Higher Implantation Temperatures Research Articles

Analysis of Lattice Damage in 4H-SiC Epiwafers Implanted with High Energy Al Ions at Elevated Temperatures

4H-SiC wafers with 12 µm epilayers were blanket implanted to a depth of 12 µm with 5 x 1016 cm-3 Al ions via Tandem Van de Graaff accelerator located at Brookhaven National Laboratory with energy range of 13.8 to 65.7 MeV at room temperature, 300 °C and 600 °C. High resolution X-ray diffraction measurements reveal the implanted layers are characterized by tensile strains. However, the dynamic annealing process reduces the level of tensile strains as the temperature of implantation is increased. Analysis indicates that the implant temperature of 600 °C is not sufficient to minimize lattice damage due to implantation and a higher implantation temperature will be required. This preliminary experiment will guide the optimization of implantation conditions for fabricating superjunction devices.

Insights into the effects of Al-ion implantation temperature on material properties of 4H-SiC

In this study, Al implantation in 4H-SiC at the dose of 1 × 1014 cm−2 was investigated. The impacts of implantation temperature on the lattice quality, microstructure, surface composition, and band structure were all studied experimentally and theoretically. Atomic force microscope (AFM) images showed the difference in surface morphology between high-temperature and low-temperature implantation. Transmission electron microscopy (TEM) characterization indicated the lattice damage induced by implantation was recovered after the post-annealing at 1750 °C, except for the samples implanted at room temperature. X-ray photoelectron spectroscopy (XPS) analysis suggested an oxidation effect during and after the implantation process, and it was more serious at lower implantation temperatures. As the implantation temperature incremented, the ratio of Si-C composition with high binding energy increased, the element valence became closer to that of ideal Al-doped 4H-SiC calculated by density functional theory (DFT); and the Fermi level shifted toward the valence band maximum (VBM), demonstrating the formation of efficient p-type doping. A more obvious asymmetric broadening in Raman spectroscopy was observed at higher implantation temperature. The theoretically obtained band structures and bond lengths from DFT calculations corroborated the experimental results, providing physical insights into the possible effect mechanism. In sum, correlations between the implantation process, external material properties, and internal crystal structure were recorded, paving the way for further research and future applications.

Intrinsic color centers in 4H-silicon carbide formed by heavy ion implantation and annealing

We study the generation and transformation of intrinsic luminescent centers in 4H-polytype of silicon carbide via heavy ion implantation and subsequent annealing. Defects induced by the implantation of germanium (Ge) or tin (Sn) have been characterized by photoluminescence (PL) spectra recorded at cryogenic temperatures. We find three predominant but as-yet-unidentified PL signatures (labeled as DI1–3) at the wavelength of 1002.8 nm (DI1), 1004.7 nm (DI2), and 1006.1 nm (DI3) after high dose implantation (> 4 × 1013 cm−2) and high temperature annealing (> 1700°C). The fact that the DI lines co-occur and are energetically close together suggest that they originate from the same defect. Regardless of the implanted ion (Ge or Sn), a sharp increase in their PL intensity is observed when the implantation damage becomes high (vacancy concentration > 1022 cm−3), indicating that the lines stem from an intrinsic defect caused by the damage. By tracking the PL signals after stepwise annealing, we examine how the overall intrinsic defects behave in the temperature range of 500 – 1800°C; the silicon vacancies formed by the implantation transform into either divacancies or antisite-vacancy pairs with annealing at about 1000°C. These spectral signatures are strongly reduced at 1200°C where the so-called TS defects are maximized in luminescence. As a final stage, the DI defects, which are most likely formed of antisites and vacancies, emerge at 1700°C. Our results provide a knowledge on how to incorporate and manipulate the intrinsic luminescent centers in SiC with ion implantation and annealing, paving the way for fully integrated quantum technology employing SiC.

