Proceedings Article | 24 March 2009
Chih-Ming Ke, Jimmy Hu, Willie Wang, Jacky Huang, H. Chung, C. R. Liang, Victor Shih, H. H. Liu, H. J. Lee, John Lin, Y. Fan, Tony Yen, Noelle Wright, Ruben Alvarez Sanchez, Wim Coene, Marc Noot, Kiwi Yuan, Vivien Wang, Kaustuve Bhattacharyya, Karel van der Mast
Proc. SPIE. 7272, Metrology, Inspection, and Process Control for Microlithography XXIII
KEYWORDS: Carbon, Lithography, Refractive index, Birefringence, Scatterometry, Finite element methods, Critical dimension metrology, Semiconducting wafers, Absorption, Anisotropy
A brand new CD metrology technique that can address the need for accuracy, precision and speed in near future
lithography is probably one of the most challenging items. CDSEMs have served this need for a long time,
however, a change of or an addition to this traditional approach is inevitable as the increase in the need for better
precision (tight CDU budget) and speed (driven by the demand for increase in sampling) continues to drive the
need for advanced nodes.
The success of CD measurement with scatterometry remains in the capability to model the resist grating, such as,
CD and shape (side wall angle), as well as the under-lying layers (thickness and material property). Things are
relatively easier for the cases with isotropic under-lying layers (that consists of single refractive or absorption
indices). However, a real challenge to such a technique becomes evident when one or more of the under-lying
layers are anisotropic.
In this technical presentation the authors would like to evaluate such CD reconstruction technology, a new
scatterometry based platform under development at ASML, which can handle bi-refringent non-patterned layers
with uniaxial anisotropy in the underlying stack. In the RCWA code for the bi-refringent case, the elegant
formalism of the enhanced transmittance matrix can still be used. In this paper, measurement methods and data
will be discussed from several complex production stacks (layers). With inclusion of the bi-refringent modeling,
the in-plane and perpendicular n and k values can be treated as floating parameters for the bi-refringent layer, so
that very robust CD-reconstruction is achieved with low reconstruction residuals. As a function of position over
the wafer, significant variations of the perpendicular n and k values are observed, with a typical radial fingerprint
on the wafer, whereas the variations in the in-plane n and k values are seen to be considerably lower.
