Role of hydrogen in the peeling of hydrogenated microcrystalline silicon films

Thin film transistors and solar cells consist of multilayer stacks of silicon-based materials. In those devices, a strong adhesion of the various layers is a necessary condition for their reliability. Hydrogenated microcrystalline silicon (μc-Si:H) is raising strong expectations, thanks to its optical and electronic properties and its low fabrication cost. However, during device processing, μc-Si:H thin films deposited from SiF₄ tend to peel off from their substrate, thus ruining the entire device. In this work, we have studied the adhesion of μc-Si:H films deposited on silicon nitride, in order to find an explanation for the film peeling. Secondary ion mass spectroscopy, hydrogen gas evolution, and scanning electronic microscopy provide clues that hydrogen accumulation is responsible for the peeling. We propose an explanation for this accumulation, and one way to reduce or even eliminate peeling.