Yoshinori Kinase

Evaluation of image placement of EPL stencil masks

200-mm stencil masks for electron beam projection lithography (EPL) have been developed. Since they are not so rigid as photomasks because of their structure, 200-mm wafers with about 8,000 membrane windows, new metrological techniques dedicated to stencil masks have be introduced. Image placement (IP) accuracy of an EPL mask is evaluated with a suspension-type electrostatic chuck introduced to a Leica LMS IPRO. The dynamic repeatability of global IP measurements was 27 nm (3σ). It was confirmed that global IP errors were reduced to 60 nm (3σ, max) by linear-term and gravity corrections.

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

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.