Tungsten heavy alloy: an alternative plasma-facing material in terms of hydrogen isotope retention

We performed a systematic study of the deuterium retention in the tungsten heavy alloy W-2Ni-1Fe (HPM 1850 from HC Starck, Germany). Consisting of two different phases with generally two distinctly different heats of solution, such alloys represent a special class of materials with respect to hydrogen isotope transport and retention. Deuterium was implanted from a plasma with an energy of 38 eV D−1 at sample temperatures of 100 °C, 175 °C, and 250 °C in the fluence range 1023 D m−2 to 4 × 1025 D m−2. For each combination of implantation temperature and fluence, two alloy samples were exposed together with one sample of bulk hot-rolled tungsten (from Plansee SE). The amount of retained deuterium was determined by thermal desorption with heating up to 850 °C for the alloy and 1050 °C for the bulk tungsten. The outgassed deuterium was detected by mass spectroscopy at the mass channels 3, 4, 19, and 20 corresponding to HD, D2, HDO, and D2O, respectively. The near-surface deuterium concentration was determined by 3He nuclear reaction analysis. The retention in the alloy as compared to the bulk tungsten decreases systematically with increasing implantation fluence for each of the investigated implantation temperatures. For the higher fluences the ratio decreases systematically also, as a function of implantation temperature. This means that especially for high implantation fluences and temperatures the alloy HPM 1850 systematically retains less hydrogen isotopes than bulk tungsten. This property represents an important qualification criterion as a plasma-facing material for a future fusion reactor.

Recent Advances in the Doping of 4H-SiC by Channeled Ion Implantation

The effect of lattice thermal vibrations on the channeling of 100 keV Al ions in 4H-SiC is investigated. By implanting at room temperature in the direction, the depth distribution of the incident ions is shown to be about 7 times deeper than for random implantations. At higher implantation temperatures, the channeling is reduced by the lattice vibrations and, for instance, at 600 °C implantation the distribution is about 3-4 times deeper than for a RT random implantation. The results are of technological interest for further development of implantation technology for 4H-SiC device manufacturing.

Inducing defects in 3.3 kV SiC MOSFETs by annealing after ion implantation and evaluating their effect on bipolar degradation of the MOSFETs

Process-induced basal plane dislocations (BPDs) formed by annealing after aluminum ion implantation were investigated, and their effect on the bipolar degradation of body diodes in 3.3 kV SiC MOSFETs was evaluated. Contact resistance in the p+ region decreases with ion dose but increases with implantation temperature due to the formation of the recrystallized layer at SiC surface and difference of acceptor activation rates in high and low temperature implantation. In the case of high ion dose implantation at room temperature, contact resistance was of 1.3 × 10−3 Ωcm2. However, process-induced BPDs formed with high ion dose implantation at room temperature, and could be suppressed with low ion dose or high implantation temperature. They were formed after activation annealing, and expanded to form stacking faults (SFs) under both continuous irradiation from a Hg lamp and current stress. Bipolar degradation occurred in the case of MOSFETs fabricated using high ion dose implantation at room temperature, but was not observed in the case of either low ion dose or high implantation temperature. The activation energy for SF expansion velocity in the 〈1–100〉 direction was estimated to be 0.20 eV at a forward current density of 125 A cm−2. Moreover, the results of a long duration current stress test with high current density and high junction temperature indicate that low ion dose or high implantation temperature can suppress the formation of process-induced BPDs. MOSFETs fabricated using optimized ion implantation conditions show high reliability under bipolar operation.

Suppression of tin precipitation in SiSn alloy layers by implanted carbon

By combining transmission electron microscopy and Rutherford backscattering spectrometry, we have identified carbon related suppression of dislocations and tin precipitation in supersaturated molecular-beam epitaxial grown SiSn alloy layers. Secondary ion mass spectrometry has exposed the accumulation of carbon in the SiSn layers after high temperature carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. The possibility for carbon assisted segregation-free high temperature growth of heteroepitaxial SiSn/Si and GeSn/Si structures is argued.

