Global tilt extraction for BEOL contact landing displacement control

Abstract

3D NAND has become mainstream storage devices in a past decade and the stacking cell layers now reaches to more than 300 layers. As stack gets higher, more and more etching process challenges are brought into 3D NAND high aspect ratio (HAR) structure patterning. Among the HAR etching processes, the deep contact etches in the back-end-of-line (BEOL) are patterned after other HAR structures such as channel holes, deep trenches or other dummy patterns. Any unexpected overlapping of deep contacts with other patterns would lead to fatal product yield loss due to such wrong circuit connections and leakage currents. Hence, a reliable and fast monitoring methodology for profile tilting is extremely important.In this article, it is first time to demonstrate the employment of the small angle X-ray scattering (SAXS) technology and global tilt extraction (GTE) by using Axion @TM from KLA-Tencor to measure bottom tilting behavior for deep contact structure in 200+ layers of 3D NAND product. As regarding for the necessaries of gathering layout pitch, detail film stacks and hole dimensions by regular model base approach, the GTE is a pure modeless method by using X-ray scattering images to determine the central point shifting of the bottom relative to the topmost on the target pattern. With GTE help, the development cycle time for etch recipe tuning and BEOL process optimization is effectively improved, as well as demonstrating better process control to sustain product yield.