Evidence for a time dependent excitation process in silane radio frequency glow discharges

Abstract

A new phenomenon in rf glow discharges has been observed, namely the existence of a strongly time dependent excitation of atomic levels. The observed excitation width of 10 ns (FHWM) is short compared to the 37-ns duration of a half-cycle of the 13.56-MHz applied rf power. This implies a similar time dependence of the density of those electrons responsible for the excitation. Moreover, the excitation propagates through the glow away from the nearer electrode. The nature of this propagation phenomenon is uncertain. These results are deduced from a time resolved study of the λ=288.2 nm emission from neutral excited silicon, Si(4s1,1P0) and λ=656.3 nm emission from H(n=3), generated within the rf silane glow discharge. The radiative lifetimes of these two states are 5.2 and 10 ns, respectively. A study of the Si to H yield ratio, together with some Langmuir probe measurements, indicates that the electrons are themalized in the glow regions.