the present invention relates generally to the field of semiconductor device manufacturing , and more specifically to a method for cleaning and preconditioning a dome in a chemical vapor deposition system . during cleaning , the direction of flow of cooling water through an induction coil in the dome is reversed . during preconditioning , the direction of cooling water flow is preferably reversed again , such that it is the same direction as during deposition . the preconditioning portion of the method comprises introducing a hydrogen gas into the cvd chamber , and then introducing a mixture of hydrogen gas and nitrogen gas into the chamber .