200-mm EPL stencil mask fabrication and metrology at DNP: IP and CD accuracy within subfield

Abstract

Electron beam projection lithography (EPL) has been developed for application to 65 nm node devices and beyond. 200-mm EPL masks have also been developed keeping pace with the exposure tool. Image placement (IP) accuracy is a necessary quality assurance item to bring masks into production. A suspension type electrostatic chuck designed for EPL mask measurement for an IP metrology tool Leica LMS IPRO was prepared for measurement of local IP errors, defined for each subfiled. The chuck holds the mask on its membrane-side surface right side up. Three 200-mm stencil masks with tensile membrane stresses of 8, 18, and 43 MPa were fabricated. The IP error is found to increase as the stress increases. Marks in the area of a high pattern density with a void fraction of 0.2 moved toward the area of a low pattern density with a void fraction of 0.016. The IP errors did not strongly depend on the kinds of dummy patterns (either hole or L&S) having the same void fraction of 0.25 and macroscopic uniformity. If the stress is less than 10 MPa, the IP error (3 sigma) is less than 10 nm, satisfying the EPL mask requirement. Local CD accuracy was also evaluated for a mask with a membrane stress of 8 MPa.