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Ohmori K.,Renesas Electronics Corporation | Mori K.,Renesas Electronics Corporation | Maekawa K.,Renesas Electronics Corporation | Kohama K.,Kyoto University | And 6 more authors.
2010 IEEE International Interconnect Technology Conference, IITC 2010 | Year: 2010

We have studied key factors of Ti-based self-formed barrier technique on interconnect reliability. A performance of time dependent dielectric breakdown shows superior endurance, using quite a thin Ti -based self-formed barrier. However, to achieve a superior electromigration performance using Ti-based self-formed barrier, much more amount of Ti is needed compared with that of TDDB performance. This is why the control of excess Ti atoms is important to suppress the electromigration. We also discuss the mechanism that why the excess Ti improve reliability performance. ©2010 IEEE. Source

Kohama K.,Kyoto University | Ito K.,Kyoto University | Matsumoto T.,Kyoto University | Shirai Y.,Kyoto University | Murakami M.,Ritsumeikan Trust
Acta Materialia | Year: 2012

To understand the role of Cu film texture in grain growth at room temperature (RT) in relation to twin boundary formation Cu films were deposited on various barrier materials and the Cu film texture was investigated by X-ray diffraction. Cu grain growth was rapid on a barrierless SiO2/Si substrate and very slow on a Ta barrier due to strong (1 1 1) texture. The growth rate and the average grain diameter after being kept at RT for up to ∼60 days were maximum at a (2 0 0)Cu peak to (2 2 2)Cu peak area ratio of ∼1.0, where {1 1 1}, {1 0 0} and {5 1 1} grains coexisted. Such coexistence of three or more orientations of grains is essential in facilitating Cu grain growth at RT. Similarly, the average twin boundary (TB) density was maximum when Cu grain growth was facilitated. TB formation in nano-sized Cu grains was not controlled by grain size, but due to grain growth. The TB could be annealing twins caused by irregularities in the stacking sequence during relatively fast grain growth. The Cu film texture is concluded to be determined at the beginning of deposition, and the wettability of various barrier materials by the Cu films plays a key role in determining the film texture. © 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved. Source

Uehara S.,Kyoto University | Ito K.,Kyoto University | Kohama K.,Kyoto University | Onishi T.,Kobe Steel | And 2 more authors.
Materials Transactions | Year: 2010

Low-resistivity and excellent-adhesion Cu(Ti) alloy films were prepared on glass substrates. Cu(0.3∼4 at%Ti) alloy films were deposited on the substrates, and subsequently annealed in vacuum at 400°C for 3 h. Resistivity of the annealed Cu(Ti) alloy films was significantly reduced to about 2.8 μ.ficm. Tensile Ωstrength of the Cu(Ti)/glass interface increased to about 60 MPa after annealing. The low resistivity and excellent adhesion resulted from Ti segregation at the film surface and the Cu(Ti)/glass interface. The segregated Ti atoms reacted with atmospheric oxygen at the surface and with oxygen in glass and/or from atmosphere at the interface, and formed a TiO2 layer at the surface and a TiO2 layer with a small amount Of Ti2O3 and TiO at the interface. The layers were non-crystalline. Columnar grains in the alloy films were seen to enhance Ti segregation and subsequent Cu grain growth. The Cu grain growth also contributed to low resistivity of Cu(Ti) alloy films. © 2010 The Japan Institute of Metals. Source

Uehara S.,Kyoto University | Uehara S.,Kobe Steel | Ito K.,Kyoto University | Kohama K.,Kyoto University | And 4 more authors.
Materials Transactions | Year: 2011

Cu(Ti) alloy films with low-resistivity and excellent-adhesion have been successfully prepared on glass substrates. To gain further resistivity reduction and adhesion strength, growth of a Ti-based interface layer was investigated using Ruüierford backscattering spectrometry (RBS) in the present study. Cu(0∼5 at%Ti) alloy films were deposited on glass substrates and subsequently annealed in vacuum at 400∼600°C for 0.5~24 h. Results were compared with those for samples on SiO2 substrate previously obtained. Ti peaks were obtained in RBS spectra only at the interfaces for bout Cu(Ti)/glass and Cu(Ti)/SiO2 samples. Molar amounts of Ti atoms segregated to the interfaces (n) were estimated from Ti peak areas. The m values estimated from the slopes of the log n versus log t lines were almost similar for all the samples (m = 0.10∼0.12), suggesting that growth of the Ti-based interface layers was controlled by a similar mechanism. The activation energy of the Cu(Ti)/glass samples was similar to that of the Cu(Ti)/SiO2 samples, while a pre-exponential factor (Z) of the Cu(Ti)/glass samples was approximately half of the value of the Cu(Ti)/SiO2 samples. The Z value shows the frequency with which the Ti atoms meet oxygen in the glass substrates. Impurities in the glass substrates lowered the frequency. These factors lead to the conclusion mat growth rate of me Ti-based interface layers on glass substrates was slower than that on SiO2. The Ti-based interface layer growth was also influenced by microstructure of Cu(Ti) alloy films formed on the glass substrates. Columnar grains in the Cu(Ti) alloy films were seen to enhance Ti segregation. However, an equiaxed zone above the interface retarded Ti diffusion to the interface, leading to lack of Ti atoms for me reaction. © 2011 The Japan Institute of Metals. Source

Ito K.,Kyoto University | Ohmori K.,Renesas Electronics Corporation | Kohama K.,Kyoto University | Mori K.,Renesas Electronics Corporation | And 3 more authors.
AIP Conference Proceedings | Year: 2010

Cu interconnects have been used extensively in ULSI devices. However, large resistance-capacitance delay and poor device reliability have been critical issues as the device feature size has reduced to nanometer scale. In order to achieve low resistance and high reliability of Cu interconnects, we have applied a thin Ti-based self-formed barrier (SFB) using Cu(Ti) alloy seed to 45nm-node dual damascene interconnects and evaluated its performance. The line resistance and via resistance decreased significantly, compared with those of conventional Ta/TaN barriers. The stress migration performance was also drastically improved using the SFB process. A performance of time dependent dielectric breakdown revealed superior endurance. These results suggest that the Ti-based SFB process is one of the most promising candidates for advanced Cu interconnects. TEM and X-ray photoelectron spectroscopy observations for characterization of the Ti-based SFB structure were also performed. The Ti-based SFB consisted of mainly amorphous Ti oxides. Amorphous or crystalline Ti compounds such as TiC, TiN, and TiSi formed beneath Cu alloy films, and the formation varied with dielectric. © 2010 American Institute of Physics. Source

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