Fundamental Electron Interactions with Plasma Processing Gases

This volume deals with the basic knowledge and understanding of fundamental interactions of low energy electrons with molecules. It pro­ vides an up-to-date and comprehensive account of the fundamental in­ teractions of low-energy electrons with molecules of current interest in modern technology, especially the semiconductor industry. The primary electron-molecule interaction processes of elastic and in­ elastic electron scattering, electron-impact ionization, electron-impact dissociation, and electron attachment are discussed, and state-of-the­ art authoritative data on the cross sections of these processes as well as on rate and transport coefficients are provided. This fundamental knowledge has been obtained by us over the last eight years through a critical review and comprehensive assessment of "all" available data on low-energy electron collisions with plasma processing gases which we conducted at the National Institute of Standards and Technology (NIST). Data from this work were originally published in the Journal of Physical and Chemical Reference Data, and have been updated and expanded here. The fundamental electron-molecule interaction processes are discussed in Chapter 1. The cross sections and rate coefficients most often used to describe these interactions are defined in Chapter 2, where some recent advances in the methods employed for their measurement or calculation are outlined. The methodology we adopted for the critical evaluation, synthesis, and assessment of the existing data is described in Chapter 3. The critically assessed data and recommended or suggested cross sections and rate and transport coefficients for ten plasma etching gases are presented and discussed in Chapters 4, 5, and 6.

1. Fundamental Electron-Molecule Interactions and their Technological Significance.- 1 Introduction.- 2 Low Energy Electron-Molecule Interaction Processes.- 2.1 Interactions of Low-Energy Electrons with Ground-State Molecules.- 2.2 Interactions of Low-Energy Electrons With Excited Molecules.- 2.3 Interactions of Low-Energy Electrons with Molecules in High Pressure Gases, Liquids, Clusters, and with Molecules at Surfaces.- 2.4 Interactions of Low-Energy Electrons With Transient Species (Radicals).- 3 Significance of Electron-Molecule Interactions in Plasma Processing.- 3.1 Low-Temperature, Low-Density, Non-Equilibrium Plasmas.- 3.2 Generation, Use, and Modeling of Low-Pressure Plasmas.- 3.3 Primary and Secondary Reactions.- 4 The Present Work.- 5 References.- 2. Electron-Molecule Interactions in the Gas Phase: Cross Sections and Coefficients.- 1 Introduction.- 2 Collision Cross Sections.- 2.1 Cross Sections for Elastic Electron Scattering.- 2.2 Cross Sections for Inelastic Electron Scattering.- 2.3 Partial Cross Sections.- 2.4 Total Electron Scattering Cross Section, ?sc,t (?).- 2.5 Methods of Measurement.- 2.6 Calculations.- 3 Coefficients and Rate Constants.- 3.1 Electron Transport Coefficients.- 3.2 Coefficients for Electron Attachment, and Electron-Impact Ionization and Excitation.- 3.3 Rate Constants.- 3.4 Methods of Measurement.- 4 Boltzmann-Code-Generated Collision Cross-Section Sets.- 5 References.- 3. Synthesis and Assessment of Electron Collision Data.- 1 Introduction.- 2 Synthesis, Assessment, and Recommendation of Data.- 2.1 Determination of the Cross Section for Momentum Transfer, ?m(?) of CF4.- 2.2 Determination of the Total Electron Scattering Cross Section, ?sc,t (?) of CF4 Below 1 eV 117.- 2.3 Determination of the Total Electron Attachment Cross Section, ?a,t (?), of Cl2.- 2.4 Consistency Between the Assessed Cross Sections.- 3 Deduction of Unavailable Data and Understanding from Assessed Data, New Measurements, and Data Needs.- 3.1 Deduction of Unavailable Data.- 3.2 A Better Understanding from Assessed Data.- 3.3 Determination of Data Needs and New Related Measurements and Calculations.- 4 Dissemination and Updating of the Database.- 5 References.- 4. Electron Interactions with CF4, C2F6, AND C3F8.- 1 Introduction.- 2 Electron Interactions with CF4.- 2.1 Electronic and Molecular Structure of CF4.- 2.2 Electron Scattering from CF4.- 2.3 Electron-Impact Ionization of CF4.- 2.4 Electron-Impact Dissociation of CF4 into Neutral Fragments.- 2.5 Electron Attachment to CF4.- 2.6 Electron Transport in CF4.