Vacuum Cleanliness in the Semiconductor Industry

Alan Webb

Caswell

Semiconductor Processing

• Dry process techniques are fundamental in being able to produce the desired architectures required for today's and future semiconductor devices

• Economic considerations dictate large device

densities on wafers, implying smaller and smaller chips.

• As device sizes shrink, the need to work in cleaner

conditions becomes more apparent.

Completed Wafers – 2, 3 and 6”

High Yield – Low Cost

Smaller chip size - enhanced performance

Larger packing density - more chips per wafer

Contamination and cleanliness - becomes a major yield limiting factor

Protecting the wafer is the prime concern

A Bonded Chip

Layer Structures

Device Fabrication • Key Process Steps

• Lithography

• Etching

• Contact

technologies

• Annealing

• Dielectrics

• Implantation

Contamination and Cleanliness

• Minimise Contamination and Enhance Cleanliness

• Work in a controlled environment (e.g. a cleanroom )

• Tight specification of temperature, humidity and

particle control

• Temperature controlled to 1-2 °c

• Humidity within a 5% range

• Cleanroom designated “Class”

Cleanroom Specification

• Defined by “Class”, which is a particulate measurement

• US Federal Standard No. 209 (BSI BS 5295) “Environmental Cleanliness in Enclosed Spaces”

• A Cleanroom of Specification Class X has no more than X particles of size 0.5 μm present in a cubic

foot of air

• Example : Class 10 cleanroom Particle count NOT to exceed a total of 10 particles per cu. ft. of size 0.5 μm

Process Equipment in the Cleanroom

Process Equipment in the Cleanroom

Residual Gases

• The number of unwanted atoms and molecules within the environment can have a detrimental effect on dry processing.

• Both gas phase and surface effects can occur, which produce unwanted results.

• Poor quality etching could be the result or poor characteristic films could be produced.

Monitoring and Control In-situ measuring and monitoring Non obtrusive for example : Optical Emission Spectroscopy (OES) Residual Gas Analysis (RGA) A method that provides a unique “fingerprint” of the constituents within the plasma. This consists of the source gases, products of

surface interactions and contaminants.

Schematic of RGA Monitoring

Mass Spectrometry Data

Identification of Contamination

A Methane Hydrogen Etch Process

High Resolution Mass Scan

Batch Processing

Time Resolved ‘Specta’

Complex Features Realised

Chip-on-tile for Angled Waveguide Output

Summary

Lots of nothing is a vacuum A good vacuum implies good cleanliness Clean processes produces enhanced yield Greater yield gives greater profitability More profit means more money Lots of nothing making lots of money Good for Business !

All Clear ?

Questions ?