Formation of Silicon Nanocrystals and Interface Islands in Synchrotron-Radiation SiO2 Films on Si(100)

Nucleation of nanocrystalline Si (nc-Si) in SiO₂ films irradiated with vacuum ultraviolet and soft x-ray radiation has been investigated by using in-situ spectroscopic ellipsometry, cross-sectional transmission electron microscopy, reflectivity measurement, and reflection high-energy electron diffraction. The formation of nc-Si proceeds in the repetition of two steps: (i) conversion of SiO₂ to SiO_x through the creation of Frenkel pairs and the subsequent desorption of O₂, and (ii) separation of SiO_x into Si and SiO₂ domains. The average diameter of nc-Si increases from 2 to 10 nm as the irradiation temperature increases from 470°C to 610°C. Above 700°C, oxide domains are gone and solid-phase recrystallization produces Si islands terminated by the Si(100) substrate interface. At temperatures higher than 800°C, these islands collapse and an atomically flat Si(100) interface appears.