Effects of particles on He-SiH₄ modulated RF discharges

The effects of particles on helium-diluted silane RF discharges are studied using a power modulation method for various Values of relevant parameters. Compared with CW discharge cases, close correlation is clearly found between the particle growth, the self-bias voltage and the phase shift between the current and voltage of the RF discharge. Total particle number and optical emission intensity in the bulk plasma region increase monotonically after RF power-on. With these increases, the magnitude of self-bias voltage and the current-voltage phase shift decrease considerably to their minimum values and then slightly increase to their quasi-steady values. The decreases can be explained by the fact that particles in plasmas behave as very heavy negative ions. The increases may be related to the increase in the diffusion rate of electrons. It is also confirmed through this study that the modulation is very effective in the suppression of particle growth. In particular, for a duty cycle of 20%, the discharge parameters are close to those for a pure He discharge. This tendency is consistent with the result that no particles can be observed for this duty cycle.