Control of electron energy distributions and plasma characteristics of dual frequency, pulsed capacitively coupled plasmas sustained in Ar and Ar/CF4/O2

The fluxes of radicals and ions to the wafer during plasma processing of microelectronics devices determine the quality of the etch or deposition. These fluxes are largely controlled by controlling the electron energy distribution function f (ε) which determines the dissociation patterns of feedstock gases. In quasi-steady state operation, an equilibrium condition for f (ε) results from a real time balance between electron sources and sinks. Using pulsed power, electron sources and sinks do not need to instantaneously balance—they only need to balance over the longer pulse period. This provides additional leverage to customize f (ε). In this paper, the f (ε) in a two-frequency, pulsed capacitively coupled plasma sustained in Ar and Ar/CF4/O2 mixtures are discussed with results from a two-dimensional plasma hydrodynamics model. The f (ε) are obtained from a Monte Carlo simulation which includes electron–electron collisions. We found that the f (ε) and rate coefficients can be controlled by pulse repetition frequency (PRF) and duty cycle (DC) of the pulsed power in a manner not otherwise easily attainable using continuous excitation. The tail of the f (ε) is enhanced with smaller PRF and DC in order to compensate for the electron losses during the power-off portion of the cycle. (Some figures may appear in colour only in the online journal)