Tungsten patterning as a technique for selective area III–V MBE growth

Abstract

A new scheme for selective area molecular beam epitaxial (MBE) growth is proposed which employs a tungsten masking layer deposited in situ within the MBE growth chamber. The complimentary etching characteristics of W and the III–V semiconductor in fluorine and chlorine based plasmas, allows for pattern definition in the tungsten mask layer without affecting the GaAs and a preetch of the GaAs exposed through the mask without disturbing the mask. This latter step was performed in an integrally connected plasma facility in the sample introduction vacuum chamber of the MBE system just prior to growth, thus miminizing surface contamination. Liftoff of the W mask and overlying polycrystalline GaAs is achieved using a fluorine based plasma etching step, leaving single-crystal free-standing selectively grown structures ∼1000 Å high and 1–5 μm wide with submicron step profiles. The GaAs surface, reexposed after removal of the W, is as smooth as that of the original starting wafer. The regrowth step can be preceeded by a plasma etch-back of the exposed GaAs to yield selectively regrown planar structures. Finally the process should eventually be able to be performed entirely in vacuum and is extendable to the broad range of other III–V compounds.