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A two-dimensional fluid model has been developed to study plasma chemical behaviour of etch products as well as reactants during inductively coupled CF 4 plasma etching of SiO 2 . The plasma fluid model consisted of Maxwell's equations, continuity equations for neutral and charged species including gas-phase and surface reactions and an energy balance equation for electrons. The surface reaction model assumed Langmuir adsorption kinetics with the coverage of fluorine atoms, fluorocarbon radicals and polymers on SiO 2 surfaces. Numerical results indicated that etch product species occupy a significant fraction of reactive ions as well as neutrals in the reactor chamber during etching, which in turn leads to a change in plasma and surface chemistry underlying the processing. In practice, the density of SiF 4 was typically about 10% of that of the feedstock CF 4 , being comparable to that of the most abundant fluorocarbon radical CF 2 ; moreover, the density of SiF + 3 was typically about 5% of that of the most abundant fluorocarbon ion CF + 3 . The density and the distribution of such product species in the reactor chamber were changed by varying the ion bombardment energy on the substrate surfaces, gas pressure, mass flow rate and coil configuration, which arises in part from gas-phase reactions depending on plasma electron density and temperature. Surface reactions on the chamber walls and on the substrate also affect the product density and distribution in the reactor; in particular, the surface reactions on the SiO 2 dielectric window as well as substrate surfaces were found to largely affect the product density and distribution.

SUMMARY This paper explores the potential of orbital angular momentum (OAM) multiplexing as a means to enable high-speed wireless transmission. OAM is a physical property of electro-magnetic waves that are characterized by a helical phase front in the propagation direction. Since the characteristic can be used to create multiple orthogonal channels, wireless transmission using OAM can enhance the wireless transmission rate. Comparisons with other wireless transmission technologies clarify that OAM multiplexing is particularly promising for point-to-point wireless transmission. We also clarify three major issues in OAM multiplexing: beam divergence, mode-dependent performance degradation, and reception (Rx) signal-to-noise-ratio (SNR) reduction. To mitigate mode-dependent performance degradation we first present a simple but practical Rx antenna design method. Exploiting the fact that there are specific location sets with phase differences of 90 or 180 degrees, the method allows each OAM mode to be received at its high SNR region. We also introduce two methods to address the Rx SNR reduction issue by exploiting the property of a Gaussian beam generated by multiple uniform circular arrays and by using a dielectric lens antenna. We confirm the feasibility of OAM multiplexing in a proof of concept experiment at 5.2 GHz. The effectiveness of the proposed Rx antenna design method is validated by computer simulations that use experimentally measured values. The two new Rx SNR enhancement methods are validated by computer simulations using wireless transmission at 60 GHz.

The defect generation process in Si surface layer induced by plasma exposures is studied by two optical analyses, spectroscopic ellipsometry (SE) and photoreflectance spectroscopy (PR). Two plasma sources with Ar-gas mixtures are employed; one is DC plasma and the other, electron cyclotron resonance (ECR) plasma. In the case of Ar-DC plasma exposure with 300 V bias, the SE analysis with an optimized optical model determines 1-nm-thick interfacial layer (IL) between the surface layer and the substrate, while in the case of the ECR, approximately 0.5-nm-thick interfacial layer is identified. This difference is attributed to that in self-bias voltages (Vdc) between two plasma sources. In order to quantify the damage, we have modified the PR analysis technique in order to evaluate the plasma-induced carrier trap site density, by correlating the Si surface potential change to the trapped carrier density. Combined with the results by plasma diagnostics, we found that the calculated defect generation probabilities by an impinging ion were the orders of 10-2 and 10-5 in the present DC and ECR plasma conditions, respectively, and that the probability depends on the Vdc. The obtained results enable us to predict the plasma-induced physical damage to the devices in advance at the stage of plasma process designs.

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