Laser-Induced Deposition of Gold Micropatterns from Metallopolymer Thin Films: A Photochemical Approach
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LASER-INDUCED DEPOSITION OF GOLD MICROPATTERNS FROM METALLOPOLYMER THIN FILMS: A PHOTOCHEMICAL APPROACH V.H. FOULDING, N.S. CLEMENTS, K.W. BEESON, AND G.A. WEST Corporate Technology, Allied-Signal Corporation, P.O Box 1021R, Morristown, New Jersey 07960 ABSTRACT The deep ultraviolet (250 nm) photopatterning of spin-on films of polymeric Au mercaptide results in formation of adherent Au patterns. Fxcimer laser projection patterning and standard contact printing techniques give excellent pattern resolution on the micron scale. Laser direct write produces lines at very fast writing speeds. Exposed areas are less soluble than unexposed areas, i.e. the film behaves as a negative photoresist. Bakeout of developed patterns at 2500C yields good purity Au micropatterns up to 500 2 thick. Mechanistic information about pattern formation is gained from uv-visible, infrared, and mass spectrometric monitoring of the photolysis process, and from Auger analysis of films. Adherent patterns are apparently formed by photochemical cleavage of Au-S bonds followed by evaporation of a small amount of free mercaptide. The loss of ligand in the exposed areas renders them less soluble than unexposed film. Thermal decomposition of both photolyzed and unphotolyzed films has the same result of volatilizing all film material except Au. INTRODUCTION Laser microchemical processing has been an active research area for several years [1,2,3), and has important applications in the manufacture of VLSI and other electronic circuits. The deposition of gold and other metallic lines on the 1-50 micron scale by laser direct write or projection patterning is important as a means of fabricating and repairing interconnects. Gold has an advantage over other metals because of its high conductivity and its compatibility with processing in air. It is also the major component of alloys used to make ohmic contact to GaAs [4]. Recently, gold has been deposited onto silicon and other substrates by laser direct write and other photoassisted techniques from the gas phase [5,6), aqueous solution [7,8,9), and thin solid films [10-141. Although some of these processes utilize bandgap irradiation of the substrate or photolysis of surface adsorbates in the deposition process, the majority of techniques are pyrolytic in nature and involve localized heating of the substrate to high temperatures to initiate and drive deposition. This complicates their use in conjunction with heat-sensitive electronic materials and devices. We are interested in the photodecomposition of thin films containing Au or other metal complexes as a route to micrometallization, and have reported the first known examples of purely photolytic deposition of metal patterns from thin solid films by excimer laser projection patterning [15) and uv laser direct write [16] of commercially available Au and Pt mercaptide resinates. In theory, fast deposition rates can be achieved simultaneously with high resolution in thin solid films because
Mat. Res. Soc. Symp. Proc. Vol. 75. ý 1987 Materials Research Society
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