Wide Range Of Process Conditions Research Articles

Photochemical Dry Etching of Doped and Undoped Silicon Oxides

The photochemical dry etching of doped and undoped silicon oxides with and gas has been investigated. Etching rates of several hundred angstroms per minute have been achieved with bulk substrate temperatures below 300°C. Borophosphosilicate glass‐to‐thermal oxide etching rate selectivity is near 1‐to‐1 over a wide range of process conditions. The addition of gas is found to significantly reduce the etching rates of both doped and undoped silicon oxide under these conditions. The photochemical dry cleaning of a 10 to 20 Å chemical oxide layer from trench and via bottoms is discussed.

Chemical vapor deposition TiN process for contact/via barrier applications

Chemical vapor deposition (CVD) TiN is an attractive replacement for PVD TiN as a barrier and glue layer for subhalf-micron contacts and vias. CVD TiN films have been deposited in a commercial reactor via the thermal decomposition of tetrakis-dimethyl-amino-titanium (TDMAT) precursor in an N2 ambient. The deposition can be characterized by a simple Arrhenius rate expression with a half-order dependence on TDMAT concentration and an activation energy of 0.53 eV. Designed experiments show that the deposition transitions from being kinetically limited at high TDMAT flow rates and low temperatures to transport limited at the other extreme. In the kinetically limited regime, the deposition rate increases with increasing TDMAT mole fraction and increasing temperature. Step coverage simulations have been performed by coupling SPEEDIE (a profile evolution program) with the Arrhenius rate expression. Experimental and simulated step coverages show good agreement over a wide range of process conditions. Step coverage improves with increasing deposition rate and decreasing temperature. Adequate deposition rates (≳400 Å/min) with good deposition uniformity and high step coverage (50%–85%) can be achieved. Film stress and roughness are mostly invariant with process conditions. These films are close to stoichiometric (i.e., 1:1 Ti:N ratio), but contain up to 30% carbon. Exposure of these films to air causes rapid oxidation with a steady state concentration of 15%–20% oxygen after 24 h of air exposure. The high carbon concentration results in high film resistivity (5000 μΩ cm), which doubles after 24 h of air exposure due to oxidation of the film. Film resistivity decreases and film stability improves with increasing N2 flow rate. Electrical characterization of two process variants have been performed. The first provides a film with 85% step coverage with a resistivity of 5600 μΩ cm, while the second process achieves a lower resistivity of 3700 μΩ cm and a lower step coverage of 50%. Electrical performance of both films is similar. Contact induced diode leakage is lower for CVD TiN compared to PVD TiN. Contact resistance for 100–200 Å CVD TiN is comparable or lower than 500 Å PVD TiN. A 100 Å CVD TiN barrier is adequate; 300 Å CVD TiN is too thick because of high film resistivity. An Al–Cu/100–300 Å CVD TiN/Si stack shows lower resistance increase after 450–500 °C, 30 min N2 anneal compared to a Al–Cu/200 Å PVD TiN/Si stack indicating that CVD TiN is a superior barrier and is more inert than PVD TiN.

A Catalytically Active Membrane Reactor for Fast, Highly Exothermic, Heterogeneous Gas Reactions. A Pilot Plant Study

Membrane reactors have been frequently studied because of their ability to combine chemical activity and separation properties into one device. Due to their thermal stability and mechanical strength, ceramic membranes are preferred over polymeric ones, but small transmembrane fluxes obstruct a widespread industrial use of a membrane reactor. Consequently, a bench-scale membrane reactor with a tubular, macroporous membrane (d, = 700 nm) was developed in order to attain increased fluxes. A cooling pipe was concentrically placed inside the tubular membrane to remove heat from the membrane surface, so the present membrane reactor was suitable to conduct exothermic reactions. As a model reaction, the heterogeneous oxidation of carbon monoxide over platinum, with separated feed of carbon monoxide and oxygen, was performed in the present setup. First, the present membrane reactor was characterized by the determination of the transport parameters, structure parameters of the membrane, and the external transfer coefficients. Subsequently fluxes of the reactants and products were measured over a wide range of process conditions. Especially the influence of a transmembrane pressure difference was studied extensively. Furthermore overall conversion of carbon monoxide was measured under various process conditions, and the results were compared with the simulations of a simplified, overall reactor model. From the results of the present investigation, it could be concluded that the application of a pressure difference over the membrane turned out to be a major process control parameter. It increases the product yield and preferentially directs the fluxes toward one side of the membrane. It was shown that even for macroporous catalytic membranes substantial pressure differences are allowed without any slip of unconverted reactants through the membrane. Furthermore, high degrees of conversion were observed in the present setup, and the simulations of the overall reactor model were in reasonable agreement with the experimental data. The overall model contained no adjustable parameters. From this study, the catalytically active, ceramic membrane reactor with separated feed of reactants turned out to be highly flexible and easy to control.

