Angle-resolved scatterfield microscope for linewidth measurement

Abstract

Angle-resolved scatterfield microscope (ARSM) is developed for several years. It combines the optical microscope and angle-resolved scatterometer with a relay lens and an aperture. In our research, the spatial light modulator (SLM) is used to instead of the relay lens and the aperture. In the SLM, the phase modulation is used to simulate the Fresnel lens, and then an incident plane wave is modulated and focused on the back focal plane of the objective lens. A plane wave with an angle which is according to the position of focused point on the back focal plane is emitted from the entrance pupil of the objective lens. By modulating the SLM, the angle of plane wave from the objective lens can be changed. In our system, an objective lens with NA 0.95 and the magnification of 50 is used for wide angle scan. A bare silicon wafer and a grating with the pitch of 417nm are measured with full-angle scan. By using the SLM, the advantage is full-optical modulation, that is, the mechanical motion is not needed in the ARSM. Thus, the system will have higher throughput and stabilization.