Room-temperature ultrasonic annealing of radiation defects in silicon

Room-temperature ultrasonic annealing of point radiation defects in the bulk of silicon is demonstrated for the first time. The radiation defects in single crystal silicon were generated by the exposure to γ radiation from a ⁶⁰Co source. A qualitative model of processes in the system of radiation defects under the action of ultrasound is proposed.     

The effect of radiation on ion-implanted silicon detectors

Investigations on changes of characteristics of ion-implanted silicon-junction detectors when exposed to various doses of radiation (< 10⁵ and >10⁶ rad) were performed. It was found that the increase of leakage current depends not only on the dose but also on the gradient of irradiation.For doses higher than 10⁶ rad, the fully depleted layer thickness of the detector before irradiation decreases and becomes dependent on temperature. Also the most probable energy loss decreases and the width of the noise distribution broadens.     

High speed scanning electron beam annealing of ion-implanted silicon layers

Sawtooth scanning with a 40 keV electron probe at frequencies of 10⁵–10⁶ Hz can be used for generating in a silicon surface a quasi-line-shaped temperature field. With a power of 70–80 W and a spot diameter of 50 μm this yields a surface temperature of about 1500 K. The procedure was tentatively used for solid state annealing of ⁷⁵As-ion-implanted silicon layers to a depth of 1000 Å. These beam parameters permit an areal throughput of 10 cm² s^-1 without back side cooling since the substrate temperatures at the back side can be kept below 800 K.     

Synthesis of silicon carbide nanorods without defects by direct heating method

High quality silicon carbide single crystal nanorods were successfully synthesized through gas–solid reaction between silicon and multiwall carbon nanotubes (CNTS) by direct heating methods. The X-ray diffraction (XRD) analysis showed that the reaction product of Si vapor with CNTS is β-SiC. SEM and HRTEM images suggested that the SiC nanorods are 3C-SiC single crystals almost free of defects. Based on these results, it is presumed that the reaction first took place at an end of CNTS giving β-SiC nuclei, one of which with its [111] parallel to the tube direction could grow consecutively along this direction so that a straight and solid SiC single crystal rod was formed without defects.     

Ellipsometric analysis of ion-implanted polycrystalline silicon films before and after annealing

A study of arsenic ion-implanted polycrystalline silicon films before and after annealing at various temperatures has been performed using spectroscopic ellipsometry in the ultraviolet to the visible spectral region. Using the Bruggeman effective medium approximation, an optical/structural model is presented for all the annealed samples explaining the measurements. Ellipsometric measurements reveal important structural changes as a function of annealing temperature which provide an interesting inside into the annealing kinetics of ion-implanted polycrystalline silicon films. This work also demonstrates the importance of spectroscopic ellipsometry in determining non-destructively the dielectric functions in materials that have undergone complex processing.     

Growth of silicon carbide surface nanocrystals on silicon under high-temperature vacuum annealing

The formation and subsequent time-evolution of silicon carbide nanocrystals grown on a silicon surface by high-temperature vacuum annealing was investigated, with the effects of carbon contamination on the properties of these nanostructures being examined. The presence of higher contaminant levels during an annealing step was found to strongly enhance the nanocrystal growth rate, yet conversely to have no effect upon the density of nanocrystals which nucleated on the silicon surface. The physical structure of these objects was then studied in detail using high-resolution imaging and surface analysis techniques.     

Microstructure stability of fine-grained silicon carbide ceramics during annealing

Fine-grained silicon carbide ceramics with an average grain size of 140 nm or smaller were prepared by low-temperature hot-pressing of very fine -SiC powders using Al₂O₃-Y₂O₃-CaO (AYC) or Y-Mg-Si-Al-O-N glass (ON) as sintering additives. The microstructure stability of the resulting fine-grained SiC ceramics was investigated by annealing at 1850°C and by evaluating quantitatively the grain growth behavior using image analysis. The phase transformation of SiC in AYC-SiC was responsible for the accelerated abnormal grain growth of platelet-shaped grains. In contrast, the phase transformation in ON-SiC was suppressed, which resulted in a very stable microstructure.     

Growth of silicon carbide surface nanocrystals on silicon under high-temperature vacuum annealing

The formation and subsequent time-evolution of silicon carbide nanocrystals grown on a silicon surface by high-temperature vacuum annealing was investigated, with the effects of carbon contamination on the properties of these nanostructures being examined. The presence of higher contaminant levels during an annealing step was found to strongly enhance the nanocrystal growth rate, yet conversely to have no effect upon the density of nanocrystals which nucleated on the silicon surface. The physical structure of these objects was then studied in detail using high-resolution imaging and surface analysis techniques.     

