Role of an Electron Beam in the Modification of a GaAs Oxide Mask for in situ EB Lithography

The electron beam (EB)-induced modification of GaAs oxide for the in situ lithography process has been investigated. The oxide formed on an as-grown GaAs surface is irradiated with an electron beam at doses in the range of 1.5×1017 to 4×1019 electrons/cm2 at beam energies of 10-25 keV. Subsequent Cl2 gas exposure results in selective etching only in the irradiated area. EB-induced modification of the GaAs oxide is found to involve a partial removal of oxygen by in situ Auger measurements. The threshold dose for the etching depends on electron energy, whereas it is independent of the wafer temperature between 25 and 100°C during EB-irradiation. These results indicate that the modification is not a thermally activated process, but a direct interaction of the electron beam with the oxide.