Temperature dependent defects evolution and hardening of tungsten induced by 200 keV He-ions

Tungsten has been selected as one of the potential candidate materials to cover some parts of the divertor in the future International Thermonuclear Experimental Reactor (ITER). The accumulation of defects and He induced by neutron irradiation and their impact on the mechanical properties of tungsten are of very importance. In this work, the high pure polycrystalline tungsten samples were implanted by 200keV He+ with a fluence of 5×1016He+/cm2 at temperatures of room temperature (RT), 200, 400 and 800°C. Vacancy-type defects were detected in all implanted samples by means of positron annihilation spectroscopy. Vacancy-type defects produced by He implantation exist in the damaged layer and are decorated by He atoms. At higher implantation temperature, He–V complexes could grow larger through absorbing mobile vacancies. The nano-hardness values were measured by nano-indentation technique. It is observed that implantation hardening occurred for all the implanted samples. With increasing implantation temperature from 200°C to 800°C, the change of the average hardness values which are lower than the value at RT has a tendency of enhancement for the shallower layer and degradation for the deeper layer. The hardness variations are discussed to be the pinning effects of the defects with different density or size.

Determination of Ni Release in NiTi SMA with Surface Modification by Nitrogen Plasma Immersion Ion Implantation

NiTi SMA is a promising material in the biomedical area due to its mechanical properties and biocompatibility. However, the nickel in the alloy may cause allergic and toxic reactions and thus limiting its applications. It was evaluated the influence of surface modification in NiTi SMA by nitrogen plasma immersion ion implantation (varying temperatures, and exposure time as follows: <250 °C/2 h, 290 °C/2 h, and 560 °C/1 h) in the amount of nickel released using immersion test in simulated body fluid. The depth of the nitrogen implanted layer increased as the implantation temperature increased resulting in the decrease of nickel release. The sample implanted in high implantation temperature presented 35% of nickel release reduction compared to reference sample.

Microstructure of Cs-implanted zirconia: Role of temperature

The aim of this study was to identify experimentally the phase which includes cesium in yttria stabilized zirconia (YSZ). The solubility and retention of cesium in YSZ were studied at high temperature (HT). Cesium was ion implanted (at 300 keV) into YSZ at room temperature (RT), 750 °C, or 900 °C at fluences up to 5×1016 cm−2. The temperature dependence of the radiation-induced damage and of the cesium distribution in YSZ single crystals was investigated by Rutherford backscattering spectrometry and ion channeling. Transmission electron microscopy (TEM) studies were performed in order to determine the damage nature and search for a predicted ternary phase of cesium zirconate. Whatever the implantation temperature, the thickness of the damaged layer increases inwards with ion fluence. At RT, amorphization occurs, caused by the high Cs concentration (7at.%). In situ TEM during postannealing shows recrystallization of cubic zirconia after release of cesium. A high implantation temperature has a significant influence on the nature of radiation defects and on the retained Cs concentration. At HT, dislocation loops and voids are formed but no amorphization is observed whereas polygonization occurs at high fluence. The implanted cesium concentration reaches a saturation value of 1.5 at. % above which Cs can no longer be retained in the matrix and is then released at the surface. At that concentration, cesium forms a solid solution in YSZ; no other phase is formed, neither during irradiation nor after thermal annealing.

Amorphous Ge quantum dots embedded in SiO2 formed by low energy ion implantation

Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO2, i.e., Ge–SiO2 quantum dot composites, have been formed by ion implantation of Ge+74 isotope into (0001) Z-cut quartz at a low kinetic energy of 9keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO2 obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed.

