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The Source of Transient Enhanced Diffusion in Sub-keV Implanted Boron in Crystalline Silicon E. Napolitani1, A. Carnera1, V. Privitera2, E. Schroer2, G. Mannino2, F. Priolo3, S. Moffatt4 1 INFM and Dept. of Physics, Padova, ITALY. 2 CNR-IMETEM, Catania, ITALY. 3 INFM and Dept. of Physics, Catania, ITALY. 4 Applied Materials, 2727 Augustine Drive, Santa Clara California 95054, USA. ABSTRACT The transient enhanced diffusion (TED) during activation annealing of ultra low energy implanted boron (0.5 keV & 1 keV, 1x1013/cm2 & 1x1014/cm2) in silicon is investigated in detail. Annealing in the temperature range from 450°C to 750°C is either performed directly after implantation or after the removal of a surface layer before annealing. The kinetics revealed two regimes of enhanced diffusion ruled by different decay constants and different activation energies. The dependence of these two processes on implantation energy and annealing temperature is described and explained from the microscopical point of view. The annealings performed after surface layer removal, revealed that the defects responsible for the faster diffusion are located deeper than the defects responsible for the slower process. INTRODUCTION According to the International Technology Roadmap for Semiconductors [1], the reduction of the junction depth is one of the critical issues for the introduction of CMOS devices with a gate length of less than 100nm. This demand has recently led to the introduction of high throughput ultralow energy (≤ 1 keV) implanters, which are capable to introduce the dopants with the required shallow depth distribution into silicon. Due to the transient enhanced diffusion (TED) during the activation annealing, however, the junction depth is considerably increased, even for ultralow energy implanted B. The TED in the ultralow energy regime has different characteristics [2] and is governed by different type of defects with respect to the standard energy regime. Therefore, an improved understanding of the defects in the ultralow energy regime is necessary in order to improve the control of the TED. In this paper we report a detailed investigation of the TED phenomena at temperatures in the 450-750 °C range. EXPERIMENT Epitaxially grown, (100) oriented, pure silicon layers, were implanted with 1x1014/cm2 or 1x1013/cm2 B, with an energy of 0.5 or 1 keV by a xR LEAPTM implanter at the Implant Division of Applied Materials in Horsham, UK, and annealed in the 450-750 °C range for times ranging from 1 to 1200 s by Rapid Thermal Processing (RTA). For selected implanted samples the surface layer was removed before the thermal process, by repeated growth (by immersion in boiling 5% H2O2 solution) and etching (by immersion in 3% HF solution) of the native oxide. The thickness removed by etching (about 2 nm/cycle) was measured by comparison between the as-etched and as-implanted chemical profiles, with an overall accuracy of about 1 nm. The chemical profiles of the samples were measured by means of high depth resolution secondary ion mass spectrome