Chemical sputtering of silicon by F+, Cl+, and Br+ ions: Reactive spot model for reactive ion etching

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Abstract
Chemical sputtering yields of silicon resulting from the incidence of isotopically pure 19F+, 35Cl+, and 81Br+ ion beams were measured in the 100–3000 eV energy range. It is found for these cases that the chemical sputtering yields saturate in the high energy range of more than 600 eV. The saturated yields (atoms/ion) are 0.18 for F+/Si, 0.45 for Cl+/Si, and 0.23 for Br+/Si. The yields increased with increasing ion energy in the 100–500 eV region with different slopes. The steepest slope is observed for the case of Br+/Si, and the smallest is the F+/Si case. This difference in the slope indicates that the chemical reaction between Br+ and Si cannot be activated without high acceleration of Br+, and the same occurs for Cl+/Si. On the other hand the F+ ion is assumed to react with Si with a relatively high probability even when the energy is low. On the basis of these results, a reactive spot model is proposed for the ion-assisted chemical etching process. A generalized method to get anisotropic profiles is also presented for reactive ion etching of Si with fluorine-, chlorine-, and bromine-containing gases.

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