1,720,982 research outputs found
Selective low pressure chemical vapour deposition epitaxy using silane only for advanced device applications
No full textSelective epitaxial growth of silicon in windows opened in a mask is usually carried out using source gases in the Si–Cl–H system in low pressure chemical vapour deposition (LPCVD) systems. These gases offer good control over growth but are associated with mask distortion, which is intolerable in submicrometre device geometries. The silane only selective growth process possible in the Southampton University Microelectronics Centre (SUMC) LPCVD machine is highly selective, allowing growth of epitaxial layers four times thicker than the mask without lateral overgrowth. Surface facets are observed at the edges of 〈110〉 direction oxide features, in common with selective epitaxy by other techniques. The material under the facets is shown to include defects. Increased planarity can be obtained by orienting mask features along 〈100〉 directions, where faceting is not observed. The selectively grown material can be doped n type to give carrier concentrations from 2×1015 to 2×1019 cm−3, and p type from 1×1017 to 1×1019 cm−3. In terms of selectivity, planarity, and carrier concentration, the material produced by the SUMC LPCVD epitaxy machine is suitable for device production
Reduction of boron transient enhanced diffusion in silicon and silicon-germanium by fluorine implantation
No full textCharacterisation of morphology and defects in silicon-germanium virtual substrates
No full textSilicon-germanium heterostructures incorporating virtual substrates are successfully used for both microelectronic and optoelectronic applications. However, their use is limited by their surface morphology (e.g. roughness) and defect (e.g. threading dislocations) density. High quality silicon-germanium heterostructures incorporating virtual substrates have been grown epitaxially using different methods. This study reports the effects of the growth parameters on the morphology and defects in different silicon-germanium heterostructures incorporating virtual substrates grown in the Southampton University Microelectronics center (SUMC) by low pressure chemical vapor deposition (LPCVD). Two types of structures: one with a linear and the other with a step variation of the germanium concentration in the virtual substrate, were grown and characterized. Results obtained were in good agreement with others already reported in the literature for similar structures grown using different epitaxial techniques
Suppression of boron diffusion due to carbon during rapid thermal annealing of SiGe based device materials: some comments
No full textDiffusion studies of antimony and boron in Si and SiGe under point defect injections by Rapid Thermal Anneal
No full textThe effect of point defect injection on the diffusion of antimony and boron in silicon and silicon-germanium alloys has been studied by comparison of inert with injection diffusions. In this work, Sb and B in Si were used as control wafers to investigate Sb and B diffusion behavior in Si0.9Ge0.1. The point defect injection technique was carried out by rapid thermal annealing (RTA) Sb and B in Si and Si0.9Ge0.1 samples with the various surface coatings in either oxygen or ammonia atmospheres to inject either interstitial or vacancy defects. The diffusion profiles for as-grown and RTA annealed samples were measured by Secondary Ion Mass Spectrometry (SIMS). Diffusivities for B in Si and Si0.9Ge0.1 were obtained using computer simulations of the measured boron profiles for their annealed samples. Sb diffusion in Si and Si0.9Ge0.1 was found enhanced by vacancy injection and retarded by interstitial injection. The enhanced B diffusion in Si and Si0.9Ge0.1 was found by interstitial injection. These results confirm that Sb diffusion in Si0.9Ge0.1 is primarily dominated by vacancy-mediated mechanism, while B diffuses in Si0.9Ge0.1 by an interstitially mediated mechanism
Study of fluorine behaviour in silicon by selective point defect injection
No full textThis letter reports a point defect injection study of 185 keV 2.3x1015cm?2 fluorine implanted silicon. After an inert anneal at 1000°C, fluorine peaks are seen at depths of 0.3Rp and Rp and a shoulder between 0.5–0.7Rp. The shallow peak (at 0.3Rp) is significantly smaller under interstitial injection than under both inert and vacancy injection conditions. For a longer anneal under interstitial injection, both the shallow peak and the shoulder are eliminated. These results support earlier work suggesting that the shallow fluorine peak is due to vacancy-fluorine clusters which are responsible for suppression of boron thermal diffusion in silicon. The elimination of the shallow fluorine peak and the shoulder is explained by the annihilation of vacancies in the clusters with injected interstitials
Single-hole tunneling in SiGe nanostructures
No full textWe have fabricated quantum dots and quantum wires in p-type silicon germanium grown on SOI substrates. Electrical characteristics at low temperature show clear Coulomb blockade and Coulomb staircases in both structures. Gate-controlled experiments show conductance oscillations with a single period in quantum dots and multiple periods in quantum wires. While single-hole tunnelling is easily achieved in quantum dots, a more complicated hole transport results in quantum wires with a narrow control range for a true single-hole tunnelling
Leakage current mechanisms associated with selective epitaxy in SiGe heterojunction bipolar transistors
No full textSiGe Heterojunction Bipolar Transistors (HBT's) have been fabricated using selective epitaxy for the Si collector, followed in the same growth step by non-selective epitaxy for the SiGe base and Si emitter cap. E/B leakage currents are compared with cross section TEM images to identify sources of leakage currents associated with the epitaxy. In addition, the influence of the position of the extrinsic base implant with respect to the polysilicon emitter on the leakage currents is studied. The emitter/base leakage currents are modelled using Shockley-Read-Hall recombination, trap-assisted tunnelling and Poole-Frenkel generation. The position of the extrinsic base implant is shown to have a strong influence on the leakage currents. The Poole-Frenkel effect dominates the emitter/base leakage current in transistors in which the collector area is smaller than the polysilicon emitter. This result is explained by penetration of the emitter/base depletion region into the p+ polysilicon extrinsic base at the perimeter of the emitter. These leakage currents are eliminated when the collector area is increased so that the extrinsic base implant penetrates into the single-crystal silicon at the perimeter of the emitter
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