Yoshiro Nishimoto

Photodisplacement Measurement by Interferometric Laser Probe

A highly sensitive optical heterodyne interferometer was developed for the purpose of measuring the photodisplacement of a sample induced by the absorption of modulated light. The sensitivity is 1 pm in the 1 Hz bandwidth, sufficient to measure the photodisplacement. A good correlation was obtained between the amplitude of the photodisplacement and the subsurface structures of aluminum thin-film samples. The experimental results revealed that this technique is applicable to thickness measurement and to imaging of subsurface structures for opaque thin films.

A New Method of Photothermal Displacement Measurement by Laser Interferometric Probe -Its Mechanism and Applications to Evaluation of Lattice Damage in Semiconductors

A new, highly sensitive technique for measuring photothermal displacement using a laser heterodyne interferometric probe has been developed. This technique is based on the detection of phase changes in the probe beam and is very sensitive to the presence of lattice damage in semiconductors. It has been found that the phase change is caused by the thermal expansion of a sample surface induced by absorption of a modulated pump beam. The displacements of metals and semiconductors measured by this technique coincided with the results predicted by a thermal diffusion model. These displacements simply depended upon the ratio of the thermal expansion coefficient to the thermal conductlvity of a sample.

Dose and Damage Measurements in Low Dose Ion Implantation in Silicon by Photo-Acoustic Displacement and Minority Carrier Lifetime

Photo-acoustic displacement (PAD) generated with a modulated laser beam pumping is studied for As+ or B+ implanted Si. At doses above 1×1013 ions/cm2, the PAD has a close relationship to damage density. An ion implantation dose down to 2×109 ions/cm2 can be detected by the PAD measurement. Doses below 2×1010 ions/cm2 can be monitored by minority carrier lifetime measurement. A non-destructive high-sensitive dose monitor can be achieved by the PAD and minority carrier lifetime measurements. This monitoring leads to tight control of the threshold voltage of a MOS transistor.

ANALYSIS OF LATTICE DEFECTS INDUCED BY ION IMPLANTATION WITH PHOTO-ACOUSTIC DISPLACEMENT MEASUREMENTS

Subsurface lattice defects in silicon induced by ion implantation were studied by the use of the photo‐acoustic displacement (PAD) method based on the sensitive measurements of the surface displacement due to the absorption of laser‐light energy. A definite correlation between PAD and displaced atoms density (DAD) was found because PAD reflects the change in thermal conductivity associated with the net amount of displaced atoms in the crystal lattice beneath the surface. According to the linear dependence of 1/PAD on DAD, defects below a DAD of 1014/cm2 (corresponding to implant doses of 2×1011, 8×1010, and 6×1010 ions/cm2 for 100 keV B+, P+, and As+, respectively) were concluded to be point defects. After the DAD reached 1014/cm2, the PAD showed a gentle increase, and this can be attributed to the growth of point‐defect clusters. A marked dependence of the PAD on the DAD was not observed beyond a DAD of 1016/cm2. In this region, the presence of an amorphous layer was observed by cross‐sectional transmiss...

Effects of ambient gas on photo‐acoustic displacement measurement by laser interferometric probe

The effect of gas adjacent to the sample surface on the photo‐acoustic displacement (PAD) measurement was studied by using an extremely sensitive laser interferometric probe with a sensitivity of 0.1 picometers. For silicon, the PAD signal measured at atmospheric pressure increased about 18% as compared to the signal obtained in vacuum, and varied by less than 0.7% for a change in pressure of 5% around 1 atm. It is shown, by a simple theoretical model, that the variation of the PAD is caused by a change in refractive index of the gas and the real PAD can be accurately obtained by correcting this effect.

A feature-based stereo model using disparity histograms of multi-resolution channels

A feature-based stereo model designed to perform matching multi-resolution features is described. The multi-resolution features are zero-crossings (ZCs) of images convolved with different sized Laplacian-Gaussian operators. ZCs corresponding to small contrasts are removed according to the gradient values of images convolved with Gaussian operators. Candidate disparity intervals are determined using a disparity histogram of the total ZCs over the entire image. The image is then divided into small areas and a local disparity histogram is computed for the candidate intervals. Local disparity histograms in all the resolution channels are searched for the most promising disparity in each area. If the disparity is found successfully, the disparities for all the ZCs in the area are determined by searching only for the neighbour of the promising disparity. Once a disparity for a ZC is determined, the matching pair of ZCs is removed from the set of ZCs. This process is iterated until no more disparities are determ...

Liner thickness measurement for zirconium lined zircaloy cladding tube using dual frequency eddy current method

Abstract This paper describes an automatic system for measuring the liner thickness of zirconium lined zircaloy cladding tubes (liner tubes) using a dual frequency eddy current method. The system consists of four components: probe coil, eddy current instrument, scanning mechanism, and mini-computer. Eddy current signals contain thickness information mixed with undesirable information resulting from variations in electrical conductivity of zirconium and zircaloy, and coil to conductor spacing. In order to calculate the liner thickness without a disturbance by such undesirable signals, an optimal equation is formed using signals obtained from a dual frequency eddy current method. It is revealed that the system is able to measure the liner thickness of liner tubes ranging from approximately 40 to 130 μm with an accuracy of a few micro-meters.