Takanori Ninomiya

A charge-coupled-device-based heterodyne technique for parallel photodisplacement imaging

A heterodyne interferometry technique for parallel photodisplacement imaging is presented. In the parallel photodisplacement technique, a linear region of photothermal displacement is excited using a line-focusing intensity-modulated laser beam and is detected with a parallel heterodyne interferometer in which a charge-coupled device linear image sensor is used as a detector. The integration and sampling effects of the sensor provide spatiotemporally multiplexing of the interference light. To extract the spatially resolved photodisplacement component from the multiplexed sensor signal for heterodyne interferometry, a scheme of phase-shifting light integration under an undersampling condition is developed. The frequency relation for the heterodyne beat signal, modulation signal, and sensor gate signal is optimized so as to eliminate undesirable components, allowing only the displacement component to be extracted. Preliminary experimental results using a point-focused laser beam demonstrate that the techniq...

Automated visual inspection for lsi water multilayer patterns by cascade pattern matching algorithm

This paper reports on the defect detection algorithm for the LSI wafer multilayer patterns, together with the result of evaluation. The multilayer patterns are constructed by the exposure after alignment between the wafer pattern and the reticle pattern for each chip. Consequently, the position relation between layers is different even for adjacent chips (interlayer registration error). The developed algorithm compares the gray-level images of adjacent chips on the wafer and extracts the defect without being affected by the inter-layer registration error. First, the pattern edge is extracted from the gray-level image, and the position alignment is executed using the edges. Then, by eliminating the region where gray levels are equal, the regions are extracted for which the position alignment is unsatisfactory. The position alignment is attempted again for that region. This procedure is iterated. When the unmatched region of the pattern edge is sufficiently small, it is decided that the interlayer registration error is absorbed, and the unmatched region is extracted as the defect. An automatic visual inspection system was constructed and evaluated experimentally. As a result, it was verified that the whole chip area can be inspected, and the defect of 0.5 μm or more can be detected in a stable way.

Practical realization of high-speed photodisplacement imaging by use of parallel excitation and parallel heterodyne detection: a numerical study.

A new parallel photodisplacement technique that achieves extremely high-throughput imaging is proposed, and its practical realization is studied numerically. In this technique, a linear region of photothermal displacement is excited by use of a line-focusing intensity-modulated laser beam and detected with a parallel heterodyne interferometer in which a charge-coupled device linear image sensor is used. Because of the integration and sampling effects of the sensor, the interference light is spatiotemporally multiplexed. To extract the photodisplacement component from the multiplexed sensor signal, a scheme of phase-shifting light integration under an undersampling condition is proposed for parallel interferometry. The frequencies of several control signals, including the heterodyne beat signal, modulation signal, and sensor gate signal, are optimized so as to eliminate undesirable components, allowing only the displacement component to be extracted. Preliminary numerical simulation results show that the proposed technique has the potential to perform photodisplacement imaging more than 10,000 times faster than conventional photoacoustic microscopy.

Automated solder joint inspection system using optical 3-D image detection

An automated system has been developed for visually inspecting the solder joints of SMDs (Surface Mounted Devices). The system is capable of inspecting fine pitch components down to 0.3 mm pitch QFPs (Quad Flat Packages). A unique image detection method was also developed to obtain precise 3-D images of solder joints. The principle of a confocal microscope is employed but plural sensors are used to detect reflected light at different focusing positions simultaneously. The system is unaffected by secondary reflection and dead angles. The warp in a PC (Printed Circuit) board surface is calculated in real time using the detected 3-D images, and board height to be detected in successive areas is predicted based on this calculation. Real-time automatic focusing control is then performed using newly developed defect detection algorithms, the system can recognize leads, pads and solder fillets from the detected images. Because 3-D shape features are extracted and used for defect judgment, user-defined parameters have been made easy to understand and/or to modify. Operational evaluation of the system confirms a 100% defect detection rate and a very low false alarm rate (0.16%).

Real-time photodisplacement imaging using parallel excitation and parallel heterodyne interferometry

A parallel photodisplacement technique that achieves real-time imaging of subsurface structures is presented. In this technique, a linear region of photothermal displacement is excited by a line-focused intensity-modulated laser beam and detected with a parallel heterodyne interferometer using a charge-coupled device linear image sensor as a detector. Because of integration and sampling effects of the sensor, the interference light is spatiotemporally multiplexed. To extract the spatially resolved photodisplacement component from the sensor signal, a scheme of phase-shifting light integration combined with a Fourier analysis technique is developed for parallel interferometry. The frequencies of several control signals, including the heterodyne beat signal, modulation signal, and sensor gate signal, are optimized so as to eliminate undesirable components, allowing only the displacement component to be extracted. Two-dimensional subsurface lattice defects in silicon are clearly imaged at a remarkable speed ...

