Wafer process-induced distortion study for x-ray technology

X-ray synchrotron radiation is a promising source for submicron lithography. For x-ray lithography to be a useful technology, the combined overlay for the mask, stepper, and wafer processes must be less than that required by the product device specification. X-ray lithography uses a 1× proximity printing technique. Unlike n× optical stepper lithography, a lens cannot be varied nor can a reticle be moved to correct for magnification distortions due to wafer processes. Wafer processes (such as film formation) stress the wafer, causing pattern-magnification distortion and wafer warpage. This paper examines the process’ contribution to the overlay tolerance. Several wafer experiments have been performed using simulated 64 Mbit dynamics random access memory (DRAM) processes. Test wafers, etched with periodic ‘‘L’’ image measurement targets, were both hot processed and trench processed. The ‘‘L’’ targets on the wafers were measured using a long-distance xy measurement system and wafer flatness system. The measurements, before and after each process, show the wafer-induced distortion. One of the experiments discussed in this paper is a hot process used for gate oxidation. This rapid-thermal-oxidation-furnace experiment generated less than 2 ppm distortion. Other examples of hot-process distortion and trench-process distortion data are presented.