Clean resistant windows for ultraviolet thermal processing

A semiconductor processing system comprising:

• one or more substrate processing apparatuses, each substrate processing apparatus including a substrate processing chamber, wherein each substrate processing chamber includes:
• chamber walls defining a chamber interior, the chamber walls comprising a UV transmissive window, wherein:
• the UV transmissive window is a dual pane window that comprises an interior pane exposed to the chamber interior and an exterior pane exposed to an exterior of the substrate processing chamber,
• the interior pane is comprised of a first material that is non-reactive with fluorine containing chemistries, and
• the exterior pane is comprised of a second material that is reactive with fluorine-containing chemistries;
• a substrate holder disposed inside the chamber interior, and
• a UV source disposed outside the chamber interior to shine UV radiation into the substrate processing chamber through the UV transmissive window;
• a purge gas flow path that is between the interior pane and the exterior pane of the UV transmissive window and that includes an inlet and an outlet, wherein the interior pane is offset from the exterior pane in a first direction, wherein the inlet is positioned radially outward of the interior pane and is radially interposed between the interior pane and the outlet, and wherein the outlet is positioned radially outward of the inlet;
• and
• a controller for operating the one or more substrate processing apparatuses, the controller comprising instructions to:
• flow a purge gas into the purge gas flow path, and
• flow a first process gas into the chamber interior.