Kenneth A. Goldberg, Ph.D., Optical Physicist
Center for X-Ray Optics • Lawrence Berkeley National Laboratory
Extreme Ultraviolet Optics • Ultra-High-Accuracy Interferometry • EUV Lithography
EUV 'Actinic' Mask Inspection • Optical System Modeling • Synchrotron Light • Coherence
|NANOSCALE OPTICAL SYSTEM MODELING|
The laws of physics can be used to predict how light interacts with matter on the scale of wavelengths. For large systems like lenses and mirrors, it is much easier to study and predict the behavior of light. For those systems, reflection, and refraction describe most effects. But shrink the systems down to the nanoscale and the world is dominated by diffraction, and interference.
How much light can we squeeze through a pinhole that's just 25-nm wide? Can we engineer nanostructures to steer and filter light in new and unusual ways? Can we concentrate available light to make measurements more sensitive? Before any physical structures are built, and before any experiments are performed, optical system modeling is a tool we can use to answer questions like these.
Recently, I've studied how 25-nm-wide pinhole spatial filters transmit focused beams of EUV light, developed ways to measure the focal-plane position in lithography tools, modeled concentrated beams of ultraviolet light used to detect defects in EUV lithography masks (reticles), and I've studied the light-concentrating properties of microlens-arrays.
My primary tool for this analysis is TEMPEST-3D a finite-different time-domain (FDTD) full-vector electromagnetic-field simulation program, developed by the Neureuther group in UC Berkeley's EECS Department. TEMPEST-3D divides the three-dimensional simulation volume into equally spaced simulation nodes, and solves Maxwell's Equations at each point.
The individual calculations made for any simulation use a purely coherent, monochromatic model of light propagation. Many researchers faced with modeling complex structures stop at a monochromatic plane-wave model and risk missing subtle and important real-world effects. Through careful bookkeeping, we can use the superposition of numerous TEMPEST calculations to model partially-coherent illumination, and non-monochromatic illumination.
Other scientists who contribute to this work include Eric Gullikson, and J. Alexander Liddle. Essential computer support comes from Ron Tackaberry and Jeff Gamsby. Special thanks are due to the Neureuther group and students who have created and upgraded TEMPEST: Alfred Wong, Tom Pistor, and Yunfei Deng, among others.
"EUV Focus Sensor: Design and Modeling," K. A. Goldberg, M. E. Teyssier, J. A. Liddle, Proc. SPIE 5751, 312-19 (2005). [LINK]
"Preparations for extreme ultraviolet interferometry of the 0.3 numerical aperture Micro Exposure Tool optic," K. A. Goldberg, P. P. Naulleau, P. E. Denham, S. B. Rekawa, et al. JVST B 21 (6), 2706-10 (2003). [LINK]
"Extreme Ultraviolet Interferometry," K. A. Goldberg, Doctoral Dissertation, Department of Physics, University of California, Berkeley (1997).