Showing papers on "Silicon published in 1979"

A gas chromatographic air analyzer fabricated on a silicon wafer

Abstract: A miniature gas analysis system has been built based on the principles of gas chromatography (GC). The major components are fabricated in silicon using photolithography and chemical etching techniques, which allows size reductions of nearly three orders of magnitude compared to conventional laboratory instruments. The chromatography system consists of a sample injection valve and a 1.5-m-long separating capillary column, which are fabricated on a substrate silicon wafer. The output thermal conductivity detector is separately batch fabricated and integrably mounted on the substrate wafer. The theory of gas chromatography has been used to optimize the performance of the sensor so that separations of gaseous hydrocarbon mixtures are performed in less than 10 s. The system is expected to find application in the areas of portable ambient air quality monitors, implanted biological experiments, and planetary probes.

The etching of silicon with XeF2 vapor

Abstract: It is shown that silicon is isotropically etched by exposure to XeF2(gas) at T=300 K. Si etch rates as large as 7000 A/min were observed for P (XeF2) <1.4×10−2 Torr and the etch rate varies linearly with P (XeF2). There was no observable etching of SiO2, Si3N4, or SiC, demonstrating an extremely large selectivity between silicon and its compounds. Therefore, thin masks constructed from silicon compounds can be used for pattern delineation. The implication of these experimental results for understanding mechanisms associated with plasma etching (including RIE) will be discussed.

Micromechanical membrane switches on silicon

Abstract: A new class of electronic devices, micromechanical membrane switches, has been developed. These switches have operating characteristics that fill the gap between conventional silicon transistors and mechanical electromagnetic relays. Although they are batch fabricated on silicon using conventional photolithographic and integrated circuit processing techniques, their unique properties allow them to perform functions not ordinarily associated with silicon. The devices are basically extremely small, electrostatically controlled mechanical relays, typically less than 100 µm long. Their high off-to on-state impedance ratio and all-metal conduction paths make them ideally suited for ac signal switching arrays. This paper describes the design, fabrication, operating behavior, and potential applications of these voltage-controlled, micromechanical switches.

ESR centers, interface states, and oxide fixed charge in thermally oxidized silicon wafers

Abstract: The ESR Pb center has been observed in thermally oxidized single‐crystal silicon wafers, and compared with oxide fixed charge Qss and oxidation‐induced interface states Nst. The Pb center is found to be located near the interface on (111) wafers. Its g anisotropy is very similar to that of known bulk silicon defects having SiIII bonded to three other Si atoms; the Pb unpaired electron orbital, however, is exclusively oriented normal to the (111) surface. The Pb center cannot be identified with any other known defect in Si or SiO2; in particular, it is totally unlike the common E′ center of SiO2. In contrast to Qss, both Pb and Nst were found to be greatly reduced by steam oxidation and hydrogen annealing. Both Pb and Nst may be regenerated by subsequent N2 anneals at 500 °C. In a graded series of samples, Pb and Nst are found to be proportional and nearly equal in concentration. This possible confirmation of SiIII at the interface, and correlation with Nst, support the theoretical indication of an SiIII b...

Reaction-bonded silicon nitride: its formation and properties

Abstract: The theme of the review is the construction of a model embracing the mechanism of formation of reaction-bonded silicon nitride, the development of microstructure and mechanical properties. Possible nitridation reactions are discussed, with emphasis on kinetics and on phase composition and microstructure of the reaction product. The influence of Fe, a common impurity in silicon powders, and of H2, as an additive to the nitriding atmosphere, is considered in some detail. The optical, electrical and thermal properties are briefly discussed and areas for further research and development studies identified.

Picosecond laser‐induced melting and resolidification morphology on Si

Abstract: Ultrafast melting and resolidification on the surface of a silicon crystal has been induced by picosecond laser pulses at 532 and 266 nm Optical microscopy and electron diffraction revealed the formation of amorphous silicon Details of surface morphology are sensitive functions of pulse intensity, energy, wavelength, and crystallographic orientation

Crystallographic orientation of silicon on an amorphous substrate using an artificial surface‐relief grating and laser crystallization

Abstract: Uniform crystallographic orientation of silicon films, 500 nm thick, has been achieved on amorphous fused‐silica substrates by laser crystallization of amorphous silicon deposited over surface‐relief gratings etched into the substrates. The gratings had a square‐wave cross section with a 3.8‐μm spatial period and a 100‐nm depth. The 〈100〉 directions in the silicon were parallel to the grating and perpendicular to the substrate plane. We propose that orientation of overlayer films induced by artificial surface patterns be called graphoepitaxy.

