Mechanism of charging damage during plasma-enhanced silicon nitride/oxide thin-film deposition

Charging damage during plasma-enhanced dielectric thin-film deposition is a surprisingly severe problem. Given that the dielectric films are good insulators, it is counterintuitive to have a charging damage problem in the first place, let alone one that is severe. More surprising still is that while most of the damaging plasma processes show diminished (measurable) impact when gate oxide has been scaled down to 3 nm or less in thickness, charging damage from dielectric deposition remains a serious problem. A photoconduction mechanism was proposed by Cheung and Pai [IEEE Electron Dev. Lett., vol. 16, p' 220, 1995] to explain charging damage in plasma-enhanced dielectric deposition. However, the model did not account for the effect of non ohmic contact that limits current flow. It is shown here that the combination of photoconduction, internal photoemission, and high-temperature acceleration of breakdown is needed to explain the charging damage during plasma-enhanced dielectric deposition. Details of the conduction process, including polarity effect, are discussed. The recently measured oxide photoconductivity is shown to be in agreement with expectation.