Slope and amplitude asymmetry effects on low frequency capacitively coupled carbon tetrafluoride plasmas

We report investigations of capacitively coupled carbon tetrafluoride (CF4) plasmas excited with tailored voltage waveforms containing up to five harmonics of a base frequency of 5.5 MHz. The impact of both the slope asymmetry, and the amplitude asymmetry, of these waveforms on the discharge is examined by combining experiments with particle-in-cell simulations. For all conditions studied herein, the discharge is shown to operate in the drift-ambipolar mode, where a comparatively large electric field in the plasma bulk (outside the sheaths) is the main mechanism for electron power absorption leading to ionization. We show that both types of waveform asymmetries strongly influence the ion energy at the electrodes, with the particularity of having the highest ion flux on the electrode where the lowest ion energy is observed. Even at the comparatively high pressure (600 mTorr) and low fundamental frequency of 5.5 MHz used here, tailoring the voltage waveforms is shown to efficiently create an asymmetry of both the ion energy and the ion flux in geometrically symmetric reactors.

[1]  J. Booth,et al.  Controlling the shape of the ion energy distribution at constant ion flux and constant mean ion energy with tailored voltage waveforms , 2016 .

[2]  D. J. Economou,et al.  Effect of gas properties on the dynamics of the electrical slope asymmetry effect in capacitive plasmas: comparison of Ar, H2 and CF4 , 2016 .

[3]  J. Booth,et al.  Strong ionization asymmetry in a geometrically symmetric radio frequency capacitively coupled plasma induced by sawtooth voltage waveforms. , 2015, Physical review letters.

[4]  W. Graham,et al.  Tailoring the nonlinear frequency coupling between odd harmonics for the optimisation of charged particle dynamics in capacitively coupled oxygen plasmas , 2015 .

[5]  J. Booth,et al.  Control and optimization of the slope asymmetry effect in tailored voltage waveforms for capacitively coupled plasmas , 2014 .

[6]  J. Booth,et al.  Ion flux asymmetry in radiofrequency capacitively-coupled plasmas excited by sawtooth-like waveforms , 2014 .

[7]  R. Cariou,et al.  Ion Energy Threshold in Low-Temperature Silicon Epitaxy for Thin-Film Crystalline Photovoltaics , 2014, IEEE Journal of Photovoltaics.

[8]  J. Maurice,et al.  Effect of Ion Energy on Microcrystalline Silicon Material and Devices: A Study Using Tailored Voltage Waveforms , 2014, IEEE Journal of Photovoltaics.

[9]  D. Coumou,et al.  Ion Energy Distribution Skew Control Using Phase-Locked Harmonic RF Bias Drive , 2014, IEEE Transactions on Plasma Science.

[10]  M. Kushner,et al.  Control of ion energy distributions using phase shifting in multi-frequency capacitively coupled plasmas , 2014, 2014 IEEE 41st International Conference on Plasma Sciences (ICOPS) held with 2014 IEEE International Conference on High-Power Particle Beams (BEAMS).

[11]  O. Zatsarinny,et al.  B-spline R-matrix-with-pseudostates calculations for electron-impact excitation and ionization of oxygen , 2014 .

[12]  J. Booth,et al.  Radio-frequency capacitively coupled plasmas excited by tailored voltage waveforms: comparison of experiment and particle-in-cell simulations , 2013 .

[13]  U. Czarnetzki,et al.  The effect of the driving frequencies on the electrical asymmetry of dual-frequency capacitively coupled plasmas , 2012 .

[14]  J. Booth,et al.  Control of the ion flux and ion energy in CCP discharges using non-sinusoidal voltage waveforms , 2012 .

[15]  J. Booth,et al.  Separate control of the ion flux and ion energy in capacitively coupled radio-frequency discharges using voltage waveform tailoring , 2012 .

[16]  R. Boswell,et al.  Enhanced sheath heating in capacitively coupled discharges due to non-sinusoidal voltage waveforms , 2012 .

[17]  J. Schulze,et al.  Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas. , 2011, Physical review letters.

[18]  J. Schulze,et al.  Electron heating and the electrical asymmetry effect in dual-frequency capacitive CF4 discharges , 2011 .

