Spectroscopic EUV metrology for nanoscale gratings

• Applicant: Professor Dr. Carlo Holly, since 7/2021
• Subject Area: Measurement Systems ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 415848294

Constantly decreasing feature sizes in semiconductor manufacturing lead to increasing demands on the metrology used in the production process. The metrology of nanoscale grating structures for the determination of the critical dimension is one of the core tasks.Since currently used spectroscopic metrology methods using infrared, visible and ultraviolet light are reaching their limits with respect to the sensitivity to very small feature sizes, alternative metrology methods are being explored. Especially metrology methods using X-rays have been extensively tested over the last years. However, these do not provide sufficiently small measuring spots and demonstrate only limited throughput. Metrology methods in the EUV spectral range, on the other hand, have the potential to overcome the mentioned disadvantages. The applicability of EUV metrology as a metrology method for nanoscale gratings should therefore be theoretically and experimentally investigated within the planned project.Spectroscopic EUV reflectometry at grazing angles of incidence will be used to identify contrasts in EUV reflectance of nanoscale gratings of different geometries (line width, trapezoidal angle). For this purpose, theoretical investigations will be carried out by means of rigorous electromagnetic diffraction simulations. After that, the simulation results will be used to extract spectral ranges and illumination settings for which particularly high contrasts between gratings of different geometries are expected. Based on these results, a set of samples with relevant geometry variations will be fabricated. Subsequently, the EUV reflectance of the fabricated samples will be determined experimentally in the applicant’s existing experimental setup for spectroscopic EUV reflectometry. In a further step, the grating geometry parameters will be reconstructed from the experimentally acquired EUV reflectance values by an iterative fit of simulated reflectance values to the experimentally measured ones. Conclusively, the theoretical limits of EUV metrology for nanoscale gratings will be evaluated, taking into account real measurement uncertainties, and including spectral ranges and illumination settings that are not directly accessible in the experiment. Finally, a comparison to the already existing metrology methods will be made with respect to the applicability to future feature sizes in semiconductor manufacturing.A successful outcome of the project will show that EUV metrology has the necessary sensitivity even for the smallest semiconductor feature sizes. EUV metrology can thus become an integral part of quality assurance and process control in future semiconductor manufacturing.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Peter Loosen, until 7/2021