Observation of CaF2 Growth on Si(111)7*7 Surface by RHEED.

Abstract

Thin film growth of CaF2 on Si(111)7×7 depending on the substrate temperature has been studied by Reflection High-Energy Electron Diffraction (RHEED). In this study, three aspects such as solid-phase epitaxy, vapor-phase epitaxy and electron stimulated desorption (ESD) effect were investigated. In the solid-phase epitaxy, a 7×1 surface structure has been newly found at a very narrow temperature range of 840-850oC. In the vapor-phase epitaxy, RHEED intensity oscillations were observed at the substrate temperature range of 100-450oC, which suggests a layer by layer growth due to 2-dimensional nuclei. In the range of 500-700oC, the oscillation disappears but the reflection intensity is kept at a high level, which suggests a step-flow growth mode. It was judged from the change of Kikuchi pattern that CaF2 thin films grown at the substrate temperature range of 200-700oC were all of type-B; however, that grown at 100oC was of type-A. Since the ESD effect on the CaF2 surface is generally serious, the effect is also examined.