Showing papers on "Silicon nitride published in 1974"

Crack propagation and failure prediction in silicon nitride at elevated temperatures

Abstract: A technique for studying high temperature crack propagation in ceramic materials is developed. The technique is used to obtain relationships between the crack propagation rate and the stress intensity factor for hot-pressed silicon nitride up to 1400° C. The data are then used to develop proof test diagrams which give values for the safe working stress levels for this material after proof testing (or any other flaw detection procedure).

The microstructures of silicon nitride ceramics during hot-pressing transformations

Abstract: The microstructure of silicon nitride hot-pressed with a magnesium oxide additive has been studied by transmission electron microscopy. This includes material at various stages in a hot-pressing process: the initial (∼ 90%α) silicon nitride powder; specimens partially densified and partially transformed from α-silicon “nitride” (Si11.5N15O0.5) to β-silicon nitride (Si3N4); and almost fully dense and fully transformed β-Si3N4. The observations substantiate a solid/liquid/solid transformation mechanism, whereby Si and N are transported from α grains through a silicate liquid phase to nucleation sites for β at α/liquid interfaces or to β grains nucleated homogeneously in the liquid phase.

Selective plasma etching and deposition

Abstract: This invention relates to a method of selectively treating the surface of an article comprising silicon in part and either silica or silicon nitride in part wherein either the silicon or the silicon compound is etched at a greater rate or a fluoropolymer is deposited on the article by placing the article in a plasma containing fluorine, carbon and reducing species and adjusting the concentration of the reducing species to selectively etch the silicon at a greater rate, etch the silicon compound at a greater rate or deposit polymer.

The identification of a grain-boundary phase in hot-pressed silicon nitride by Auger electron spectroscopy

Abstract: The presence of magnesium, calcium and oxygen has been detected in the intergranular fracture surface of an Si3N4-7% MgO hot-pressed material by Auger electron spectroscopy, together with a chemical shift in the silicon Auger peak. The composition of this grain-boundary phase has been estimated as (0.40 ± 0.03) CaO. (0.75 ± 0.10) MgO. 2SiO2 by comparison with spectra obtained from a bulk glass specimen of similar composition. The reduction in strength of the hot-pressed material at temperatures above 1000° C has been attributed to the decrease in viscosity of this phase.

The microstructures of silicon nitride/alumina ceramics

Abstract: The microstructures of materials formed by sintering or hot-pressing mixtures of silicon nitride and alumina have been studied by transmission electron microscopy. The probable mechanism of transformation of the reactants to form β′-silicon aluminium oxynitride (β′-sialon) via a liquid phase sintering process, which is analogous to a similar transformation in hot-pressed silicon nitride containing a magnesia additive, is proposed. The origin and crystal symmetry of an unknown second phase is discussed. The residual quantity of this phase, known as the X-phase, is controlled mainly by the silica impurity content of the initial silicon nitride powder.

Pressureless sintering silicon nitride powders

Abstract: A method of producing a silicon nitride article by powder techniques, wherein silicon nitride powder is used as a starting material. The silicon nitride powder, mixed with a densification aid, is heated rapidly to the sintering/densification temperature (1500° to 1750° C) in the absence of pressure, held there a short, closely controlled time (5 to 30 minutes) and thereafter rapidly cooled. This provides a strong product with controlled dimensional tolerances.

Synthesis of high purity, alpha phase silicon nitride powder

Abstract: A method is provided for preparing alpha silicon nitride powder in which very high purity, liquid silicon tetrachloride is reacted with an excess of ammonia gas in dry deoxygenated benzene or normal hexane at about 0°C, yielding a precipitate of silicon diimide and ammonium chloride After removal of the benzene or n-hexane from the precipitate, the mixture of silicon diimide and ammonium chloride powder is heated under a vacuum from room temperature to a temperature in the range of 1200° to 1350°C and maintained at the latter temperature for a period of about 2 to 8 hours The product obtained is a high purity, submicron, alpha phase silicon nitride powder which is eminently suitable for the fabrication of dense, high strength, creep resistant and thermal shock resistant bodies for use in high performance gas turbine engines and in radome applications

Fatigue life of high-speed ball bearings with silicon nitride balls

Abstract: Hot-pressed silicon nitride was evaluated as a rolling-element bearing material. The five-ball fatigue tester was used to test 12.7-mm- diameter silicon nitride balls at maximum Hertz stresses ranging from 4.27 x 10 to the 9th power n/sq m to 6.21 x 10 to the 9th power n/sq m at a race temperature of 328K. The fatigue life of NC-132 hot-pressed silicon nitride was found to be equal to typical bearing steels and much greater than other ceramic or cermet materials at the same stress levels. A digital computer program was used to predict the fatigue life of 120-mm- bore angular-contact ball bearings containing either steel or silicon nitride balls. The analysis indicates that there is no improvement in the lives of bearings of the same geometry operating at DN values from 2 to 4 million where silicon nitride balls are used in place of steel balls.