- 2.7 Electron Interactions with CF4 Neutral Fragments.- 2.8 Summary of Recommended and Suggested Electron Collision Cross Sections and Electron Transport Coefficients for CF4.- 3 Electron Interactions with C2F6.- 3.1 Electronic and Molecular Structure of C2F6.- 3.2 Electron Scattering from C2F6.- 3.3 Electron-Impact Ionization of C2F6.- 3.4 Electron-Impact Dissociation of C2F6 into Neutral Fragments.- 3.5 Electron Attachment to C2F6.- 3.6 Electron Transport in C2F6.- 3.7 Summary of Recommended and Suggested Electron Collision Cross Sections and Electron Transport Coefficients for C2F6.- 4 Electron Interactions with C3F8.- 4.1 Electronic and Molecular Structure of C3F8.- 4.2 Electron Scattering from C3F8.- 4.3 Electron-Impact Ionization of C3F8.- 4.4 Ionization Coefficients for C3F8.- 4.5 Electron-Impact Dissociation of C3F8 Producing Neutrals.- 4.6 Electron Attachment to C3F8.- 4.7 Electron Transport in C3F8.- 4.8 Summary of Recommended and Suggested Electron Collision Cross Sections and Electron Transport Coefficients for C3F8.- 5 References.- 5. Electron Interactions with CHF3, CF3I, AND c-C4F8.- 1 Introduction.- 2 Electron Interactions with CHF3.- 2.1 Electronic and Molecular Structure of CHF3.- 2.2 Electron Scattering from CHF3.- 2.4 Electron-Impact Dissociation of CHF3 into Neutral Fragments.- 2.5 Electron Attachment to CHF3.- 2.6 Electron Transport Coefficients for CHF3.- 2.7 Electron-Impact Induced Light Emission from CHF3.- 2.8 Electron Interactions with CHF3 Neutral Fragments.- 2.9 Summary of Recommended and Suggested Cross Sections and Coefficients for CHF3.- 3 Electron Interactions with CF3I.- 3.1 Electronic Structure and Basic Properties of CF3I.- 3.2 Electron Scattering Cross Sections for CF3I.- 3.3 Electron-Impact Ionization of CF3I.- 3.4 Electron Attachment to CF3I.- 3.5 Optical Emission from Electron Impact on CF3I.- 3.6 Summary of Suggested Cross Sections and Coefficients for CF3I.- 4 Electron Interactions with c-C4F8.- 4.1 Structural and Electronic Properties of c-C4F8.- 4.2 Electron Scattering Cross Sections for c-C4F8.- 4.3 Electron-Impact Ionization of c-C4F8.- 4.4 Electron-Impact Dissociation of c-C4F8 into Neutral Fragments.- 4.5 Electron Attachment to c-C4F8.- 4.6 Electron Transport Coefficients for c-C4F8.- 4.7 Ion-Molecule Reactions in c-C4F8.- 4.8 Summary of Suggested and Recommended Cross Sections and Coefficients for c-C4F8.- 5 References.- 6. Electron Interactions with Cl2, CCl2F2, BCl3, AND SF6.- 1 Introduction.- 2 Electron Interactions with Cl2.- 2.1 Electronic and Molecular Structure of Cl2.- 2.2 Electron Scattering from Cl2.- 2.3 Electron-Impact Ionization of Cl2.- 2.4 Electron-Impact Dissociation of Cl2 into Neutral Fragments.- 2.5 Electron Attachment to Cl2.- 2.6 Electron Transport in Cl2.- 2.7 Optical Emission from Cl2 Gas Discharges.- 2.8 Suggested Cross Sections and Coefficients for Cl2.- 2.9 Electron Collision Data for Cl and Cl+.- 2.10 Electron Detachment, Electron Transfer, and Recombination and Diffusion Processes Involving Cl2.- 2.11 Summary of Data for Other Species and Processes Involving Cl2 Plasmas.- 3 Electron Interactions with CCl2F2.- 3.1 Electronic and Molecular Structure of CCl2F2.- 3.2 Electron Scattering from CCl2F2.- 3.3 Electron-Impact Ionization of CCl2F2.- 3.4 Electron-Impact Dissociation of CCl2F2 into Neutral Fragments.- 3.5 Electron Attachment to CCl2F2.- 3.6 Electron Transport in CCl2F2.- 3.7 Optical Emission Under Electron Impact on CCl2F2.- 3.8 Recommended and Suggested Cross Sections and Coefficients for CCl2F2.- 4 Electron Interactions with BCl3.- 4.1 Structural and Electronic Properties of BCl3.- 4.2 Electron Scattering from BCl3.- 4.3 Electron-Impact Ionization of BCl3.- 4.4 Electron Attachment to BCl3.- 4.5 Electron Transport Coefficients for BCl3.- 4.6 Suggested and Needed Data for BCl3.- 5 Electron Interactions with SF6.- 5.1 Electronic and Molecular Structure of SF6.- 5.2 Electron Scattering by SF6.- 5.3 Electron-Impact Ionization of SF6.- 5.4 Cross Sections, ?dis,neut (?), for Electron-Impact Dissociation of SF6 into Neutral Fragments.- 5.5 Electron Attachment to SF6.- 5.6 Electron Transport in SF6.- 5.7 Autodetachment, Thermally Induced Detachment, Photo detachment, and Collisional Detachment of SF6?.- 5.8 Ion Transport in SF6.- 5.9 Recommended and Suggested Electron Collision Cross Sections and Electron Transport Coefficients for SF6.- 6 References.