Chris Mack: Stochastics and the phenomenon of line-edge roughness

Presented at SPIE Advanced Lithography 2017.

15 March 2017

Extreme Ultraviolet lithography (EUVL) has the potential to enable 15nm half-pitch resolution in semiconductor manufacturing, but faces a number of persistent challenges.

In this talk, Gentleman Scientist Chris Mack of, addresses the "stochastic thinking" gap of the lithography community by providing a tutorial covering the fundamentals of roughness formation:

  • Characterizing LER with metrology. Measuring roughness with a CD-SEM, then analyzing the data to extract the important parameters of roughness standard deviation, correlation length, and roughness exponent (that is, roughness power as a function of frequency).
  • How LER affects printed features. Using the parameters of roughness standard deviation, correlation length, and roughness exponent to predict three lithographic outcomes: within-feature variation, feature-to-feature variation (local CDU), and extreme events (shorts and bridges).
  • Stochastic variations that cause roughness. Explaining the nature of stochastic variations such as photon shot noise, absorption, chemical concentration shot noise, and reaction-diffusion in the resist.
  • How to reduce roughness. Using our models of stochastic variations, define the best approaches for reducing roughness (including the role of exposure dose, resist formulation, and post-processing).
  • Future work. What research is needed to fill in the unknowns and complete our understanding of the fundamentals of LER formation?

Chris A. Mack received BS degrees in physics, chemistry, electrical engineering, and chemical engineering from Rose-Hulman Institute of Technology in 1982, a MS in electrical engineering from the University of Maryland in 1989, and a PhD in chemical engineering from the University of Texas at Austin in 1998.

He is Editor-In-Chief of the SPIE Journal of Micro/Nanolithography, MEMS, and MOEMS (JM3). Currently, he writes, teaches, and consults on the field of semiconductor microlithography in Austin, Texas. He is a fellow of SPIE and IEEE.

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