NANOMETER-SCALE PATTERN-FORMATION OF GAAS BY IN-SITU ELECTRON-BEAM LITHOGRAPHY USING SURFACE OXIDE LAYER AS A RESIST FILM

We have studied the effects of the microscopic roughness of a GaAs epi taxial surface on the oxide layer, which is used as a resist-mask mate rial in in situ electron-beam lithography. When electron beam patterni ng, followed by Cl-2 gas etching, was carried out for an oxide-mask la yer formed on a rough surface, an indented pattern edge elongated alon g the [1(1) over bar0$] direction, typically having a size of several tens of nm, was formed. On the other hand, when we used a misoriented substrate in order to obtain a smooth epitaxial surface by introducing the so-called step-flow growth mode, the resulting pattern exhibited a sufficiently sharp edge. Based on this improvement, together with th e optimized electron-beam patterning system, we successfully fabricate d an ultrafine trench structure with a width as small as 20 nm. (C) 19 95 American Vacuum Society.