Grain Size And Cap Layer Effects On Electromigration Reliability Of Cu Interconnects: Experiments And Simulation

Li-juan, Zhang; Kraatz, Matthias; Aubel, Oliver; Hennesthal, C.; Zschech, Ehrenfried; Ho, Paul S.

doi:10.1063/1.3527136

Cited by 14 publications

(17 citation statements)

References 12 publications

(21 reference statements)

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“…Such grain boundary/interface junctions can act as flux divergent sites for void formation. Based on our EM test results [2] and the observed grain structures, we were able to calculate the flux divergence and identify the critical void formation sites.…”

Section: B Diffusivity Determination and Microstructure-based Flux Dmentioning

confidence: 99%

“…The effective diffusivities D eff for Cu interconnects with SiCN capping were determined from the resistance traces observed in EM tests [2]. As shown in Table I, the effective diffusivity is larger for the SG structure, reflecting the larger contribution of grain boundary diffusion from the small grains.…”

Section: B Diffusivity Determination and Microstructure-based Flux Dmentioning

confidence: 99%

“…(a) CDF plots of CoWP capped samples with LG and SG structures from EM tests[2]. (b) Simulated CDF plots for LG and SG structures with N = 1, 2, 4 in the probability scale.…”

mentioning

confidence: 99%

“…The emergence of polycrystalline Cu grain structure in fine lines for the 65 nm node technology and beyond markedly reduced the Cu EM reliability due to the addition of grain boundary diffusion to the overall mass transport [1]. Recently, we investigated the grain structure effect on Cu interconnects with SiCN and CoWP cap layers for the 45 nm node with a 70 nm line width [2]. The results showed significant grain structure effects, particularly for CoWP capping where the interface diffusion is suppressed.…”

mentioning

confidence: 99%

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Analysis of grain structure by precession electron diffraction and effects on electromigration reliability of Cu interconnects

Cao

Ganesh

Zhang

et al. 2012

2012 IEEE International Interconnect Technology Conference

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In this paper, a recently developed high resolution electron diffraction technique is employed to characterize the grain orientation and grain boundaries for 45 nm node Cu interconnects with SiCN capping. The results are applied to evaluate the grain structure effect on electromigration (EM) reliability. We first calculate the flux divergence for void formation using interfacial and grain boundary diffusivities extracted from the resistance evolution of test structures observed during EM tests. To further correlate grain structure statistics with EM failure statistics, the EM lifetime distribution for Cu interconnects with CoWP capping is analyzed using a microstructure-based statistical model

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Section: B Diffusivity Determination and Microstructure-based Flux Dmentioning

confidence: 99%

Section: B Diffusivity Determination and Microstructure-based Flux Dmentioning

confidence: 99%

“…(a) CDF plots of CoWP capped samples with LG and SG structures from EM tests[2]. (b) Simulated CDF plots for LG and SG structures with N = 1, 2, 4 in the probability scale.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

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Analysis of grain structure by precession electron diffraction and effects on electromigration reliability of Cu interconnects

Cao

Ganesh

Zhang

et al. 2012

2012 IEEE International Interconnect Technology Conference

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“…With its higher electrical and thermal conductivity, its better thermal stability and its smaller coefficient of thermal expansion compared to Al, Cu pushed the limits for clock frequencies and power consumption for semiconductor devices. In frontend applications the Cu grain size gains more and more importance on the overall performance and reliability of the interconnect system [1][2]. Apart from the importance for frontend applications, the development of highly integrated 3D systems, as well as power applications creates a need for Cu based backend technologies, such as direct Cu-Cu Bonding and Cu to Cu wire bonding.…”

Section: Introductionmentioning

confidence: 99%

Influence of liner-system and Cu-layer thickness on the grain structure of electroplated Cu

