Studies of the thermal stability and crystallization behavior of electroless and evaporated nickel and cobalt alloy films.

摘要

Electroless Ni and Co alloy films are currently being studied for the purpose of replacing dielectric materials as Cu diffusion barriers in microelectronic devices. Electroless films offer the advantages of selectivity, conformality, reduced Cu electromigration, and reduced cost. Amorphous films are preferred, to eliminate grain boundaries, which are fast diffusion paths. It is desirable for these films to remain amorphous up to ∼700°C to be able to maintain their barrier properties throughout the fabrication process.; Previously studied films include various Ni and Co alloys containing dopants such as P, B, W, Mo, and Re, which are added to inhibit nucleation. These films have limited thermal stability and do not maintain their barrier properties above 500°C.; The studies presented here focus on understanding the roles of the different types of dopants in suppressing nucleation of the electroless films to be able to design a new film that remains amorphous at higher temperatures.; Ni-P films were studied for the purpose of developing an atomic level model of the nucleation process and how the P inhibits f.c.c. Ni nucleation. Ni-W-P and Ni-P films with the same amount of P were compared to determine the impact of added W. Results show that W suppresses Ni3P and not Ni formation. This result suggests that to suppress Ni nucleation, W (and other similar atoms such as Mo and Re) should be replaced with an atom that has limited mutual solubility with Ni and a deep eutectic in its phase diagram with Ni, for example Ce.; To test this hypothesis, Ni-B-Ce and Ni-B-Mo films, with ∼20 atom % B and ∼6-7 atom % Ce or Mo, were compared. Both remained amorphous up to 600°C because Ce and Mo suppress Ni3B nucleation while B suppresses Ni nucleation. Ni-Ce and Ni-Mo films, with ∼6-7 atom % Ce or Mo, contain Ni as deposited, but the Ni-Ce film has smaller crystallites. The Ni-Ce film with ∼12-13 atom % Ce is amorphous as deposited, while the analogous Ni-Mo film contains crystalline Ni. This result shows that Ce has greater ability to suppress Ni nucleation than atoms such as W and Mo.