MICROLOADING EFFECT IN INP WET ETCHING

The microloading effect in the anisotropic wet etching of InP is quantitatively studied for distributed feedback-LD grating fabrication. In this study, 240 nm pitch gratings based on resist patterns with various space widths defined by E-beam lithography were etched in saturated bromine water (SBW) and hydrobromic acid (SBW + 10 HBr + 40 H2O). The etched depth and the shape show a clear dependence on the space width, and this microloading effect can be explained by the diffusion of the reactant, the length of which is comparable to the grating size. Dry-etching is found to reduce the loading effect. The wet etching model and controllability of the coupling coefficient for DFB-LD gratings are discussed.