Origins of sample-surface contaminants in loadlock chamber

The sample contamination in a loadlock chamber, caused by particle sticking, adsorption of gas and moisture in a loadlock chamber and back stream from pumping systems, was investigated. In order to eliminate the first two sources of contamination, a clean silicon sample was prepared in a glove box filled with particle-free nitrogen gas, and the sample was transferred to the loadlock chamber without exposing to air. To observe the contamination during pumping, the last source of contamination, a clean sample was set in the loadlock chamber and after evacuation surface contaminant was evaluated by C1s intensity of XPS spectra. Several evacuation procedures were compared and we concluded that oil-free pumping system is essentially important for contaminant-free introduction of a clean sample.