W. Beezhold

FORMATION OF SiC IN SILICON BY ION IMPLANTATION

The production of SiC in single‐crystal silicon by C12+ implantation to fluences of 1017/cm2‐side followed by annealing has been detected by the characteristic infrared absorption of the TO phonon of SiC. Immediately following room‐temperature implantation and after 20‐min isochronal anneals up to temperatures ≤ 825°C, a previously unreported broad absorption band centered at 700–725 cm−1 is observed. SiC is observed to form at temperatures ≈ 850°C. For anneals ≥ 850°C, most of the broad absorption band shifts into the SiC‐TO phonon absorption band. From the infrared absorption measurements together with the results of He+ backscattering, we conclude that about half of the implanted atoms are incorporated into microregions of SiC which are surrounded by bulk silicon.

Electron paramagnetic resonance of the lattice damage in oxygen‐implanted silicon

The nature of the lattice damage produced at room temperature in ion‐implanted intrinsic and n‐type silicon has been studied as a function of 160‐keV O+ ion fluence using electron paramagnetic resonance (EPR). The known EPR spectra observed were the negative divacancy (Si‐G7), the neutral vacancy‐oxygen (Si‐S1), the neutral 4‐vacancy (Si‐P3), and the isotropic resonance at g = 2.0055 which is indicative of amorphous silicon. In addition, a new spectrum, labeled Si‐S2, was observed which may be the negative 4‐vacancy. Concentrations (number/cm2) for the various paramagnetic defects were determined as a function of ion fluence for fluences ranging from 1010 to 1017 O+/cm2. From these measurements we conclude that the lattice damage produced in crystalline silicon by individual ions whose maximum calculated energy density into atomic processes is ≲ 15 eV/A ion consists of simple defects such as observed in electron‐ and neutron‐irradiated silicon. Furthermore, overlap effects in the lattice damage produced b...

Depth‐resolved cathodoluminescence in undamaged and ion‐implanted GaAs, ZnS, and CdS

Here we report a variety of results obtained by using sequences of luminescence spectra excited by 1–20‐keV electron irradiation to carry out in situ studies of depth‐dependent optical activity in luminescent crystals. Data are shown for various samples subjected to localized damage from ion implantation: GaAs implanted with Cu+, ZnS implanted with Ar+ and Cu+, and CdS implanted with Ar+ and H+. Semiquantitative interpretation of the results shows that the depth‐resolved cathodoluminescence measurements can have unique value in characterizing the effects of ion‐implantation lattice damage. In this case cathodoluminescence can be excited from depths ranging from much shallower to much deeper than typical implant depths. In addition, the use of depth‐resolved measurements on nominally undamaged ZnS crystals reveals the presence of weak near‐surface luminescence bands despite careful surface preparation. This result makes it clear that luminescent center profiling by layer removal methods can lead to erroneo...

The Response of MOS Devices to Dose-Enhanced Low-Energy Radiation

A series of experiments has been performed to investigate the response of MOS structures to low-energy radiation. A 10-keV x-ray source was used to irradiate MOS capacitors through a gold/aluminum bilaminate. As expected, the device response when the gold side of the bilaminate faces the device is enhanced strongly with respect to its response when the aluminum side of the bilaminate faces the device. The degree to which the enhanced radiation affects the device response, as determined by the buildup of oxidetrapped charge, depends on the thickness of the gate insulator and the thickness of the capacitor gate in ways similar to those expected from previous work. In addition, striking dependences of the enhanced device response on the energy of the incident radiation, and on the magnitude and direction of the electric field across the gate insulator during the irradiation were observed. These results may provide new insights into the details of the interaction of low-energy radiation with MOS devices.

Effect of Ionizing Radiation on Displacement Damage in Ion-Bmcbarded Single Crystal α-A1 2 O 3 and α-SiO 2

Volume changes in ion-bombarded single crystals of sapphire and α-quartz have been investigated as functions of ion mass and initial energy and of the energy partitioning into atomic and ionization processes. In addition, channeled proton-induced X-ray measurements were made of displacement damage after ion bombardment. Results indicate an ionization stimulated annealing effect of the radiation damage in sapphire which prevents this material from becoming amorphous even at high ion fluences. In contrast, α-quartz shows no such annealing effect and loses its crystallinity completely at high ion fluences.

