Sub-surface analyses of defects in integrated devices by scanning probe acoustic microscopy

Acoustical analyses of integrated devices have been performed at the nanometer level by the detection of acoustical waves locally generated by a modulation of the load force of a scanning probe microscope tip onto a device. Monitoring the acoustical signal measured at the reverse side of the device under test allows us to localize sub-surface defects due to the corresponding signal change with approximately 150 nm spatial resolution.     

Metallization defect detection in 3D integrated components using scanning acoustic microscopy and acoustic simulations

In the context of More than Moore 3D integration concepts, the μm to nm sized failure detection and analysis represents a highly demanding task. In this work, micron sized artificially induced metallization defects in open TSVs are detected by scanning acoustic microscopy (SAM). Micro X-ray computed tomography (μXCT) and scanning electron microscopy (SEM) are used to validate the SAM results. Notably, the SAM results show that the failures for certain TSVs are located at a different position as illustrated by μXCT and SEM. In order to interpret these controversial results, 2D elastodynamic finite integration technique (EFIT) simulations are performed. We discuss the results by taking the excitation of surface acoustic waves (SAWs) or Rayleigh waves into account which are leading to characteristic interference patterns within the TSV. The simulation and understanding of such interference effects can be highly beneficial for the use of SAM with respect to modern failure detection and analyses.     

Gray scale for scanning acoustic microscopy

The principle of a true acoustic Gray-scale standard is presented and experimentally applied to the scanning acoustic microscope (s.a.m.). The implementation is based on the impedance-matching property of a quarter-wave impedance transformer through which precise changes in reflection coefficient may be produced in a single material. The performance of the first implementation designed for 375 MHz operation is described.     

Simultaneous scanning optical and acoustic microscopy

We have demonstrated a combined scanning acoustic and optical microscope capable of simultaneously recording acoustic and optical images of the same field of view. The estimated resolution of the optical (6328 ?) and acoustic (550 MHz) images is 2 ?m, in good agreement with theory. The system is ideally suited to photoacoustic microscopy.     

Bond integrity evaluation using transmission scanning acoustic microscopy

Low frequency transmission scanning acoustic microscopy is capable of revealing voids and delaminations at substantial depths inside a solid material. The technique is demonstrated with reference to the bond between a carbon diamond compound sintered to a steel base. A resolution comparable to the wavelength inside the solid material is achieved.     

New CW imaging mode for scanning acoustic microscopy

The application of frequency-modulated continuous waves (FMCW) to the scanning acoustic microscope (SAM) is described. The technique provides a convenient way of separating specimen topography from reflectivity while enjoying the advantages of pulse compression. Furthermore, the system will enable sophisticated signal processing to be carried out at audio frequencies.     

Scanning electron mirror microscopy and scanning electron microscopy of integrated circuits

The recently developed scanning electron mirror microscope (SEMM) is compared with other types of electron microscopes, such as the electron mirror microscope (EMM) and the scanning electron microscope (SEM), for examining integrated circuits. Potential advantages of the SEMM include high resolution, elimination of electron bombardment damage, and high sensitivity of voltage gradients, magnetic fields, and topography. Preliminary observations of integrated, circuits obtained with the feasibility SEMM at various specimen potentials are discussed.     

High-speed integrated circuit probing using a scanning forcemicroscope sampler

Using a scanning force microscope as a high-speed all-electrical sampler, the authors have probed voltages on internal nodes of integrated circuits. The authors have demonstrated non-invasive probing through a passivating layer and probing of an Intel 80486 microprocessor     

Automated inspection and classification of flip-chip-contacts using scanning acoustic microscopy