Mueller

Kriz

Meinhold

et al. 2012

2012 4th Electronic System-Integration Technology Conference

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The grain structure of 1.2 µm electroplated Cu layers with undoped Cu seed layer has been investigated using electron backscatter diffraction (EBSD). Therefore orientation imaging microscopy (OIM) was carried out on samples with five different liner systems (Ti, Ta, WTi, TiN and TaN), three different annealing steps (self-anneal at room temperature, 1 h at 110 °C and 0.5 h at 380 °C) and two plating chemistries with varying acid content. In addition, samples with 1 µm and 3 µm electroplated Cu on an Al-doped Cu seed layer have been analyzed in order to investigate the influence of the plated layer thickness on grain structure.The results show that the grain structure is dominated by low energy CSL boundaries, especially Σ3 twins, which can be found in almost every grain. This twinning causes a typical deviation from the expected {111} orientation parallel to the sample surface towards {115} orientations. This is the result of the self-annealing process (caused by recrystallization).Differences in orientation caused by the liner system will be shown as well as influences of the Cu-plating thickness on the fraction of {101} orientations. Finally, changes in grain size and twinning fraction due to subsequent annealing steps will be presented. IntroductionSince Cu was successfully implemented in semiconductor processes, the variety of applications of Cu based devices has grown steadily. With its higher electrical and thermal conductivity, its better thermal stability and its smaller coefficient of thermal expansion compared to Al, Cu pushed the limits for clock frequencies and power consumption for semiconductor devices. In frontend applications the Cu grain size gains more and more importance on the overall performance and reliability of the interconnect system [1-2]. Apart from the importance for frontend applications, the development of highly integrated 3D systems, as well as power applications creates a need for Cu based backend technologies, such as direct Cu-Cu Bonding and Cu to Cu wire bonding. The properties of Cu such as surface oxidation or the mechanical behavior like hillock formation and Cu protrusion in through silicon vias (TSV) are only some of the challenges, which need further process related investigations on microstructure in order to make Cu based interconnection technologies more reliable.Cu thin films are deposited by electrochemical deposition because of its good filling properties (compared to physical vapor deposition), its availability due to the frontend applications, and the fast and cost efficient process implementation. The resulting grain structure undergoes a so called self-annealing process after plating that causes a microstructure evolution at room temperature accompanied by decreasing resistance and hardness [3][4][5][6][7][8]. Investigations by

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Electromigration in Cu(Al) and Cu(Mn) damascene lines

Hu¹,

Ohm²,

Gignac³

et al. 2012

Journal of Applied Physics

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The effects of impurities, Mn or Al, on interface and grain boundary electromigration (EM) in Cu damascene lines were investigated. The addition of Mn or Al solute caused a reduction in diffusivity at the Cu/dielectric cap interface and the EM activation energies for both Cu-alloys were found to increase by about 0.2 eV as compared to pure Cu. Mn mitigated and Al enhanced Cu grain boundary diffusion; however, no significant mitigation in Cu grain boundary diffusion was observed in low Mn concentration samples. The activation energies for Cu grain boundary diffusion were found to be 0.74 ± 0.05 eV and 0.77 ± 0.05 eV for 1.5 μm wide polycrystalline lines with pure Cu and Cu (0.5 at. % Mn) seeds, respectively. The effective charge number in Cu grain boundaries Z*GB was estimated from drift velocity and was found to be about −0.4. A significant enhancement in EM lifetimes for Cu(Al) or low Mn concentration bamboo-polycrystalline and near-bamboo grain structures was observed but not for polycrystalline-only alloy lines. These results indicated that the existence of bamboo grains in bamboo-polycrystalline lines played a critical role in slowing down the EM-induced void growth rate. The bamboo grains act as Cu diffusion blocking boundaries for grain boundary mass flow, thus generating a mechanical stress-induced back flow counterbalancing the EM force, which is the equality known as the “Blech short length effect.”

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Grain Size And Cap Layer Effects On Electromigration Reliability Of Cu Interconnects: Experiments And Simulation

Cited by 14 publications

References 12 publications

Analysis of grain structure by precession electron diffraction and effects on electromigration reliability of Cu interconnects

Analysis of grain structure by precession electron diffraction and effects on electromigration reliability of Cu interconnects

Influence of liner-system and Cu-layer thickness on the grain structure of electroplated Cu

Electromigration in Cu(Al) and Cu(Mn) damascene lines

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