Takeshi Nokuo

Micro‐Scale Evaluation Of Interface Strength On The Patterned Structures In LSI Interconnects

Reliability of electronic devices has been an issue of serious importance. One of the potential factors to spoil the reliability is possible local drops of strength on the interface of multilayered structure. A new technique for the evaluation of local interface adhesion energy was applied to the interface between Cu and cap layer in a Cu damascene interconnect structure, in order to elucidate variation in adhesion strength as a function of measurement location.

A New Method for Failure Analysis with Probing System Based on Scanning Electron Microscope

This newly developed instrument can provide new techniques for failure analysis by direct interpretation of AEI and VDIC signatures, and transistor characterization by nanoprobing. These methods enable analysis from the top surface to the bottom of the device. The authors conclude that this instrument provides an effective alternative solution for semiconductor failure analysis.

Local electrical properties of n-AlInAs/i-GaInAs electron channel structures characterized by theprobe-electron-beam-induced current technique

We developed a probe-electron-beam-induced current (probe-EBIC) technique to investigate the electrical properties of n-Al(0.48)In(0.52)As/i-Ga(0.30)In(0.70)As electron channel structures for a high-electron-mobility transistor, grown on a lattice-matched InP substrate and lattice-mismatched GaAs (001) and Si (001) substrates. EBIC imaging of planar surfaces at low magnifications revealed misfit dislocations originating from the AlInAs-graded buffer layer. The cross-sections of GaInAs channel structures on an InP substrate were studied by high-magnification EBIC imaging as well as cathodoluminescence (CL) spectroscopy. EBIC imaging showed that the structure is nearly defect-free and the carrier depletion zone extends from the channel toward the i-AlInAs buffer layer.

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.

Ultra High Solid Angle EDS System Advanced STEM Analysis for FE-SEM

EDS (Energy dispersive X-ray spectrometry) is a technique used for elemental analysis of a sample, through detection of characteristic X-rays generated from a sample impacted by an electron beam. STEM (Scanning Transmission Electron Microscopy) is a method to obtain high spatial resolution images with Z-contrast [1]. STEM-in-SEM has recently become a technique of choice for high spatial resolution imaging in SEM of ultra-thin specimens and can be combined with the EDS for compositional analysis of nanostructures, with the ability to resolve structures previously unattainable with bulk EDS analysis.

An Evaluation of FIB Cross-Sectioning Using a Cooling Stage for Metals and Alloys with Low Melting Point

Functions of an observation and an analysis in electron microscope, such as scanning electron microscope (SEM) or transmission electron microscope (TEM) are indispensable to evaluate advanced materials. Therefore a specimen preparation technique, that is a front end of the electron microscopy, has become highly important, thus a choice of it affects a result of the evaluation. The authors was combined a cooling stage in FIB and applied it for evaluation of metals with low melting point. The electron microscopic evaluation of Lead solder, Indium, Tin and Bismuth, metals with low melting point, has been always discussed if the results represent the actual physics. Metals with low melting point are heat sensitive materials, so the comparison of cross-sectioning with room and low temperature, it can be said that low temperature cross-sectioning has less effect and keeps the actual physics of the sample. In this paper, some knowledge from comparisons of cross-sectioning with room and low temperature for metals with low melting point are reported.

The Study of “Window-less” EDS Detector With Low Voltage FE-SEM

Energy Dispersive X-ray Spectrometry (EDS) with an SEM is very popular for elemental analysis of bulk materials, and this method is called SEM/EDS. The element range capability of conventional EDS is from Be to U. However, in fact, it is not easy to analyze Be contained in a compound, because the film located in front of conventional EDS detector causes strong absorption of characteristic X-rays from light elements. This film is called the “window”. The “Window” is mounted to keep the high vacuum condition of EDS detector. Therefore a window-less EDS detector is more suitable for EDS analysis of light elements.

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.