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 ion bombardment. This enhancement is studied in a multiple-beam setup by looking at the response of reaction product signals upon ion pulses on time scales of 1–100 s in a multiple-beam setup. On a time scale of 100 s, it is found that ion bombardment causes fluorine depletion of the reaction layer and 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 from 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 reaction layer to SiF₄. Second, XeF₂ reacts with these species with a higher reaction probability, thus enhancing the SiF₄ production. The relative importance of both mechanisms is determined. Further, the limiting steps during spontaneous and ion-assisted etching are discussed, revealing that the creation of dangling bonds is the reason for the higher sticking probability of XeF₂ during ion-assisted etching. © 1999 American Vacuum Society.