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COPPER LASER INDUCED CHEMICAL VAPOR DEPOSITION OF Al FILMS M. I. YANKOVA, W. SHANOV", and B. IVANOV*" *Illinois Institute of Technology, Department of Metallurgical and Materials Engineering, Chicago, IL 60616 -Higher Institute of Chemical Technology, Sofia, Bulgaria ABSTRACT The focused output from a copper laser (X = 510nm) has been used for direct writing of Al on silicon substrates by pyrolitical decomposition of trimethilaluminum (TMA). These results demonstrate that direct writing can be accomplished at room temperature by a single-step deposition process induced by a single light source. For a laser power density between 5 and 50 kW cm 2 , the widths of the stripes varied between 60 and 200 Mim with corresponding thickness between 0.5 and 0.8 Mm. The width of the stripes proved to be independent of the scanning velocity, Vs, within the range 50 Mzm s' < V, < 300 Mm st. The analysis included scanning electron microscopy (SEM) to study the film morphology, a step profiler to evaluate the thicknesses and the profiles of the stripes, and energy dispersive spectroscopy (EDS) to provide their chemical compositions.

INTRODUCTION Laser chemical vapor deposition (LCVD) has been extensively studied in recent years [1-3]. The rapid expansion of this field stems not only from basic scientific interest, but also the potential for technological applications in material processing. More specifically, the direct writing of Al on silicon wafers is of a great interest for maskless device fabrication techniques [4] and for circuit mask repair [5]. Contrary to conventional patterning techniques such as, for example, standard chemical vapor deposition (CVD) or plasma chemical vapor deposition (PCVD), which are used in conjunction with mechanical masking or lithography, LCVD is not limited to planar substrates, but allows three-dimensional fabrication as well. The lateral dimensions of the patterns may range from about few tens of a micrometer up to several centimeters [2,6]. Several authors have described one- or two-step processes in order to deposit thin aluminum films from metalorganic precursors. Higashi and Fleming [7] used UV laser photolysis of organoaluminum adlayers to activate the deposition of Al via thermal decomposition of triisobutylaluminum (TIBA). Motooka et al. [8] reported photodissociation of dimerised TMA by Kr-F UV laser irradiation. Tsao and Ehrlich [9] used focused CW UV laser irradiation followed by CW IR laser irradiation to activate the decomposition of TIBA and the growth of aluminum films. In this paper we describe experiments in which a visible quasi-CW copper laser activates pyrolitical decomposition of TMA in the presence of Ar, and deposits thin Al stripes.

EXPERIMENTAL PROCEDURES Experimental apparatus The experimental apparatus for LCVD used in this study is schematically shown in Fig. 1. Mat. Res. Soc. Symp. Proc. Vol. 201. c 1991 Materials Research Society

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Fig. 1 : Experimental apparatus for LCVD with visible quasi-CW Cu laser: 1 - Laser; 2 - Laser beam; 3 - Mirror; 4 - Focusing optic