Master Class: Electronegative Plasmas September 28-30

Diagnostics for Electronegative Plasmas Winfred Stoffels

Master Class: Electronegative Plasmas September Outline Introduction Standard diagnostics Specific diagnostics Using negative ion diagnostics for neutrals Dusty plasma

Master Class: Electronegative Plasmas September Electronegative plasmas

Master Class: Electronegative Plasmas September Example plasma: capacitively coupled radiofrequency low pressure plasma

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 28-30

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

Master Class: Electronegative Plasmas September We can use traditional diagnostics to follow negative ions: resistance

Master Class: Electronegative Plasmas September We can use traditional diagnostics to follow negative ions: optical emission

Master Class: Electronegative Plasmas September We can use traditional diagnostics to follow negative ions: Charge neutrality

Master Class: Electronegative Plasmas September We can use traditional diagnostics to follow negative ions: Transport

Master Class: Electronegative Plasmas September We can use traditional diagnostics to follow negative ions: Plasma structure and current

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September Outline Introduction Standard diagnostics Specific diagnostics Using negative ion diagnostics for neutrals Dusty plasma

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

Master Class: Electronegative Plasmas September 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.

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 28-30

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

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

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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 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)

Master Class: Electronegative Plasmas September Selectivity depends on electron affinity EA of F eV (364nm) (Haverlag)

Master Class: Electronegative Plasmas September 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

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

Master Class: Electronegative Plasmas September 28-30

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

Master Class: Electronegative Plasmas September Photodetachment in combination with probe (Bacal)

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

Master Class: Electronegative Plasmas September Photodetachment in combination with microwave resonance

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

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

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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September Electron Attachment Mass Spectrometry

Master Class: Electronegative Plasmas September Polymerization in C 2 F 6 plasma: Negative ion fragmentsPositive ion fragments

Master Class: Electronegative Plasmas September Combinations of Mass spectrometry and photodetachment After Boesl, Muenchen

Master Class: Electronegative Plasmas September Combinations of Mass spectrometry and photodetachment

Master Class: Electronegative Plasmas September 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

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

Master Class: Electronegative Plasmas September 28-30

Solar Cells

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 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)

Master Class: Electronegative Plasmas September Solar Cells Roca i Cabarrocas et al, Thin Solid Films (2002) cr:Sia:Si pm:Si

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

Master Class: Electronegative Plasmas September Neutral chemistry Particles Electrons and ions Internal plasma parameters:

Master Class: Electronegative Plasmas September 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:

Master Class: Electronegative Plasmas September 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:

Master Class: Electronegative Plasmas September 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:

Master Class: Electronegative Plasmas September 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

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

Master Class: Electronegative Plasmas September Emission increases with time After some time particles are ejected Time delay depends on temperature video

Master Class: Electronegative Plasmas September 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

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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September 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

Master Class: Electronegative Plasmas September mm

Master Class: Electronegative Plasmas September m m 500 nm

Master Class: Electronegative Plasmas September The End