Amorphous semiconductors equivalent to crystalline semiconductors

Abstract: An amorphous semiconductor body, most advantageously a glow discharge deposited silicon-containing host matrix film, is provided containing at least fluorine as a compensating or altering agent, and most preferably at least one complementary compensating or altering agent, such as hydrogen, both of which reduce the localized defect states in the energy gap of the amorphous semiconductor material to a degree which either one alone could not achieve. The silicon and/or other elements of the host matrix film are deposited by the glow discharge decomposition of gaseous compounds preferably with fluorine as one element of a compound, the hydrogen and other compensating and altering material being preferably a molecular gas or an element of a compound of silicon or other host matrix element.

Passivation of grain boundaries in polycrystalline silicon

Abstract: Preferential diffusion of various gases down the grain boundaries in polycrystalline silicon is shown to promote significant changes in the density of defect states in these regions. A plasma of monatomic hydrogen provides a significant reduction in both the state density and the accompanying grain‐boundary potential barrier while plasmas of oxygen, nitrogen, and sulfur hexafluoride are shown to increase this density of states. Boundaries passivated with hydrogen have as much as a factor of 1000 larger transconductance after treatment. Hydrogenated barriers are stable over long periods at 375 °C and essentially indefinitely at 23 °C. The results have important implications for the development of low‐cost thin‐film silicon photovoltaic devices.

Temperature dependence of the optical properties of silicon

Abstract: The spectral dependence of the absorption coefficient of silicon for photon energies up to 2.7 eV was determined for several temperatures in the range 298–473 K. The effect of a temperature increase appears as a red shift of the absorption spectrum. The magnitude of the shift is larger than that of the fundamental energy gap, increases with increasing photon energy in the range 1.1–1.7 eV, and is constant for energies greater than 1.7 eV. A phenomenological expression deduced by analysis of the data may be used to calculate α (E) at elevated temperature, given α (E) at room temperature. The reflectance was also measured at 299, 413, and 516 K in the photon energy range 2.5–3.8 eV.

Microstructure of plasma‐deposited a‐Si : H films

Abstract: Using transmission and scanning electron microscopy, it is shown that plasma deposition of amorphous silicon hydrogen films from silane or silane/argon mixtures proceeds via nucleation and growth of islands of average lateral dimensions ∼100 A. If these islands do not coalesce into a homogeneous film, subsequent growth produces columnar morphology with low‐density interstitial regions. There is a strong correlation between the columnar structure and the presence of nonradiative recombination centers.

Dependence of Interface State Density on Silicon Thermal Oxidation Process Variables

Abstract: The structural or intrinsic type of interface state charge, related to thermal oxidation and annealing processes, has been characterized with respect to silicon thermal oxidation variables using quasistatic C‐V techniques. Those variables include oxidation ambient (, , ), annealing/cooling ambient (, , Ar), oxidation temperature (800°–1200°C), silicon type (p‐ and n‐type), and orientation [(111) and (100)]. Oxides (1200–2200A thick) annealed and cooled from any oxidation temperature in nitrogen or argon exhibit large interface state densities as oxidized. However after a low temperature hydrogen anneal these densities are lower than those of comparable oxygen‐cooled oxides. Interface state densities of oxides cooled in oxygen vary inversely with oxidation temperature before and after postmetallization anneals. This temperature relationship is very similar to that reported previously for oxide fixed charge and helps to substantiate a model based on a common origin of interface states and oxide fixed charge.

Absorption coefficient of silicon for solar cell calculations

Abstract: The optical absorption coefficient is an important parameter in calculating the performance characteristics of solar cells. For silicon solar cells it is desirable to know the absorption coefficient over the range of 1.1–4.0 eV and over a wide range of temperature, particularly when evaluating the concentration type systems. An analytical (empirical) expression has been developed for this purpose. We have interpreted the available experimental data in terms of three bands of silicon. With our fit, the experimental data can be explained to within an accuracy of 20% and its validity extends from 1.1 to 4.0 eV and over the temperature range of 20–500°K.

