Effect of UHV annealing on morphology and roughness of sputtered $Si(111)-(7\times 7)$ surfaces

Abstract

$A{r}^{+}$ ion has been used regularly for the cleaning of semiconductor, metal surfaces for epitaxial nanostructures growth. We have investigated the effect of low-energy $A{r}^{+}$ ion sputtering and subsequent annealing on the $Si(111)-(7\times 7)$ surfaces under ultrahigh vacuum (UHV) condition. Using $in-situ$ scanning tunnelling microscopy (STM) we have compared the morphological changes to the $Si(111)-(7\times 7)$ surfaces before and after the sputtering process. Following $500eVA{r}^{+}$ ion sputtering, the atomically flat $Si(111)-(7\times 7)$ surface becomes amorphous. The average root mean square (rms) surface roughness $({\sigma }_{avg})$ of the sputtered surface and that following post-annealing at different temperatures $(500^{\circ }-700^{\circ })C$ under UHV have been measured as a function of STM scan size. While, annealing at $\sim 500^{\circ }C$ shows no detectable changes in the surface morphology, recrystallization process starts at $\sim 600^{\circ }C$. For the sputtered samples annealed at temperatures $\ge 600^{\circ }C,log{\sigma }_{avg}$ varies linearly at lower length scales and approaches a saturation value of $\sim 0.6nm$ 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, $650^{\circ }C$ is the optimal annealing temperature for recrystallization. The results offer a method to engineer the crystallinity of sputtered surface during nanofabrication process.

20 Pages, 4 Figures