Shallow Junction Engineering by Phosphorus and Carbon Co-implantation: Optimization of Carbon Dose and Energy
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Shallow Junction Engineering by Phosphorus and Carbon Co-implantation: Optimization of Carbon Dose and Energy Nathalie Cagnat1, Cyrille Laviron2, Daniel Mathiot3, Chris Rando4, and Marc Juhel5 1 Ion Implantation R&D, STMicroelectronics, 850 rue Jean Monnet, Crolles, 38926, France, Metropolitan 2 CEA-LETI, 17 rue des Martyrs, Grenoble, 38054, France, Metropolitan 3 InESS, 23 rue du Loess, Strasbourg, 67037, France, Metropolitan 4 Freescale, 870 rue Jean Monnet, Crolles, 38926, France, Metropolitan 5 STMicroelectronics, 850 rue Jean Monnet, Crolles, 38926, France, Metropolitan
ABSTRACT Carbon co-implantation after pre-amorphization implantation (PAI) has been studied for Boron shallow implants and can be also used to reduce Phosphorus diffusion. The expected role of Carbon is to trap Si interstitials responsible of Phosphorus diffusion. A known drawback of this kind of co-implantation is junction leakage caused by Carbon deep levels. To find a compromise between diffusion reduction and leakages, it is necessary to optimize the location and the amount of Carbon with respect to Si interstitials. In this work, we present full sheet experiments optimizing Carbon implanted energy and dose in order to minimize Phosphorus diffusion. First, we performed a PAI with Germanium. Then Carbon was implanted at several energies and doses to locate its projected range (Rp) at various locations with respect to the Phosphorus peak and the amorphous/crystalline interface. Finally the Phosphorus implant was placed completely within the amorphized area. Dopants were activated by a spike anneal at 1080∞C, 1055∞C or 1000∞C. SIMS analysis and Rs measurements were used to understand Carbon action on Phosphorus diffusion and activation. The role of C in suppressing P diffusion is discussed in regards of the specificities of P diffusion mechanism. INTRODUCTION The continual decrease of the transistor size, necessary to improve the performances of integrated circuits, induces the emergence of new secondary effects, which were of minor importance until now. Among them, residual defects in Silicon are a critical issue for present and future CMOS technologies. Indeed, beyond the fact that interstitials and/or vacancies help dopant diffusion, defects remaining after annealing are the root causes of some deleterious effects like hot carriers, salicide encroachment, leakagesÖ In order to minimize these effects, Phosphorus is more and more considered as an alternative to Arsenic for the shallow junctions of NMOS devices. However, Phosphorus diffusion is much less controllable than Arsenic, as it is a light ion which behaves more like Boron (interstitial diffusion mechanism). A possible technological way to meet the junction depth and abruptness requirements is to use co-implantation of nondoping species with classical implantations. Carbon co-implantation after pre-amorphization implantation (PAI) has been studied for B shallow implants [1, 2] and can be also used to reduce P diffusion [3]. The expected role of C is to trap Si interstitial
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