Characteristics of RF hybrid plasma produced by capacitively and inductively coupled discharges using mixtures of hydrogen and methane for preparing carbon nano-walls

An RF hybrid plasma, that consists of a capacitively coupled plasma (CCP) with a ring-shaped hollow cathode and an inductively coupled plasma (ICP), using CH₄ and H₂ gas mixtures has been investigated for preparing carbon nano-walls. The positive ion flux is found to increase as a function of the ICP power in the capacitively coupled plasma at various CCP powers. The floating and the plasma potentials are changed by the ICP power, i.e., they show a peak at an ICP power of approximately 150 – 200 W, whereas the electron temperature is almost independent of the ICP power. Likewise, the ratio R of the negative charge saturation current to the positive ion saturation current is affected by the ICP power; specifically, R is less than 10 and decreases with increasing the ICP power and attains a minimum at an ICP power of approximately 150 – 200 W. The electronegativity increases with increasing ICP power and reaches a peak of approximately 9, which is ten times greater than that in the other CCPs reported using hydrocarbon gases, at an ICP power of nearly 150 – 200 W. The influence of the ICP on the negative ion production will have a positive effect for producing various hydrocarbon radicals and hydrogen radicals relevant to the preparation of carbon nano-walls.