Pulsed Laser Induced Melt and Phase Transformation of Ni Silicide Layers on Si Substrate
- PDF / 892,479 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 47 Downloads / 207 Views
PULSED LASER INDUCED MELT AND PHASE TRANSFORMATION OF Ni SILICIDE LAYERS ON Si SUBSTRATE
P.BAERI*
M. G. GRIMALDI
F.PRIOLO*,
E.RIMINI
A.G.CULLIS
N.C.CHEW * Dipartimento **
Royal
di Fisica, Catania Italy Signals and Radar Establishment,
Malvern
U.
K.
ABSTRACT Thermally grown Ni 2 Si and NiSi 2 layers on Si substrates were irradiated b4 40 ns Nd laser pulses in the energy density range 0.3-2.0 J/cm . The samples were analyzed by time-resolved reflectivity, 2.0 MeV He + Rutherford backscattering in combination with channeling and by transmission electron microscopy. In the NiSi 2 /Si system the melt starts at the free surface (1280 K) and propagates towards the inside. Dissolution of substrate silicon atoms occurs when the silicon temperature reaches the liquidus temperature (1400 K). In the Ni 2 Si/Si samples the melt starts instead at the interface when it reaches the eutectic temperature (1250 K). The subsequent propagation towards the surface is limited by the mass transport of silicon atoms to maintain a composition near that of the eutectic. In some cases the surface may melt also at the congruent melting temperature (1570 K), giving rise after solidification to a quite complex structure. The different behaviour of the two silicides/silicon systems is explained in terms of phase diagram.
INTRODUCTION Pulsed laser, ion or electron beam irradiation has been extensively adopted in these last years to induce phase transformations in binary systems [1]. Several metal-silicon systems for the technological relevance of silicides have been carefully examined [2]. A variety of different phenomena have been found and explained in terms of the phase diagram of the two elements and of the initial structure of the samples. Laser irradiation of nickel films on top of Si results usually in a mixing between the two elements and in the formation of a number of different compounds. Experimental evidences, mainly due to ion beam irradiation of Ni,Co and Pt on Si (3,41,or on laser irradiation of Ni on Si [51, suggest that interfacial mixing occurs at near the eutectic composition. Reactions start below the melting points of either the metal or the silicon, probably at the lowest eutectic temperature. The role played by equilibrium thermodynamics in the phase transformations which occur in the nanosecond time scale, is not quite clear due to the simultaneous presence of compositions ranging, in principle, from 100% of the metal element to 100% of
silicon. To investigate restricted portions of the phase diagram, we have irradiated nickel silicides in contact with silicon. The experiments have been performed on Ni 2 Si/Si and NiSi 2 /Si thermally grown layers. The Ni 2 Si is a congruent compound with a melting point of about 1570 K and the NiSi 2 is a non congruent one which exhibits a peritectic decomposition at 1266 K and whose liquidus temperature is 1400 K. Moreover there are two Mat.Res. Soc.Symp. Proc.Vol. 74. 1987Materials Research Society
212
eutectic
points
in
the Ni-Si phase diagram (both at about 1250
K)
Data Loading...
