Intrinsic stress of phosphorus- and boron-doped amorphous silicon films

Abstract

The relationship between the intrinsic stress and hydrogen-bonding configuration for plasma-produced hydrogenated amorphous silicon (a-Si: H) films doped with phosphorus and boron has been studied in the gas-phase doping ratios from 0 to 5 × 10⁻³ prepared with different substrate temperatures. We found the same strong correlation between the sign and strength of intrinsic stress σ_i and the infrared stretching-mode absorption ratio I(SiH₂)/I(SiH) (= R) as in a previous study on undoped films. The compressive stress rapidly increases as R decreases below 1·2, while the tensile stress increases and finally saturates as R increases above 1·2; consequently, zero stress is reached at R ≊ 1.2. This stress change was found not to be associated with the dopants and the doping levels but with the plasma conditions. The experimental σ_i-R curve has been interpreted by a phenomenological theory based on a simplified two-phase structural model.