Coherent Fourier Scatterometry combined with Interferometry

Coherent Fourier Scatterometry is considered as an emerging optical grating scatterometry technique for semiconductor metrology. However, presently it can only have information about phase difference of successive orders, not their individual phases. Further utilization of coherence can be made through additional measurements using the principle of Temporal Phase Shifting Interferometry. This interferometric extension in Coherent Fourier Scatterometry can similarly be conceived for other branches of scatterometry, for example, to Goniometric Scatterometry. Through numerical simulation, we found how scanning and interferometry can be coupled together to improve the sensitivity of Coherent Fourier Scatterometry and to extend its range of applicability. Though dependent on the pitch of the grating, the calculated gain in sensitivity leads to a sensitivity gain of almost one order of magnitude from Incoherent Fourier Scatterometry, which is the present standard in industrial scatterometry. Practical experiments, which are planned to be performed shortly, will be used to verify these predictions.