Jarig Politiek

Proximity gettering of transition metals in silicon by ion implantation

We compare the gettering efficiency of C, O and He implantation into Cz-grown silicon. After the getter implantation, with a projected range of 1.2 μm, we introduce a controlled amount of either Fe or Cu through low-energy implantation. Subsequently, we study the distribution of the impurities for various annealing conditions by means of secondary ion mass spectroscopy. In contrast to the C and O implantations which already show gettering behaviour at relatively low doses, the He implantation requires a dose in excess of 6 × 1015 ions/cm2 before observable gettering occurs. When sufficiently high doses of He are implanted its gettering efficiency significantly exceeds that of comparable C and O implantations, i.e. implantations with the same projected ranges and doses, subjected to the sa me annealing treatment. The shape of the getter profile in the sample implanted with He is strongly influenced by the annealing treatment.

Low energy boron implantation in silicon and room temperature diffusion

Abstract In the semiconductor industry Complementary Metal Oxide Semiconductor Technology is the main stream. The continuing trend towards reduction of the transistor gate length allows for more complex integrated circuits. This puts stringent demands on other transistor properties such as source and drain junction depth. Source and drain are formed using ion implantation. For transistors where source and drain are boron-doped very low implantation energies are needed to obtain shallow implantation profiles. We have characterized boron implants, concentrating on the 100 eV to 1 keV energy range. As-implanted and annealed implant profiles are presented together with an overview of electrical activation and sheet resistance showing that ion implantation is a viable technique for shallow source/drain formation. In this paper some of the mechanisms underlying the formation of implantation profiles are discussed. Using a deactivation technique, we have measured the room temperature silicon self-interstitial diffusivity, D I . It was found to be at least 10 −7 cm 2 s −1 . This appears to be a new record experimental value, approaching theoretical values for the silicon di-interstitial. Room temperature migration and clustering behaviour of implanted boron has been investigated by performing ion implantation of the boron isotope 11 B into Molecular Beam Epitaxy-grown in situ doped layers. We, for the first time, show that a fraction of the implanted boron migrates deep into the bulk of the Si with substitutional 10 B acting as trap centers for migrating 11 B.

Light- and heavy-ion channeling profiles in silicon

Abstract Channeling of 200 keV 11 B, 27 Al 69 Ga and 165 Ho ions near the 〈100〉 axis of Si is investigated for tilt angles between 0° an 1.5°, both by experiment and simulation. Implantations are carried out at room temperature in Si(100) wafers, 4 in. in diameter, using an electrostatically scanned beam (angular variation is ± 1°). Alignmeent of the Si 〈100〉 axis parallel to the mean incident beam direction is done by monitoring the backscattering yield of 720 keV protons near the centre of the target. Implantation doses are kept low ((2–5) × 10 12 cm −2 ) to minimize damage buildup. The ion depth distributions are measured with secondary-ion mass spectrometry, at a number of locations distributed over the entire wafer, yielding data for the indicated range of tilt angles. The measured profiles are compared with simulations of implanted depth distributions in crystalline targets using the Monte Carlo code MARLOWE (version 12). Different impact-parameter-dependent electronic stopping models as well as the effect of a small amount of damage buildup are discussed.

Strong wear reduction of high-dose carbon-implanted AISI 52100 steel

Abstract AISI 52100 steel was implanted at 100 keV with doses in the range 4 × 1017−3 × 1018C+/cm2. Tribological tests were carried out on an oscillating ball-on-disk tester. The friction coefficient of the steel implanted with a dose of 3 × 1018/cm2 was reduced by a factor of 3 for far more than 6 h. The wear behaviour of the steel shows normal wear up to a depth of 0.15 μm, being the range of the implanted carbon ions. Thereafter, a very low wear rate is obtained for more than 6 h (1.5 × 105 cycles). The ball shows also no wear during this period. The steel was also studied by Mossbauer spectroscopy for various doses. At the lowest dose, ϵ-carbide is formed. For the higher doses the amount of ϵ-carbide increases, and the composition approaches that of ϵ-Fe2.2C. The ϵ-carbide was also found by glancing-angle X-ray diffraction. Fe and C profiles were obtained from the Rutherford backscattering spectra. It was found that besides the ϵ-carbide a large amount of pure carbon is present in the implanted layer.

A dual source low-energy ion implantation system for use in silicon molecular beam epitaxy

Abstract Recently an ion implanter for low-energy ion doping during molecular beam epitaxy has been developed. The unit consists of a dual source injection system operating at 30 kV extraction, a beam transport system and a deceleration stage, located in an ultrahigh-vacuum MBE chamber. Tests have shown that in the energy range of 150–2000 eV target currents of up to 100 μ A can be reached with controllable beam focusing. For uniform wafer implantation the decelerated beam can be electrostatically scanned with a lateral displacement from + 70 to −70 mm at target position. To obtain sharp doping transitions, the system is designed to switch: within 1 s between the two independent microwave sources.

Low-energy implantations of decaborane (B/sub 10/H/sub 14/) ion clusters in silicon wafers

Low-energy implantation with decaborane (B/sub 10/H/sub 14/) ion clusters is suitable for ultra-shallow junction formation. Using a high-voltage research implanter with a microwave ion source, decaborane implantation has been performed at energies in the range 2.8 to 440 keV, with doses up to 10/sup 14/ decaborane/cm/sup 2/ (10/sup 15/ B atoms/cm/sup 2/). A study of the implantation damage shows that the number of displaced Si lattice atoms in the near-surface region is considerably larger for the decaborane implants than for the corresponding B/sup +/ implants. Ultrashallow dopant profiles have been achieved by 2.8 keV B/sub 10/H/sub 14//sup +/ implantation, equivalent to an energy of 255 eV per incoming B atom. In such a case the B peak concentration is located only a few atomic layers below the Si surface, and implantation damage is virtually absent. Transient enhanced diffusion effects during rapid thermal annealing were negligible, apart from the slight movement associated with migration of interstitial B atoms onto substitutional sites.