Microscopic investigation of the structural and electronic properties of ion implanted Mn–Ge alloys

AbstractWe review recent results of an extensive experimental study of ion implanted Mn–Ge(100) alloys fabricated by systematically varying the Mn dose (in the range 1–4 × 1016 at/cm2) and the Ge substrate temperature (from room temperature up to 300 °C) during the implantation. The samples have been investigated by means of X‐ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, and scanning tunneling microscopy and spectroscopy. The combined investigation allows to determine, with an unprecedented deal of information at the nanometer scale, the morphological, structural, and electronic properties of such alloys. We evidence a porous to continuous transition in the surface morphology of the implanted layer when passing from 190 to 240 °C implantation substrate temperature. At higher implantation temperatures we directly demonstrate Mn dilution in the Ge matrix and also show the presence of extrinsic phases like Mn rich clusters. The presence of Mn rich precipitates is directly evidenced with transmission electron microscopy and corresponding energy loss Mn elemental maps taken at the Mn L3 edge. Larger clusters (with diameter greater that 10 nm) are in the Mn5Ge3 phase and are metallic, as demonstrated with scanning tunneling spectroscopy. Smaller clusters are still Mn rich but typically in an amorphous phase. These clusters are semiconducting with 0.45 eV energy gap. The results on the local electronic structure of the alloys investigated with scanning tunneling spectroscopy are also discussed in comparison with ab‐initio calculations. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

High-dose carbon implantations into silicon: fundamental studies for new technological tricks

Depending on the implantation temperature, the implantation of carbon ions into silicon at high doses results in the formation of either amorphous SiCx or crystalline 3C-SiC precipitates. Various aspects of the precipitation behaviour observed, such as the impeded nucleation, the limited growth and the resulting sensitivity to ballistic destruction are attributed to the large interfacial energy between crystalline silicon and 3C-SiC. Periodically arranged amorphous SiCx nanoclusters, which are formed at lower temperatures, are shown to promote amorphisation by their surrounding stress field and to represent sinks for silicon self-interstitials, which can be activated by annealing at 900 °C. By control of the depth distribution of equally sized, oriented 3C-SiC precipitates formed at higher implantation temperatures, it is possible to establish suitable starting conditions for the formation of buried homogeneous, single-crystalline 3C-SiC layers during a post-implantation anneal. The properties of these ion-beam-synthesised SiC layers are described and attempts to combine them with insulating and metallic layers are reviewed. A survey is given of the emerging applications of ion-beam-synthesised buried SiC layers and microstructures in electronic, optical and micromechanical devices and as large-area SiC pseudosubstrates.

Correlation between annealing effects of damage and implanted deuterium release from graphite

In the present study the correlation between annealing effects of damage and release of implanted deuterium into graphite was investigated through the behavior of deuterium in the graphite during D 2 + implantation. From the results of TDS experiments, the thermalized deuterium participated to form trapping sites. However the energetic deuterium would directly form CD x−1 ( x=2, 3, and 4) and simultaneously its kinetic energy was transferred to carbon atoms, and then this resulted in changing the electronic state of carbon from the sp 2 state to the sp 3 state. Those processes dominated during D 2 + implantation at lower temperatures below 573 K. On the other hand, at higher implantation temperatures above 573 K, the disordered structure of the graphite was recovered to a crystalline graphite structure and then deuterium release was started. The effects of heating the sample, known as thermal annealing effects, were correlated with the hydrogen release from the graphite.

Structural relation between Si and SiC formed by carbon ion implantation

The formation of crystalline SiC by implantation of C ions into silicon is not a single-step process. The implantation results in an elastic distortion of the Si matrix lattice and in the formation of crystalline SiC particles, depending on ion fluence and thermal conditions during implantation and postannealing. The growth of the SiC particles in the Si matrix was studied with various synchrotron x-ray scattering techniques and high-resolution transmission electron microscopy. Crystallites of the 3C–SiC polytype are formed in a buried layer. Three groups of crystallites with different orientation relative to the Si matrix are found: with a random orientation like in a powder material, with a fiber texture axis parallel to the surface normal, and completely aligned to the Si matrix lattice due to a partially coherent growth of SiC in the Si matrix. The thermal treatment favors the growth of highly oriented material: a higher implantation temperature is more efficient than a postimplantation treatment even at higher temperatures.

