OCD Enhanced: Implementation and Validation of Spectral Interferometry for Nanosheet Inner Spacer Indentation

Authored by: D. Schmidt, C. Durfee, S. Pancharatnam, M. Medikonda, A. Greene, J. Frougier, A. Cepler, G. Belkin, D. Shafir, R. Koret, R. Shtainman, I. Turovets, S. Wolfling | SPIE 2021, February 1, 2021

In this work, the novel enhancement to multichannel scatterometry data collection, Spectral Interferometry, is introduced
and discussed. The Spectral Interferometry technology adds unique spectroscopic data by providing absolute phase
information. This enhances metrology performance by improving sensitivity to weak target parameters and reducing
parameter correlations. Spectral Interferometry enhanced OCD capabilities were demonstrated for one of the most critical
and challenging applications of gate-all-around nanosheet device manufacturing: lateral etching of SiGe nanosheet layers
to form inner spacer indentations. The inner spacer protects the channel from the source/drain regions during channel
release and defines the gate length of the device. Additionally, a methodology is presented, which enables reliable and
reproducible manufacturing of reference samples with engineered sheet-specific indent variations at nominal etch
processing. Such samples are ideal candidates for evaluating metrology solutions with minimal destructive reference
metrology costs. Two strategies, single parameter and sheet-specific indent monitoring are discussed, and it was found
that the addition of spectroscopic information acquired by Spectral Interferometry improved both optical metrology
solutions. In addition to improving the match to references for single parameter indent monitoring, excellent sheet-specific
indent results can be delivered.
Keywords: OCD, Spectral Reflectometry, Spectral Interferometry, gate-all-around, nanosheet FET, indent, inner spacer