Ellen Meeks

Modeling of SiO2 deposition in high density plasma reactors and comparisons of model predictions with experimental measurements

High-density-plasma deposition of SiO2 is an important process in integrated circuit manufacturing. A list of gas-phase and surface reactions has been compiled for modeling plasma-enhanced chemical vapor deposition of SiO2 from SiH4, O2, and Ar gas mixtures in high-density-plasma reactors. The gas-phase reactions include electron impact, neutral–neutral, ion–ion, and ion–neutral reactions. The surface reactions and deposition mechanism is based on insights gained from attenuated total reflection Fourier transform infrared spectroscopy experiments and includes radical adsorption onto the SiO2 surface, ion-enhanced desorption from the surface layer, radical abstractions, as well as direct ion-energy-dependent sputtering of the oxide film. A well-mixed reactor model that consists of mass and energy conservation equations averaged across the reactor volume was used to model three different kinds of high-density plasma deposition chambers. Experimental measurements of total ion densities, relative radical dens...

Computational simulation of diamond chemical vapor deposition in premixed C2H2/O2/H2 and CH4O2-strained flames

We have modeled combustion synthesis of CVD diamond in a stagnation-flow reactor under atmospheric conditions. In this configuration a premixed flat flame flows over a flat deposition substrate that lies perpendicular to the flow and parallel to the burner face. Optimal growth conditions occur when the flame is lifted from the burner surface and stabilized at the deposition surface. A similarity transformation for the stagnation flow field reduces the governing equations to a one-dimensional boundary value problem, significantly simplifying the computational task. The simulations include elementary gas-phase and surface chemistry as well as multicomponent molecular transport in the flame gas. Our model shows good qualitative agreement with observed growth parameters for the experimental conditions of Murayama et al. [1], who employed a premixed C2H2/H2/O2 gas mixture. Modeling CH4O2 flame synthesis demonstrates that methane is less effective for diamond growth due to the decreased flame temperature and stability compared with C2H2 combustion.

Modeling the plasma chemistry of C2F6 and CHF3 etching of silicon dioxide, with comparisons to etch rate and diagnostic data

A detailed chemical reaction mechanism is reported that describes the C2F6 and CHF3 plasma etching of silicon dioxide, which is widely used in the fabrication of microelectronic devices. The gas-phase part of the C2F6 mechanism involves 28 species and 132 reactions, while the surface part involves 2 materials, 6 species, and 85 reactions. Rate parameters are generally taken from independent studies in the literature, or estimated from rates measured for related species. Zero-dimensional simulations using these mechanisms compare well with a large body of etch rate and diagnostic measurements in three different high-density plasma reactors. The diagnostic measurements include electron and negative ion absolute densities, CF, CF2, and SiF densities, gas temperatures, and ion current densities. An analysis of the dominant reaction paths shows the importance of gas-phase electron impact reactions and the need to include reactions of the etch-product species. On the surface, the etching reactions are dominated...

SIMULATIONS OF BCL3/CL2/AR PLASMAS WITH COMPARISONS TO DIAGNOSTIC DATA

A reaction mechanism is reported that describes BCl3/Cl2/Ar plasmas used in the etching of metal lines in microelectronics fabrication processes. Although many of the fundamental electron-impact cross sections for this system are not well known, a reasonable set of reaction paths and rate coefficients has been derived to describe low-pressure reactors with high plasma density. The reaction mechanism describes 59 possible gas-phase events and 18 plasma-surface interactions. A well-mixed reactor model is used to develop the reaction set and to test it against absolute experimental measurements of electron and Cl− densities, as well as relative measurements of BCl and Cl radicals in an inductively coupled research reactor. The experimental data cover a wide range of operating conditions and gas mixtures. The model provides quantitative agreement with measurements over the whole range of conditions and diagnostics, capturing most of the observed trends. In addition, the model predicts relative ion ratios and ...

Modeling of plasma-etch processes using well stirred reactor approximations and including complex gas-phase and surface reactions

A 0-D or well stirred reactor model determines spatially and time-averaged species composition in plasma-etch reactors, through solution of species, mass, and electron-energy balance equations. The use of well stirred reactor approximations reduces the computational expense of detailed kinetics calculations and allows investigation of the dependence of plasma chemistry on etch-process parameters. The reactor is characterized by a chamber volume, surface area, net mass flow or residence time, pressure, energy loss to surroundings, power deposition, and inlet-gas composition. The electron-energy equation includes a detailed power balance with losses to ions and electrons through the sheath, as well as inelastic and elastic collision losses. The model employs reaction-rate coefficients for electron-impact reactions, which require an assumption of the electron energy distribution function (EEDF). We compare model results using Maxwellian EEDFs, as well as reaction-rate coefficients determined as a function of average electron energy through solution of the Boltzmann equation, for chlorine chemistry. The Boltzmann rates are determined by time-lagging the equilibration of electrons with applied electric fields. The Maxwellian reaction rates give higher ionization fractions than the Boltzmann rates, affecting the predicted electronegativity and positive ion composition for chlorine plasmas. The model also shows a strong sensitivity of the plasma composition to the assumed surface-recombination probability of atomic chlorine. >

Scaleable stagnation‐flow reactors for uniform materials deposition: Application to combustion synthesis of diamond

We describe two inherently scaleable geometries for chemical‐vapor‐deposition and heat‐transfer processes that are based on stagnation flows. The ‘‘coflow’’ and ‘‘trumpet‐bell’’ designs result in radially uniform fluxes to surfaces and they optimize the use of reagents. Using a trumpet‐bell burner, we have grown uniform films of diamond from a substrate‐stabilized flat flame of C2H2/H2/O2.

