The authors present a fabrication process of large-area (1.7x1.7 mm(2)) dielectric and metal-coated lamellar freestanding gratings structured at the micrometer scale. Both the stress management and the drying problems have been carefully optimized for the fabrication of drilled membranes. Transmission spectra measurements of freestanding gold-coated gratings demonstrate the achievement of high quality, accurately controlled optical filters in the midinfrared wavelength range.