VACUUM ARC DEPOSITION IN INTERIOR CAVITIES   Physical and Engineering Principles and Ideas for Interior Implementations Ra...
Background and Objectives <ul><li>Vacuum Arc Deposition  </li></ul><ul><ul><li>(a.k.a. cathode arc deposition, arc evapora...
Outline <ul><li>I. Physics of the Vacuum Arc </li></ul><ul><ul><li>The Arc Discharge </li></ul></ul><ul><ul><li>Cathode Sp...
I. Physics of the Vacuum Arc – The Arc Discharge <ul><li>D.C. Discharges </li></ul><ul><ul><li>Corona </li></ul></ul><ul><...
Difference between Glow and Arc –  cathode electron emission process <ul><li>Glow </li></ul><ul><li>‘ individual’ secondar...
Cathode Spot Characteristics <ul><li>Diam:   m’s </li></ul><ul><li>Lifetime: ns’s to   s’s </li></ul><ul><ul><li>Extingu...
Cathode Spot Plasma Jets <ul><li>~Fully Ionized </li></ul><ul><ul><li>Multiple ionizations common  </li></ul></ul><ul><ul>...
Cathode Spot Theory <ul><li>Two Approaches: </li></ul><ul><ul><li>Quasi-continuous (~steady state) </li></ul></ul><ul><ul>...
Beilis Model: Cathode Spot & Cathode Plasma Jet Cathode Cathode Spot Region Hydrodynamic Plasma Flow SHEATH Electron relax...
Beilis Model <ul><li>TF emission of electrons </li></ul><ul><li>Evaporation of atoms </li></ul><ul><li>Acceleration of ele...
Beilis Model – cont’d <ul><li>Back-flow of electron and ions to cathode </li></ul><ul><ul><li>Heats cathode spot </li></ul...
Beilis Model –  Hydrodynamic Plasma Expansion <ul><li>Like in jet engine – conversion of thermal  directed kinetic energy...
Explosive Electron Emission (Mesyats  et al. ) <ul><li>Cathode spot is a sequence of explosion of protuberances </li></ul>
EEE (Mesyats  et al. ) – cont’d <ul><li>Each explosion creates further protuberances, which can then explode </li></ul><ul...
Macroparticles
Macroparticles <ul><li>Spray of liquid metal droplets from the cathode spot </li></ul><ul><li>small fraction of cathode er...
II. Vacuum Arc Engineering <ul><li>Coating forms on any substrate intercepting part of plasma jet </li></ul><ul><li>In vac...
II. Vacuum Arc Engineering <ul><li>Arc Ignition </li></ul><ul><li>Cathode Spot Confinement and Motion </li></ul><ul><li>He...
Arc Ignition <ul><li>Problem: extremely high voltage needed to break-down vacuum gap (~100 kV/cm) </li></ul><ul><li>Drawn-...
Controlling Cathode Spot Location and Motion <ul><li>Objectives: </li></ul><ul><ul><li>Locate CS’s on ‘front’ surface of c...
Magnetic Control of Cathode Spots
Passive Border
Strelnitski Shield
Pulse Control <ul><li>Basic Idea: arc duration shorter than CS travel time to edge </li></ul><ul><ul><li>Short Pulse </li>...
Heat Removal <ul><li>Total power P = V arc I arc </li></ul><ul><ul><li>V arc  ~20-40 V </li></ul></ul><ul><ul><li>I arc  ~...
Heat Removal from Cathode <ul><li>Cool cathode important to </li></ul><ul><ul><li>minimize MP generation </li></ul></ul><u...
Heat Removal from Cathode, cont’d <ul><li>Then average surface Temp (far from C.S.) given by </li></ul>h c  – contact heat...
 
Substrate Temperature Control <ul><li>T s  critical in determining coating properties </li></ul><ul><li>Measure with IR ra...
Macroparticle Control <ul><li>3 Approaches </li></ul><ul><ul><li>Ignore </li></ul></ul><ul><ul><ul><li>Get good results (e...
Minimize MP Production/Transmission <ul><li>Choose refractory cathode material </li></ul><ul><ul><li>“ Poison” (i.e. nitri...
