Diffraction Grid Fabricated By Advanced Microelectronics Techniques For Hipparcos Astrometry Mission

The grid, made up of 2688 3.2 micron wide and 22 mm long, transparent slits, and several auxiliary patterns has to be written on the spherical side (radius 1400 mm) of an odd-shaped quartz block. By using electron beam pattern generation in conjunction with classical chromium mask fabrication techniques, it has been possible to satisfy the tight specifications imposed on pattern registration and on critical dimension control of the individual slits. The originality of our approach lies in the fact that a dedicated wri-ting strategy is used which allows us to provide extended compensations for substrate height variations on both beam focus and beam deflection parameters. A dedicated calibration programme running on a second electron beam pattern generator has been used in order to provide a measuring tool with extended nanometer accuracy.