Ultra-low Pressure Research Articles

Determination of vapor pressure from droplet evaporation kinetics

Evaporation kinetics of suspended single droplets are investigated in the temperature range 20 to 55°C, using Mie resonance spectroscopy. Experiments are carried out with a single-component organic droplet electrodynamically suspended either in a flowing N 2 gas or in a vacuum, depending upon the volatility of the organic compound. A data analysis method is developed, which produces a best-fit empirical correlation in the form 1 n p= A+ B T +C 1 n T+DT k, that is valid over a temperature range spanning up to 9 decades on the vapor pressure scale. No estimate of the actual value of either the diffusivity or the evaporation coefficient is needed. This is accomplished by combining the high-temperature vapor pressure data available in the literature with the droplet evaporation rates measured in this work at lower temperatures. Results presented here for methanesulfonic acid, glycerol, oleic acid, and dioctyl phthalate clearly demonstrate the usefulness of the technique for ultra-low vapor pressure determinations.

Electrical characterization of junctions and bipolar transistors formed with in situ doped low-temperature (800 degrees C) epitaxial silicon

The results of characterization of junctions and bipolar transistors formed with in situ doped low-temperature (800 degrees C) epitaxial silicon are presented. The epitaxial silicon layers were deposited by ultra-low pressure chemical vapor deposition (U-LPCVD) preceded by an in situ Ar sputter clean, which makes possible 800 degrees C fabrication of bipolar transistors. For emitter layer depositions, the U-LPCVD process was plasma enhanced to attain high donor incorporation. Three typical structures of bipolar transistors (A: with epitaxial collector, base, and emitter; B: with epitaxial base and emitter; and C: with epitaxial base) were fabricated and compared in this study. The junction characteristics of the fabricated transistors were also investigated. Functional transistors were obtained for all three structures. Ideality factor of the junctions formed within the epitaxial silicon were near unity (1.01). These results support the claim that the bulk quality of the low-temperature epitaxial silicon is good enough for device application.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High structural quality epi/oxide boundaries of selective epitaxy grown by SiH4/H2 chemical vapor deposition using growth-sputter cycles

This letter presents results of high structural quality epi/oxide boundaries of selective epitaxy grown on (100) oxide patterned Si wafers by ultralow pressure chemical vapor deposition from SiH4 /H2 at 800 °C using growth-sputter cycles. The epitaxial films were characterized by cross-sectional transmission electron microscopy and Nomarski optical microscope. About 2.1 μm silicon epitaxy was grown on the exposed silicon windows with about 0.27 μm lateral epitaxial growth over the oxide near {011} epi/oxide sidewalls. Almost no lateral epitaxial overgrowth was observed near {010} sidewalls. The epi/oxide boundary and the epitaxy grown over the oxide were found to be of high structural quality and defect-free.

Structural Defects of Silicon Epitaxy and Epi/Substrate Interface Related to Improper In-Situ Surface Cleaning at Low Temperatures

ABSTRACTThis paper investigates the defect formation at the epi/substrate interface and epitaxial layers due to an improper in–situ Ar or Ar/H2 plasma cleaning at 500–800 °C Deposition process was carried out immediately after the in–situ cleaning process by ultralow pressure chemical vapor deposition process (ULPCVD) from SiH4/H2. Characteristics of the defects and their relationship with damage or impurity contaminations at the interface are presented. Finally, an optimum cleaning condition which ensures high quality epitaxial growth is addressed.

Material Characterization of Low-Temperature Silicon Epitaxial Growth on Patterned Oxidized Wafers by ULPCVD From SiH4/SiF4/H2

ABSTRACTLow temperature silicon selective epitaxial growth on patterned oxidized wafers is becoming crucial to ultra large scale integration (ULSI) technologies. Low temperature processes can reduce dopant redistribution via solid state diffusion so that a sharp transition region can be obtained. This paper presents material characterization of epitaxial films grown on patterned oxidized wafers by ultralow pressure chemical vapor deposition (ULPCVD) from SiH4/SiF4/H2 (≤ 10 mTorr), in which SiF4 was used to explore its capability for selective epitaxial growth. The deposition temperature is 800°C. The effects of the SiF4 addition to SiH4/H2 are discussed. Defects in epitaxial layers resulting from a high composition of the SiF4 during deposition were characterized. Results of in–situ surface cleaning using a SiF4/H2 plasma are also presented.

