Abstract:
Inspection of photomasks for defects in phase-shifters is enhanced using optical techniques based on multiple modified radiation collection techniques, which allows allow for errors in phase-shifters to be more accurately detected. The system includes an illumination system (105), at least on collection system (107R, 107T), and a data analysis section (108). In one embodiment, the intensities of two slightly defocused images of phase objects corresponding to the same photomask location are compared. In a second embodiment, radiation having two Zernike point spread functions is used to obtain two slightly different phase sensitive images. Data collected and analyzed by the data analysis section (108) using this method provides much greater sensitivity to phase objects and errors in phase objects than prior art inspection systems. Embodiments include both scanning-type and projector type optical architectures and may utilize radiation transmitted or reflected by a sample.
Abstract:
Provided are apparatus and methods for detecting phase defects. The invention relies generally on the distortion of light as it passes through defects in phase shift masks (310) to detect these defects. Light traveling through a defect, such as a bump in an etched area will travel at a different rate than light traveling through air. In order to enhance the signals generated from the defects, the invention in several embodiments provides a defocused light beam (302) by setting the focus of the beam to a level above or below the photomask subject to inspection. The light from the photomask is collected by a detector (314) that is split into at least two portions, each generating a signal. A resulting differential signal produced from the signals generated at each of two detector portions is used to determine whether a defect in the photomask is present, in one embodiment, by generating an image from the resulting signal.