Dr.LiTHO

Dr.LiTHO is a comprehensive simulation environment for photolithography, developed at the Fraunhofer IISB. Its main focus is on development and research applications.

Dr.LiTHO includes models and algorithms for the simulation, evaluation, and optimization of lithographic processes using optical or EUV image projection. These models describe advanced mask illumination schemes, the light diffraction from the mask, the image formation in dry and immersion projection systems, the interaction of light and the photoresist, and the resist processing during baking steps and chemical development. Several modules of Dr.LiTHO support the evaluation of the computed images and resist profiles with respect to process variations. The flexible scripting concept of Dr.LiTHO supports the setup of complex simulation flows and the coupling with other simulation packages, such as advanced optimization algorithms developed at IISB and third-party software packages. Additionally, Dr.LiTHO comes with simulation models that describe the projection printing processes in semiconductor lithography. And Dr.LiTHO can also be used for the simulation of alternative exposure methods and for applications of lithography in other fields of micro- and nanofabrication.

Features

  • Rigorous electromagnetic field solvers for accurate simulation of light diffraction: finite-difference time-domain (FDTD) and the Waveguide Method.
  • Scalar and vector models for the description of projection systems, including various standard and user-defined illuminator shapes, polarized illumination, and Zernike and Jones-pupil type representations of the projector lens.
  • Transfer matrix algorithms for the vectorial description of light propagation in planar wafer stacks; the Dill model for the description of lithographic exposures.
  • Continuous and mesoscopic resist models including solvers for coupled diffusion/kinetics equations for the modeling of post exposure bake; various development rate models, and level set and cell-removal algorithms for the modeling of the chemical development of the resist.
  • Various tools for the process evaluation, including threshold-based aerial image evaluations, extraction of CD data and side walls from simulated resist profiles, and computation and evaluation of process windows.
  • Interfaces for the modeling of other exposure techniques such as contact- and proximity printing, interferometric exposures and for the integration of other electromagnetic field solvers.

Applications

  • Simulation studies for the evaluation of the impact of mask, optical system, and resist parameters on the lithographic process performance.
  • Optimization of mask materials, geometries, and illumination settings.
  • Defect printability studies.
  • Early exploration of future lithography options.
  • Simulation of lithography for alternative applications.

Usability

Dr.LiTHO is available under Linux and Windows. In order to provide a high degree of flexibilty, Dr.LiTHO uses Python as a frontend language. But to use it, one does not have to be an expert in programming or Python. Standard tasks require nothing more than setting parameters or selecting simulation steps. Plus, Dr.LiTHO comes with several software tutorials and a large scripting library for various applications.

If that's not enough, numerous tutorials will support the user in writing customized scripts. Since Python is a modern, object-oriented programming language, it is easy to define new workflows or integrate special-purpose algorithms and models. In addition, the user can access a large number Python modules for all kinds of tasks including numeric and visualization.

  Dr.LiTHO

Aerial Image
Aerial Image
EUV mask
Reflected light of an EUV mask
Resist Profile
Resist profile