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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
 
Final Report Year 2023

Final Report Abstract

Continuously decreasing sizes of the functional structures in semiconductor manufacturing led to an increasing demand on corresponding metrology to be used in the production process. The characterization of nanoscale grating structures regarding their geometrical properties is one of the core tasks. Currently used spectroscopic metrology methods using infrared, visible and ultraviolet radiation are reaching their limits with respect to the sensitivity to very small feature sizes. Due to this fact, alternative characterization methods are being explored to keep pace with the industrial demands. Especially metrology methods using X-rays have been extensively tested over the last years. However, these do not provide sufficiently small measuring spots or a too low throughput for an integration within the fabrication process depending on the measurement configuration. 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 has been investigated theoretically and experimentally within the project. Spectroscopic EUV reflectometry at grazing incidence angles is used to identify contrasts in EUV reflectance of nanoscale gratings with different geometries (line width, trapezoidal angle, etc.). For this purpose, theoretical investigations are carried out by means of rigorous electromagnetic diffraction simulations. After that, the simulation results are used to extract spectral ranges and illumination settings for which particularly high contrasts between gratings of different geometries is expected. Based on these results, a set of samples with relevant geometry variations is fabricated. Subsequently, the EUV reflectance of the fabricated samples will be determined experimentally in the applicant’s experimental setup used for spectroscopic EUV reflectometry. In a further step, the grating geometry parameters are reconstructed from the experimentally acquired EUV reflectance by an iterative fit of simulated reflectance values to the experimentally measured ones. Conclusively, the theoretical limits of EUV metrology for nanoscale gratings is evaluated, taking into account real measurement uncertainties, including spectral ranges and illumination settings that are not directly accessible in the experiment. Finally, a comparison to the already existing metrology methods is made with respect to the applicability to future feature sizes in semiconductor manufacturing. The successful outcome of the project shows that lab-based spectroscopic EUV reflectometry has the required sensitivity and can be even applied for complex grating geometries with the single-digit nanometer accuracy. This EUV metrology method has thus the potential to become an integral part of quality assurance and process control in future semiconductor manufacturing.

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