As a premetal dielectric, borophosphosilicate glass (BPSG) has been widely used for device planarization. in order to meet the stringent gap filling requirements as the device evolves toward smaller feature sizes, the current BPSG deposition process using ozone/tetraethoxysilane chemistry was fully characterized to explore its extendibility for achieving high aspect ratio gap filling. Based on the characterization results, a two-layer film deposition process was developed to accommodate the gap filling capability as well as the system throughput. Without stretching the thermal budget, the current process is able to achieve void-free gap filling at a >6:1 aspect ratio, 0.06 mu m width, even with reentrant profile. Other film properties, including film stress, moisture absorption, dopant profile and flow, were also studied extensively. Postdeposition film reflow can be performed using either conventional furnace or rapid thermal annealing, the reflowed profile depends on annealing temperature as well as ambient gases. A low thermal budget can be maintained using a steam anneal.