Oxygen-free from A to B

Article of 29 April 2020 

Oxygen-free transport of wafers

Whether for sensors and electronics for vehicles, smartphones, energy-saving lamps or refrigerators, semiconductors are indispensable in many electrical devices. Wafers play an important role in semiconductor production. The approximately one-millimetre thick discs act as a base plate for electronic structures and elements such as circuits or photoelectric coatings. The challenge is transporting the wafers oxygen-free and storing them. But a solution has been found: a container with a permanent and constant supply of nitrogen.

For use in sensors, computers, food processors and the like, wafers are obtained from a block of raw material, the so-called ingot, and then processed into microchips. The discs are usually made of a semimetal, such as silicon. Great caution is required when processing semiconductors. Since elements measuring in the micro- or even nanometre range are applied, no impurities whatsoever may get onto the discs. Even a single human hair or flake of skin can render the end product unusable. As such, strict clean conditions in a clean room must be observed at all times.

Oxygen-free transport in FOUP

Particular care is required when transporting the discs from one processing station to the next. As soon as the wafers come into contact with oxygen, they oxidize and become unusable.

The discs are transported in a Front Opening Unified Pod, called FOUP for short. This special container is specially designed for transport in a clean room. The FOUP is permanently supplied with nitrogen and is therefore oxygen-free. It is important that the nitrogen supply is constant over the entire period. Even small fluctuations can destroy the sensitive wafers.

Constant nitrogen supply with the N2 purge system

Festo’s solution is the N2 purge system, which ensures a constant nitrogen supply to the containers. A pre-assembled flow controller continuously supplies the FOUP with inert nitrogen. A piezo valve and a flow sensor allow for an exact and energy-saving flow of nitrogen using coordinated control technology.

Festo’s N2 purge system prevents oxygen from oxidising the wafers.
Festo’s N2 purge system prevents oxygen from oxidising the wafers.

Furthermore, the design of the piezo valve reduces the risk of contamination of the gas flow by particle abrasion. The peak value is about one particle the size of 0.1 micrometre per circuit, whereas conventional solutions produce five times the particle content. In this way, a constant nitrogen supply is ensured throughout the process.