Inductively coupled Ar/CH4/H2 plasmas for low-temperature deposition of ordered carbon nanostructures

Abstract

The results of numerical simulations, optical emission spectroscopy (OES), and quadrupole mass spectrometry (QMS) of inductively coupled Ar/CH4/H2 plasmas in the plasma enhanced chemical vapor deposition (PECVD) of self-assembled vertically aligned carbon nanostructures (CNs) are presented. A spatially averaged (global) discharge model is developed to study the densities and fluxes of the radical neutrals and charged species, the effective electron temperature, methane conversion factor under various growth conditions. The numerical results show a remarkable agreement with the OES and QMS data. It is found that the deposited cation fluxes in the PECVD of CNs generally exceed those of the radical neutrals.

Predicting the amount of carbon in carbon nanotubes grown by CH4 rf plasmas

“…Among the radicals, the absolute densities of CH 3 and C 2 H 5 were 2-3 orders of magnitude higher than those of CH 2 and CH. The quantitative order of the fluxes, ⌫ C 2 H 4 Ͼ⌫ CH 3 Ͼ⌫ C 2 H 2 Ͼ⌫ C 2 H 6 Ͼ⌫ CH 2 Ͼ⌫ CH , is similar to the results by Tachibana et al 30 Considering the factors of the sticking coefficients of radicals, 10 it is speculated that the positive ions, CH 3 and C 2 H 5 are main species that fulfill the role of supplying carbon to the substrate in the present modeling.…”

“…22 The reaction rate coefficients k for H 2 , CH 2 , CH 3 , C 2 H 2 , C 2 H 4 , C 2 H 5 , C 2 H 6 were estimated from their reaction cross sections. 10,23,24 The mobilities and diffusion coefficients of charged species, except electron mobility, the secondary electron emission coefficient ͑␥ ion = 0.01͒, the initial energy for secondary electrons ͑=1.0 eV͒, the detachment coefficient ͑=3.69ϫ 10 −11 cm 3 /s͒ and the recombination coefficient ͑=0.0 cm 3 /s͒ are cited from Gogolides et al 20 D j of neutral species in the CH 4 plasma were calculated as referred to in Herrebout et al 25 An overview of the species ͑nonradi-cal neutrals, ions, radical neutrals͒ taken into account in the present model is given in Table II. The reaction processes among electrons, ions, excited atoms and molecules taken here and their reaction rate coefficients are listed in Tables III-V: 28 for electron-neutral, 15 for ion-neutral, and 25 for neutral-neutral reactions.…”

“…At the electrode surface, reflection and loss of radicals, CH, CH 2 , CH 3 , C 2 H 5 , and H are assumed, and their sticking coefficients are 0.025, 0.025, 0.01, 0.01, and 0.01, respectively. 10 The input parameter of this model, the electron drift velocity W e , and the rate coefficients k of electron-CH 4 reactions were obtained from a Boltzmann equation analysis using a set of the electron collision cross sections of CH 4 . 22 The reaction rate coefficients k for H 2 , CH 2 , CH 3 , C 2 H 2 , C 2 H 4 , C 2 H 5 , C 2 H 6 were estimated from their reaction cross sections.…”

“…Plasma modeling is suitable for analysis of the overall behavior of plasma species. Denysenko et al 10 analyzed an inductively coupled Ar/ CH 4 /H 2 plasma for PECVD of vertically aligned carbon nanostructures using quadrupole mass spectrometry and OES, and compared the results of the number densities of neutrals and ions with estimations by a zero-dimensional rate equation. Delzeit et al 6 used a zero-dimensional model to characterize CH 4 /H 2 plasmas for CNT growth and suggested enhancement in CH 4 dissociation by collision of H atoms.…”

“…[6][7][8][9][10][11] OES has an advantage in its spatial resolution of the measurements, while mass spectrometry can detect even nonradiative species of high molecular weight. Plasma modeling is suitable for analysis of the overall behavior of plasma species.…”