Silicon Carbide Components Research Articles

Iron Cross-Contamination Dynamics at Elevated Temperatures in Oxygen Gas Flow

One major source of metals contamination during high temperature processing are metals pre-deposited on the wafers surface before thermal treatment and metals cross- contamination from other wafers and/or furnace components. This study investigates the mechanism of metals transfer via gas phase vs. temperature and oxygen gas flow conditions. We also investigated the cross-contamination from Silicon Carbide (SiC) components at elevated temperatures. Cross-contamination from SiC can be explained as (a) metal diffusion from the direct contact area between silicon wafer and SiC (MDD - Metals Direct Diffusion) and (b) metal desorption from the SiC surface and re-adsorption on the silicon wafer surface from the gas phase (MAG - Metals Adsorption from Gas Phase). Both MDD and MAG contamination components are driven by SiC surface metal contamination. Using high resolution Surface Photo- Voltage (SPV) iron mapping we investigated the character of iron cross-contamination. Iron diffusion and desorption activation energies were experimentally determined.

The use of MgO-coated SiC powders as low temperature densification materials

The densification of silicon carbide powders at relatively low temperatures (i.e. 1900 °C and below) has been investigated as a means of lowering the cost of the production route for dense silicon carbide components. The work has concentrated on the use of MgO, as a coating on α-SiC powder deposited by chemical methods to allow densification by a liquid phase mechanism. Samples of SiC containing additions of MgO, both alone and as a coating on the surface of the SiC powder have been either hot pressed at temperatures between 1500 and 1750 °C or pressureless sintered at temperatures up to 1750 °C. Densification of the MgO-coated powder was observed to take place below 1650 °C and in certain cases a considerable amount of densification had taken place at temperature as low as ∼1450 °C.

Wafer Surface Contamination Reduction from Silicon Carbide Components at Elevated Temperatures

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Crack Healing in Silicon Carbide

Crack healing in silicon carbide was investigated by introducing cracks into specimens and subsequently heat‐treating the specimens. It was observed that cracks were healed, dramatically increasing the strength, by being filled with amorphous silica produced by the oxidation of silicon carbide. It was shown that the residual stress produced by the thermal expansion mismatch between silica within cracks and surrounding silicon carbide played a major role in the increase of the strength. Our results imply that a simple oxidation heat treatment can improve the reliability of silicon carbide components.

Material defects in 4H-silicon carbide diodes

Crystallographic defects revealed by synchrotron white beam x-ray topography, electron beam induced current, optical microscopy, and electroluminescence are correlated with the electrical characteristics of medium-voltage epitaxial 4H-silicon carbide diodes. Diodes that include macroscopic crystallographic defects show a significantly reduced reverse breakdown voltage with typical microplasma current fluctuations under reverse bias. Microplasma current paths are revealed by increased electroluminescence both under forward and reverse bias of the diodes and coincide with the locations of screw dislocations in the epitaxial layers of the diodes. The role of crystallographic imperfections on the formation of stacking faults responsible for the degradation of bipolar silicon carbide components is discussed.

Inductive switching of 4H-SiC gate turn-off thyristors

The high-temperature operation of a silicon carbide gate turn-off thyristor is evaluated for use in inductively loaded switching circuits. Compared to purely resistive load elements, inductive loads subject the switching device to higher internal power dissipation. The ability of silicon carbide components to operate at elevated temperatures and high power dissipations are important factors for their use in future power conversion/control systems. In this work, a maximum current density of 540 A/cm/sup 2/ at 600 V was switched at a frequency of 2 kHz and at several case temperatures up to 150/spl deg/C. The turn-off and turn-on characteristics of the thyristor are discussed.

Reaction-Bonded Silicon Carbide by Reactive Infiltration

Exothermic reactions between a porous matrix and an infiltrating melt provide a more economic alternative for synthesizing many ceramics, intermetallics, and composites. It has recently been demonstrated that infiltration of cast microporous carbon preforms by silicon melt can be used to fabricate high-density, nearly net-shaped silicon carbide components at significantly reduced cost. This paper describes the synthesis of reaction-bonded silicon carbide by reactive infiltration of microporous carbon preforms. The kinetics of unidirectional infiltration of silicon melt into microporous carbon preforms as a function of pore morphology and melt temperature is investigated in this paper. Qualitative agreement between experimental data and a mathematical model for capillarity-driven fluid flow through cylindrical pores is demonstrated. Experimental evidence of high parametric sensitivity is also presented. A simplified model relating fluid flow, transport, and reaction phenomena is formulated to interpret experimental evidence of pore closing and free silicon entrapment. A robust numerical formulation is also described.

Laser-induced surface drilling of silicon carbide

Laser microdrilling was performed on the surface of silicon carbide components, in order to investigate the surface modification in relationships with the laser processing parameters. Several SiC surfaces were laser textured with blind microholes different in shape and size and were analyzed. CO 2 laser irradiation was proved to be efficient in producing regular shaped microholes due to the advantages of both small and focused spot size and complete control of individual pulse shape and power. Hole size (diameter and depth) and microstructural modification were related to laser processing parameters. On the basis of the preliminary tests carried out, regularly patterned surfaces were produced with a suitable choice of laser parameters.

