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A plasma kinetics model: analysis of wall loss reactions in dry etching of silicon dioxide

Journal of Alloys and Compounds
Publication Date
DOI: 10.1016/s0925-8388(98)00612-4
  • Plasma Chemistry
  • Composition
  • Surface Reaction
  • Chemistry


Abstract Computational models for gas-phase chemical reactions in plasmas and for sticking reactions on metallic Al walls have been developed and applied to the plasma chemistry of dry etching of silicon dioxide. Dissociation paths and threshold energies of gases are determined by using an ab initio density functional molecular orbital method, and dissociation cross sections are approximated. The electron energy distribution function is determined by using a particle-in-cell model with the Monte Carlo collision method, and dissociation reaction rates are determined. Plasma densities, electron temperatures. and radical densities are calculated by a kinetic model which consists of the fluid equations for plasmas and rate equations for radicals. The model effectiveness was confirmed by results comparison for the Ar discharge in an radio-frequency device. The chemical compositions of the dry etching plasmas have been investigated for C 4F 8. Calculated electron temperatures and densities agree with experimental results within factors of three. Correlations could be found between the composition of radicals in the plasma and the etch selectivities in C 4F 8. Adsorption potentials of fluorocarbon radicals on Al (III) surface clusters have been calculated by using molecular orbital method, and sticking coefficients are estimated. Sticking coefficient of fluorine atom is the largest and decrease in order of F, C, CF, H, CF 2, and CF 3. Effects of hypervalence bonding at Al surface are discussed. Phenomena [1]of no film depositions in CF 4 RF plasma and film depositions in RF plasma of CF 4 mixed with H 2 were explained by hypervalence reactions of Al.

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