Effect of UHV annealing on morphology and roughness of sputtered Si(1 1 1)-(7 × 7) surfaces

Abstract

Ar⁺ ion has been used regularly for the cleaning of semiconductor, metal surfaces for epitaxial nanostructures growth. We have investigated the effect of low-energy Ar⁺ ion sputtering and subsequent annealing on the Si(1 1 1)-(7 × 7) surfaces under ultrahigh vacuum (UHV) condition. Using in-situ scanning tunnelling microscopy (STM) we have compared the morphological changes to the Si(1 1 1)-(7 × 7) surfaces before and after the sputtering process. Following 500 eV Ar⁺ ion sputtering, the atomically flat Si(1 1 1)-(7 × 7) surface becomes amorphous. The average root mean square (rms) surface roughness (${\sigma }_{\mathrm{avg}}$) of the sputtered surface and that following post-annealing at different temperatures (500–700 °C) under UHV have been measured as a function of STM scan size. While, annealing at ∼500 °C shows no detectable changes in the surface morphology, recrystallization process starts at ∼600 °C. For the sputtered samples annealed at temperatures ≥600 °C, ${log\sigma }_{\mathrm{avg}}$ varies linearly at lower length scales and approaches a saturation value of ∼0.6 nm for the higher length scales confirming the self-affine fractal nature. The correlation length increases with annealing temperature indicating gradual improvement in crystallinity. For the present experimental conditions, 650 °C is the optimal annealing temperature for recrystallization. The results offer a method to engineer the crystallinity of sputtered surface during nanofabrication process.