Occupational exposure to airborne nanomaterials: An assessment of worker exposure to aerosolized metal oxide nanoparticles in a semiconductor fab and subfab

ABSTRACT

This occupational exposure assessment study characterized potential inhalation exposures of workers to engineered nanomaterials associated with chemical mechanical planarization wafer polishing processes in a semiconductor research and development facility. Air sampling methodology was designed to capture airborne metal oxide nanoparticles for characterization. The research team obtained air samples in the fab and subfab areas using a combination of filter-based capture methods to determine particle morphology and elemental composition and real-time direct-reading instruments to determine airborne particle counts. Filter-based samples were analyzed by electron microscopy and energy-dispersive x-ray spectroscopy while real-time particle counting data underwent statistical analysis. Sampling was conducted during worker tasks associated with preventive maintenance and quality control that were identified as having medium to high potential for inhalation exposure based on qualitative assessments. For each sampling event, data was collected for comparison between the background, task area, and personal breathing zone. Sampling conducted over nine months included five discrete sampling series events in coordination with on-site employees under real working conditions. The number of filter-based samples captured was: eight from worker personal breathing zones; seven from task areas; and five from backgrounds. A complementary suite of direct-reading instruments collected data for seven sample collection periods in the task area and six in the background. Engineered nanomaterials of interest (Si, Al, Ce) were identified in filter-based samples from all areas of collection, existing as agglomerates (>500 nm) and nanoparticles (100–500 nm). Particle counts showed an increase in number concentration above background during a subset of the job tasks, but particle counts in the task areas were otherwise not significantly higher than background. Additional data is needed to support further statistical analysis and determine trends; however, this initial investigation suggests that nanoparticles used or generated by the wafer polishing process become aerosolized and may be accessible for inhalation exposures by workers performing tasks in the subfab and fab. Additional research is needed to further quantify the degree of exposure and link these findings to related hazard research.

KEYWORDS:

• Chemical mechanical planarization
• engineered nanomaterials
• inhalation
• metal oxide nanoparticles
• occupational exposure assessment
• semiconductor fabrication

Acknowledgments

The authors thank the management and employees of the participating companies and study site. Laboratory analysis was conducted by Galson Laboratories (East Syracuse, NY) and Bureau Veritas North America (Novi, MI) for mass concentration and by iATL (Mount Laurel, NJ) for TEM/EDS. Additional TEM and EDS analyses were conducted by Bureau Veritas North America (Kennesaw, GA). Special thanks also to Alan Segrave for on-site and phone discussions and guidance regarding sampling collection and preparation. Thank you to current and former members of the Brenner Research Team – Gary Roth, Ph.D., M.S. and Michele N. Shepard, Ph.D., CIH – for slurry nanoparticle characterization (G.R.) and work on previous qualitative and quantitative exposure assessments (M.S.).

Additional information

Funding

This work was supported by CDC-NIOSH grant OH-009990-01A1 and the NanoHealth and Safety Center, New York State, awarded to S.B.