Industrial applications often require failure analysis methods working non-destructively, enabling either a rapid quality control or fault isolation and defect localization prior to a detailed defect investigation requiring target preparation. Scanning acoustic microscopy in the frequency range above 100 MHz provides high axial and lateral resolution, a moderate penetration depth and the required non-destructivity. In this study a method for an automated detection of defects in flip-chip-contacts was developed. Chip samples were manufactured in flip-chip technology containing a 750 μm thick die with solder balls (80 μm diameter) and underfill attached to an organic-layer substrate. For acoustic inspection a scanning acoustic microscope in combination with a 175 MHz transducer was used. Recorded echo signals were analyzed off-line applying custom-made MATLAB software. For differentiation between the flip-chip-contacts and the underfill, the recorded echo signals were pre-analyzed. Signals obtained from the contacts were then inspected by wavelet-, pulse separation- and backscatter amplitude integral analysis. Complementary X-ray- and SEM-inspection was performed for defect verification. The separation of pulses obtained from the interfaces of the contacts, the absolute values and the distribution of wavelet coefficients corresponded to the interconnecting condition. The success rate of detecting voids was 96.8% as verified by SEM-imaging, while manual X-ray inspection showed success only in 64% of the analysed cases.     

Thermo-acoustic effects on images for high resolution scanning acoustic microscopy

A novel scanning acoustic microscopy (SAM) technique employing thermal effects to improve the contrast of acoustic images has been demonstrated. Experiments were performed on a buried channel in a thick perspex block; it was found that short periods of sample heating can lead to a stronger image contrast.<>     

Automatized failure analysis of tungsten coated TSVs via scanning acoustic microscopy

In 3D integrated microelectronics, the failure analysis of through silicon vias (TSVs) represents a highly demanding task. In this study, defects in tungsten coated TSVs were analysed using scanning acoustic microscopy (SAM). Here, the focus lay on the realization of an automatized failure detection method towards rapid learning. We showed that by using a transducer of 100 MHz center frequency, established with an acoustical objective (AO), it is possible to detect defects within the TSVs. In order to interpret our analysis, we performed acoustic wave propagation simulations based on the elastodynamic finite integration technique (EFIT). In addition, high resolution X-ray computed tomography (XCT) was performed which corroborated the SAM analysis. In order to go towards automatized defect detection, firstly the commercially available software “WinSAM8” was enhanced to perform scans at defined working distances automatically. Secondly, a pattern recognition algorithm was successfully applied using “Python” to the SAM scans in order to distinguish damaged TSVs from defect-free TSVs. Besides the potential for automatized failure detection in TSVs, the SAM approach exhibits the advantages of fast and non-destructive failure detection, without the need for special preparation of the sample.     

New findings in the occurrence of false-healing in plasticencapsulated microcircuits using scanning acoustic microscopy

“False-healing” refers to the occasionally observed reduction of delamination in plastic encapsulated microcircuits, In previous studies, “false-healing” was reported only at the leadframe-plastic interface. It was thought that the chemical contaminants present in the flux enter the package and form corrosive products which fill up the internal air gaps. This paper reports on some new findings in the occurrence of false-healing in plastic packages using scanning acoustic microscopy. This study found that false-healing also occurs in instances where there was no exposure to corrosive media. Additionally, false healing was observed at the die-plastic interface, where chemical contaminants could not reach. Alternate explanations for this phenomenon are suggested and its impact on damage assessment of plastic encapsulated microcircuits is discussed     

Characteristic material signatures by acoustic microscopy

Image contrast in the scanning acoustic microscope is affected by axial translation of the object along the lens axis. The explanation lies in the recognition that the acoustic reflection coefficient varies with axial translation in a manner that is unique and characteristic of the material involved. Examples of material signatures are given and used to explain the observed image contrast. The instrument's ability to obtain crystallographic information is suggested.     

Characterization of defects in hydrogenated amorphous silicon devices using charge collection scanning electron microscopy

Electron-beam-induced current (EBIC) and secondary electron image (SEI) modes of a scanning electron microscope (SEM) are utilized for characterization of charge collection inhomogeneities in hydrogenated amorphous silicon devices. These inhomogeneities are due to such fabrication defects as substrate surface roughness, pin holes, blistering and lift-off. SEM observations are correlated with the electrical properties of the devices. Electronirradiation-induced damage in these devices is also investigated by measuring the EBIC time decay at continuous electron irradiation as a function of both the electron -beam energy and current. This decay mechanism is based on the formation of electron-irradiation-induced microscopic defects that act as recombination centers and reduce the lifetime of carriers.     

