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Silicon dioxide is the primary dielectric fabric of silicon integrated circuits, and the need to pattern it accounts for a large percentage of all photolithographic operations. As shrinking device dimensions place extreme demands on both lithography and etching, patterned oxide films are finding yet additional applications as intermediate `hard masks.' For example, polysilicon gate and metal layers may be etched with greater selectivity and linewidth control through a thin patterned oxide mask, rather than through a thicker photoresist layer (which is used to pattern the oxide and removed before pattern transfer). However, any advantages of such schemes must be weighed against the costs of increasing process complexity. We recently reported a new all-dry photolithographic process based on the plasma deposition and patterning of organosilicon resists. These materials, as best exemplified by plasma polymerized methylsilane (PPMS), possess amorphous Si-Si bond backbone structures and undergo efficient photo-oxidation to give glasslike siloxane network material. Patterns are developed using chlorine plasma etching to selectively remove unexposed regions, providing a negative tone image. In previous papers we have demonstrated the use of these materials in bilevel processes, using oxygen reactive ion etching to transfer patterns in thin PPMS layers through underlying organic planarizing layers. Using 248 nm deep UV exposure tools, such schemes afford sub-0.25 micrometers design rule capabilities and are well suited for difficult device topography. Here we describe the discovery and development of a fundamentally different application unique to PPMS: a new direct approach to patterned silicon dioxide.
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