Phase and microstructural study of surface layers produced by plasma immersion ion implantation of stainless steel X6CrNiTi1810

A complex study of austenitic stainless steel X6CrNiTi1810 modified by nitrogen plasma immersion ion implantation (PI3) at 300 and 400°C is presented. To obtain detailed information on the structure and phase compositions, conversion electron Mössbauer spectroscopy, XRD, TEM, and Rutherford back scattering spectroscopy are applied. Depending on the treatment temperature a mixture of several phases is observed by Mössbauer phase analysis and confirmed by TEM. The dominant component in specimens treated at 300°C is a paramagnetic oversaturated austenitic phase. A higher implantation temperature (400°C) evokes more pronounced diffusion of nitrogen into the specimen volume, causing a decrease of nitrogen concentration but an increase of stress in the surface layer. This influences the defect density and results in a change of the expanded austenitic phase. Nitride formation is also different depending on the temperature. Furthermore, a texturing of the grains is observed after the PI3 treatment at both temperatures.

Si and SiC layer transfer by high temperature hydrogen implantation and lower temperature layer splitting

High quality Si and SIC layers which were implanted by H at 400 and 800/spl deg/C, respectively, were transferred onto an Si substrate and glass by wafer bonding and layer splitting at temperatures lower than the corresponding H-implantation temperatures.

Measurement and Modelling of the Radiation Damage of Silicon by MeV Ag Ions

AbstractDepth profiles of the radiation damage produced by 4 MeV Ag ions in Si(111) at temperatures of 210-450 K are studied by optical reflectivity depth profiling and TEM for doses between 1012 and 1015 Ag/cm2. For high implantation temperatures, the depth of maximum damage is shown to be dose dependent. Point defect diffusion is shown to result in long tails of defect depth profiles. High-temperature amorphization is observed to proceed via the formation and bridge-like coalescence of isolated amorphous volumina. The damage at the depth of the maximum in the nuclear stopping power is described as a function of dose and temperature by the Hecking model. The model parameters and a comparison with those obtained for lighter ions reflect the particular properties of heavy ion collision cascades.

Structure and wear resistance of 20X13 steel ion-implanted with nitrogen at a high beam-current density

X-ray diffraction and optical and electron microscopy were used to analyze microstructural variations in the surface layers of 20X13 steel after low-energy, high current-density ion implantation. These data show that nitrogen implantation produces solid solutions and precipitates of new phases in surface layers which are several μm thick. Tribological measurements made on steel blocks in a block-on-ring tester show that implantation increases wear resistance and reduces the friction coefficient on the surface. The phases formed are controlled by the temperature of implantation and the ion fluence. Higher implantation temperatures, which induce a more effective hardening of surfaces, yield a heterogeneous structure which is unsuitable for some tribological applications and is less corrosion-resistant than the homogeneous structure observed at lower temperatures.

Investigation of the effects of high temperature implantation and post implantation annealing on the electrical behavior of nitrogen implanted β-SiC films

Nitrogen was implanted into p-type β -SiC at implantation temperatures between 300 K and 1473 K. The implanted samples were characterized by Secondary Ion Mass Spectroscopy (SIMS) and electrically by resistivity and Hall measurements. The analysis was done with as-implanted samples and with samples that were annealed at 1473 K in a nitrogen atmosphere or in a vacuum. The implantation profiles did not show a significant dependence on the implantation temperature whereas the number of active dopants increased when the implantation temperature was raised. The electron mobility was also higher for high implantation temperatures, indicating a decrease in the implantation damage with increasing T impl . As expected for the samples with T impl < T anneal , the annealing step caused a further rise in the number of electrically active dopants. The trend of electrical activation and the electron mobilities increasing with a higher implantation temperature remained unchanged also after the annealing step.