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.

The Ar+-ion enhanced Si(100)/XeF2 reaction is studied in a multiple beam setup for silicon temperatures from 100 K up to 1000 K. The XeF2 flux is 2.7 monolayers/s and the Ar+ flux 0.033 monolayers/s at an energy of 1000 eV. Both the XeF2 consumption and the SiFx production are measured by mass spectrometry. The enhancement of the etch rate peaks around 250 K as is observed in both the XeF2 and SiFx signals. The gradual decline above 250 K is attributed to a diminished surface fluorination and XeF2 precursor concentration. The dropoff below 250 K is presumably caused by sputtering of the XeF2 precursor, as is concluded from the temperature dependence of the XeF+/XeF2+ signal ratio. Around 175 K this decrease is so strong that the ions seem to no longer enhance, but rather reduce, the etch rate. Below 150 K the ions are driving the etch process. In this range the spontaneous process is blocked by XeF2 condensation, but the ion-assisted process continues due to sputtering or dissociation of the condensate.