Overview of FOREST

Physically based simulators like SUPREM IV-GS, and PISCES-2ET are used for modeling devices and process steps in a virtual factory. Such programs numerically solve partial differential equations on discrete points (called a computational grid) that is representative of the continuous physical device structure. One of the key factors determining the efficiency and accuracy of the computed solution is the allocation of the discrete grid. The thrust of our research is to automatically generate an optimum grid for both device and process simulation.

Forest, a 2D geometry and grid program, provides these capabilities. It stores and manipulates both geometry and grid data and can be used for diffusion, oxidation and device simulation. Quadtree based grid generation proceeds by enclosing the structure geometry in a root square and recursively dividing the root square resulting in a terminated lines mesh. The level of decimation can be controlled by a number of factors including user specification, solution variation, etc. The terminal squares are then triangulated using templates. The triangles are optimized for aspect ratio. For oxidation simulation, the geometry of the device is first evolved; the quadtree is rehashed and retriangulated. These operations are illustrated in the figures.

Used in a stand alone configuration,Forest produces PISCES-2ET mesh or SUPREM IV structure files as output. It requires cross sectional geometry and doping information as input; the input file can be a SUPREM IV structure, a PIF geometry, or a forest geometry file. For PISCES-2ET, heterojunction devices can also be specified with varying ternary and quaternary material compositions.

Additionally, Forest, is being used as an integration tool for the various process simulators. Forest's independent manipulation of grid and geometry allow it to be used with grid based programs like SUPREM IV-GS and with geometry based etching and deposition programs like SPEEDIE 3.0.


[1] Z. Sahul, R. Dutton, M. Noell. "Grid and Geometry Techniques for Multi-Layer Process Simulation." Proc. of SISDEP'93. Springer-Verlag. pp. 417-420.

[2] Z. Sahul, E. McKenna, R. Dutton. "Grid Techniques for Multi-Layer Device and Process Simulation." Proc. of TECHCON'93. SRC. pp. 164-166.

Grid generation proceeds by enclosing the geometry (a) in a root square (b) and recursively dividing the root square resulting in a terminated lines mesh (c). The terminated lines mesh is then triangulated (d).

Use of Forest for oxidation simulation. Geometry, quadtree mesh and triangulation before oxidation (a) and after several oxidation steps (b).