Showing papers on "Silicon nitride published in 1995"

A covalent micro/nano-composite resistant to high-temperature oxidation

Abstract: ADVANCED ceramic materials that can withstand high temperatures (over 1,500 °C) without degradation or oxidation are needed for applications such as structural parts for motor engines, gas turbines, catalytic heat exchangers and combustion systems1,2. Hard, oxidation-resistant ceramic composites and coatings are also in demand for use on aircraft and spacecraft. Silicon nitride (Si3N4) and silicon nitride/carbide (Si3N4 /SiC) composites are good candidates for such high-temperature applications2,3. Commercial Si3N4 parts can be used in oxidizing environments up to 1,200–1,300 °C (ref. 4), but are oxidized at still higher temperatures. Here we describe the synthesis of a covalent ceramic composite which is resistant to oxidation at temperatures up to 1,600 °C. The composite is formed from an amorphous silicon carbonitride, which crystallizes at high temperature into a composite of α-Si3N4 microcrystals and α-SiC nanocrystals. The oxidation resistance stems from the formation of a passivating surface layer of SiO2 a few micrometres thick.

Optical properties of silicon nitride films deposited by hot filament chemical vapor deposition

Abstract: Silicon nitride films were deposited at low temperatures (245–370 °C) and high deposition rates (500–1700 A/min) by hot filament assisted chemical vapor deposition (HFCVD). Optical properties of these amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photoluminescence excitation, and electroluminescence measurements. The optical band gap of the films was varied between 2.43 and 4.74 eV by adjusting the flow rate of the disilane source gas. Three broad peaks at 1.8, 2.4, and 3.0 eV were observed in the PL spectra from these films. A simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features. The photoluminescence intensity observed in these films was 8–10 times stronger than films deposited by plasma enhanced chemical vapor deposition, under similar conditions. The high deposition rates obtained by HFCVD is believed to introduce a large number of these optically active defects.

Processing Strategy for Producing Highly Anisotropic Silicon Nitride

Abstract: Silicon nitride with a preferred orientation of large elongated grains was obtained by tape casting of raw powder slurry seeded with rodlike {beta}-Si{sub 3}N{sub 4} particles, followed by a gas pressure sintering under 1 MPa nitrogen pressure. The large elongated grains developed from seeds lay in planes parallel to the casting direction in a two-dimensional distribution. Increased fracture toughness (11.1 MPa {center_dot} m{sup 1/2}) and bending strength (1,100 MPa) were achieved in the direction perpendicular to the grains alignment compared to specimens with a random distribution of elongated grains. Moreover, the specimens exhibited a high Weibull modulus of 46 due to the uniform distribution of large grains.

Diesel particulate filter apparatus

Abstract: According to the present invention, a filter body for collecting particulates is constituted of a fiber laminate material produced by laminating a fiber material comprising a core material in the form of a fiber, and a covering layer of a material different from that of the core material formed around the outer periphery of the core material by coating. The core material of the fiber material is selected from among inorganic fibers such as glass or ceramic fibers containing alumina, and heat-resistant alloy fibers each made of a heat-resistant alloy selected from among Ti-Al alloys, Fe alloys containing at least one of Mo, Cr and Ni, and Fe-Cr-Al-Y alloys. The covering layer is made of a material selected from among silicon carbide ceramics respectively derived from polytitanocarbosilane, polysilazane and polycarbosilane, thermoplastic materials, silicon carbide ceramics such as Si-C, Si-Ti-C-O and Si-C-O or silicon nitride ceramics such as Si-N-C-O, alumina ceramics, and zirconia ceramics.

Thermal conductivity and diffusivity of free‐standing silicon nitride thin films

Abstract: The thermal conductivity and diffusivity of free‐standing silicon nitride (Si‐N) films of 0.6 and 1.4 μm in thickness are measured. A new experimental technique, the amplitude method, is proposed and applied to measurement of the thin‐film thermal diffusivity. The thermal diffusivity is determined by three independent experimental approaches: the phase‐shift method, the amplitude method, and the heat‐pulse method. Good agreement among the measured thermal diffusivities obtained by the three methods indicates the validity of the amplitude method. High‐resolution electron microscopy studies show a large quantity of voids in the 1.4 μm Si‐N films. In contrast, very few voids are found in the 0.6 μm films. This difference may be responsible for the measured lower conductivity of the 1.4 μm Si‐N films as compared to the 0.6 μm thin films.

