Volume 3. number 3 MATERIALS LETTERS January 1985 ATOMICSTRUCTUREOFCOLLISIONCASCADESINION-IMPLANTEDSILICON ANDCHANNELINGEFFECTS J. NARAYAN zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA M icroelectronics Center of North Carolina, Research Triangle Park, NC 2 7709, USA and M aterials Engineering Department, North Carolina State University, Raleigh, NC 27695.7907, USA O.S. OEN Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA and D. FATHY and O.W. HOLLAND M icroelectronics Center of North Carolina, Research Triangle Park, NC 27709, USA Received 29 October 1984 We have investigated the atomic structures of collision cascades in Bi+-implanted silicon. The formation of subcascades or bunching of the primary cascades is clearly observed. The central regions of the cascades were found to be amorphous with a high density of disorder in the surrounding regions. The experimental results are discussed in terms of the computer simulation of the deposited damage energy profiles. The effect of channeling on the deposited damage energy profile is examined. The peak and integrated damage energies are considerably lower in channeling directions compared to random directions. Ion implantation represents a crucial step in the fabrication of microelectronic devices. The implanta- tion by monoenergetic ions into a random amorphous solid produces an approximate gaussian profile of dopant, and displacement damage. The dopant as well as displacement damage profiles are very sensitive to the incident directions with respect to axes and planes in crystalline solids. The critical angle for channeling is particularly sensitive to the nuclear charge of the in- cident ion (Zl) and substrate atoms (Z2), and energy of the incident ions (E) [ 1,2 1. There is a critical angle for channeling [JI a (Z1, Z2/E)li2] below which signif- icant deviations from a gaussian profile corresponding to a random solid are observed. Knowledge of the do- pant and damage profiles for a given set of variables is necessary to determine the characteristics of the p-n junctions formed by ion implantation. In the previous studies, TEM techniques were used to investigate the structure and amorphous nature of collision cascades. However, detailed studies of atomic structure of the cascades were lacking [3]. In this paper, we have used high-resolution trans- mission electron microscopy [4] to study the atomic structure of individual cascades. Clear evidence of bunching or subcascade formation is observed. The effect of ion implantation conditions and channeling are examined theoretically and experimentally. Pene- trating damage profiles with significant reduction in total damage production in the channeling directions are emphasized. Single crystals of (100) and ( 110) orientations were implanted with 100 keV, 208Bi+, 50 keV, 3oSi+, and 35 keV, l1 B+ ions to doses ranging from 1 .O X 1012 to 1 .O X 1015 cmM2 while the substrate temperature was kept either at liquid-nitrogen (LN2) or at liquid-helium (LHe) temperature. The (011) cross sections from (100) specimens were prepared by an ion thinning pro- cedure, whereas (110) plan-view specimens were pre- pared by a chemical polishing technique. The (110) cross-section and plan-view specimens were studied by a JEOL 2OOcx electron microscope operating at 200 0 167-577x/85/$ 03.30 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division) 67