Stephen Moffatt

The Applied Materials xRLEAP ion implanter for ultra shallow junction formation

As semiconductor device design rule dimensions continue to shrink, there is a demand for transistor junction depths to decrease. New processes are required that involve lower energy implants but the reduced beam currents available due to space charge limits in beam generation and transport at these lower energies can limit productivity to such a level that other non-implant technologies become attractive. The Applied Materials xR80 implanter uses state of the art beam generation and extraction optics coupled to an open geometry, short beamline to produce enhanced performance to energies down to 2 keV. The xRLEAP significantly increases beam currents at these energies and further reduces the energies at which product worthy beam currents can be obtained by the use of high transmission energy retardation optics added to the xR80 system. The milliampere beam currents achieved down to energies of a few hundred electron volts will extend the capability of ion implantation to manufacture product worthy shallow junction devices.

Range and damage distributions in ultra-low energy boron implantation into silicon

An ultra high vacuum, low energy ion implanter was used in conjunction with a range of analytical techniques to study the range and damage distributions of B/sup +/ ions implanted at normal incidence into Si(100) samples held at room temperature. Samples were implanted over a dose range from 1E14 ions/cm/sup 2/ with and without a surface oxide layer and those implanted at 1 keV and below were capped with a nominal 20 nm layer of /sup 28/Si by ion beam deposition in situ in order to produce an oxygen equilibration layer for subsequent secondary ion mass spectrometry depth profiling. The samples were analysed using secondary ion mass spectroscopy, medium energy ion scattering, spectroscopic ellipsometry, spreading resistance profiling and high resolution, cross section transmission electron microscopy to obtain the range and damage distributions and junction depths. The general observations were that channelling occurs at all energies studied, and that the relationship between the damage and range distributions depends strongly on bombardment energy. Comparison of the range and damage profiles was carried out to ascertain the role of the surface in determining the behaviour of defects produced very close to it by the low energy implants required for the production of junctions at depths in the 20 to 50 nm range. The role of the surface or silicon/silicon dioxide interface as a defect sink significantly influences the B redistribution behaviour during rapid thermal annealing.

Analysis of sub-1 keV implants in silicon using SIMS, SRP, MEISS and DLTS: the xRLEAP low energy, high current implanter evaluated

Ultra shallow junctions can be formed, amongst other techniques, by very low energy ion implantation. The Implant Division of Applied Materials have recently developed a low energy, high current ion implanter, the xRLEAP (xR family, Low Energy Advance Process). This implanter is capable of delivering product worthy beam currents, in the milli-ampere regime down to energies of few hundred electron volts. A series of B and BF/sub 2/ implants were carried out onto non-amorphised, 200 mm Si wafers using beam energies in the range 0.2 keV<E<1 keV. As-implanted and annealed samples were profiled using Secondary Ion Mass Spectrometry (SIMS). Surface damage due to implantation was evaluated using Medium Energy Ion Scattering Spectroscopy (MEISS). The carrier concentration profiles and junction depths of the annealed samples were investigated using Spreading Resistance Probe (SRP). Samples with ultra shallow junctions, <0.07 /spl mu/m, were examined using Deep Level Transient Spectroscopy (DLTS) for the first time.

Evolution of dopants and defects in silicon under various annealing sequences

Several decades of research into understanding the mechanisms responsible for diffusion and activation of group-III acceptor and group-V donor impurities in silicon has been driven by the technological need for creating electrical junctions in the S/D and extensions of transistors in semiconductor integrated circuits. It is now conclusively known that anomalous diffusion of implanted impurities during annealing results from their interaction with the non-conservative evolution of excess point-defect damage created by the original implantation, and the effect annealing ambients, co-impurities, interfaces and surfaces have on that evolution [1–8]. Early experiments shown in Ref. [2] conclusively proved this by etching away the surface region containing implant damage before annealing, and demonstrating that the anomalous behavior disappeared. Starting from the as-implanted damage, the nucleation, growth and dissolution of a sequence of larger defects at the expense of smaller ones during the anneal, sets the point defect flux and super-saturation levels (the ratio of point defect concentration to its temperature equilibrium value), which then determine the magnitude and durations of the various phases of anomalous diffusion [9].