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A novel gettering method using cavitation impacts is presented. Gettering is very important technique for IC manufacturing. Silicon wafers used as a substrate for semiconductors are often exposed to contamination during the device processes. If crystal defects are intentionally introduced into back-side of silicon wafer, metal impurities such as Cu and Fe in the wafer are trapped in the defects and gather into the region during heat cycles. As a result, the zone near the surface of the wafer that is used as active device region is kept off unwanted impurities. This technique is called gettering. In this paper, to introduce backside damage, which is one of the gettering techniques, cavitation impacts are utilized. Cavitation bubbles produce high-pressure impacts upon collapsing. The suitable damage can be introduced by controlling the intensity of cavitation impacts. The high speed submerged water jet with cavitation, i.e., a cavitating jet, was used to cause cavitation impacts. The cavitating jet can introduce backside damage without the use of particles, as in shot blasting that is popular technique. In order to confirm the gettering effectiveness of the damage introduced by a cavitating jet, an experimental study was carried out. The silicon wafer treated by the cavitating jet was intentionally contaminated with solution of Cu(NO3)2. The wafer was then thermally treated. The surface was observed after etching that makes defects on the surface observable. On the surface of the wafer having no gettering effectiveness, defects which were induced by contamination are observed. If the wafer has gettering effectiveness, defects are not observed on the surface. Gettering effectiveness of the damage introduced by the cavitating jet was shown.

Damage for gettering can be introduced by a high speed submerged water jet with cavitation, i.e., a cavitating jet, into a silicon wafer. Gettering is an important technique for removing unwanted impurities from the surface of the silicon wafer that is active device region. Metal contaminations diffuse in bulk of the wafer and adhere to the defects through the thermal treatments in semiconductor processes. If the damage was intentionally introduced into the silicon wafer, these contaminations can be gathered within the intended region. Consequently, the surface of the wafer can be kept free from impurities. The method presented here utilizes cavitation impacts to introduce the damage for gettering. By using cavitation impacts, the damage can be introduced without the use of particles which form sources of contamination during farther wafer handling, as in shot blasting that is a popular technique. The cavitation impacts caused by a cavitating jet were used since the intensity of cavitation impacts can easily be controlled by controlling hydraulic parameters. The gettering effect of the damage introduced by the cavitating jet was already confirmed, but the detail information of the introduced damage has not been obtained. After applying thermal treatment to the wafer treated by the cavitating jet, there are Oxidation-induced stacking faults (OSF) which would be gettering sites. However, the source of OSF is not yet confirmed. In this paper, the damage on the silicon wafer surface introduced by the cavitating jet for gettering is observed to evaluate the source of OSF.

In order to predict and avoid cavitation erosion, it is necessary to know the resistance of materials to cavitation impacts. It is proposed that only cavitation impacts with energy larger than a certain threshold level affect the cavitation erosion of materials. Weak cavitation impacts have small impact energy, which cannot produce elastic or plastic deformation on materials. Cavitation erosion does not take place in this situation. On the other hand, strong cavitation impacts have large impact energy, which generates plastic deformation and/or causes damage with mass loss. It is proposed that only cavitation impacts that are larger than a certain threshold level affect the cavitation erosion of materials. In this paper, the existence of such a threshold level is revealed experimentally. The fundamental threshold level of the material is a new parameter suitable for the prediction of cavitation erosion rate. The erosion rates for several materials were determined by using a cavitating jet erosion test, which forms a new ASTM standard, ASTM G 134. The cavitation impacts induced by the cavitating jet were measured by means of a specially made PVDF transducer and the energy of the cavitation impacts were then calculated. The fundamental threshold levels for several materials were obtained from the relationship between the erosion rate and the energy of the cavitation impacts. A method to predict cavitation erosion quantitatively from the fundamental threshold level of the material and the measurement of cavitation impacts is proposed.

H2O vapor-activated ZnO layers have been grown on the a-face of sapphire substrates. The grown ZnO layers revealed a crystalline orientation of c-face ZnO ‖ a-face sapphire. For the II/VI flux ratio of 14, the ZnO layers showed a bandedge luminescence with the emission energy of 3.376 and 3.304 eV at 17 K and room temperature, respectively. The amount of the blue-shifted energy in the Zn-rich ZnO is estimated to be ~30 meV in comparison to the donor-bound exciton emission reported previously. The energy shifting towards the higher level could be attributed to the drastic reduction of carrier concentration in the order of ~10¹⁷ cm^—3 for the II/VI flux ratio of 14. With this growth condition, electron mobility is recorded typically to be ~90 cm²/Vs which is considerably higher for the same carrier concentrations reported previously with plasma as oxygen source.

