The Ritsumeikan Trust

We demonstrate that origin of the long-standing contact issue in silicon carbide devices can be understood and technologically manipulated at the atomic level. Using advanced transmission electron microscopy, we attribute qualitatively the formation of ohmic contacts to silicon carbide to an epitaxial, coherent, and atomically ordered interface. Quantitatively, first-principles calculations predict that this interface can trap an atomic layer of carbon and hence enable lowered Schottky barrier and enhanced quantum electron transport. The combined experimental and theoretical studies performed provide insight into the complex electronic and electric effects of the buried contact interface, which are fundamental for improving the contact in future electronics based on wide-band-gap semiconductors such as silicon carbide and diamond.

Growth and microstructure of ternary Ti3SiC2 compound layers on 4H-SiC, which play am important role in formation of TiAl-based ohmic contacts to p-type SiC, were investigated in this study. The Ti3SiC2 layer was fabricated by deposition of Ti/Al contacts (where a slash “/” indicates the deposition sequence) on the 4H-SiC(0001) substrate and subsequent rapid thermal anneal at 1000°C in ultra high vacuum. After annealing, reaction products and microstructure of the Ti3SiC2 layer were investigated by X ray diffraction analysis and transmission electron microscopy observations in order to understand the growth processes of the Ti3SiC2 layer and determination of the Ti3SiC2/4H-SiC interface structure. The Ti3SiC2 layers with hexagonal plate shape were observed to grow epitaxially on the SiC(0001) surface by anisotropic lateral growth process. The interface was found to have a hetero-epitaxial orientation relationship of (0001)TSC||(0001)S and [0\\bar110]TSC||[0\\bar110]S where TSC and S represent Ti3SiC2 and 4H-SiC, respectively, and have well-defined ledge-terrace structures with low density of misfit dislocations due to an extremely low lattice mismatch of 0.4% between Ti3SiC2 and 4H-SiC.

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 μΩcm. Tensile strength 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.

With continuous shrinkage of advanced ultralarge scale integrations (ULSI), the impact of line resistance on the devices has become more and more important. In order to achieve low resistance and high reliability of Cu interconnects, we have applied a thin Ti-based self-formed barrier layer using Cu–Ti alloy seed to 45 nm node dual-damascene interconnects and evaluated its performance. The microstructure analysis by transmission electron microscope and energy dispersive X-ray fluorescence spectrometer has revealed that 2-nm-thick Ti-based barrier layer is self-formed at the interface between Cu and low- k dielectrics. The line resistance and via resistance decrease significantly, compared with those of conventional Ta/TaN barrier system. The stress migration performance is also drastically improved using self-formed barrier process. These results suggest Ti-based self-formed barrier process is one of the most promising candidates for advanced Cu interconnects.

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 TiO 2 , Ti 2 O 3 , 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.

In our previous studies, Ti atoms in Cu(Ti) alloy films were found to segregate at the film surface and the interface between Cu(Ti) alloy films and dielectric layers after annealing in Ar atmosphere at elevated temperatures. Such self-formed Ti-rich interface layers can act as a diffusion barrier layer. This technique was called “self-formation of the diffusion barrier,” which is attractive for the fabrication of ultra-large scale integrated interconnects. In the present study, we investigated the growth of Ti-rich barrier layers in Cu(Ti)/dielectric-layer samples with a low Ti content (1 at%) after annealing in ultra high vacuum (UHV). Ti atoms were found to segregate only to the Cu(Ti)/dielectric-layer interface under annealing in UHV. The microstructures were analyzed by transmission electron microscopy and Rutherford backscattering spectrometry, and correlated with the electrical properties of the Cu(Ti) films. It was concluded that Ti-rich interface layers were formed in all the Cu(Ti)/dielectric-layer samples. The Ti-rich interface layers were identified to consist of TiC or TiSi in addition to Ti oxides. The growth of the Ti-rich interface layers consisting of TiC was faster than those consisting of TiSi. Similarly, the resistivities of Cu(Ti)/dielectric-layer samples in which the TiC formation was observed were quickly reduced and those in which the TiSi formation was observed were gradually reduced. Compositions of the self-formed Ti-rich interface layers were concluded to be determined by the C concentration in the dielectric layers rather than by the enthalpy of formation. The growth of the self-formed Ti-rich interface layers consisting of TiC may be controlled by C diffusion in the Ti-rich interface layer. The composition of the dielectric layers was concluded to play an important role on the growth of the Ti-rich interface layers.

Most navigation systems use electronic maps to show routes to destinations. However, elementary school children find it difficult to read such a map and use such a system. This paper proposes a route indication system using the vibration function of a smartphone for children. A smartphone vibrates when a user turns the device in the direction of a next relay point, and thus the user knows which direction to move. A preliminary experiment was conducted to evaluate the optimal angle of vibration to the direction of a relay point. The result showed that a range of 20 degrees from the desired destination direction is optimal for navigation to any target point. Using this parameter in our system, an experiment was conducted with six children. The results of this experiment showed that the children were able to use the proposed system and reach the target destination easily.

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.

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, SiO2, and SiCN were used as dielectrics. The Ti-based barrier layers consisted mainly of amorphous Ti oxides such as TiO2, Ti2O3, 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.

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 2 O 5 , and contained a large amount of oxygen. The barrier layer, which consisted of Ta 2 O 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 2 O formation above the TiO x SFB, and the Cu 2 O formation caused discontinuity of the TiO x SFB, leading to the barrier failure. The less oxidized Ti 2 O 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 2 O formation above the barrier. Thus, for suppressing the Cu 2 O formation, it is essential to increase oxygen barrier ability of the TiO x SFB (probably increasing Ti concentration of the TiO x SFB).