Quantitative assessment of sintering behavior of silicon carbide with additions of alumina and yttria

Silicon carbide has potentially useful properties for exploitation in high temperature refractory and structural applications [1] and as a matrix material in ceramic matrix composites (CMCs) [2]. However silicon carbide’s retention of chemical stability and mechanical integrity at high temperatures also indicate that it will be difficult to sinter and in fact densification has not been achieved in the pure state, even under extremes of temperature and pressure. Additives such as boron plus carbon to promote diffusion [3] or alumina and yttria to form an intergranular liquid phase [4] must be added to facilitate sintering. In spite of recent advances it is paramount to obtain a more detailed understanding of the sintering of silicon carbide as further reductions in the sintering temperature are sought in order to make routine production of silicon carbide components economic without any detrimental effects on properties. For example, the option of adding large volumes of a relatively low melting point liquid phase while allowing full densification, produces a ceramic with poor resistance to oxidation and creep and is therefore not viable. Optimistic sintering at a temperature too low to produce adequate densification is also unsatisfactory, and will not produce the required strength and stiffness. Thus, the development and industrial application of silicon carbide would be significantly advanced by sintering at the lowest temperature possible and with the minimum amount of sintering additives while still achieving a dense product. Other sintering conditions, such as hold time and environment, can also be manipulated. Blanket testing of all permutations of processing conditions would doubtless result in the production of the optimum product. A more efficient approach is to sample a statistical selection of conditions and assess the relative importance of each variable on the densification outcome; this requires fewer experiments to be carried out and may allow the prediction of promising variable combinations. The latter was the approach taken in the present work to determine the effects of

Periphery protection for silicon carbide devices: state of the art and simulation

Silicon carbide (SiC) is well known for its large potentiality for power device applications. SiC presents a high critical electric field, allowing small dimensions and relatively high doping levels, favorable for reduced power losses in the on-state together with high blocking voltage capability, SiC has a wide band-gap, inducing very low intrinsic carrier concentrations even at high temperature, and consequently allows very low leakage currents and off-state power losses. The present paper focuses on problems related to the high voltage capability of SiC components. After dealing with the bulk breakdown voltage of a SiC semi-infinite parallel-plane abrupt junction, a short review of the methods allowing the potential distribution spreading near the periphery of the real junction is given. Some methods have been implemented and the edge-termination protection has been optimized by the way of numerical simulation. This includes equipotential rings, junction termination extension as planar protections, and MESA as an etched-contour periphery. Examples of realizations are given, and electrical characteristics are presented. They show a better capability of the junction termination extension periphery over the MESA technique to reach a 1500 V-blocking voltage objective,

Sintered silicon carbide for slide bearings and seal rings

In the past, two problems have prevented the widespread use of sintered silicon carbide (SiC) components for wear-reducing applications: firstly a complicated production process marked by relatively high costs and inadequate availability, and secondly the brittleness of ceramic materials. Progress has been made in both areas during the past years. The technology used for producing sintered SiC has become cost competitive, and much has been learned about ceramic-oriented materials design. In the following article concepts of product development for improved reliability of silicon carbide sliding bearings and mechanical seals will be discussed. Materials optimization steps will be concentrated on and their results on tribological performance as well as on ceramic design criteria for reliably working pump components.

95/01777 Reaction bonded silicon carbide components for burners, radiant heating and heat exchangers

95/01777 Reaction bonded silicon carbide components for burners, radiant heating and heat exchangers

A Robust LPCVD Nitride Integrated Process for High Density Non-Volatile Eprom Memories

ABSTRACTA robust 6" hotwall flatzone nitride system is developed for scaled ONO interpoly. dielectric application in a high density EPROM memory cell. This system is designed to operate at low temperature (660° C) and gas ratio (4:1 NH3: DCS) with integrated silicon carbide components. The obtained key features are low defects (0.25 #/cm2 particles), smooth topography (measured by atomic force microscopy) and superior electrical interface as measured by electrical and optical methods.

A Methodology for Cost/Benefit Safety Analysis for Fusion Reactors

AbstractA methodology is presented that can be used to determine if a proposed fusion power plant design modification, directed at improving plant safety, is cost-effective. Both normal and accident conditions can be handled. An approach for evaluating the maximum justified spending on safety is outlined. The incremental costs involved with a dose reduction measure are identified, and models for their assessment are given. By comparing the spending on the design modification to the justified expenditure ceiling, the cost-effectiveness of the design can be assessed.The utility of this approach is illustrated through two examples. For normal plant conditions, the cost-effectiveness of replacing the steel alloy PCA by low-activation silicon carbide (SiC) in the STARFIRE design is assessed. Based on a specified set of assumptions, it was determined that if the installed cost of SiC components is less than $110/kg, then the low-activation design is cost-effective.The second example illustrates the applicabilit...

Special purpose materials for fusion application

Originally in 1978 the Special Purpose Materials Task Group was concerned with tritium breeding materials, coolants, tritium barriers, graphite and silicon carbide, ceramics, heat-sink materials, and magnet components. Since then several other task groups have been created, so that now the category includes only materials for superconducting magnets and ceramics. For the former application copper-stabilized Nb 3Sn (Ti) insulated with polyimides will meet the general requirements, so that testing of prototype components is the priority task. Ceramics are required for several critical components of fusion reactors either as dielectrics or as a structural material. Components near the first wall will receive exposures of 5–20 MW y/m 2. Other ceramic applications are well behind the first wall, with lower damage levels. Most insulators operate near room temperature, but ceramic blanket structures may operate up to 1000°C. Because of a meager data base, one cannot identify optimum ceramics for structural application; but MgAl 2O 4 is an attractive dielectric material.