Silicon selective epitaxial growth at 800 °C using SiH4/H2 assisted by H2/Ar plasma sputter

This letter presents the results of silicon selective epitaxial growth at 800 °C by ultralow pressure chemical vapor deposition using SiH4 /H2 assisted by H2 /Ar plasma sputter. By utilizing growth-sputter cycles, selective epitaxial layers can be grown on exposed silicon windows of silicon wafers with oxide patterns to the thickness needed. The growth process was carried out by flowing SiH4 (3.5 mTorr)/H2 (7 mTorr), while the sputter step was performed by using H2 (7 mTorr)/Ar(1.5 mTorr) plasma at a susceptor dc bias from −100 to −300 V. Characterized by cross-sectional transmission electron microscopy, Nomarski optical microscopy, and spreading resistance profiling, the epitaxial films were found of high structural and electrical quality.

Low-energy membrane nanofiltration for removal of color, organics and hardness from drinking water supplies

The field of desalination is becoming increasingly more complex and interesting. The original concept of the production of potable water from seawater and brackish water now describes only one area in which desalination technology may be applied to the supply of safe drinking water. Reverse osmosis membrane manufacturers are becoming adept at tailor-making membranes to fill other water treatment applications. Ultra-low pressure nanofiltration is a new tool for removal of hazardous organic contaminants in preference to low molecular weight salts. Demands for water quality are becoming increasingly more stringent. In 1986, the USEPA targeted 83 contaminants for which regulations will be developed. Maximum contamination levels MCL's) have already been set for certain constituents which have been identified as possible carcinogens, such as trihalomethanes (THMs). THMs are reaction products from chlorination of water containing natural substances such as humic and fulvic acids, called THM Precursors (THMPs). MCLs for total trihalomethanes (TTHMs) have been set at 100 ppb and will probably be lowered to 50 ppb in the near future. Because of the number of components which are being considered for regulation and because of the diversity of their physical and chemical properties, their removal presents a formidable challenge to the water treatment/desalination engineer. Because of their ability to reject high percentages of many dissolved components, nanofiltration membranes offer a single treatment alternative for removing many of these contaminants. Recent developments in membrane technology have created a new generation of membranes which are much more cost-competitive for treating lower TDS waters for removal of specific contaminants. These new membranes are classified as nanofiltration or ultra-low pressure membranes, typically providing 90–95% rejection of THMPs, 85 to 95% rejection of hardness and over 70% rejection of monovalent ions when operated at only 70 to 100 psi driving pressure. Field testing is now underway in Florida, where substantial THMPS are found in the shallower aquifers. This new technology should be of particular interest where water resource conservation procedures involve blending of desalted water product with untreated groundwater, surface water and/or catchment storage, followed by chlorine disinfection.

Enhanced electrical quality of low-temperature (Tdep≤800 °C) epitaxial silicon deposited by plasma-enhanced chemical vapor deposition

We report in this letter the results of experiments comparing the electrical properties of low-temperature epitaxial silicon deposited by plasma-enhanced chemical vapor deposition (PECVD) and ultralow pressure chemical vapor deposition (U-LPCVD). Diode characteristics indicate a strong dependence of the electrical quality of the PECVD films on the plasma power. The data indicate that, in contrast to a purely thermal deposition (the U-LPCVD films), a low-power PECVD deposition (2.5–5 W) improves the electrical quality of the epitaxial layers and lowers the minimum epitaxy temperature. A high-power plasma (20 W), however, degrades the electrical characteristics in comparison to a strictly thermal deposition.

