Cu gap-fill is enhanced by replacing the conventional Ta liner with a Co liner in a 22 nm width interconnect structure. The improvement with Co liner seen at the line-end area is attributed to a better resputtered Cu seed profile, which is thicker and exhibits no agglomeration compared to that on Ta liner. The mechanism of Co offering better Cu seed coverage than Ta was further studied and determined to be associated with its better wetting and higher sticking coefficient with Cu during the resputtering process. Similar gap-fill performance was also demonstrated with a reflow Cu seed process. The initial highly conformal Cu seed coverage profile on Co helps ensure a uniform Cu reflow process within the interconnect structure, therefore providing better top-open dimension for electrochemical plating process compared to reflow Cu seed on Ta. . This paper is part of the JES Focus Issue on Electrochemical Processing for Interconnects.As advanced microelectronics move toward the 20 nm node and beyond, back-end of line (BEOL) interconnects are shrinking to sub-80 nm pitch dimensions. 1 Driving toward smaller pitch encounters numerous integration challenges, including Cu metallization. From a circuit performance perspective, one particular issue is the increase of Cu line resistance (R). As metal line widths approach and even become smaller than the electron mean free path within Cu, line resistance no longer linearly scales with dimension. Instead, Cu resistivity starts to increase dramatically due to the increased electron surface scattering. 2 The subsequent increase of the RC (resistance × capacitance) delay within the interconnect circuit will negatively impact the circuit speed. Meanwhile, higher R will also consume more energy and complicate heat dissipation, both of which are not ideal for low-power devices.Besides metallization-related performance challenges, another critical issue in these fine lines is reliability, particularly electromigration (EM). It is increasingly difficult to control microstructure within the metal line and as well as interface qualities at fine dimension. Cu microstructure does not easily form a bamboo grain structure by grain growth from electrochemical plated (ECP) Cu overburden in sub-40 nm metal widths. 3 Connected grain boundaries within polycrystalline Cu lines could act as fast Cu diffusion paths. 4 Meanwhile, the other two critical interfaces, Cu-liner and Cu-cap, need to maintain their strong bonding for EM extendibility. 5,6 But before these performance and reliability issues can even be considered, first these sub-40 nm wide dual-damascene structures must be metallized without Cu-voiding defects. The conventional approach for metallization is to first deposit a layer of barrier and liner (usually TaN and Ta, correspondingly), followed by a Cu seed. The coated wafer will go into a plating bath with ECP Cu nucleation initiated on the PVD Cu seed surface first, and then be filled bottom-up with Cu ECP process. Bottom-up growth results from faster ECP Cu growth at the feature bo...

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Abstract:Permeability of a streambed is an important factor regulating nutrient and oxygen availability for aquatic biota. In order to investigate the relationship, an accurate permeability should be measured. However, it is difficult to measure permeability in a coarse gravel bed using a conventional permeability test. Moreover, turbulent flow may occur in coarse bed material, and then deviations from Darcy's law do occur. Thus, permeability calculated following Darcy's law may be overestimated under turbulent flow conditions and should be corrected. The packer test can be used in highly permeable gravel beds. We developed a field method applicable to a gravel bed using the packer test and derived an equation adopting a law of turbulent flow to study the problems under any type of flow condition. The accuracy of the equation was examined using a laboratory flume with a gravel bed. The results suggested that permeability calculated from Hvorslev's equation is overestimated for turbulent flow. In contrast, our equation, developed here, could evaluate permeability accurately under any type of flow condition.

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Cobalt film with tungsten addition [Co(W)] has the potential to be an effective single-layered barrier/liner in Cu-interconnects owing to its good adhesion with Cu, a lower resistivity than TaN, and an improved barrier property with respect to cobalt films. Our previous study on chemical-vapor-deposited (CVD) Co(W) using carbonyl precursors clarified, however, that WO3 included in the films increased the resistivity. In this current study, to reduce the resistivity of Co(W), oxygen-free process for Co(W) films were designed using two oxygen-free amidinato precursors, bis(N-tert-butyl-N′-ethylpropionamidinato) cobalt and bis(tert-butylimino)bis(dimethylamino)tungsten, by chemical vapor deposition (CVD) and atomic layer deposition (ALD) at 350–400°C. Deposition process were designed by employing quantum chemical calculation, in which NH3 were chosen as a reducing reagent for the sake of the low activation energy of deposition. NH3 actually acted effective reducing reagent for Co or Co(W) deposition using amidinato precursors in our research. Co(W) films using amidinato precursors and NH3 contained no oxygen and a few amounts of nitrogen. Nitrogen, however, were easily eliminated by annealing at 400°C. Therefore, Co(W) films using amidinato precursors were so high quality to have lower resistivity than Co(W) films using carbonyl precursors or conventional PVD-TaN.