According to Deloitte, we can expect the global shortage of semiconductor chips to continue well into 2022 as supply catches up with rising demand. Manufacturing these highly sought-after chips requires very precise manufacturing conditions where noise, vibration, and dust are kept to a minimum. Here, Chris Johnson, managing director at specialist bearings supplier SMB Bearings, explains the crucial part that bearings play in the manufacturing of semiconductor chips.
Semiconductor chips store data and programs on almost every modern digital device that we use — whether this is a smartphone, our work computers, or games consoles. According to ASML, in 2020, more than one trillion chips were produced around the world, which equates to about 130 chips for every person on earth. Despite their ubiquity in the products we rely on, the manufacturing process is complex and requires precision.
Manufacturing any chip involves multiple processes. First, silicon wafers are sliced and polished before being covered with a light-sensitive “photoresist” coating. The chip wafer is then inserted into a lithography machine where it’s exposed to deep ultraviolet (DUV) or extreme ultraviolet (EUV). Once the degraded resist is removed, the necessary patterns are etched in the wafer. After the components have been fabricated onto the wafer, they are diced into dye, tested, and packaged. Bearings can be found on various semiconductor processing equipment, and their configurations will facilitate the specific process involved.
To accomplish this complex production process, manufacturers must operate in delicate working conditions in the form of cleanrooms. The environment must be enclosed, with airborne particles, room temperature, air pressure, noise, and lighting all tightly controlled. The site will often be compliant with ISO 14644-1 Class 5 or lower, which specifies a minimum allowed particle count of 3,520 particles 0.5µm or smaller. Cleanrooms must also comply with ISO 14644-2 and any industry-specific requirements.
Semiconductor fabrication plants need to conform to the most rigorous protocols. A single wafer can go through as many as 200 steps before it reaches industry standard, which means the production site must be completely sterile, with the air free of particulates that could damage the chips.
Meeting these stringent industry standards means installing powerful cleanroom heating, ventilation, and air condition (HVAC) and filtration systems to purify and circulate the air to remove any particles up to the allowed limits. Furthermore, some machines in these cleanrooms may come with their own exhaust systems to also remove unclean air and particles.
Airborne molecular contamination (AMC) is a concern in precision manufacturing, especially when producing microelectronics like semiconductors. The release of vapor from equipment materials in cleanrooms, like silicon, germanium, and gallium arsenide, is the most significant contamination source for volatile organic compounds (VOC), which can negatively impact production tools and increase costs.
Maintaining steady semiconductor production means constantly monitoring AMC levels to identify contamination sources and prolong the service life of the cleanroom’s equipment and filtration units. The choice of bearing material and lubricant can help facility managers avoid complications by minimizing outgassing potential. In terms of material, we recommend using stainless steel for vacuum or cleanroom applications because it exhibits low outgassing. Although nitrile rubber is often a popular choice, there can be issues if surfaces are sensitive to contamination. Plastic bearings made from PEEK and full ceramic silicon nitride alternatives maybe be considered but the choice will depend on the application’s requirements.
If we turn to lubricants, most greases will often vaporize, contaminating the environment and preventing the grease from lubricating sufficiently. Those working in semiconductor manufacturing environments should select special low-volatility, perfluorinated greases with low outgassing rates since these are designed for cleanroom conditions. If the machinery is operating at low speeds, using no lubricant at all, or opting for a “dry” lubricant like molybdenum disulfide is also an option.
The heating, cooling and filtration processes used to achieve the clean air needed means investing in pumping, pipes, ducts, and fan systems — all of which generate unwanted vibration unless sufficiently isolated. Vibrations both in and outside a cleanroom can severely impact the final image transposed onto the wafer.
High-quality bearings, correctly matched to the application, are essential to minimize excess noise and vibration. In cleanrooms, they must be low noise to prevent disruptive vibration that could disturb highly sensitive machinery, like lithography machines. Rough or damaged balls or raceways, poor roundness, and inadequate lubrication all create noise that can impede semiconductor production. Therefore, regularly monitoring surface finish and the roundness of the balls and bearing rings is a must.
As with outgassing, the choice of lubrication is also critical for controlling vibration. We suggest using finely filtered low noise greases since these contain fewer, smaller solid particles that generate noise when they pass between the balls and raceway.
If the dicing equipment, probing machine, or other equipment is being used for long periods of time, a low noise lubricant is also recommended to keep the bearing running quietly and maintain rollability. The choice of lubrication should be carefully considered based on the cleanroom’s internal environment and temperature, and the application’s speed requirements. In the event that bearings are inadequately lubricated, or filled with the incorrect grease, manufacturers should contact a supplier like SMB Bearings, who can offer relubrication services to prevent outgassing and disruptive noise.
The global shortage of semiconductor chips may be destined to continue into 2022, but making small changes at the mechanical level can help manufacturers stay on track by preventing machine downtime and unplanned rework caused by disruptive surroundings. Selecting low noise bearings and applying the necessary lubrication can help facility managers and engineers in semiconductor fabrication plants avoid disturbing highly sensitive equipment, limit outgassing, and maintain a steady semiconductor production at a time when the industry desperately needs resilience.