Abstract
The sidewall angle (SWA) of a nanostructure exerts influence on the performance of the nanostructure and plays an important role in processing nano-structural chips. It is still a great challenge to determine steep SWAs from far field measurements especially when the SWAs are close to 90°. Here, we propose a far-field detection system to determine steep SWA of a cliff-shape step structure on a silicon substrate by combining a split detector with a scanning method. The far-field radiation field is asymmetric due to the scattering of the step structure, and further numerical analysis demonstrates the reliability of this far-field measurement method. In the simulations, two key variables, i.e. the polarization state and the focus position of the incident laser beam, are considered to explore their impacts. By scanning over the structure laterally and longitudinally with both TE and TM polarizations, polarization effects on the far-field occur. These effects show higher sensitivity to steep SWA variation for TM polarization as compared to TE. Furthermore, with a comprehensive longitudinal scanning analysis for the TM polarization case, a feasible focus interval can be optimized to retrieve the steep SWA. As the proposed method is fast, highly sensitive and easy to implement, it provides a powerful approach to investigate the scattering behavior of nanostructures.
Highlights
IntroductionThe photomask is a key component in the lithographic system
In the semiconductor industry, the photomask is a key component in the lithographic system
The proposed approach is appropriate for all values of sidewall angle (SWA) but here we focus on steep SWAs because there it is still a lot of challenges associated with them
Summary
The photomask is a key component in the lithographic system. A strictly precise description of the shape of the groove on the photomask plays an important role in the in-line process control and process development. Those structures are often gratings whose shape can be described by some geometrical parameters, such as period, middle critical dimension (MidCD), height and sidewall angle (SWA).
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