Airborne molecular contamination (AMC) that can deposit on product and processing equipment is a growing concern in cleanrooms. Using a newly installed class 10 cleanroom in our laboratory, we have investigated the deposition of AMC on witness wafers. Since it was expected that more outgassing of construction materials would occur immediately after the cleanroom came on-line, a goal of the work was to evaluate how quickly this outgassing rate changed with time. Silicon wafers were exposed to the cleanroom environment for varying periods of time and were subsequently analyzed using Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). Because TOF-SIMS can be used to directly analyze wafer or product surfaces, it provides information about the types of AMC that adsorb onto surfaces of interest. In addition, ionic species such as halides and metals can be detected simultaneously. Molecular species, including silicones, phthalates, fatty acids, organic amines and alcohol amines are observed on the wafers. The relative intensities of most of these organic species reached a maximum approximately 1-2 months after the cleanroom came on-line. After that time, the intensities of these species actually decreased. Inorganic species detected included sulfur oxides and halides, along with the dopant species boron and phosphorus. These species typically reached an equilibrium concentration after 1-2 months, but did not show the same decrease that was noted for the organic compounds.
