Real-Time Fab-Wise Airborne Molecular Contaminant (AMC) Monitoring System Using Multiple Fourier Transform Infrared (FTIR) Spectrometers in a Semiconductor Plant

Abstract

The objective of this study was to investigate the airborne pollutant emission sources and fluctuations around the indoor and outdoor environments of a semiconductor manufacturing plant using monitoring data that were collected over 4 consecutive days via three Fourier transform infrared (FTIR) spectrometers located near an outdoor make-up air unit and an indoor Fab and sub Fab. Based on a total of 1,032 five-minute-interval records, fourteen chemicals were detected. Six of these chemicals, namely, carbon tetrafluoride, nitrous oxide, carbon monoxide, silane, sulfur hexafluoride, and methane, had significant concentration correlations between the indoor and outdoor environments. With the exception of silane and sulfur hexafluoride, the percentage of indoor/outdoor concentration ratios that were greater than one ranged from 62.2% to 73.1%, indicating that the indoor chemical concentrations were typically higher than the outdoor concentrations. Based on the regression models derived for the indoor and outdoor nitrous oxide concentrations, the nitrous oxide was believed to be originally emitted from the sub Fab vented to the outdoors and then partially returned to the Fab. It was estimated that for one ppb of nitrous oxide detected in the Fab, 2.58 ppb of nitrous oxide could be detected at the make-up air unit, which might result from the sub Fab emission being at a high level of 6.60 ppb. Furthermore, elevated outdoor concentrations of chemicals, such as carbon tetrafluoride, nitrous oxide and carbon monoxide, were observed without previous indoor emission peaks, indicating that these chemicals might accumulate in the outdoor surrounding area. This study successfully illustrated the dynamically changing relationship between indoor and outdoor chemical concentrations in a semiconductor clean room. These results can be used to prevent subtle and potential adverse impacts of airborne molecular contaminant (AMC) in various manufacturing facilities of technological industries, including the semiconductor and optoelectronics industries.