Quartz crystal microbalance study of tungsten atomic layer deposition using WF 6 and Si 2H 6

Abstract

The atomic layer deposition (ALD) of tungsten can be accomplished using sequential exposures of WF 6 and Si 2H 6 (disilane). In this paper, W ALD is explored using in situ quartz crystal microbalance (QCM) measurements as a function of the reactant exposure and deposition temperature. The QCM measurements revealed that the WF 6 reaction is self-limiting. In contrast, W ALD growth rates exhibited a slow and continual increase for disilane exposures > 4 × 10 4 L. The W ALD growth rate was also weakly temperature-dependent with an activation energy of 1.5 ± 0.1 kcal/mol at T < 250 °C and a lower activation energy of 0.6 ± 0.3 kcal/mol at T > 275 °C. The QCM results and previous Auger results for W ALD yield the relationship between the silicon coverage deposited during the Si 2H 6 exposure and the tungsten coverage deposited during the WF 6 exposure. The W/Si atomic ratio of ∼ 1:1 is consistent with earlier Auger investigations of the surface chemistry during W ALD at 200 °C. The QCM measurements are also consistent with silicon coverages of 1.7–2.1 monolayers after the Si 2H 6 exposures. These high silicon coverages are believed to result by silylene insertion from Si 2H 6 into surface Si–H bonds.