In this paper, IR-LBIC (Infrared Light Beam Induced Current) is applied using the laser wavelength of 1064 nm in order to analyze polycrystalline thin-film solar cells. The spatially high-resolved map of the short circuit current (~3 µm) has been obtained by performing the IR-LBIC measurement. The results of the measurement showed higher signal response from the grain boundary compared to that from the grain interior. This difference has been explained by the light trapping effect due to the trench-shaped grain boundary profile, which is possibly accompanied by two stage excitation effects via electronic grain boundary states. It has been additionally investigated, whether LBIC measurement could be used to extract local illuminated cell characteristics. However, since the dark current, which has a decisive influence on the solar cell characteristic, is flowing in the entire cell area, this is not possible. A circuit network simulation demonstrates that LBIC cannot be used for extraction of the local open circuit voltage, and the short circuit current is the only parameter that can be locally defined and therefore clearly observed.

Crystalline silicon used for fabrication of solar cells, such as multicrystalline silicon (mc-Si), contains a high density of extended crystal defects. Since mc-Si wafers exhibit an inhomogeneous defect distribution, there is a need to combine the spectral capabilities with the ability of spatially resolving the defect areas. This paper reports application of luminescence and electron-beam-induced current (EBIC) techniques for characterization of defects in solar Si. The first part introduces luminescence features of defective Si and discusses application examples. The second part starts with explanation of the EBIC technique, including details about the temperature dependence of the EBIC defect contrast c(T). Then, application examples of the c(T) behavior and the analysis of the "interaction" of grain boundaries with p-n junctions are discussed. The paper demonstrates the potential of luminescence for nondestructive characterization of Si wafers and solar cells in terms of in-line defect detection and process control.

The temperature dependence of photocurrent of polycrystalline Si (poly-Si) thin-film solar cells on glass with interdigitated mesa structure has been locally investigated using Infrared Light Beam Induced Current (IR-LBIC) in the temperature range of -25 to +70 °C. The temperature dependence of electrical characteristics of poly-Si thin-film solar cells in reverse bias has been also analysed and compared with the monocrystalline thin-film solar cells. The poly-Si solar cell shows a temperature coefficient (TC) for the photocurrent of around +0.8 and +0.6 %/°C in the grain interior and grain boundary, respectively. The activation energy of the reverse current and also the photocurrent due to the IR laser stimulation has been evaluated, which provide information about traps and their energy levels in the absorber layer of the poly-Si thin-film solar cell. The obtained average value of the activation energy associated with the photocurrent of the poly-Si cell suggests the existence of a shallow acceptor level at around 0.045 eV in the grain boundary and 0.062 eV in the grain interior of the absorber layer of the poly-Si thin-film solar cell. The activation energies of the reverse current for poly-Si and monocrystalline cells have been calculated when the device is biased at -1 and -2 V and the results compared with the activation energy of the saturation current obtained from extrapolation of the I-V curve in the SRH (Shockley-Read-Hall) regime. The results show strong voltage dependence. In both cases the activation energy of the reverse current decreases in the reverse bias voltage, approaching the values obtained from the photocurrent.

Experimental devices in a deteriorated state were encountered after 168 hours of inductive operating life stress, (IOL) testing. A metal grain boundary breakdown mechanism was found during the analysis of the device, which was creating a low resistance current path between terminals. The AlSiCu top metal was breaking down along the grain boundaries. In addition there was alloying of the Aluminum into the underlying silicon. This alloying was creating a short to the gate, source, and drain. Several variations in the metal stack, testing conditions, number, and dimensions of bond wires die size and mold compound were evaluated to better understand the cause of the inability to withstand IOL stress and to provide a process solution. The prevention of the AlSiCu front metal grain boundary breakdown during inductive life stress testing required a die size, bond wire dimension, and testing condition change to meet the performance specification. This change resulted in a reduced grain boundary breakdown and consequently prevented Al grain boundary breakdown, TiW barrier breakdown, and Al alloy spiking. The die change and modified testing conditions resulted in a successful pass through the IOL stress testing.

This paper presents the result of a study of a particular failure mechanism of BaTiO3 MLCC (multiple layer ceramic capacitor). A unique technique of cross-section alternating with emission microscope analysis is developed to precisely locate the failure site for capacitors exhibiting low leakage current in μA range. Thermal Imaging Microscope, Photon Emission Microscope, SEM, STEM/EDS and TEM electron diffraction pattern are employed for the characterization of these low leakage failures. Evidence of high concentration impurities are detected in the dielectric layer of BaTiO3 grain boundaries as well as inside certain grains. TEM diffraction imaging at the failure site shows distinguishingly different diffraction patterns within the matrix of BaTiO3 crystal structure. The evidences point to a combination of impurities at grain boundaries and BaTiO3 crystal change induced by impurity as the failure mechanism.

A wealth of literature has arisen in the past couple of decades regarding the phenomenon of electromigration. In addition, stress voiding has received considerable attention from the research community. Some of the work on the structural character of these phenomena has focussed on the roles of crystallographic texture and grain boundary structure. It is an experimental fact that the strength of the (111) fiber texture is an indication of interconnect reliability, the stronger the texture, the more reliable the interconnect. It is also presumed that grain boundary diffusivity is a controlling factor in electromigration behavior of polycrystalline lines. Undesirable grain boundary structure is likely a cause of failure in lines with a bamboo structure as well because they are often sites of stress concentration and local incompatibilities. The present study focuses upon electromigration failures in test structures of Al-Cu lines and stress voiding in Cu lines. Texture and grain boundary structure were measured directly on the specimens using electron back-scatter diffraction and orientation imaging. It is observed that a correlation exists between grain boundary structure and void formation in strongly textured polycrystalline lines. Results indicate that secondary orientation (not just the (111) fiber), and boundary structure may be of primary importance in optimizing interconnect microstructure.