Donald R. Burgess

Numerical study of low- and high-temperature silane combustion

Self-ignition and flame propagation properties of silane combustion systems have been studied through computer simulations using a database of kinetic and thermodynamic information that is consistent with current understanding of the elementary processes. These new inputs include the mechanism for chain branching through the SiH3 radical, rate constants for the reactions of HO2 with silane and its breakdown products, and the reaction of SiO with oxygen. Over the entire temperature range, the simulations show two distinct mechanisms. At low temperatures, the kinetics of SiH3 is controlling, whereas at high temperatures, SiH2 chemistry is of key importance. The results demonstrate that the upper explosion limit and ignition at room temperature and 1 bar can be described by the same set of reactions. With the new database, many of the experimental observations can be reproduced, and predictions are made regarding dependencies on process parameters. These include the critical conditions for chain ignition, the dependence of the critical pressure on the ratio of silane and oxygen concentration, and the temperature dependence of the critical ratio of silane to oxygen concentration. A scenario for low-temperature ignition is presented. At high temperatures, the importance of condensation processes for accurate prediction of flame velocities is clear. For very lean flames, the maximum reaction rate occurs at the lower temperature region of the flame zone.

An Investigation of Particle Dynamics in a Rotating Disk Chemical Vapor Deposition Reactor

This paper describes a numerical model for the nucleation, growth, and transport of gas-phase particles formed during the chemical vapor deposition (CVD) of epitaxial silicon from silane. These particles can lower the deposition rate by consuming precursor, and contaminate the growing film via diffusion to the surface. This model has been constructed for use with the Sandia SPIN code, which contains a solver for the reacting flow and heat transfer in a vertical, rotating disk CVD reactor. A detailed gas-phase chemical kinetic mechanism for the thermal decomposition of silane was developed to simulate formation of small silicon clusters and the depletion of reactive intermediates through condensation. The particle model uses a moment transport formulation to examine the effects of total reactor pressure, temperature, rotation rate, inlet gas composition, and rate of particle growth via condensation on the characteristics of the particle population. Numerical results are presented in terms of the integral moments of the particle distribution which correspond physically to the particle number concentration, average particle diameter, and particle light scattering intensity. In situ validation experiments have been performed in an optically accessible reactor under conditions typical of silicon CVD. The rate of particle growth via condensation, controlled numerically by a global condensation parameter (GCP), was found to control the characteristics of the particle population. The numerical results were found to compare favorably with experiment if this GCP was properly chosen.

In Situ Gas Phase Diagnostics for Hafnium Oxide Atomic Layer Deposition

Atomic layer deposition (ALD) is an important method for depositing the nanometer-scale, conformal high κ dielectric layers required for many nanoelectronics applications. In situ monitoring of ALD processes has the potential to yield insights that will enable efficiencies in film growth, in the development of deposition recipes, and in the design and qualification of reactors. This report will describe the status of a project to develop in situ diagnostics for hafnium oxide ALD processes. The focus is on an examination of the utility of Fourier transform infrared spectroscopy and diode laser spectroscopy for optimizing deposition conditions, rather than simply monitoring precursor delivery. Measurements were performed in a single-wafer, warmwall, horizontal-flow reactor during hafnium oxide ALD involving tetrakis(ethylmethylamino) hafnium and water. Measurements were performed near the wafer surface under a range of deposition conditions in an effort to correlate gas phase measurements with surface processes.

Inhibitor influence on the bistability of a CSTR

Methane combustion in a continuously stirred flow tank reactor (CSTR) in the presence and absence of chemical inhibitors such as CF{sub 3}I, CF{sub 3}Br, CF{sub 3}H, and a chemically inert gas with high heat capacity is simulated with the CHEMKIN program. The aim of the work is to determine the differences in results arising from the use of the various inhibitors with the aim of establishing the capability of CSTR experiments to give a rank ordering of suppressant power. The chemical inhibitors have the general tendency to raise the steady-state temperature. A high heat capacity inert gas leads to the opposite effect. Only near extinction and self-ignition can one obtain a proper scale of flame suppression capability. The curves for combustion efficiency, (CO{sub 2}/[CO + CO{sub 2}]), near the extinction point lead to results where the data for the additives all fall within the envelope for stoichiometric methane/air combustion in the extinction region. For self-ignition, the transition from the mushroom to the isola form of the stability curves appears to be another property that is highly sensitive to suppression power. These observations may serve as a basis for testing inhibition capabilities.

A numerical/experimental investigation of microcontamination in a rotating disk chemical vapor deposition reactor

Driven by a relentless decrease in feature size, the allowable particle contaminant size during semiconductor fabrication is now less than 100 nm. Particles in this size range (microcontaminants) in chemical vapor deposition (CVD) reactors are primarily gas-phase generated and are poorly understood. The purpose of the investigation described here is to enhance the understanding of the formation, transport and growth of microcontaminants in thermal CVD reactors. The approach being employed is to carry out a combined numerical/experimental study in which the particle dynamics are both modeled and optically probed in a rotating disk CVD reactor. The rotating disk configuration is utilized because of its simple and well-defined flow in which a particle layer forms in a highly accessible region of the reactor just above the substrate. Numerical/experimental comparisons of layer location and shape as a function of disk rotation rate are shown to be excellent if two empirically-determined parameters in the model...

A Microcontamination Model for Rotating Disk Chemical Vapor Deposition Reactors

This paper presents preliminary results from a model currently under development for gas-phase generated submicron-size contaminant particles (i.e., microcontaminants) in rotating disk chemical vapor deposition reactors. These particles present a problem during semiconductor processing, and this model is intended as a useful tool for gaining a better understanding of this problem. A one-dimensional formulation is employed to model the central section of the reactor, a technique which allows the use of detailed chemical reaction sets. The existing Sandia SPIN code, which contains a solver for the reacting flow, is modified by the addition of an aerosol model for the particles. This model utilizes a moment transport formulation which accounts for convection, diffusion, gravity, thermophoresis, chemical production, coagulation and condensation. Results are presented primarily in terms of reactor performance maps which indicate film growth and contamination rates as functions of substrate temperature. The eff...

Editorial: Greetings from the New Co-Editors

It is our pleasure to assume the duties of Co-Editors of Journal of Physical and Chemical Reference Data JPCRD . Mal Chase’s many years of service as Editor have left us with some big shoes to fill it takes two of us to replace him! , but we are committed to maintaining the high quality of papers published in JPCRD. We will split the technical editorship duties. Allan will shepherd articles primarily in the areas of thermophysical properties of fluids and phase-equilibrium thermodynamics including the IUPAC-NIST Solubility Data Series . Don will shepherd articles primarily in the areas of thermochemical and chemical kinetic data and of atomic and molecular spectroscopy including the Atomic Energy Level data publications . Both of us are grateful to be able to draw on the wealth of expertise of our colleagues at NIST and in the wider scientific community. We are also grateful for the support provided by NIST’s Measurement Services Division, including Bob Watters who serves as Co-Editor and as NIST’s representative to the JPCRD Management Board and Linda Diane Decker who continues to be invaluable as the JPCRD Editorial Assistant . We also thank Mal Chase for leaving the journal in good shape, and for his continuing assistance as we transition into our editorial roles. While we foresee no radical changes in the course charted for JPCRD by previous Editors, this transition does afford an opportunity to think about enhancements to improve both the quality of the journal and the quality of the journal process for our authors and reviewers. For the publication process, we are exploring ways to make greater use of the Internet for the submission, review, and editing processes, which may include AIP’s web-based Peer X-Press PXP system. We have also revised and