Development of a nondeforming chucking technique for EUV lithography

Abstract

Extreme ultraviolet (EUV) lithography has edged closer to practical use as the next-generation exposure technique for replicating 10-nm-order patterns. Since this replication takes place in a vacuum, the mask and wafer are usually clamped by electrostatic force. However, an electrostatic chuck has the following limitations: the force is smaller than the vacuum force, dust adheres to the tops of the chuck pins, and deformation occurs during chucking. The authors have developed a new nondeforming chucking technique that does not use electrostatic force or vacuum force and does not damage the contact surface. This paper describes the principle and features of this nondeforming chucking technique and evaluates the cooling temperatures required to solidify the freezing liquid and fix the quartz substrate using the finite element method. The various forces between the quartz specimen and the pin and the deformation of the quartz wafer due to chucking are also discussed. By lapping the pin tops after coating with oil repellent, the average shear strength of a 10-mm-square quartz specimen on a 0.5-mm-diameter, 2-mm-pitch pin chuck was increased to 5.1±0.9N/cm2, which is more than 1000 times for the acceleration force. The deformations after being fixed with the above pin chuck were less than ±0.15μm for a 100-mm-diameter, 1.2-mm-thick quartz wafer, with a maximum convex warpage of 8μm. It was concluded that the 6-mm-thick, 152-mm-square quartz mask with a thermal expansion coefficient of 5×10−9/K can be clamped without deformation at temperatures below 50°C using the new freezing pin chuck with the pitch of 2mm.