• Current researchers: Josh Stillahn
• Related Fisher group references:
  • Surface Reactivity and Energetics of CH Radicals during Plasma Deposition of Hydrogenated Diamond-Like Carbon Films, J. Zhou and E. R. Fisher, J. Phys. Chem. B 110, 21911-21919 (2006).
  • Investigation of Inductively Coupled Ar and CH4/Ar Plasmas and the Effect of Ion Energy on DLC Film Properties, J. Zhou, I. T. Martin, R. Ayers, E. Adams, D. Liu, and E. R. Fisher, Plasma Sources Sci. Technol. 15, 714-726 (2006).
  • Correlation of Gas-Phase Composition and Film Properties in the Plasma-Enhanced Chemical Vapor Deposition of Hydrogenated Amorphous Carbon Nitride Films, D. Liu, J. Zhou, and E. R. Fisher, J. Appl. Phys. 101, 023304 (2007).
  • Comparison of Surface Reactivity of CN, NH, and NH2 Radicals During Deposition of Amorphous Carbon Nitride Films from Inductively Coupled rf Plasmas, D. Liu and E. R. Fisher, J. Vac. Sci. Technol. A 25, 368-377 (2007).
  • CN Surface Interactions and Temperature-Dependent Film Growth During Plasma Deposition of Amorphous, Hydrogenated Carbon Nitride, J.M. Stillahn, E.R. Fisher, J. Phys. Chem. C, 113, 1963-1971 (2009).

Hydrogenated amorphous carbon nitride (a-CNx:H) is a hard material that has been investigated for use in a variety of potential applications. These include LCD backlighting, anti-reflective optical coatings, and wear-resistant coatings on computer hard disks and artificial joints. However, the effective development of these applications requires a more complete understanding of the dominant chemical processes. Plasma-enhanced chemical vapor deposition provides a means of depositing these materials at relatively low substrate temperatures, and the Fisher group’s work in this area has focused on identifying gas-phase species that contribute to the deposition of a-CNx:H and elucidating their chemical behavior at the surface.

Previous studies in our group have focused on mixed-precursor plasmas containing separate sources of nitrogen (N2 or NH3) and carbon (CH4, C2H4, or C2H2). Larger hydrocarbon ions have been observed in N2/C2H2 plasmas, and correlation of these data with atomic force microscopy (AFM) measurements suggests that these larger hydrocarbon ions may contribute to the growth of rougher films. Relatively high surface reactivity values were measured for the CN radical using the IRIS technique, and it is possible that these surface reactions involve atomic hydrogen (detected in these systems by OES) and result in the formation of surface active sites during deposition.

More recently, these studies have been extended to acetonitrile (CH3CN) plasmas, which allow the more direct generation of CN radicals. As in mixed precursor systems, CN radicals in acetonitrile plasmas exhibit high surface reactivity values under a variety of conditions, with no apparent dependence on gas pressure, rf power, or substrate temperature. Films deposited in acetonitrile plasmas were analyzed by AFM, and a representative image is shown at right for a film deposited at a substrate temperature of 100°C. Analyses like this indicate that films deposited in acetonitrile plasmas have roughness factors greater than those observed in the N2/CH4 or N2/C2H4 systems but less than those seen in the N2/C2H2 system. Profilometry was used to further explore the effect of substrate temperature on film deposition in acetonitrile plasmas. We find that increases in the initial substrate temperature cause a decrease in the deposition rate (lower-left figure with blue symbols), indicating a change in film nucleation. However, increases in substrate temperature after deposition has started do not affect the deposition rate (lower-right figure). This suggests that the steady-state formation of these films is controlled by mass transport of the precursor.

Continued characterization of these deposition systems is underway, and some of the long-term goals of this project include the continued comparison of pure and mixed precursor systems as well as the investigation of hot-filament CVD as an alternative method for depositing these films.