High‐precision automatic ellipsometer and whereby evaluation of a very thin silicon‐oxide layer

Abstract

AbstractTo measure automatically both the thickness and the refraction of films of several tens of angstroms, e.g., a barrier oxide for MNOS memory with high precision, a high‐speed automatic ellipsometer has been developed which can measure accurately the extinction positions of polarizer and analyzer. Hence, the polarizer/analyzer extinction positioning accuracy of 1 × 10−4 degrees has been obtained in the repeatability test during the same sample measurements. By aligning and calibrating many optical components, a perfect extinction has been obtained in crossed Nicols with a quarterwave plate (PCA). For the position detection, the optical encoder scales drawn by electron beam exposure system are read by a laser beam detector, resulting in positioning accuracy of 10−4 degrees. Next, an example is shown where the thickness of a native oxide formed on a silicon wafer is measured by this system. the possibility is shown of evaluating the oxide surface roughness with the standard deviation around the average thickness from the polarizer/analyzer extinction curve, the measured extinction factor, and the deduced value from the oxide model.