In this study, the challenges to transfer the microelectronics failure analysis techniques to the photovoltaic industry have been discussed. The main focus of this study was the PHEMOS as a tool with strong technological research capacity developed for microelectronics failure analysis, and OBIC (Optical Beam Induced Current) as a non-destructive technique for detecting and localizing various defects in semiconductor devices. This failure analysis tool was a high resolution optical infrared photon emission microscope used mainly in microelectronics for qualitative analysis and localization of semiconductor defects. Such failure analysis equipment was designed to meet requirements for modern microelectronic devices. Characterization of current photovoltaic device often requires quantitative analysis and should provide information about the electrical and material properties of the solar cell. Therefore, in addition to the demand for further data processing of the obtained results we had to study the corresponding operating regime of solar cells to allow for a correct interpretation of measurement results. In this paper, some of the related problems we faced during this study, e.g. large amount of data processing, the spatial misalignment of the images obtained as EL (Electroluminescence) and IR-LBIC (Infrared Light Beam Induced Current), the implemented laser wavelength, its profile and power density for IR-LBIC measurement. These topics have been discussed in detailed to facilitate a reliable transfer of these techniques from microelectronics to the photovoltaic world.

The theoretical fundamentals of diffractive solid immersion lenses (dSILs) were revised and adapted to a new application: the direct single-step chemistry-assisted creation of binary dSILs in silicon with a focused ion beam (FIB). Current results were able to prove the general functionality of this technique, but also showed the limitations still present. These limitations were identified; the underlying problems were analyzed and were addressed by optimizing several aspects of the process. The presented dSIL has a diameter of 150 ìm and is created in 15 minutes of processing time. It is designed for a sample thickness of 70 µm, which can be well adjusted if needed. For this sample thickness, the theoretical numerical aperture is about 2.5, offering a significant improvement in resolution. Furthermore a comparison of diffractive and refractive solid immersion lenses is presented, both created in a similar process. Apart from general aspects of dSILs and rSILs (refractive SILs), details of the designs presented in this work are compared. This leads to the insight of which method (dSIL or rSIL) has its advantages for which type of application.

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.

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.

Focused Ion Beam has proven to create refractive solid immersion lenses in silicon that can significantly improve the resolution of optical backside analysis tools. The SIL performance in our previous works has been limited though, mostly due to a pure sputtering process. This problem is addressed by developing a chemistry-assisted FIB process, offering the ability to create larger SIL shapes. A 50 µm wide SIL shape is presented with a lens area two and a half times larger than the largest FIB SIL we created so far. The resulting wider opening angle has the potential of better spatial resolution and higher photon collection efficiency. 370 nm wide image features are resolved using the FIB created SIL expanding the resolution capabilities of the used laser scanning microscope considerably.

The topic of this work is the sequential use of Solid Immersion Lenses (SILs), created in bulk silicon in less than 20 minutes of processing time, using a focused ion beam and a bitmap milling process. Fibbed SILs can be removed by polishing, and the silicon back surface resumes a perfect planar shape for further backside analysis or the creation of more SILs. The influence of the progressively thinner sample thickness on the magnification of the SIL was analyzed. As fibbed SILs in this work are about 1.4 µm thick and have an additional magnification of 2.4, a second process after removal has been found to decrease magnification not more than 20%. The presence of interference rings in the SIL image could be almost completely removed by anti-reflective coating. Photon emission microscopy, performed using fibbed SILs, allowed to clearly distinguish between sources that were separated by 240 nm wide structures.

The carrier collection properties of polycrystalline Si (poly-Si) thin film solar cells on glass with interdigitated mesa structure have been locally analysed with Infrared Light Beam Induced Current (IR-LBIC) and compared to LBIC measurements using visible light. The low absorption of IR light leads to a low current level when the light is coupled vertically into the active volume. An enhanced carrier collection has been detected at the corners of the mesa because the etch allows to couple the light horizontally into the solar cell, This investigation shows that IR-LBIC is sensitive to light trapping structures in silicon based thin film solar cells.

This work describes how Solid Immersion Lenses (SILs) can be created in bulk silicon using a focused ion beam and a bitmap milling process. The optical properties are in good agreement with the expected results for the achieved lens geometries. An improvement in lateral spatial resolution by a factor of 1.8 and in image contrast by 170 % for backside analysis is demonstrated. The presented SILs are 32 µm in diameter with a field of view of about 10 μm. This process can be an alternative when a regular SIL placement on the chip is impossible or complex. The advantages of this method are the use of a single kind of material (no air gaps and no additional lens material with different n value), the ability to precisely position the SIL on the circuitry and the fact that a SIL may be created in less than twenty minutes of processing time.

