Yoshihiro Midoh

3D analysis of benign positional nystagmus due to cupulolithiasis in posterior semicircular canal.

Conclusions: The characteristic of both the vertical-torsional positional nystagmus with long time constant and its disappearance at the neutral head position could diagnose cupulolithiasis in posterior semicircular canal (PSCC) in the eight patients with the PSCC type of benign paroxysmal positional vertigo (P-BPPV). Objective: The aim of the study was to diagnose cupulolithiasis in patients with P-BPPV. Patients and methods: We used three-dimensional rotation axis analysis of nystagmus of the vertical-torsional positional nystagmus in 111 patients with P-BPPV and evaluated its time constant. We then examined whether the vertical-torsional positional nystagmus with long time constant disappeared at the neutral head position where the axis of the heavy cupula of the affected PSCC is aligned with gravity. Results: The first parameter showed a wide variation that could be divided into two groups: one lasting more than 40 s in 8 patients and another below 20 s in 103 patients. Since the time constant of the positional nystagmus induced by cupulolithiasis was much longer than that induced by canalolithiasis, this finding suggests that cupulolithiasis in the PSCC induced the vertical-torsional positional nystagmus with a long time constant in the group of eight patients. The vertical-torsional positional nystagmus disappeared in these patients at the neutral head position, where the axis of the cupula of affected PSCC aligned with gravity.

THz emission characteristics from p/n junctions with metal lines under non-bias conditions for LSI failure analysis

We have investigated the characteristics of THz emissions from p/n junctions with metallic lines under non-bias conditions. The waveforms, spectra, and polarizations depend on the length and shape of the lines. This indicates that the transient photocurrents from p/n junctions flow into the metallic lines that emit THz waves and act as an antenna. We have successfully demonstrated the non-contact inspection of open defects of multi-layered interconnects in a large-scale integrated circuit using the laser THz emission microscope (LTEM). The p/n junctions connected to the defective interconnects can be identified by comparing the LTEM images of normal and defective circuits.

Laser THz emission microscope as a novel tool for LSI failure analysis

Abstract We have proposed and developed a novel technique for a non-contact inspection of defective interconnections in an LSI chip using a laser terahertz emission microscope (LTEM). The LTEM measures the THz emission images of an LSI chip by scanning it with fs laser pulses. When a fs laser pulse irradiates a p–n junction in an LSI chip, transient photocurrent flows into interconnections resulting in the emission of the THz pulse into free space. We investigated the characteristics of the THz emissions from simple test element group samples which consist of p–n junctions connected to metal lines. It was found that the metallic lines connected to photo-excited p–n junctions worked as THz emission antennae which enhance the emission efficiency of THz pulses near their resonant frequencies corresponding to the line lengths. This result indicates that THz emission signals from p–n junctions in circuits strongly depend on the structure of the interconnections. We show the successful results on the inspection of defective interconnections in MOSFET devices and C7552 ISCAS’85 benchmark circuits using LTEM. By comparing the THz emission images between a normal circuit and a defective one, it is possible to identify the p–n junctions connected to the defective interconnections without electrical contacts.

Object size measurement method from noisy SEM images by utilizing scale space

We proposed an object size measurement method from noisy scanning electron microscope (SEM) images with shot noise by utilizing the scale space approach. The proposed measurement algorithm consists of six steps: (1) specifying an object to be measured, (2) estimating the noise level, (3) constructing Gaussian and gradient scale spaces, (4) determining a starting scale for edge tracking, (5) edge tracking and (6) object size measurement. For the object size measurement, the model parameters of SEM images are estimated from regions segmented by edge positions at the finest scale. Then the appropriate scale for the object size measurement is automatically selected by estimated model parameters and an optimal scale parameter for smoothing filter in the Canny edge detector. And then, the object size is measured. We applied the algorithm to model SEM images and an SEM image. Though the processing time for our proposed method took about 13 times longer than that of the Canny detector, the range of the probability of extracting true edge positions was extended from 94% in the Canny detector to 80% in our method: the measurable region of the edge tracking was more extensive than that of the Canny detector.

