| AVS 59th Annual International Symposium and Exhibition | |
| Vacuum Technology | Tuesday Sessions |
| Session VT-TuP |
| Session: | Vacuum Technology Poster Session and Student-built Vacuum System Poster Competition |
| Presenter: | J.Y. Lim, KRISS, Republic of Korea |
| Authors: | J.Y. Lim, KRISS, Republic of Korea W.J. Kim, KRISS, Republic of Korea S.H. Nam, KRISS, Republic of Korea S.Y. In, Korea Atomic Energy Research Institute, Republic of Korea D.Y. Koh, Korea Institute of Machinery and Materials, Republic of Korea W.S. Cheung, KRISS, Republic of Korea |
| Correspondent: | Click to Email |
Advanced industrial processes such as semiconductor and display manufacturing continuously requires the precise measurement and control of the low mass flow of gases. The requirements include very low mass flows of less than 1sccm or 2 x 10-2 mbar∙l/s. However, the lower limit of traceable mass flow ranges are not well defined even in the sophisticated NMIs (National Measurement Institute). Since the primary standard for mass flow (kg/s) must provide a method for deriving mass flow directly from its base units, almost all mass flow systems heavily rely on the gravimetric method. Current technical measurement limit of mass flow rate with the gravimetric method is 2 x 10-8 kg/s (10-2 ~ 10-3 mbar∙l/s).
Ensuring mass flow traceability ability in the range of greater than 102 mbar ∙ l/s with the Korea Research Institute of Standards and Science (KRISS) standard system, an attempt to trace the lower mass flows down to 10-4 mbar ∙ l/s has been undertaken with constant volume flow meters (CVFM), sonic nozzle systems, and orifice method. In this work we briefly demonstrate the systematic attempt for the completion of the traceability chain from 104 to 10-4 mbar ∙ l/s.
Meanwhile the most effective way of ensuring completion of the traceability chain is, to say, characteristics monitoring of the mechanical rotary machines such as vacuum pumps used in advanced industry since these pumps have normally clean and smooth pumping capabilities during their stable operation.
Utilizing the combined mass flow systems mentioned above, the measurement of pumping speed has been performed with the throughput and orifice methods dependent on the mass flow regions. However, in the HV range of the molecular flow region, the high uncertainties of the gauges, mass flow rates, and conductance are too critical to precisely accumulate reliable data. In order to solve the uncertainty problems of pumping speeds in the HV range, we introduced an SRG with 1 % accuracy and CVFMs to measure the finite mass flow rates down to 10-3 mbar ∙ l/s with 3 % uncertainty for the throughput method. In this way we have performed the measurement of pumping speed down to less than 10-6 mbar with an uncertainty of 6 %. In this article we suggest that the CVFM has an ability to measure the conductance of the orifice experimentally with flowing the known mass through the orifice chambers, so that we may overcome the discontinuity problem encountering during introducing two measurement methods in one pumping speed evaluation sequence.