Novel Contact-Plug Process with Low-Resistance Nucleation Layer Using Diborane-Reduction Tungsten Atomic-Layer-Deposition Method for 32 nm Complementary Metal–Oxide–Semiconductor Devices and Beyond

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The effect of employing diborane (B2H6) instead of silane (SiH4) in a tungsten (W) atomic layer deposition (ALD) nucleation layer on contact resistance is studied. A low resistance of 50–70 $\Omega$ in a 32-nm-node contact with a diameter of about 50 nm is achieved with optimized barrier and nucleation processes. This result indicates that the resistance required for 32 nm complementary metal–oxide–semiconductor (CMOS) devices can successfully be satisfied without employing a copper plug process. It is revealed that a W film with a B2H6-reduced nucleation layer has a larger grain size and a lower fluorine concentration in nucleation W and barrier metal layers, resulting in a lower resistivity than that with a SiH4-reduced nucleation W layer. On the other hand, the B2H6-reduced nucleation process still shows a poorer crystallization and a higher fluorine concentration in the filling W layer than the SiH4-reduced nucleation process. We revealed that a further decrease in the resistivity of a W film with the B2H6 nucleation process is achieved by improving these issues.
2008-04-25