On the Indium Precipitation in Silicon
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ON THE INDIUM PRECIPITATION IN SILICON E. Ganin, W. Krakow IBM T.J. Watson Research Center, Yorktown Heights, NY 10598 Abstract Indium precipitation in Si after ion implantation and rapid thermal annealing was studied using plan-view and cross-sectional TEM and SIMS analysis. The precipitates were found to be single crystalline with the bulk In body-centered tetragonal lattice based on periodicity data in two dimensions. The orientation relationship between the precipitate and Si lattice has been derived to be:
[Oll]si 11[Ill1an (100)si II(011)In Introduction Indium is rarely used as a main p-type dopant in silicon due to it's relatively low solubility limit'. However, the equilibrium solubility limit can be significantly exceeded using ion implantation and low temperature annealing. Channeling experiments performed on Si implanted by high dose In ions showed that the equilibrium solubility limit can be exceeded by as much as 60 times, when the annealing temperature is kept sufficiently low to avoid diffusion2 . However, when diffusion takes place, phase separation occurs. Indium is precipitating out of solid solution. Precipitation may occur by impurity segregation on defects and in some cases may even form a second phase particles, which can be observed by conventional TEM. Earlier experiments3 showed strong redistrib-
ution of In after ion implantation and rapid thermal annealing (RTA). In this case In was used for amorphizing the substrate Si, prior to implanting the main dopant, B. Precipitation of In was observed to occur upon very short annealing times in the 950-1150 0 C range. In the present paper we report on the details of precipitation, the structure and orientation relationship with the host Si lattice. Experimental Indium was implanted with an energy 200 keV and a dose of 3 x 101' / cm2 into n-type, (100) oriented Si wafers. The main purpose of In implantation was to amorphize Si substrate. Successively the wafers were implanted by the main dopant B at 17 keV with 1 x 10'5 / cm 2 dose (Sample 1). Some wafers were implanted by In only (Sample 2). Subsequent annealing treatments were performed in a rapid thermal annealing apparatus (HEATPULSE 410) in the 950-11500C range for various times. The In and B concentration versus depth profiles were measured using SIMS analysis as reported elsewhere3 . The In precipitates were studied by both plan-view and cross-sectional TEM, using a Philips EM 430 microscope. Lattice images were digitized via digital television fr2ne store system, from which computer generated equivalents of optical diffraction patterns were obtained for localized structural analysis. Results and Discussion During ion implantation by In, the top layer of Si extending to - 165 nm in depth became completely amorphous, as was shown elsewhere3 by channeling RBS and cross-
sectional TEM. Subsequent annealing resulted in epitaxial solid phase regrowth from the
Mat. Res. Soc. Symp. Proc. Vol. 139. C1989 Materials Research Society
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crystal beneath the amorphous region. Fig. 1 demonstrates
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