Structural relaxation of amorphous silicon carbide thin films in thermal annealing

Amorphous Si_0.4C_0.6 thin films were deposited by radio frequency magnetron sputtering onto non-heated single crystal Si substrates, followed by annealing at 800 °C or 1100 °C in the vacuum chamber. The chemical bond properties and atomic local ordering as a function of the annealing temperature were characterized by Auger electron spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Infrared absorption spectroscopy, X-ray diffraction, and Raman spectroscopy measurements. We have examined the evolution of microstructure in annealing-induced relaxation process, and investigated the initial stages of thermal crystallization of amorphous Si_0.4C_0.6. Meanwhile, the structure of excess C in the films also has been studied.     

Tensile strength of silicon carbide fibre bundles at elevated temperatures

The mechanical properties of commercially available SiC-based ceramic fibres were measured in the temperature range from 400–1300°C. The measurements were performed in air and in inert gas atmospheres, respectively. The Nicalon and Tyranno fibres were tested as filament bundles and the decrease in strength occurring at temperatures above 600 °C was found in both atmospheres. To obtain a well-defined gauge length at the testing temperature, a furnace with very steep temperature gradients at both ends was built. To eliminate grip-induced damage in the heating zone the fibre bundles were fixed outside the furnace with cold grip units. These grips guaranteed the uniformity of load distribution imposed on to each of the individual filaments in the fibre bundle. A significant shrinkage of the fibres occurring during the creep test performed under low loads indicates a change in the microstructure of the fibres at high temperatures.     

Interaction between silicon carbide and a nickel-based superalloy at elevated temperatures

A study has been made of the reaction of hot-pressed SiC and a nickel-based superalloy at temperatures between 700 and 1150° C. Under conditions of reduced oxygen pressure at the reaction interface, obtained by applying pressure to the couple, some degree of reaction was observed in both metal and ceramic at all temperatures studied. Preliminary studies utilizing the same techniques at 1000° C with a Si-SiC ceramic composite, Si₃N₄, MgO, Al₂O₃, and SiO₂ also indicated some degree of reaction in the metal for all ceramics examined.     

Photoluminescence of porous silicon layers formed in ion-implanted silicon wafers

Implantation of the B⁺ and N⁺ ions or a B⁺ + N⁺ combination into silicon substrates affects the photoluminescence properties of porous silicon (por-Si) layers prepared on the ion-modified wafers. The postimplantation anneals lead to significant changes in the por-Si emission bands. Models explaining the observed phenomena are suggested.     

Diffusion of Pb in carbon ion-implanted silicon: Discovery of a new crystalline phase after electron beam annealing

A novel phase has been discovered by dual low-energy ion implantation and high vacuum electron beam annealing. (100) p-type Si was implanted with (a) 20 keV ¹²C⁺ ions to the fluence of 6 × 10¹⁶ cm⁻² and (b) 7 keV Pb⁺ ions to the fluence of 4 × 10¹⁵ cm⁻². The ¹²C ion implantation results in an understoichiometric shallow SiC_x layer that intersects with the surface. The implanted Pb ions decorate a shallow subsurface region. High vacuum electron beam annealing at 1000 °C for 15 s using a temperature gradient of 5 °C s⁻¹ leads to the formation of large SiC nanocrystals on the surface with RBS measurements showing Pb has diffused into the deeper region affected by the ¹²C implantation. In this region, a new crystalline phase has been discovered by XRD measurements.     

The elastic properties of ion-implanted silicon

The elastic properties of silicon implanted with As⁺ and Si⁺ in the dose range 10¹⁴ to 10¹⁵ ion cm^–2 has been investigated. Reflection scanning acoustic microscopy techniques have been used to determine changes in the velocity of surface elastic waves (Rayleigh waves) on ion-implanted silicon. With the aid of theoretical models for this mode of wave propagation, the experimental velocity changes have been interpreted in terms of changes in the elastic constants of the implanted layer. These changes have been found to be dependent upon the level of radiation damage produced by the implantation process. Decreases of 30% in the bulk and shear elastic constants have been deduced for damage levels present at the onset of implantation-induced amorphization.     

Preparation of nanosized silicon carbide powders by chemical vapor deposition at low temperatures

Liquid carbosilane was synthesized and analyzed by infrared (IR) and H-NMR (nuclear magnetic resonance) spectroscopy. Silicon carbide (SiC) powders were prepared by chemical vapor deposition (CVD) at 850°C and 900°C from liquid carbosilanes. The product powders were characterized by IR spectroscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results show that liquid carbosilane synthesized was the mixture of several oligomers that had a Si-C backbone. The powders prepared at 850°C contain some organic segments, and those prepared at 900°C are pure nanosized SiC powders, which are partly crystallized, the size of which is about 50–70 nm. Translated from Journal of Functional Materials and Devices, 2006, 12(5): 447–450 (in Chinese)     

Defects in silicon carbide

Defects in various forms of SiC, both single crystal and polycrystalline, have been examined using transmission electron microscopy. Dislocations were not as common as stacking faults, which were observed in all materials examined. The mechanism of formation of stacking faults is discussed and two types of both intrinsic and extrinsic faults are shown possible. The stacking-fault energy of SiC was measured to be 1.9 ergs/cm² by the extended node method.