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CRYSTALLIZATION AND MELTING OF AMORPHOUS SILICON ON A MICROSECOND TIME SCALE G.L. OLSON,* J.A. ROTH,* E. NYGREN,** A.P. POGANY,** and J.S. WILLIAMS** * Hughes Research Laboratories, Malibu, CA 90265 ** Microelectronics Technology Centre, RMIT, Melbourne, Australia ABSTRACT Measurements of the competition beween solid phase epitaxy, solid phase random nucleation, and melting in amorphous Si on a microsecond time scale are reported. We find that the behavior of amorphous Si under microsecond pulsed dye laser irradiation depends strongly on film thickness and temperature. In "thin" (1330°C. The observation of a solid phase transformation at these temperatures is in good agreement with the data previously obtained using cw laser heating [4 5] Second, in contrast with the cw laser results, we find that meltin occurs in "thick" (2600 A) amorphous films (both intrinsic and doped) at a significantly lower temperature (-I 190'C). The latter result is in agreement with measurements of phase transformation kinetics in Si(a) using Q-switched laser heating [1]. We will describe the experimental methods used for these measurements and will discuss results obtained on samples containing intrinsic (Si+-implanted) and As+- and In+-implanted films of different thicknesses. EXPERIMENTAL The experimental arrangement used for measuring the kinetics of phase transformations on a microsecond time scale is shown in Fig. 1. A flashlamp-pumped dye laser (Candela LFDL-6) was used as the heating source. The pulse-forming network of the laser was modified in order to extend the width of the output pulse from the normal 0.8 tis (FWHM) to approximately 5 ýis (see Fig. 2). This modification was performed because it is necessary to heat an amorphous film for

Mat. Res. Soc. Symp. Proc. Vol. 74. c 1987 Materials Research Society

110

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Fig. 1. Experimental arrangement used for monitoring phase transformations on a microsecond time scale. Flashlamp-pumped dye laser is used as heating source; TRR used to monitor transformation kinetics.

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Fig. 2. Temporal profile of flashlamp pumped dye laser pulse

at least 2 lis to induce a measurable amount of solid phase crystallization. A dye laser was selected for this application because it does not exhibit the intensity "spiking" phenomena and relaxation oscillations characteristic of solid state lasers operated in this pulse duration regime, and because the pulsewidth can be varied from 0.5 to -12 [ls by a straightforward modification of the flashlamp pulse forming network. The dye laser wavelength was 0.59 Wim (Rhodamine 590 dye), the single pulse energy was 1 J, and the risetime (0 to 90% intensity) was -1.5 R±s. The principal advantage of the dye laser over a "chopped beam" cw laser for this application is the increased energy deposition rate and the concomitant decrease in the time required to reach a steady s