高融点金属のＥＢ溶解に関する研究

Refractory and reactive metals such as W, Ta, Mo, Nb and Ti were melted by a 300kW Electron Beam (EB) Melting Furnace and the evaporation behavior of metallic and gaseous impurities was investigated.It was found that, when the vapor pressure of a metallic element, poi, was higher than 104Pa at the temperature 100°C over the melting point of mother metal, the content of the element could be decreased to less than 1ppm. The decrease of oxygen content was also observed except for the melting of Ti. However, the other metallic elements with low vapor pressure and gaseous species such as C and N were less removable, in spite of the melting under the condition of ultra high temperature and ultra low pressure.

Bulk-quality bipolar transistors fabricated in low-temperature (Tdep =800 °C) epitaxial silicon

In this letter we report for the first time the fabrication of bulk-quality bipolar transistors in low-temperature (Tdep =800 °C) epitaxial silicon. The epitaxial layers were deposited by an ultra-low pressure chemical vapor deposition technique utilizing an in situ predeposition argon sputter clean. The critical parameter affecting the quality of the epitaxial films is the deposition temperature. The junction leakage current decreases by two orders of magnitude, the ideality factor improves from 1.36 to 1.04, and the minority-carrier lifetime increases from 1.3 to 46 μs as the deposition temperature is increased from 750 to 800 °C. Analysis of the base-emitter and base-collector junction characteristics indicates that bipolar transistors fabricated in epitaxial films deposited at 800 °C have characteristics at least as good as control fabricated in bulk silicon.

Cross-Sectional TEM Investigation of Low-Temperature Epitaxial Silicon Films Grown by Ultra-Low Pressure CVD

AbstractIn this paper, cross-sectional TEM is used to investigate the quality of silicon epitaxial films grown by ultra-low pressure chemical vapor deposition at 750°C. The dislocation density and epi.- substrate interface width were investigated for different predeposition Argon sputter cleaning condltions. Epitaxial films with dislocation densities of less than 10 cm−2 and interfacial width of about 13 Å were obtained.

Pilot field test Data for prototype ultra low pressure reverse osmosis elements

The need for ultra low pressure RO elements has been evident since the membrane softening idea was conceived over a decade ago, especially in water short areas such as the peninsula of Florida. Circumstances in Florida are ripe for the emergence of ultra low pressure membrane elements, for example: • Florida has been plagued with two serious droughts recently, one in 1981 and the ongoing drought of 1984–1985. • Florida's population is projected to double within the next thirty-five years and the water budget deficit may be as much as 430 MGD by that time. 1 1 The Feasibility of Meeting Future Water Supply Needs in Florida by Desalination , C D. Hornburg, March 1984. • Conventional water treatment processes have become unit processes and will require additional processes in combination in order to meet federal, state and local water standards. • The advent of the triennial testing for synthetic organic contaminants required by the Florida Department of Environmental Regulation (FDER) may uncover a contaminant necessitating additional unit processes for existing conventional plants. Many plants have already added another unit process to handle THM's. It is tha author's opinion that membrane manufacturer's have the technology to formulate and produce membranes to meet specific treatment needs. The pilot field test data for prototype ultra low pressure reverse osmosis membranes contained herein proves this to be factual. An in depth case study and cost analysis proves that the membranes softening process using ultra low pressure elements can be competitive with conventional treatment processes and may be the answer to Florida's predicted water shortage, potential problems with organic contaminants and salt water intrusion.

Mineral Resources and the Economy

The economic strength of the modern state and accelerated rates of technical progress depend largely on the scale and effeciency of the use of the mineral wealth extracted from the earth. At present there is hardly a single branch of industry that does not make direct or indirect use of mineral raw materials. Powerful thermal power stations, metallurgical production units, railroad and shipping, all consume large quantities of mineral fuels coal, gas, and oil. Natural gas and oil are also the most important technological raw materials of the modern chemical industry. Uranium has played an essential role in the development of nuclear energy. Every branch of machine building and every means of land, sea, and air transport, all equipment and instruments of the modern electrotechnical and radio industries, electronics and space technology, new trends in science and technology, with their dependence on superhigh and ultralow temperatures, high pressure and superhigh speeds, use as their basic materials large a...

