Patterning of GaAs by in situ electron beam lithography toward nanometer-scale structures

An in situ electron beam (EB) lithography process using GaAs for making nanometer-scale structures is described. This process employs an ultrathin GaAs oxide layer as a mask material for Cl2 gas etching. The oxide mask can be patterned by EB irradiation under a Cl2 ambient for positive-type lithography. For negative-type lithography, an oxide mask is selectively formed by EB irradiation under an O2 ambient. To avoid surface contamination, the entire process is performed in situ in an ultrahigh-vacuum environment without exposing the wafer surface to air. By using an EB gun with a beam diameter of less than 40 nm, together with the use of ultrathin oxide mask layers, lateral patterning with a dimension as small as 100 nm has been successfully demonstrated on GaAs surfaces.