1 .Yield
Process is expensive and must be done in large quantities (batch processing)
yield = nombre de devices qui fonctionnent réellement en provenance du même wafer. (microparticules contaminent certains devices)
Miniaturisation
Everything becomes smaller but external contamination by particles is a bigger problem
particule size > 1/3 structural dimension = destruction of the component is likely
2. Contaminations & defects
Main contamination sources
Main contamination occurs via particles but also chemical contaminants that are invisible under microscope
Defects caused by particles
Interruption of conductive path or short-circuit
Incorrect lithography
incorrect thermal oxidation
incorrect spin coating
incorrect coating deposition
A wafer exposed to normal air will be completely contaminated
Particle diffuse on the surface of the wafer
How to avoid disturbing particles ? → use a clean room
Defects caused by chemical contamination
Chlorine atom react with water → HCL and dissolve layers
3. Cleanrooms
How to measure number of particules: with light diffusion (measurement of scattered light)
Principles
Multiple zone : black, grey , white with different classes
Reduce number of people
Don’t move
clean tools and materials when entering (with alcohol, wet chemistry process)
behavior is crucial
Air processing
Air is cleaned via filters and heat, humidity saturation and humidity removal
Temperature and humidity is controlled
Particle sources
Body: hair, grease, breath, sweat
Clothing: particles, fibers
Cosmetic: doping metals
Jewellery: metal particles