Challenges in materials characterization of thin photoresist films for EUV lithography
Dr. Roberto Fallica (R & D engineer, IMEC)
To make the semiconductor devices of the future, we need to be able to produce increasingly smaller patterns. Today, the cutting-edge technology for this purpose is optical lithography that uses extreme ultraviolet (EUV) light at 13.5nm wavelength. But EUV-sensitive photoresists also have been shrinking alongside: a film of just 30 nm thickness is now exposed to light and developed to be transferred into a substrate. Characterization of these thin photosensitive films is becoming increasingly challenging due to unavoidable damage induced by the characterization tool, both light-based as ellipsometer or electron-beam based as scanning electron microscope (SEM). For instance, SEM inspection of patterned photoresist is known to introduce significant damage and deformation in the pattern, which prevents its accurate measurement. Chemical composition and thickness also vary irreversibly after lithography due to outgassing of some components of photoresist. Finally, chemical inhomogeneity in the composition of the photoresist, such as the segregation of photoacid generator (a catalyst molecule blended into the compound) can also have detrimental consequences on the pattern fidelity, the manufacturability and throughput. In this talk, I will provide an overview of challenges that we are facing in high volume manufacturing (HVM) for semiconductor devices, specifically for the highest resolution patterns that are produced by EUV lithography in back-end-of-line (BEOL) and the photoresists/stacks of films involved.
Dr. Roberto Fallica received his master's degree in Electronics Engineering from Politecnico di Milano (Italy) in 2007 and completed the PhD school in Nanotechnology from University of Milano-Bicocca in 2012 with a thesis on the characterization of phase-change chalcogenide nanowires for nonvolatile data storage. He was postdoctoral researcher at the Paul Scherrer Institute (Switzerland) working at the X-ray interference lithography beamline for characterization and patterning of nanoscale photoresist structures. Since 2018, he is staff researcher in the Advanced Patterning department of IMEC (Belgium). His duties include the screening of lithography materials and stacks to develop the technology that will enable future semiconductor devices in BEOL (back-end of line).