Lock-in thermography (LIT) has been successfully applied in different excitation and analysis modes including classical LIT, analysis of the time-resolved temperature response (TRTR) upon square wave excitation and TRTR analysis in combination with arbitrary waveform stimulation. The results obtained by both classical square wave- and arbitrary waveform stimulation showed excellent agreement. Phase and amplitudes values extracted by classical LIT analysis and by Fourier analysis of the time resolved temperature response also coincided, as expected from the underlying system theory. In addition to a conceptual test vehicle represented by a point-shaped thermal source, two semiconductor packages with actual defects were studied and the obtained results are presented herein. The benefit of multi-parametric imaging for identification of a defect’s lateral position in the presence of multiple hot spots was also demonstrated. For axial localization, the phase shift values have been extracted as a function of frequency [4]. For comparative validation, LIT analyses were conducted in both square wave and arbitrary waveform excitation using custom designed and sample-specific stimulation signals. In both cases result verification was performed employing X-ray, scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) as complementary techniques.

We demonstrate how electro optical terahertz pulse reflectometry (EOTPR) can be used in conjunction with a new one-dimensional lump circuit simulation software to quickly and non-destructively isolate faults in advanced IC packages. In the case studies presented, short failures are accurately located in a series of advanced IC package.

Modern 2D and 3D X-ray technologies are among the most useful non-destructive testing methods that enable the inspection of an object's internal features without cutting or disassembling the sample. This paper discusses the basic operating principle, advantages, and disadvantages of 2D and 3D X-ray based approaches for testing and failure analysis and describes how these different methods have practical application for failure analysis and dimensional metrology. The techniques discussed are radiography, classical laminography, computed tomography, and computed laminography.

We report and demonstrate a new methodology for the localization of dielectric breakdown sites in through-silicon via (TSV) structures. We apply a combination of optical beam induced resistance change (OBIRCH) and mechanical/chemical chip deprocessing techniques to localize nm-sized pinhole breakdown sites in a high aspect ratio 3x50 ìm TSV array. Thanks to the wavelength-selective absorption process in silicon, we can extract valuable defect depth localization info from our laser stimulation measurement. After chip deprocessing we inspect and localize the defect site in the dielectric liner using a scanning electron microscope (SEM). We confirm our results and analysis by cross-sectioning a TSV with a focused-ion beam (FIB).

GHz-SAM using toneburst transducers is a method currently lacking the possibility to measure warped samples easily because large parts of such samples are out of focus due to the limited depth of focus of these types of transducers. This paper shows an approach to use the already established HiSA (High Speed Axis) method to overcome this disadvantage. Therefore warpage of the sample is measured by a white-light interferometer. The detected bow is parametrized and submitted in the control electronics of the HiSA. With this data the HiSA is enabled to keep the distance between sample and transducer precisely constant. This allows eliminating the influence of the warpage on the performance of this method and therefore highly increases the image quality.

This paper discusses the implementation of GHz-Scanning Acoustic Microscopy (GHz-SAM) into a wafer level scanning tool and its application for the detection of delamination at the interface of hybrid bonded wafers. It is demonstrated that the in-plane resolution of the GHz-SAM technique can be enhanced by thinning the sample. In the current study this thinning step has been performed by the ion beam of a ToF-SIMS tool containing an in-situ AFM, which allows not only chemical analysis of the interface but also a well-controlled local thinning (size, depth and roughness).

Signal processing and data interpretation in scanning acoustic microscopy is often challenging and based on the subjective decisions of the operator, making the defect classification results prone to human error. The aim of this work was to combine unsupervised and supervised machine learning techniques for feature extraction and image segmentation that allows automated classification and predictive failure analysis on scanning acoustic microscopy (SAM) data. In the first part, conspicuous signal components of the time-domain echo signals and their weighting matrices are extracted using independent component analysis. The applicability was shown by the assisted separation of signal patterns to intact and defective bumps from a dataset of a CPU-device manufactured in flip-chip technology. The high success-rate was verified by physical cross-sectioning and high-resolution imaging. In the second part, the before mentioned signal separation was employed to generate a labeled dataset for training and finetuning of a classification model based on a one-dimensional convolutional neural network. The learning model was sensitive to critical features of the given task without human intervention for classification between intact bumps, defective bumps and background. This approach was evaluated on two individual test samples that contained multiple defects in the solder bumps and has been verified by physical inspection. The verification of the classification model reached an accuracy of more than 97% and was successfully applied to an unknown sample which demonstrates the high potential of machine learning concepts for further developments in assisted failure analysis.

This paper discusses the Failure Analysis methodology used to characterize 3D bonded wafers during the different stages of optimization of the bonding process. A combination of different state-of-the-art techniques were employed to characterize the 3D patterned and unpatterned bonded wafers. These include Confocal Scanning Acoustic Microscopy (CSAM) to determine the existence of voids, Atomic Force Microscopy (AFM) to determine the roughness of the films on the wafers, and the Double Cantilever Beam Test to determine the interfacial strength. Focused Ion Beam (FIB) was used to determine the alignment offset in the patterns. The interface was characterized by Auger Spectroscopy and the precession electron nanobeam diffraction analysis to understand the Cu grain boundary formation.

This paper demonstrates the application of GHz-SAM for the detection of local non-bonded regions between micron-sized Cu-pads in a wafer-to-wafer hybrid bonded sample. GHz-SAM is currently the only available non-destructive failure analysis technique that can offer this information on wafer level scale, with such high resolution.

The paper demonstrates the moving of lock-in thermography (LIT) spot location by adjusting the lock-in frequency from low to high. Accurate defect localization in stacked-die devices was decided by the fixed LIT spot location after the lock-in frequency was higher than a specific value depending on the depth of the defect in the IC. Physical failure analysis was performed based on LIT results, which provided clear physical defect modes of the stacked-die devices.

