Post-Irradiation Annealing of Laser-Formed Silicide Layers
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533
and Materials Processing
POST-IRRADIATION ANNEALING OF LASER-FORMED SILICIDE LAYERS M. Wittmer, Brown Boveri Research Center, Switzerland
CH-5405 Baden,
and M. von Allmen, Institute of Applied Physics, CH-3012 Bern, Switzerland
University of Bern,
ABSTRACT We have investigated the post-irradiation annealing effects of laser-formed Pt, Pd, Rh and Ni-silicides. It was found from Rutherford backscattering and x-ray analysis that compositional changes occur during subsequent high temperature annealing in a vacuum furnace. Generally, a single silicide phase tends to form at the expense of the other phases present following laser irradiation. The surviving phase is not necessarily identical to the end-phase found in a binary solid-state reaction couple of the same system. INTRODUCTION Irradiation of metal films deposited on single crystal Si with a laser heat pulse has been used recently to produce silicide layers :1-5'. The formation of the silicide takes place by melting of the surface layer, liquid phase interdiffusion of the constituents and rapid solidification of the liquid. Cooling rates dur0 ing solidification are in the order of 1010 K/sec and greatly exceed those obtained with conventional splat cooling techniques [61. It is therefore not surprising that composition and microstructure of pulse-laser reacted silicide layers have been found to be very different from those observed in furnace annealed silicides. These differences are associated with rather large deviations from thermodynamic equilibrium of the pulse laser-produced silicides, and are a result of rapid solidification. In view of the use of silicides formed by pulse laser annealing as electrical contacts in integrated circuit technology, it is of great interest to know the metallurgical stability 8 f these silicides during subsequent thermal annealing up to 600 C, as required for passivation and packaging purposes after the metallization process. We have therefore investigated the post-irradiation annealing effects upon laser-formed Pd, Pt, Rh and Ni silicides. The results presented below encourage the use of pulse laser-formed silicides in microelectronics. Furthermore, interesting insight in the thermal stability of various metal-silicides is gained. EXPERIMENTAL Commercial silicon wafers of (111) orientation and 10 Qcm resiswere used throughout this work. After standard cleaning tivity procedures the wafers were loaded in a dry UHV system. Films of
534 Pd, Pt, Rh and Ni of 1000 or 2000 R thickness were then evaporated 8 Torr. The onto the wafers with an e-gun at pressures of 5x10coated wafers were cleaved and small samples were irradiated with a Q-switched Nd:YAG laser (A = 1.06 pm) operating in the TEMoo mode. The laser pulse had a duration of 35 nsec and the beam was focused to a spot of 3.8 mm in diameter. Extended areas of the film were reacted by multiple irradiation with an overlap of 75 % between subsequent laser spots. The laser fluence was adjusted by in the beam path so that the entire introducing neutral filters metal film w
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