Welcome to Lawrence J. Overzet's Web Pages

UNDER RECONSTRUCTION (slowly...)   Updated: 10/97

Engineers using plasma processing need to understand a wide range of topics related to both the technology of reactors and the properties of plasmas. This is an outline of the practical information an engineer needs to understand in order to successfully integrate plasmas into a process flow.

We cover four major topics: Requirements for Plasmas, Equipment Technology, Plasma Chemistry, and Plasma Generation and Properties. Each of these topics can be studied independently. This outline covers more material than can be taught in a single semester 3 SCH course and so I offer some flexibility in what is covered each time.

I welcome your comments and suggestions on this outline.  Send them to overzet@utdallas.edu

I. Semiconductor Requirements for 2000 and beyond

Semiconductor Industry Association Roadmap

• Feature size and scaling, metal levels
• Process rates, uniformity, damage tolerance
• Anisotropy, selectivity and conformality of etch and deposition
• Active, insulating, contacting materials

• Why and how plasma facilitates Deposition, Oxidation, Implant, Etching, Ashing

• Feed forward, feed back, observability, controllability
• Process monitoring, reproducibility, sources of variation
• Models

Integration of plasma processes into process flow

• Effect on pre and post processing steps
• Cluster tools and multistep plasma processes

• Basic cost of ownership issues
• The economic factors related to a plasma process reactor
.

Vacuum system requirements

• Chamber pump systems
• Cryo - pump, turbo pump - hybrid pumps, RVP
• Flow vs pressure in various regimes
• Load lock systems
• O2, H2O and other contamination problems
• Speed issues
• Mass Flow Systems
• Controller principles and operation
• Purge systems
• Inert gas flow
• Corrosive gases
• Hazardous gas handling and protection systems
• Effluent control / clean up
• Pressure gauges / control
• Piranhi, thermocouple, ionization, baratron, convectron
• Ranges of operation, gas compatibility, theory of operation
• Wafer chucks
• Clamps
• Electrostatic chucks

• Thermal expansion coefficients
• Outgassing and contamination
• Inertness and sputtering
• Electrical / magnetic characteristics
• Strength

• FCC allowed frequencies
• Power sources
• Matching networks
• Feedthroughs and coupling to plasma

• Geometries
• Excitation methods
• Gases used
• Corrosion, toxicity and environmental issues
• Problems and (some) solutions

III. Surface Chemistry and Processing

Sputtering

• Physics of sputtering
• Energy dependencies
• Angular dependencies
• Damage

• Plasma Immersion Ion Implantation (PIII)

• Oxygen chemistry with hydrocarbons
• Gas additives

• Necessary conditions for chemical removal of surface atoms
• Fluorine and Chlorine chemistry for silicon etching
• Neutral reactions
• Role of ions and ion energy
• Gas additives - oxidants and reductants
• Competition between etching and deposition
• Significance of temperature
• Factors affecting anisotropy
• Problems in fine line etching
• loading, microtrenching, electron shading
• Bromine reactions
• Metal etching
• Al, Cu, W, Ti
• Insulator etching
• SiO2, Si3N4, Al2O3, Polyimide, etc.
• III - V, II - VI and novel materials

• PECVD, HDPCVD
• a:Si-H, SiO2, Si3N4
• Polymers, diamond like carbon
• Source gases
• Reaction models
• Gap fill and step coverage
• Dep - etch - dep
• Sputter deposition

• Crystal lattice damage
• Subsurface F, Cl
• Charging and electrostatic punch through
• Power effects on surfaces
• Geometry effects
• Substrate holders, temperature variations, He cooled chucks
• Particulate contamination

• Wall erosion and sputtering
• Surface coating and reactor aging
• Neutral gas formation and degassing from reactor walls

IV. Anatomy and Taxonomy of Plasma Discharges

Basic characteristics

• low pressure, weakly ionized, electrically excited, non-thermodynamic equilibrium, self-sustained
• Plasma constituents (electrons, +ve and -ve ions, neutrals, radicals, excited species)
• Typical density and energy ranges

• Spatial variations of plasma potential, electric field, charge density and energy, optical emission
• Sheaths at powered, grounded and floating surfaces
• Negative glow
• Bulk glow

V. Introduction to Plasmas - Bulk Behavior

Motion of individual electrons and ions in electric and magnetic fields

• Single, collisionless particles in DC and AC electric fields
• Particle orbits in magnetic fields

• Debye shielding
• Plasma oscillations and plasma frequency
• Plasma shielding and plasma sheaths

• Langevin equation, conductivity and dielectric constant
• Response to DC, RF and microwave fields
• Plasma heating by ohmic effects

• Continuity equation, conservation of charge
• Momentum conservation, pressure and temperature
• Energy conservation and flow of electrical, thermal and electrochemical energy

• Electromagnetic waves in cold plasmas including magnetic fields
• Microwave interferometry as a plasma diagnostic

VI. Introduction to Plasmas - Sheaths and Surface Behavior

Space charge and potential distribution at a surface

• Child's law solution of Poisson's equation
• Monoenergetic beam approach and Bohm criterion
• Langmuir solution
• Plasma potential
• Behavior for collisional media

• Dependence of V - I characteristic on EEDF
• Use as a diagnostic tool

• Characteristic electron and ion transit times
• Stochastic heating effects

• Time and energy distributions
• Frequency dependence
• Effects of pressure, power, etc.

VII. Reaction processes in plasmas

Collision processes and cross sections in typical process gases

Electron energy distribution functions and calculation of reaction rates

Excited species production, destruction and measurement

• radiative species
• actinometry
• metastable species
• saturation effects
• LIF

• dissociation
• recombination
• excited state chemistry
• effects of pressure and power

Influence of collisions on EEDF

.

VIII. Producing and Maintaining Plasmas

Ionization mechanisms

• electron neutral collisions,
• electron - excited state collisions,
• excited state - excited state collisions,
• Penning ionization, photoionization,
• heavy particle collisions,
• secondary emission,
• thermionic emission

• Diffusion
• Space charge effects and ambipolar diffusion
• Role of negative ions
• Diffusion in magnetic fields
• Transition to free diffusion
• Recombination
• electron - ion
• ion - surface
• Attachment
• electron - neutral

• DC and RF breakdown
• Townsend's ionization coefficients
• Paschen curve
• Parasitic discharges
• Frequency effects and microwave breakdown

• V - I relations in collisional (bulk) plasmas
• Capacitively driven RF discharges
• Inductively driven RF discharges

.

IX. Capacitively coupled RF discharges

Typical parameters and matching networks

Spatial / temporal dependencies of potential, density

Simple models, self biasing

Ion bombardment - energy / time / frequency/ power dependencies

Scaling, uniformity, control

.

X. Inductively coupled RF discharges

Characteristics, benefits, problems

Planar coupled discharge

• Skin depth
• Transformer coupled model
• Matching networks

Scaling, uniformity, control

.

XI. Wave coupled discharges

ECR

Helicon

.

XII. Additional process diagnostics and control issues

Multi-channel optical systems

End point detection

Mass spectrometry

Ellipsometry

Full wafer interferometry
 

Main Page	L.J.O. Vita	P.A. Lab	Presentations	Course Info.	Teaching On-Site	Consulting