Photon-induced dry etching of Si(100) in the VUV

The photon-induced dry etching of Si(100) using synchrotron radiation (SR) in the VUV range and a halogen containing gas (XeF2) has been investigated. Replica of a mask are etched in Si wafers with a sub-micrometer lateral resolution by irradiation with filtered or monochromatized radiation. The total quantum efficiency of etching reaches a value above unity for wavelenghts shorter than 122 nm. This very high efficiency, which exceeds that in the visible spectral range by more than four orders of magnitude, is attributed to a selective electronic excitation of a thin fluorosilyl layer on top of the Si wafer. The topology indicates that single photons initiate chain reactions with an amplification of about 3 · 105 for using Ar as buffer gas. The overall quantum efficiency combined with the amplification factor leads to a reaction stimulation probability per incident photon of 6 · 10−5. Addition of O2 increases the amplification factor but reduces the quality, selectivity and excitation probability.