A New Flexible Rapid Thermal Processing System

ABSTRACTA highly flexible Rapid Thermal Multiprocessing (RTM) reactor is described. This flexibility is the result of several new innovations: a lamp system, an acoustic thermometer and a real-time control system. The new lamp has been optimally designed through the use of a “virtual reactor” methodology to obtain the best possible wafer temperature uniformity. It consists of multiple concentric rings composed of light bulbs with horizontal filaments. Each ring is independently and dynamically controlled providing better control over the spatial and temporal optical flux profile resulting in excellent temperature uniformity over a wide range of process conditions. An acoustic thermometer non-invasively allows complete wafer temperature tomography under all process conditions - a critically important measurement never obtained before. For real-time equipment and process control a model based multivariable control system has been developed. Extensive integration of computers and related technology for specification, communication, execution, monitoring, control, and diagnosis demonstrates the programmability of the RTM.

A New Flexible Rapid Thermal Processing System

AbstractA highly flexible Rapid Thermal Multiprocessing (RTM) reactor is described. This flexibility is the result of several new innovations: a lamp system, an acoustic thermometer and a real-time control system. The new lamp has been optimally designed through the use of a “virtual reactor” methodology to obtain the best possible wafer temperature uniformity. It consists of multiple concentric rings composed of light bulbs with horizontal filaments. Each ring is independently and dynamically controlled providing better control over the spatial and temporal optical flux profile resulting in excellent temperature uniformity over a wide range of process conditions. An acoustic thermometer non-invasively allows complete wafer temperature tomography under all process conditions - a critically important measurement never obtained before. For real-time equipment and process control a model based multivariable control system has been developed. Extensive integration of computers and related technology for specification, communication, execution, monitoring, control, and diagnosis demonstrates the programmability of the RTM.

Towards improved automation for desalination processes, Part I: Advanced control

The desalination process industries have largely tried to solve control problems by conventional rather than modern control techniques that are attracting widespread industrial applications and revolutionizing process control as a result of advances in control theory. Control systems are designed from mathematical models that are generally imperfect descriptions of real processes. It is widely accepted that conventional PID or PI controllers may not provide satisfactory performance in view of non-linearity and uncertainty in the real world of desalination processes. It is essential that control systems operate satisfactorily over a wide range of process conditions. The practice of multi stage flash (MSF) desalination process control, process design, optimization, conspicuously lags behind contemporary theoretical developments. Conventional process control techniques do not ensure the safest and the most profitable operation of processes when compared with advanced process control which uses the knowledge of process economics and provides insight into the process to maintain essential variables at optimum setpoints. This paper is an attempt to promote excellence and innovation in desalination engineering and to remove barriers to advanced process control. Attempted here is brief clarification of some aspects of advanced control strategies in terms of answers to the questions: Advance control strategies: What are they? Where and when are they applicable? and What can be expected of them? Although the reference here is to MSF plants, some of the observations and remarks are also relevant to process control practice in general. In the end, the conclusions point out the complexity of the real world control problem which behoves us to advocate the application of techniques such as self-optimizing control strategies and artificial intelligence (AI) leading to an integrated system of intelligent control.

Rapid thermal multiprocessing for a programmable factory for adaptable manufacturing of ICs

This paper presents an overview of research at Stanford University on the development of concepts of a programmable factory, based on a new generation of flexible multifunctional equipment implemented in a smaller flexible factory. This approach is demonstrated through the development of a novel single wafer Rapid Thermal Multiprocessing (RTM) reactor with extensive integration of sensors, computers and related technology for specification, communication, execution, monitoring, control, and diagnosis to demonstrate the programmable nature of the RTM. The RTM combines rapid thermal processing and several other process environments in a single chamber, with applications for multilayer in-situ growth and deposition of dielectrics, semiconductors and metals. Because it is highly instrumented, the RTM is very flexible for in-situ multiprocessing, allowing rapid cycling of ambient gases, temperature, pressure, etc. It allows several processing steps to be executed sequentially in-situ, while providing sufficient flexibility to allow optimization of each processing step. This flexibility is partially the result of a new lamp system with three concentric rings each of which is independently and dynamically controlled to provide for better control over the spatial and temporal optical flux profile resulting in excellent temperature uniformity over a wide range of process conditions namely temperatures, pressures and gas flow rates. The lamp system has been optimally designed through the use of a newly developed thermal simulator. For equipment and process control, a variety of sensors for real-time measurements and a model based control system have been developed. >

