Monitoring subwavelength grating structures for vertical-cavity surface-emitting laser applications by spectroscopic ellipsometry

GaAs based vertical cavity surface emitting lasers (VCSELs) have one of the fastest growing marketsdue to their numerous applications in imaging technology, optical sensors, and interconnects. Stable,single-mode operation of these laser diodes is often achieved by forming subwavelength structures onthe surface of the GaAs semiconductor. Quick and preferably noncontact inspection of the formednanostructures is desired during the fabrication process. Nanostructure characterization by spectralellipsometry-based metrologies has become an indispensable tool in the semiconductor industry. Anadvanced method of ellipsometry is the application of Mueller-matrix ellipsometry, which enables thecharacterization of structure details difficult to measure or not reachable by using standard ellipsometry measurements. In this paper, the authors present the results of nanostructure characterizationby model-based dimension metrology using spectral ellipsometry and Mueller-matrix spectralellipsometry of line gratings formed on GaAs substrates during the process of VCSELfabrication