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SiO 2 ETCH RATE AND PROFILE CONTROL USING PULSE POWER IN CAPACITIVELY COUPLED PLASMAS* Sang-Heon Song a) and Mark J. Kushner b) a) Department of Nuclear.

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Presentation on theme: "SiO 2 ETCH RATE AND PROFILE CONTROL USING PULSE POWER IN CAPACITIVELY COUPLED PLASMAS* Sang-Heon Song a) and Mark J. Kushner b) a) Department of Nuclear."— Presentation transcript:

1 SiO 2 ETCH RATE AND PROFILE CONTROL USING PULSE POWER IN 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 b) Department of Electrical Engineering and Computer Science University of Michigan, Ann Arbor, MI 48109, USA mjkush@umich.edu http://uigelz.eecs.umich.edu September 21 st, 2011 * Work supported by DOE Plasma Science Center and Semiconductor Research Corp.

2 AGENDA  Motivation for controlling f(  )  Description of the model  Typical Ar/CF 4 /O 2 pulsed plasma properties  Etch property with different PRF  Constant Power with DC Bias  Constant Voltage with DC Bias  Without DC Bias  Concluding remarks University of Michigan Institute for Plasma Science & Engr. SHS_MJK_ISPC

3 CONTROL OF ELECTRON KINETICS – f(  )  Controlling the generation of reactive species for technological devices benefits from customizing the electron energy (velocity) distribution function. University of Michigan Institute for Plasma Science & Engr. e + CF 4 CF 3 + F + e k SHS_MJK_ISPC

4 ETCH RATE vs. FLUX RATIOS University of Michigan Institute for Plasma Science & Engr. Ref: D. C. Gray, J. Butterbaugh, and H. H. Sawin, J. Vac. Sci. Technol. A 9, 779 (1991) Flux Ratio (F/Ar + )Flux Ratio (CF 2 /Ar + ) Etching Yield (Si/Ar + )  Large fluorine to ion flux ratio enhance etching yield of Si.  Large fluorocarbon to ion flux ratio reduce etching yield of Si. SHS_MJK_ISPC

5 Ref: K. Ono, M. Tuda, H. Ootera, and T. Oomori, Pure and Appl. Chem. Vol 66 No 6, 1327 (1994)  Large chlorine radical to ion flux ratio makes undercut in etch profile due to too much chemical reactions.  Etch profile result in ECR Cl 2 plasma after 200% over etch with different flux ratios p-Si University of Michigan Institute for Plasma Science & Engr. ETCH PROFILE vs. FLUX RATIOS  Flux Ratio (Cl / Ion) = 0.3  Flux Ratio (Cl / Ion) = 0.8 SHS_MJK_ISPC

6 HYBRID PLASMA EQUIPMENT MODEL (HPEM)  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 E, N i, n e Fluid Kinetics Module Fluid equations (continuity, momentum, energy) Poisson’s equation T e, S b, S eb, k Electron Monte Carlo Simulation University of Michigan Institute for Plasma Science & Engr. SHS_MJK_ISPC

7 MONTE CARLO FEATURE PROFILE MODEL (MCFPM)  The MCFPM resolves the surface topology on a 2D Cartesian mesh.  Each cell has a material identity. Gas phase species are represented by Monte Carlo pseuodoparticles.  Pseuodoparticles are launched with energies and angles sampled from the distributions obtained from the HPEM  Cells identities changed, removed, added for reactions, etching deposition. PCMCM Energy and angular distributions for ions and neutrals MCFPM Etch rates and profile University of Michigan Institute for Plasma Science & Engr.  Poisson’s equation solved for charging HPEM SHS_MJK_ISPC

8 REACTOR GEOMETRY: 2 FREQUENCY CCP  2D, cylindrically symmetric  Ar/CF 4 /O 2 = 75/20/5, 40 mTorr, 200 sccm  Base conditions  Lower electrode: LF = 10 MHz, 500 W, CW  Upper electrode: HF = 40 MHz, 500 W, Pulsed University of Michigan Institute for Plasma Science & Engr. SHS_MJK_ISPC

9 PULSE POWER Time  = 1/PRF Duty Cycle Power(t) P min P max 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 ON period – ionization only needs to equal electron losses averaged over the pulse period.  Pulse power for high frequency.  Duty-cycle = 25%, PRF = 50, 100, 200, 415, 625 kHz  Average Power = 500 W SHS_MJK_ISPC

10 Typical Plasma Properties SHS_MJK_ISPC

11 PULSED CCP: n e, T e, f(  ) University of Michigan Institute for Plasma Science & Engr.  Pulsing with a PRF and moderate duty cycle produces nominal intra-cycles changes [e] but does modulate f(  ).  [e] TeTe MIN MAX f(  ) ANIMATION SLIDE-GIF  40 mTorr, Ar/CF 4 /O 2 =75/20/5  LF = 10 MHz, 500 W  HF = 40 MHz, pulsed 500 W  PRF = 100 kHz, Duty-cycle = 25% SHS_MJK_ISPC

