This is how it's done now. Tool lines are flushed with chemically regenerated atmosphere (basically getting LOX + LN2 bottles from air liquide, and mixing them,

This is how it's done now. Tool lines are flushed with chemically regenerated atmosphere (basically getting LOX + LN2 bottles from air liquide, and mixing them,) or argon, or nitrogen only. Older, and cheaper fabs still rely on natural atmosphere, and other, less sure tricks to keep halogens out.