Embodiments of a mechanism for forming a shallow trench isolation (STI) structure filled with a flowable dielectric layer are provided. The mechanism involves using one or more low-temperature thermal anneal processes with oxygen sources and one or more microwave anneals to convert a flowable dielectric material to silicon oxide. The low-temperature thermal anneal processes with oxygen sources and the microwave anneals are performed at temperatures below the ranges that could cause significant dopant diffusion, which help dopant profile control for advanced manufacturing technologies. In some embodiments, an implant to generate passages in the upper portion of the flowable dielectric layer is also used in the mechanism.