Method and apparatus for decreasing thermal loading and roughness sensitivity in a photoacoustic film thickness measurement system

摘要

Disclosed are methods and apparatus for reducing thermal loading of a film disposed on a surface of a sample, such as a semiconductor wafer, while obtaining a measurement of a thickness of the film in an area about a measurement site. The method includes steps of (a) bringing an optical assembly of the measurement system into focus; (b) aligning a beam spot with the measurement site; (c) turning on one of a dither EOM or a dither AOM or a piezo-electric dither assembly to sweep the beam spot in an area about the measurement site, thereby reducing the thermal loading within the measurement site; (d) making a measurement by obtaining a signal representing an average for the film under the area; (e) recording the measurement data; and (f) analyzing the measurement data to determine an average film thickness in the measurement area.