A process for filling a trench having sidewalls and a floor in a semiconductor device or integrated circuit comprises: forming an insulating layer on the sidewalls and floor of a trench in a semiconductor substrate, substantially filling the trench with semiconductor material, removing semiconductor material from an upper portion of the trench, depositing a first layer of BPSG in the upper portion of the trench, heating the substrate to a first temperature greater than about 850° C. and up to about 1100° C., depositing a second layer of BPSG above the first layer of BPSG, and heating the substrate to a second temperature greater than about 850° C. and up to about 1100° C. The first and second BPSG layers each comprises boron and phosphorus in a weight ratio of boron: phosphorus of greater than 1:1.