R.D Goldberg

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 300 °C. For all doses examined, B implantation at 25 and 300 °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 −150 °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 600 °C, being arrested near Rp by clusters containing B. The dependence of B transient enhanced diffusion on the implant temperatur...

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 (−120 °C, +25 °C, and +300 °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 975 °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 925 °C annealing with the 25 °C implant showing the deepest diffusion. Between 925 and 975 °C annealing, the As diffusion rate in the 300 °C exceeded that of the 25 °C implant. Significantly, the −120 °C implant displayed less TED of As compared to the higher temperature implants foll...

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 5×1015 cm−2 were annealed for 10 s between 700 and 1100 °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.

Damage profiles of ultrashallow B implants in Si and the Kinchin-Pease relationship

Damage distributions resulting from 0.1–2keV B+ implantation at room temperature into Si(100) to doses ranging from 1×1014 to 2×1016cm−2 have been determined using high-depth-resolution medium-energy-ion scattering in the double alignment mode. For all B+ doses and energies investigated a 3–4nm deep, near-surface damage peak was observed while for energies at and above 1keV, a second damage peak developed beyond the mean projected B+ ion range of 5.3nm. This dual damage peak structure is due to dynamic annealing processes. For the near-surface peak it is observed that, at the lowest implant energies and doses used, for which recombination processes are suppressed due to the proximity of the surface capturing interstitials, the value of the damage production yield for low-mass B+ ions is equal or greater than the modified Kinchin-Pease model predictions [G. H. Kinchin and R. S. Pease, Rep. Prog. Phys. 18, 1 (1955); G. H. Kinchin and R. S. Pease, J. Nucl. Energy 1, 200 (1955); P. Sigmund, Appl. Phys. Lett. ...

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.

Damage and Dopant Profiles Produced by Ultra-Shallow Boron And Arsenic Ion Implants into Silicon at Different Temperatures Characterised by Medium Energy Ion Scattering.

Medium energy ion scattering (MEIS), operated at sub-nm depth resolution in the double alignment configuration, has been used to examine implant and damage depth profiles formed in Si(100) substrates irradiated with 2.5 keV As+ and 1 keV B+ ions. Samples were implanted at temperatures varying between 150°C, and 300°C to doses ranging from 3X1014 to 2X1016 cm-2. For the As implants the MEIS studies demonstrate the occurrence of effects such as a dopant accommodation linked to the growth in depth of the damage layer, dopant clustering, as well as damage and dopant movement upon annealing. Following epitaxial regrowth at 600°C, approximately half of the As was observed to be in substitutional sites, consistent with the reported formation of AsnV complexes (n≤4), while the remainder became segregated and became trapped within a narrow, 1.1 nm wide layer at the Si/oxide interface MEIS measurements of the B implants indicate the formation of two distinct damage regions each with a different dependence on implant dose, the importance of dynamic annealing for implants at room temperature and above, and a competing point defect trapping effect at the Si/oxide interface. B+ implantation at low temperature resulted in the formation of an amorphous layer due to the drastic reduction of dynamic annealing processes. Notably different dopant distributions were measured by SIMS in the samples implanted with As at different temperatures following rapid thermal annealing (RTA) up to 1100°C in an oxidising environment. Implant temperature dependent interactions between defects and dopants are reflected in the transient enhanced diffusion (TED) behaviour of As.

Characterisation Of The Beam Plasma In High Current, Low Energy Ion Beams For Implanters

The effective transport of high current, positive ion beams at low energies in ion implanters requires the a high level of space charge compensation. The self‐induced or forced introduction of electrons is known to result in the creation of a so‐called beam plasma through which the beam propagates. Despite the ability of beams at energies above about 3–5 keV to create their own neutralising plasmas and the development of highly effective, plasma based neutralising systems for low energy beams, very little is known about the nature of beam plasmas and how their characteristics and capabilities depend on beam current, beam energy and beamline pressure. These issues have been addressed in a detailed scanning Langmuir probe study of the plasmas created in beams passing through the post‐analysis section of a commercial, high current ion implanter. Combined with Faraday cup measurements of the rate of loss of beam current in the same region due to charge exchange and scattering collisions, the probe data have p...

Charge exchange and neutral transport contributions to energy contamination in decel mode, sub-keV ion implantation

The use of a deceleration lens close to the wafer to obtain high currents at sub-keV energies carries with it the risk of energy contamination. The extent to which this contamination affects the implant depth profile depends on a number of factors related both to hardware design and choice of deceleration conditions. While the beamline length and pressure have a linear effect on the extent of beam neutralization, the choice of pre-accel energy and the ratio of this energy to the final energy are also significant due to (a) the energy dependence of the charge exchange cross-sections and (b) the energy dependence of the probability that the fast neutrals formed in charge exchange collisions will reach the wafer. In this paper, measurements of the σ10 charge exchange cross-sections of B+ ions in argon, a common plasma flood feed gas, over the energy range from 200 eV to 10 keV, have been combined with beam trajectory calculations in the section of beamline between the magnet exit and the final section of the decel lens. By this means, the dependence of the energy contamination on the pre-accel energy was determined. The results have been compared with secondary ion mass spectrometry (SIMS) measurements of the high-energy neutral content of the relevant decelerated ion implants. The fact that good agreement can be obtained when appropriate currents are used in the beam trajectory calculations confirms the importance of a knowledge of both the charge exchange cross-sections and the neutral transport efficiency.

High depth resolution characterization of the damage and annealing behaviour of ultra shallow As implants in Si

The relationship between damage formation/annealing and As profile redistribution has been studied using low energy As implants into Si at 2.5 keV at doses between 3 × 1013 cm-2 and 2 × 1015 cm-2 at room temperature. Samples were annealed at temperatures between 600 and 1050°C. High depth resolution medium energy ion scattering (MEIS) and secondary ion mass spectrometry (SIMS) were used to characterise the damage build up and As profiles as a function of implant dose and anneal temperature. MEIS studies showed that damage does not accumulate according to the energy deposition function but proceeds from the surface inwards. This is ascribed to the accumulation of collision cascade produced interstitials that are attracted to and settle at initially the oxide/Si interface and later to the advancing amorphous/crystalline interface. Dopant depth profiles agreed well with TRIM calculations for doses ≥ 4 × 1014 cm-2. However, for lower doses the dopant was observed to have a profile nearer to the surface, due to trapping in the narrow surface damaged layer, in which it is more easily accommodated. Following epitaxial regrowth at 700°C, MEIS showed that -50 % of the As has moved into substitutional sites, consistent with activation and/or the formation of inactive AsnV clusters (n ≤ 4), while the remainder had segregated to and become trapped in a ≤1 nm wide layer, clearly located on the Si side of the oxide/Si interface. Very low energy SIMS analysis at normal incidence is able to resolve these ultra shallow peaks, including the As pileup following epitaxial regrowth. They also confirmed that As retention was complete during dose build up and annealing.