Effects of substrate bias frequency in an electron cyclotron resonance plasma reactor

The effects of varying the substrate bias frequency on both substrate and plasma parameters have been studied in an electron cyclotron resonance plasma reactor. The frequency was varied between 13.56 and 76.0 MHz. The plasma density at the substrate was in the mid-10¹¹/cm³ range. It was generally found that as the frequency was increased, less rf power was coupled to the ions accelerated across the sheath to the substrate, and more rf power was coupled to the plasma bulk. Thus, more power was needed to achieve the same self-bias voltage as the bias frequency was raised. The same trend was seen as the plasma density increased—i.e., more rf power was needed to achieve the desired self-bias voltage at higher densities. These effects are analyzed in terms of a simple sheath model of the reactor.