Real-time photodisplacement microscope for high-sensitivity simultaneous surface and subsurface inspection

We have developed a new photodisplacement microscope system for practical use that achieves high-sensitivity simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram. In this system a linear region of photothermal displacement is excited on the sample surface for subsurface imaging by a line-focused intensity-modulated laser beam. Surface information such as reflectivity and topography along with the displacement is detected with a charge-coupled device sensor-based parallel heterodyne interferometer. Surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions based on a frequency-optimized undersampling scheme, allowing each to be discretely reproduced by using a real-time Fourier analysis technique. Preliminary experiments demonstrate that this system is effective, simultaneously imaging reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects in silicon, at a remarkable speed of only 0.26 s/256x256 pixel area. This new microscope is promising for nondestructive hybrid surface and subsurface inspection and other applications.

Automatic screen-printed circuit pattern inspection using connectivity preserving image reduction and connectivity comparison

Describes a new automatic pattern inspection method which can reliably detect fatal circuit defects without giving false alarms due to circuit patterns with slightly jagged edges. Also described is a high-speed automatic inspection system for screen-printed circuit patterns of an unbaked ceramic layer, known as a green sheet. For fatal defect detection, the connectivity comparison method was adopted. In order to speed up this method and to further improve it, connectivity preserving image size reduction, a new concept, was developed.<<ETX>>

Three-Dimensional Vision Systems Using the Structured-Light Method for Inspecting Solder Joints and Assembly Robots

The structured light method is effective for detecting a sectional view or range data for industrial applications. This article presents two three-dimensional vision systems developed at the Production Engineering Research Lab of Hitachi, Ltd., Japan. One system is for inspecting solder joints and the other was for automatic part assembly by robots. The inspection system can detect and correctly judge the shape of solder joints. The assembly robot vision system consists of a fixed 3-D detector and a small X-type slit detector attached on the robot hand. The former detects the overall range data of robot work-fields, and finds and detects the position and posture in 3-D space of a particular object. The latter detects the precise position and posture of an object.

Simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed photodisplacement interferogram

A new parallel photodisplacement technique has been developed that achieves simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram, which greatly simplifies the system and the optical alignment. A linear region of photodisplacement is excited on the sample for subsurface imaging by use of a line-focused intensity-modulated laser beam, and the displacement and surface information on reflectivity and topography are detected by a parallel heterodyne interferometer with a charge-coupled device linear image sensor used as a detector. The frequencies of three control signals for excitation and detection, that is, the heterodyne beat signal, modulation signal, and sensor gate pulse, are optimized such that surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions, allowing each to be discretely reproduced from Fourier coefficients. Preliminary experiments demonstrate that this technique is capable of simultaneous imaging of reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects at a remarkable speed of only 0.26 s per 256 x 256 pixel area. This new technique is promising for use in nondestructive hybrid surface and subsurface inspection and other applications.

General solution of undersampling frequency conversion and its optimization for parallel photodisplacement imaging

A general solution of undersampling frequency conversion and its optimization for parallel photodisplacement imaging is presented. Phase-modulated heterodyne interference light generated by a linear region of periodic displacement is captured by a charge-coupled device image sensor, in which the interference light is sampled at a sampling rate lower than the Nyquist frequency. The frequencies of the components of the light, such as the sideband and carrier (which include photodisplacement and topography information, respectively), are downconverted and sampled simultaneously based on the integration and sampling effects of the sensor. A general solution of frequency and amplitude in this downconversion is derived by Fourier analysis of the sampling procedure. The optimal frequency condition for the heterodyne beat signal, modulation signal, and sensor gate pulse is derived such that undesirable components are eliminated and each information component is converted into an orthogonal function, allowing each to be discretely reproduced from the Fourier coefficients. The optimal frequency parameters that maximize the sideband-to-carrier amplitude ratio are determined, theoretically demonstrating its high selectivity over 80 dB. Preliminary experiments demonstrate that this technique is capable of simultaneous imaging of reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects at a speed corresponding to an acquisition time of only 0.26 s per 256 x 256 pixel area.