Mass transport: semiconductor microstructure fabrication by surface energy

Surface energy of an etched microstructure can induce mass transport during heat treatment and transform the structure. This phenomenon has been utilized to fabricate useful device structures for optoelectronic applications. The material process has been systematically investigated especially in the fabrication of large-numerical-aperture microlenses using deeply etched preforms. A reactor has been developed for a contamination-free process with controlled high phosphorus overpressure. Strong interactions between the phosphorus vapor and the wafer surface have been uncovered and investigated. Simple techniques have been developed for effectively maintaining the group III vapor equilibrium for complete wafer protection against erosion and defect generation. Comprehensive one- and two-dimensional models of the mass transport kinetics have been developed and have yielded useful guiding principles. These developments have led to reproducible fabrication of near perfect powerful microlenses and have opened considerable possibilities for more applications.