Tungsten ͑W͒ thin films were deposited using the modified chemical vapor deposition ͑CVD͒, the so-called pulsed CVD, and their properties were characterized as nucleation layers for the chemical vapor deposited W ͑CVD-W͒ technology of sub-50 nm memory devices. W growth per cycle was extremely linear with a higher growth rate of ϳ0.58 nm/cycle as compared to that ͑ϳ0.28 nm/cycle͒ of the atomic layer deposition ͑ALD͒ process using the same chemistry. From the X-ray diffractometry, the pulsed CVD-W film was formed as an amorphous structure, which was the same as the atomic layer deposited W. This led to the formation of a low resistivity bulk CVD-W film deposited on it with the grain size of ϳ180 nm at 200 nm thick film, and its resistivity was further decreased with the B 2 H 6 post-treatment before the deposition of bulk CVD-W film ͑ϳ13 ⍀ cm at a 50 nm thick film͒. However, we found that the adhesion performances of CVD-W growing on the B 2 H 6 -based pulsed CVD-W nucleation layer were significantly degraded as both the deposition temperature of the nucleation layer and the B 2 H 6 posttreatment time increased. High resolution transmission electron microscopy and energy-dispersive spectroscopy analysis clearly demonstrated that a discontinuous boron layer was formed at the bulk CVD-W/nucleation layer interface, which was dominantly due to the B 2 H 6 decomposition during the B 2 H 6 post-treatment. We strongly suggest that a boron-containing discontinuous layer degrades the adhesion properties of CVD-W films growing on it. Considering the thermodynamics of the B 2 H 6 decomposition, we can improve the adhesion properties by increasing the H 2 flow rate at the post-treatment step.The chemical vapor deposited W ͑CVD-W͒ technology has been traditionally used in the semiconductor devices as a contact and via plug material. Recently, there has been an increased interest in its applications on the gate or the bit line and plug material to source/drain. 1 The CVD-W process is composed of two steps: The first step is the W nucleation layer deposition, which is basically the reduction of WF 6 using SiH 4 with a fast nucleation on a typical glue/barrier layer, TiN films, and the second is the bulk-W deposition accomplished by H 2 reduction of WF 6 because of its excellent step coverage. 2 However, as the minimum feature size is continuously shrinking, the application of CVD-W technology has been more challenging. First, as the contact size decreases, a limited conformality of the nucleation layer at ultrahigh aspect-ratio ͑UHAR͒ contact can induce the potential problems such as the seam and void when the subsequent CVD-W film is deposited into the contact, causing a degradation in the contact resistance. 3 These issues can be solved by adopting the nucleation layer deposited by atomic layer deposition ͑ALD͒, which is known to provide an excellent step coverage. The studies on the nucleation of atomic layer deposited W ͑ALD-W͒ using Si 2 H 6 , SiH 4 , and B 2 H 6 as reducing agents of WF 6 have been reported. 3-8 Second, the...

The resistivity of chemical-vapor-deposited ͑CVD͒-W film was reported to be significantly reduced using a B 2 H 6 -based atomic layer deposited ͑ALD͒-W nucleation layer for continuously shrinking memory devices. But, we found that the adhesion performances of CVD-W films growing on the B 2 H 6 -based ALD-W nucleation layer were poor compared to those on the SiH 4 -based W nucleation layer. Scanning electron microscopy and secondary ion mass spectrometry analysis clearly suggest that the boron penetration into the interface between underlying TiN and SiO 2 during the deposition of W nucleation layer is a possible reason to degrade the adhesion performances of CVD-W films with B 2 H 6 -based W nucleation layers. By rigorous selection of both the deposition conditions for W nucleation layer and diffusion barrier materials, we can demonstrate the successful deposition of CVD-W film with a very low resistivity of ϳ12 ⍀ cm ͑50 nm in thickness͒ without an adhesion failure. Noticeably, the application of 5 nm thick sputter-deposited WN x film as a glue layer was found to present an excellent adhesion performance, which was due to its excellent diffusion barrier performance with amorphous structure.Chemical-vapor-deposited ͑CVD͒-W thin film has a long tradition as a metallization material for fabricating the interconnects of semiconductor devices. Generally, CVD-W film has been used for plugging processes or filling the contact or via plug with a high aspect ratio for multilevel metallization of semiconductor devices 1-3 due to its excellent step coverage. CVD-W is even being considered as a word line and a metal line in the damascene trench structure of memory devices. But, as the metal linewidth in the semiconductor devices shrinks to the sub 50 nm dimensions, the electron mean-free path of W ͑ϳ41 nm͒ 4 becomes comparable with some of its physical dimension such as film thickness, surface roughness, and grain size, resulting in the drastic increase in the resistance of the metal line, which is called "size effect." 5 Thus, to overcome the size effect on the resistivity of W film and realize the excellent speed performance of the circuit, a new process on CVD-W film should be investigated.Generally, CVD-W films are deposited by a two-step process: a deposition of a very thin W nucleation layer and a subsequent growth of relatively thick bulk-W film. This gives the possibility that the properties of the CVD-W film, including its resistivity, can be controlled and improved by controlling the process of the W nucleation layer because the underlying film can have considerable effects on the properties of the metal film growing on it. 6,7 In fact, it has been reported that the resistivity of bulk CVD-W film could be reduced by using a B 2 H 6 -based W nucleation layer as compared to a SiH 4 -based one, and even more, the resistivity increase by the size effect could be mitigated. 7-11 It was also reported that the structural properties of the B 2 H 6 -based W nucleation layer, such as its phase ͑amorphous, ␤, and ␣-phase͒, cr...