Abstract

Ion energy distributions (IEDs) have been determined at the radio frequency (rf)-biasedelectrode in an inductively coupled acetylene–argon plasma for various substrate bias voltagesand frequencies under conditions suitable for diamond-like carbon (DLC) and polymer-likefilm deposition. These are compared with those obtained at a capacitively coupled plasmagrounded wall. In the former, for pressures <25mTorr, the IEDs exhibit bimodal structureswith peak separation values that follow the expected voltage and frequency dependences. Athigher pressures, 120mTorr, the bimodal structure is replaced by a single peak. For allconditions the dominant ion is Ar+ or ArH+ despite the set flow ratio of C2H2 : Ar of 2 : 1 andthis can be attributed to the high electron dissociation of the parent molecule. DLC filmsindicate a peak hardness at an ion energy of around 90 eV and a very sharp fall in hardness isnoted beyond this value. This is similar to the observed sp3-bond formation in hydrogen-freetetrahedral amorphous carbon or bias-sputtered films. However, due to the lack ofcarbon-based ions, an alternative mechanism is likely based on argon knock-on implantationof surface adsorbed carbon species. The results have shown that the use of high-frequency biasor bias harmonics may lead to much narrower IEDs.