Laser interference lithography allows fast and large area periodical structure to be made using simple equipment and inexpensive fabrication techniques. The principle of the LIL is based on two-laser beam interference. Diffraction gratings can be focus a diffracted beam, even if the substrate surface of the grating is flat, when the groove spacing varies with the groove position. A thin layer of photoresist is deposited on a flat substrate such as silicon or glass using a spin coater. The substrate is placed in the optical setup. In the metod the laser beam is filtered and expanded by a lens and pinhole. The laser beam is incident on a mirror and the substrate which are penrpendicular. Both the mirror and the substrate are mounted on a rotation stage with a 90 degree angle between them. The photoresist is exposed to the interference frings during a time that is adjusted according to the intensity of the light. Since there is a short path length between substrate and miror, LIL is very inexpensive to mechanical vibration. Calculation must be done to optimize the grating for the laser diode wavelength..
