Abstract
As the lithographically manufactured nanostructures are shrinking in size, conventional techniques, such as Scanning Electron Microscopes and Atomic Force Microscopes reach their resolution limits [1]. Novel inline scatterometry techniques not only provide the opportunity to bridge this gap, but they can also advance characterization of the lithographic process. The particular, Critical-Dimension Grazing incidence Small Angle X-ray Scattering (CDGISAXS) has emerged as one such promising modality to extract the profile of line gratings [2]. With the advent of brighter x-ray sources with tunable energies and faster detectors, there is a possibility for combining fast X-ray acquisition with high-speed data treatment to reach the timescale for an effective in-line characterization method.
Due to recent progress in the ability to model data acquired from CD-GISAXS, we extended our model in order to study the impact of roughness. A set of twelve samples were studied. First, periodic line edge roughness (LER) and line width roughness (LWR) were measured, leading to the apparition of several semi-circle of Bragg spots as illustarted on Figure 1a. Using HIpGISAXS software, the GISAXS patterns were reproduced, allowing the extract of the periodicity of the roughness.
On the second part of the line gratings, aperiodic roughness were designed with different frequencies and amplitudes. These samples led to the superposition of a semi-circle of Bragg spots with a “palm tree” feature coming from the profile of the gratings, illustarted on figure 1b. In a fist step, we extracted the in-depth profile of the gratings by fitting the modulations of the palm tree, in a similar approach as the CD-GISAXS one. In a second step, we modeled the impact of the roughness on the CD-GISAXS pattern and proposed a model to extract the roughness amplitude and frequency.
References:
[1] ITRS (2013). International Technology Roadmap for Semiconductors, http://www.itrs.net/.
[2] Freychet, G. et al. (2018) Proc. SPIE, 10585, 1058512.
[3] Freychet et al. (2018) Nanoscale Horizons, submitted.
[4] Chourou, S. T., Sarje, A., Li, X. S., Chan, E. R. & Hexemer, A. (2013). J. Appl. Cryst. 46, 1781–1795.
