Filtered cathodic arc deposition of fully ionized boron (B) was used to fill similar to 2 mu m wide trenches in silicon, having a depth:width ratio of up to 3:1. Optimal, void-free, infill is achieved with proper balance between deposition and self-sputtering, as controlled by the substrate bias. Previously, this technique was used to fill similar trenches with copper [O. R. Monteiro, J. Vac. Sci. Technol. B 17, 1094 (1999)]. In this work, successful extension of this process to B was found to require up to ten times higher bias voltage (up to 1000 V) for the sputtering phase and to benefit from a stronger angular dependence of self-sputtering yield for this lighter element.