Microdeposition of metals by femtosecond excimer laser

Microablation and transfer of thin metal films using ultrashort, ultraviolet laser radiation has been studied. A KrF excimer laser (lambda = 248 nm) having 500-fs pulse duration is coupled to a high-power image projection micromachining workstation. The laser irradiation is focused onto thin Cr films through the supporting transparent quartz substrates. Single pulses are used to completely remove the metal film. The ablated material is transferred onto a receiving target glass substrate placed parallel to the source film. Experiments were conducted in a miniature vacuum cell under a pressure of 10(-1) Torr. The distance between the source and target surfaces is variable from near-contact to several hundreds of microns. Serial writing of well-defined metal lines and isolated dots, is accomplished using the x-y sample micropositioning system. Optical microscopy and surface profilometry showed deposition of highly reproducible and well-adhering features of a few microns in width for a source-target distance in the neighborhood of 10 mu m. The short pulse length limits thermal diffusion, thereby enabling superior definition of the deposited features. Metal patterns were also directly deposited via a parallel-mode mask projection scheme. In a first demonstration of this method, deposited diffractive structures were shown to produce high-quality computer-generated holograms. (C) 1998 Elsevier Science B.V.