Physics of Thin Films

PES 449 / PHYS 549

Introduction and Overview

Ohring: Historical Perspective p. xix

What is a "thin film" ?

thin = less than about one micron ( 10,000 Angstroms, 1000 nm)
film = layer of material on a substrate

(if no substrate, it is a "foil")

Applications:

microelectronics - electrical conductors, electrical barriers, diffusion barriers . . .
magnetic sensors - sense I, B or changes in them
gas sensors, SAW devices
tailored materials - layer very thin films to develop materials with new properties
optics - anti-reflection coatings
corrosion protection
wear resistance
etc.

Special Properties of Thin Films:

different from bulk materials
Thin films may be:

not fully dense

under stress

different defect structures from bulk

quasi - two dimensional (very thin films)

strongly influenced by surface and interface effects

This will change electrical, magnetic, optical, thermal, and mechanical properties.

Typical steps in making thin films:

emission of particles from source ( heat, high voltage . . .)
transport of particles to substrate (free vs. directed)
condensation of particles on substrate (how do they condense ?)

Simple model:

How do the variables effect film structure and properties ?

What physics is in all this ?

thermodynamics and kinetics
- phase transition - gas condenses to solid
- nucleation
- growth kinetics
- activated processes
  - desorption
  - diffusion
- allowed processes and allowed phases
solid state physics
- crystallography
- defects
- bonding
electricity and magnetism
- optics
- conductivity - resistivity
- magnetic properties
mechanics
- stresses in films
- friction and wear

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