Critical dimension AFM tip characterization and image reconstruction applied to the 45-nm node

Abstract

Three significant critical dimension atomic force microscopy (CD AFM) advances are presented in this paper. First, scanning probe image reconstruction methodologies that were formerly limited to parabolic type tip shapes and single-valued surfaces (i.e., non-reentrant topography), are extended to multi-valued surfaces and reentrant tip geometries. This crucial step allows the elimination of image artifacts associated with CD AFM scanning of complex feature shapes using reentrant tips. Second, in situ AFM tip images are provided in an automated tool that enables full image reconstruction. Consequently, for the first time, the combination of in situ tip reconstruction with the inherent reference measurement qualities of the AFM and full morphology reconstruction allow CD AFM metrology essentially free of tip shape effects. CD AFM is now primarily driven by development of tip geometries that contact the entire specimen surface while retaining adequate tip lifetime. The background of CD AFM image dilation is described, and the limitations of legacy 1D image reconstruction width subtraction) are illustrated with idealized probe shapes. Initial validation of the automated software is provided by comparison with TEM micrographs. Tip characterizations are presented for a morphologically complex ~20 nm diameter carbon nanotube tip and reentrant silicon CD32 tips (tip width ~ 30nm). Finally, the capability for CD AFM to scan a reentrant sub-45 nm width trench is demonstrated. An EUV resist trench was scanned with a CD32 tip (tip width = 27.4 nm). Minimum CD ranged from 42 to 45 nm. Reentrant image reconstruction is shown for the scan cross-section.