1. Master Class: Electronegative Plasmas September 28-30

2. Diagnostics for Electronegative Plasmas Winfred Stoffels

3. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics Using negative ion diagnostics for neutrals Dusty plasma

4. Master Class: Electronegative Plasmas September 28-30 Electronegative plasmas

5. Master Class: Electronegative Plasmas September 28-30 Example plasma: capacitively coupled radiofrequency low pressure plasma

6. Master Class: Electronegative Plasmas September 28-30 Properties of electronegative plasmas Negative ions  Charged  Heavy  Trapped in the discharge  polymerization Ne + N_ = N+  Changed ionization and loss rates  plasma quenching (switches)  Changed transport  different I-V characteristics

7. Master Class: Electronegative Plasmas September 28-30

8. Standard diagnostics show influence of negative ions Approach Use electropositive plasma as comparison Measure as a function of dilution Beware that transition electropositive to electronegative can occur at small dilutions

9. Master Class: Electronegative Plasmas September 28-30 We can use traditional diagnostics to follow negative ions: resistance

10. Master Class: Electronegative Plasmas September 28-30 We can use traditional diagnostics to follow negative ions: optical emission

11. Master Class: Electronegative Plasmas September 28-30 We can use traditional diagnostics to follow negative ions: Charge neutrality

12. Master Class: Electronegative Plasmas September 28-30 We can use traditional diagnostics to follow negative ions: Transport

13. Master Class: Electronegative Plasmas September 28-30 We can use traditional diagnostics to follow negative ions: Plasma structure and current

14. Master Class: Electronegative Plasmas September 28-30 Conclusion Transition from electropositive to electronegative plasma occurs at small dilution Visible in:  Resistance  Voltage  Current  Emission  Charge balance  Plasma and sheath structure Measurable by traditional plasma diagnostics

15. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics Using negative ion diagnostics for neutrals Dusty plasma

16. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics  Probes  Mass spectrometry  Photo detachment Using negative ion diagnostics for neutrals Dusty plasma

17. Master Class: Electronegative Plasmas September 28-30 Direct negative ion measurement with Probes (Amemiya) + simple and cheap setup - “not” species selective - difficult to measure Negative ion current is visible in the second derivative of the probe characteristic as a small peak just above 0 V.

18. Master Class: Electronegative Plasmas September 28-30 Ion Mass Spectrometry (QMS, TOF, …) + Well known technique + Direct ion measurement + Mass selective  most often chemical identification possible + Sensitive - Detects a flux not a density  plasma model is needed - Mass dependent transmission  model is needed - Poor spatial and temporal resolution

19. Master Class: Electronegative Plasmas September 28-30 Ion Mass Spectrometry (negative ions) - Negative ions are trapped in glow Solutions:  positive bias  disturbs plasma  typical approach in ion sources  Pulse plasma »Afterglow measurement »Diffusion model needed

20. Master Class: Electronegative Plasmas September 28-30

22. Pulse plasma. Negative and positive ions in SiH 4 plasma (after Howling)

23. Master Class: Electronegative Plasmas September 28-30 direct measurement : Surface produced negative ions Example: O - produced at kathode and measured at anode

24. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics  Probes  Mass spectrometry  Photo detachment Using negative ion diagnostics for neutrals Dusty plasma

25. Master Class: Electronegative Plasmas September 28-30 Photodetachment X - + hv  X + e  The negative ion is transformed into a free electron  Lasers provide the needed photon  Electron can be measured easily  Optogalvanic  Probe  Microwave resonance  Electron and ion kinetics can be measured

26. Master Class: Electronegative Plasmas September 28-30 Photodetachment X - + hv  X + e + Local measurement + High time resolution (pulsed laser) + Kinetic information +/- Specific on species depends on threshold - Electron diagnostic needed (and its minus points) - Need to check for other laser induced effects (ionization of neutrals)

27. Master Class: Electronegative Plasmas September 28-30 Selectivity depends on electron affinity EA of F - 3.4 eV (364nm) (Haverlag)

28. Master Class: Electronegative Plasmas September 28-30 Photodetachment can be done in two regimes linear +less disturbing - cross section must be known saturation + independent of cross section -hard to acchieve After Bacal

29. Master Class: Electronegative Plasmas September 28-30 + easy +/- spatial information modified by transport true plasma - difficult to make quantitative Photodetachment in combination with Optogalvanic method

30. Master Class: Electronegative Plasmas September 28-30

31. Photodetachment in combination with probe (Bacal) + easy - need theory - laser hits probe and can result in photo electrons from probe

32. Master Class: Electronegative Plasmas September 28-30 Photodetachment in combination with probe (Bacal)

33. Master Class: Electronegative Plasmas September 28-30 + quantitative + no model needed + gives information on ion kinetics +/- line of sight - complex Photodetachment in combination with microwave resonance (Eindhoven)

34. Master Class: Electronegative Plasmas September 28-30 Photodetachment in combination with microwave resonance

35. Master Class: Electronegative Plasmas September 28-30 negative charge in dusty plasma Beginning: only negative ions  n e = 10 13 m -3 Slow electron capture After 1 sec: charged particles  n e = 10 14 m -3 Fast electron capture

36. Master Class: Electronegative Plasmas September 28-30 particle charge: measured by photodetachment As particles grow: -Charge on particles increases -Recharging time decreases

37. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics  Probes  Mass spectrometry  Photo detachment  Using negative ion diagnostics for neutrals Dusty plasma Optogalvanic Probe Microwave resonance