The growth of polycrystalline silicon on molybdenum, tantalum, tungsten, and their disilicides

Silicon was electron beam vaporized in an ultralow pressure system on substrates of molybdenum, tantalum, and tungsten between 550–850 °C. Polycrystalline silicon was grown on the molybdenum and tungsten substrates at 550 °C with grains measuring ∼0.3 μm in cross section and having a {110} orientation. This orientation was attributed to the deposition technique and substrate temperature. At 670 °C silicon reacted with the tantalum substrates to form a thin interfacial layer of TaSi2 but grew with a {110} and {111} orientation. At this same sample temperature {111} and {110} polycrystalline silicon was detected on molybdenum and tungsten. By increasing the substrate temperature to 750 °C, silicon reacted with the metals to produce ’’columnar’’ structures composed of {110}, {111}, {100}, {311}, or {331} silicon crystallites that grew on a layer of the respective metal disilicide. Phosphorus coevaporated with the silicon retarded the rate of the silicide growth at 670 and 750 °C. Only the refractory metal disilicides MoSi2, TaSi2, and WSi2 were obtained at 850 °C by reaction of the vapor deposited silicon with the substrate metal.

パルスカウント法によるイオン電流測定の精度向上を目指す二次電子増倍管計数効率の新しい測定方法

A new method to precisely measure ion counting efficiencies of electron multipliers (SEM) has been developed in order to improve the accuracy of the pulse counting vapor pressure measurement over the ultra low vapor pressure range. This method combines the pulse counting as well as the SEM output current measurement by use of a pulse height analyser with the SEM multiplication factor measurement by use of a Faraday cup system. By using the proposed method, the ion counting efficiencies of SEM for the ions except H2+ have been determined to be 1.0 for ion energies higher than a threshold value close to 7 keV. While, that of H2+ was 1.1. Further, a new method to precisely measure SEM multiplication factors using PHA has also been presented.

Selective hydrogenation of soybean oil: X. Ultra high pressure and low pressure

AbstractSoybean oil was partially hydrogenated with copper‐chromite catalyst at 170 C and up to 30,000 psig hydrogen pressure. Catalyst activity increased with increase in pressure up to 15,000 psig. The linolenate selectivity (SLn) of the reaction remained essentially unchanged over 50–1000 psig pressure range. A SLn of 5.5 to 5.6 was achieved at 15,000 to 30,000 psig pressure range. This value is somewhat lower than the selectivity at 50–1000 psig, but much higher than that obtained with nickel catalysts. Geometric isomerization increased as pressure increased up to 200 psig; above this pressure, the percenttrans remained the same up to 500 psig.trans Isomer content decreased when the pressure was increased to 30,000 psig. cis,trans Isomerization of linoleate was greater at 1000 psig and 15,000 psig than at 50 psig. At 15,000 psig, part of the linoleate in soybean oil was hydrogenated directly without prior conjugation, whereas at low pressures, all of the double bonds first conjugate prior to hydrogenation. This difference in mechanism might explain the lower selectivities obtained at high pressures. Conjugated diene isomers were found in the products up to 200 psig. Above this pressure conjugated diene was not measurable. No significant differences were found in the double bond distribution oftrans monoenes even though the amount oftrans monoene formed decreased as pressure was increased to 30,000 psig.

Proposed method for mass spectrometric analysis for ultra-low vapor pressure compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTProposed method for mass spectrometric analysis for ultra-low vapor pressure compoundsRobert T. McIver, Edward B. Ledford, and Judith S. MillerCite this: Anal. Chem. 1975, 47, 4, 692–697Publication Date (Print):April 1, 1975Publication History Published online1 May 2002Published inissue 1 April 1975https://doi.org/10.1021/ac60354a047RIGHTS & PERMISSIONSArticle Views79Altmetric-Citations37LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (728 KB) Get e-Alerts Get e-Alerts