 
Macroparticle Removal <ul><li>Filtered Vacuum Arc Deposition </li></ul><ul><ul><li>Use magnetic field to bend plasma beam ...
VENETIAN BLIND
Two quarter-torus filtered arcs at Tel Aviv University
 
 
Filtered Arc –  Advantages and Disadvantages <ul><li>Advantages </li></ul><ul><ul><li>High quality, very smooth coatings <...
Other Arc Modes <ul><li>Hot Anode Vacuum Arc </li></ul><ul><ul><li>Crucible anode </li></ul></ul><ul><li>Hot Refractory An...
10   m
III. How can we coat  the inside of:
Approach 1: Ignore MPs
Approach 1: Ignore MPs <ul><li>Cavity serves as vacuum chamber and anode </li></ul><ul><li>Various techniques for magnetic...
Approach 2: Miniature Filter: Example – Welty Rect. Filter
Approach 2: Miniature Filter: Another Example <ul><li>Progress in Use of Ultra-High Vacuum  Cathodic  Arcs for Deposition ...
Approach III. Beilis “black-body” HRAVA deposition device
Interior Coatings - Considerations <ul><li>Use cavity as vacuum chamber </li></ul><ul><ul><li>Need complicated end seal to...
Summary and Conclusions <ul><li>VAD uses inherent properties of cathode spot plasma jets to rapidly deposit dense, high qu...
Summary and Conclusions, cont’d <ul><li>Several approaches exist for efficiently and rapidly coating interior of RF caviti...
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Vacuum Arc Deposition in interior cavities (Yan Valsky), Lecture Prof. R..LBoxman

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Vacuum Arc Deposition in interior cavities (Yan Valsky), Lecture Prof. R..LBoxman

  1. 1. VACUUM ARC DEPOSITION IN INTERIOR CAVITIES Physical and Engineering Principles and Ideas for Interior Implementations Raymond L. Boxman Electrical Discharge and Plasma Laboratory School of Electrical Engineering Tel-Aviv University  
  2. 2. Background and Objectives <ul><li>Vacuum Arc Deposition </li></ul><ul><ul><li>(a.k.a. cathode arc deposition, arc evaporation) </li></ul></ul><ul><ul><li>Most popular method for applying hard coatings in tool industry </li></ul></ul><ul><ul><li>… but less well known than other PVD (e.g. sputtering, e-beam evaporation) and CVD methods </li></ul></ul><ul><li>Objectives of this lecture: </li></ul><ul><ul><li>Review: </li></ul></ul><ul><ul><ul><li>Physics of vacuum arc </li></ul></ul></ul><ul><ul><ul><li>Engineering issues in vacuum arc deposition </li></ul></ul></ul><ul><ul><li>Suggest implementations with interior cavity </li></ul></ul>
  3. 3. Outline <ul><li>I. Physics of the Vacuum Arc </li></ul><ul><ul><li>The Arc Discharge </li></ul></ul><ul><ul><li>Cathode Spots and Cathode Spot Plasma Jets </li></ul></ul><ul><ul><ul><li>Observations </li></ul></ul></ul><ul><ul><ul><li>Theory </li></ul></ul></ul><ul><ul><li>Macroparticles </li></ul></ul><ul><li>II. Vacuum Arc Engineering </li></ul><ul><ul><li>Arc Ignition </li></ul></ul><ul><ul><li>Cathode Spot Confinement and Motion </li></ul></ul><ul><ul><li>Heat Removal </li></ul></ul><ul><ul><li>Macroparticle Control </li></ul></ul><ul><li>III. Suggestions for Coating Interior Cavities </li></ul>
  4. 4. I. Physics of the Vacuum Arc – The Arc Discharge <ul><li>D.C. Discharges </li></ul><ul><ul><li>Corona </li></ul></ul><ul><ul><ul><li>High V, Low I </li></ul></ul></ul><ul><ul><ul><li>At sharp point </li></ul></ul></ul><ul><ul><li>Glow Discharge </li></ul></ul><ul><ul><ul><li>V ~ 100’s V, I ~mA’s </li></ul></ul></ul><ul><ul><ul><li>Cathode fall 150-550 V, depends on gas and cathode material </li></ul></ul></ul><ul><ul><li>Arc </li></ul></ul><ul><ul><ul><li>10’s of volts, A-kA </li></ul></ul></ul><ul><ul><ul><li>Cathode spots </li></ul></ul></ul>