38. Master Class: Electronegative Plasmas September 28-30 Electron Attachment Mass Spectrometry Use electronegative character to analyze neutrals XY + e  XY - or X - + Y + negative ions can be mass specific detected by QMS + lower electron energy needed  less fragmentation + resonant process  possible to selectively create negative ions

39. Master Class: Electronegative Plasmas September 28-30 Electron Attachment Mass Spectrometry

40. Master Class: Electronegative Plasmas September 28-30 Polymerization in C 2 F 6 plasma: Negative ion fragmentsPositive ion fragments

41. Master Class: Electronegative Plasmas September 28-30 Combinations of Mass spectrometry and photodetachment After Boesl, Muenchen

42. Master Class: Electronegative Plasmas September 28-30 Combinations of Mass spectrometry and photodetachment

43. Master Class: Electronegative Plasmas September 28-30 Figure 1: Partial cross section for the process K- + γ - K(5s) + e- in the photon energy range from 4.19 eV to 4.26 eV. Curves: present results in dipole velocity (solid) and dipole length (dotted) approximations After Chien-Nan Liu

44. Master Class: Electronegative Plasmas September 28-30 Outline Introduction Standard diagnostics Specific diagnostics  Probes  Mass spectrometry  Photo detachment Using negative ion diagnostics for neutrals Dusty plasma

45. Master Class: Electronegative Plasmas September 28-30

47. Solar Cells

48. Master Class: Electronegative Plasmas September 28-30 a solar cell Consists of multiple layers with different functions Produced in low pressure RF plasma Layer is an amorphous hydrogen rich silicon layer wall Amorphous H-Si rf C

49. Master Class: Electronegative Plasmas September 28-30 The Staebler-Wronski effect After Roca i Cabarrocas et al, Ecole Polytechnique, Palaiseau, France Solar cell degradation induced by exposition to sun light Initial degradation during the first 200 kWh/m 2 Embedded nanocrystalline structures increase solar cell lifetime and efficiency (pm-Si)

50. Master Class: Electronegative Plasmas September 28-30 Solar Cells Roca i Cabarrocas et al, Thin Solid Films 403-404 (2002) 39-46 cr:Sia:Si pm:Si

51. Master Class: Electronegative Plasmas September 28-30 Dust Particles 0.1nm1nm10nm100nm1μm moleculemacro-moleculenano-particleagglomeratepowder α-regime γ´-regime amorphousnot usable

52. Master Class: Electronegative Plasmas September 28-30 Neutral chemistry Particles Electrons and ions Internal plasma parameters:

53. Master Class: Electronegative Plasmas September 28-30 Neutral chemistry Emission spectroscopy: ASDF, dissociation RGA, FTIR, LIF: dissociation, polymerization, ASDF Infrared absorption spectroscopy: dissociation, polymerization, temperature Infrared CRD: radical densities Ellipsometry: surface chemistry Particles Electrons and ions Results available Available if needed Under construction Internal plasma parameters:

54. Master Class: Electronegative Plasmas September 28-30 Neutral chemistry Particles Electrons and ions Microwave resonance: electron density Photodetachment: negative ion density Doppler resolved LIF, energy resolved QMS: IEDF, E-field Langmuir probe, Thomson scattering: EEDF Results available Available if needed Under construction Internal plasma parameters:

55. Master Class: Electronegative Plasmas September 28-30 Neutral chemistry Results available Available if needed Under construction Particles Mie Scattering: density, size, spatial distribution Laser heating, LIPEE: presence, size Photodetachment: particle charge; charging kinetics FTIR: particle composition Infrared CRD: particle formation Electrons and ions Internal plasma parameters:

56. Master Class: Electronegative Plasmas September 28-30 Experimental setup rf CCP plasma Homogeneous gas flow though top rf showerhead and bottom grid in closed configuration Controled temperature using heater/cooling system Variable gas: today only 5% SiH 4 in Ar

57. Master Class: Electronegative Plasmas September 28-30 The “neutral chemistry” setup Infrared CRDS FTIR OES The “electrons and ions” setup Microwave resonance Photodetachment PIM

58. Master Class: Electronegative Plasmas September 28-30 Emission increases with time After some time particles are ejected Time delay depends on temperature video 14.39 15.40 16.19

59. Master Class: Electronegative Plasmas September 28-30 Plasma impedance monitor a small capacitance and a pickup coil in rf line Determines: Voltage, current en phase between them For the fundamental frequency and the first 6 harmonics With a time resolution of 0.1 s VI RF

60. Master Class: Electronegative Plasmas September 28-30 Measurement Scheme Particle detection Dissociation processes Electric parameters He-Ne laser beam OMA - PIM

61. Master Class: Electronegative Plasmas September 28-30 p=0.133 mbar f=10 sccm 5%SiH 4 in Ar V=155 mV (P=8 W) current voltage phase 353K 393K 290K 3 rd harmonic 1 st harmonic fundamental

62. Master Class: Electronegative Plasmas September 28-30 HE-NE HaHa SiH 17 0 C= 290K 80 0 C= 353K120 0 C= 393K 100 sec p=0.133 mbar f=10 sccm 5%SiH 4 in Ar P=8 W

63. Master Class: Electronegative Plasmas September 28-30 Same behavior in electron density measured by microwave resonance -fast decay with several phases -oscillations as several generations grow -electron density growth as particles are expelled

64. Master Class: Electronegative Plasmas September 28-30 5 mm

65. Master Class: Electronegative Plasmas September 28-30 10 m m 500 nm

66. Master Class: Electronegative Plasmas September 28-30 The End