Multiple-incidence-plane ellipsometer with shared detection arm for inspection of solar cell industry samples

In photovoltaic manufacturing, in-line characterization must accommodate both flat surfaces (e.g., TOPCon backside structures) and textured morphologies (e.g., alkaline-etched front surfaces). Conventional ellipsometry approaches typically address these conflicting geometries either by mechanical reconfiguration or by deploying multiple dedicated measurement heads/stations, which increases system footprint at the line level and overall cost. We present a device and method for specular reflection measurements on samples requiring different incidence planes, enabling retooling-free spectroscopic ellipsometry for in-line PV manufacturing. The core innovation is a geometric arrangement in which two non-parallel incidence planes intersect along a single common line. By placing the detection arm on this shared axis and using separate illumination arms, two incidence-plane modes can be realized with a compact three-arm configuration (two illumination arms and one shared detection arm), instead of four arms in a conventional implementation with two independent incidence planes. While the acquisition (integration) time is comparable to that of dedicated metrology heads, the proposed concept eliminates morphology-dependent mechanical changeover, i.e., retooling-related downtime is reduced to 0. The instrument was validated on a native-oxide reference, TOPCon stack measurements, and SiN layers on textured silicon. Owing to the robust mechanical design and mechanically registered geometry, maintenance and calibration are not expected to be more frequent than for conventional ellipsometer-head designs.