  5. 5. Difference between Glow and Arc – cathode electron emission process <ul><li>Glow </li></ul><ul><li>‘ individual’ secondary emission of electrons by: </li></ul><ul><ul><li>Ions (depends on ionization energy, not kinetic energy) </li></ul></ul><ul><ul><li>Excited Atoms </li></ul></ul><ul><ul><li>Photons </li></ul></ul><ul><li>Not enough! </li></ul><ul><ul><li>Multiplication in avalanche near cathode </li></ul></ul><ul><ul><li>Need high cathode drop (100’s of V’s) </li></ul></ul><ul><ul><li>Used in sputtering to accelerate bombarding ions into ‘target’ cathode </li></ul></ul><ul><li>Arc </li></ul><ul><li>Collective electron emission </li></ul><ul><ul><li>Current at cathode concentrated into cathode spots </li></ul></ul><ul><ul><li>Combination of thermionic and field emission of electrons </li></ul></ul><ul><ul><li>Can get sufficient electron current </li></ul></ul><ul><ul><li>Low cathode voltage drop (10’s of V’s) </li></ul></ul><ul><ul><li>High temp. in cathode spot gives high local evaporation rate – used in vacuum arc deposition </li></ul></ul>
  6. 6. Cathode Spot Characteristics <ul><li>Diam:  m’s </li></ul><ul><li>Lifetime: ns’s to  s’s </li></ul><ul><ul><li>Extinguish, reignite at adjacent location </li></ul></ul><ul><ul><li>Apparent ‘random walk’ motion </li></ul></ul><ul><ul><li>In B field, “retrograde motion” in -J  B direction </li></ul></ul>
  7. 7. Cathode Spot Plasma Jets <ul><li>~Fully Ionized </li></ul><ul><ul><li>Multiple ionizations common </li></ul></ul><ul><ul><ul><li>Z av (Ti) ~2 </li></ul></ul></ul><ul><li>Ion directed kinetic energy 20-150 eV </li></ul><ul><ul><li>Flow velocity ~10 4 m/s </li></ul></ul><ul><li>~cos  distribution </li></ul><ul><li>T i , T e ~few eV </li></ul><ul><li>Supersonic ions, thermal electrons </li></ul><ul><li>I i  -0.1 I arc , I e  1.1 I arc </li></ul>
  8. 8. Cathode Spot Theory <ul><li>Two Approaches: </li></ul><ul><ul><li>Quasi-continuous (~steady state) </li></ul></ul><ul><ul><li>Explosive Emission </li></ul></ul><ul><li>Quasi-continuous approach: </li></ul><ul><ul><li>Must account simultaneously for: </li></ul></ul><ul><ul><ul><li>Cathode heating (for e - and atom emission) </li></ul></ul></ul><ul><ul><ul><li>Electron emission </li></ul></ul></ul><ul><ul><ul><li>Atom emission </li></ul></ul></ul><ul><ul><ul><li>High ion energy / plasma velocity </li></ul></ul></ul>
  9. 9. Beilis Model: Cathode Spot & Cathode Plasma Jet Cathode Cathode Spot Region Hydrodynamic Plasma Flow SHEATH Electron relaxation zone. Ion diffusion Kinetic flow Knudsen Layer Plasma Jet Expansion  Acceleration Region e  i e  a
  10. 10. Beilis Model <ul><li>TF emission of electrons </li></ul><ul><li>Evaporation of atoms </li></ul><ul><li>Acceleration of electrons into vapor </li></ul><ul><ul><li>Collisionless sheath </li></ul></ul><ul><ul><li>Collisionless Knudsen layer </li></ul></ul><ul><ul><li>Electrons loose energy to vapor in relaxation zone </li></ul></ul>
  11. 11. Beilis Model – cont’d <ul><li>Back-flow of electron and ions to cathode </li></ul><ul><ul><li>Heats cathode spot </li></ul></ul><ul><li>Joule heating under cathode surface </li></ul><ul><li>Joule heating of plasma </li></ul><ul><li>Hydrodynamic plasma expansion </li></ul>
