Hydrogenation and surface density changes in hydrocarbon films during erosion using Ar/H2 plasmas

Abstract

We report interactions of low pressure Ar, H 2 , and Ar/H 2 mixture plasmas with a-C:H films. Surface evolution and erosion of a-C:H films were examined for ion energies up to 200 eV by rf biasing the substrates. Film surfaces were characterized using in situ ellipsometry, x-ray photoelectron spectroscopy, and atomic force microscopy. Multilayer models for steady-state modified surface layers are constructed using ellipsometric data and compared with results of molecular dynamics (MD) simulations and transport of ions in matter (TRIM) calculations. We find that Ar plasma causes a modified layer at the surface that is depleted of H atoms. The depth and degree of this modification is strongly depending on Ar ion energies. This depletion saturates quickly during plasma exposure (<1 s) and persists during steady-state erosion. We find that the thickness and density of the H-depleted layer are in good agreement with MD and TRIM simulations. The degree of surface densification decreases when small amounts of H 2 are added to Ar plasmas. When more than 5% H 2 is added to the plasma, long term loss in surface density is observed, indicating rehydrogenation and saturation of H in the film. As the H 2 fraction increases, the near-surface atomic H increases and the ion composition bombarding the surface changes. This causes incorporation of H deeper into the a-C:H film. For a-C:H films exposed to pure H 2 plasmas, H is introduced into the near-surface region to a depth of up to $8 nm from the surface. As the rf bias is increased the ion energy transitions from solely chemical sputtering to one involving physical sputtering, causing the yield of C atoms from the surface to greatly increase. The increasing yield suppresses H incorporation/saturation and decreases the magnitude of the modified surface layer. V

Isotope effects on plasma species of Ar/H2/D2 plasmas

“…4 Recent works have aimed at characterizing plasma properties and surface interacting species in Ar/H 2 plasmas. [4][5][6][7][8][9][10][11][12] At low pressure (1-100 mTorr), major surface interacting species in Ar/H 2 plasmas are ions, reactive H atoms, UV/VUV photons, and Ar metastable atoms. Gudmundsson first measured the ion mass and energy distributions for most ion types present (H þ , H 2 þ , H 3 þ , and Ar þ ).…”

“…4 The etch rate becomes significantly higher and large degrees of surface re-hydrogenation of the H-depleted surface is observed. When etching hydrocarbons at low pressures, we found that the plasma-surface interactions transitions from a purely physical sputtering regime to a chemical sputtering regime when up to 20% H 2 is added to Ar plasma.…”

Ion chemistry in H2-Ar low temperature plasmas

“…Furthermore, H 2 -Ar mixtures were successfully applied for hydrogenation of thin film transistors 12 and to control the surface properties of polymers 13 . Hopf et al observed chemical sputtering of hydrocarbon films with very high rates if energetic Ar and atomic hydrogen interact simultaneously 14 with carbonaceous surfaces.…”

Quantitative determination of mass-resolved ion densities in H2-Ar inductively coupled radio frequency plasmas

“…H 2 -Ar mixtures were successfully applied for hydrogenation of thin film transistors 12 and to control the surface properties of polymers 13 . Hopf et al observed chemical sputtering of hydrocarbon films with very high rates when energetic Ar and atomic hydrogen were interacting simultaneously 14 .…”