Method of etching silicon nitride film

Abstract: A method for etching a silicon nitride film, includes the steps of supplying a fluorine radical, a compound of fluorine and hydrogen, and an oxygen radical close to a substrate having the silicon nitride film, and selectively etching the silicon nitride film from the substrate with the fluorine radical, the compound of fluorine and hydrogen, and the oxygen radical. A method for etching a silicon nitride film, includes the steps of exciting gas containing fluorine and oxygen gas, thereby generating a fluorine radical and an oxygen radical, supplying the fluorine radical and the oxygen radical close to a substrate having the silicon nitride film and supplying gas of a compound containing a hydroxyl close to the substrate, reacting the fluorine radical, the oxygen radical and the compound containing the hydroxyl, thereby generating a compound of the fluorine radical, the oxygen radical and a compound of fluorine and hydrogen, and selectively etching the silicon nitride film from the substrate with the compound of the fluorine radical, the oxygen radical and the compound of fluorine and hydrogen.

Transistor with low resistance tip and method of fabrication in a CMOS process

Abstract: A novel transistor with a low resistance ultra shallow tip region and its method of fabrication in a complementary metal oxide semiconductor (CMOS) process. According to the preferred method of the present invention, a first gate dielectric and a first gate electrode are formed on a first portion of a semiconductor substrate having a first conductivity type, and a second gate dielectric and a said gate electrode are formed on a second portion of semiconductor substrate having a second conductivity type. A silicon nitride layer is formed over the first portion of the semiconductor substrate including the first gate electrode and over the second portion of the semiconductor substrate including the second gate electrode. The silicon nitride layer is removed from the second portion of the silicon substrate and from the top of the second gate electrode to thereby form a first pair of silicon nitride spacers adjacent to opposite sides of the second gate electrode. A pair of recesses are then formed in the second portion of the semiconductor substrate in alignment with the first pair of sidewall spacers. A selectively deposited semiconductor material is then formed in the recesses.

Micromachined Fabry-Perot cavity pressure transducer

Abstract: A surface micromachined Fabry-Perot cavity used as a pressure sensor has been fabricated using standard IC technology. Dielectric film stacks consisting of layers of silicon dioxide and silicon nitride were used as mirrors. Polysilicon was used as a sacrificial layer that was then removed to form an air gap cavity. The Fabry-Perot sensor was optically interrogated using a multimode optical fiber. The measured response of the sensor agrees well with theoretical simulation, which takes into account the averaging effect caused by the shape of the deflected mirror in the cavity.

Cavitation Contributes Substantially to Tensile Creep in Silicon Nitride

Abstract: During tensile creep of a hot isostatically pressed (HIPed) silicon nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress ({dot {var_epsilon}} {proportional_to} {sigma}{sup n}, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at silicon nitride multigrain junctions. Small-angle X-ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual grains t slide past one another. During tensile creep the silicon nitride grains remain rigid; cavitation in the multigrain junctions allows the silicate tomore » flow from cavities to surrounding silicate pockets, allowing the dilation of the microstructure and deformation of the material. Silicon nitride grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution-reprecipitation of silicon nitride.« less

Effect of the Grain Boundary Thermal Expansion Coefficient on the Fracture Toughness in Silicon Nitride

Abstract: The effect of thermal expansion mismatch stress between silicon nitride and different grain boundary phases on the fracture toughness of silicon nitride was investigated. Different sintering aids in the Y-Mg-Si-Al-O-N system produced silicon nitride specimens with very similar microstructures but different grain boundary phase compositions and different values of fracture toughness. The fracture toughness of the silicon nitride increased as the thermal expansion coefficient of the grain boundary phase increased. The presence of tensile residual stress at the grain boundary caused by thermal expansion mismatch between the silicon nitride and the grain boundary phase enhanced crack deflection and grain bridging.

