The temperature dependence of the Si͑100͒/XeF 2 etch reaction is studied quantitatively in a molecular beam setup. At a sample temperature of 150 K the reaction probability reaches unity initially, after which the XeF 2 condenses on the surface and blocks the etching process. For increasing temperatures the XeF 2 reaction probability initially decreases from 100% at 150 K down to 20% around 400 K, but for temperatures above 600 K it increases again up to 45% at 900 K. In a simple reaction scheme the high etch rate at low temperatures is explained by a XeF 2 -precursor, with an activation energy for desorption of 32Ϯ4 meV. Furthermore the increased etch rate at high temperatures is explained by the desorption of SiF 2 with an activation energy of 260Ϯ30 meV. The steady-state fluorine content of the SiF x reaction layer, measured using thermal desorption spectroscopy, reaches a maximum of 5.5 monolayers at 300 K. For increasing temperatures it decreases to a submonolayer coverage above 700 K. The temperature dependence of the formation of the reaction layer is described well by including the XeF 2 -precursor in a previously developed adsorption model.

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