The mechanism of highly selective etching of SiO2 using pulsed-microwave electron-cyclotron-resonance plasma was investigated by analyzing the relationship between plasma dissociations and fluorocarbon layers formed on surfaces during etching with a cyclo-C4F8/Ar gas mixture. Dissociated molecules of CxFy and CFx species were measured without fragmentations using ion attachment mass spectrometry, and both thicknesses and atomic concentrations of reaction layers formed on etched surfaces were analyzed using x-ray photoelectron spectroscopy. Thus, the impact of CxFy molecules on the formation of fluorocarbon layers were analyzed using this measurement system. The authors found that the process window of highly selective etching of SiO2 over Si was enlarged by using pulsed-microwave plasma because a thinner fluorocarbon layer was formed by controlling C4F8 dissociation by changing the duty cycle of the pulsed-microwaves. With conventional continuous plasma, an etch stop occurred at low wafer bias conditions because a thicker fluorocarbon layer, which protects the SiO2 surface from the ion bombardment, was formed on the SiO2 surface. The thicker fluorocarbon layer was formed from a large amount of CxFy species, such as C2F2, which were generated in the highly dissociated continuous plasma. On the contrary, with pulsed plasma, a thinner fluorocarbon layer was formed due to the lower flux of CxFy species because the dissociation of C4F8 was controlled by reducing the duty cycle of the pulsed-microwave plasma. As a result, the process window was enlarged to the low wafer bias conditions using the pulsed-microwave plasma.
Clamping and residual clamping forces of a Johnsen–Rahbek-type (JR-type) bipolar electrostatic chuck (ESC), which has electrically independent dual electrodes, were measured. Area ratios of the ESC’s two electrodes ranged from 1 to 4.6. It was found that the clamping force per unit area decreases with increasing area ratio and that the residual clamping force per unit area increases with increasing area ratio. To reveal the mechanism of residual clamping force, an equivalent circuit model of a JR-type bipolar ESC was devised. The model showed that the residual clamping force is caused by the residual charge that results from the charge difference in two monopolar ESCs. The charge difference is due to the resistance dependency on voltage of the dielectric layer of the ESC. The wafer voltage calculated from the model agreed well with the voltage measured by an electrostatic voltmeter. It can be concluded that the model is suitable for simulating the performance of a bipolar ESC.
Background/purpose Although aesthetic wire coating has been increasing in demand, it has problems that changes in mechanical properties and increase in frictional force. The aim of this study was to evaluate the coating of the wire, as characterized by aesthetics, in terms of low and constant friction and mechanical properties. Materials and methods Hard chrome carbide-plated (HCCP) wires (HCCP group), commercially available polymer-coated wires (P group), rhodium-coated wires (R group), and uncoated wires (control group) were used. For all wire types, a stainless steel wire of dimensions 0.017 inch × 0.025 inch was used. They were evaluated by three-point bending, friction testing, surface observation, and colorimetric testing. Results The HCCP group was not significantly different from the control group in terms of flexural strength ( σ ) and flexural modulus ( E ) ( σ : p = 0.90, E : p = 0.35). However, it was significantly inferior compared to the three other groups in terms of the maximum static and kinetic frictional forces under both dry and wet conditions ( p < 0.05). In the surface observation, scratches were observed on the wire after the friction test. In the colorimetric test, no significant difference was observed between the HCCP group and the R group ( p > 0.05). Conclusion The mechanical properties of the HCCP wire were not significantly different compared to the control group. The frictional force of the HCCP wire was significantly lower than the other group. Therefore, the HCCP wire was suggested to increase the efficiency of tooth movement in clinics.
We derive an improved prescription for the merging of matrix elements with parton showers, extending the CKKW approach. A flavour-dependent phase space separation criterion is proposed. We show that this new method preserves the logarithmic accuracy of the shower, and that the original proposal can be derived from it. One of the main requirements for the method is a truncated shower algorithm. We outline the corresponding Monte Carlo procedures and apply the new prescription to QCD jet production in e + e − collisions and Drell-Yan lepton pair production. Explicit colour information from matrix elements obtained through colour sampling is incorporated in the merging and the influence of different prescriptions to assign colours in the large N C limit is studied. We assess the systematic uncertainties of the new method.
In order to understand the chemical vapor deposition (CVD) reaction mechanism, forming a thin film from the gas phase, it is important to identify the intermediate chemical active species (radicals) for each reaction. Radicals generally have very short lifetimes; therefore, it is very difficult to detect them. Molecular beam sampling (MBS) is a method that can extract radicals in the gas phase using free jet expansion. A vacuum system using a MBS method was designed to analyze the CVD reaction mechanism in the gas phase near the surface of the wafer. The system consists of a thermal flow-through type CVD reactor and three differential pumping vacuum chambers with a quadrupole mass analyzer. The performance of the MBS system was tested with various gases. The system was applied to detect radicals produced in the region near the wafer in a thermal TEOS/O3 (tetraethylorthosilicate) CVD reaction to deposit SiO2 thin films. It is proved that the radicals, from which ethoxy bases of TEOS are extracted, are formed in the gas phase and can play an important role in the thermal TEOS/O3 CVD reaction.
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