[en] A two-dimensional Monte Carlo simulation code has been applied to trench implantation as a function of incident angle to investigate the influence of tapered sidewalls in Si trenches on doping uniformity and efficiency. Oblique implantation in trenches provides uniform concentration profiles of dopants at sidewalls, whereas nonuniform concentrations due to the reflection of ions at the sidewall are obtained in the trench bottom. A slightly tapered sidewall with an angle of 3deg results in higher doping efficiency by oblique implantation than vertical sidewalls. (orig.)