In this paper, a methodology based upon laser stimulation and a comparison of continuous wave and pulsed laser operation will be presented that localizes the fault relevant sites in a fully functional scan chain cell. The technique uses a laser incident from the backside to inject soft faults into internal nodes of a master-slave scan flip-flop in consequence of localized photocurrent. Depending on the illuminated type of the transistors (n- or p-type), injection of a logic ‘0’ or ‘1’ into the master or the slave stage of a flip-flop takes place. The laser pulse is externally triggered and can easily be shifted to various time slots in reference to clock and scan pattern. This feature of the laser diode allows triggering the laser pulse on the rising or the falling edge of the clock. Therefore, it is possible to choose the stage of the flip-flop in which the fault injection should occur. It is also demonstrated that the technique is able to identify the most sensitive signal condition for fault injection with a better time resolution than the pulse width of the laser, a significant improvement for failure analysis of integrated circuits.

Editing inside an integrated circuit (IC) is critical to debug new devices. Current flipchip circuit edit techniques are limited by spot resolution and chemistry constraints of Focused Ion Beam (FIB) systems. The newly proposed technique for circuit edit (CE) employs FIB to contact circuit nodes directly on transistor level, offering a wide range of applications since it allows accessing every signal on a chip. The general functionality and the influence on chip performance are evaluated for an Intel 65nm process technology.

Backside circuit edit techniques on integrated circuits (ICs) are becoming common due to increase number of metal layers and flip chip type packaging. However, a thorough study of the effects of these modifications has not been published. This in spite of the fact that the IC engineers have sometimes wondered about the effects of backside circuit edit on IC behavior. The IC industry was well aware that modifications can lead to an alteration of the intrinsic behavior of a circuit after a FIB edit [1]. However, because alterations can be controlled [2], they have not stopped the IC industry from using the FIB to successfully reconfigure ICs to produce working “silicon” to prove design and mask changes. Reliability of silicon device structures, transistors and diodes, are investigated by monitoring intrinsic parameters before and after various steps of modification.

Direct measurements of circuit node signals without changing the performance of the circuitry are essential in modern FA but often impossible for recent IC technologies. This paper shows new methods, based on FIB backside circuit edit, allowing access to every existing circuit node at the device level, and discusses options for probing and discrete characterization.

One method of dynamic probing in modern integrated circuits (ICs) is performed through the backside of the device. The established techniques are limited in lateral resolution because they use infrared (IR) light. This paper demonstrates how state of the art FIB circuit edit (CE) processes enable the application of E-Beam probing through chip backside on current and future IC technologies with low risk of device performance degradation.

The feasibility of low-ohmic FIB contacts to silicon with a localized silicidation was presented at ISTFA 2004 [1]. We have systematically explored options in contacting diffusions with FIB metal depositions directly. A demonstration of a 200nm x 200nm contact on source/drain diffusion level is given. The remaining article focuses on the properties of FIB deposited contacts on differently doped n-type Silicon. After the ion beam assisted platinum deposition a silicide was formed using a forming current in two configurations. The electrical properties of the contacts are compared to furnace anneal standards. Parameters of Schottky-barriers and thermal effects of the formation current are studied with numerical simulation. TEM images and material analysis of the low ohmic contacts show a Pt-silicide formed on a silicon surface with no visible defects. The findings indicate which process parameters need a more detailed investigation in order to establish values for a practical process.

Process options of FIB circuit edit accessing active area in silicon through chip backside are presented. The full process is divided in modules. The technological readiness of the different modules is discussed. New results for the two most critical modules, endpoint detection of the global FIB trench in silicon, and contact resistivity of FIB deposited metal interconnect on diffusion, are presented. Investigated endpoint detection processes are FIB image contrast of the wells and of STI (shallow trench isolation). The contact to diffusion is in the range of 2-5 x 10-7 Ωcm2 on highly doped n-Si, about 10x higher on highly doped p-Si, with linear I-V characteristic.

One approach for the measurement of circuit internal currents is the measurement of the magnetic field caused by a current flow through a conducting line. Due to its inherent superior spatial resolution in the topography modus magnetic field measurement techniques based on Scanning Force Microscopy seem to be a good basis for advanced measurement techniques for circuit internal failure analysis. Magnetic field measurement can be done by Magnetic Force Microscopy (MFM) using commercial and reproducible magnetic probes. In this paper the state-of-the-art of current measurement via MFM and a real failure analysis of an actual IC where standard failure analysis techniques failed will be demonstrated.

The step into the production line environment is a quantum leap for physical failure analysis (PFA) and will change its work in the near future. Wafer sacrifice for analysis becomes obsolete. The main benefits are: 1. reduction of wafer costs, 2. more splits per development lot, 3. reduced cycle time of analysis and technology development. Machines needed for that purpose are dual beam SEM/FIB tools. In the following we present solutions how PFA in a broad range can be carried out inside of a production line. The analyzed wafers can be fed back into the production flow which results in lower overall costs and the feedback loop to production engineers is dramatically shortened leading to reduced down times of production tools etc. The highest risk that has kept the majority of semiconductor manufacturers from proceeding into this direction is the contamination of the productive wafer with Ga, the FIB beam particle, that may diffuse into productive parts of the wafer during heat cycles after the analysis step. We show that the risk of contamination by Ga and other materials can be controlled.