Spatially resolved optical emission spectroscopy of the secondary glow observed during biasing of a microwave plasma

A secondary glow region is commonly observed between the main plasma ball a nd the substrate during biased enhanced nucleation (BEN) of diamond films g rown using the process of microwave plasma-enhanced chemical vapour deposit ion. Under conditions of very careful optimisation BEN can allow (1 0 0) or iented polycrystalline diamond films to be grown on (1 0 0) silicon substra te; such films are industrial important. Recently it has been suggested tha t this secondary plasma plays a key role in nucleation density enhancement and orientation effects of the BEN process. However to-date this region of the plasma has received little study. We have used spatially resolved optic al emission spectroscopy (OES), optical photography and electrical measurem ents as diagnostics to qualitatively investigate this region. The measureme nts show that the appearance of the secondary glow exhibits threshold behav iour which correlates with the I-V measurements carried out during BEN. OES measurements show that the glow region is located about 2 mm above the sub strate surface and suggest that it can act as a strong source of atomic hyd rogen supporting its role as a region below which strong etching occurs as suggested in recent models of the BEN process. (C) 2000 Published by Elsevi er Science Ltd. All rights reserved.