A thermal process for cleaning equipment surfaces of undesired silicon nitride in semiconductor processing chamber with thermally activated source of pre-diluted fluorine is disclosed in the specification. The process comprising:
(a)flowing pre-diluted fluorine in an inert gas through the chamber;
(b)maintaining the chamber at an elevated temperature of 230° C. to 565° C. to thermally disassociate the fluorine;
(c)cleaning undesired silicon nitride from the surfaces by chemical reaction of thermally disassociated fluorine in (b) with the undesired silicon nitride to form volatile reaction products;
(d)removing the volatile reaction products from the chamber.