David George Armour

Characterization by medium energy ion scattering of damage and dopant profiles produced by ultrashallow B and As implants into Si at different temperatures

High depth resolution medium energy ion scattering (MEIS) has been used to examine the influence of dynamic defect annealing on the damage formed in silicon substrates irradiated with ultralow energy ions (1 keV B+, 2.5 keV As+). Samples were implanted to doses ranging from 3×1014 to 2×1016 cm−2 at sample temperatures −150/−120, 25, and 300u200a°C. For all doses examined, B implantation at 25 and 300u200a°C produced a near-surface disordered layer 3–4 nm thick. For doses above 1×1015 cm−2, a second, deeper damaged layer was resolved at a depth greater than the peak of the projected range (Rp) of the implanted ions. For irradiations at −150u200a°C, MEIS and transmission electron microscope studies indicated the formation of a continuous amorphous layer, extending from the deeper damage region to the surface. However, epitaxial regrowth of this layer was not complete after a 30 s anneal at 600u200a°C, being arrested near Rp by clusters containing B. The dependence of B transient enhanced diffusion on the implant temperatur...

High resolution medium energy ion scattering analysis for the quantitative depth profiling of ultrathin high-k layers

Ultrathin high-k layers such as hafnium oxide (HfO2) in combination with a subnanometer SiO2 or Hf silicate have emerged as Si compatible gate dielectric materials. Medium energy ion scattering (MEIS) analysis has been carried out on a range of such metal oxide chemical vapor deposition grown HfO2∕SiO2 and HfSiOx(60%Hf)∕SiO2 gate oxide films of thickness between 1 and 2nm on Si(100), before and after decoupled plasma nitridation (DPN). The ability of MEIS in combination with energy spectrum simulation to provide quantitative layer information with subnanometer resolution is illustrated and the effect of the DPN process is shown. Excellent agreement on the deduced layer structures and atomic composition with the as grown layer parameters, as well as with those obtained from cross section electron microscopy and other studies, is demonstrated. MEIS analysis of a high-k, metal gate TiN∕Al2O3∕HfO2∕SiO2∕Si stack shows the interdiffusion, after thermal treatment, of Hf and Al from the caplayer, inserted to modi...

The dependence of arsenic transient enhanced diffusion on the silicon substrate temperature during ultralow energy implantation

The redistribution of As during high-temperature annealing has been investigated as a function of the Si(100) substrate temperature (−120u200a°C, +25u200a°C, and +300u200a°C) during 2.5 keV implantation (to 1.5×1015atoms/cm2). Each implant produced a damaged near-surface region, the extent of which varied with implant temperature. Samples implanted at each temperature were annealed in a nitrogen ambient with a few percent oxygen for 10 s at 550, 925, and 975u200a°C. The changes in implant damage and dopant distributions both prior to and following annealing were investigated using medium energy ion scattering and secondary ion mass spectrometry. Transient enhanced diffusion (TED) of the dopant was observed for all implant temperatures after 925u200a°C annealing with the 25u200a°C implant showing the deepest diffusion. Between 925 and 975u200a°C annealing, the As diffusion rate in the 300u200a°C exceeded that of the 25u200a°C implant. Significantly, the −120u200a°C implant displayed less TED of As compared to the higher temperature implants foll...

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.

Cluster formation during annealing of ultra-low-energy boron-implanted silicon

The clustering of low-energy ion-implanted boron has been investigated. Two 1 keV boron implantations at doses of 1×1015 and 5×1015u200acm−2 were annealed for 10 s between 700 and 1100u200a°C. The evolution of the boron concentration profiles was monitored using secondary ion mass spectrometry. Electrical activation was measured with four-point-probe measurements and spreading resistance profiling. The displaced Si concentration profiles were determined from medium-energy ion-scattering measurements.

Insitu study of processes taking place on silicon surface during its bombardment by CFx/Ar ions: Etching versus polymerization

The application of a Kaufman ion source in the study of the etching/polymerization processes taking place at the surface of a silicon substrate being exposed to ion beams generated from CF4/Ar gas mixtures is reported. The processes were analyzed by means of in situ mass and energy spectroscopy of the secondary ions sputtered from the substrate surface and the charge‐exchange ions, respectively. These analytical methods confirmed the growth of the polymer C–F thin films on the silicon surface at higher concentrations of CF4 in the mixture. It was found that there existed a primary beam threshold energy above which the polymer thin film stopped growing and the etch yield of silicon atoms was increased. The simplified activated growth model presented here describes this behavior qualitatively as a competition between creative and destructive processes leading to deposition and removal of the thin polymer film, respectively.

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.

Implant temperature dependence of transient-enhanced diffusion in silicon (100) implanted with low-energy arsenic ions

The diffusion of arsenic implanted into silicon at low ion energies (2.5 keV) has been studied with medium-energy ion scattering, secondary ion mass spectrometry and four-point probe measurements. The dopant redistribution together with the corresponding damage recovery and electrical activation produced by high-temperature (550–975°C) rapid thermal anneals has been investigated for a range of substrate temperatures (+25, +300 and −120°C) during implant. Initial results show an implant temperature dependence of the damage structure and arsenic lattice position prior to anneal. Solid-phase epitaxial regrowth was observed following 550°C, 10 s anneals for all implant temperatures and resulted in approximately 60% of the implanted arsenic moving to substitutional positions. Annealing at 875°C resulted in similar arsenic redistribution for all implant temperatures. Following annealing at 925°C, transient-enhanced diffusion was observed in all samples with more rapid diffusion in the +25°C samples than either the −120 or +300°C implants, which had similar dopant profiles. In the 975°C anneal range, similar rates of implant redistribution were observed for the +300 and +25°C implants, while diffusion in the −120°C sample was reduced. These observations are discussed qualitatively in terms of the nature and density of the complex defects existing in the as-implanted samples.

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.

MOS Memory Using Silicon Nanocrystals Formed by Very-Low Energy Ion Implantation

Metal Oxide Semiconductor Field Effect Transistor (MOSFET) memory devices using silicon nanocrystals as charge storage elements have been fabricated. The nanocrystals are obtained by Si ion implantation at very low energy (1keV) into a thin thermal oxide (8 nm) and subsequent annealing. The memory characteristics of the devices under static and dynamic operation are reported. These devices exhibit fast write/erase characteristics at low voltage operation. The presence of interface states and defects that originate from the nanocrystal formation process is also found to have a strong effect on the device transfer characteristics.