Seeking enhanced lead/acid battery performance through the use of conductive tin-dioxide-coated glass-flakes

The aim of this research is to raise the level of active-material utilization in the positive plates of lead/acid batteries (without diminishing other performance characteristics) and, thereby, to increase the energy output per unit weight. The strategy is to increase the electrical conductivity of the material by adding a proprietary particulate that consists of glass-flakes coated with a thin (<5 μm) layer of tin dioxide. The particulates are incorporated in positive plates that are prepared as automotive designs under a wide range of processing conditions, i.e., paste densities, acid-to-oxide ratios, low-/high-temperature (3BS/4BS) curing. Plate performance is evaluated in terms of active-material utilization, cold-cranking capability, repetitive reserve capacity, and life endurance under the Japanese Industrial Standard (JIS) procedure. Compared with untreated cells, the following benefits of adding the particulates to positive plates have been confirmed: (i) acceleration of the formation process; (ii) increase in the BET surface area of formed materials; (iii) improvement in active-material utilization at the 5-h and 20-h discharge rates; (iv) maintenance of cycleability under repetitive, reserve-capacity duty; (v) increase in cycle life under the JIS schedule. The encouraging outcomes of this research suggest that further benefits are likely to be gained by designing elongated particulates of lighter weight. This will increase the number of counts per unit area and, thereby, will improve the contact between the individual particles of the positive active material and will further enhance the electrical conductivity of the plate.

Relationships between residence time and process variables in a corotating twin-screw extruder

Degerminated yellow corn meal was extruded with a Werner and Pfleiderer ZSK-30 corotating twin-screw extruder under a wide range of processing conditions. The effects of process variables on mean residence time were examined by changing one variable at a time, as well as by applying statistical models to analyze situations when two or more process variables were changing. The most significant process variables affecting mean residence time were screw speed followed by throughput. Moisture content had only borderline effect, while die pressure and die temperature had no significant effect.

Incorporation of zinc in continuous jarosite precipitation

Ammonium jarosite was precipitated in a 1.5 l continuous Mixed Suspension Mixed Product Removal crystallizer in the presence of varying feed Zn 2+, Mg 2+, Li + and NH + 4 concentrations. The feed Fe 3+ concentration and SO 2− 4 concentration were kept constant at 0.25 M and 1.6 M, respectively. The experiments were carried out at 95°C and pH 1.5, using residence times varying between 0.8 and 2.0 h. The following parameters were determined: steady state conversion, the jarosite crystal growth rate, the nucleation rate, the specific surface area, the solids density in the suspension, the production rate, the supersaturation and the incorporation of zinc or magnesium in the jarosite lattice. The residence time distribution of the system was determined by adding alunite as tracer. Additional experiments were carried out at a pH of 1.2 and 1.8 respectively, in order to determine the influence of the pH on the precipitation. Based on the results obtained the incorporation of zinc in jarosite or the jarosite production rate may be predicted for a wide range of process conditions. The incorporation of zinc in ammonium jarosite, probably via isomorphous substitution, is about 2–10 g/kg depending on the process conditions. This implies that in industrial practice the loss of zinc due to the removal of iron as jarosite ranges between 0.12 and 0.6 wt%, for a zinc concentrate containing 52 wt% zinc and 8 wt% iron.

Analysis of C films formed on single-crystal Cu by ion implantation and laser annealing

Single-crystal Cu has been ion implanted with C to fluences of 1×1018/cm2 followed by laser annealing with nanosecond pulses from an excimer laser and subsequently etched in dilute nitric acid. Raman spectroscopy, Rutherford backscattering, and electron microscopy have been used to identify the distribution and morphology of the carbon at different stages of sample processing. Polycrystalline graphite and amorphous carbon films are typically produced over a wide range of processing conditions; well-ordered graphite can be formed as well. Small Cu crystallites are seen in areas where the etch lifted the C films off the substrate. However, extensive analysis by Raman spectroscopy and electron microscopy provides no evidence for the formation of the diamond phase of carbon.

