Applicability test for synchrotron radiation x-ray lithography in 64-Mb dynamic random access memory fabrication processes

Abstract

To evaluate the applicability of synchrotron radiation x-ray lithography (SRXL) in ultra-large-scale integration manufacturing processes, we simulate a part of a dynamic random access memory process using SRXL. Four levels of x-ray masks (field, gate, bit contact, and bit line), including fiducial patterns for coordinate/overlay measurement, alignment marks, and 0.4-μm-rule memory cells were fabricated using an i-line stepper. The maximum overlay error between the different level masks was 60–100 nm. In SRXL processes alignment errors of the x-ray stepper were 60–100 nm (3σ), and the overlay errors over a 20-mm-exposure field were 130–160 nm (‖mean‖+3σ) in most of alignment levels. Critical dimension control of 27–47 nm was obtained for gate length and contact hole diameter.