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Recently, we reported on a smart, nickel-free electroless copper bath specifically designed for ultra-thin (≤ 150 nm) deposits for SAP applications. Although this bath, henceforth referred to as Bath A, is not capable of achieving thicker deposits during conventional plating times as a result of its self-limiting behavior, it does offer other significant benefits such as excellent electrical reliability, throwing power, deposit purity and crystallinity as well as good deposit adhesion to smooth substrates. Furthermore, deposits from Bath A demonstrate a low specific resistance, which is close to that of bulk copper. In view of these benefits and of the fact that the industry is still challenged in efficiently handling electroless copper deposits in the sub-200 nm regime on a mass-production scale, we decided to design a bath system that allows for easy and flexible switching between desired deposit target thicknesses using one and the same fundamental bath formulation. Consequently, by adding a certain moderating component composition to Bath A, the still nickel-free Bath B is obtained, in which the self-limiting feature of Bath A is lifted, and the deposition speed is accelerated. Bath B is therefore capable of blister-free deposition on established build-up films at thicknesses of up to 250 nm using typical plating time durations. To obtain blister-free deposits with thicknesses greater than 250 nm, one can use Bath C, which is prepared by simply adding nickel to Bath B. Since all three baths are based on the same fundamental composition defined by Bath A, enhanced throwing power, deposit purity and crystallinity as well as conductivity are ensured for all three baths. We expect Bath C to meet current and near-future industry requirements regarding electroless copper deposit properties including thickness. Thinner deposits with increasingly better conductivity can be readily accomplished by just "switching off" the nickel and the moderating component composition supply in succession, which will allow the easy transition to Bath B and finally to Bath A. Baths A-C thus constitute a modular electroless copper bath system, which is suitable for immediate deployment and is also future-ready. We expect this bath system will offer the industry unparalleled flexibility, agility and adaptability as it transitions to a state in which it is able to handle thinner and thinner electroless copper deposits on a mass-production scale.