Reaction layer dynamics in ion-assisted Si/XeF2 etching: Ion flux dependence

The etch rate of Si by XeF2 can be enhanced by more than a factor of 8 by i on bombardment. This enhancement is studied in a multiple-beam setup by loo king at the response of reaction product signals upon ion pulses on time sc ales of 1-100 s in a multiple-beam setup. On a time scale of 100 s, it is f ound that ion bombardment causes fluorine depletion of the reaction layer a nd changes the structure of the reaction layer. This lower fluorine content results in a lower contribution of the spontaneous SiF4 production during ion bombardment. For the enhanced SiF4 production two processes are found f rom pulse measurements on the time scale of 1-10 s. First, ion bombardment creates weakly bound surface species, e.g., SiF2, that can react in the rea ction layer to SiF4. Second, XeF2 reacts with these species with a higher r eaction probability, thus enhancing the SiF4 production. The relative impor tance of both mechanisms is determined. Further, the limiting steps during spontaneous and ion-assisted etching are discussed, revealing that the crea tion of dangling bonds is the reason for the higher sticking probability of XeF2 during ion-assisted etching. (C) 1999 American Vacuum Society. [S0734 -2101(99)00806-4].