The acronym TEMPEST3 stands for "Time-domain Electromagnetic Massively Parallel Evaluation of Scattering from Topography." The computer program solves Maxwell's equations using a time-domain finite-difference algorithm, where the electric and magnetic field nodes are spatially and temporally staggered over a three-dimensional topography of interest. Version 3.0 takes advantage of the inherent parallel nature of electromagnetic wave propagation and is implemented on the computer architecture connection machine 5 (CM-5)8. Due to the limited availability of the CM-5, version 4.0 is implemented on any single-processor computer architecture such as a work station or even a personal computer. Version 5.0 is also intended for single processor architectures but offers several improved features. The simulation domain may represent periodic, symmetric or isolated topographies. The algorithm is capable of simulating problems such as scattering from asymmetrical alignment marks, transmission through phase-shifting masks, effects of line-edge profiles in metrology as well as dynamic bleaching of photoresist over arbitrary non-planar, inhomogeneous wafer topographies.
Illumination is assumed to be monochromatic, with the electric field linearly polarized in any user-specified direction. The incident angle can take on discrete values depending on the illumination wavelength and the dimension of the simulation domain. Illumination is assumed to be coherent and can consist of any intensity and phase profile such as that calculated from SPLAT9 or other computer programs. The photosensitizer concentration is calculated if photoresit is present. The matrix containing this concentration information can be used in other simulation programs such as SAMPLE4 for simulation of resist development.
TEMPEST parses topography information from an input file which can be checked for correctness. The input geometry is then simulated until the electromagnetic field reaches steady-state or, in the case of non-convergence, the simulation domain is excited for a user chosen number of wave cycles. Information on the simulation parameters is written to an output file. Topography and field data are written to files where they can be analysed.
New in Version 5.0:
Version 5.0 of the program TEMPEST has several extensions from the previous version (version 4.0). First and foremost is TEMPEST's new ability to update nodes representing different materials with different updating equations. This allows more computation time and memory to be devoted to nodes which represent complicated materials (such as a dispersive metal) rather than wasted on nodes representing simple materials (such as air or glass).
This localization of the updating equations leads to a new implementation of boundary conditions. TEMPEST 5.0 treats boundary conditions merely as nodes with "special" updating equations. This conveniently allows the implementation of the newly invented boundary condition, the PML boundary condition[references].
Other side effect improvements:
- PML boundary condition now allows the simulation of fully isolated topographies.
- Excitation is no longer limited to a single planar distribution of excited nodes near the top of the domain. Plane sources with x,y and z directed normals and point sources can be placed anywhere in the domain.
- Convergence checking considers the convergence status of a 3D grid of points distributed evenly throughout the domain rather than a single plane near the top. This helps to avoid false convergences.
- Output data is no longer written in the PLOTMTV format as in version 4.0 but rather in a binary data format which requires much less disk space and is more portable.
Rather than writing output data (such as the steady state fields and refractive index) in the PLOTMTV format it is written in a binary format which uses much less space and can be read by a number of other programs. One such program is the MATLAB[ref] program. The new philosophy is to use MATLAB to analyse the data since MATLAB is a welldeveloped, and widely used program. Several MATLAB script files have been developed for this purpose. Move the TEMPEST-SPLAT interface out of TEMPEST and into MATLAB script files.
TEMPEST is capable of simulating a number of optical phenomena occurring in photolithography and optical metrology applications. These include bleaching of photoresist over arbitrary topography (e.g., reflective notching), dark-field and bright-field imaging of wafer features (e.g., alignment marks and line structures), generation of image profiles through masks (e.g., reduction phase-shift mask), and calculation of the electric and magnetic fields at all points in the three-dimensional simulation domain at any instant in time. Several studies involving these topics have already been performed, and the user is encouraged to refer to these publications2,3,6,7,11,12,13,14. In general, TEMPEST simulations can be placed into two categories: Lithography which involves dynamic changes during exposure, and Scattering analysis. These categories are distinguished primarily by the desired output. For lithography the desired output is the final PAC concentration. For scattering purposes the primary output desired are the electromagnetic fields and the diffraction harmonics.
Documentation Included with the Tape:
- A. Wong and T. Pistor, TEMPEST Version 5.0 (UCB/ERL M98/50, August 1998). Available separately for $5.00
Additional Documentation Available:
- A. Wong, TEMPEST Version 4.0 User's Guide (UCB/ERL M95/14, March 1995). Available separately for $5.00
- A. Wong, "Rigorous Three-Dimensional Time-Domain Finite-Difference Electromagnetic Simulation," Ph.D. thesis (UCB/ERL M94/69, September 1994) $5.00.
- A. Wong, "Two-Dimensional Electromagnetic Simulation of Topography Scattering and Diffraction for Optical Lithography," M.S. thesis (UCB/ERL M92/115, October 1992) $5.00.
- K. H. Tadros, "Investigation of Optical Phenomena in Photolithography and Optical Metrology Using Massively Parallel Simulation," M.S. thesis (UCB/ERL M91/72, August 1991) $11.00.