The effect of the recess shape on performance analysis of the gas-lubricated bearing in optical lithography

Gas-lubricated bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. As the extreme precise positioning accuracy of these equipments has reached nanometer level, and almost approaches the physical limit, the effect of the recess shape of the gas bearings cannot be neglected any longer. This paper studies the effect of the recessed shape of the bearing on the performance analysis through numerical method. The pressure distribution, as well as the loading capacity and mass flow rate for the case of different shape (no pocketed bearing, rectangular shape and spherical shape bearing, respectively) of the bearing is achieved with the well-known CFD-control element procedures in Quad meshes. The results show that the average loading capacity reduces as the following sequence: rectangular recessed bearing, spherical recessed bearing and non-recessed bearing. The mass flow rate in the bearing with spherical recess is smaller than that of with rectangular recess, and bigger than that of with non-recess. Vortexes, which can cause higher temperature in gas film, are also found in the spherical recess or rectangular recess. It means that only the bearing with non-recess is fitted to use in ultra-high precision equipments.