Optimization of plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon

An experimental study of the optimization of plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon is presented. The correlations between deposition parameters and layer properties are discussed. The conditions involve two deposition regimes, collisional “wave riding” at the sheath boundaries (the so-called α-regime) and “Joule heating” in the bulk (the so-called γ′-regime). For low growth rates in the α-regime optimum density of states values and the lowest microvoid densities are obtained in layers with a high compressive stress. For high growth rates in the γ′-regime, layers with a high density of states and a high microvoid density are obtained. The stress in these layers is tensile and correlates with the microvoid density. For moderate growth rate hydrogen-diluted deposition conditions in the γ′-regime near optimum density of states values and low microvoid densities can be obtained in layers with a low compressive stress. Furthermore, using hydrogen-diluted growth, an improved reproducibility and layer-thickness uniformity is obtained in a wider process window. For device applications, a design adapted for the use of hydrogen-diluted growth in the γ′-regime is recommended.