Lock-in thermography (LIT) phase data is used to generate phase shift versus applied lock-in frequency plots to estimate defect depth in semiconductor packages. Typically, samples need to be tested for an extended time to ensure data consistency. Furthermore, determining the specific point on the thermal emission site to collect data from can be challenging, especially if it is large and dispersive. This paper describes how the use of new computational algorithms along with streamlined and automated workflows, such as self-adjusting thermal emission site positioning and phase measurement auto-stop, can result in improvements to data repeatability and accuracy as well as faster time to results. The new software is applied to generate the empirical phase shift versus applied lock-in frequency plot using 2.5D IC devices with known defect location. Subsequently, experimental phase shift data from reject 2.5D IC devices with unknown defect locations are obtained and compared against the empirical phase shift plot. The defect Z-depth of these devices are determined by comparing where the experimental phase shift data points lies with respect to empirical phase shift plot and validated with physical failure analysis (PFA).

Dynamic Digital Modulation, an adaptation of Lock-In Thermography, has been shown to be a useful technique to establish the relative Z-depth of thermal sources in integrated circuits. In order to determine the specific depth of a thermal source it is necessary to correlate known depths to measured thermal rise time. In this work, multi-die stacked memory devices are used as calibration sources to correlate a thermal source at individual die to the measured thermal rise time.

3D integration takes more and more importance in the microelectronics industry. This paper focuses on two types or objects, which are copper pillars (25 micrometer of diameter) and hybrid bonding samples. It aims at a statistical morphology observation of hybrid bonding structures, which underwent an electromigration test at 350 deg C and 20 mA. The goal of the study is two-fold. It is both to limit the overall time needed to perform a whole process flow, from sample preparation to reconstructed volume, and to limit the time of human intervention. To achieve this goal, three strategies are presented: improving the sample preparation scheme, reducing the number of projections with iterative algorithms and the Structural SIMilarity function, and automating the post-processing. The post-processing of the data is fully automated and directly renders the reconstructed volume. The high signal to noise ratio allows for further segmentation and analysis.

Tremendous research efforts have been devoted particularly to the development and improvement of through silicon vias (TSV) in order to provide a key enabling technology for vertical system integration. To achieve high processing yield and reliability efficient failure analysis techniques for process control and root cause analysis are required. The current paper presents an advanced approach for non-destructive localization of TSV sidewall defects applying high resolution Lock-in Thermography and Photoemission Microscopy imaging and defocusing series.

Electro Optical Terahertz Pulse Reflectometry (EOTPR) is an E-FA (Electrical Failure Analysis) technique in the semiconductor industry for non-destructive electrical fault isolation for shorts, leakages and opens. This paper introduces the capability and presents several case studies identifying the physical location of defects where EOTPR is useful as a non-destructive analysis technique. In this paper, the methodology and application of EOTPR on open and short failure isolations in advanced 2.5D IC and wafer level packages (WLP) have been presented. The experimental results of P-FA (Physical Failure Analysis) verify the accuracy of the EOTPR system in determining the distance to defect.

Here, we demonstrate how electro optical terahertz pulse reflectometry (EOTPR) can be used to quickly and non-destructively isolate faults in 2.5D packages. We present case studies to show how EOTPR can unambiguously differentiate between faults located in the C4 bump, TSV, RDL, and micro-bump of a 2.5D package.

NCF (Non Conductivity Film) is a material used for under-fill purpose in the TSV (Through Silicon Via) process, and is a key material for ensuring TSV 3D Package (PKG) reliability. Among the types of defects generated by the NCF, the most typical type is delamination. Particularly in NCF delamination frequently occurs during reliability test, we analyzed chemical state change of NCF according to reliability test step/condition by utilizing FTIR and TMA. Through these studies, we clarify the cause of Delamination.

Through Silicon Via (TSV) Package (PKG) technology that forms a 3D stack with chip to chip or wafer to wafer contact, uses a variety of wet chemicals unlike conventional package technology. Therefore, new kinds of defects related to the wet chemical occur. In this a new failure mode of disappeared Al pad will be presented, a problem came up to disappear Al pad, which served as the fiducial key during the metal residue removal process after forming the TSV PKG front bump, the mechanism of disappearance of Al pad was investigated. Through chemical analysis of process and equipment, we found that Cu etchant (including H3PO4) can damage for Al pad. The process simulation demonstrated that Al pad actually disappeared. Therefore, it confirmed that it needs to be removed through sufficient rinsing time after applying the wet chemical applied to the TSV PKG process. As a result we solved problem through modified equipment and increased rinsing time.

Temperature-dependent die warpage measurements show the possibility to analyze the thermomechanical behavior during assembly, e.g. within soldering processes. The warpage data acquisition is realized by confocal chromatic white light profilometry in combination with a precision heating/cooling chuck encapsulated in a chamber with optical access. The combination of these two tools allows precise die warpage evaluation under varied device temperature up to +400°C. This method helps to solve emerging challenges due to warpage during assembly of state of the art packages including thin dies and stacked dies as in e.g. 3D-SIPs.

This paper discusses the application of two different techniques for failure analysis of Cu through-silicon vias (TSVs), used in 3D stacked-IC technology. The first technique is GHz Scanning Acoustic Microscopy (GHz- SAM), which not only allows detection of defects like voids, cracks and delamination, but also the visualization of Rayleigh waves. GHz-SAM can provide information on voids, delamination and possibly stress near the TSVs. The second is a reflection-based photoelastic technique (SIREX), which is shown to be very sensitive to stress anisotropy in the Si near TSVs and as such also to any defect affecting this stress, such as delamination and large voids.