Thin Film, Evaporation Deposition

Question 1

Physical vapour deposition vs thin film deposition

Answer 1

PVD - condensation of hot vapour onto a cold surface
Needs a supersaturated vapour, exceeds the saturated vapour pressure of the evaporant at the temperature of the substrate

TFD - always limited by the kinetics of the situation (how far can diffuse before next atom comes)
Always insufficient energy to activate all processes and produce ideal material
Thin film properties are always non-ideal and different to bulk materials
Difficult to get good crystalline material from TF

Question 2

What are the three classifications of initial growth

Answer 2

1. Franck-van-der-Merwe (layer-by-layer) Surface energy prefers being spread
   Tension of surface greater than film
2. Vollmer-Weber (island growth) Tension of film greater than surface … more cohesion than adhesion
3. Stranski-Kranstanov (initial layer by layer followed by island growth) Component in the film is increasing and balance of adhesion and cohesion flips

Interplay of adhesion and cohesion

Question 3

Zone model

Answer 3

Z1 - shadowing dominates, voids, promoted by substrate roughness, oblique deposition, high deposition rates.
Decrease in mobility
T=30%melting point

Z2 - Competition between diffusion and deposition
dense columns
voids filled by diffusion atoms
Up to 50% melting point

Z3 - Isotropic grains
Deposited atoms can diffuse through film
Bulk like properties
More than 50% melting point

Question 4

Name the components of and describe pulsed laser deposition

Answer 4

Substrate heater stage and shutter
Laser
ceramic targets (carousel)

Can deposit compounds via congruent evaporation
Highly energetic technique (100 eV per atom)
Poor uniformity
Good for refractory metals

Question 5

What is evaporation depostion

Answer 5

Evaporant source is heated via crucible, boat source, wire source.
Source vaporises and travels across vacuum
until condenses on substrate which is cooler (also heated)

Question 6

Types of evaporation deposition

Answer 6

Knudsen effusion cell
e-beam evaporation

Question 7

What is e-beam evaporation. What are benefits

Answer 7

Electrons directed by magnetic field to be incident on evaporant source.

Question 8

3 types of evaporation source

Answer 8

Point source
Cylindrical source
Planar source

Question 9

Nucleation theory

Answer 9

Nucleation sites tend to be imperfections on substrate:
- kinks, dislocations, impurity, damage region

Impinging atoms may be absorbed directly or more probably following a period of diffusion

Question 10

What happens when two nuclei meet

Answer 10

Temp a significant fraction of the melting point they coalesce to reduce energy

If not they aggregate
leads to columnar growth