Abstract
This thesis reports a study of a viable way to produce ultra-shallow n-p junctions for the next generation of CMOS devices (10-20nm node or logic technology). The ion implantation of an alternative species to arsenic (As) namely antimony (Sb) for n-type doping in silicon has been investigated. Being a heavier ion, antimony has the potential to give rise to very sharp doping profiles with little lateral and longitudinal straggling. It experiences no implant induced Transient Enhanced Diffusion (TED), as it is a vacancy-assisted diffuser. A detailed study of the electrical characteristics of the antimony implanted at energies ranging from 2 keV to 40 keV into silicon layers as a function of annealing conditions is made in the range 600?C to ll00?C for times of seconds to hours. A comparison between antimony and arsenic is made with respect to electrical activation and sheet resistance. A novel Differential Hall Effect technique has been developed to obtain doping profiles at a depth resolution down to 2nm with junction depths of about 20nm. A comparison has made between single implants [(5keV Sb+, 5x1014cm-2), (2 keV Sb+, 1x1015cm-2)] and double implants [(5 keV Sb+, 5x10 14cm-2 + 70 keV Sb+, 3x1013cm-2), (2 keV Sb+, 1x10 15 + 30 keV Sb+, 2x1013cm-2)] in terms of electrical profiling. Double implants enable profiling down to the 1018 cm-3 carrier concentration level. We include a comparison between differential Hall effect (DHE) measurements of carrier concentration and mobility profiles and Secondary Ion Mass Spectroscopy (SIMS) measurements of the atomic profiles for different annealing temperatures. Rutherford Back Scattering (RBS) has been used to calculate the retained dose of the samples both as implanted and after thermal treatment, and to obtain information about the atomic distribution of the dopant inside the layer, especially in terms of its lattice ocation, and of the damage induced by the bombardment. The key findings in the thesis are: It has been demonstrated that a low thermal budget causes negligible diffusion and the formation of shallow junctions in low energy (2-5 keV) antimony implanted silicon. Antimony implants for ultra-shallow junctions in silicon. We have confirmed that the electrical activation decreases and the sheet resistance increases for antimony implanted Si with increasing temperature and time, however, arsenic behaves in the opposite way. A Hall effect profiling technique has been developed to measure shallow doping profiles (<20nm) in ion implanted silicon with nanometre resolution. The technique has been applied to electrical profiling of 2-5 keV implants of antimony in silicon. We have successfully profiled single low energy implants of antimony and also double implants; the latter enables complete profiles to be measured down to a concentration of about 1018 cm-3. Finally the main conclusion from this work is that low energy (2-5 keV) implants of antimony followed by annealing in the range 600-800°C produce ultra shallow junctions which are close to meeting the specifications of the ITRS for future generations of CMOS devices.