  Background: To ensure consistent and high-quality semiconductor production at
future logic nodes, additional metrology tools are needed. For this purpose,
grazing-incidence small-angle X-ray scattering (GISAXS) is being considered
because measurements are fast with a proven capability to reconstruct average
grating line profiles with high accuracy.
  Aim: GISAXS measurements of grating line shapes should be extended to samples
with pitches smaller than 50 nm and their defects. The method's performance
should be evaluated.
  Approach: A series of gratings with 32 nm pitch and deliberately introduced
pitchwalk is measured using GISAXS. The grating line profiles with associated
uncertainties are reconstructed using a Maxwell solver and Markov-Chain Monte
Carlo (MCMC) sampling combined with a simulation library approach.
  Results: The line shape and the pitchwalk are generally in agreement with
previously published transmission small-angle X-ray scattering (SAXS) results;
however the line height and line width show deviations of (1.0 +/- 0.2) nm and
(2.0 +/- 0.7) nm, respectively. The complex data evaluation leads to relatively
high pitchwalk uncertainties between 0.5 nm and 2 nm.
  Conclusions: GISAXS shows great potential as a metrology tool for small-pitch
line gratings with complex line profiles. Faster simulation methods would
enable more accurate results.
