Md. Whitfield et al., Spatially resolved optical emission spectroscopy of the secondary glow observed during biasing of a microwave plasma, VACUUM, 56(1), 2000, pp. 15-23
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.