Effects of space charge on ion energy in ionized cluster beam film deposition

In ionized cluster beam (ICB) deposition, thin films are said to be deposited from a beam of ionized, accelerated atom clusters. Unique properties have been reported for ICB films even though it is becoming apparent that the large (1000 atom) clusters reported in earlier work have not been duplicated by homogeneous nucleation with nozzle sources. Instead, recent results at a number of laboratories using different cluster measurement methods for gold, aluminum, gallium, silver, and other materials show what appears to be small clusters up to ten atoms in size and suggest that the nozzle may be unnecessary. It is not known whether these small clusters or other characteristics of the deposition technology are responsible for the deposited film qualities that have stirred interest in recent years. The subject of this presentation is a detailed electrostatic analysis of an ICB source to determine the fundamental parameters of ICB depositions and thus to elucidate other factors such as the effects of self‐ion bombardment. Energy analysis of gold and background gas ion beams produced in the source shows that the ICB source can operate in two distinct modes. For low crucible and ionizer electron bombardment conditions the effect of space charge on the energy of ions incident on the substrate is negligible. Above critical bombardment conditions, space charge has a very significant effect, resulting in incident ion energy being raised as much as 50% above that expected based upon applied electrode potentials alone. Computer modeling of ICB source electrostatic characteristics is used to explain these findings.