MICRODEPOSITION OF METALS BY FEMTOSECOND EXCIMER-LASER

Microablation and transfer of thin metal films using ultrashort, ultra violet 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 focus ed onto thin Cr films through the supporting transparent quartz substr ates. Single pulses are used to completely remove the metal film. The ablated material is transferred onto a receiving target glass substrat e placed parallel to the source film. Experiments were conducted in a miniature vacuum cell under a pressure of 10(-1) Torr. The distance be tween the source and target surfaces is variable from near-contact to several hundreds of microns. Serial writing of well-defined metal line s and isolated dots, is accomplished using the x-y sample micropositio ning system. Optical microscopy and surface profilometry showed deposi tion of highly reproducible and well-adhering features of a few micron s in width for a source-target distance in the neighborhood of 10 mu m . The short pulse length limits thermal diffusion, thereby enabling su perior definition of the deposited features. Metal patterns were also directly deposited via a parallel-mode mask projection scheme. In a fi rst demonstration of this method, deposited diffractive structures wer e shown to produce high-quality computer-generated holograms. (C) 1998 Elsevier Science B.V.