1 / 19

PROPERTIES OF NONTHERMAL CAPACITIVELY COUPLED PLASMAS GENERATED IN NARROW QUARTZ TUBES FOR SYNTHESIS OF SILICON NANOPART

PROPERTIES OF NONTHERMAL CAPACITIVELY COUPLED PLASMAS GENERATED IN NARROW QUARTZ TUBES FOR SYNTHESIS OF SILICON NANOPARTICLES * Sang-Heon Song a ) , Romain Le Picard b) , Steven L. Girshick b) , Uwe R. Kortshagen b) , and Mark J. Kushner a) a) University of Michigan, Ann Arbor, MI 48109, USA

dudley
Download Presentation

PROPERTIES OF NONTHERMAL CAPACITIVELY COUPLED PLASMAS GENERATED IN NARROW QUARTZ TUBES FOR SYNTHESIS OF SILICON NANOPART

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. PROPERTIES OF NONTHERMAL CAPACITIVELY COUPLED PLASMAS GENERATED IN NARROW QUARTZ TUBES FOR SYNTHESIS OF SILICON NANOPARTICLES* Sang-Heon Songa), Romain Le Picardb), Steven L. Girshickb), Uwe R. Kortshagenb), and Mark J. Kushnera) a)University of Michigan, Ann Arbor, MI 48109, USA ssongs@umich.edu, mjkush@umich.edu b)University of Minnesota, Minneapolis, MN 55455, USA rlepicar@umn.edu, slg@umn.edu, kortshagen@umn.edu 40th IEEE International Conference on Plasma Science (ICOPS) San Francisco, USA, June16-21, 2013 * Work supported by National Science Foundation and DOE Plasma Science Center.

  2. University of Michigan Institute for Plasma Science & Engr. AGENDA • Plasma nanoparticle synthesis • Description of the model • Typical Ar/SiH4plasma properties • Nanoparticle density • Power • Pressure • Flow rate • SiH4fraction • Concluding remarks ICOPS_2013

  3. University of Michigan Institute for Plasma Science & Engr. NANOCRYSTALS (QUANTUM DOT) • Size-dependent photoluminescence from Si nanocrystals • Si nanocrystals fluoresce with properties akin to direct band-gap semiconductors. The emission wavelength is a function of the size of the nanocrystal. • Applications • Photovoltaic device • Light emitting device • Quantum computing • Biological imaging Ref: I. L. Medintz et al., Nature Material 4, 435 (2005). ICOPS_2013

  4. University of Michigan Institute for Plasma Science & Engr. PLASMA-SYNTHESIZED SILICON NANOCRYSTALS • Gas-phase plasma processes for Si nano-crystal production are environmentally friendly without producing liquid effluents. • The silicon nanoparticles (SiNP) are formed by clustering of the dissociation products of SiH4 passing through the plasma zone. • Exothermic reactions of H-atoms on the surface of nanoparticles likely produce temperatures sufficient to anneal amorphous particles to crystals. • The quality of silicon nanocrystal (SiNC) can be controlled by injecting additional gases downstream of the primary plasma. Ref: R. J. Anthony et al., Adv. Funct. Mater. 21, 4042 (2011). ICOPS_2013

  5. University of Michigan Institute for Plasma Science & Engr. HYBRID PLASMA EQUIPMENT MODEL (HPEM) • Fluid Kinetics Module: • Heavy particles – Continuity, momentum, and energy equations • Electron – Continuity and energy equations • Poisson’s equation • Electron Monte-Carlo Module (eMCS): • Secondary electron emission • HPEM is parallelized using OpenMP • Parallel successive over relaxation (SOR) utilized red-black scheme for electron energy, gas temperature, and Poisson’s equations. • eMCS optimized for parallel execution ICOPS_2013

  6. University of Michigan Institute for Plasma Science & Engr. GLOBAL CHEMISTRY MODEL (GLOCHE) Gas Phase Reaction Mechanism Time Dependent Kinetics • Plug flow reactor model • Reaction mechanism is compatible with HPEM. • Time dependent gas phase reaction kinetics are calculated using predictor-corrector scheme (Adams-Bashforth-Moulton method). ICOPS_2013

  7. University of Michigan Institute for Plasma Science & Engr. REACTOR GEOMETRY: CCP TUBE • 2D, cylindrically symmetric • Tube radius = 0.3 cm • Electrode separation = 2.2 cm • Operating conditions • Ar/SiH4 = 95/5 (range 99/1 – 90/10) • Pressure = 2 Torr (range 0.5 – 4 Torr) • Flow rate = 50 sccm (range 10 – 100 sccm) • Frequency = 25 MHz • Power = 1 W (range 1 – 10 W) ICOPS_2013

