Kohei Shima

Precursor-based designs of nano-structures and their processing for Co(W) alloy films as a single layered barrier/liner layer in future Cu-interconnect

The drive to continuously downscale Cu interconnects in ultra-large-scale integrated (ULSI) devices requires strategic improvements in materials and their design processes. For example, development of thinner single-layer barrier/liner materials is desired, because Cu line widths approaching the mean free path greatly increase RC signal delays. We designed Co films with the addition of W [Co(W)] for use as a single-layer barrier/liner material using principles from surface engineering and metallurgy. Dupres equation was used to evaluate the adhesion of metals to Cu, which suggested Co as the main component of our proposed single-layer barrier/liner material. Metallurgical analysis suggested that the addition of W would lead to nanostructural improvements and increased barrier performance in Co films. The Co–W phase diagram suggested that W would segregate at grain boundaries, thereby improving barrier performance due to grain-boundary stuffing. Amidinato, metallocene, and carbonyl Co and W precursors were evaluated in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes for the formation of Co(W) films. Oxygen and halogen inclusions were undesirable, because they were predicted to increase the resistivity and cause deviation from the Co–W binary system. To reduce the prevalence of grain boundaries through formation of an amorphous structure, sequential feeding of Co and W precursors in an ALD process was developed for each set of precursors. Oxygen-free Co(W) CVD and ALD processes were achieved using amidinato and metallocene precursors, both of which led to stuffed grain-boundary structures. ALD-Co(W) films exhibited amorphous structures with sufficient barrier performance and low resistivity, which was consistent with our material and process design.

Role of W and Mn for reliable 1X nanometer-node ultra-large-scale integration Cu interconnects proved by atom probe tomography

We used atom probe tomography (APT) to study the use of a Cu(Mn) as a seed layer of Cu, and a Co(W) single-layer as reliable Cu diffusion barriers for future interconnects in ultra-large-scale integration. The use of Co(W) layer enhances adhesion of Cu to prevent electromigration and stress-induced voiding failures. The use of Cu(Mn) as seed layer may enhance the diffusion barrier performance of Co(W) by stuffing the Cu diffusion pass with Mn. APT was used to visualize the distribution of W and Mn in three dimensions with sub-nanometer resolution. W was found to segregate at the grain boundaries of Co, which prevents diffusion of Cu via the grain boundaries. Mn was found to diffuse from the Cu(Mn) layer to Co(W) layer and selectively segregate at the Co(W) grain boundaries with W, reinforcing the barrier properties of Co(W) layer. Hence, a Co(W) barrier coupled with a Cu(Mn) seed layer can form a sufficient diffusion barrier with film that is less than 2.0-nm-thick. The diffusion barrier behavior was pres...

Large electron capture-cross-section of the major nonradiative recombination centers in Mg-doped GaN epilayers grown on a GaN substrate

Complementary time-resolved photoluminescence and positron annihilation measurements were carried out at room temperature on Mg-doped p-type GaN homoepitaxial films for identifying the origin and estimating the electron capture-cross-section ( σ n ) of the major nonradiative recombination centers (NRCs). To eliminate any influence by threading dislocations, free-standing GaN substrates were used. In Mg-doped p-type GaN, defect complexes composed of a Ga-vacancy (VGa) and multiple N-vacancies (VNs), namely, VGa(VN)2 [or even VGa(VN)3], are identified as the major intrinsic NRCs. Different from the case of 4H-SiC, atomic structures of intrinsic NRCs in p-type and n-type GaN are different: VGaVN divacancies are the major NRCs in n-type GaN. The σ n value approximately the middle of 10−13 cm2 is obtained for VGa(VN)n, which is larger than the hole capture-cross-section (σp = 7 × 10−14 cm2) of VGaVN in n-type GaN. Combined with larger thermal velocity of an electron, minority carrier lifetime in Mg-doped GaN becomes much shorter than that of n-type GaN.Complementary time-resolved photoluminescence and positron annihilation measurements were carried out at room temperature on Mg-doped p-type GaN homoepitaxial films for identifying the origin and estimating the electron capture-cross-section ( σ n ) of the major nonradiative recombination centers (NRCs). To eliminate any influence by threading dislocations, free-standing GaN substrates were used. In Mg-doped p-type GaN, defect complexes composed of a Ga-vacancy (VGa) and multiple N-vacancies (VNs), namely, VGa(VN)2 [or even VGa(VN)3], are identified as the major intrinsic NRCs. Different from the case of 4H-SiC, atomic structures of intrinsic NRCs in p-type and n-type GaN are different: VGaVN divacancies are the major NRCs in n-type GaN. The σ n value approximately the middle of 10−13 cm2 is obtained for VGa(VN)n, which is larger than the hole capture-cross-section (σp = 7 × 10−14 cm2) of VGaVN in n-type GaN. Combined with larger thermal velocity of an electron, minority carrier lifetime i...

Separate evaluation of multiple film-forming species in chemical vapor deposition of SiC using high aspect-ratio microchannels

The effect of multiple film-forming species on the film quality during chemical vapor deposition (CVD) of SiC from CH3SiCl3/H2 was examined by separating each species using high aspect-ratio (AR) parallel-plate microchannels. Profiles of the chemical and physical properties of the grown SiC films, including the composition, crystallinity and surface roughness, were characterized along the microchannel depth. The exceptionally high AR, which was typically more than , allowed film growth with a variety of film-forming species that significantly changed with depth. We were thus able to examine the effect of each film-forming species on film growth. The exceptionally large depth, which was typically centimeter-scale, allowed depth profile analysis using various kinds of film characterization techniques having large detection areas. For CVD SiC from CH3SiCl3/H2, multiple film-forming species with different sticking probabilities of 8 × 10−7, 1 × 10−4, and 2 × 10−2 provided almost the same film quality.

Comparative study on ALD/CVD-Co(W) films as a single barrier/liner layer for 22−1x nm generation interconnects

ALD-Co(W) was found to have a potential to replace the conventional PVD-Ta/TaN bi-layer in further shrinking interconnects as a single-layered barrier/liner material. We could confirm good barrier property of CVD/ALD-Co(W) film by BTS-TVS method after 350°C annealing. ALD-Co(W) showed lower resistivity of 60 μΩ-cm and good adhesion to Cu. Complete trench filling with Co(W) followed by Cu seed deposition was demonstrated. These properties were confirmed to be derived from W stuffing into grain boundaries of oxygen-free ALD-Co(W) films. We would like to suggest ALD-Co(W) as a next-generation barrier/liner layer for future development.