06.03.2023
Figure: top: Reconstructed parameters of the grating line profile (h: height, w: width, β: sidewall angle, rbtm: bottom corner radius, rtop: top corner radius, pSiO2: mass density of fused silica at the sample surface). bottom: Comparison of the reconstruction uncertainties with their normalized density (ND) distributions at the laboratory-based EUV scatterometer from RTWH Aachen University (red) and at the beamline scatterometer at the PTB (blue).
The semiconductor industry needs metrology systems to characterize the dimensions of transistor structures in the nanometer range in a fast, non-destructive, and metrologically reliable manner. A major challenge here is the limitation of the resolution of the measurement systems by the wavelength of the radiation used. Therefore, the use of short-wavelength extreme ultraviolet (EUV) radiation is investigated at PTB and RWTH Aachen University. To validate the results, measurements with the laboratory-based EUV scatterometer setup of RWTH have now been compared against the scatterometer of the PTB operated at BESSY II.
Both scatterometers detect the extreme ultraviolet (EUV) radiation scattered from a sample. While the PTB at BESSY II uses monochromatized synchrotron radiation of high stability for this purpose, laboratory instruments can be designed by using compact plasma-based (broadband) radiation sources. However, these show inherent intensity fluctuations which are challenging for the measurement process. A prototype of a laboratory based EUV scatterometer developed by the RWTH Aachen University was investigated in detail in collaboration with the PTB Working Group 7.14 “EUV Nanometrology”. The statistical investigations based on Monte Carlo simulations of the individual performed experiments showed that the prototype enables measurements with almost the same reconstruction accuracy as the scatterometer of the PTB. For the benchmarking studies, the measurement range of PTB’s scatterometer was matched to the measurement range of the RWTH laboratory-based scatterometer. Uncertainties in the sub-nanometer range can be achieved in the reconstruction of the investigated nanostructured surfaces. Even significantly smaller dimensional uncertainties might be possible in the future when higher diffraction orders of the scattered EUV radiation are included.
Link to publication:
L. M. Lohr, R. Ciesielski, S. Glabisch, et al. Appl. Opt. 62(1), 117-132 (2023)
https://doi.org/10.1364/AO.475566
Contact:
L. M. Lohr, 7.14, e-mail: 
leonhard.lohr(at)ptb.de
V. Soltwisch, 7.14, e-mail: victor.soltwisch(at)ptb.de