Method of forming a trench structure

The invention relates to a method of forming a trench structure. Forming a shallow trench isolation (STI) structure filled with a flowable dielectric layer involves performing an implant to generate passages in the upper portion of the flowable dielectric layer. The passages enable oxygen source in a thermal anneal to reach the flowable dielectric layer near the bottom of the STI structure during the thermal anneal to convert a SIONH network of the reflowable dielectric layer to a network of SiOH and SiO. The passages also help to provide escape paths for by-products produced during another thermal anneal to convert the network of SiOH and SiO to SiO2.