Billy L. Crowder

1 µm MOSFET VLSI technology: Part VII—Metal silicide interconnection technology—A future perspective

A major limitation of polycrystalline silicon as a gate material for VLSI applications is its limited conductivity which restricts its usefulness as an interconnection level. An alternative approach which combines a doped polycrystalline silicon layer with a high-conductivity metal silicide such as WSi2(polycide) is described. Such polycide layers are demonstrated to provide at least an order of magnitude improvement in interconnection resistance relative to polycrystalline silicon while maintaining the reliability of the polycrystalline silicon gate and the ability to form passivating oxide layers under typical polycrystalline silicon processing conditions.

New uses of ion accelerators

1. Ion-Excited X-Ray Analysis of Environmental Samples.- I. Introduction.- II. General Considerations for Ion Beam Analysis of Environmental Samples.- III. Formalism and Optimization.- IV. The UCD/ARB Aerosol Analysis System.- A. The Primary Ion Beam.- B. Detection of X-Rays.- C. Data Acquisition and Reduction.- D. System Calibration.- E. Target Preparation and Matrix Effects.- F. Estimation of Analytical Costs.- G. Validation of System Operations.- V. Ion-Excited X-Ray Analysis Programs.- Appendix (Forward Scattering).- Acknowledgments.- References.- 2: Material Analysis by Nuclear Backscattering.- A. Introduction.- General Comments on Nuclear Backscattering.- Appendix (Numerical Examples).- References.- B. Applications.- I. Introduction.- II. Ion Implantation.- III. Thin Films: Growth and Deposition.- IV. Thin Film Reactions: Interdiffusion and Compound Formation.- V. Bulk Effects: Composition, Diffusion and Solubility.- VI. Concluding Remarks.- Acknowledgments.- References.- Formalism.- 1. Three Basic Concepts in Backscattering.- A. Backscattering Kinematic Factor Mass ? Analysis.- B. Differential Scattering Cross Section ? Quantitative Analysis.- C. Energy Loss ? Depth Analysis.- 2. Depth Scale in Backscattering Analysis [S].- A. Depth Scale in Backscattering Analysis.- B. Surface Approximation.- C. Linear Approximation.- 3. Height of an Energy Spectrum.- A. Surface Approximation for Spectrum Height.- B. Thick Target Yield.- C. Backscattering Yield of a Thin Film.- 4. Applications of Backscattering from Elemental Targets.- A. Surface Contamination and Ion Implantation.- B. Doping Level of a Bulk Sample.- C. Film Thickness Measurement and dE/dx Measurements.- D. Yield Formula and dE/dx Measurements.- E. Differential Scattering Cross Section Measurement.- 5. Application of Backscattering to Compound Targets.- A. Thin Film Analysis.- B. Thick Compound Targets.- C. Analysis on Composition Varying Continuously with Depth.- Appendix 1. Notations.- Appendix 2. Formulae.- Appendix 3. Sources for dE/dx Information.- References.- 3: Material Analysis by Means of Nuclear Reactions.- Charged Particle Activation Analysis.- Charged Particle Activation Analysis - Examples.- Prompt Radiation Analysis.- Nonresonant Nuclear Reactions - Gamma Rays Observed.- Nonresonant Nuclear Reactions - Nuclear Particles Observed.- Resonant Nuclear Reactions.- Summary.- Acknowledgment.- References.- 4: Lattice Location of Impurities in Metals and Semiconductors.- I. Introduction.- II. Impurity Detection.- III. The Channeling Technique.- 1. Channeling Concept.- 2. Experimental Technique.- IV. Lattice Location Analysis.- V. Examples.- 1. Substitutional Impurities.- 2. Nearly Substitutional Impurities.- 3. Interstitial Impurities.- 4. High Impurity Concentrations.- 5. Radiation-Induced Change in Impurity Sites.- VI. Summary of the Literature on Channeling Lattice Location Data.- VII. Limitations.- VIII. Conclusions.- References.- 5: Ion Implantation in Metals.- Historical Perspective.- Friction and Wear.- Corrosion.- 1. Oxides with Anion Defects.- 2. Oxides with Cation Defects.- Ion Backscattering.- Titanium and Stainless Steel.- Zirconium.- Aluminum.- Copper.- Aqueous Corrosion.- Practical Applications in Corrosion.- Electrochemistry and Catalysis.- Implantation Metallurgy.- Equipment for the Ion Implantation of Metals.- Conclusions.- References.- 6: Ion Implantation in Superconductors.- Definition of the Superconducting Parameters.- Influence of Radiation Damage on the Superconducting Properties.- a. Non-Transition Metals.- b. Transition Metals.- c. Transition Metal Alloys.- d. Superconductors with A-15 and NaCl-Structure.- e. Transition Metal Layer Compounds.- f. Quantitative Estimation of Damage in Superconductors.- Influence of Implanted Ions on the Superconducting Transition Temperature.- a. Magnetic Impurities in Non Transition Metals.- b. Pd-, Pd-Noble Metal Alloy, -Hydrogen System.- c. Ion Implanted Transition Metal Systems.- d. Aluminum Based Ion Implanted Systems.- Application to Superconducting Devices.- Conclusions.- References.- 7: Ion-Induced X-Rays from Gas Collisions.- 1. Introduction.- 2. Collision Models.- 2.1. Survey of Models.- 2.2. Coulomb Ionization.- 2.3. The Molecular-Orbital Model.- 3. Measurements of Inner-Shell Excitations.- 3.1. Introduction.- 3.2. Theory of Energy-Loss Measurements.- 3.3. X-Ray and Electron Emission.- 3.4. Typical Apparatus-Ionization and Inelastic Energy Loss.- 3.5. Scattered- Ion-X-Ray/Electron Coincidence Apparatus.- 4. Discussion of Typical Data.- 4.1. Ionization States.- 4.2. Inelastic Energy Loss.- 4.3. Electron Emission Cross Sections.- 4.4. Fluorescence Yield Effects.- 4.5. X-Ray-Scattered-Ion Coincidence Data.- 4.6. X-Rays from Highly Stripped Fast Ion Beams.- 5. Summary.- References.- 8: Ion-Induced X-Rays in Solids.- 1. Introduction.- 2. Accelerators and Target Chambers.- 2.1. Ion Sources.- 2.2. Target Chambers.- 3. The Detection and Analysis of X-Rays.- 3.1. The Gas Flow Proportional Counter.- 3.2. The Si(Li) Detector.- 3.3. The X-Ray Crystal or Grating Spectrometer.- 4. The Use of Protons and Helium Ions to Generate X-Rays from Solid Targets.- 4.1. Current Areas of Fundamental Interest.- 4.2. Applications.- 5. The Use of Heavy Ions to Generate X-Rays from Solid Targets.- 5.1. General Background.- 5.2. Physical Processes.- 5.3. Applications.- 6. Conclusions.- References.- Author Index.

