Influence of shadow mask design and deposition methods on nonplanar dielectric material deposition

Abstract

In this paper, we report on the deposition of nonplanar SiO2 and SiNx dielectric layers using plasma-enhanced chemical vapor deposition (PECVD), radio frequency (rf) sputtering and reactive rf sputtering through metal and dielectric shadow masks. The layers were analyzed for trends in deposition rate and curvature as a function of shadow mask material and geometry, as well as the deposition method. Increasing the top hole diameter, which is the limiting aperture of the shadow mask cavity, increased the rate of deposition inside the cavity, but it also decreased the curvature of the resulting aspheric microlens. As the height of the shadow mask cavity was increased, both the cavity deposition rate and microlens curvature increased. An alumina shadow mask created microlenses with higher deposition rates and more curvature than a nickel shadow mask for the three deposition methods. SiO2 deposited by PECVD produced aspheric microlenses with the most curvature, whereas rf sputtering SiO2 produced microlenses with the highest process efficiency. These results could be exploited to produce single or multilayer dielectric films for use in focal-plane arrays of microlenses, light-emitting diode encapsulations or curved Bragg mirrors for vertical-cavity surface-emitting lasers.