Mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CH₄ plasmas

Mass analysis was carried out on neutral species in the downstream region of Ar/CH₄ plasmas. The ionization of the neutral species by Li ⁺ attachment, which can inhibit the fragmentation accompanied by ionization in most cases, successfully led to the observation of high-mass neutral hydrocarbons containing up to twenty-seven carbon atoms. Pure Ar and Ar/H₂ plasmas were also used to investigate the influence of sputtering of an amorphous hydrocarbon (a-C:H) film deposited during the generation of the Ar/CH₄ plasmas. In addition, time dependence of intensity in several neutral species accompanied by the growth of the a-C:H film and its CH₄ partial pressure dependence were observed for the first time. On the basis of the present experimental results, the desorption of high-mass neutral molecules from the film to the gas phase is concluded.