Targeting mass-selected cluster ions for the deposition of advanced carbonaceous materials using an inductively coupled plasma

Abstract

Study has been initiated of the deposition of thin films using cluster ions in differing abundances generated in a pulsed inductively coupled plasma. A pulse unit controlling the “on” and “off” timing ratio of a 13.56 MHz rf power supply is used to alter systematically the composition of the contents of the plasma. Adamantane (C10H16) vapor, in argon or nitrogen, was selected as precursor for the deposition of CxHy or CxNyHz thin films using this pulsed source. The effect of varying the relative abundances of the cluster ions present in the resultant plasmas on the films produced, by changing driving power on/off ratio, is investigated. The mass-energy diagnostic data recorded under 50/150 and 150/50 μs on/off pulse sequences showed that fragmentation of C10H16 is a function of the switching ratio selected, i.e., clusters of different sizes and abundances are thus produced. Langmuir probe data also suggest that the electrical characteristics of the plasma generated under these regimes can be monitored. Postdeposition x-ray photoelectron spectroscopy (XPS) analysis of specimen films deposited under the same on/off regimes, within a 200 μs cycle, indicate clear differences are present in these films in terms of the atomic concentration, the C 1s envelope bandwidths, and profiles. Contact angle measurements and optical data performed were found to reflect the variations in the differently deposited films already indicated in the XPS data. For example, specimens deposited under a 50/150 on/off ratio show a high contact angle (low surface energy) and lower refractive index, whereas those deposited under a 150/50 ratio exhibit a low contact angle (high surface energy). Films prepared using the same precursor streams but with the further on/off ratios, 20/180, 100/100, and 20/180 μs, were also considered. Postdeposition analyses confirmed the same tends in the fragmentation behavior of C10H16. Finally, the significance of such a cluster ions selection technique is discussed.