Application of the rigorous treatment for the characterization of sub-micron structures on photomasks

We evaluate the optical response of binary quarter micron slits and gratings in thin opaque chromium layers for measuring critical dimensions on photomasks. At present the CD is typically inspected by time expensive SEM measurements. A main disadvantage of the SEM measurements is that it determines only the geometric parameters. Starting from the optical properties that come closer to the application of the masks we have evaluated a new approach to inspect the CD of test structures like quarter micron slits and gratings. The CD of the test structures has been varied between 100nm and 400nm. Slit widths of these structures have been characterized. Based on the combination of spectral and polarization resolved transmission and reflection measurements in a spectral range between 500 nm and 1700 nm with RCWA calculations we propose a new method for measuring the CD of test structures below the resolution limit of the classical microscopy with visible and infrared light.