Emerging Non-Noble-Metal Atomic Layer Deposited Copper as Seeds for Electroless Copper Deposition.

Copper metal catalyst seeds have recently triggered much research interest for the development of low-cost and high-performance metallic catalysts with industrial applications. Herein, we present metallic Cu catalyst seeds deposited by an atomic layer deposition method on polymer substrates. The atomic layer deposited Cu (ALD-Cu) can ideally substitute noble metals Ag, Au, and Pd to catalyze Cu electroless deposition. The optimized deposition temperature and growth cycles of an ALD-Cu catalyzed seed layer have been obtained to achieve a flexible printed circuit (FPC) with a high performance electroless plating deposited Cu (ELD-Cu) film. The ELD-Cu films on the ALD-Cu catalyst seeds grown display a uniform and dense deposition with a low resistivity of 1.74 µΩ·cm, even in the through via and trench of substates. Furthermore, the ALD-Cu-catalyzed ELD-Cu circuits and LED devices fabricated on treated PI also demonstrate excellent conductive and mechanical features. The remarkable conductive and mechanical characteristics of the ALD-Cu seed catalyzed ELD-Cu process demonstrate its tremendous potential in high-density integrated FPC applications.

Improved Electrical Resistivity of Atomic-Layer-Deposited Copper Thin Films on Polyimide Substrates by an In Situ ZnO Interlayer.

The low-temperature atomic layer deposition of metal on polymer surfaces is often challenging owing to the deficiency of functional groups and reactivity. Here, the deposition of ALD-Cu employing Cu(hfac)2 and Et2Zn at a low temperature (120 °C) on polyimide (PI) substrates is improved by the utilization of an in situ ultrathin ALD-ZnO buffer layer. A conformal and continuous ALD-Cu thin film with low resistivity (6.07 µΩ cm) is fabricated on an ALD-ZnO/PI substrate. The findings demonstrate that the ALD-ZnO buffer layer provides chemisorption and a nucleation site for the initial growth of ALD-Cu. Transmission electron microscopy and energy-dispersive X-ray analysis reveal that the ALD-ZnO layer plays a buffer role in the fitness of ALD-Cu on PI substrates and its ability to elicit the formation of an ALD-ZnO nanocluster and polar surface. ALD-ZnO can be effectively utilized as a buffer layer for polymer-based ALD-metal processes, showing potential in flexible electronic applications.