Yasuo Kobayashi

Environmental effect of fatigue crack propagation of magnesium alloy

Fatigue crack propagation tests were carried out for a magnesium alloy in various kinds of environment. The presence of oxygen causes the production of oxide film on the fresh fracture surfaces made during the cyclic loading. Therefore, the fatigue crack behavior depends strongly upon the environment. The fatigue tests have been conducted in dry and wet argon gas as well as in air. The wet atmosphere, in particular, accelerated the fatigue crack propagation rate. The presence of the oxide film would restrict the deformation of the matrix beneath the hard film and promote hydrogen embrittlement in the wet condition.

Mechanical modeling and microstructural observation of pure aluminum crept under constant stress

Precise constant stress creep tests were conducted on five nine pure aluminum specimen between 293 and 623 K. A well-defined steady state creep was not observed under these conditions. The macroscopic stress response of the aluminum was examined by mechanical modeling, using combinations of the Maxwell and the Voigt elements. The plastic strain changes were well described by a serial combination of the two elements using experimentally determined viscosity coefficients for both elements. These results suggested that a dual phase substructure would form in crept aluminum under constant stress and this was confirmed by direct observation, which revealed a cellular structure. The viscosity coefficient is identified with the mobility of dislocations in both phases. The temperature dependencies of both coefficients were similar with the activation energy close to that for lattice self-diffusion in pure aluminum.

Electrical Characteristics of Novel Non-porous Low-

A novel non-porous low-k dielectric, fluorocarbon, deposited by new microwave excited plasma enhanced chemical vapor deposition was successfully integrated into Cu damascene interconnects for the first time. Electrical characteristics of fluorocarbon/Cu damascene lines are investigated. A compatible line to line leakage current to the one with porous low-k carbon doped silicon oxide and a low effective dielectric constant as a value of 2.5 are achieved. The novel non-porous ultralow-k dielectric, fluorocarbon, is considered as a promising candidate to extendible for 22 nm generation and beyond.

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We have carried out experiments on the creep behaviors of pure aluminums at lower temperatures from a phenomenological viewpoint. The creep curves are classified into three regions; the transient, steady-state and terminal ones. The creep curve changes from a logarithmic to a constant strain rate curve at a higher applied stress. The creep curves yield a constant creep rate for a long period though lattice diffusion is less active at 293 K. The creep rate depends upon the applied stress. Cyclic stressing has an effect on the creep life of the materials. Both increasing and decreasing the applied stress reduce the rupture time. Since the steady-state creep is associated with the stable structure, is takes time to shift to the new structure built under the different applied stress. The hysteresis effect does some damage to the creep life of the pure aluminum.

Dielectric Fluorocarbon on Cu Interconnects for 22 nm Generation and Beyond

Integration of an organic non-porous ultralow-k dielectric, fluorocarbon (k= 2.2), into advanced Cu interconnects was demonstrated. The challenges of process-induced damage, such as delamination and variances of both the structure and electrical properties of the fluorocarbon during fabrication, were investigated on Cu/fluorocarbon damascene interconnects. A titanium-based barrier layer, instead of a tantalum-based barrier layer, was used to avoid delamination between Cu and fluorocarbon in Cu/fluorocarbon interconnects. A moisture-hermetic dielectric protective layer was also effective to avoid damage induced by wet chemical cleaning. On the other hand, a post-etching nitrogen plasma treatment to form a stable protective layer on the surface of the fluorocarbon was proposed for the practical minimization of damage introduction to fluorocarbon in the following damascene process, such as post-etching cleaning.

Creep behaviors of highly pure aluminum at lower temperatures

Abstracts are not published in this journal

Integration Process Development for Improved Compatibility with Organic Non-Porous Ultralow-k Dielectric Fluorocarbon on Advanced Cu Interconnects

The SiO 2 film deposition employing inductively coupled plasma (ICP) with SiCl 2 H 2 /O 2 occurred rapidly in the low-density plasma region due to production of precursors of SiCl 2 H 2 O x (x = 1-4). In an ICP CVD apparatus made with optimized distances between the antenna and the stage, and between the SiCl 2 H 2 gas ring and the stage, a SiO 2 film was with high deposition rate of more than 1 μm/min, 1.5 times the BHF etch rate of thermal oxide, and low Cl inclusion at a pressure of around 0.1 Torr. To supply ions to the Si wafer located in the ion-deficient plasma region, another time-modulated ICP antenna was set near the stage. Since deposition rate decreased with increasing wafer temperature, the laser the interference measurement of a Si wafer set on an RF-biased stage revealed the importance of the tight adhesion of the wafer to the stage. Ar + ion bombardment during discharge on and off-time of 5 μs enabled us to fill Si trenches with SiO 2 at a V dc of 500 V.

Fatigue fracture toughness of AZ91D alloy at ambient temperature

Wafer temperature in high rate and low bias RF boltage SiO2 deposition process was monitored by pulse modulated infrared laser interferometric thermometry. With RF bias, wafer temperature sharply rose to more than 600 degree(s)C due to poor thermal conductivity between a silicon wafer and cooling stage which led to no SiO2 deposition on silicon trenches. However, after improving the thermal conductivity, silicon trenches were successfully filled. Also, temperature dependence of fluorocarbon film deposition on a chamber wall in C4F8/H2 inductively coupled plasma process was investigated. The result implies that wall temperature should be controlled over 300 degree(s)C in order to maintain CFx radical supply on SiO2 surfaces.

High-Rate Bias Sputtering Filling of SiO2 Film Employing Both Continuous Wave and Time-Modulated Inductively Coupled Plasmas

A robust fluorocarbon film was successfully deposited on a substrate at a temperature above 400 °C by the new microwave plasma-enhanced chemical vapor deposition (MWPE-CVD) method using the linear C5F8 precursor instead of a conventional cyclic C5F8 one. The fluorocarbon performed keeping the dielectric constant low as a value of 2.25 by controlling the molecular structure forming cross-linked poly(tetrafluoroethylene) (PTFE) chains with configurational carbon atoms. The novel fluorocarbon demonstrates less fluorine degassing at an elevated temperature, with high mechanical strength and without degradation of adhesion of the fluorocarbon film to SiCN and SiOx stacked films after thermal stress at 400 °C and 1 atm N2 for 1 h. Consequently, this robust fluorocarbon film is considered a promising candidate for general porous silicon materials with applications to practical integration processes as an interlayer dielectric.

In-situ Si wafer temperature measuring using pulse modulated infrared laser interferometric thermometry for CVD film deposition

Polymers are vital materials in better performance of specific strength. However their application can be restricted by the lower glass transition temperature, Tg. Some polymers have been developed as engineering plastics for the high temperature applications. We examined the high temperature strength of polymers at constant applied stress. The creep rupture and viscoelastic behavior were scrutinized for PC (polycarbonate) and PMMA (polymethyl methacrylate), which were quite different in the molecular structures. The former contains benzene rings and the latter is a single polymer. Tg is 423 K for PC and 378 K for PMMA. The large difference in the creep behavior was observed near Tg. The creep life strongly depends upon the applied stress just below Tg. The creep life is a function of the applied stress as follows. n life t − µ s . The stress exponent, n depends upon the temperature. Mechanical models were applied to evaluate the viscoelastic properties of the polymers at high temperatures. The viscosity rapidly decreased near Tg , regardless of the smaller decrease in the elastic constant. The results would be due to the difference in the molecular structures. The benzene ring could contribute to the higher resistance against the creep deformation through the higher viscosity.