Experimental Research On Photomask Repair System Using Laser Induced Chemical Vapor Deposition(LCVD) Method

LCVD processes, which are the main method of repairing the clear defects of photomask, are divided into two categories: pyrolytic and photolytic. Pyrolytic LCVD is a thermally driver process in which the energy of a laser beam is used to heat the surface of a substrate to the temperature required for chemical deposition. Photolytic LCVD uses photons from a laser beam to break chemical bonds within the reactive gas. In order to repair the clear defects of photomask, photolytic LCVD process is required to initiate the chemical reactions. When a laser beam irradiates the surface of a subustrate directly, the temperature of the film growing on the substrate gets high, so pyrolytic LCVD begins. Because the deposition rates for Pytolytic LCVD are orders of magnitude higher than for Phtolytic LCVD, pyrolytic LCVD becomes dominant.In order to repair the photomask with defects in the open air, reaction chamber and gas control unit are designed to ensure the cleanness of the substrate and prevent growing film from the air. The experiment shows that, long time radiation in the open air results in low quality of the film. To get the Cr film with good adhesion and extinction on transparent substrate, firstly we use 355nm UV laser with the intensity of 1.2×10~7W/cm~2, and the total radiation time is 60s. With these parameters, we get some more thick film, but the structure of the film is loose. Then we use 351nm UV laser with the intensity of 1.3×10~8W/cm~2 and get high quality and good adhesion film after short duration.Result shows that, in the open air, the method with high intensity and short radiation time can get high quality film. In future, the reaction chamber and laser flux uniformity should be improved and an online detecting system should be carried out.