This report will discuss numerical techniques used in the general feature profile evolution simulator FPS-3D. We call it general because it does not have any hardcoded dependencies, such for example, as etch or deposition rates, or dependencies on energy or angle of incident reactive particles (ions as well as neutral radicals and gases). The code thus can be applied to targets consisted of any set of solid materials and exposed to any fluxes of reactive particles with any distribution on energy and angle. Although the code is called FPS-3D, it actually has two options, 2D and 3D, which allow convenient comparison between 2D and 3D results for similar targets and fluxes. The 2D option has advantage of much higher speed of calculations, mainly because the number of cells is typically much smaller and the calculations are simpler than that for 3D, but the 3D option becomes indispensable when the target cannot be approximated by 2D geometry, or when the essentially 3D tasks are considered, such as roughness, for example. The FPS-3D code can comfortably treat up to one million cells, or maybe, a few times of that, depending on the speed of a computer. Correspondingly, the 2D option of FPS-3D allows consideration of a wide range of target sizes, from nanometers to micrometers, as well as treating them in great detail, such for example, as 1000x1000 cells. For the 3D option, a typical run is limited to about 100x100x100 cells, thus leading to each cell containing significantly more molecules than for 2D. One of the main advantages of FPS-3D relative to all other similar software is its GUI-graphics interface based on the TPSOFT package from HFS [1]. This interface is capable of producing high-speed and high-quality 2D and 3D graphics not only for initial parameters, distributions, geometry and fluxes, but also dynamically while the code is running and the feature profile and other parameters evolve, with a unique characteristic of not slowing down the calculations. The authors are thankful to S.-Y. Kang of TEL TDC for valuable discussions.

[1] www.highfactor.com [about:www.highfactor.com] .