Diffusion, Solubility and Segregation of Implanted Cu, Ag and Au in Amorphous Si
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DIFFUSION, SOLUBILITY AND SEGREGATION OF IMPLANTED Cu, Ag AND Au IN AMORPHOUS Si D. C. JACOBSON,* R. G. ELLIMAN,* J. M. GIBSON,* G. L. OLSON,** J. M. POATE,* AND J. S. WILLIAMS* * AT&T Bell Laboratories, Murray Hill, NJ 07974 ** Hughes Research Laboratories, Malibu, CA 90265 ABSTRACT The diffusion of Cu, Ag and Au has been measured in implanted, amorphous Si, over the range 150-600"C. The diffusion coefficients are characterized by Arrhenius relationships with activation energies for Cu, Ag and Au of 1.25, 1.6 and 1.4 eV respectively. The solubility of Au in amorphous Si was measured to be 6 orders of magnitude greater than crystalline Si at a temperature of 515'C. The Cu, Ag and Au are segregated ahead of the moving amorphous-crystalline interface. The presence of Au can increase the velocity of the interface. INTRODUCTION The study of diffusion in crystalline materials has been of major importance in elucidating some of the kinetic and defect properties of condensed matter. There have been few studies, however, of diffusion in the amorphous state. One of the best known amorphous systems is amorphous Si (a-Si), but experimental studies of diffusion have been hampered by the fact that a-Si recrystallizes at low temperatures. We [11 have increased the time-temperature window for diffusion measurements by preparing thick amorphous layers by high energy Ar ion implantation. In this way we have been able to measure [21 the diffusion of Cu, Ag and Au in a-Si. These species have very high solubilities in a-Si and we have examined their segregation at the moving amorphouscrystalline phase boundary. EXPERIMENTS AND RESULTS Samples were prepared by implanting Cu, Ag and Au into (100) Si wafers at energies between 100 and 400 keV and doses between 5x1014 and lx 1016 atom/cm 2 . These implantations typically produced a-Si layers -2000A thick which, under normal solid phase epitaxial regrowth conditions, would completely recrystallize in 200 s at 600°C. To increase the window for diffusion measurements some of the samples were amorphized to depths of 21tm using Ar ion bombardment at energies of 0.5, 0.8, 1.4, and 2.1 MeV and doses of 2, 2.5, 3, and 3.5x l0 14 ions/cm 2 respectively with the samples held at liquid nitrogen temperatures. We [31 have shown that this recipe for Ar implantation will produce a uniform amorphous layer whose solid phase regrowth obeys the normal
Mat Res. Soc. Symp. Proc. Vol. 74. 1987 Materials Research Society
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Arrhenius dependence. To prepare amorphous Si samples to study segregation and regrowth kinetics, thin layers were prepared by Si 29 implantation at 70 and 120 key with doses of 1.0 and 2.0 x 1015 /cm 2 respectively with the samples held at 77 K. This produces an amorphous layer about 2500A thick. The as-implanted impurity depth distributions were analyzed using the Rutherford backscattering (RBS) and channeling of 2 MeV 4 He ions. Figure 1 shows channeled RBS spectra of a 2700A amorphous layer with implanted Au before and after annealing at 450'C for 30 min. These data illustrate sever
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