2002 Volume 43 Issue 7 Pages 1615-1620
It is essential to decrease RC delay in order to increase the IC device speed. Cu is now adopted to decrease the resistivity of interconnects. Several low k materials have been studied to decrease the dielectric constant. Ag is one of the candidates after Cu as a low resisitivity interconnect metal although it has not yet been adopted in the actual products. It is also studied to decrease the effective dielectric constant values by considering the device configuration such as the cap layer only on the metal. Co–W–P is reported as one of the cap material candidates for Cu. Ni–B is proposed herein as the cap material for Cu and Ag. The study results confirmed that an Ni–B layer can be selectively deposited on Ag metal by the electroless plating method, using DMAB (dimethylamine borane) as the reducing agent; that a deposition rate of 150 nm/min and a B content of 3.2 at% can be obtained under conditions of pH 10 and 353 K; that an Ni–B layer with a 3.2 at%B content provides a barrier effect that prevents Ag and Cu diffusion through thermal processes (in this case, Ni–B remained crystalline before and after a thermal process); and that an Ni–B layer with a 13.5 at%B content does not provide a barrier effect that would prevent Cu diffusion through thermal processes (in this case, the Ni–B structure changed from amorphous to crystalline after the thermal process). Damascene interconnects with Ag metal and a Ni–B cap layer were also formed as part of the trial effort.
