Portable Vacuums found to be mobile particle generators at Semiconductor Manufacturing Facility

History

Semiconductor Manufacturer identifies a transient particle issue detected via remote automated room particle sensors. Several remote particle counting sensors that detect and record particle levels at critical locations within the facility are monitoring particle levels by collecting One-CFM data samples in real time at 10-minute intervals at locations across the facility. Out-of-spec excursions are observed at random locations on a weekly basis in areas that normally have very low or zero particle excursions. There is no obvious pattern to these excursions.

Scope

One Source Environmental was tasked with conducting airborne particle counting throughout the facility with the goal of identifying sources of contamination. On the third day of airborne particle counting our technician encountered housekeeping performing routine cleaning within the cleanroom. A portable vacuum was being used near our sensor and particle levels were off the charts. The Technician asked the housekeeper to turn “off” the vacuum while maintaining the active particle counter at the same location and within minutes the particle levels recovered to their intended design conditions. The Technician then had the housekeeper turn the vacuum back “on’ and continue with her work while he watched the particle levels rise to unacceptable levels once again.

The vacuum being used was a generic HEPA vacuum that did not completely encapsulate both container debris and motor particulate using a total vacuum HEPA filtration system. In other words, the vacuum was not designed for use in a Cleanroom. As the vacuum was innocently being used around the facility, it was acting as a transient particle generator.

Conclusions

An evaluation of all portable vacuums being used within the facility was accomplished which found that many different so called HEPA vacuums were being used by different entities throughout the site. Each different brand was subsequently tested, and it was discovered that only Nilfisk portable GM-80 vacuums were performing at the desired cleanliness levels.

Subsequently, facilities management instituted a rule that only Nilfisk vacuums with ULPA filters were to be used within the “Cleanroom” areas of the facility. Also, a requirement was established that both Company and Vendor vacuums were to be “Certified” on an annual basis with labels affixed to the units demonstrating Certification date and due date was also instituted.

After implementation of these procedures the random particle excursions ceased.