Research

Model and software development covers the process steps pre-bake, exposure, post-exposure bake, and chemical development of the photoresist. Specific simulation algorithms developed by the IISB include:

  • Rigorous electromagnetic field modeling of light diffraction from advanced masks, including defect-free and defective optical and EUV masks by the waveguide method and by finite-difference time-domain (FDTD) algorithms

  • Scalar and vector modeling of partial coherent imaging including advanced and user defined source shapes, polarized illumination, Zernike aberrations, Jones pupils, flare, and scanner specific effects

  • Efficient models for the simulation of contact and proximity printing with mask aligners

  • Computation of light propagation inside the photoresist on the top of a planar wafer stack by transfer-matrix algorithms

  • Numerical modeling of coupled diffusion and kinetic reactions during the post-exposure bake of chemically amplified and DNQ-type photoresists

  • Numerical modeling of photoresist development by fast marching and cell removal algorithms

  • Various methods for the evaluation of projected images and final resist profiles including full process evaluation by process windows etc.

  • Local and global optimization algorithms including hill climbers, downhill simplex, genetic algorithms, differential evolution etc. and combinations thereof

The software modules are combined in the IISB in house research and development simulator Dr.LiTHO. The advanced features of the flexible lithography simulator Dr.LiTHO are applied for the development and optimization of advanced lithographic processes. Typical applications include simulation studies for

  • hyper numerical aperture imaging systems using immersion lithography,

  • advanced mask materials,

  • mutual source and mask optimization,

  • contact and proximity printing with mask aligners, and

  • photoresist model calibrations.

Typical simulation flow of a lithographic process
Typical simulation flow of a lithographic process