Direct Writing of Al on Si by UV Exposure Prior to Laser-Assisted CVD
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DIRECT WRITING OF Al ON Si BY UV EXPOSURE PRIOR TO LASER-ASSISTED CVD J.E. BOUREE*, J. FLICSTEIN** and Y.I. NISSIM** *C.N.R.S., Laboratoire de Physique des Solides, F-92195 Meudon, France **C.N.E.T., Laboratoire de Bagneux, F-92220 Bagneux, France ABSTRACT Photodissociation of trimethylaluminum molecules with a UV lamp is shown to be an effective technique for predisposing the irradiated silicon surface prior to subsequent aluminum film growth via visible laser induced pyrolysis. The Al deposits thus obtained are carbon contamination free. The UV exposure time needed for the onset of Al nucleation and growth is deduced from an in situ laser reflectometry technique. Direct laser writing is obtained using this two-step process and a microscopic analysis of the lines is made in correlation with the experimental procedure. INTRODUCTION Laser-induced processes have been investigated in the last few years in the field of microelectronic devices. They offer many applications of localized reactions like etching, doping, oxidation and deposition of thin films [1-4]. More precisely, photodeposition of metal films from the vapor phase is of great interest for maskless device fabrication techniques as well as for circuit mask repair. Due to the importance of aluminum in integrated circuit metallization, our attention has been focused on the technique of laser direct writing of Al on silicon substrates [5,6] , by first irradiating a flow of trimethylaluminum (TMA) molecules with ultraviolet light (photolytic deposition process (7]) , following this by visible laser irradiation (pyrolytic deposition process [27). Oxygen and carbon contamination are the main problems to overcome for Al deposition. In previous work [8], it has been shown that the pyrolytic decomposition of the TMA molecule obtained with an Ar ion laser resulted in incomplete dissociation of the molecule, leading to a high level of C contamination in the deposited film. On the contrary, the photolytic decomposition obtained with a low pressure mercury lamp emitting preferentially at 254 nm gave rise to a low level of C contamination in the film, but due to the low power of the lamp, the deposition rate was too slow for a possible technological application [9] . In this work, it has been demonstrated that a simple exposure of the Si surface to the UV lamp can initiate the nucleation of Al. The growth of pure Al can be obtained following this exposure by irradiating with the Ar ion laser. In the present work, the experimental determination of the onset of Al growth and the kinetics of nucleation are
Mat Res. Soc. Symp. Proc. Vol. 75. c1987 Materials Research Society
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described. In the two-step process (UV exposure followed by the cw visible laser irradiation), Al deposition is observed at laser powers below the threshold of pyrolytic decomposition of the TMA molecule : the UV exposure induces a subsequent enhanced surface pyrolysis. Two main features result from this process the Al films are contamination free and the deposit width is determined by the laser s
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