Chemical sputtering by H\u3csub\u3e2\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e and H\u3csub\u3e3\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e ions during silicon deposition

Abstract

\u3cp\u3eWe investigated chemical sputtering of silicon films by H\u3csub\u3ey\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e 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\u3csub\u3e2\u3c/sub\u3e 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\u3csub\u3e2\u3c/sub\u3e inlet flows, we were able to model this process with a chemical sputtering mechanism. The obtained chemical sputtering yields were (0.3-0.4) ± 0.1 Si atom per bombarding H\u3csub\u3ey\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e ion at the grounded electrode and at the powered electrode the yield ranged from (0.4 to 0.65) ± 0.1. Subsequently, we investigated the role of chemical sputtering during PECVD deposition with a series of silane fractions S\u3csub\u3eF\u3c/sub\u3e (S\u3csub\u3eF\u3c/sub\u3e(%) = [SiH\u3csub\u3e4\u3c/sub\u3e]/[H\u3csub\u3e2\u3c/sub\u3e]∗100) ranging from S\u3csub\u3eF\u3c/sub\u3e = 0% to 20%. We experimentally observed that the SiH\u3csub\u3ey\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e flux is not proportional to S\u3csub\u3eF\u3c/sub\u3e but decreasing from S\u3csub\u3eF\u3c/sub\u3e = 3.4% to 20%. This counterintuitive SiH\u3csub\u3ey\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e flux trend was partly explained by an increasing chemical sputtering rate with decreasing S\u3csub\u3eF\u3c/sub\u3e and partly by the reaction between H\u3csub\u3e3\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e and SiH\u3csub\u3e4\u3c/sub\u3e that forms SiH\u3csub\u3e3\u3c/sub\u3e \u3csup\u3e+\u3c/sup\u3e.\u3c/p\u3