It was recalled that it had been proposed that long-range surface transport of F atoms could precede eventual binding to a Si atom. The rate of binding increased if the Si was bombarded with high-energy ions. The lateral etching of a Si layer, sandwiched between 2 silicon dioxide layers, was studied here in order to investigate and extend these hypotheses. The under etching of the Si layer was higher for wafers which suffered ion bombardment, showing that this mechanism was important even for horizontal etching. At the same time, the thickness of the Si layer was varied. In all cases, the thinner Si layer etched much faster then the thicker layer, indicating that F surface transport was much more important than re-emission for these processes. The etch rate increase with ion bombardment could be explained by the fact that part of the energy of the incoming ions was transferred to the F compounds which were on the horizontal surfaces and that ion bombardment enhanced the F surface transport.

The Influence of Diffusion of Fluorine Compounds for Silicon Lateral Etching. P.Verdonck, A.Goodyear, N.S.Braithwaite: Thin Solid Films, 2004, 459[1-2], 141-4

Figure 5

Diffusion of F in Si