Modelling of radio frequency plasmas in tetrafluoromethane (CF4): the gas phase physics and the role of negative ion detachment

A fluid model is used to study a radio frequency (RF) CF4 discharge at various powers, pressures and electrode spacings and is found to compare successfully with experimental data. The discharge shows an electronegative behaviour with a high concentration of negative ions. The role of electron detaching radicals CFx is subsequently studied by varying their density. At high radical densities (1%), the discharge behaviour and operating point change drastically and attachment-induced ionization instabilities develop. The implications to plasma etching and experiments are discussed.

[1]  J. Boeuf.  A two‐dimensional model of dc glow discharges , 1988 .

[2]  David B. Graves.  Plasma processing in microelectronics manufacturing , 1989 .

[3]  Toshiaki Makabe,et al.  Spatiotemporal optical emission spectroscopy of rf discharges in SF6 , 1993 .

[4]  Daniel L. Flamm,et al.  Computer simulation of a CF4 plasma etching silicon , 1984 .

[5]  J. Meichsner,et al.  Negative Ions in a Glow Discharge of Tetrafluoromethane , 1985 .

[6]  H. Sawin,et al.  Evaluation of CF4 plasma chemistry by power modulation , 1992 .

[7]  Y. Ikegami,et al.  Measurements of electron drift velocities and positive ion mobilities for gases containing CF4 II , 1992 .

[8]  G. Kroesen,et al.  Measurements of negative ion densities in 13.56-MHz rf plasmas of CF4, C2F6, CHF3, and C3F8 using microwave resonance and the photodetachment effect , 1991 .

[9]  N. Suetin,et al.  Experimental and theoretical study of the CF4 DC glow discharge positive column , 1993 .

[10]  L. Christophorou,et al.  Ionization coefficients in selected gas mixtures of interest to particle detectors , 1992 .

[11]  M. Naidu,et al.  Mobility, diffusion and attachment of electrons in perfluoroalkanes , 1972 .

[12]  W. Nighan,et al.  Influence of negative-ion processes on steady-state properties and striations in molecular gas discharges , 1974 .

[13]  F. F. Young,et al.  Two-dimensional, self-consistent, three-moment simulation of RF glow discharge , 1993 .

[14]  H. Toyoda,et al.  Appearance mass spectrometry of neutral radicals in radio frequency plasmas , 1992 .

[15]  G. Turban,et al.  Radio-frequency glow discharges in methane gas: modelling of the gas-phase physics and chemistry , 1994 .

[16]  H. Sawin,et al.  Continuum modeling of radio‐frequency glow discharges. II. Parametric studies and sensitivity analysis , 1992 .

[17]  R. Bonham,et al.  Positive ion pair production by electron impact dissociative ionization of CF4 , 1992 .

[18]  Hunter,et al.  Electron motion in the gases CF4, C2F6, C3F8, and n-C4F10. , 1988, Physical review. A, General physics.

[19]  H. Sawin,et al.  Power modulation study of chemical kinetics in rf discharges , 1992 .

[20]  R. Seydel.  From Equilibrium to Chaos: Practical Bifurcation and Stability Analysis , 1988 .

[21]  L. Christophorou,et al.  Electron attachment and ionization processes in CF4, C2F6, C3F8, and n‐C4F10 , 1987 .

[22]  L. Christophorou,et al.  Gases of possible interest to SSC muon detectors , 1991 .

[23]  Evangelos Gogolides,et al.  Comparison of experimental measurements and model predictions for radio‐frequency Ar and SF6 discharges , 1989 .

[24]  H. Sawin,et al.  Measurement and analysis of radio frequency glow discharge electrical impedance and network power loss , 1990 .

[25]  E. V. Veldhuizen,et al.  Absolute densities of reaction products from plasma etching of quartz , 1985 .

[26]  S. Suganomata,et al.  Excitation of ionization waves in a SF6 positive column , 1981 .

[27]  Ma,et al.  Absolute partial and total electron-impact-ionization cross sections for CF4 from threshold up to 500 eV. , 1991, Physical review. A, Atomic, molecular, and optical physics.

[28]  Tilmann D. Märk,et al.  Absolute partial and total electron impact ionization cross sections for CF/sub 4/ from threshold up to 180 eV , 1985 .

[29]  I. Walker,et al.  Electron swarm characteristic energies (Dr/μ) in tetrafluoromethane (CF4) at low E/N , 1988 .

[30]  S. Suganomata,et al.  Ionisation waves in low pressure SF6 gas , 1984 .

[31]  J. Verdeyen,et al.  Enhancement of the negative ion flux to surfaces from radio‐frequency processing discharges , 1989 .

[32]  L. Christophorou,et al.  Electron attachment to the perfluoroalkanes n‐CNF2N+2 (N=1–6) and i‐C4F10 a) , 1983 .

[33]  G. Kroesen,et al.  Temporal behavior of the electron and negative ion densities in a pulsed radio‐frequency CF4 plasma , 1991 .

[34]  Y. Hikosaka,et al.  Spatial Distribution and Surface Loss of CF3 and CF2 Radicals in a CF4 Etching Plasma , 1993 .

[35]  I. C. Plumb,et al.  A model of the chemical processes occurring in CF4/O2 discharges used in plasma etching , 1986 .

[36]  H. Sawin,et al.  Direct calculation of time-periodic states of continuum models of radio-frequency plasmas , 1992 .

[37]  W. Goedheer,et al.  A two‐dimensional fluid model for an argon rf discharge , 1993 .

[38]  S. A. Mani,et al.  Attachment instability in an externally ionized discharge , 1974 .

[39]  G. Kroesen,et al.  Negative ions in a radio-frequency plasma in CF4 , 1991 .

[40]  H. Sawin,et al.  Continuum modeling of radio‐frequency glow discharges. I. Theory and results for electropositive and electronegative gases , 1992 .

[41]  D. Manos,et al.  Plasma etching : an introduction , 1989 .

[42]  J. Wormhoudt,et al.  Radical and molecular product concentration measurements in CF4 and CH4 radio frequency plasmas by infrared tunable diode laser absorption , 1990 .

[43]  H. Tagashira,et al.  The ionisation and attachment coefficients in carbon tetrafluoride , 1983 .