We describe the fabrication of three-dimensional (3D) microstructures by high-resolution x-ray lithography (XRL) as the first step in the realization of photonic band gap (PBC) materials for infrared wavelengths. In the soft x-ray range (lambda similar to 1 nm), conventional XRL mask technology can be adopted which allowed us to pattern 3D features with relatively thick resist layers. We have checked the possibility of making diamond-like PEG microstructures by three consecutive exposures under tilt angle of 35.26 degrees with respect to the incoming beam and a rotation angle of 120 degrees between each exposure. Exposures were done in a vacuum chamber with a broadband synchrotron radiation (SuperACO) and three types of experimental configurations. As results, we obtain diamond-like structures showing several (111) lattice periods in polymethyl methacrylate resist.