Computer prediction of cycle times during rotational molding of plastics

AbstractA computer simulation program has been developed for the rotational molding of plastics. The predictions obtained from this program in terms of heating/cooling rates and overall cycle times have been compared with experimental molding trials with a range of plastics. It is shown that the computer model predicts accurately the real situation for a wide range of processing conditions. In particular, the program allows the effects of oven efficiency, mold material, mold wall thickness, and molded part thickness to be assessed quantitiatively. The article presents information on heat transfer coefficients that are applicable during rotational molding and typical cycle times for a wide range of process conditions. © 1992 John Wiley &amp; Sons, Inc.

Rheological behaviour and modelling of semi-solid Sn-15% Pb alloy

The rheological behaviour and modelling of a semi-solid, Sn-15% Pb alloy characterized by a special coaxial-cylinder rheometer over a wide range of process conditions is reported. In particular, the effect of shear rate $$\left( {\dot \gamma } \right)$$ , volume fraction of solid (f s), and cooling rate on the apparent viscosity (η) of the semi-solid Sn-15% Pb alloy under isothermal and various cooling conditions was studied. Based on the experimental data, the shear rate used in preparing the semi-solid alloy as well as the volume fraction of solid have the most dominant effects on the rheological properties of the semi-solid Sn-15% Pb alloy. A viscosity model expressed as $$\eta \left( {\dot \gamma ,f_s } \right) = \left( {1 - f_s /f_s^* } \right)^{ - m\left( {\dot \gamma } \right)} \eta _\infty \left( {f_s } \right)\left\{ {1 + \left[ {\dot \gamma ^ * \left( {f_s } \right)/\dot \gamma } \right]^a } \right\}^{n/a}$$ is proposed in which f s * is the critical solid fraction at which the apparent viscosity goes to infinity, η∞ (F s) corresponds to the asymptotic viscosity at infinity shear rate, and $$\dot \gamma ^ * \left( {f_s } \right)$$ characterizes the transition shear rate between the power-law and Newtonian regions. finally, measurements with a differential scanning calorimeter were made and used to correlate the temperature and volume fraction of solid which, in turn, was corroborated with available data from the literature.

Deformation induced defects in ReBa 2Cu 3O 7−δ

In this paper, we report the microstructural characterization of bulk rare-earth ( Re = Nd or Y) Re123 ceramic superconductors subjected to different levels of stress at various confining pressures, strain rates, and temperatures. This includes several classes of samples: (i) deformed under constant stress, (ii) deformed at a constant strain rate of 10 −4s −1, (iii) hand-ground in a mortar and pestle, and (iv) shock-compacted at 167 kbar. Deformation conditions for these samples spanned a wide range of processing conditions: 10 -7 to 10 −5s −1 in strain rate, temperatures of 25°C to 1020°C, and pressures from 1 atm to 167 kbar. Dislocations were always observed to lie on the (001) planes having Burgers vectors of 〈100〉 and possibly 〈110〉. Small amounts of strain can be accommodated by deformation twinning on the {110} planes. High temperature anneal of the Y123 results in the formation of extrinsic stacking faults with R = 1 6 [031] , with an intercalation of an extra CuO layer offsetting the Ba atoms by half a unit cell in the b-axis direction. These stacking faults are not observed in the Nd123. Further work is in progress to better understand the interactions of the line and planner defects on the superconducting properties of these materials.

Mass transfer with complex reversible chemical reactions—II. parallel reversible chemical reactions

An absorption model has been developed which can be used to calculate rapidly absorption rates for the phenomenon mass transfer accompanied by multiple complex parallel reversible chemical reactions. This model can be applied for the calculation of the mass transfer rates, enhancement factors and concentration profiles for a wide range of processes and conditions, for both film and penetration model. With the aid of this mass transfer model it is demonstrated that the absorption rates in systems with multiple reversible reactions can be substantially greater than the summation of the absorption rates derived for the single systems. This latter fact provides a scienctific basis for the application of aqueous mixed amine solutions for industrial sour gas treating. Also it is shown that for kinetic studies by means of abosorption experiments for reversible reactions the presence of small amounts of fast reacting contaminants can have an overruling effect on the outcome of the determination of the reaction kinetics. It is shown that the concepts of shuttle mechanism and homogeneous catalysis refer to asymptotic situations,for practical situations intermediate behaviour was observed which was previously not accessible for analysis. Experimentally determined absorption rates of CO 2 in aqueous solutions of various mixtures of alkanolamines (MMEA-MDEA, MEA-MDEA, DIPA-MDEA and MEA-DEA-MDEA) can be prdicted extremely well for the several mass transfer regimes which were studied experimentally. The experiments were carried out in a stirred vessel with a flat surface over a wide range of process conditions.