  8. University of Michigan Institute for Plasma Science & Engr. NUCLEATION REACTIONS BY NEUTRALS • 84 species are included in the mechanism • Medium sized silicon hydride = 63 species • Reaction hierarchy up to Si10H20. Higher silanes are “particles” • Nucleation reactions with neutrals • 28 reactions: Silyl formation by H abstraction. • SinH2m + H → SinH2m-1 + H2 k =2.44×10–16T1.9exp(–2190/T) cm3/s • 106 reactions for making higher silanes • SinH2m-1+ SijH2k-1 → Sin+jH2m+2k-2k = 3.32 × 10−9 cm3/s • 321 reactions for making particle (n + j ≥ 11) • SinH2m-1+ SijH2k-1 → particle k = 2.66 × 10-11Tg0.5cm3/s Ref: U. V. Bhandarkar et al., J. Phys. D: Appl. Phys. 33, 2731 (2000) ICOPS_2013

  9. University of Michigan Institute for Plasma Science & Engr. MAX MIN PLASMA DENSITY and TEMPERATURES • SiH4 • Tgas • [e] • Te • Highest quality nano-crystals are produced with only a few W of power deposition. • Moderate gas heating to 364 K with 90% depletion of SiH4 indicates electron impact dominates dissociation. • Gas heating is dominantly by Franck-Condon processes. • Electron density (4 x 1010 cm-3) is moderated by high rates of diffusion loss but low rates of attachment. • 1 W, 2 Torr, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  10. University of Michigan Institute for Plasma Science & Engr. MAX MIN • H • SiH3 • SiH3– • SiNP • SiH2 SILICON HYDRIDES • Exothermic recombination of H atoms on nano-crystals is believed to be important in annealing. • Negative ions are confined at the peak of the time average plasma potential at the center of the tube. • Silicon nanoparticles (SiNP) grow by successive radical addition, and so accumulate downstream. • 1 W, 2 Torr, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  11. University of Michigan Institute for Plasma Science & Engr. DENSITIES vs POWER • In spite of low rates of attachment, confinement of negative ions produces largely electronegative plasmas. • Depletion of SiH4 and consumption of radicals to form nanoparticles limits increase of SiHx with power. • HPEM, 2 Torr, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  12. University of Michigan Institute for Plasma Science & Engr. NANO PARTICLE vs POWER • More silyl radicals are produced by hydrogen abstraction reaction due to increased density of hydrogen radicals at higher power. • As a result, silyl species are more likely to find higher silyl partners to form nanoparticles and saturated silanes. • GLOCHE, 2 Torr, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  13. University of Michigan Institute for Plasma Science & Engr. DENSITIES vs PRESSURE • Electron density decreases with increasing pressure due more efficient power deposition. • Due to longer residence time at higher pressure there is more accumulation of dissociation products. • HPEM, 1 W, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  14. University of Michigan Institute for Plasma Science & Engr. NANO PARTICLE vs PRESSURE • Due to increased residence time at higher pressure silyl density increases but saturates by forming nanoparticles. • Since nanoparticle particle formation is irreversible at low temperature, the density of particles increases in this pressure range, provided sufficient silyl radicals. • GLOCHE, 4 W, Ar/SiH4=95/5, 50 sccm ICOPS_2013

  15. University of Michigan Institute for Plasma Science & Engr. DENSITIES vs FLOW RATE • SiH4 dissociation fraction decreases with increasing flow rate at constant power. • Electron density decreases due to larger average density of SiH4. • H, SiH3, and SiH3– increase but saturate due to the shorter residence time at higher flow rate. • HPEM, 1 W, 2 Torr, Ar/SiH4=95/5 ICOPS_2013

  16. University of Michigan Institute for Plasma Science & Engr. NANO PARTICLE vs FLOW RATE • Due to smaller electron density and shorter residence time at higher flow rate, the production of silyl radicals capable of forming nanoparticles is limited. • GLOCHE, 4 W, 2 Torr, Ar/SiH4=95/5 ICOPS_2013

  17. University of Michigan Institute for Plasma Science & Engr. DENSITIES vs SiH4 FRACTION • Plasma density decreases with SiH4 fraction due to electronegativity, while SiH3and SiH3–increase due to larger average density of SiH4. • H increases but quickly saturates due to the smaller electron densityat higher fraction of SiH4. • HPEM, 1 W, 2 Torr, 50 sccm ICOPS_2013

  18. University of Michigan Institute for Plasma Science & Engr. NANO PARTICLE vs SIH4 FRACTION • The nanoparticle density increases by increasing SiH4 fraction due to the increasing density of silyl species provided by electron impact and H abstraction. • Due to the smaller electron density at higher SiH4 fraction the nanoparticle density decreases with SiH4 fraction. • GLOCHE, 4 W, 2 Torr, 50 sccm ICOPS_2013

  19. University of Michigan Institute for Plasma Science & Engr. CONCLUDING REMARKS • As power increases, the electron density increases and nanoparticle density increases due to more silyl species produced by H radicals. • As pressure increases, the electron density decreases but the nanoparticle density increases due to the increased concentration and residence time of H, SiH3, and SiH3– • As flow rate increases, the electron density decreases and the nanoparticle density decreases due to the reduced residence time. • As SiH4 fraction increases, the electron density decreases but the nanoparticle density is maximized at optimum fraction of SiH4 due to trade off between electron and silyl production from SiH4. ICOPS_2013

More Related