Characterizations of Pulsed Chemical Vapor Deposited-Tungsten Thin Films for Ultrahigh Aspect Ratio W-Plug Process

Abstract

Tungsten ͑W͒ thin films were deposited using a modified chemical vapor deposition ͑CVD͒ process, called pulsed CVD, and the film properties were characterized as nucleation layers for a W-plug fill process. In this study, the deposition stage is composed of four steps, resulting in one deposition cycle: ͑i͒ reaction of WF 6 with SiH 4 , ͑ii͒ inert gas purge, ͑iii͒ SiH 4 exposure, and ͑iv͒ inert gas purge. The W growth per cycle was extremely linear with a growth rate of ϳ1.32 nm/cycle at 400°C. The growth rate was further enhanced to 1.5-1.9 nm/cycle by increasing the SiH 4 flow rate in the first step and/or by adding H 2 in the first and the third steps. The W film deposited by pulsed CVD showed a much lower roughness ͑ϳ0.7 nm͒ and a better conformality at the contact holes with an aspect ratio of 14, compared to W films deposited by conventional CVD using WF 6 and SiH 4 . The film resistivity was closely related with its phase ͑body-centered cubic ␣-W or primitive cubic ␤-W͒ and microstructure characterized by grain size as well as the film thickness ͑the "size effect"͒. Transmission electron microscopy analysis showed that H 2 addition into the first and third steps increased the grain size from ϳ7 to ϳ13 nm and prevented the film from forming a ␤-W phase with high resistivity, resulting in a lower resistivity of 100 ⍀-cm compared to that of the W film deposited without H 2 addition ͑210 ⍀-cm͒. H 2 addition was also effective in reducing the F and Si impurities in the films. Finally, the film resistivity was discussed on the basis of impurity, roughness, microstructure, and film phase.

Electrical Properties of Carbon Nanotube Via Interconnects Fabricated by Novel Damascene Process

“…This characteristic is ohmic, which has been attributed to electron-phonon scattering [7]. The corresponding resistivity of 379 μΩ·cm was obtained for 520-nm-height CNT vias, which are of the same order of magnitude as the value of CVD-tungsten (W) plugs (100-210 μΩ·cm) [8].…”

Integration of Low Resistive CVD-W Interconnects for sub-50nm FEOL application

“…It was interesting that with the amorphous-WN barrier metal, the resistivity of CVD-W films was decreased dramatically even though CVD-W was deposited on the SiH 4 -reduced W nucleation layer. [Compare split (1) and (5)] Generally, it is known that the grain-boundary scattering is the dominant factor to determine the W resistivity and the resistivity reduction of CVD-W is due to the increase of final W grain size [3]. From this result, we conclude that the growth properties of CVD-W films are strongly dependent upon the barrier metals and their phases and the deposition condition of W nucleation layer.…”

Effects of B[sub 2]H[sub 6] Pretreatment on ALD of W Film Using a Sequential Supply of WF[sub 6] and SiH[sub 4]

“…The resistivity of ALD-W film without B 2 H 6 pretreatment is ϳ138 ⍀ cm, which is significantly higher than that of conventional CVD-W film ͑ϳ25 ⍀ cm͒. 12 With 5 s B 2 H 6 pretreatment, its resistivity is slightly decreased to ϳ128 ⍀ cm. However, when the B 2 H 6 pretreatment is continued up to 30 s, the resistivity of ALD-W film is increased up to ϳ178 ⍀ cm.…”

“…These results indicate that the film properties, affecting the film resistivity such as roughness, grain size, crystallinity, and phase, z E-mail: soohyun.kim@hynix.com change with B 2 H 6 pretreatment conditions. 12 Figure 1b shows the root-mean-square ͑rms͒ surface roughness of W films. As shown in this figure, the 5 s B 2 H 6 pretreatment significantly reduces the film roughness.…”