Time Resolved Reflectivity Measurements on Pulsed Laser Irradiated Silicon Immersed in Water
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TIME RESOLVED REFLECTIVITY MEASUREMENTS ON PULSED LASER IRRADIATED SILICON IMMERSED IN WATER X. D. Wu*,
D. DIJKKAMP+ AND T. VENKATESAN
Bell communications Research Inc., Red Bank, NJ 07701 *Physics Department,
Rutgers University,
Piscataway, NJ 08854
+Philips Research Laboratories, Eindhoven, The Netherlands
ABSTRACT Time resolved reflectivity (TRR) measurements were carried out during pulsed laser irradiation of silicon immersed in water. It was found that the TRR in water was similar to that in air though the signal deteriorated after about 100 ns from the starting point of the laser for incident energy densities above 1.4 J/cm2 (unlike what is observed in air). The total melt duration in water was about 2.8 to 1.6 times less than that in air at the same absorbed energy density. It was estimated that 20 % of the absorbed energy was taken away by the water layer.
For the same energy coupled into
the solid the melt-in/regrowth kinetics was speeded up by the presence of the water layer at the surface by about a factor 2 consistant with the 5
results of Polman et. a1 .
INTRODUCTION
The original goal of pulsed laser processing of semiconductors was to electrically activate ion implanted dopants by removing the lattice damage caused by the implantation process 1 , 2 . In terms of fundamental understandings, pulsed laser irradiation has been used as a technique to study very interesting physical phenomena, such as nonequilibrium freezing and melting 3 and explosive crystallization4 in solid. Recently, first results of buried marker experiments on irradiation of amorphous silicon under water were reported 5 . It was believed that the water layer will have influence on both melting and solidification dynamics. Since the energy coupling to silicon was different in air and under water, the data could be compared only at one point, namely at the threshold for epitaxy of the amorphous layer, to see the effect of the water layer. At the same absorbed energy density the melt duration of silicon under water was estimated to be about 2-3 times less than that in air, from redistribution of the implanted marker after laser irradiation 5 . In this paper, we present the results of time resolved reflectivity (TRR) measurements on silicon immersed in water, which yield a direct measurement of the surface melt duration. By comparing the results in air and water, the effect of the water on the melting and regrowth dynamics is determined. It Is seen that for the same absorbed energy density the melt-in and regrowth kinetics under water is speeded up by about a factor of two.
EXPERIMENTAL A Lambda Physik EMG-200 excimer laser ( 248 nm, 30 ns) was used for melting the silicon surface. Only the central part of the laser beam was Mat. Res. Soc. Symp. Proc. Vol. 100. 01988 Materials Research Society
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2 focused with a quartz lens to a spot of about 2x3 mm . Using quartz plates as attenuators, the energy density could be varied between 0.1 and 2.5 J/cm2 . The probe beam was an Ar+ laser beam ( 514 nm) ,with an incident angle of
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