Statistical optimization of Canny edge detector for measurement of fine line patterns in SEM image

For the purpose of developing a recognition system for fine line patterns in the LSI, a statistical optimization method of the Canny edge detector for scanning electron microscope (SEM) images is proposed. The analysis of variance (ANOVA) is applied to the estimation of parameters in the SEM image: the grey level in the background, contrast, the line width and the noise level. These parameters are used to optimize statistically the Canny parameters, a scale parameter of the smoothing filter and a binarization threshold, by using noise characteristics of the SEM image. The proposed method is applied to model images and a real SEM image to show its validity.

Boundary extraction in the SEM cross-section of LSI

We have proposed a boundary extraction algorithm for cross-sectional critical dimension (CD) measurements of the scanning electron microscope (SEM) images in machine/computer vision. Noisy SEM images have the image discontinuity of roof edge with peak. A task is to extract a low contrast boundary or edge with about one pixel width in a noisy cross sectional SEM image. Also CD measurements require that the algorithm locate a boundary or an edge at the correct position. Our policy is to detect the edges with high degree of confidence at first, and then to extract the edges with the high probabilities of edge that are calculated by using gray levels of neighboring pixels. Our proposed algorithm integrates the Gaussian pyramid to suppress noise, morphological operations to detect the edges with high degree of confidence, the relaxation method to recover the gaps in the detected edges, and the hierarchical approach. Application of the proposed algorithm to cross sectional SEM images of DRAMs shows its validity.

Non-electrical-contact LSI failure analysis using non-bias laser terahertz emission microscope

We have developed the laser terahertz emission microscope that does not require Vdd-biasing and signal input: NB (non-bias)-LTEM. The NB-LTEM, also, does not require signal output via electrodes. In this paper, first of all, the position of non-electrical contact tools, in failure analysis, is show. Secondary, the basic concept and the system schematic of the NB-LTEM are described. Thirdly, how to use the NB-LTEM in fault localization is explained. Then, some examples of fault localization or defect detection using the NB-LTEM are shown. Finally, we would like to compare the NB-LTEM and the other non-electrical contact tool (L-SQ, laser SQUID microscope).

The combinational or selective usage of the laser SQUID microscope, the non-bias laser terahertz emission microscope, and fault simulations in non-electrical-contact fault localization

Abstract Recently, in the field of fault localization of LSI chips, several non-electrical contact techniques have been proposed. The techniques include the laser SQUID microscope (L-SQ) and the non-bias laser terahertz emission microscope (NB-LTEM). Both techniques have pros and cons. The L-SQ, for examples, can localize open defects in some cases, but it requires closed circuit. The NB-LTEM can localize open defects and short defects, and not requires closed circuit. The NB-LTEM, however, cannot localize open defects in some cases. The fault simulation specially designed for the L-SQ or the NB-LTEM makes it precise or efficient to localize defects. The combinational or selective usage of the L-SQ, the NB-LTEM and the related simulations makes it possible to localize defects in many cases. In this paper, we would like to review our results and organize them from the viewpoint of failure mode and defect sites.

Boundary extraction in the SEM cross-section of LSI by multiple Gaussian filtering

We proposed a boundary extraction method by utilizing the scale space in order to extract boundaries flexibly from the cross-sectional SEM images. The Gaussian scale space is constructed by convolving the original image with Gaussians of increasing standard deviation, that is, multiple Gaussian filtering. Setting the appropriate range of standard deviations for a target CD measurement part gives a high degree of flexibility to the edge detection method. Though the locations of the edges at the coarse scales may be shifted form their true locations, the true edge location is estimated by tracing the edges detected at coarse scales back to finer scales. By utilizing the edge-location-scale map, the blurring of image acquisition system is also estimated. By applying the proposed method to a model image, the edge location and the blurring estimation accuracies were evaluated. The accuracy in estimated edge locations was less than 0.5 pixels and the blurring very close to the true value was obtained. Next, the proposed method was applied to a cross-sectional SEM image of the DRAM that had a very low contrast boundary to show its validity.

Non-bias inspection of electrical failures in LSI interconnects using LTEM prototype system

Logic LSI chips fabricated by 180nm process were measured by a prototype system of the laser terahertz emission microscope (LTEM). By comparing the LTEM images between a normal circuit and a defective one, p-n junction connected to the defective interconnect such as open or short circuits can be successfully determined under non-bias measurement condition. This result indicates that LTEM can be a useful tool which realizes a non-bias measurement of the defect localization in failure analysis of LSIs fabricated by 180nm process.