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Distributed Sensors for the Detection of Moisture in Gases

IP.com Disclosure Number: IPCOM000019400D
Publication Date: 2003-Sep-12
Document File: 2 page(s) / 33K

Publishing Venue

The IP.com Prior Art Database

Abstract

The semiconductor fabrication industry has stringent specifications on the purity of inert gases used in the fabrication process. Typical specifications require < 1 ppb of impurities like H2O, O2, CO2 , CH4 etc. in inert gases like Ar, N2, H2, O2. As the linewidths of the fabricated devices continues to shrink, it is anticipated that the specifications will become tighter and will approach 100 ppt. The advances in analytical instrumentation has made it possible to analyze for impurities at < 1 ppb, albeit at a high cost. Atmospheric Pressure Ionization Mass Spectrometry(APIMS) is capable of achieving limits of detection at levels below 100 ppt. However APIMS instrumentation is very expensive and bulky.

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Distributed Sensors for the Detection of Moisture in Gases

The semiconductor fabrication industry has stringent specifications on the purity of inert gases used in the fabrication process. Typical specifications require < 1 ppb of impurities like H2O, O2, CO2 , CH4 etc. in inert gases like Ar, N2, H2, O2. As the linewidths of the fabricated devices continues to shrink, it is anticipated that the specifications will become tighter and will approach 100 ppt. The advances in analytical instrumentation has made it possible to analyze for impurities at < 1 ppb, albeit at a high cost. Atmospheric Pressure Ionization Mass Spectrometry(APIMS) is capable of achieving limits of detection at levels below 100 ppt. However APIMS instrumentation is very expensive and bulky.

In order to maximize the benefit from an APIMS instrument one can, in principle, locate the instrument at a fixed place within a semiconductor fabrication facility and pipe samples from different locations. This strategy can work for impurities that do not interact with the surfaces of the sampling lines. Unfortunately moisture exhibits very strong interaction with the surfaces of the sampling line. Thus small transient changes in the moisture concentration at the sampling point will be totally damped out by the sampling line. Thus even if there is an actual transient change in the moisture concentration the APIMS will not detect any change in moisture level. If there is a change in the moisture concentration, there will be a large delay before the APIMS will detect the change, with the delay depending upon the length and nature of the sampling line.

In order to remove the effect due to the interact...