Plugging of Al Films Into Submicron Diameter Via Holes by Excimer Laser Irradiation
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PLUGGING OF Al FILMS INTO SUBMICRON DIAMETER VIA HOLES BY EXCIMER LASER IRRADIATION R.MUKAI, N.SASAKI AND M.NAKANO Fujitsu Limited, Advanced Technology Division 1015 Kamikodanaka, Nakahara-ku, Kawasaki 211, Japan ABSTRACT Via-hole filling technique by momentarily melting an aluminum film has been developed, whereby planarization of aluminum films for multilevel interconnects on integrated circuits can be achieved. The melting is performed with an optical pulse irradiation from an ArF excimer laser without the problem of junction spiking. This technique is applicable to filling submicron-diameter vias having a diameter of O.6pm with 0.7km depth(aspect ratio:-1.2). Very high aspect ratio(2.0) via-hole filling is achieved by heating the sample. During the laser irradiation, the sample substrate was kept at 300 0 C. INTRODUCTION Aluminum or aluminum alloys that are deposited by evaporation or magnetron sputtering are widely used for metallization on integrated circuits. Step-coverage of the deposited film over via-holes is poor because the film at the sidewall of vias is relatively thin due to the shadow effect. This condition gets worse as dimensions shrink. The step-coverage problem can be solved if the vias are filled by a plug of metal. Selective tungsten chemical vapor deposition [1], metal deposition by bias sputtering [2,3], or aluminum deposition with the combination of evaporation and resputtering in a multiple alternation sequence [4] show promise for filling vias. However, the resulting surface is not found to be planar. The planarization is needed especially when the vias are stacked vertically in multilevel metallization. The planarization is achieved by melting the metal film with pulsed laser irradiation [5]. This phenomenon is brought about by the mass transport of metal during the melting procedure. The technique planarizes gold and aluminum film covering a conductor-line, insulated with silicon dioxide. However, the technique is useless in the case of planarization of a circuit with very high aspect ratio via-holes because the vias cannot be filled by a plug of metal. The filling problem can be solved if the molten metal is transported actively.
Mat. Res. Soc. Symp. Proc. Vol 74.
1987 Materials Research Society
230
This paper demonstrates an approach in which active mass-transport of aluminum during the melting procedure can be performed. In this approach, the aluminum film is melted with an optical pulse irradiation from an ArF excimer laser(wavelength 193nm). During the laser irradiation, the sample is kept at 300 0C. By this sample heating, the active mass-transport is realized. The optical beam has high absorption coefficient in aluminum (1.3x10 6 cm-1). The pulse duration is short(15ns). Therefore this irradiation brings absorption of the laser beam at a shallow layer in the film, and the ultra-rapid heating results in prevention of undesirable metallurgical reactions. VIA HOLE FILLING BY USING EXCIMER LASER IRRADIATION An approximately 1lum-thick pure aluminum film was conventionally deposi
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