In this work we discuss an original analysis about a method to reduce the dislocation density in the devices that use the Shallow Trench Isolation (STI). It is well known that a high mechanical stress in silicon combined with an amorphizing implantation damage can generate many dislocations. So we propose to release the mechanical stress in silicon before implanting. A high temperature treatment indeed can trigger the viscous behaviour of the filling oxide inducing the relaxation of the stress field in silicon. For the first time a systematic study of the effect of different furnace and RTP annealings in the stress relaxation was done by Raman measurements. Different temperatures (from 3000C to 11000C) and different durations (from few seconds to one hour) were explored and the experimental results were compared with the numerical simulation with a good agreement. Finally we study the effect of the most promising annealings selected by Raman in a complete process flow.