Abstract
Hydrogenated amorphous carbon (a-C:H) films have attracted much attention, because of their excellent physical and chemical properties, such as high mechanical hardness, chemical robustness, a wide variety of optical bandgaps, and so forth. Although an ion bombardment energy has been regarded as essential in the well-know subplantation model, it alone is inadequate especially in complicated reactions of a plasma-enhanced chemical vapor deposition process. In this study, an ion bombardment energy flux (ΓEi) was proposed as a crucial factor to determine chemical compositions and structures of a-C:H films. To obtain the amounts of ΓEi, electron densities, hydrogen (H) excitation temperatures, and negative direct current (DC) self-bias voltage (-VDC) were measured. The deposition rate increased, and sp2-C clusters incorporation was induced by the ΓEi. With increasing ΓEi, photoluminescence (PL) backgrounds in Raman spectra decreased, while spin densities in electron spin resonance (ESR) measurements increased. These results suggested the H content of a-C:H film decreased depending on the amount of ΓEi. The ΓEi is one of the crucial factors to determine the properties of the a-C:H films.
Highlights
Amorphous carbon (a-C) films have attracted much attention, because of their excellent properties, such as high mechanical hardness, chemical inertness, a wide variety of optical bandgaps, and so forth [1,2,3,4,5,6,7,8]
The lower plasma source is dual-frequency capacitively coupled plasma (DF-CCP) generated by 20 and 250 W of a 100 MHz very high frequency (VHF) power to the showerhead for controlling the radical generation. 13.56 MHz radio frequency (RF) power ranging from 30–150 W was applied to the sample stage for controlling -V direct current (DC) which related to the Ei
The ΓEi was estimated from the plasma density at the sheath of plasma and Bohm speed based on the measurements of electron density, H excitation temperature, and negative self-bias voltage
Summary
Amorphous carbon (a-C) films have attracted much attention, because of their excellent properties, such as high mechanical hardness, chemical inertness, a wide variety of optical bandgaps, and so forth [1,2,3,4,5,6,7,8]. Hydrogen (H) content is important when it is included in the a-C film, usually called hydrogenated a-C (a-C:H). Their properties strongly depend on the mixture ratios among sp2 -C bonding states, sp3 -C ones and H atoms. The a-C:H films deposited by the PECVD usually contain H atoms, because hydrocarbon molecular
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