To investigate effects of pore seals on self-formation of Ti-rich barrier layers, Cu(1 at. % Ti) alloy films were deposited on porous SiO x C y H (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 the samples 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 low- k 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.

To understand the electromigration degradation in Cu interconnects that utilize the TiOx self-formed barrier (SFB) probably due to Cu oxidation at the Cu/barrier interface, Cu films deposited on TiOx SFB and conventional Ta/TaN barriers were annealed in atmospheres of various oxygen concentrations. The Ta layer was preferentially oxidized to give Ta2O5, and contained a large amount of oxygen. The barrier layer, which consisted of Ta2O5 and Ta(O), could not suppress Cu diffusion. The TaN layer seemed to remain even after annealing at 400 °C in 10 ppm O2, 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 TiOx SFB after annealing at 500 °C in 5 ppm O2 and more. Oxygen facilitated Cu2O formation above the TiOx SFB, and the Cu2O formation caused discontinuity of the TiOx SFB, leading to the barrier failure. The less oxidized Ti2O3 and TiO in the TiOx SFB were not further oxidized to TiO2 by oxygen in atmospheres, and thus they would not be oxygen absorbers suppressing the Cu2O formation above the barrier. Thus, for suppressing the Cu2O formation, it is essential to increase oxygen barrier ability of the TiOx SFB (probably increasing Ti concentration of the TiOx SFB).

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 Rutherford 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 both 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 logn versus logt 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 that growth rate of the 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 the reaction.

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.

In this paper, the amorphous phases in the Ti-based barrier layers are identified. More so, X-ray photoelectron spectroscopy (XPS) technique is employed to study its composition.

There are many different musical abilities, and previous researchers have developed various tests to measure them. For a DJ, the ability to find the changing points in phrases and melodies while listening to music is essential. This beat count ability cannot be measured by existing music aptitude tests because it is completely different from other musical abilities. In this research, we developed a measurement system for beat count ability and verified its reliability and validity. First, we selected appropriate tracks and created a method to accurately measure this ability. Then we developed a system and conducted an experiment with users who had various levels of musical experience. The results suggest that our measurement system can accurately measure one's beat count ability, especially for beginners who are learning how to DJ.

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, SiO2, and SiCN were used as dielectrics. The Ti-based barrier layers consisted mainly of amorphous Ti oxides such as TiO2, Ti2O3, 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.

Thin Ti‐rich diffusion barrier layers were found to be formed at the interface between Cu(Ti) films and SiO2/Si substrates after annealing at elevated temperatures. This technique was called “self‐formation of the diffusion barrier,” which is attractive for fabrication of ultra‐large scale integrated (ULSI) interconnects. In the present study, we investigated the applicability of this technique to Cu(Ti) alloy films deposited on low dielectric constant (Low‐k) materials (SiOxCy). In addition, SiCO and SiCN were also used as dielectric layers, which are potential dielectric layers for future ULSI‐Si devices. The microstructures were analyzed by transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS), and correlated with the electrical properties of the Cu(Ti) films. The resistivity of the Cu(1 at.%Ti)/dielectric‐layer samples was reduced to about 2.5 μΩcm after annealing in Ar at 400° C for 2 h. It was concluded that the Ti‐rich interface layers were formed in all the Cu(Ti)/dielectric‐layer samples. The Ti‐rich interface layers consisted of crystalline TiC or TiSi in addition to Ti oxide based on its amorphous nature. The TiC compounds with the high melting point of 3100° C are also expected to show thermal stability as barrier layers. The primary factor to control the composition of the Ti‐rich interface layers was the C concentration in the dielectric layers rather than the enthalpy of formation of the Ti compounds (TiC, TiSi and TiN). The crystalline TiC was formed on the dielectric layers with a C concentration higher than 17 at.%. For systematic investigation of growth of the Ti‐rich interface layers in the annealed Cu(Ti)/dielectric‐layer samples, the RBS technique was employed. The relationship (log n vs log t) between a molar amount of Ti atoms segregated to the interface (n) and annealing time (t) suggests that a growth mechanism of all the samples is similar. Activation energies (E) for the samples consisted of dielectric layers with carbon tended to decrease with decreasing k (decreasing C concentration), and those without carbon (SiO2) were much higher than others. This suggests that composition of the dielectric layers plays an important rule in the reaction of the Ti atoms with dielectric layers, and the carbon may be a key element to control the reaction.

Self-study is not well-established in Japan even in the 2nd cycle of Certified Evaluation and Accreditation System. The reason is in system issue &, simplism of means. Self-study design, including strategic plan making and self-directive improvement at site, is needed for Quality Assurance in the contextual situation of Japan.

An immediate evacuation is essential for safety when a big earthquake and a tsunami occurred. For example, Great East Japan Earthquake in 2011 killed over 10 thousand people and over 90 percent of them drowned by the tsunami, that is, people who failed to escape from the tsunami after the earthquake occurred got losses by it. If they evacuated immediately after an earthquake, it would be possible that the losses could be limited. In this study, we analysis text-based information expression on a mobile device to induce immediate evacuation. We implemented an application which provides disaster information on a smartphone, and compare text expression about information of tsunami height, arrival time of tsunami, an expected number of evacuees, damage of buildings and so on. The results of the comparison verification show the sentence based on damage of building using fear-arousing communication is the most effective to induce evacuation in this study. However, in over seventies, the effectiveness of the sentence is less than half.