EVALUATION AND OPTIMIZATION OF LARGE-AREA III-V EPITAXIAL THICKNESS UNIFORMITY USING A FABRY-PEROT MICROCAVITY TEST STRUCTURE

We report a technique for simply and conveniently measuring epilayer t hickness uniformity to 0.5% over an entire wafer. The technique requir es epitaxial growth of a Fabry-Perot microcavity test structure. Mappi ng is performed by measuring the wavelength-dependent optical reflecti vity at different points on the wafer and then fitting the reflectivit y data to deduce the thickness uniformity. The mapping technique was u sed to determine the optimal growth conditions in a vertical rotating disk reactor that resulted in better than +/-1% uniformity over a 2 in ch wafer. The high precision of the optical reflectivity mapping techn ique can provide information not easily obtained with other techniques . For example, we show that the presence of wafer flat adversely affec ts the thickness uniformity.