Process for fabricating a cup-shaped DRAM capacitor using a multi-layer partly-sacrificial stack

Abstract: This invention is a process for fabricating a dynamic random access memory (DRAM) having a stacked capacitor with hemispherical-grain (HSG) polysilicon asperities on an amorphous silicon storage-node plate. The process enables the selective formation of HSG polysilicon asperities on the storage-node plates and a subsequent deposition of a high-quality silicon nitride cell dielectric layer on the asperity-covered storage-node plates. The process is preferably initiated following field oxide formation, wordline formation, access transistor source/drain region formation, deposition of a planarizing dielectric layer, formation of bitline contact and storage-node contact openings in the planarizing layer, and formation of conductive plugs in both types of contact openings. The process is implemented by sequentially depositing a first tetraethylorthosilicate (TEOS) oxide layer, a first silicon nitride layer, a second TEOS oxide layer, a second silicon nitride layer, and a boro-phospho-silicate glass (BPSG) layer to form a multi-layer partly-sacrificial stack. Depressions are etched in the partly-sacrificial stack and amorphous silicon cup-shaped storage-node plates are formed in the depressions. Following removal of the BPSG layer and the second silicon nitride layer, HSG polysilicon asperities are formed on the plates. The second TEOS oxide layer is then removed, exposing the first silicon nitride layer. A silicon nitride cell dielectric layer is then deposited over the surface of the array.

Integrated array sensor for detecting organic solvents

Abstract: A new sensor array device has been designed to detect organic solvents; it comprises an array of six interdigital sensors lying upon a micromachined 0.5 μm thick silicon nitride membrane. There are three separate micromachined cells with two sensors per cell. In each cell, a thin film platinum resistance thermometer/heater is sandwiched in the middle of the silicon nitride layer in order to either monitor or control the temperature of the active layer. The array device has a low power consumption of ≈ mW/sensor at 400 °C and is capable of operating at temperatures in excess of 600 °C, making it suitable for inorganic (e.g., SnO2) as well as organic gas-sensitive materials. The sensor array device has been coated with both polymers and semiconducting oxides and its response to toluene, n-propanol and n-octane has been studied. The low power consumption and good thermal stability of this array device make it useful for application in portable gas monitoring equipment.

Deposition of plasma silicon nitride

Abstract: PURPOSE:To allow deposition of P-SiN with high adhesion to the underlying layer by conducting plasma irradiation while supplying a gas containing Si (e.g. SiH4) and a gas containing N (e.g. NH3+N2). CONSTITUTION:Only a gas containing N is supplied at first while conducting plasma irradiation to deposit N rich SiN and then a gas containing Si is suppled to deposit SiN 8 continuously.

Transparent article having protective silicon nitride film

Abstract: Transparent articles comprising transparent, nonmetallic substrate and a transparent film stack is sputter deposited on the substrate. The film stack is characterized by including at least one infrared reflective metal film, a dielectric film over the metal film, and a protective silicon nitride film of 10 Å to 150 Å in thickness over the said dielectric film. The dielectric film desirably has substantially the same index of refraction as does silicon nitride and is contiguous with the silicon nitride film.

Atomic force microscope lithography using amorphous silicon as a resist and advances in parallel operation

Abstract: Lithography on (100) single‐crystal silicon and amorphous silicon is performed by electric‐field‐enhanced local oxidation of silicon using an atomic force microscope (AFM). Amorphous silicon is used as a negative resist to pattern silicon oxide, silicon nitride, and selected metals. Amorphous silicon is used in conjunction with chromium to create a robust etch mask, and with titanium to create a positive AFM resist. All lithographies presented here were patterned in parallel by arrays of two piezoresistive silicon or two silicon‐nitride cantilevers. Parallel arrays of five piezoresistive cantilevers were fabricated and used in imaging and lithographic applications. A 400 μm×100 μm parallel image is obtained in the time it would normally take to obtain a 100 μm×100 μm image. In our method of parallel operation, it is only possible to image and lithograph in modes that do not require feedback. In imaging, this limits the possible applications of the parallel AFM. During parallel lithography, discrepancies a...

Fourier transform infrared study of rapid thermal annealing of a-Si:N:H(D) films prepared by remote plasma-enhanced chemical vapor deposition

Abstract: Fourier transform infrared spectroscopy has been used to study the behavior of bonded hydrogen and bonded deuterium in hydrogenated amorphous silicon nitride films [a‐Si:N:H(D)] that were deposited by remote plasma‐enhanced chemical vapor deposition (RPECVD) and had been subjected to rapid thermal annealing (RTA) from 400 to 1200 °C after film deposition. The amount of bonded hydrogen in the film and its distribution between Si–H and SiN–H bonding groups is correlated to the ratio (R) of the source gases: NH3 to SiH4. Chemical reaction pathways are proposed to account for bond dissociation and release of hydrogen from the films in the form of molecular H2 and NH3. As the bonded hydrogen population decreases with increasing RTA temperature, the Si–N bond population increases. This postdeposition bonding of nitrogen to silicon upon thermal release of hydrogen species is consistent with improvements in the electrical properties of RPECVD silicon nitride films after an RTA treatment at 900 °C.

