Analysis of Köhler illumination for 193 nm scatterfield microscope

A scatterfield microscope using 193 nm laser light was developed that utilizes angle-resolved illumination for high resolution optical metrology. An angle scan module was implemented that scans the illumination beam in angle space at the sample by linearly scanning a fiber aperture at a conjugate back focal plane. The illumination light is delivered directly from a source laser via an optical fiber in order to achieve homogeneous angular illumination. A unique design element is that the conjugate back focal plane (CBFP) is telecentric allowing the optical axis of the fiber to be scanned linearly. Initial results from full field and angle-resolved illumination are presented and potential applications in semiconductor metrology are described.