Selectivity in dry etching of Si(100) with XeF2 and VUV light

Replica of a mask were etched in Si(100) wafers with a sub-micrometer lateral resolution by VUV irradiation using XeF2. A high selectivity is achieved if the spontaneous reaction of XeF2 is suppressed by a buffer gas and if the unselective light induced reaction is avoided. The strength of unselective etching is strongly wavelength dependent and follows the XeF2 gas phase absorption coefficient. Fragments from the XeF2 gas phase dissociation reach the Si surface and thus cause unselective etching. Optimal dry etching is achieved around 120 nm because the selectivity is high and also the quantum efficiency is very large. The absolute quantum efficiency at 120 nm corresponds to 10 etched Si atoms per incident photon.