Advanced Optical Modeling of TiN Metal Hard Mask for Scatterometric Critical Dimension Metrology

Authored by: Peter Ebersbacha, Adam M. Urbanowiczb, Dmitriy Likhacheva, Carsten Hartiga | SPIE 2017, February 1, 2017

The majority of scatterometric production control models assume constant optical properties of the materials and only
dimensional parameters are allowed to vary. However, this assumption, especially in case of thin-metal films, negatively
impacts model precision and accuracy. In this work we focus on optical modeling of the TiN metal hardmask for
scatterometry applications. Since the dielectric function of TiN exhibits thickness dependence, we had to take this fact
into account. Moreover, presence of the highly absorbing films influences extracted thicknesses of dielectric layers
underneath the metal films. The later phenomenon is often not reflected by goodness of fit. We show that accurate
optical modeling of metal is essential to achieve desired scatterometric model quality for automatic process control in
microelectronic production. Presented modeling methodology can be applied to other TiN applications such as diffusion
barriers and metal gates as well as for other metals used in microelectronic manufacturing for all technology nodes.
Keywords: TiN hardmask, optical properties, thin metals, optical modeling, scatterometry, OCD