Chemical Reaction Mechanisms for Modeling the Fluorocarbon Plasma Etch of Silicon Oxide and Related Materials

As part of a project with SEMATECH, detailed chemical reaction mechanisms have been developed that describe the gas-phase and surface chemistry occurring during the fluorocarbon plasma etching of silicon dioxide and related materials. The fluorocarbons examined are C{sub 2}F{sub 6}, CHF{sub 3} and C{sub 4}F{sub 8}, while the materials studied are silicon dioxide, silicon, photoresist, and silica-based low-k dielectrics. These systems were examined at different levels, ranging from in-depth treatment of C{sub 2}F{sub 6} plasma etch of oxide, to a fairly cursory examination of C{sub 4}F{sub 8} etch of the low-k dielectric. Simulations using these reaction mechanisms and AURORA, a zero-dimensional model, compare favorably with etch rates measured in three different experimental reactors, plus extensive diagnostic absolute density measurements of electron and negative ions, relative density measurements of CF, CF{sub 2}, SiF and SiF{sub 2} radicals, ion current densities, and mass spectrometric measurements of relative ion densities.

Flame-centered grid transformation for numerical simulation of strained flames

This communication presents a method for greatly reducing the computational solution time for simulating a series of one-dimensional, laminar, premixed, strained flames

Simulation of dielectric etch in high density plasma reactors

High density plasma (HDP) reactors applied to dielectric etch of fine-line, high aspect ratio features poses a challenge for future technology (below 0.25 jum). The complex nature of HDP reactors and the lack of basic chemical information has made it difficult to apply numerical simulation to enhance process development. This work focuses on a threestep process for modeling complex chemical HDP processes, where some of the necessary reaction rates, excitation energies and surface reactivities are not available. We will concentrate specifically on a C2F6 plasma for oxide etch, although the strategy can be applied to other plasma systems. The first step in modeling a HDP process is to develop gas phase and surface etch mechanisms from available data. Sensitivity analysis is applied to reduce the number of species and reactions ,this is required for performing 2D simulations. The second step is to validate the mechanism and the plasma models through data comparisons. A suite of three simulation tools was used during this process: Aurora, MPRES and Icarus. Experimental data used for mechanism refinement and validation included Langmuir probe data, laser diode data and oxide etch rate data taken in both an experimental and a commercial reactor. The final step is application of the developed model to investigate a commercial process. 2D plasma model results are presented to Currently resides at IBM Microelectronics Hopewell Junctions, NY 12533. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Introduction The trend in semiconductor manufacturing towards higher aspect ratios and larger wafer diameters (300mm) continues to require higher uniformity and larger selectivity for etch processes. It is expected that dielectric, high density plasma (HDP) etch processes will face this challenge. Current commercial dielectric etch processes have been developed empirically. The process operates in a regime where a delicate balance exists between polymer deposition and ion assisted etch.. The challenge of improving this fragile etch process to meet new process requirements has generated incentive to improve process understanding. One approach to enhance process understanding and decrease process development time is through process simulation. Applying models to enhance understanding of these systems is nontrivial due to the complex chemistry (both gas and surface) and the lack of fundamental reaction rate information. To compensate for the lack of reaction rate data, simulations and experimental validation data can be combined to develop a mechanism that is valid for a defined operating regime. This work focuses on a three-step process of mechanism development for a HDP reactor. Specifically, a C2F6 plasma mechanism will be developed to predict oxide etch rates for a commercial reactor. The first step in modeling an HDP process the mechanism compilation. The initial C2F6 mechanism was built with data from the literature. When gas phase and surface reaction rates were not available, extrapolations from similar chemistries were used. Sensitivity analysis was applied to reduce the number of reactions and species in the mechanism while still capturing the salient features of the plasma. Species with low densities and reactions that did not significantly impact electron properties or ion fluxes were removed. For example, the initial C2p6 mechanism contained approximately 40 species while the reduced mechanism contains 14 species; fewer species are necessary for convergence and improved run times of the 2-D models. Surface chemistry mechanisms were required for the different wall materials and the oxide wafer. At this time a photoresist etch mechanism has not been developed. This work was funded by a Sandia-SEMATECH CRADA and was performed at Sandia National Laboratories which is operated for DOE under Contract DE-AC04-76DP00789. Copyright© 1998, American Institute of Aeronautics and Astronautics, Inc. The second step in HDP modeling is validating the mechanism and the models through comparison to experimental data. The reduced C2F6 mechanism was refined and validated by comparing 0-D and 2-D reactor simulations to data. Data was taken on a commercial HDP reactor and a Gaseous Electronics Conference (GEC) reference cell modified with an inductive coil and a quartz liner. The computational codes applied in this study include; Aurora, a OD model, MPRES, a 2D continuum finite element code and Icarus, a 2D Direct Simulation Monte Carlo (DSMC) code6. Data comparisons included Langmuir probe data, CF laser diode measurements, and oxide etch rate data. The third step in the process of HDP modeling is to apply the final mechanism to investigate process questions. The focus of this work was to investigate the changes in etch rates and selectivity (oxide to photoresist) as a function of gas injection location and flowrates for a commercial oxide etch reactor. Icarus simulations are presented to explain reported etch rate and selectivity variations.

Chemical kinetics models for semiconductor processing

Chemical reactions in the gas-phase and on surfaces are important in the deposition and etching of materials for microelectronic applications. A general software framework for describing homogeneous and heterogeneous reaction kinetics utilizing the Chemkin suite of codes is presented. Experimental, theoretical and modeling approaches to developing chemical reaction mechanisms are discussed. A number of TCAD application modules for simulating the chemically reacting flow in deposition and etching reactors have been developed and are also described.