Charging was found to be the cause of the largest number of defects in integrated circuits produced by plasma etching for high aspect ratio submicron structures (200 nm resolutions and smaller). Further improvement of the existing plasma processing tools requires accurate representation of charging and modeling of the development of etched profiles. lit this paper we compare the results of fluxes of ions in micro trenches as a benchmark to verify the simpler and faster Direct Numerical Procedure that was used to model the plasma surface interface in more complex comprehensive codes. A reasonably good agreement is achieved except that numerical diffusion reduces the angular and spatial structures, which actually may be pronounced. Angular and energy dependences of incoming ions are also studied.