Development of a test setup for the characterization of an optical microscope for high precision length metrology applications

A test setup to qualify the performance of optical microscopes has been designed and optimized using FEM calculations to exhibit a minimal susceptibility to thermal and mechanical influences of the ambient environment. The alignment is performed using an alignment autocollimator and alignment targets. The data acquisition of the camera and the position sensors of the stage is synchronized. The short-term repeatability (1s) of the line position and -width measurement obtained with the integrated UV microscope are 1 nm and 0.2 nm respectively. In long-term measurements the maximum lateral and focus drift rate observed were 30- and 20 nm / hour respectively. The measured point spread function contained only radial symmetric optical aberrations. Using the Zernike-Nijboer theory including only the defocus and spherical aberrations, fit residuals were obtained that contain systematic deviations in the order of the noise level