Wet Chemical Etching for Ultrafine Periodic Structure: Rectangular InP Corrugations of 70 nm Pitch and 100 nm Depth

Rectangular corrugations of 70 nm pitch and 100 nm depth were formed on InP using electron beam lithography and two-step wet chemical etching. In electron beam lithography, line distributions were measured to estimate the narrowest possible period, and a fine periodic resist pattern with a 50 nm period was formed. It is pointed out that two-step wet chemical etching with a thin epitaxial mask has the advantage of suppressing the undercut etching because of good adhesion of the epitaxial mask. This etching method was applied to InP etching by HCl utilizing the material-selective and anisotropic properties. Compositions of etchant were optimized to overcome the deformation of mesas in the nanometer range.