Frequency response in pulsed DC reactive sputtering processes

By simple arguments as well as results from a recently developed computer simulation model we have found out that for high frequency pulsed DC reactive sputtering the target poisoning does not reflect the periodicity of the pulsed DC power supply. The degree of target poisoning does not change markedly during a single duty cycle. The degree of poisoning essentially exhibits the same continuous time independent behavior as observed for the conventional continuous reactive sputtering process. Furthermore, it is shown that the distribution width of the transit times for sputtered atoms by far exceeds the period time for pulsed DC frequencies higher than 5-10 kHz. This causes a large overlap between sputter eroded material between consecutive pulses during processing resulting in an essentially continuous arrival rate of sputtered atoms to the substrate surface. This implies also that the deposition rate will be constant and will not follow the pulsed sputter erosion variation from the target. These findings show that, with respect to film stoichiometry and homogeneity, the high frequency pulsed DC reactive sputtering process behaves identically as the continuous reactive sputtering process. No chemical reaction effects or gas gettering variations will follow the periodicity of the pulsed DC power supply at high frequencies. (C) 2000 Elsevier Science S.A. All rights reserved.