74 Applied Surface Science 43 (1989) 74-80 North-Holland LASER WRITING OF HIGH PURITY GOLD TRACKS M. JUBBER, Ll.B. WILSON Department of Physics. Heriot-Watt Unit,ersitv, Riccarton, Edinburgh Ett14 4AS, Scotland, UK J.L. DAVIDSON, P.A. FERNIE and P. JOHN Department of ChemistD,, Heriot-Watt Unit,ersi{;, Riccarton, Edinburgh EHI4 4AS, Scotland, UK Received 30 May 1989; accepted for publication 29 June 1989 Gold tracks have been deposited on thermally oxidised silicon wafers by pyrolytic decomposition of gaseous methyl(triethylphos- phine) gold (I), using focused 514 nm radiation from an argon ion laser. The precursor, AuMe(Et3P), is a white crystalline solid with a room temperature vapour pressure of a few reTort and is one of a series of compounds being evaluated for laser deposition. Tracks were deposited at speeds from 4.5 to 35 /Lm s -1 with a focused spot size of about 12 /~m. LIMA, SIMS and EDAX were used to analyse the chemical composition of the tracks; the purity of better than 98% is consistent with the low value of room temperature resistivity (4.2 btf~ cm, compared with approximately 2 p.f~ cm for bulk gold). Stylus profilometry and SEM analysis showed the lines to have an almost rectangular cross section suggesting that deposition is more rapid on the gold surface than on the SiO 2 substrate. 1. Introduction Despite the widespread use of doped polysili- con for conducting interconnects in integrated cir- cuits, there are still requirements for higher con- ductivity tracks which can only be satisfied by metallic conductors. Thick film circuit techniques also use metallic conductors; commonly these are precious metals in the form of polymer metallor- ganic inks which are thermally cured in air [1-7]. A way of avoiding the costly waste of gold-filled materials, but without changing to less conducting materials, is to use volatile gold compounds which can be decomposed selectively only over the areas to be coated. This has previously been demon- strated using volatile gold (III) compounds such as dimethyl(acetylacetonate) gold (III) [8-11] or trimethyl(trimethylphosphine) gold (III) [12]. In contrast to these previous studies, we have in- vestigated the laser chemical vapour deposition of gold using low oxidation state gold complexes of the type methyl(trialkylphosphine) gold (I), and specifically methyl(triethylphosphine) gold (I). 0169-4332/89/$03.50 ,%'Elsevier Science Publishers B.V. (North-Holland) 2. Experimental The output from an argon ion laser (Coherent Innova 100-10) of up to 10 W at 514 nm is collimated and expanded to 10 mm diameter be- fore being focused by a quartz meniscus lens (see fig. 1). At focus, the (1/e 2) spot size is 12 ,am. Substrates are 100 nm of thermally grown SiO 2 on 100 n-type single crystal silicon wafers; these are mounted on a copper heatsink within a stainless steel reaction cell. A quartz window is fitted to the reaction cell to allow the laser beam to be focused on the substrate. The reaction cell is translated under the focused beam by a high resolution X-Y translation stage with 0.1 btm step size; the trans- lation speed can be varied between 2 and 200/~m s ~. A computer is used to control the laser power, open and close a shutter and move the reaction cell through a series of predefined motions. Before deposition, the reaction cell is pumped out to a base pressure of 10 5 mbar using a rotary backed turbomolecular pump. The precursor is a white crystalline solid, pre-