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TIME-RESOLVED STUDY OF SILICON DURING PULSED-LASER ANNEALING* B. C. LARSON, C. W. WHITE, T. S. NOGGLE, J. F. BARHORST, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 and D. M. MILLS Cornell High Energy Synchrotron Source and School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14850 ABSTRACT Near surface temperatures and temperature gradients have been studied in silicon during pulsed laser annealing. The investigation was carried out using nanosecond resolution xray diffraction measurements made at the Cornell High Energy Synchrotron Source. Thermal-induced-strain analyses of these real-time, extended Bragg scattering measurements have shown that the lattice temnerature reached the melting point during 15 ns, 1.1-1.5 J/cm• ruby laser pulses and that the temperature of the liquid-solid interface remained at that temperature throughout the high reflectivity phase, after which time the surface temperature subsided rapidly. The temperature gradients below the7 liquid-solid interface were found to be in the range of 10 0C/cm. INTRODUCTION Real-time investigations [1] of pulsed laser annealing in silicon have been carried out using optical reflectivity, optical transmission, Raman scattering, electrical conductivity, and x-ray diffraction. These studies have provided rather detailed information on the time scale of the annealing process under varying laser conditions, and significant progress has been made in understanding the transient structural and temperature aspects of the process as well. Electrical conductivity [2] and nanosecond resolution x-ray diffraction [3] measurements have provided depth information on the liquid phase of the annealing process and the x-ray diffraction measurements have provided time resolved temperature profiles in silicon following laser annealing as well. In this paper we report time resolved x-ray diffraction measurements of the temperature and temperature gradients in silicon during the annealing process. THEORY The theoretical framework one-dimensional near-surface dynamical diffracton theory. by the following differential

for Bragg scattering of x-rays from crystals with strains is well understood [4] in the context of The x-ray reflectivity for such a system is given equation

*Research sponsored by the Division of Materials Sciences, U.S. Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation. The CHESS portion of this research was supported by the National Science Foundation. Mat. Res.

Soc. Symp. Proc. Vol. 13 (1983) Published by Elsevier Science Publishing Co.,

Inc.

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i ý=dX X2(l+ik) - 2X(y+ig) + (1+ik)

(1)

where X(A) = XI + iX 2 is the normalized scattering amplitude as a function of the reduced spatial (or depth) coordinate, A. For thermal induced strain the effect of thermal motion (not considered in ref. 3) on the scattering factor must be considered and is introduced through the Debye-Waller factor e-M. In this case, the x-ray scattering factor f = f'+if" is replaced by fe-ý and A is then writ