LONG-TERM MEASUREMENT OF MOLECULAR CONTAMINATION IN A CLEANROOM USING A TEMPERATURE-CONTROLLED QUARTZ CRYSTAL MICROBALANCE (TQCM)

摘要

TQCMs have been operated in the Spacecraft System Development and Integration Facilityrn(SSDIF) cleanroom at Goddard Space Flight Center (GSFC) since 1993 to provide a measure ofrnmolecular contamination. This has resulted in long term data that gives an indication of the rate ofrnmolecular contamination deposited on a surface (such as an optical mirror) and gives an indication ofrnfacility cleanliness. Long term trends in contamination deposition and facility cleanliness can berndetected by this method.rnOne TQCM has been operated at room temperature in the same location within the cleanroomrnwith the same controller, test cables, and computer for over six years. The cleanroom has beenrnmaintained at essentially the same temperature and relative humidity during this period. A secondrnTQCM has been operated at different locations within the cleanroom with different cables, but duringrnperiods of constant operation it has shown a similar rate of accumulation.rnData collected over the six year period shows an average increase of about 30 Hz per year for 15rnMHz TQCMs with a sensitivity of 1.56 x 10~(-9) gms/cm~2/Hz. This equates to a mass accumulation ofrn0.047 x 10~(-6) gms/cm~2 per year which is about one 20th of that allowed for MIL STD 1246 Level A (1.0 xrn10~(-6) gms/cm~2). The accumulation rate has been relatively constant over the six years.rnAnalysis of the contamination deposited on the TQCM surface was performed using FTIRrn(Fourier Transform Infrared Spectroscopy) and GC/MS (Gas Chromatography/Mass Spectroscopy). Thernresults show typical cleanroom molecular contaminants detected over the years by other means (witnessrnmirrors and collection plates).