Beyond 3 sigma: roughness metrology evolution at the last 20 years (in memory of Ben Bunday)

The importance of Critical Dimension (CD) roughness metrics, including line edge and contact edge roughness (LER, CER) and their associated feature dimension metrics line width and contact diameter roughness (LWR, CWR), has been acknowledged in the semiconductor industry automatic process control (APC) at early stage of CD SEM (Scanning Electron Microscope) Metrology. The evolution of roughness metrology follows three strategical directions: the enhancing of roughness metrics for comprehensive automatic process control in advanced technological nodes, development of precise algorithms to remove apparatus bias for accurate roughness estimation and extensive search of roughness metrics related applications for yield increase through their use in Process Window definition. The roughness metrics development from the standard deviation based to the advanced measurements challenging by technology development for 3D NAND and under 20 nm nodes is described. The review of mutual developments in the apparatus bias removal for period from the seminal Ben Bunday paper devoted to the SEM shot noise bias removal from roughness measurements is presented. The developments in the roughness metrics generalization for complex shapes or non-elliptic/non straight lines features geometries include consideration of roughness spectrum metrics, analysis of local perturbations of general shape features, and general shapes roughness. The novel directions in the CD roughness metrology with using of Deep Learning for roughness analysis are considered.