Chemical sputtering by H2+ and H3+ ions during silicon deposition

We investigated chemical sputtering of silicon films by H-y(+) ions (with y being 2 and 3) in an asymmetric VHF Plasma Enhanced Chemical Vapor Deposition (PECVD) discharge in detail. In experiments with discharges created with pure H-2 inlet flows, we observed that more Si was etched from the powered than from the grounded electrode, and this resulted in a net deposition on the grounded electrode. With experimental input data from a power density series of discharges with pure H-2 inlet flows, we were able to model this process with a chemical sputtering mechanism. The obtained chemical sputtering yields were (0.3-0.4) 6 0.1 Si atom per bombarding H-y(+) ion at the grounded electrode and at the powered electrode the yield ranged from (0.4 to 0.65) 6 0.1. Subsequently, we investigated the role of chemical sputtering during PECVD deposition with a series of silane fractions S-F (S-F(%) = [SiH4]/[H-2]*100) ranging from S-F = 0% to 20%. We experimentally observed that the SiHy+ flux is not proportional to S-F but decreasing from S-F = 3.4% to 20%. This counterintuitive SiHy+ flux trend was partly explained by an increasing chemical sputtering rate with decreasing S-F and partly by the reaction between H-3(+) and SiH4 that forms SiH3+. Published by AIP Publishing.