Formation of a Metastable NiSi Phase On <111> Si Induced By Pulsed Laser Irradiation
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FORMATION OF A METASTABLE PULSED LASER IRRADIATION
NiSi
PHASE
ON
F.PRIOLO, P.BAERI, M.G.GRIMALDI and E.RIMINI Dipartimento di Fisica dell'UniversitA, Corso Catania, ITALY
Italia
Si
INDUCED
57,
BY
195129
ABSTRACT Thermally grown NiSi layers on Si substrates were laser pulses in the energy by 35 nsec Nd glass irradiated 2 density range 0.3-2.0 J/cm . Time resolved reflectivity measurements were performed during the irradiation to detect 2.0 MeV He+ by The samples were analyzed melting. surface Rutherford Backscattering Spectrometry in combination with channeling effect. The measured threshold for surface melting higher than at energy densities was 0.5 J/cm 2 . Irradiation 2 1.3 J/cm changed the silicides layer composition because of the mixing with the underlying silicon. In the intermediate energy density range (0.7-1.1 J/cm ) slight changes in composition were observed, a strong alignement of NiSi molecules along the substrate direction was however observed. The measured Xmin was about 30%. It seems then that an epitaxial NiSi phase can be grown by pulsed laser irradiation with a suitable choice of the this energy density. Work is in progress to identify incident new NiSi phase by TEM. However this ordered phase is a metastable one since after anunealing at 250*C,30min the channeling yield reduction disappeared without any appreciable change in composition.
INTRODUCTION During the past years there has been considerable interest in studying epitaxial metal silicide layers in view of their applications in the VLSI technology [1]. The understanding and control of interactions between metal thin films and silicon in solid state appear to be relatively well understood and large effort is nowadays devoted to novel deposition techniques in order to achieve epitaxial silicide layers which surpass the policrystalline ones in conductivity, thermal stability and reproducibility of interface properties. Single crystal epitaxial NiSi 2 films on Si have been obtained with the very sophisticated "template" techniques [2]. In this
case single NiSi
2
crystals on Si both of A type (epitaxial
with the substrate) and of B type orientation (epitaxial but rotated 180* around the substrate direction) have been grown. Very recently it has been reported that an epitaxial NiSi layer of exagonal structure on Si substrate has been also obtained with the "template" technique [3]. Pulsed laser annealing, as a mean to form metal silicide contacts on Si, provide the advantage of transferring the energy density only to a very localized region instead of heating up the entire wafer. Large efforts have been made to understand the physical processes leading to metal silicon interaction via liquid phase in the transient regime, tipical of pulsed laser heating. Often a mixture of different silicides with large lateral disuniformity and cellular structures formation have been observed. However, under suitable conditions, metastable Mat. Res. Soc. Symp. Proc. Vol. 91. 11987 Materials Research Society
492
phases as well as amorphous ph
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