Method of making an insulated gate field effect transistor

Abstract: An improved insulated gate field effect transistor is achieved by using a material such as silicon nitride as an ion implantation and oxidation mask overlying a channel region, forming source and drain regions or extensions thereof by implanting ions of a conductivity modifier into a semiconductor substrate, and subjecting the implanted ions to a drive-in diffusion whereby the conductivity modifier ions are redistributed. The ion implantation allows greater control over the amount of conductivity modifier implanted in the lightly doped source and drain regions, the more uniform distribution of conductivity modifier increases the source-drain breakdown voltage, while the use of the silicon nitride mask provides simultaneously for general alignment of the channel region with the effective gate length.

Method of making a triple density silicon nitride article

Abstract: A method of making a triple density article of silicon nitride is disclosed. A first element is formed by hot pressing silicon nitride particles. The general shape of a second element is formed by injection molding silicon metal particles and a binder and subsequently burning out the binder. The general shape of a third element is slip cast adjacent and in bonding relationship to at least a portion of the second element. The so combined second and third elements are nitrided in a nitriding operation. Facing surface areas of the first element and the third element are bonded together by applying heat to both elements and pressure to at least one of the elements while the other element is held in a fixed position.

High reliability, low leakage, self-aligned silicon gate FET and method of fabricating same

Abstract: An improved FET structure and method of making same is disclosed. The gate structure of the FET includes a phospho-silicate glass as the insulator and polysilicon as the gate conductor. A thin layer of silicon nitride is formed over the polysilicon and selectively etched so as to remain only over gate areas and other areas where it is desired to extend the polysilicon as a conductor. The unmasked polysilicon is oxidized to form the thick oxide surface coating. The disclosure also describes the use of oxide rings and epitaxial layers to reduce parasitic effects between adjacent FET devices in an integrated circuit.

Dielectric optical waveguides

Abstract: Dielectric optical waveguides can be made having a core of vitreous silica doped with nitrogen in the form of silicon nitride, and a cladding of pure vitreous silica. Silicon nitride may be present in the core material in quantities varying between .1% to 10% by weight. The silicon nitride doped silica glass can be formed in a boule by passing a mixture of gaseous compounds containing silicon and nitrogen through a induction coupled plasma discharge. The outside of the doped silica boule may be oxidized to reduce the nitrogen content.

Conduction in amorphous thin films of silicon nitride under non-uniform electric fields

Abstract: It is observed that amorphous thin films of silicon nitride with dissimilar (aluminium and silicon) electrodes exhibit conduction properties with a consistent dependence on the polarity of the applied electric field and the film thickness. In particular, for a given average field (voltage/thickness) it is found that: (i) conduction is larger for (aluminium) negative than for positive polarity; (ii) this effect is more pronounced with 500 A films than with 1000 A films; and (iii) for both polarities, conduction is larger for the 500 A than for the 1000 A films. This is surprising in view of the evidence in this paper that conduction in these films is by a bulk-controlled process. A model based on unequal trapping near the two electrodes, which creates a variation in the electric field with position into the film, is in qualitative agreement with all of the experimental results.

Chemical vapor deposition in the systems silicon-carbon and silicon-carbon-nitrogen

Abstract: This report relates to the chemical vapor deposition and morphology of the systems Si + β -SiC, Si + Si 3 N 4 , and Si + β -SiC + Si 3 N 4 , which were produced from the following mixtures at temperatures ranging from 1100 to 1300 °C: SiCl 4 + CCl 4 + H 2 , SiCl 4 + N 2 + H 2 , and SiCl 4 + CCl0 4 + N 2 + H 2 . The solid phases form an unoriented, extremely fine-grained but dense mixture. These solid phases do not reveal any coherent or semicoherent intergrowth. The unoriented growth is a consequence of the permanent carbidization or nitridation of the free silicon surface and covering of the resultant crystals of silicon carbide and/or silicon nitride. At ⩽ 1200 °C Si 3 N 4 becomes amorphous and at ⩾ 1300 °C α-Si 3 N 4 is deposited in addition. In the neighbourhood of 1300 °C β-Si 3 N 4 formation cannot be excluded with certainty. As the CCl 4 concentration in the vapor phase increases, the nitridation is suppressed by the carbidization.

Process for producing a solid solution of aluminum oxide in silicon nitride

Abstract: A method of producing a sinterable refractory material having a low coefficient of thermal expansion and comprising essentially a dispersion of aluminum oxide throughout a silicon nitride matrix, herein called SIALON. The process includes obtaining aluminum and silicon from generally readily available raw material sources.

Oxidation resistant mask layer and process for producing recessed oxide region in a silicon body

Abstract: An oxidation resistant masking layer for a semiconductor body having a first layer of oxygenated silicon nitride material having a refractive index in the range of 1.60 to 1.85, and a second overlying layer of Si3N4 bonded to the first layer having a thickness of at least 100 Angstroms. A process for forming recessed thermal SiO2 isolation regions in a silicon semiconductor body wherein a masking layer is deposited on the silicon body by depositing a blanket layer of oxygenated silicon nitride and an overlying blanket layer of Si3N4, forming openings in the resultant composite masking layer and etching grooves into the silicon semiconductor layer to the desired thickness thus defining the desired recessed isolation regions, and exposing the resultant structure to an oxidizing environment for a time sufficient to form the desired silicon oxide recessed regions.