[19]  U. Czarnetzki,et al.  The electrical asymmetry effect in multi-frequency capacitively coupled radio frequency discharges , 2011 .

[20]  D. Voloshin,et al.  Two modes of capacitively coupled rf discharge in CF4 , 2010 .

[21]  J. Vanel,et al.  Nanocrystalline silicon film growth morphology control through RF waveform tailoring , 2010 .

[22]  V. Schulz-von der Gathen,et al.  The challenge of revealing and tailoring the dynamics of radio-frequency plasmas , 2010 .

[23]  U. Czarnetzki,et al.  Optimization of the electrical asymmetry effect in dual-frequency capacitively coupled radio frequency discharges: Experiment, simulation, and model , 2009 .

[24]  Zoltan Donko,et al.  PIC simulations of the separate control of ion flux and energy in CCRF discharges via the electrical asymmetry effect , 2009 .

[25]  P. Awakowicz,et al.  The role of the relative voltage and phase for frequency coupling in a dual-frequency capacitively coupled plasma , 2008 .

[26]  U. Czarnetzki,et al.  On the possibility of making a geometrically symmetric RF-CCP discharge electrically asymmetric , 2008 .

[27]  R. Brinkmann.  Beyond the step model: Approximate expressions for the field in the plasma boundary sheath , 2007 .

[28]  Z. Donkó,et al.  Analysis of a Capacitively Coupled Dual-Frequency CF4 Discharge , 2006 .

[29]  A. Wendt,et al.  Arbitrary substrate voltage wave forms for manipulating energy distribution of bombarding ions during plasma processing , 2006 .

[30]  A. Bogaerts,et al.  Plasma characteristics of an Ar/CF4/N2 discharge in an asymmetric dual frequency reactor: numerical investigation by a PIC/MC model , 2006 .

[31]  A. Bogaerts,et al.  Numerical simulation of dual frequency etching reactors: Influence of the external process parameters on the plasma characteristics , 2005 .

[32]  A. Lichtenberg,et al.  Principles of Plasma Discharges and Materials Processing: Lieberman/Plasma 2e , 2005 .

[33]  Jean-Paul Booth,et al.  Ion energy uniformity in high-frequency capacitive discharges , 2005 .

[34]  A. Bogaerts,et al.  Numerical investigation of ion-energy-distribution functions in single and dual frequency capacitively coupled plasma reactors. , 2004, Physical review. E, Statistical, nonlinear, and soft matter physics.

[35]  A. Bogaerts,et al.  Numerical study of Ar/CF4/N2 discharges in single- and dual-frequency capacitively coupled plasma reactors , 2003 .

[36]  T. Makabe,et al.  Transport coefficients and scattering cross-sections for plasma modelling in CF4-Ar mixtures: a swarm analysis , 2000 .

[37]  A. Wendt,et al.  Control of ion energy distribution at substrates during plasma processing , 2000 .

[38]  K. Nanbu,et al.  Probability theory of electron-molecule, ion-molecule, molecule-molecule, and Coulomb collisions for particle modeling of materials processing plasmas and cases , 2000 .

[39]  K. Nanbu,et al.  Self-Consistent Particle Simulation of Radio Frequency CF4Discharge: Effect of Gas Pressure , 2000 .

[40]  K. Nanbu,et al.  Self-consistent particle simulation of radio-frequency CF4 discharge with implementation of all ion–neutral reactive collisions , 1998 .

[41]  K. Nanbu,et al.  Monte Carlo Collision Simulation of Positive-Negative Ion Recombination for a Given Rate Constant , 1998 .

[42]  T. Makabe,et al.  Influence of driving frequency on narrow-gap reactive-ion etching in SF6 , 1995 .

[43]  R. Bonham.  Electron Impact Cross Section Data for Carbon Tetrafluoride. , 1994 .

[44]  V. M. Donnelly,et al.  Anisotropic etching of SiO2 in low‐frequency CF4/O2 and NF3/Ar plasmas , 1984 .

[45]  Vincent M. Donnelly,et al.  The design of plasma etchants , 1981 .