1 / 23

CONTROL OF ELECTRON ENERGY DISTRIBUTIONS AND FLUX RATIOS IN PULSED CAPACITIVELY COUPLED PLASMAS *

CONTROL OF ELECTRON ENERGY DISTRIBUTIONS AND FLUX RATIOS IN PULSED CAPACITIVELY COUPLED PLASMAS * Sang-Heon Song a) and Mark J. Kushner b) a) Department of Nuclear Engineering and Radiological Sciences University of Michigan, Ann Arbor, MI 48109, USA ssongs@umich.edu

sorley
Download Presentation

CONTROL OF ELECTRON ENERGY DISTRIBUTIONS AND FLUX RATIOS IN PULSED CAPACITIVELY COUPLED PLASMAS *

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CONTROL OF ELECTRON ENERGY DISTRIBUTIONS AND FLUX RATIOS IN PULSED CAPACITIVELY COUPLED PLASMAS* Sang-Heon Songa) and Mark J. Kushnerb) a)Department of Nuclear Engineering and Radiological Sciences University of Michigan, Ann Arbor, MI 48109, USA ssongs@umich.edu b)Department of Electrical Engineering and Computer Science University of Michigan, Ann Arbor, MI 48109, USA mjkush@umich.edu http://uigelz.eecs.umich.edu Oct 2010 AVS * Work supported by DOE Plasma Science Center and Semiconductor Research Corp.

  2. University of Michigan Institute for Plasma Science & Engr. AGENDA • Motivation for controlling f(e) • Description of the model • Typical Ar pulsed plasma properties • Typical CF4/O2 pulsed plasma properties • f(e) and flux ratios with different • PRF • Duty Cycle • Pressure • Concluding Remarks SHS_MJK_AVS2010_02

  3. k SiH3 + H + e e + SiH4 University of Michigan Institute for Plasma Science & Engr. CONTROL OF ELECTRON KINETICS- f() • Controlling the generation of reactive species for technological devices benefits from customizing the electron energy (velocity) distribution function. • Need SiH3 radicals* • LCD • Solar Cell * Ref: Tatsuya Ohira, Phys. Rev. B 52 (1995) SHS_MJK_AVS2010_03

  4. University of Michigan Institute for Plasma Science & Engr. HYBRID PLASMA EQUIPMENT MODEL (HPEM) Te,S, k Fluid Kinetics Module Fluid equations (continuity, momentum, energy) Poisson’s equation Electron Monte Carlo Simulation E,Ni, ne, Ti • Fluid Kinetics Module: • Heavy particle and electron continuity, momentum, energy • Poisson’s equation • Electron Monte Carlo Simulation: • Includes secondary electron transport • Captures anomalous electron heating • Includes electron-electron collisions SHS_MJK_AVS2010_04

  5. University of Michigan Institute for Plasma Science & Engr. REACTOR GEOMETRY • 2D, cylindrically symmetric • Ar, CF4/O2, 10 – 40 mTorr, 200 sccm • Base conditions • Lower electrode: LF = 10 MHz, 300 W, CW • Upper electrode: HF = 40 MHz, 500 W, Pulsed SHS_MJK_AVS2010_05

  6. PULSE POWER University of Michigan Institute for Plasma Science & Engr. • Use of pulse power provides a means for controlling f(). • Pulsing enables ionization to exceed electron losses during a portion of the period – ionization only needs to equal electron losses averaged over the pulse period. Pmax Power(t) Duty Cycle Pmin Time = 1/PRF • Pulse power for high frequency. • Duty-cycle = 25%, PRF = 100 kHz, 415 kHz • Average Power = 500 W SHS_MJK_AVS2010_06

  7. Ar SHS_MJK_AVS2010_07

  8. University of Michigan Institute for Plasma Science & Engr. MAX MIN PULSED CCP: Ar, 40 mTorr • Pulsing with a PRF and moderate duty cycle produces nominal intra-cycles changes [e] but does modulate f(). • LF = 10 MHz, 300 W • HF = 40 MHz, pulsed 500 W • PRF = 100 kHz, Duty-cycle = 25% ANIMATION SLIDE-GIF • [e] VHF 226 V VLF 106 V f(e) • Te SHS_MJK_AVS2010_08

