A New Damascene Structure for Submicrometer Interconnect Wiring

A newly developed damascene structure to form high-density interconnect wiring is presented. The structure results in improved o‘en and short yields, lower sheet resistances, comparable contact/ via resistances, and shows excellent filling of high-aspect-ratio long lines with high copper content compared to currently used wiring fabricated by reactively ion etching (RIE) of Ti/ Al-Cu/ Ti/ TiN. The key leverage of this technique is the ability to combine soft and low resistance metal (A1 alloy, Cu alloy, etc.) deposited by physical vapor deposition (PVD) and a hard metal (W) deposited by chemical vapor deposition (CVD) with high wear resistance. As a result a structure with a good polish stop and better alloying capability, and high yields, while maintaining planarity at all levels can be fabricated. This structure is applied to a dense 512K SRAM (2-ns cycle/ 3.8-ns access time) design with 0.5-µm minimum ground rules resulting in improved yield of partially functional chips at second-level metal compared to the conventional RIE structure. © 1993 IEEE