High-density capacitively coupled plasma with electron density of 1011cm−3 was produced with the effects of the multihollow cathode discharge and the high-secondary-electron emission from radio frequency (rf)-biased electrode using Ar gas. It was found that the optimum pressure was around 3–15Pa. In the case of only multihollow cathode discharge, the plasma density increased from 1.2×1010to8×1010cm−3 with the increasing distance z from the cathode electrode for 5mm<z<15mm. Moreover, plasma density increased with increasing voltage of rf-biased electrode. The rate of deposited amorphous hydrocarbon thin films of about 200nm∕min was attained with the high-density rf plasma enhanced chemical vapor deposition using CH4 gas.
A high-density plasma driven by a capacitive discharge with a radio frequency of 13.56 MHz has been developed using a powered electrode with a ring-shaped trench for dry processing. It was found that a hollow cathode discharge was produced in the trench at a wide range of pressures from 10 to 400 mTorr. In order to satisfy the hollow cathode discharge, it was clarified that the trench width was twice as long as the sheath thickness formed in the trench experimentally. It became clear that a wider trench width easily produced the hollow cathode discharge under lower pressure conditions. A maximum plasma density of 10 11 cm −3 was attained at Ar gas pressures of 100-350 mTorr and/or an input power density of 0.64 W cm −2 . It was indicated that the radial profile of plasma density had a peak near the ring-shaped trenches and was uniform inside the ring-shaped trench.
The inactivation of Bacillus subtilis spores in a low pressure RF oxygen plasma was studied. The experiments were especially designed to discriminate the relative importance of the competing spore inactivation agents. The decimal reduction values, characteristic for the action on the spores of heat, optical radiation and plasma particles, respectively, were estimated for different injected RF powers. These results indicated that during the initial stage of sample treatment, the most important inactivation agent is the optical radiation, whereas during the second stage of treatment, the leading role is assumed by the plasma particles. The dependence of spore inactivation kinetics on the injected RF power was also studied, by using the Z‐value.
In order to achieve high-density capacitively coupled plasma, a radio-frequency (RF) ring-shaped hollow cathode discharge has been developed as a candidate for processing plasma sources. The plasma density in the hollow cathode discharge reaches a high magnitude of 1010–1011 cm−3. The RF ring-shaped hollow cathode discharge depends on the pressure and mass of the working gas. Criteria required for producing a RF ring-shaped hollow cathode discharge have been investigated for various gas pressures using H2 and Ar gases for high-density plasma production. The results reveal that the criteria for the occurrence of the hollow cathode effect are that the trench width should be approximately equal to the sum of the electron-neutral mean free paths and twice the sheath thickness of the RF powered electrode.
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