Effect of microstructural coarsening on Hertzian contact damage in silicon nitride

Abstract: The critical role of grain size in determining the nature of damage accumulation in silicon-nitride ceramics is evaluated using Hertzian contact testing. Single-cycle tests are conducted on materials of two grain sizes, 0.5 Μm (fine) and 2.0 Μm (coarse). Damage patterns for these two materials are compared and contrasted using a special bonded-interface specimen to investigate the subsurface regions. Optical and thermal wave-imaging techniques provide complementary pictures of the damage patterns: whereas the optical image maps elements of both deformation and fracture, the thermal wave image maps only the fracture. Taken together, these two imaging methods disclose a fundamental transition in the mechanical response in the two silicon nitrides, from cone-crack-dominated in the fine material to distributed-microcrack-dominated in the coarse material. Scanning electron microscopy (SEM) confirms the incidence of microfracture in the latter case. Thermal-wave measurements also allow a quantitative evaluation of the microfracture damage. Multiple-cycle tests on the coarse material show a build up of subsurface damage with increasing number of cycles, indicating mechanical fatigue. The results are discussed in terms of a shear-fault model, in which subsurface microcracks initiate from intrinsic planes of shear weakness in the microstructure. Implications concerning the microstructural design of silicon nitride ceramics for strength and wear applications are briefly considered, with reference to countervailing resisting and driving forces in the long-crack and short-crack toughness characteristics.

Fine‐Grained Silicon Nitride Ceramics Prepared from β‐Powder

Abstract: Fine {beta}-powder with an average particle size of 0.28 {micro}m was prepared by grinding and centrifugal sedimentation of submicrometer {beta}-powder. Fine- and uniform-grained ceramics were fabricated from the powder by hot pressing. The average grain size of the ceramic was 0.21 {micro}m. It was shown that this kind of microstructure was desirable for the matrix of in situ composite. It was also shown that the ceramics could be superplastically deformed at a temperature as low as 1,500 C.

Fracture Resistance Behavior of Highly Anisotropic Silicon Nitride

Abstract: The R-curve behavior was characterized by the Vickers indentation flaw technique, for highly anisotropic silicon nitride, a silicon nitride whose fibrous grains are highly aligned. The measured crack lengths ranged from 30 to 500 μm. The fracture resistance of a conventional self-reinforced silicon nitride was determined for comparison using the same procedures. While in the self-reinforced material several hundred micrometers of crack extension were required to obtain a high fracture toughness, the highly anisotropic material exhibited a high toughness from the beginning of the measured crack length range with little increase in the following range. It is suggested that the toughness of the highly anisotropic material steeply rises in a very short crack extension, which is advantageous in avoiding catastropic fractures.

Using Microstructure to Attack the Brittle Nature of Silicon Nitride Ceramics

Abstract: The evolution of silicon nitride ceramics over the last two decades has brought about the advancement of materials which were first fabricated by the application of mechanical pressure and temperature (i.e., hot pressing) resulting in high flexure strengths (e.g., 700–800 MPa) but rather poor resistance to creep at temperatures of ~1200°C. At the same time, these ceramics remained quite brittle with fracture-toughness values of 4–5 MPa m½, such that strengths were very sensitive to flaw or crack sizes. As a result, measured strengths exhibited considerable scatter, as reflected by a low Weibull modulus. In the ensuing years, approaches were sought to develop more economical methods of fabricating silicon nitride components by densifying to near-net shape. Methods were also sought for increasing the elevated-temperature reliability by minimizing the additives employed to promote densification and by utilizing additives that produced more stable and refractory grain boundary phases. The application of gas-pressure sintering methods, utilizing gaseous environments of 10–100 atmospheres, led to the ability to produce dense near-net shaped components with very high fracture strengths (e.g., ≥1000 MPa). At the same time, advances in processing and additive chemistry, sometimes combined with additional fabrication methods (e.g., hot isostatic pressing), have resulted in ceramics with excellent creep resistances at temperatures in excess of 1300°C. Some of these silicon nitride ceramics exceed the elevated-temperature capability of superalloys by 200°C. The initial desire for light-weight ceramic components that could sustain tensile loads for high-temperature applications is, indeed, beginning to bear fruit. One of the most impressive examples of the development of a complexly shaped lightweight component is the silicon nitride turbocharger rotor used in a number of Japanese automobiles, which is currently manufactured at a cost approaching that of the opposing superalloy rotor and provides exceptionally high mechanical reliability and production yields. Currently, there are also earnest efforts to incorporate silicon nitride valves for engines, as well as in a variety of other components (e.g., combustion swirl chambers, valve-lifter pads, etc.). The acceptance and use of this class of brittle materials, which were once considered prohibitively expensive for fabrication into complex shapes and not suited for such applications, is a remarkable testimony of the progress that has been made.

