AVS 53rd International Symposium
    Plasma Science and Technology Friday Sessions
       Session PS1-FrM

Paper PS1-FrM4
Spectroscopic Studies of Ammonia Plasmas

Friday, November 17, 2006, 9:00 am, Room 2009

Session: Plasma-Surface Interactions III
Presenter: S.J. Kang, University of Houston
Authors: S.J. Kang, University of Houston
V.M. Donnelly, University of Houston
Correspondent: Click to Email
Surprisingly, there is little understanding of the basic chemical mechanisms in PE-CVD of carbon-containing materials such as carbon nanotubes, including the role of added NH@sub 3@. In this study we investigate the plasma chemistry of NH@sub 3@ decomposition in NH@sub 3@/Ar-containing plasmas at 1 Torr. Absolute NH@sub 3@ number densities were measured as a function of inductively-coupled plasma power and substrate temperature (T@sub s@) by ultraviolet (UV) absorption spectroscopy. Plasma-induced optical emission was used to qualitatively identify species such as NH and H, formed from NH@sub 3@ electron impact dissociation and subsequent reactions. A new "self-actinometry" method was introduced to measure the absolute number density of N@sub 2@ that is formed following dissociation of NH@sub 3@ and secondary reactions. In this approach, small amounts of N@sub 2@ were added to the NH@sub 3@-containing plasma, leading to an increase in the N@sub 2@ C->B state emission intensity, above the level of intensity observed in the absence of added N@sub 2@. By extrapolating to zero added N@sub 2@, we obtain the calibration factor that allows us to convert relative N@sub 2@ C-> B emission intensities into absolute number densities. We assume that very little of the added N@sub 2@ is dissociated; given its strong bond energy and low T@sub e@ at 1 Torr, this assumption is valid. The number densities of NH@sub 3@ decreased with increasing power and T@sub s@, reaching >90% dissociated at 400W and 900K. Conversely N@sub 2@ densities increased with power and T@sub s@. It appears that the majority of dissociated NH@sub 3@ leads to the formation of N@sub 2@ (i.e. the total nitrogen content is conserved in the sum of these two species).