Reaction of the fluorine atom and molecule with the hydrogen-terminated Si(111) surface

To establish the self-limiting reaction process that is necessary to achieve the atomic layer-by-layer etching for the damageless fabrication of nanometer-electronics devices, the initial reaction of fluorine (F) atoms and $F2$ molecules with hydrogen (H)-terminated Si(111) was studied employing a combined system of Fourier transform infrared (FTIR)-attenuated total reflection (ATR) and x-ray photoelectron spectroscopy (XPS). In the ATR measurement, peaks of $2086 cm−1$ $(B2)$ and $2090 cm−1$ $(B3)$ newly appeared instead of a decrease in the original Si–H peak at $2083 cm−1$ $(B1)$ with initial exposure of $XeF2.$ The sum area of $B1$⁠, $B2$⁠, and $B3$ peaks until $∼2000 L$ was almost constant. This implies that $B2$ and $B3$ peaks also resulted from Si–H bonds. The XPS measurement revealed that the initial exposure of $XeF2$ generated nonbonded F atoms at first, followed by $SiF1$ bonds. Based on the good correspondence between ATR and XPS results, first the F atoms penetrate just underneath the Si–H bond, generating the $B2$ peak. After further exposure the $B3$ peak appears arising from the bonding of an F atom with a Si–H bond at the five-coordination state. However, further exposure of F atoms caused higher order $SiFx$ $(x=1,2,3)$ products. Hence, an $F2$ gas that was less reactive than F atoms was investigated. It was found that the exposure of H-terminated Si(111) to 5% $F2/He$ reached a plateau value at $5×105 L,$ where terminated H atoms completely disappeared. The SiF monolayer corresponded exactly to the formation of an atomic layer of Si(111). This indicates that the self-limiting process for the Si/F system is realized first.