The effect of strain on abnormal grain growth in Cu thin films

Moriyama, Miki; Matsunaga, Kentaro; Murakami, Masanori

doi:10.1007/s11664-003-0219-7

Cited by 37 publications

(30 citation statements)

References 14 publications

(19 reference statements)

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“…Although several parameters (such as surface energy, grain boundary energy, impurities, etc) to control the grain growth of the Cu thin films were proposed, [5][6][7][8] we demonstrated experimentally in our previous papers 9,10) that the strain (or stress) introduced into the thin films was the primary factor to enhance the grain growth specially at low temperatures in addition to surface/grain boundary energy.…”

Section: Introductionmentioning

confidence: 99%

Grain Growth Mechanism of Cu Thin Films

et al. 2005

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Since Cu was found to be attractive as interconnect materials for ultra-large scale integrated (ULSI) Si devices, the electrical properties of Cu films have been extensively studied to prepare low resistance films. It was found in our previous papers that reduction of the electrical resistance of the Cu films was achieved by increasing grain sizes of the Cu films and large-grained Cu films were essential for the low resistance Cu interconnects. The primary factor to increase the grain sizes was also found to be intrinsic and/or extrinsic strain (or stress) introduced into the films. The present paper addresses the driving force of the grain growth of the Cu thin films based on the strain energy criterion model.

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Section: Introductionmentioning

confidence: 99%

Grain Growth Mechanism of Cu Thin Films

et al. 2005

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“…1 and 2, the reduction of the values could be explained by the reduction of the grain-boundary density in the films due to grain growth, as observed previously. 20) Thus, the grain growth rate of the 6N-Cu film is smaller than that of the 4N-Cu film.…”

Section: Cu Films With Thickness Of 100 Nmmentioning

confidence: 97%

“…We concluded that the organic additives (needed for electroplating) were not the only primary factor causing Cu grain growth. 20) Because the Cu films have intrinsic strain when deposited on the rigid substrates, the strain introduced in individual grains of the Cu film was concluded to be the primary factor to induce abnormal grain growth. 20) Strain in the polycrystalline metal films is generally relaxed by several deformation (or strain relaxation) mechanisms, which are influenced by film microstructure and impurities in the films.…”

Section: Inrtoductionmentioning

confidence: 99%

“…20) Because the Cu films have intrinsic strain when deposited on the rigid substrates, the strain introduced in individual grains of the Cu film was concluded to be the primary factor to induce abnormal grain growth. 20) Strain in the polycrystalline metal films is generally relaxed by several deformation (or strain relaxation) mechanisms, which are influenced by film microstructure and impurities in the films. Thus, if the strain is the primary factor that enhances grain growth at room temperature, the grain-growth rate in the sputtered Cu films would be affected by the purities in the Cu films and the grain-growth rates are different for the films sputter-deposited using Cu targets with different impurity levels.…”

Section: Inrtoductionmentioning

confidence: 99%

“…We reported previously that significant grain growth was observed during room-temperature storage in sputtered Cu films deposited on the rigid substrates, but no grain growth was observed during roomtemperature storage in the free-standing Cu films. 20) Previous experimental results suggest that the grain growth in the Cu films could not occur at room temperature unless additional energetic assistance was given to the films. Intrinsic strains, which were introduced into the films from the substrates, were found to provide the energetic assistance for grain growth in Cu films bonded to the rigid substrates.…”

Section: Driving Force For Grain Growth In Cu Filmsmentioning

confidence: 99%

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The Effect of Target Purities on Grain Growth in Sputtered Copper Thin Films

et al. 2005

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Grain growth rates in sputtered Cu thin films were found to be influenced by impurity levels of the sputtering targets. The Cu thin films with thickness of 100 nm or 1 mm were deposited on the rigid substrates by a sputter-deposition technique using the Cu target with purity of 99.99% (4N) or 99.9999% (6N), then subsequently annealed at room temperatures. The microstructures of the Cu films were analyzed by scanning-ion microscopy and the sheet resistivities was measured by a four-point probe method. Significant grain growth and reduction of the electrical resistivities was observed during room-temperature storage in these sputtered Cu films. For the Cu films with a thickness of 1 mm, the grain growth rates of the Cu films were not influenced by the impurity levels of the targets. However, for the films with a thickness of 100 nm, the rate of the grain growth in the 6N-Cu films was found to be slower than that in the 4N-Cu films. This was contradictory to the grain growth mechanism of bulk Cu. The grain growth rates of the Cu films at room temperature, which were strongly influenced by the existence of a small amount of impurities in the Cu films, were well explained by the difference of the strain relaxation mechanisms in the films.

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Novel Crosslinking of High‐order and Multiple Copper Twins in Advanced Microelectronics Packaging

2004

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The microelectronics packaging industry is flourishing and continuingly reinvesting its past success into the more advanced development. Nowadays copper has become principally important as the common metallization material. [1,2] However, studies about the metallization itself are seldom reported. Here we show, to our knowledge for the first time, that the complex configuration of high-order and multiple copper twins were formed in the metallization/solder interconnect subjected to the thermal aging, which simulates working environments for the electric devices in ultra largescale integration (ULSI). This surprising finding may illustrate a universal metallization failure, which will have immediate implications for choosing the metallization materials in advanced microelectronics packaging. Meanwhile, novel copper nanocrystals in situ originated from those twins crosslinking sheds a novel light on the synthesis approach of fascinating nanocrystalline metals. [3±6] The combination of disadvantage and advantage may interest correlated researches in a variety of multidisciplinary areas, such as materials science, electrical engineering, condensed-matter physics and nanotechnology.The morphologies of the copper/tin-bismuth interconnect samples for microelectronics packaging (see Experimental) are shown in Figure 1, consisting of Cu metallization, {CuSn} intermetallics and Sn-Bi solder. Contrast to the as-reflowed state, the thermal aging promoted the growth of the intermetallics evidently. Figure 2 is a typical cross-sectional TEM image of Cu metallization and the intermetallics after the aging. It can be found that many cracks and Kirkendall voids occurred around their interface, just as reported in the literature. [7] Such nature of stress concentration must have resulted in the development of microstructures of the copper metallization.Large amounts of transmission electron microscopy (TEM) observations reveal that after the aging, profuse high-order and multiple copper twins are formed in the metallization. Such complex crosslinking of twins constituted many highangle copper nanocrystals, marked by the numbers in Figure 3a. While in the as-reflowed coarse-grained copper metallization, the grain size is of the magnitude of micrometers. So here the formation of the unique nanocrystals of which boundaries are approximate to low-energy {111} twinning planes, could be attributed to the minimization of the system energy [8] under the treatment. It is well known that such nanocrystals will impart high strength and hardness, as expected from an extrapolation of the Hall-Petch relationship and also by the interfaces generated between twinned seg-COMMUNICATIONS 232

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The effect of strain on abnormal grain growth in Cu thin films

Cited by 37 publications

References 14 publications

Grain Growth Mechanism of Cu Thin Films

Grain Growth Mechanism of Cu Thin Films

The Effect of Target Purities on Grain Growth in Sputtered Copper Thin Films

Novel Crosslinking of High‐order and Multiple Copper Twins in Advanced Microelectronics Packaging

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