Advanced tungsten plug process for beyond nanometer technology

This investigation elucidates various tungsten (W) nucleation layers in different W-plug fill processes. Four W-plug nucleation layers are evaluated. They involve an atomic layer deposition (ALD) W nucleation with SiH₄-base sequential nucleation layers, an ALD W nucleation with B₂H₆-base sequential nucleation layers, a conventional W chemical vapor deposition (CVD) nucleation layer, and a pulsed nucleation layer, respectively. Bulk deposition includes high pressures of 300 Torr and conventionally 90 Torr with hydrogen as a reductant of WF₆. A scanning electron microscopic analysis of the ALD W nucleation layer is conducted; it is a thin, smooth and dense film, which enhances the bulk deposition grain growth to increase grain size with low resistivity. Electrical results for ALD W processes are comparable to those for conventional W process in general barrier process condition. However, as the W-plug fills process on the weak and thin metal organic chemical vapor deposited (MOCVD) TiN barrier is varied, the ALD W processes retain their original electrical resistance performance. Unlike ALD W processes, the conventional W CVD suffers from serious contact resistance opening and tail bits. Transmission electron microscope profiles reveal that the thin and dense B₂H₆-base sequential nucleation layers prevent WF₆ molecular penetration through the TiN/Ti_x interface. Additionally, various W-plug fill processes are implemented in the tungsten damascene test vehicle, and the ALD B₂H₆-base sequential nucleation layers and subsequently formed bulk deposition at 300 Torr have lower resistance than under other conditions. The contact profile obtained using the transmission electron microscope reveals that the ALD B₂H₆-base W-plug has favorable fill-in capability for both 100 nm and 60 nm contact sizes. Their lower resistivity and thinner nucleation layer suit them in particular to implement at a contact size of 100 nm and smaller. The ALD B₂H₆-base sequential nucleation layers and subsequently formed bulk deposition at 300 Torr can be used in the next generation of W-plug fill process.