Haruhisa Shigeyama

Micro- and macro-creep damage formation for P92 under multiaxial stress related to circular notched specimen

Abstract In this study, to clarify the behaviour of micro- and macro-creep damage progression for P92 under multiaxial stress field, interrupted creep tests, analysis of multiaxial stress and detailed the cross-sectional observations were conducted on a circular notched round bar specimen which produces the multiaxial stress field due to the plastic constraint. As a result, creep voids were initiated at the early stage and they were formed up to the final fracture. These phenomena were found to be detected using direct current potential drop (DCPD) method. These results concern the development of the measurement of creep crack initiation. The distribution of high void area fraction was in good agreement with that of high hydrostatic stress and high multiaxial stress. This result indicates that multiaxial stress affects the void formation. Furthermore, the micro-creep damage of each interrupted specimen was evaluated by using the electron backscatter diffraction (EBSD) method which can analyse crystallographic misorientation caused by creep strain. The results of EBSD analyses indicated that the value of grain reference orientation deviation (GROD) closely concerns the void initiation.

Prediction of Stress Induced Voiding Reliability in Cu Damascene Interconnect by Computer Aided Vacancy Migration Analysis

The method of computer aided vacancy migration analysis has been developed to predict the stress induced voiding (SiV) reliability. In this method, distribution of hydrostatic stress was calculated by the finite element analysis (FEA), and vacancy concentration distribution was calculated by the finite difference analysis (FDA). In this paper, SiV acceleration tests were conducted in various widths of Cu lines in organic ultralow-k dielectric (Cu/Ta/ULK/SiCN) or silicon oxide dielectric (Cu/Ta/SiO2/SiCN) and these results were compared with the results of the vacancy migration analyses. The number of SiV failures increased in the line with width of 0.35 µm for Cu/Ta/SiO2/SiCN interconnects and 0.20 µm for Cu/Ta/ULK/SiCN interconnects, respectively, under SiV acceleration tests. The results obtained by vacancy migration analysis show similar behavior as the results of SiV acceleration tests. These results reveal that the vacancy migration analysis is useful to predict reliability of interconnects.

Analysis of Stress Induced Voiding Using by Finite Element Analysis Coupled with Finite Difference Analysis

In this paper, the vacancy migration in Cu interconnect of large scale integration caused by stress induced voiding was calculated using the α multiplication method. Then, the effect of weight coefficient, α, on stress induced vacancy diffusion analysis was investigated and the validity of the α multiplication method was verified. Furthermore, the method of the vacancy diffusion analysis coupled with thermal stress analysis which can consider the history of thermal stress due to temperature changes was proposed. The results of the vacancy diffusion analysis coupled with the thermal stress analysis were compared with the analytical results of the vacancy migration without the effect of history of thermal stress. As a result, the maximum site of vacancy accumulation was found to be qualitatively in good agreement between them. However, the quantitative value of maximum vacancy concentration obtained by the vacancy diffusion analysis coupled with thermal stress analysis was found to be much higher and the vacancy distribution is found to be much more localized.

Effect of Multi-Axial Stress on Creep Damage Behavior for Notched Specimen of P92 Steel

In this study, interrupted creep crack growth tests were conducted using C(T) specimen with side-grooves and circular notched round bar specimen of P92 steel. After the interrupted tests, to investigate the creep crack growth and damage progression behaviors of P92 steel under the multi-axial stress field, cross-sectional observations around the notch and crack tip were conducted. From the measurement results of the change of micro Vickers hardness and void area fraction with creep time, it was indicated that the region of low hardness and high void area fraction were existed near the notch or crack tip. Then, three-dimensional elastic-plastic creep analyses were conducted for each specimen. From the results of finite element analyses, the regions of high hydrostatic stress and high tri-axiality factor were in good agreement with the region of high void area fraction for each specimen. This result indicated that the multi-axial stress field contributes to the void formation. Furthermore, the effects of the absolute value and gradient of tri-axiality factor on void formation were discussed.Copyright