Bolted joints in heat exchangers, cylinder heads in combustion engines, and so on are subjected to heat fluxes. It is necessary to examine the mechanical behavior of such bolted joints under thermal changes in order to establish an optimal design. This paper deals with mechanical behavior of bolted joints, in which two hollow cylinders and two rectangular thick plates made of aluminum are fastened at room temperature by a bolt and nut made of steel, and are subjected to thermal changes or steady heat conduction. Temperature distributions of the joints are analyzed using the finite difference method. Then, methods for estimating an increment in axial bolt force and a maximum stress produced in the bolts are proposed. In the experiments, the aforementioned bolted joints are put in a furnace. Furthermore, the rectangular thick plates fastened by a bolt and nut are heated by an electric heater. Then, the temperatures on the surfaces of the clamped parts and the bolts are measured with thermocouples. The increase in axial bolt force and the maximum stress produced in the bolts under steady heat conduction or thermal changes are measured. The analytical results are in fairly good agreement with the experimental ones.

The behavior of a bolted connection, using several aluminum alloy pipe flanges with steel bolts and nuts, was examined under the condition of thermal conduction. Using the finite difference method, temperature distributions in the connection subjected to transient thermal conduction were analyzed. A method for obtaining an increment in axial bolt force and the maximum stress produced in the bolts was demonstrated. In the experiments, the temperature distribution in the connection was measured by use of thermocouples. In addition, both the increment and the maximum stress due to the difference in coefficients of linear expansion as well as the stress produced in the hub were measured by strain gages when the inner circumference of the pipe flanges was subjected to thermal conduction and the outer circumference was kept at room temperature. The analytical results were fairly consistent with the experimental ones.

Characteristics of cosmic-ray hadronic interactions in the 1015− 1017eV range are studied by observing a total of 429 cosmic-ray families of visible energy greater than 100 TeV found in emulsion chamber experiments at high mountain altitudes, Chacaltaya (5200 m above sea level) and the Pamirs (4300 m above sea level). Extensive comparisons were made with simulated families based on models so far proposed, concentrating on the relation between the observed family flux and the behaviour of high-energy showers in the families, hadronic and electromagnetic components. It is concluded that there must be global change in characteristics of hadronic interactions at around 1016eV deviating from thise known in the accelerator energy range, specially in the forwardmost angular region of the collision. A detailed study of a new shower phenomenon of small-pTparticle emissions, pTbeing of the order of 10 MeV/c, is carried out and its relation to the origin of huge “halo” phenomena associated with extremely high energy families is discussed as one of the possibilities. General characteristics of such super-families are surveyed.

MgS naturally forms the rocksalt structure, but zincblende MgSZnSesuperlattices were grown with atmospheric-pressure MOVPE. The lattice constant of zincblende MgS was determined to be 5.59 Å from a series of X-ray measurements. The purging effect during the growth of MgSZnSeheterointerfaces was studied. While purging with a Se precursor resulted in the formation of an extra MgSe-related interface layer, purging with a Zn precursor improved the abruptness of the heterointerfaces.

The behavior of a bolted connection, using several aluminum alloy pipe flanges with steel bolts and nuts, was examined under the condition of thermal conduction. Using the finite difference method, temperature distributions in the connection subjected to transient thermal conduction were analyzed. A method for obtaining an increment in axial bolt force and the maximum stress produced in the bolts was demonstrated. In the experiments, the temperature distribution in the connection was measured by use of thermocouples. In addition, both the increment and the maximum stress due to the difference in coefficients of linear expansion as well as the stress produced in the hub were measured by strain gages when the inner circumference of the pipe flanges was subjected to thermal conduction and the outer circumference was kept at room temperature. The analytical results were fairly consistent with the experimental ones.

Bolted joints in heat exchangers, cylinder heads in combustion engines, and so on are subjected to heat fluxes. It is necessary to examine the mechanical behavior of such bolted joints under thermal changes in order to establish an optimal design. This paper deals with mechanical behavior of bolted joints, in which two hollow cylinders and two rectangular thick plates made of aluminum are fastened at room temperature by a bolt and nut made of steel, and are subjected to thermal changes or steady heat conduction. Temperature distributions of the joints are analyzed using the finite difference method. Then, methods for estimating an increment in axial bolt force and a maximum stress produced in the bolts are proposed. In the experiments, the aforementioned bolted joints are put in a furnace. Furthermore, the rectangular thick plates fastened by a bolt and nut are heated by an electric heater. Then, the temperatures on the surfaces of the clamped parts and the bolts are measured with thermocouples. The increase in axial bolt force and the maximum stress produced in the bolts under steady heat conduction or thermal changes are measured. The analytical results are in fairly good agreement with the experimental ones.

Abstract: The contact stress of a bolted joint, in which a clamped part was fastened to a body with a threaded bolt, was measured using sensitive pins, sensitive films and ultrasonic waves. The contact stress distribution was analyzed as a contact problem by an axisymmetrical theory of elasticity. Numerical calculations were performed. The experimental results were in fairly good agreement with the analytical results.