Strategies for lot acceptance testing using CMOS transistors and ICs

Direct-correlation and simple overstress methods for estimating IC response in strategic and space environments from laboratory transistor and IC data are investigated. Transistors and ICs were irradiated at dose rates from 0.2 rad(SiO/sub 2/)/s to 10/sup 6/ rad(SiO/sub 2/)/s. Over a wide range of process conditions and hardness levels, laboratory measurements of threshold voltage shift due to oxide trapped charge correlate well with IC leakage current at high dose rates for ICs with gate-oxide-dominated response. For ICs whose response is dominated by parasitic field-oxide structures, laboratory measurements of both transistor and IC leakage currents correlate well with IC hardness at high dose rates. For dose levels up to approximately=500 krad(SiO/sub 2/), it is shown that a simple factor-of-three overtest can be used as a conservative estimate of radiation hardness for strategic applications, provided that both functional and parametric testing is performed following X-ray irradiation at a dose rate of approximately=2000 rad(SiO/sub 2/)/s. For space environments, a laboratory irradiation to 1.5 times the required system level followed by a one-week 100 degrees C biased anneal gave conservative estimates of IC hardness. >

Mass transfer with complex chemical reactions

An absorption model has been developed which is able to calculate the simultaneous absorption rates (and corresponding enhancement factors) of two gaseous components into a reactive liquid. In the liquid phase multiple complex parallel reversible reactions may take place. This model, for example, can be used for design and development of gas-treating processes for the selective removal of hydrogen sulphide. Due to the implementation of an additional transformation of the spatial coordinate, the required computational time could be reduced substantially without loss of accuracy. The present model can be incorporated into an overall absorption module for column design and simulation. Experimentally determined simultaneous absorption rates of H2S and CO2 in aqueous solutions of alkanolamines and mixtures of alkanolamines can be predicted satisfactorily well for the conditions where both gases have a mutual interaction on the respective rates. The experiments were carried out in a stirred vessel with a flat surface over a wide range of process conditions.

Comparison of experimental and computed results on arsenic- and phosphorus-doped polysilicon emitter bipolar transistors

This paper presents a detailed comparison of the measured and computed electrical characteristics of polysilicon emitter bi-polar transistors over a wide range of processing conditions. Detailed electrical measurements are made of both the emitter resistance and the base and collector current as a function of base-emitter voltage. Devices with arsenic- and phosphorus-doped emitters are considered, as well as both with and without a deliberately grown interfacial oxide layer. The theoretical characteristics are computed using a unified model that incorporates both transport and tunneling mechanisms. It is shown that the measured emitter resistances across a wide range of processing conditions can be satisfactorily explained using a tunneling model with a single value for the electron effective barrier height (0.4 eV). Values for the modeling parameters are obtained, in some cases uniquely by measurement, and in others by fitting the experimental results. In devices with a deliberately grown interfacial oxide, the base current is suppressed to such an extent that recombination in the single-crystal emitter and in the base becomes important.

Advances in digital alignment strategies for step-and-repeat optical imaging

To support the needs of submicron lithography, a new digital alignment technique has been developed. This technique incorporates both global and local alignment strategies. High speed digital image processing of video images allows for the rapid collection and analysis of large, statistically valid data samples to ensure accurate results. Sophisticated algorithms including thresholding, convolution analysis and autocorrolation symmetry analysis, allow pattern recognition under a wide range of process conditions.

Nitrogen in Crystalline Si

ABSTRACTUse of N doping, N gas ambients and N implantation in Si processing has stimulated study of the incorporation and behaviour of N in Si. Studies of N-implanted Si and comparisons with melt-doped Si have shown that N pairing is the dominant mode for bonding of N into crystalline Si for a wide range of processing conditions. Studies have also shown that laser annealing quenches a small percentage of implanted N into a substitutional site. Nitrogen diffusion and aggregation have been shown to occur in N-implanted Si upon furnace annealing at temperatures &gt;700°C and there is a simultaneous formation of shallow donors. Interactions between N and other impurities occur in both as-grown and ion-implanted Si. Additional studies are needed to describe more fully the electrical and structural consequences of N-N, Nimpurity and N-defect interactions in Si.