EFFECT OF WALL CHARGING ON AN OXYGEN PLASMA CREATED IN A HELICON DIFFUSION REACTOR USED FOR SILICA DEPOSITION

A continuous oxygen plasma operating at a radio frequency power of 800 W and a pressure of 2 mTorr has been created in a helicon diffusion r eactor used for the deposition of silicon dioxide films. An energy sel ective mass spectrometer and a Langmuir probe attached to the wall of the silica covered aluminum diffusion chamber below the source have be en used td characterize the plasma [ion energy distribution function ( IEDF), plasma potential, floating potential, plasma density]. The IEDF of the O-2(+) ions escaping from the plasma to the sidewalls of the c hamber consists of a single peak at an energy corresponding to the pla sma potential in the chamber (approximate to 32 V). This rather high v alue is a consequence of the charging effect of the insulating walls a t the initiation of the discharge, and would need to be taken account of when estimating the energy of the ions arriving at a biased substra te. (C) 1995 American Vacuum Society.