Theoretical research on suppression ratio of dynamic gas lock for extreme ultraviolet lithography contamination control

Abstract

Dynamic gas lock (DGL) is an important technology for contamination control of extreme ultraviolet (EUV) lithography. DGL prevents contamination diffusion from the dirty compartment into the clean one and allows passage of EUV light between compartments. A number of DGL structures have been proposed for EUV scanners. The suppression ratio is the key index of DGL, but there are few theoretical studies on it. Using the Péclet number to represent the suppression ratio just ignores the variable cross section of DGL and the effect of the total mass flow. A new suppression ratio formula is derived here based on the convection-diffusion equation, including the constant and variable cross section of DGL. In order to verify the theoretical calculation, an experiment is carried out on a self-developed DGL device, obtaining the gas flow utilization and suppression ratio of various mass flows. The results show that the suppression ratio increases exponentially with mass flow, which is consistent with the theoretical expectation. At the same time, the important influence of the convection segment has also been demonstrated. It is concluded that the theoretical approach can well predict the suppression ratio and provide structural design guidance for DGL, which has an important practical application value.