Kozo Koiwa

Macroscopic and microscopic interface adhesion strength of copper damascene interconnects

Macroscopic and microscopic adhesion strength of damascene interconnects was investigated by evaluating local strength through delaminating different scales of adhesion area under SEM observation. Macroscopic strength obtained by the areas larger than the copper grain was almost constant after considering the macroscopic plastic deformation. However, microscopic strength obtained by the areas smaller than the copper grain spread around the macroscopic strength and was highly sensitive to the copper grain structure, especially the grain boundary.

Development of cu/insulation layer interface crack extension simulation with crystal plasticity

A novel scheme for the evaluation of interface adhesion energy was examined by a detailed numerical simulation of interface crack extension. The effects of crystal orientation on the Cu/SiN interface adhesion strength of LSI was evaluated using the finite element method. Crack extension simulation was conducted with a model of the actual specimen used for the interface fracture test. The characteristics of elastic–plastic deformation, which changes significantly depending on crystal orientation, were taken into account in the model. With this scheme, the effect of orientation of single crystals on the maximum load Pmax was investigated under the condition of a constant bonding energy of the interface at the beginning of unstable crack propagation during the fracture test. The values of Pmax obtained with a number of different crystal orientations ranged over 179–311 µN. The result indicates that the crack propagates more easily in the case that slip deformation of Cu near the interface starts with a low stress, as in the case of the (111) surface. It implies that the apparent interface adhesion strength represented by the load required to debond the interface strongly depends on Cu crystal orientation, because the amount of energy used for plastic deformation of the Cu crystal changes with crystal orientation near the interface.

Scenario for catastrophic failure in interconnect structures under chip package interaction

This paper describes the critical importance of interfacial strength between copper lines and cap layer for catastrophic failure due to chip-package interaction (CPI). Recently, copper interconnects and insulating layers are stacked alternately in semiconductor devices. Especially, copper/low-k structures are widely selected. However, the low-k materials have weak mechanical properties, which sometimes induces reliability issues, especially, chip package interactions. In our previous works, the interfacial strength of Cu/Cap has been successfully measured on the sub-micron scale. In this paper, based on the measured results, we try to simulate the initiation and propagation of failure in interconnect structures and discuss the scenario for catastrophic failure under CPI.

Evaluation of adhesion energy and its correlation to apparent strength for Cu/SiN interface in copper damascene interconnect structures

Local apparent strength of interface between copper and cap layer on top was diverse depending on the crystal orientation underneath. For a comprehension of this diversity, physical adhesion energy to separate the interface was evaluated. It essentially does not include mechanical energy dissipating in plastic deformation in the process of crack extension. Sub-micron scale torsion test for elastic-plastic deformation properties and fracture tests on a number of different crystal orientations revealed that difference in adhesion energy is much smaller than difference in plastic dissipation energy. It is highly likely that small difference in the former is intensified through the latter, leading to a huge scatter in strength of LSI interconnect structures.

Shear stress with hydrogen, not oxygen, matters to the fatigue lifetime of silicon

This paper presents a new discovery over a long-lasting mystery of fatigue mechanism in silicon. We found that fatigue degradation possibly takes place due to defect accumulation in crystal with the aid of not only humidity but also hydrogen as well, and shear stress which is newly discussed in this study. Fatigue lifetime was eventually shorter with larger shear stress working on the crystal slip plane. Striation-like fracture surface patterns generated before unstable fracture were also discovered. Now we know that silicon may behave in a much more metallic manner with the aid of hydrogen even at room temperature than ever believed before, no wonder leading to fatigue fracture.

Microscale torsion test to investigate initial yielding phenomenon of a single crystal copper

Mechanical property of copper is very important for the reliable design of semiconductor devices, because the interface between a copper line and the dielectric barrier layer is the week point in the device. In general, the line width of copper line is in the range from tens nanometer to micrometer, and the plastic property of a crystalline metal with small dimensions is highly sensitive to its dimension [1]. In addition, it appears that the loading condition significantly affects the plastic behavior of a micron scale metal. C Motz et al found the follow stress of almost 1GPa (i.e. nearly equal to theoretical strength of copper crystal) at the micro-bending test [2]. Considering these reports, in order to comprehend deformation behavior of the copper embedded in semiconductor device, we need to investigate mechanical response of the copper with small dimensions under heterogeneous stress distribution. In this paper, we twisted micron copper specimens with different dimensions, and investigated the size effect of its plasticity, especially focused on the initial yielding.

Development of Cu/insulation layer interface crack extension simulation with single crystal plasticity

1 Nagoya Institute of Technology. 817 room, building No.3, Gokiso-cho, Showa-ku, Nagoya, Aichi, 466-8555 Japan Phone: +81-052-735-5280 E-mail: koiwa.kozo@nitech.ac.jp 2 Japan Science and Technology Agency, Chiyoda-ku, Tokyo, 102-0075, Japan 3 Keio Univ. 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, 223-8522, Japan 4 Fujitsu laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, 243-0197, Japan 5 JEOL Ltd., 3-1-2 Musashino, Akishima, 196-0022, Japan