Tungsten (W) thin film was deposited at 400 oC using pulsed chemical vapor deposition (pulsed CVD); film was then evaluated as a nucleation layer for W-plug deposition at the contact, with an ultrahigh aspect ratio of about 14~15 (top opening diameter: 240~250 nm, bottom diameter: 98~100 nm) for dynamic random access memory. The deposition stage of pulsed CVD has four steps resulting in one deposition cycle: (1) Reaction of WF6 with SiH4. (2) Inert gas purge. (3) SiH4 exposure without WF6 supply. (4) Inert gas purge while conventional CVD consists of the continuous reaction of WF6 and SiH4. The pulsed CVD-W film showed better conformality at contacts compared to that of conventional CVD-W nucleation layer. It was found that resistivities of films deposited by pulsed CVD were closely related with the phases formed and with the microstructure, as characterized by the grain size. A lower contact resistance was obtained by using pulsed CVD-W film as a nucleation layer compared to that of the conventional CVD-W nucleation layer, even though the former has a higher resistivity (~100 μΩ-cm) than that of the latter (~25 μΩ-cm). The plan-view scanning electron microscopy images after focused ion beam milling showed that the lower contact resistance of the pulsed CVD-W based W-plug fill scheme was mainly due to its better plug filling capability.

We report the effect of the fabric of the surface microstructure on the CO gas sensing properties of SnO2 thin films deposited on self-assembled Au nanodots (SnO2/Au) that were formed on SiO2/Si substrates. We characterized structural and morphological properties, comparing them to those of SnO2 thin films deposited directly onto SiO2/Si substrates. We observed a significant enhancement of CO gas sensing properties in the SnO2/Au gas sensors, specifically exhibiting a high maximum response at 200˚C and quite a low detection limit of 1 ppm level in dry air. In particular, the response of the SnO2/Au gas sensor was found to reach the maximum value of 32.5 at 200˚C, which is roughly 27 times higher than the response (~1.2) of the SnO2 gas sensor obtained at the same operating temperature of 200˚C. Furthermore, the SnO2/Au gas sensors displayed very fast response and recovery behaviors. The observed enhancement in the CO gas sensing properties of the SnO2/Au sensors is mainly ascribed to the formation of a nanostructured morphology in the active SnO2 layer having a high specific surface-reaction area by the insertion of a nanodot form of Au nucleation layer.