Directly sputtered stress-compensated carbon protective layer for silicon stencil masks

Silicon stencil masks for ion beam projection lithography have a protective layer stopping the ions and thus preventing a change in the Si membrane st ress. This is needed to maintain extremely tight pattern placement specific ations even when they are irradiated with high exposure doses. The fabricat ion of carbon protective layers by indirect sputter coating which are suita ble for helium ion beam exposure has already been reported. This article de scribes a method of forming very low stress carbon protective layers based on direct radio frequency sputter coating with nitrogen added to the argon sputter gas and in situ thermal treatment using commercially available equi pment. The carbon layers thus produced are stable in conventional environme nts. The article deals also with the physical characterization of carbon la yers and the protection performances of these coatings under helium ion bea m exposure using accelerated lifetime testing. (C) 1999 American Vacuum Soc iety. [S0734-211X(99)17106-3].