The authors present a breakthrough multistage dry-etch process to create 100 nm half-pitch gratings in silicon with depths up to 6 mu m. Interference lithography was used to pattern gratings in an optically matched stack of materials to form a 400-nm-thick silicon oxide hard-mask. The oxide was then used to mask the subsequent deep reactive-ion etching of silicon. In this article, the authors describe their grating patterning, pattern transfer, and deep etch processes, and present progress toward combining this technique with coarser scale lithography steps designed to form an integrated mechanical support structure to produce freestanding x-ray diffraction gratings. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3507427]