Extreme Ultraviolet Lensless Microscopy: Development and Potential Applications to Semiconductor Metrology

The development and integration of next-generation semiconductor devices is experiencing significant metrology challenges. These devices are ever more complex and three-dimensional in shape and contain ever more types of materials, with critical dimensions of only a few tens of nanometers, or even down to a few nanometers. The structure and composition of these devices, while critical to their overall performance, is extremely difficult to measure non-destructively. Thus, there is an urgent need for non-destructive nano-imaging techniques for general next generation samples. In this thesis, I present the recent development of EUV lensless microscopy by combining the tabletop coherent extreme ultraviolet light sources based on high harmonic generation and the state-of-the-art computational phase retrieval algorithms (ptychography), as well as their potential applications to semiconductor metrology In particular, I will present our work on designing and commissioning a tabletop EUV actinic microscope that is capable of performing at-wavelength EUV photomask imaging and defect inspection. We further demonstrated for the first time that fast, reliable and robust ptychographic imaging of periodic structures can be achieved by careful illumination design. This is both a critical advancement for the modern ptychography technique and a promising and economic solution for actinic EUV photomask metrology.

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