Metrology method and apparatus

Abstract

Disclosed is a method for measuring a target located on a substrate beneath at least one layer. The method comprises exciting said at least one layer with pump radiation comprising at least one pump wavelength, so as to generate an acoustic wave within said at least one layer which reflects of said target thereby generating an acoustic replica of said target at a surface of said substrate and illuminating said acoustic replica with probe radiation comprising at least one probe wavelength and capturing the resultant scattered probe radiation, scattered from the acoustic replica. One or both of said exciting step and said illuminating step comprises generating Surface Plasmon Polaritons (SPPs) on residual topography of said at least one layer resultant from said target.

Dependencies are inferred from the claim text.