Diffusion and Defect Structure in Nitrogen Implanted Silicon
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DIFFUSION AND DEFECT STRUCTURE IN NITROGEN IMPLANTED SILICON Omer Dokumaci, Richard Kaplan, Mukesh Khare, Paul Ronsheim, Jay Burnham*, Anthony Domenicucci, Jinghong Li, Robert Fleming, Lahir S. Adam**, and Mark E. Law** IBM SRDC, Hopewell Junction, NY 12533 * IBM Microelectronics, Burlington, VT. * Electrical Engineering Dept. , University of Florida, Gainesville, FL 32611 ABSTRACT Nitrogen diffusion and defect structure were investigated after medium to high dose nitrogen implantation and anneal. 11 keV N2+ was implanted into silicon at doses ranging from 2x1014 to 2x1015 cm-2. The samples were annealed with an RTA system from 750oC to 900oC in a nitrogen atmosphere or at 1000oC in an oxidizing ambient. Nitrogen profiles were obtained by SIMS, and cross-section TEM was done on selected samples. TOF-SIMS was carried out in the oxidized samples. For lower doses, most of the nitrogen diffuses out of silicon into the silicon/oxide interface as expected. For the highest dose, a significant portion of the nitrogen still remains in silicon even after the highest thermal budget. This is attributed to the finite capacity of the silicon/oxide interface to trap nitrogen. When the interface gets saturated by nitrogen atoms, nitrogen in silicon can not escape into the interface. Implant doses above 7x1014 create continuous amorphous layers from the surface. For the 2x1015 case, there is residual amorphous silicon at the surface even after a 750oC 2 min anneal. After the 900oC 2 min anneal, the silicon fully recrystallizes leaving behind stacking faults at the surface and residual end of range damage. INTRODUCTION Nitrogen implant into silicon has been observed to retard the rate of oxide growth [1]. Nitrogen implant has been utilized to obtain thinner and more uniform oxides. It has also been investigated to obtain multiple gate oxide thicknesses on the same chip for System-On-A-Chip applications [2]. Nitrogen implant before oxide formation also helps suppress boron diffusion through the oxide [3]. Implanted nitrogen diffuses to the oxide/silicon interface during annealing and piles up around the interface [4]. The same experiments also show that diffusivity of nitrogen is quite high even at 750oC. The diffusion of nitrogen at low doses (900oC) and longer times will be needed to obtain a more defect and nitrogen-free silicon crystal under the gate oxide. ACKNOWLEDGMENTS The authors would like acknowledge ASTC for the processing of the wafers. REFERENCES 1. C.T. Liu, Y. Ma, J. Becerro, S. Nakahara, D.J. Eaglesham, and S. J. Hillenius, IEEE Electron Device Lett. 18, 105 (1997). 2. C.T. Liu, Y. Ma, M. Oh, P.W. Diodato, K.R. Stiles, J.R. McMacken, F. Li, C.P. Chang, K.P. Cheung, J.I. Colonell, W.Y.C. Lai, R. Liu, E.J. Lloyd, J.F. Miner, C.S. Pai, H. Vaidya, J. Frackoviak, A. Timko, F. Klemens, H. Maynard, and J.T. Clemens, IEDM Tech. Dig., 589 (1998). 3. C.T. Liu, Y. Ma, H. Luftman, and S.J. Hillenius, IEEE Electron Device Lett. 18, 212 (1997). 4. L.S. Adam, M.E. Law, K.S. Jones, O. Dokumaci, C.S. Murthy, and S. Hegde, J. Appl. Phy
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