Pollutant inhibition in an extreme ultraviolet lithography machine by dynamic gas lock

Abstract

Dynamic gas lock (DGL) is an effective method to inhibit carbon deposition on optical surface in extreme ultraviolet (EUV) lithography machines. However, due to the complexity of the internal flow in DGL, relevant theoretical analyses remain incomplete. In this work, a direct simulation Monte Carlo (DSMC) method based on OpenFOAM platform is employed to study the transport process of rarefied gas in DGL and a project optics box (POB). The dsmcFoam + solver is extended and its applicability to DGL problems is verified. The results show that the number density of hydrocarbon in the POB decreases exponentially with the increase of the flow rate of clean gas, whereas the DGL inhibition rate is insensitive to the change of the pressure in the wafer chamber. Reducing the cone angle of the DGL, lowering the inlet position of the clean gas and using the clean gas with higher molar mass are all helpful to improve the inhibition effect of the DGL on the hydrocarbon diffusion. Additionally, the height of the DGL is relevant: with increase of the height, the inhibition rate rises at the same distance from the wafer surface; the number density of hydrocarbons is larger at higher heights. This study is expected to provide guidance for design of DGL technology under different EUV lithography conditions.