The reflow properties of tetraethylorthosilicate-O-3 (TEOS-O-3) borophosphosilicate glass (BPSG) under furnace and rapid thermal processing conditions that we have studied show good void-free, subquarter micron gapfill, and planarization. Thick BPSG films on reflow exhibit positive charge buildup at the oxide/Si interface that cause a shift in the flatband voltage. The amount of phosphorous in the BPSG film, the BPSG Nm thickness, and the BPSG deposition temperature determine the extent of this flatband shift. We observed a linear correlation of the flatband shift and the amount of carbon migration and pileup at the oxide/Si interface during reflow. Using current-voltage, triangular voltage sweep, and secondary ion mass spectroscopy and field threshold voltage measurements, we demonstrate that under appropriate deposition conditions the flatband shift can be brought to negligible levels.