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Calibration of test reticles for qualification of imaging properties of microlithographic projection lenses

We report on investigations and calibrations of chrome on quartz 5' test reticles with periodic line structures which are applied for qualification of optical performance of microlithographic lenses. The measurements are focused on the precise determination of the line-to-space ratio of the test grid structures which is a necessary input information for the objective lens qualification procedure applied. Calibrations of linewidths and line-to-space ratios of the test structures with nominal CD values between 280 nm and 600 nm are mainly performed with a special low-voltage scanning electron microscope (SEM) supported by optical transmission microscopy calibrations on a small number of all test structures to be measured. The requirements on the measurement uncertainties of the line-to-space ratios are about 5%. In addition to the CD calibrations, investigations were started to estimate the influence of e-beam induced carbon deposition on the mask on the objective lens imaging properties.