The reactive sputtering process involving two reactive gases has been
investigated. Sputtering titanium in the presence of oxygen and nitrog
en in argon was studied by means of optical emission and mass spectrom
etries. The experiments reveal the mechanism of the mixed target poiso
ning. Increasing the nitrogen supply in the presence of a constant oxy
gen supply forces the reactive sputtering system to avalanche from a h
igh-rate metal-sputtering mode to a low-rate compound-sputtering mode
at a lower N-2-to-Ar ratio as compared with the single reactive gas Ar
/N-2 reactive sputtering process. The amount of the oxygen admixture,
however, also affects the character of the avalanche and the correspon
ding hysteresis effect. At a definite level of constant oxygen supply
the Ar/N-2 processing behaviour becomes irreversible, successive decre
asing of the nitrogen supply to zero in this case is not sufficient to
force the process to return back to the high-rate metal-sputtering mo
de. A ''process trapping'' effect appears. The coupling effect between
the consumption of both reactive gases N-2 and O-2 during increase an
d successive decrease of N-2 in the presence of a constant O-2 Supply
is reflected in the dependencies of the respective partial pressures.
The cause of the observed trapping effect, the shift and the change of
the character of the sputtering rate hysteresis curve may be explaine
d in terms of the link between the consumption of the reactive gases a
nd the corresponding target condition. The experimental findings suppo
rt the theoretical model of the two-gases reactive-sputering process r
ecently presented by the authors.