A system and method for forming an isolation trench is provided. An embodiment comprises forming a trench and then lining the trench with a dielectric liner. Prior to etching the dielectric liner, an outgassing process is utilized to remove any residual precursor material that may be left over from the deposition of the dielectric liner. After the outgassing process, the dielectric liner may be etched, and the trench may be filled with a dielectric material.