Recent Research Developments

Atomic Layer Deposition of Zirconia and Silica

In recent work of Lijuan Zhong, Fang Chen, Steve Campblell and Wayne Gladfelter, atomic layer deposition was used to deposit alternating layers of zirconia and silica.

In a low-pressure chemical vapor deposition reactor, alternating exposure of silicon substrates at 162°C to anhydrous zirconium nitrate and tri(t-butoxy)silanol produced atomically smooth, amorphous films. The deposition rate, defined as the thickness (Å) per cycle, exhibited saturation behavior indicative of self-limiting growth of atomic layer deposition. However, the maximum rate of approximately 12 Å/cycle exceeded the thickness expected for a single monolayer each of ZrO₂ and SiO₂. Both the thickness deposited per exposure cycle and the ratio of ZrO₂ to SiO₂ requires a process involving multiple SiO₂ units added per each ZrO₂. Films deposited under conditions leading to the saturation of ZrO₂ per layer displayed an ordered structure within each bilayer, which was revealed by the singular reflection in the low angle X-ray scattering pattern. Such mixture of ZrO₂, a high dielectric constant oxide, with SiO₂, a glass-forming oxide, is a potential replacement of SiO₂ in order to conquer the direct tunneling effect associated with very thin insulator layer in field effect transistors. In this study, both the refractive indices, measured by ellipsometry, and the effective dielectric constants displayed a linear correlation to composition: a feature that may be of value in device design and construction.

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