing problem affecting yields of microelectronic devices. In this letter, we report on a computational study of particle contamination of wafers in a high plasma density inductively coupled plasma (ICP) reactor. When operating with an unbiased substrate, particles readily contaminate the wafer due to high ion fluxes which produce large ion-drag forces. Biasing the substrate with a radio frequency (rf) voltage counteracts the ion-drag forces by increasing the opposing electrostatic forces in the sheath, thereby shielding the wafer from incoming particles. We have found three regimes of particle contamination for different ICP powers and rf biases. At high rf biases and low ICP powers, particles trap at the edge of the sheath. At low rf bias and high ICP power, ion drag forces dominate, particles do not trap, and wafer contamination is problematic. At intermediate powers and biases, particles quasitrap, leading to moderate particle contamination. (C) 1996 American Institute of Physics.