Non-destructive identification of open circuit in wiring on organic substrate with high wiring density covered with solder resist

As the printed wiring density on organic substrate is increasing, the line width and spacing are reducing toward 25 μm and below. Present method of fault isolation will no longer be adequate, and capacitive voltage contrast method is proposed. The feasibility of the voltage contrast method is demonstrated, and the various key parameters for better contrast are identified and determined. Circuit model is developed to explain the experimental results and the significance of the various key parameters.     

Void-free Au-Sn eutectic bonding of GaAs dice and its characterization using scanning acoustic microscopy

A new technique to produce perfect bonding between GaAs dice and alumina substrates is reported. Utilizing this technique, void-free bondings have been achieved consistently. The quality of the bonded devices is confirmed by a Scanning Acoustic Microscope (SAM) having a spatial resolution of 25 μm. Thermal cycling between -25° C and 125° C, and thermal shock between -196° C and 135° C, have been used to assess the reliability of the specimens. The SAM was used to study the variation of the bonds in the tests. After the tests, the bonds show no sign of degradation and the GaAs dice did not crack. Shear test has also been performed. All the well bonded specimens passed the shear test. The shear strength correlated very well with the SAM images of the specimens taken before the test.     

Using scanning acoustic microscopy and LM-BP algorithm for defect inspection of micro solder bumps

Micro solder bump has been widely used in electronic packaging. Currently a number of flip-chip products are developing towards miniaturization with more I/Os at finer pitch, and defect inspection of the high density package is increasingly challenging. In this paper, the Levenberg-Marquardt back-propagation network (LM-BP) combined with the scanning acoustic microscopy technology was investigated for intelligent diagnosis of solder defect. The flip chips were detected by using a 230 MHz ultrasonic transducer. Solder bumps were segmented from the SAM image. The statistical features were extracted and fed into the LM-BP networks for bump classification. The results demonstrate that LM-BP algorithm reached a high recognition accuracy, and is effective for defect inspection of the micro solder bump.     

Defect inspection of solder bumps using the scanning acoustic microscopy and fuzzy SVM algorithm

Flip chip technology has been extensively used in high density electronic packaging over the past decades. With the decrease of solder bumps in dimension and pitch, defect inspection of solder bumps becomes more and more challenging. In this paper, an intelligent diagnosis system using the scanning acoustic microscopy (SAM) is investigated, and the fuzzy support vector machine (F-SVM) algorithm is developed for solder bump recognition. In the F-SVM algorithm, we apply a fuzzy membership to input feature data so that the different input features can make different contributions to the learning procedure of the network. It solves the problem of feature data aliasing in the traditional SVM. The SAM image of flip chip is captured by using an ultrasonic transducer of 230 MHz. Then the segmentation of solder bumps is based on the gradient matrix of the original image, and the statistical features corresponding to every solder bump are extracted and adopted to the F-SVM network for solder bump classification and recognition. The experiment results show a high accuracy of solder defect recognition, therefore, the diagnosis system using the F-SVM algorithm is effective and feasible for solder bump defect inspection.     

墙面涂料的显微共聚焦喇曼光谱无损鉴别

为了实现对墙面涂料物证的无损鉴别,提出了显微共聚焦喇曼光谱技术结合多元建模分析的无损鉴别墙面涂料方法.采用不同Savitzky-Golay(SG)平滑多项式次数及平滑点数对分类模型准确率的影响进行预处理,同时比较了不同分类模型的区分能力.结果表明,相较于径向基函数神经网络模型,多层感知器神经网络模型对各样本的区分能力更...