Coherent Fourier scatterometry for reconstruction of subwavelength features of printed nanostructures

Coherent Fourier Scatterometry (CFS)  involves a coherent source which is focused on the sample (in this project 1D silicon grating). After interacting with a sample, the reflected intensity in the pupil plane of the lens is measured and compared to rigorous simulations from which the grating parameters are determined. By using two polarizers, one for  the incident beam and the other for the reflected beam (after collimation by the lens), all combinations of incident and reflected polarizations can be obtained. Also, the wavelength influence comparison, far field sectioning and analysis of different far field simulation methods are carried out in this project.

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Objective

The goal of this research is to use degrees of freedom of the light beam in order to enhance certain key features of the nanostructure and observe them in the far field. Detection and separation of useful information obtained in the far field is the main task of this project.

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Impact

Optical inspection of periodic nanostructures is a major challenge in semiconductor industry due to constantly decreasing critical dimensions. Therefore, it becomes difficult to retrieve certain parameters with high accuracy. One way to improve present systems is to use, in addition to amplitude and phase, other degrees of freedom of the light beam such as unconventional polarization states, spectral information, angular momentum. Exploring new degrees of freedom will help to enhance the features in the far field related to a certain parameter to be retrieved from the object.

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Publications

• Wavelength influence on the determination of subwavelength grating parameters by using optical scatterometry

  L. Siaudinyte and S.F. Pereira, SPIE Proceedings Vol. 11325: Metrology, Inspection, and Process Control for Microlithography XXXIV (2020)

• Far-field sectioning for the retrieval of subwavelength grating parameters using coherent Fourier scatterometry

  L. Siaudinyte and S.F. Pereira, Measurement Science and Technology 31, 10 (2020)