Process sensitivity and robustness analysis of via-first dual-damascene process

Sacrificial layer (SACL) coating had been proposed to protect the sealing layer of underlying copper lines during trench etching as the via-first scheme is employed for dual-damascene patterning. Because the coated SACL thickness depends on via size and via density, the process window is hard to identify. In this paper, the criteria for a successful SACL process are derived. A four-step procedure for SACL process development is also proposed. It is suggested that shallow trench depth and medium etch rate selectivity between the inter-metal-dielectric and SACL material are preferred. The SACL thickness in the via can be adjusted by adjusting the overetching percentage at the SACL breakthrough step so that the criteria are satisfied. The validity of the proposed criteria is proved by the very high yield of via chains with via size ranging from 0.27 to 0.16 μm. It is concluded that the SACL process can be robust and can be employed to reduce the thickness of the capping layer effectively even beyond the 0.13-μm technology node.