Subsurface hydrogenated amorphous silicon to μc-hydrogenated silicon transformation during magnetron sputter deposition determined by spectroscopic ellipsometry

We use in situ spectroscopic ellipsometry to analyze the microstructure of the μc-Si:H/a-Si:H interface deposited by reactive magnetron sputtering of a Si target in (Ar+H₂). We increase the hydrogen pressure to promote μc-Si:H formation and observe several effects. Initially, H penetrates ∼45 Å into the a-Si:H substrate and increases its hydrogen content. Then ∼55 Å of hydrogen-rich a-Si:H deposits. Finally, μc-Si:H nucleates on top of this ∼100 Å thick, high H-content a-Si:H interface layer. As μc-Si:H grows, the thickness of the amorphous interface layer decreases by ∼40 Å; the void fraction in the μc-Si:H layer is always ≤15 vol %, ruling out the possibility that the a-Si:H is etched away. These results suggest that a-Si:H can be transformed into μc-Si:H in a subsurface region under appropriate conditions.