The effects of He plasma interactions with SiH4 in remote plasma enhanced chemical vapor deposition

Abstract

Plasma generation and the effects of the plasma on SiH4 are examined for the remote plasma enhanced chemical vapor deposition (remote PECVD) process. The electrical characteristics of two plasma generation techniques using He were compared, one at 13.56 MHz and the other at 2.45 GHz. It has been shown that the plasma generation technique has an effect upon the power coupling to the discharge in that the 13.56 MHz technique yields a capacitively coupled discharge, while the 2.45 GHz technique yields an inductively coupled discharge. There are two distinguishable methods for generating charged species in the main portion of the reactor for 13.56 MHz discharges, electron impact ionization, and Penning ionization. What has been demonstrated is that SiH4 forms polysilanes as a direct consequence of interactions with charge created with the capacitively coupled discharge (13.56 MHz) by forming polysilanes, however Penning ionizations cannot sustain appreciable gas-phase SiH4 excitation. These polysilanes account for a significant fraction of the SiH4 in the reactor. In fact, due to the chemical similarity of these polysilanes and their concentration relative to SiH4, they should be considered in models of silicon thin-film growth in remote PECVD. Hydrogen has been shown to reduce the presence of polysilane species in the plasma for conditions that are conducive to microcrystalline Si growth, and cause silane species to exhibit a higher degree of hydrogenation.