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.