Preparation and Properties of Yttrium-Silicon-Aluminum Oxynitride Glasses

Abstract: Glasses containing up to 7 at. % nitrogen were prepared in the system Y-Si-Al-O-N. The glass transition temperature, hardness, and relative fracture toughness increase and the thermal expansion coefficient decreases with increasing nitrogen content. Weight losses after 350 h in 95/sup 0/C distilled water are not simply related to nitrogen content, but for some compositions they are half that reported for fused silica. The electrical conductivity at 548/sup 0/C and 10 kHz is 7.8 x 10/sup -10/ (..cap omega...cm)/sup -1/ for one composition. Fourier transform ir spectroscopic analysis indicates the presence of Si-N bonds in the glasses. The data suggest that nitrogen substitutes for oxygen in the glass network to produce a more highly cross-linked structure.

The SIS tunnel emitter: A theory for emitters with thin interface layers

Abstract: Silicon n-p-n transistors are made with emitters consisting of a polycrystalline and monocrystalline region with a thin (20-60-A) "insulating" interfacial layer in between (SIS structure). These transistors show a remarkable increase in emitter efficiency with emitter Gummel numbers up to 7 × 1014s.cm-4, and a low positive or even negative temperature coefficient of the current gain. A model is proposed to explain the mechanism in terms of tunneling through the interfacial layer. The electrical characteristics are measured in the temperature range 290-415 K. From the measurements it is deduced that the tunnel probability for holes (P h ) is 10-2to 10-3and that for electrons (P e ) is >10-5. There also exists a band bending of 30-90 mV at the interfaces with the interfacial layer.

Electrical and optical properties of amorphous Si:F:H alloys

Abstract: Amorphous alloys based on silicon and containing hydrogen and fluorine have been fabricated using a radio-frequency glow discharge in silicon tetrafluoride and hydrogen. Films have been well characterized using conductivity, photoconductivity, field-effect and infra-red techniques. Amorphous alloys fabricated from a gas ratio of SiF4 : H2=10: 1 are shown to possess a localized density of states with a minimum value of less than 1017 cm−3 eV−1. These films are highly photoconductive, devoid of photostructural changes and are mechanically stable. Because of the low density of localized states, the alloys have been doped with 50 v.p.p.m. of arsine in the premix to attain a room temperature conductivity ≥ 5 Ω−1 cm−1.

Selective reactive ion etching of polysilicon against SiO2 utilizing SF6 -Cl2 -inert gas etchant

Abstract: Disclosed is an improved Reactive Ion Etch (RIE) technique for etching polysilicon or single crystal silicon as must be done in Very Large Scale Integration (VLSI) using silicon technology. It teaches the use of an etch gas that consists of a mixture of sulfur hexafluoride (SF 6 ) and chlorine (Cl 2 ) diluted with inert gas. This etch gas allows an RIE process which combines the very desirable features of selectivity (high Si/SiO 2 etch rate ratio) and directionality which creates vertical side walls on the etched features. Vertical side walls mean no mask undercutting, hence zero etch bias. It is particularly applicable to device processing in which micron or sub-micron sized lines must be fabricated to extremely close tolerances. It is a distinct improvement over wet chemical etching or plasma etching as it is conventionally applied.

Crystallization in amorphous silicon

Abstract: Crystallization has been studied in amorphous silicon layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow one to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.

Raman scattering in pure and hydrogenated amorphous germanium and silicon

Abstract: The Stokes Raman spectra of pure and hydrogenated amorphous germanium and silicon are discussed. First- and second-order structures due to the vibration of GeGe and SiSi bonds and also first-order structures due to GeH and SiH bonds are observed. The resonance behaviour and the polarization ratio of the observed structures are presented and interpreted in terms of a dielectric constant-bond polarizability model.

Defect Etch for Silicon Evaluation

Abstract: The Secco etch, with ultrasonic agitation, is widely used to determine dislocation densities in Si. Experiments have shown that under certain conditions, the cavitation of the ultrasonics can generate anomalous defect etch pits. A new defect etch formulation was developed for evaluating Si ingot material which does not require ultrasonic agitation. It consists of . The etching time compared to Secco etch with ultrasonics is reduced by one‐half in developing etch pits of equivalent size. This composition is useful for revealing dislocations in 0.6–15 Ωcm n‐ and p‐type silicon. In addition, dislocation etch pits are readily developed in more heavily doped Si crystals using a mixture of.

Reactive molecular beam epitaxy of aluminium nitride

Abstract: Single‐crystal films of AlN have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 1000°–1200°C. The crystal quality of the films was examined by the reflection high‐energy electron diffraction technique and the measurement of cathodoluminescence. The results suggest that the epitaxial AlN films prepared by reactive MBE have good quality as compared with bulk single crystal. Nonlinear optical coefficients and the electromechanical coupling constant of surface acoustic waves were also measured. It was shown that the AlN films have unique characteristics and are promising for nonlinear optical and surface acoustic wave devices.

