<i>In situ</i> spectroscopic ellipsometry for atomic layer processes on III–V interfaces using critical points

Plasma-enhanced atomic layer processing of III–V semiconductors requires precise control of plasma–surface interactions to achieve clean oxide-free interfaces, but conventional characterization methods are too slow to guide rapid process optimization. This work demonstrates an in situ spectroscopic ellipsometry methodology used as a rapid, model-light probe of III–V surface quality during plasma exposure. Monitoring the amplitude of the E0′ critical point from the pseudodielectric function is used as a metric of surface cleanliness. This methodology is demonstrated with Ar and Ar:H2 plasmas where the behavior of the E0′ amplitude is correlated with InAs surface modification using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). We observe an increase in E0′ with the removal of arsenic oxides in both plasmas that is confirmed by XPS and AFM roughness maps indicating that the response is dominated by interface chemistry rather than morphology. In Ar:H2 plasmas, E0′ transients exhibit an initial increase followed by a roll-over that marks the onset of metallic indium formation, which appears to be more sensitive to the presence of metallic indium on the surface than XPS. The methodology defines practical process boundaries in an accelerated manner when compared to the typical characterization process flows involving systematic characterization of large sample sets using time-intensive techniques such as XPS and AFM. Simplifying ellipsometric tracking of a small set of critical-point metrics in situ provides real-time feedback and aids in down-selection within large plasma parameter spaces and enables rapid optimization of plasma surface treatments in atomic layer processing.