High resolution profiles of 3D NAND pillars using x-ray scattering metrology

Abstract

High-performance memory production requires discovery of process anomalies that affect device performance. Optical metrology can monitor CDs of device structures, but has limited resolution for 3D NAND, especially towards the bottom of high aspect ratio (HAR) structures. Destructive, offline techniques (e.g., cross-sectional SEM, FIB, TEM) can be used for high resolution HAR profile measurement, but are time consuming, offering little statistical feedback for accurate process control. As an alternative, small angle X-ray scattering (CD-SAXS) can measure 3D HAR structures precisely and non-destructively. CD-SAXS has high sensitivity to 3D profiles, including profiles of CD, ellipticity and tilt through the entirety of the channel hole. CD-SAXS is non-destructive and used inline, providing fast time to results for efficient process characterization. In this paper, we will show data from a CD-SAXS system, including high-resolution CD, ellipticity and tilt profiles, and etch depth of 3D NAND channel holes with strong correlation to reference metrology. With this production-ready CD-SAXS system, flash memory CD profiles can be monitored inline for improved time to an optimized channel etch process.