In-situ measurement technique of contamination morphology under vacuum and low temperature condition

Molecular contamination phenomena depend on temperature. For example, the morphology of a contaminant can change from a uniform film to droplets. The authors believe that the surface morphology of thin-film contamination affects optical transmittance and reflectance of camera lenses and other sensors, so it is important to gain a better understanding of the morphology of contamination. The authors investigated a simple measurement technique to determine molecular contamination morphology in a vacuum and at low temperatures using a CMOS camera sensor chip. The CMOS camera operates down to −60°C, which covers our range of interest (i.e., from −60°C to room temperature). Furthermore, using a combination of the camera sensor and the optical measurement setup in a vacuum chamber, the morphology and optical transmittance were measured simultaneously. The advantages of the technique are that the equipment is inexpensive and can be installed in many chambers now in use.