  9. University of Michigan Institute for Plasma Science & Engr. PULSED CCP: Ar, DUTY CYCLE • Excursions of tail are more extreme with lower duty cycle – more likely to reach high thresholds. ANIMATION SLIDE-GIF • Cycle Average • Duty cycle = 25% • Duty cycle = 50% VHF 128 V VLF 67 V VHF 226 V VLF 106 V • LF 10 MHz, pulsed HF 40 MHz • PRF = 100 kHz, Ar 40 mTorr SHS_MJK_AVS2010_09

  10. University of Michigan Institute for Plasma Science & Engr. PULSED CCP: Ar, PRESSURE • Pulsed systems are more sensitive to pressure due to differences in the rates of thermalization in the afterglow. ANIMATION SLIDE-GIF • Cycle Average • 10 mTorr • 40 mTorr VHF 226 V VLF 106 V VHF 274 V VLF 146 V • LF 10 MHz, pulsed HF 40 MHz • PRF = 100 kHz SHS_MJK_AVS2010_10

  11. CF4/O2 SHS_MJK_AVS2010_11

  12. CW University of Michigan Institute for Plasma Science & Engr. MAX MIN ELECTRON DENSITY • At 415 kHz, the electron density is not significantly modulated by pulsing, so the plasma is quasi-CW. • At 100 kHz, modulation in [e] occurs due to electron losses during the longer inter-pulse period. • The lower PRF is less uniform due to larger bulk electron losses during longer pulse-off cycle. • PRF=415 kHz • PRF=100 kHz • 40 mTorr, CF4/O2=80/20, 200 sccm • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W (CW or pulse) ANIMATION SLIDE-GIF SHS_MJK_AVS2010_12

  13. CW University of Michigan Institute for Plasma Science & Engr. MAX MIN ELECTRON SOURCES BY BULK ELECTRONS • The electrons have two groups: bulk low energy electrons and beam-like secondary electrons. • The electron source by bulk electron is negative due to electron attachment and dissociative recombination. • Only at the start of the pulse-on cycle, is there a positive electron source due to the overshoot of E/N. • PRF=415 kHz • PRF=100 kHz • 40 mTorr, CF4/O2=80/20, 200 sccm • LF 300 W, HF 500 W ANIMATION SLIDE-GIF SHS_MJK_AVS2010_13

  14. CW University of Michigan Institute for Plasma Science & Engr. MAX MIN ELECTRON SOURCES BY BEAM ELECTRONS • The beam electrons result from secondary emission from electrodes and acceleration in sheaths. • The electron source by beam electron is always positive. • The electron source by beam electrons compensates the electron losses and sustains the plasma. • PRF=415 kHz • PRF=100 kHz • 40 mTorr, CF4/O2=80/20, 200 sccm • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W (CW or pulse) ANIMATION SLIDE-GIF SHS_MJK_AVS2010_14

  15. University of Michigan Institute for Plasma Science & Engr. TYPICAL f(e): CF4/O2 vs. Ar • Ar • CF4/O2 • Less Maxwellian f(e) with CF4/O2 due to lower e-e collisions. • Enhanced sheath heating with CF4/O2 due to lower plasma density. • Tail of f(e) comes up to compensate for the attachment and recombination that occurs at lower energy. VHF 226 V VLF 106 V VHF 203 V VLF 168 V ANIMATION SLIDE-GIF • 40 mTorr, 200 sccm • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W (25% dc) SHS_MJK_AVS2010_15

  16. University of Michigan Institute for Plasma Science & Engr. RATIO OF FLUXES: CF4/O2 • In etching of dielectrics in fluorocarbon gas mixtures, the polymer layer thickness depends on ratio of fluxes. • Ions – Activation of dielectric etch, sputtering of polymer • CFx radicals – Formation of polymer • O – Etching of polymer • F – Diffusion through polymer, etch of dielectric and polymer • Investigate flux ratios with varying • PRF • Duty cycle • Pressure • Flux Ratios: • Poly = (CF3+CF2+CF+C) / Ions • O = O / Ions • F = F / Ions SHS_MJK_AVS2010_16

