Effect of ion energy on the optical and structural properties of SiO2 grown by plasma-enhanced chemical-vapor deposition

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Abstract
The optical and structural properties of SiO2 films have been studied as a function of the energy of the ion bombardment applied during plasma‐enhanced chemical‐vapor deposition. The stress level, the degree of birefringence, and the type of microstructure on the surface and in the bulk showed systematic variations with energy. A theoretical model of the behavior of the stress developed in the layer during the deposition is compared to the experimental results. A second model developed to explain the birefringence enables the degree of columnar structure in the films to be estimated. The explanation for the variation of the refractive index with the ion energy requires the presence of a dense phase with refractive index greater than that of thermally grown SiO2. The volume fraction of the dense phase, and hence the film refractive index, is correlated with the magnitude of the compressive stress. Conditions of ion bombardment leading to optimum properties for our application were identified.