ESR AND OPTICAL ABSORPTION STUDIES OF ION‐IMPLANTED SILICON

The g value, line shape, and linewidth of an ESR signal in Si layers which have been damaged by ion implantation of Si, P, or As at room temperature are found to be identical to those of the electron states observed in amorphous Si films prepared by rf sputtering. Interference phenomena observed in the optical absorption spectra allow a determination of the depth to which the Si has been damaged by the energetic heavy ions. These two techniques together provide a new tool for investigating lattice disorder in ion‐implanted Si layers.

FORMATION OF AMORPHOUS SILICON BY ION BOMBARDMENT AS A FUNCTION OF ION, TEMPERATURE, AND DOSE.

The dose (fluence) of 200‐keV boron, phosphorous, and antimony ions required to produce a continuous amorphous layer in silicon is determined as a function of target temperature. EPR measurements are used to monitor the process which is also then related to annealing effectiveness. The continuous amorphous layer recrystallizes at 550°C, after which only the implanted ions within that layer are completely electrically active. Carrier concentration profiles indicate the position of the amorphous layer and allow an approximate determination of the distribution with depth of damage. At the low dose rates used, reasonable agreement with a simple model for the formation of amorphous silicon as a function of ion, temperature, and dose is obtained.

ANNEALING CHARACTERISTICS OF n-TYPE DOPANTS IN ION-IMPLANTED SILICON.

Investigations of the conditions under which the donors, P, As, and Sb, are incorporated into Si by by ion implantation (260–300 keV) in an electrically active form are reported. Above a critical dose, room‐temperature implantations followed by a 600°C post anneal are substantially more effective than implantations at 600°C.

Elastic and Anelastic Behavior of Ion‐Implanted Silicon

Ion‐implantation damage has been studied in thin reeds of silicon by resonant‐frequency and internal‐friction measurements. For a dose of 1016/cm2 of 28Si+, the principal effects are the appearance of an internal‐friction peak and a decrease in the flexural vibration frequencies. The amorphous surface layer produced by implantation is deduced to have a Youngs modulus of 1.24×1012 dyn/cm2 and a density of 0.95 of the crystal density. The internal stress in the amorphous layer has been measured and found to be far smaller than that corresponding to a purely elastic accommodation of the density change.

Range distribution of implanted ions in SiO2, Si3N4, and Al2O3

Backscattering measurements with 2.0‐MeV He+ ions were used to determine the range distribution of Zn, Ga, As, Se, Cd, and Te implanted in SiO2, Si3N4, and Al2O3 at energies between 150 and 300 keV. Values of the projected range were systematically greater than LSS predictions by factors of 1.2–1.5. In normalized LSS units, the projected range, ρp, as a function of energy, e, consistently followed within experimental error the relation ρp=2.7e, where an arithmetic average atomic number of 10 and arithmetic average atomic mass of 20 apply to all three target species.

The behavior of boron (also arsenic) in bilayers of polycrystalline silicon and tungsten disilicide

Boron doping additions in polysilicon‐WSi2 bilayers tend to segregate preferentially in the silicide layer during heat treatments at temperatures between 600 and 1000 °C. This is in contrast to arsenic impurities which under the same conditions diffuse through the silicide and evaporate. The boron analyses were obtained by means of the 10B(n, α) 7Li reaction with thermal neutrons. The arsenic analyses were obtained by means of Rutherford backscattering. The results are compared with results previously obtained from similar samples doped with phosphorous.

Boron atom distributions in ion‐implanted silicon by the (n,4He) nuclear reaction

The concentration distribution of 10B atoms ion‐implanted into silicon has been determined with a new nuclear reaction technique, The concentration profiles for implantations in the energy range 40–500 keV were determined before and after annealing at 900 °C for 30 min and show that enhanced diffusion, because of radiation damage, is of minor importance. The profile ranges and widths have been compared to LSS theory and to other experiments.

1 µm MOSFET VLSI technology: Part V—A single-level polysilicon technology using electron-beam lithography

An n-channel single-level polysilicon, 25 nm gate-oxide technology, using electron-beam lithography with a minimum feature size of 1 µm, has been implemented for MOSFET logic applications. The six-mask process employs semirecessed oxide isolation and makes extensive use of ion implantation, resist liftoff techniques, and reactive ion etching. A description of the process is given, with particular emphasis on topographical considerations. Implementation of a field etchback after source/drain implant to eliminate a low thick-oxide parasitic-device threshold is also discussed.