Formation of microgratings for III-V semiconductor integrated optoelectronics by high-voltage electron-beam lithography

The importance of low-order Bragg reflection gratings in semiconductor integrated optoelectronics is discussed and the advantages of direct-write electron-beam lithography for defining such gratings are described. We present the results of a theoretical and experimental study of this technique on bulk III-V semiconductor substrates. The use of 60-keV electron beams is shown to give improved edge resolution and relaxed tolerance on dosage compared with conventional (15-30 keV) beam energies. This enables fine patterns with high aspect ratios to be defined on thick (0.3-0.5 μm) resist films. Gratings having 0.23-μm period and 1:1 mark/space ratio have been defined on thick PMMA resist over InP substrates. Initial results for formation of gratings on GaInAsP/InP heterostructure substrates are presented.