Vertical travelling scatterometry for metrology on fully integrated devices

ABSTRACT

In this work, a novel spectral interferometry technique called vertical travelling scatterometry (VTS) is introduced,
demonstrated, and discussed. VTS utilizes unique information from spectral interferometry and enables solutions for
applications that are infeasible with traditional scatterometry approaches. The technique allows for data filtering related to
spectral information from buried layers, which can then be ignored in the optical model. Therefore, using VTS, selective
measurements of the topmost part of an arbitrarily complex stack are possible within a single metrology step. This
methodology helps to overcome geometrical complexities and allows focusing on parameters of interest through
dramatically simplified optical modelling. Such model simplifications are specifically desired for back-end-of-line
applications. Three examples are discussed in this paper: monitoring (i) critical dimensions of a first metal level on top of
nanosheet gate-all-around transistor structures, (ii) the thickness of an interlayer dielectric above embedded memory in the
active area, and (iii) critical dimensions of trenches on top of tall stacks in the micrometer range comprising many layered
dielectrics. It was found that, in all three cases, data filtering through VTS allowed for a simple optical model capable of
delivering parameters of interest. The validity and accuracy of the VTS solution results were confirmed by extensive
reference metrology obtained by traditional scatterometry, scanning electron microscopy, and transmission electron
microscopy.
Keywords: Vertical Travelling Scatterometry, Scatterometry, OCD, Spectral Reflectometry, Spectral Interferometry