Defect states associated with dislocations in silicon

Abstract: The introduction and annealing of defect states in silicon stressed at 770 °C in compression have been studied by capacitance transient spectroscopy on Schottky‐barrier structures. High‐resistivity n‐type samples are converted to p type. Low resistivity n‐type samples are compensated but recover upon annealing. A large variety of defect states are observed with prominent features at E (0.68) after deformation. The spectra simplify upon annealing at 900 °C to two dominant states, E (0.38) and H (0.35).

Recrystallization of implanted amorphous silicon layers. I. Electrical properties of silicon implanted with BF+2 or Si++B+

Abstract: Electrical properties of recrystallized amorphous silicon layers, formed by BF+2 implants or Si++B+ implants, have been studied by differential resistivity and Hall‐effect measurements. Electrical carrier distribution profiles show that boron atoms inside the amorphized Si layers can be fully activated during recrystallization at 550 °C. The mobility is also recovered. However, the tail of the B distribution, located inside a damaged region near the original amorphous‐crystalline interface, remains inactive. This inactive tail has been observed for all samples implanted with BF+2. Only in a thicker amorphous layer, formed for example by Si+ predamage implants, can the entire B profile be activated. The etch rate of amorphous silicon in HF and the effect of fluorine on the recrystallization rate are also reported.

The Role of Hydrogen in SiO2 Films on Silicon

Abstract: This review discusses within a unified framework various phenomena occurring in thermally grown films on silicon with hydrogen as the most important contaminant or additive. The possible sources of hydrogen are (i) in the oxidizing ambient, deliberately introduced or resulting from permeation through hot furnace tubes, (ii) hydrogen in the room ambient oxide film on silicon, and (iii) deliberate or unintentional or in the ambient of postoxidation heat‐treatments. The "critical oxide thickness," which separates the linear oxidation regime from the parabolic one, is a very sensitive indicator of present in the oxidizing ambient. There is plenty of evidence, both direct and indirect, of hydrogen in films. In particular, infrared spectroscopy shows that OH and groups are present whose concentration and distribution depend strongly on preparation conditions. These groups can be H‐bonded to an oxygen; this feature and the presence of distinguishes films from fused which is another form of non‐crystalline. The H‐bonded OH groups in grown films may be preferentially aligned along structural channels and responsible for various transport processes characterized by ~0.3 eV activation energy. Hydrogen greatly affects the properties of the interface, particularly its behavior under negative bias stress and irradiation. In fact, practically all properties of interface structures depend so strongly on hydrogen that its proper control and the understanding of its complicated role are probably the most important problems associated with these structures. This is particularly true for silicon‐based chemical sensors whose operation is basically determined by hydrogen in the film. Various aspects of the hydrogen in interface structures are similar to the role of hydrogen in and polymer films as well as in passivating films on metals.

An 18O study of the thermal oxidation of silicon in oxygen

Abstract: The mechanism of thermal oxidation of silicon in dry oxygen was studied using 18O as the tracer. SiO2 layers first grown in natural oxygen (1300–3000 A) were further grown in highly 18O‐enriched oxygen for 8.5 h at 930 °C. 18O profiling was carried out using the 629‐keV narrow resonance in the nuclear reaction 18O(p,α) 15N. The resulting SiO2 films consist of two 18O‐rich layers, 7% near the SiO2 surface and 93% near the Si‐SiO2 interface, while the bulk 18O concentration is very low. The results suggest that the oxide grows mainly through long‐range migration of oxygen, favoring models based on the transport of molecular oxygen.

Reactive sputtering of carbon and carbide targets in nitrogen

Abstract: Paracyanogenlike films – (CN)n– are prepared by reactive rf sputtering of carbon in nitrogen. The material is deposited on quartz, silicon, metals, sapphire, and mica from 20° to 450°C. Above 450°C, there is no film accumulation on the substrates. The sputtering process yields a deposition rate greater than ten times the best known commercial method for paracyanogen film preparation. Also described are the results of sputtering carbide targets i.e. HfC, TiC, SiC, in the presence of nitrogen. Due to the stability of the C≡N bond, for example, stoichiometric Si3N4 films unexpectedly were deposited from a SiC target sputtered in N2. Similar results are described for HfC and TiC targets.

a‐Si : H produced by high‐temperature thermal decomposition of silane

Abstract: Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.