Kyoto, Japan
Kyoto, Japan

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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.


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.


Ito K.,Kyoto University | Kohama K.,Kyoto University | Tanaka T.,Kyoto University | Mori K.,Renesas Electronics Corporation | And 3 more authors.
Journal of Electronic Materials | Year: 2010

To investigate the applicability of the technique of barrier self-formation using Cu(Ti) alloy films on porous low-k dielectric layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOCH (low-k) dielectric layers in samples with and without ∼6.5-nm-thick SiCN pore seals. Ti-rich barrier layers successfully self-formed on the porous low-k layer of both sample types after annealing in Ar for 2 h at 400°C to 600°C. The Ti-rich barrier layers consisted of amorphous Ti oxides and polycrystalline TiC for the samples without pore sealing, and amorphous TiN, TiC, and Ti oxides for the pore-sealed samples. The amorphous TiN originated from reaction ofTi atoms with the pore seal, and formed beneath the Cu alloy films. This may explain two peaks of Ti segregation at the interface that appeared in Rutherford backscattering spectroscopy (RBS) profiles, and suggests that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore seal and porous low-k layers separately. The total molar amount of Ti atoms segregated at the interface in the pore-sealed samples was larger than that in the samples without pore sealing, resulting in lower resistivity. On the other hand, resistivity of the Cu alloy films annealed on the porous low-k layers was lower than that annealed on the nonporous low-k layers. Coarser Cu columnar grains were observed in the Cu alloy films annealed on the porous low-k layers, although the molar amount of Ti atoms segregated at the interface was similar in both sample types after annealing. The cause could be faster reaction of the Ti atoms with the porous dielectric layers. © 2010 TMS.


Kohama K.,Kyoto University | Ito K.,Kyoto University | Sonobayashi Y.,Kyoto University | Ohmori K.,Renesas Electronics Corporation | And 4 more authors.
Japanese Journal of Applied Physics | Year: 2011

Self-formed Ti-based barrier layer using Cu(Ti) alloy seed applied to 45-nm-node dual-damascene interconnects was reported to have sufficient barrier strength to prevent Cu diffusion into dielectrics. The constituent Ti compounds in the self-formed Ti-based barrier layers and the barrier structures in Cu(Ti)/dielectric samples were identified by X-ray photoelectron spectroscopy (XPS) analyses. Two types of SiOC with low dielectric constants, SiO 2, and SiCN were used as dielectrics. The Ti-based barrier layers consisted mainly of amorphous Ti oxides such as TiO2, Ti 2O3, and TiO, regardless of the dielectric. In addition to Ti oxides, barrier layers containing TiC, TiSi, and TiN were observed, depending on the dielectric. TiC and TiSi were in crystalline state. They were formed beneath the Cu(Ti) alloy films, and had orientation relationship with the crystalline Cu(Ti) alloy films. The amorphous Ti oxides were formed above the amorphous dielectric layers. The amorphous Ti oxides are believed to be formed continuously above the dielectric layers and prevent Cu diffusion into the dielectric layers. © 2011 The Japan Society of Applied Physics.


Kohama K.,Kyoto University | Ito K.,Kyoto University | Sonobayashi Y.,Kyoto University | Tanaka T.,Kyoto University | And 4 more authors.
Japanese Journal of Applied Physics | Year: 2010

To investigate effects of pore seals on self-formation of Ti-rich barrier layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOxC yH (low-k) dielectric layers in samples with and without about 6.5-nm-thick SiCN pore seals. Self-formed Ti-rich barrier layers were formed on the porous low-k layers after annealing in Ar for 2 h at 400-600 °C. The samples without pore sealing had a rough interface, indicating that Ti atoms reacted with the porous low-k layers at the pore surfaces. In contrast, the pore-sealed samples had a smooth interface. The Ti-rich barrier layers in thesamples consisted of amorphous Ti oxides. In addition, polycrystalline TiC and amorphous TiN and TiC were observed to be formed beneath the Cu(Ti) alloy films in the annealed samples without pore sealing and pore-sealed samples, respectively. Note that Ti segregation at the interface was divided into two layers, suggesting that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore sealing and porous lowk layers are separated. The resistivity of the pore-sealed samples was lower than that of the samples without pore sealing. This is attributed to lower residual Ti atoms in the alloy films and coarser columnar grains in the pore-sealed samples. © 2010 The Japan Society of Applied Physics.


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.


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.


Ito K.,Kyoto University | Kohama K.,Kyoto University | Hamasaka K.,Kyoto University | Sonobayashi Y.,Kyoto University | And 3 more authors.
Japanese Journal of Applied Physics | Year: 2012

To understand the electromigration degradation in Cu interconnects that utilize the TiO x self-formed barrier (SFB) probably due to Cu oxidation at the Cu/barrier interface, Cu films deposited on TiO x SFB and conventional Ta/TaN barriers were annealed in atmospheres of various oxygen concentrations. The Ta layer was preferentially oxidized to give Ta 2O 5, and contained a large amount of oxygen. The barrier layer, which consisted of Ta 2O 5 and Ta(O), could not suppress Cu diffusion. The TaN layer seemed to remain even after annealing at 400 °C in 10 ppm O 2, and still suppressed Cu diffusion. This suggests that the TaN layer plays a key role to suppress barrier failure induced by oxygen originating from pores in dielectrics. On the other hand, the oxygen-induced barrier failure was observed in the TiO x SFB after annealing at 500 °C in 5 ppm O 2 and more. Oxygen facilitated Cu 2O formation above the TiO x SFB, and the Cu 2O formation caused discontinuity of the TiO x SFB, leading to the barrier failure. The less oxidized Ti2O 3 and TiO in the TiO x SFB were not further oxidized to TiO 2 by oxygen in atmospheres, and thus they would not be oxygen absorbers suppressing the Cu 2O formation above the barrier. Thus, for suppressing the Cu 2O formation, it is essential to increase oxygen barrier ability of the TiO x SFB (probably increasing Ti concentration of the TiO x SFB). © 2012 The Japan Society of Applied Physics.


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.


Ito K.,Osaka University | Hamasaka K.,Kyoto University | Kohama K.,Osaka University | Shirai Y.,Kyoto University | Murakami M.,Ritsumeikan Trust
Journal of Electronic Materials | Year: 2014

Cu(0.5 at.%Mg) alloy films were deposited on glass substrates, and annealed at 200-400 °C in vacuum. The resistivity of the Cu(Mg) films was reduced to about 3.0 μΩcm after annealing at 200 °C for 30 min, and the tensile strength of adhesion of the Cu(Mg) films to the glass substrates was increased to 30-40 and 35-55 MPa after annealing at 250 and 300 °C, respectively. The reduction in resistivity can be explained as reduced impurity scattering and grain-boundary scattering, since Mg segregation to the film surface and Cu(Mg)/glass interface, and consequent Cu grain growth, were observed. Increased adhesion of the Cu(Mg) films to glass substrates after annealing was also explained by the strong segregation of Mg atoms, and the formation of a reaction layer at the interface. Mg atoms were observed to have reacted with the glass substrates and formed a thin crystalline MgO layer at the interface in the samples annealed at 300 °C, while Mg atoms were highly concentrated above the Cu(Mg)/glass interface without oxide formation at the interface in the samples annealed at 250 °C. Thus, the process temperature and time to obtain low-resistivity and high-adhesion Cu alloy films on glass substrates could be reduced to 250 °C and 30 min using Cu(Mg) films. © 2014 TMS.

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