  17. University of Michigan Institute for Plasma Science & Engr. f(e): CF4/O2, PRF • Average • PRF = 100 kHz • The time averaged f(e) for pulsing is similar to CW excitation. • Extension of tail of f(e) beyond CW excitation during pulsing produces different excitation and ionization rates, and different mix of fluxes to wafer. VHF 203 V VLF 168 V ANIMATION SLIDE-GIF • 40 mTorr, CF4/O2=80/20, 200 sccm • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W (25% dc) SHS_MJK_AVS2010_17

  18. University of Michigan Institute for Plasma Science & Engr. RATIO OF FLUXES: CF4/O2, PRF • Ratios of fluxes are tunable using pulsed excitation. • Polymer layer thickness may be reduced by pulsed excitation because poly to ion flux ratio decreases. CW 100 CW 100 415 415 kHz 100 CW 415 F O Poly • 40 mTorr, CF4/O2=80/20, 200 sccm, Duty-cycle = 25% • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W SHS_MJK_AVS2010_18

  19. University of Michigan Institute for Plasma Science & Engr. f(e): CF4/O2, DUTY CYCLE • Control of average f() over with changes in duty cycle is limited if keep power constant. ANIMATION SLIDE-GIF • Cycle Average • Duty cycle = 25% • Duty cycle = 50% VHF 203 V VLF 168 V VHF 191 V VLF 168 V • 40 mTorr, CF4/O2=80/20, 200 sccm • LF 10 MHz, Pulsed HF 40 MHz, PRF = 100 kHz SHS_MJK_AVS2010_19

  20. University of Michigan Institute for Plasma Science & Engr. RATIO OF FLUXES: CF4/O2, DUTY CYCLE • Flux ratio control is limited if keep power constant. • With smaller duty cycle, polymer flux ratio is more reduced compared to the others. CW 50% 25% 50% CW 25% 50% 25% CW F O Poly • LF 10 MHz, Pulsed HF 40 MHz, PRF = 100 kHz • 40 mTorr, CF4/O2=80/20, 200 sccm SHS_MJK_AVS2010_20

  21. University of Michigan Institute for Plasma Science & Engr. f(e): CF4/O2, PRESSURE • Pulsed systems are sensitive to pressure due to differences in the rates of thermalization in the afterglow. ANIMATION SLIDE-GIF • Cycle Average • 10 mTorr • 40 mTorr VHF 233 V VLF 188 V VHF 191 V VLF 168 V • CF4/O2=80/20, 200 sccm, PRF = 100 kHz • LF 10 MHz, Pulsed HF 40 MHz SHS_MJK_AVS2010_21

  22. University of Michigan Institute for Plasma Science & Engr. RATIO OF FLUXES: CF4/O2, PRESSURE • Flux ratios decrease as pressure decreases. • Polymer layer thickness may be reduced with lower pressure in the pulsed CCP. 40 P: Pulsed excitation CW: CW excitation CW 40 mTorr P CW 10 P 10 P CW CW P 40 10 P CW CW P F O Poly • CF4/O2=80/20, 200 sccm • LF = 10 MHz, 300 W • HF = 40 MHz, 500 W • PRF = 100 kHz, Duty-cycle = 25% SHS_MJK_AVS2010_22

  23. CONCLUDING REMARKS • Extension of tail of f(e) beyond CW excitation produces different mix of fluxes. • Ratios of fluxes are tunable using pulsed excitation. • Different PRF provide different flux ratios due to different relaxation time during pulse-off cycle. • Duty cycle is another knob to control f(e) and flux ratios, but it is limited if keep power constant • Pressure provide another freedom for customizing f(e) and flux ratios in pulsed CCPs. SHS_MJK_AVS2010_23

More Related