LOCALIZED MODES AND DIVACANCY ABSORPTION IN OXYGEN-ION-IMPLANTED Si.

Optical absorption bands characteristic of localized vibrational modes for both interstitial and substitutional oxygen have been observed in crystalline Si implanted with 220‐keV oxygen ions at 300°K. In addition, the fluence dependences for the vibrational modes and also for an electronic transition of the divacancy (1.8‐μ band) have been measured. Implanted oxygen ions are found to enhance divacancy formation. This effect was not observed for Sb implantation. The sum of the observed interstitial and substitutional oxygen centers is approximately equal to the number of implanted oxygen ions. An ion fluence 300 times larger than that to detect divacancies was required to detect the vibrational modes of oxygen as expected from the relative production rates and absorption coefficients. At these high fluences the strengths of the vibrational bands increase in magnitude with fluence while the divacancy band decreases. At even higher fluences amorphous layer formation, as indicated by a milky coloration of the...

Non linear volume expansion in helium implanted erbium metal films

Abstract Large dimensional expansion has been observed at room temperature in erbium metal films implanted at room temperature with high fluences of helium. The interferometrically measured film thickness increases linearly with fluence up to a critical dose of 3 × 1017 He+/cm2 (E = 160 keV) and is superlinear at higher fluences. Annealing at 400°C causes a reduction of the induced expansion for fluences below the critical dose without apparent release of helium. Annealing of samples implanted to fluences greater than 3.5 × 1017 He+/cm2 causes accentuated expansion which is accompanied by formation and rupture of bubbles at the film surface.

Experimental Check of Bremsstrahlung Dosimetry Predictions for 0.75 MeV Electrons

Bremsstrahlung dose in CaF2 TLDs from the radiation produced by 0.75 MeV electrons incident on Ta/C targets is measured and compared with that calculated via the CYLTRAN Monte Carlo code. The comparison was made to validate the code, which is used to predict and analyze radiation environments of flash x-ray simulators measured by TLDs. Over a wide range of Ta target thicknesses and radiation angles the code is found to agree with the 5% measurements. For Ta thicknesses near those that optimize the radiation output, however, the code overestimates the radiation dose at small angles. Maximum overprediction is about 14 ± 5%. The general agreement, nonetheless, gives confidence in using the code at this energy and in the TLD calibration procedure. For the bulk of the measurements, a standard TLD employing a 2.2 mm thick Al equilibrator was used. In this paper we also show that this thickness can significantly attenuate the free-field dose and introduces significant photon buildup in the equilibrator.

Ion implantation into insulators: charge‐removal studies using ion‐induced characteristic x rays

The effectiveness of a number of charge‐removal techniques during ion implantation into insulators has been examined by monitoring the ion‐induced characteristic x‐ray emission of target atoms during proton implantation. Successful removal of charge buildup occurs for samples which are coated with a thin conducting surface layer and for samples which have intimate contact between the implanted region and a conducting mask and are flooded with a defocused ion beam.

Electron Paramagnetic Resonance of the Lattice Damage in Boron-Implanted Intrinsic Silicon

The nature of the lattice damage in boron-implanted intrinsic silicon has been studied as a function of 140-keV 11B+ ion fluence using electron paramagnetic resonance (EPR). At most of the boron fluences, the observed EPR spectra consisted primarily of neutral 4-vacancies (Si-P3) and of unresolved E spectra (defects unknown). Concentrations (number/cm2) for the Si-P3 and ? paramagnetic defects have been determined as a function of ion fluence for fluences ranging from 5 × 1012 to 1016 11B+/cm2. At the highest fluences the beginning of an isotropic resonance indicative of amorphous silicon was also observed. However, only a trace of the amorphous resonance was observed, and this resonance was found to be broadened and shifted to a lower magnetic field with a g value of 2.0071 instead of the usual 2.0055. Also observed at the higher fluences was the new anisotropic spectrum (labeled Si-SL3) arising from a defect having D2d symmetry. Finally, isochronal annealing studies indicate that the Si-P3 and ? concentrations decrease toward zero by a 225° C anneal in a manner similar to that previously observed for oxygen-implanted-silicon. No paramagnetic defects were observed in the 600 to 900° C range. It is concluded that any electrical activity annealing in the 600 to 900° C range is primarily a result of a decrease in the number of compensating non-paramagnetic or diamagnetic defect centers.