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Airborne Molecular Contamination: The Not-So-Fun and Costly Side of Semiconductor Fabrication

It’s a painstaking, arduous process to mass manufacture the silicon chips for your electronic devices.

By: Richard Xu

This is a macro of a silicon wafer. Each square is a chip with microscopic transistors and circuits. Wafers like these are diced into their individual chips which go into the processors that power our computers.

Photo and Caption by Laura Ockel on Unsplash

Though technology such as computers, smart TVs, and cell phones have become intimate companions of our everyday lives, most of us aren’t really aware of the intricacies involved in the hi-tech semiconductor manufacturing process that brings these electronic devices to existence.

It all starts in the semiconductor fabrication plants, or FABs. These clean artificial environments are closely monitored for their air composition and temperature to create the ideal conditions for chip manufacturing to take place contamination-free. Most chip manufacturers have ‘ISO Class 1’ air quality rated environments, meaning that they are required to do 500-750 air changes with a ceiling coverage of 80-100%. In addition, there can be no more than 10 particles between 100 and 200 nm in size per cubic meter of air, and none larger than 200 nm. For reference, a clean, modern hospital has about 10,000 dust particles per cubic meter. If dust finds its way onto a silicon wafer, the wafer could potentially be rendered void, i.e. scrapped.

This sensitive manufacturing process typically involves stacking hundreds of different material layers with extreme nanometer precision utilizing lithography and gas etching processes. With the delicate precision and frantic cleanliness required, it is understandable why manufacturers undertake such drastic measures to maintain steady-state conditions and prevent any detrimental contamination.

A Front Opening Unified/Universal Pod or FOUP. They are used to transport silicon wafers safely within the environment.

Throughout the entire process, manufacturers use Front Opening Unified/Universal Pods, or FOUPs, which is a specialized plastic carrier used to transport stacked silicon wafers in the FAB environment via the over-head transportation system, quite reminiscent of a gondola transporting a group of people between mountainous locations.

How the Over-head Transportation (OHT) system moves FOUPs

The challenge is that the emissions from some of the gas etching processes in one part of the FAB environment will get absorbed by the FOUP’s internal storage components. This means that when the FOUP transports new silicon wafers, those residual contaminant gasses within the FOUP, aka Airborne Molecular Contamination (AMC), will taint the wafers; this is known as cross-contamination. Cross-contamination will lead to wafers’ scrapping, hence, an economic loss, time delays, and lower yields due to the corrosion of metal connections, formation of silicon crystallites, and haze on the surface of the wafers. These effects only worsen the yield as the chip technology becomes smaller and more susceptible to contamination as a tradeoff to be more advanced. Again, a lower wafer yield translates into higher production cost and waste of precious production time.

The state-of-the art approach that Nikira Labs has developed to monitor the FAB for AMC are open-path FOUP-borne, lightweight analyzers that detect parts-per-billion quantities of gas contaminants in real-time to alert the operators in case the action-level thresholds have been reached or exceeded. This early detection activity will prevent wafer loss, save production time, and overall bolster the FAB efficiency and yield rates.

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