Pulsed Laser Melting: The Effect of Implanted Solutes on the Resolidification Velocity
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PULSED LASER MELTING: THE EFFECT OF IMPLANTED SOLUTES ON THE RESOLIDIFICATION VELOCITY
G. J. Galvin,* J. W. Mayer,* and P. S. Peercy** *Department of Material Science, Cornell University, Ithaca, NY 14853; **Sandia National Laboratories, Albuquerque, NM 87185
ABSTRACT Transient electrical conductance has been used to measure the resolidification velocity in silicon containing implanted solutes. Nonequilibrium segregation of the solutes occurs during the rapid resolidification following pulsed laser melting. The velocity of the liquid-solid interface is observed to depend on the type and concentration of the solute. A 25% reduction in solidification velocity is observed for an implanted indium concentration of three atomic percent. Implanted oxygen is also shown to reduce the solidification velocity. The dependence of the velocity on solute concentration impacts a variety of segregation, trapping and supersaturated solution studies.
INTRODUCTION Pulsed laser irradiation can be used to very rapidly melt and resolidify a submicron thick layer of silicon [1-3]. During this rapid quench, solute atoms can be incorporated into the silicon at concentrations far in excess of equilibrium solid solubilities [4]. A measure of the departure from equilibrium is given by the velocity-dependent interfacial segregation coefficient k, which is the ratio of the solute concentration in the liquid to that in the solid immediately adjacent to the interface [5]. As the liouid-solid interface moves toward the surface during resolidification, solute atoms may diffuse ahead of the interface and thereby avoid being trapped in the solid. However, if the interface velocity is sufficiently high, the solute diffusivity will be insufficient to avoid incorporation. Under these conditions, k will approach unity and the concentration of incorporated solute may far exceed thermodynamic equilibrium limits [6]. Numerous theoretical and experimental studies [7-10] have been performed in an attempt to relate k to the liquid-solid interface velocity, v. Various models have been developed to describe solute trapping ptenomena; however, previous investigations have not considered the potential effects of the solute on the resolidification velocity. Using the transient electrical conductance technique [11] for a realtime measurement of the melt depth during pulsed laser melting, we have measured the effect of solutes on the liquid-solid interface velocity. At concentrations above a few tenths of an atomic percent, all solutes studied (In, Ga, As, 0 and N) reduced v1 relative to that of pure silicon. The magnitude of the reduction in v depends on the type and concentration of solute. This paper will discuss Ehe results for In and 0 implanted solutes in silicon-on-sapphire.
Mat. Res. Soc. Syap.
Proc. Vol. 23 (1984) @Elsevier Science Publishing Co.,
Inc.
112
EXPERIMENTAL CONSIDERATIONS Samples used in the present work were prepared from nominal 0.5 micron silicon-on-sapphire (SOS). SOS was chosen because its low photoconductivity allows measurement thr
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