Experimental observations of steady anodic vacuum arcs withthermionic cathodes

Stationary plasma discharges have been investigated in a high vacuum ambient (background gas pressure <10^-2 Pa), with an externally heated cathode and a consumable hot evaporating anode. With various anode materials like chromium or copper, and electrode separations between 0.5 and 3 mm, the nonself-sustained discharge operates with DC arc currents in the range of 220 A. The waveform of the arc voltage is strongly influenced by the magnetic field of the cathode heating current, and arc voltages between a minimum of 3 V and a maximum exceeding 100 V have been observed. The voltage-current characteristics (V_CC) and the influence of the electrode separation have been measured separately for the minimum and the maximum of the arc voltages and show a different behavior. The metal plasma expands into the ambient vacuum toward the walls of the vacuum vessel and offers a macroparticle free deposition source of thin films. The arc voltage can be varied by external manipulations of the arc discharge, and the mean ion energy of the expanding metal plasma shows a linear dependence of the mean arc voltage     

Surface properties of silicon oxide films deposited using low-pressure dielectric barrier discharge

The deposition of SiO_X films from low-pressure dielectric barrier discharge plasmas has been investigated using tetraethoxysilane (TEOS)/O₂ as the feed gas. Films were analyzed using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), AFM-based nanoindentation/nanowear techniques, and conductive AFM. Film deposition rates and hydrocarbon incorporation in the SiO_X film decrease with addition of O₂. High-quality SiO_X films with extremely low surface roughness are deposited at high oxidant concertrations. Addition of oxidant to the feed gas leads to a change in the SiO_X film structure from precursor-like to a dense SiO_X structure. The SiO_X films deposited with TEOS/O₂ plasmas were found to have soft surface layers, 0.5-1.5 nm thick, which contribute to an improvement of their field emission properties. The effect of gas phase compositions on the surface properties of the conductive surface layer was discussed.     

Thickness determination of thin and ultra-thin SiO2 films by C-AFM IV-spectroscopy

Conductive atomic force microscopy was used to determine the electrical oxide thickness for five different silicon dioxide layers with thickness in the order of 1.6-5.04 nm. The electrical thickness results were compared with values determined by ellipsometry. A semi-analytical tunnelling current model with one single parameter set was used to superpose current/voltage curves in both the direct tunnelling and the Fowler-Nordheim tunnelling regime regions. The overall electrical oxide thickness was determined by statistical means from results of nearly 3000 IV-curves recorded for different conductive CoCr-coated tips. Good agreement between the shape of model and experimental data was achieved, widely independent of the oxide thickness. Compared with the ellipsometry value, the electrical thickness was larger by a value of 0.36 nm (22%) for the thinnest oxide and smaller by a value of 0.31 nm (6%) for the thickest oxide, while intermediate values yielded differences better than 0.15 nm (<6%). The physical differences between the measurement techniques were shown to contribute to this observation. In addition, statistical deviations between single and multiple measurements using a single tip and using a number of different tips were analysed. The causes, for example, natural oxide thickness variations, tip wear, air humidity induced effects and contaminations, are evaluated and discussed. The method proposed was able to determine the electrical oxide thickness with a standard deviation in the order of ±6-9%. The results suggest that for optimal results it is necessary to perform several repetitions of IV-measurements for one sample and, in addition, to employ more than one tip.     

C-AFM-based thickness determination of thin and ultra-thin SiO2 films by use of different conductive-coated probe tips

The influence of the probe tip type on the electrical oxide thickness result was researched for four differently coated conductive tip types using SiO₂ (oxide) films with optical thickness of 1.7-8.3 nm. For this purpose, conductive atomic force microscopy (C-AFM) was used to measure more than 7200 current-voltage (IV) curves. The electrical oxide thickness was determined on a statistical basis from the IV-curves using a recently published tunnelling model for C-AFM application. The model includes parameters associated with the probe tip types used. The evolution of the tip parameters is described in detail. For the theoretical tip parameters, measured and calculated IV-curves showed excellent agreement and the electrical oxide thickness versus the optical oxide thickness showed congruent behaviour, independent of the tip type. However, differences in the electrical oxide thickness were observed for the different tip types. The theoretical parameters were modified experimentally in order to reduce these differences. Theoretical and experimental tip parameters were compared and their effect on the differences in the electrical oxide thickness is discussed for the different tip types. Overall, it is shown that the proposed model provides a comprehensive framework for determining the electrical oxide thickness using C-AFM, for a wide range of oxide thicknesses and for differently coated conductive tips.