12 ELECTRON DENSITY  CW University of Michigan Institute for Plasma Science & Engr.  Duty = 50%  Duty = 25% MIN MAX ANIMATION SLIDE-GIF  At 50% duty, the electron density is not significantly modulated by pulsing, so the plasma is quasi-CW.  At 25% duty, modulation in [e] occurs due to electron losses during the longer inter-pulse period.  The lower duty cycle is more likely to reach higher value of electron density.  40 mTorr, Ar/CF 4 /O 2 =75/20/5  LF = 10 MHz, 500 W  HF = 40 MHz, 500 W (CW or pulse) SHS_MJK_ISPC

13 ELECTRON SOURCES BY BULK ELECTRONS University of Michigan Institute for Plasma Science & Engr.  CW  Duty = 50%  Duty = 25%  The electrons have two groups: bulk low energy electrons and beam-like secondary electrons.  The bulk electron source is negative due to electron attachment and dissociative recombination.  At the start of the pulse-on cycle, is there a impulsive positive electron source due to the overshoot of E/N. MIN MAX  40 mTorr, Ar/CF 4 /O 2 =75/20/5  LF 500 W, HF 500 W ANIMATION SLIDE-GIF SHS_MJK_ISPC

14 ELECTRON SOURCES BY BEAM ELECTRONS University of Michigan Institute for Plasma Science & Engr.  CW  Duty = 50%  Duty = 25% MIN MAX  40 mTorr, Ar/CF 4 /O 2 =75/20/5  LF = 10 MHz, 500 W  HF = 40 MHz, 500 W (CW or pulse)  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. ANIMATION SLIDE-GIF SHS_MJK_ISPC

15 Etch Properties SHS_MJK_ISPC

16 F / POLY FLUX RATIO: CONSTANT POWER · F to polymerizing flux ratio is largest at 200 kHz of PRF.  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz 500 W, Pulsed HF 40 MHz 500 W University of Michigan Institute for Plasma Science & Engr.

17 ETCH PROFILE IN SiO 2 & IEAD: CONST. POWER University of Michigan Institute for Plasma Science & Engr.  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz 500 W, Pulsed HF 40 MHz 500 W Angle (degree) Energy (eV) · Etch rate is fastest at 200 kHz PRF with larger ion energy and F to polymerizing flux ratio.  Cycle Average IEAD Height (  m) Width (  m) 100 kHz CW 415 200 415 200 100 CW ANIMATION SLIDE-GIF  Etch Profile (300 sec) CD 70 nm -64 V -92 V -107 V-134 VBias: SHS_MJK_ISPC

18 F / POLY FLUX RATIO: CONSTANT VOLTAGE · F to polymerizing flux ratio is controlled not only by PRF, but also by DC bias. · DC bias is manipulated by the blocking capacitor on the substrate.  Without DC Bias  With DC Bias University of Michigan Institute for Plasma Science & Engr.  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz 250 V, Pulsed HF 40 MHz 500 W

19 ETCH PROFILE IN SiO 2 & IEAD: CONST. VOLTAGE · Etch rate is fastest at 415 kHz having larger fluorine flux.  Cycle Average IEAD 100 kHz CW 415 200 415 200 100 CW  Etch Profile (300 sec) CD 70 nm -88 V -103 V -116 V-129 VBias: Angle (degree) Width (  m) ANIMATION SLIDE-GIF University of Michigan Institute for Plasma Science & Engr.  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz 250 V, Pulsed HF 40 MHz 500 W

20 ETCH PROFILE IN SiO 2 & IEAD: NO BIAS · Etch rate is fastest at CW excitation due to continuously delivered power.  Cycle Average IEAD 100 kHz CW 415 200 415 200 100 CW  Etch Profile (300 sec) CD 70 nm  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz 250 V, Pulsed HF 40 MHz 500 W University of Michigan Institute for Plasma Science & Engr.

21 POWER NORMALIZED ETCH RATE · Power normalized etch rate is dependant on the pulse repetition frequency and DC bias of the substrate. University of Michigan Institute for Plasma Science & Engr.  40 mTorr, Ar/CF 4 /O 2 =75/20/5, 200 sccm  LF 10 MHz, Pulsed HF 40 MHz, Duty 25%

22 CONCLUDING REMARKS  Extension of tail of f(  ) beyond that obtained with CW excitation produces a different mix of fluxes to substrate.  Ratios of fluxes and IEADs are tunable using pulsed excitation.  Ratios of fluxes are IEADs are tunable using blocking capacitor.  Consequently, etch rate can be controlled by pulsed power with different blocking capacitors.  With constant power operation, fastest etch rate is achieved at 200 kHz having larger F to polymerizing flux ratio.  With constant voltage operation, fastest etch rate is achieved at 415 kHz having larger fluorine flux.  Without DC bias, the etch rate decrease as pulse repetition frequency decreases. University of Michigan Institute for Plasma Science & Engr. SHS_MJK_ISPC

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