Plasma-deposited passivation layers for moisture and water protection

Abstract: The barrier properties of electron cyclotron resonance plasma deposited silicon oxide (SiO), silicon oxynitride (SiON) and silicon nitride (SiN) films against moisture and water penetration were studied as a function of the deposition parameters gas flux ratios, microwave power and reactor pressure. Three methods were used to quantify these barrier properties: measurement of film etch rate in water at different temperatures and pH values, determination of moisture permeation coefficient and electrical characterization of samples during humidity exposure. Although the dissolution rate of SiN in water is slightly higher compared with SiO the lower moisture permeation coefficient and the higher electrical stability during exposure to humidity of silicon nitride make it an attractive passivation material for different applications.

Method and device for etching silicon nitride film

Abstract: PURPOSE: To set the selective ratio of a silicon nitride film to a silicon substrate or a silicon oxide film at a relatively high value in the case of removing the silicon nitride film on the silicon substrate or the silicon oxide film by selective etching by using CDE. CONSTITUTION: In the case of removing a part of or the whole silicon nitride film formed on a silicon substrate or a silicon oxide film, mixed gas, which is composed of a gas containing fluorine, oxygen gas and a gas containing hydrogen atoms, is introduced into a discharge part 2 to generate plasma, and only the radical of the plasma active species is introduced into a process chamber 5 wherein the silicon substrate is stored. Thus, the silicon nitride film on the silicon substrate is selectively removed by etching.

Microwave processing of ceramics

Abstract: Summary form only given. We have investigated sintering, both with and without a plasma, reaction bonding of silicon nitride (RBSN), and chemical vapor infiltration (CVI) synthesis of ceramic matrix composites using microwave heating. The sintering rate of alumina in a plasma excited either by microwaves or induction coupling (5 MHz) is significantly greater than with conventional heating. The enhancement is believed to be caused by the creation of excess point defects by the plasma. Both microwave CVI and RBSN seek to take advantage of the temperature gradients inherent in volumetric heating so the reaction or deposition of matrix can take place from the center to the surface, thus enabling a greater degree of reaction than can be obtained by isothermal processing. Experimental and modeling results of these two processes are presented.

A novel bolometer for infrared and millimeter-wave astrophysics

Abstract: We are developing a novel bolometer which uses a fine mesh to absorb radiation. The filling factor of the mesh is small, providing a small heat capacity and a low geometric cross-section to cosmic rays. The mesh is patterned from a free-standing silicon nitride membrane and is thermally isolated by long radial legs of silicon nitride. A thin metallic film evaporated on the mesh absorbs radiation by matching the surface impedance to that of free space. A neutron transmutation doped germanium thermistor attached to the center of the mesh detects the temperature increase from absorbed radiation. The low thermal conductivity and heat capacity of silicon nitride provide improved performance in low background applications. We discuss the theoretical limits of the performance of these devices. We have tested a device at 300 mK with an electrical NEP = 4 × 10-17 W Hz-1/2 and a time constant r = 40 ms.

Role of the chamber wall in low‐pressure high‐density etching plasmas

Abstract: Ultraviolet‐adsorption spectroscopy has been used to examine how the chamber wall affects the concentration of gas‐phase reactants in high‐density etching plasmas. This technique was employed to detect CF2 in an inductively coupled discharge used for the selective etching of silicon dioxide relative to silicon nitride and polycrystalline silicon (polysilicon) films. In plasmas containing C2F6 and CF4, the concentration of CF2 depends strongly on the applied power and operating pressure as well as the amount of polymer on the walls of the chamber. Changes in the conditioning of the chamber during the etch process cause significant variations in the concentration of CF2 in the discharge. The selectivity of etching SiO2 relative to Si3N4 films closely follows the concentration of CF2 under a variety of plasma operating conditions. The ability to measure a fundamental plasma characteristic that reflects the level of conditioning of the chamber is an important step in the real‐time monitoring of a reactor parameter that currently can only be determined from postprocess measurements.