Optimizing the detection efficiency of a low pressure, in-situ particle monitor using aerodynamic focusing lenses

P. Liu, N. P. Rao, David B Kittelson, Peter H McMurry

Research output: Contribution to journalConference articlepeer-review

5 Scopus citations

Abstract

The past few years have witnessed a growing trend in the semiconductor industry to use in-situ particle detectors to monitor contamination levels in processing tools used for device fabrication. Such in-situ particle monitors (ISPM) generally detect particles by laser light scattering and are typically mounted on reactor pumping lines. In some designs, the laser illuminates only a small portion of the flow passage, resulting in low particle detection efficiencies (0-25%). This paper presents a method for enhancing and optimizing the detection efficiency of these devices by using aerodynamic focusing lenses placed immediately upstream of the detector. These lenses consist of one or more thin-plate orifice elements concentric with the flow passage. The highly concentrated, narrow particle beams produced by this technique may be directed through the center of the laser viewing volume to increase the detection efficiency to near 100%. This has been experimentally verified for a TSI Model 7340 vacuum particle detector with laboratory generated aerosols over a range of pressures (0.2-10 torr) typical of many semiconductor fabrication processes.

Original languageEnglish (US)
Pages (from-to)217-224
Number of pages8
JournalInstitute of Environmental Sciences - Proceedings, Annual Technical Meeting
StatePublished - Dec 1 1996
EventProceedings of the 1996 42nd Annual Technical Meeting of the Institute of Environmental Sciences - Orlando, FL, USA
Duration: May 12 1996May 16 1996

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