Ceramic electrical resistance igniter

Abstract: A ceramic resistance gas igniter comprised of 10 to 60% by weight of silicon carbide and 40 to 90% by weight of silicon nitride, slicon oxynitride, or silicon aluminum oxynitride, and having a density preferably greater than 95% of the theoretical density of the composite. As a result of the combination of high density and composition, the igniters have moduli of rupture in excess of 80,000 p.s.i., a resistivity range of from 0.1 to 104 ohm centimeters, and superior resistance to corrosive gases.

Method of fabricating silicon nitride bodies

Abstract: In a method for fabricating highly dense, polycrystalline silicon nitride bodies, a mixture of silicon nitride powder and an oxide, hydride or nitride of an element of the lanthanide series in powder form is hot pressed at a temperature ranging from 1600° to 1750° C for a period of 30 to 60 minutes. The method is particularly useful for fabricating structural components, such as stators, blades, airfoils and buckets in high performance gas turbine engines.

Method of improving impact resistance of ceramic bodies, and improved bodies

Abstract: A method of improving the impact resistance of bodies of polycrystalline ceramic such as alumina, silicon nitride and silicon carbide, and bodies produced by the method. The body is provided with a layer of a low elastic modulus polycrystalline ceramic material which has microcracks therein, formed by such factors as thermalexpansion coefficient anisotropy, differences in thermalexpansion coefficients between phases of the material, and by changes in volume during phase transformations in the material. The layer can be applied by preforming the layer and then applying, or by hot pressing the material of the layer onto the body.

Method for manufacturing a semiconductor device utilizing selective oxidation

Abstract: An N region and a P region adjacent thereto are formed on a major surface of a P silicon substrate, an N silicon layer is epitaxially grown on the major surface and the epitaxial layer is partially oxidized using silicon nitride as a mask therefor, so as to form an SiO2 layer reaching the P and N regions with a ring shape, whereby the N silicon layer surrounded by the SiO2 layer is electrically isolated from the other portions of the N silicon layer substantially without leakage current.

Method of synthesizing cubic crystal structure boron nitride

Abstract: A method of synthesizing cubic crystal structure boron nitride from hexagonal crystal structure boron nitride or other boron compound by subjecting the boron nitride or boron compound to a pressure of at least about 35,000 atmospheres and a temperature of at least about 1,000°C in the presence of, as a catalyst, silicon, silicon nitride, a preformed silicon alloy or nitride thereof, or a silicon-and-aluminum-containing mixture.

Electrically conducting material containing silicon carbide in a matrix of silicon nitride

Abstract: An electrically conducting material is produced by nitriding a mixture of silicon and a component capable of being converted to an electrically conducting phase under the conditions of the nitriding, thereby to produce a material comprising silicon nitride and the electrically conducting phase. The material produced has a low resistivity, which is retained over a wide temperature range.

Rolling Contact Fatigue of Hot-Pressed Silicon Nitride Versus Surface Preparation Techniques

Abstract: Hot-pressed silicon nitride is receiving interest as a potential antifriction bearing material1. As a result of advanced material preparation and processing techniques, bend strengths in excess of 100,000 psi are routinely achieved. In addition to its high strength, dimensional stability and corrosion resistance, silicon nitride has a density of 3.2 g/cm3, sixty percent lower than that of steel. This light weight is especially important for high speed bearings, where the maximum stresses occur in the outer race, primarily as a result of the centrifugal force loading from the rolling elements. Inasmuch as strength tends to be sensitive to surface integrity, finishing procedures are an important aspect for bearing applications. This paper will report experiments on their effect.

Plasma arc production of silicon nitride

Abstract: This is a method of producing silicon nitride in a plasma arc furnace utilizing silicon metal or silicon dioxide as a starting material. When silicon metal is used it is reacted directly with a nitrogen bearing gas to produce silicon nitride. When silicon dioxide is used a two-step process is performed wherein the silicon dioxide is first reacted with hydrogen to produce silicon monoxide gas and water and thereafter the silicon monoxide gas is reacted with hydrogen and nitrogen to produce silicon nitride and water.

Wetting of silicon nitride by alkaline-doped MgSiO3

Abstract: The wetting behaviour of Si3N4 by alkaline-doped MgSiO3 was investigated by the sessile drop method. It is shown that the alkaline oxide additions improve the wetting of MgSiO3 on Si3N4. The hot-pressing of Si3N4 is controlled by a liquid phase sintering process where the dissolution of Si3N4 in silicate glass promotes good wetting and a well bonded interface by lowering the liquid-solid interfacial energy. Controlling total alkaline impurity level between 50 and 100 ppm is suggested for an optimal strength performance.