Heterodyne polarimetry for measuring critical dimensions on semiconductor wafers

A new optical technique based on heterodyne polarimetry is developed for fast measurement of critical dimensions on semiconductor wafers, particularly on those of memory chips. Sub-wavelength periodical structure of a sample acts as a wire-grid polarizer, making both the amplitude and phase of the reflected laser beam dependent on geometrical dimensions and optical properties of the wafer pattern. The heterodyne technology based on the cross-polarized two-frequency Zeeman laser is used to simultaneously measure the amplitude and the phase of the reflected laser beam. Very fast and efficient effective medium trapezoidal algorithm is developed for extracting values of critical dimension from the measurements. The technique is most suitable for inspection of multi-periodical patterns consisting of large number of periodically distributed small areas of sub-wavelength gratings. Theoretical background, simulation, and experimental results are presented.