  12. 12. Beilis Model – Hydrodynamic Plasma Expansion <ul><li>Like in jet engine – conversion of thermal  directed kinetic energy </li></ul><ul><li>But plasma heated all along length </li></ul><ul><ul><li>Continuous heating, conversion into kinetic energy, so </li></ul></ul><ul><ul><ul><li>T i ~3ev, </li></ul></ul></ul><ul><ul><ul><li>E i ~20-150eV </li></ul></ul></ul>
  13. 13. Explosive Electron Emission (Mesyats et al. ) <ul><li>Cathode spot is a sequence of explosion of protuberances </li></ul>
  14. 14. EEE (Mesyats et al. ) – cont’d <ul><li>Each explosion creates further protuberances, which can then explode </li></ul><ul><li>Idea supported by high resolution laser shadowgraphs, showing short life time and small dimensions, spike noise in ion current, etc. </li></ul>
  15. 15. Macroparticles
  16. 16. Macroparticles <ul><li>Spray of liquid metal droplets from the cathode spot </li></ul><ul><li>small fraction of cathode erosion for refractory metals </li></ul><ul><li>large fraction of cathode erosion for low melting point cathode materials </li></ul><ul><li>exponentially decreasing size distribution function </li></ul><ul><li>most mass in the 10-20   m diam range </li></ul><ul><li>preferentially emitted close to cathode plane </li></ul><ul><li>Downward pressure from plasma jet on liquid surface </li></ul>
  17. 17. II. Vacuum Arc Engineering <ul><li>Coating forms on any substrate intercepting part of plasma jet </li></ul><ul><li>In vacuum, coating composition  cathode composition </li></ul><ul><li>In reactive gas background, can form compounds (nitrides, oxides, carbides, etc.) </li></ul>
  18. 18. II. Vacuum Arc Engineering <ul><li>Arc Ignition </li></ul><ul><li>Cathode Spot Confinement and Motion </li></ul><ul><li>Heat Removal </li></ul><ul><li>Macroparticle Control </li></ul>
  19. 19. Arc Ignition <ul><li>Problem: extremely high voltage needed to break-down vacuum gap (~100 kV/cm) </li></ul><ul><li>Drawn-arc (most common) </li></ul><ul><ul><li>Trigger electrode, mechanically operated </li></ul></ul><ul><ul><li>Connected to +voltage (e.g. anode via current limiting resistor) </li></ul></ul><ul><ul><li>Momentary contact with cathode </li></ul></ul><ul><ul><li>Arc ignited when contact broken </li></ul></ul><ul><ul><ul><li>Current transfers to main anode </li></ul></ul></ul><ul><li>Breakdown to trigger electrode </li></ul><ul><ul><li>Vacuum gap </li></ul></ul><ul><ul><li>Sliding spark </li></ul></ul><ul><li>Laser ignition </li></ul>
  20. 20. Controlling Cathode Spot Location and Motion <ul><li>Objectives: </li></ul><ul><ul><li>Locate CS’s on ‘front’ surface of cathode </li></ul></ul><ul><ul><ul><li>Maximize plasma transmission to substrates </li></ul></ul></ul><ul><ul><ul><li>Prevent damage to cathode structure </li></ul></ul></ul><ul><ul><li>Methods: </li></ul></ul><ul><ul><ul><li>Magnetic Field (retrograde and “acute angle” motion </li></ul></ul></ul><ul><ul><ul><li>Passive border </li></ul></ul></ul><ul><ul><ul><li>Strellnitski shield </li></ul></ul></ul><ul><ul><ul><li>Pulsed arc </li></ul></ul></ul>
  21. 21. Magnetic Control of Cathode Spots
  22. 22. Passive Border
  23. 23. Strelnitski Shield
  24. 24. Pulse Control <ul><li>Basic Idea: arc duration shorter than CS travel time to edge </li></ul><ul><ul><li>Short Pulse </li></ul></ul><ul><ul><li>Laser Ignition </li></ul></ul><ul><ul><li>Long Pulse - Long Cathode </li></ul></ul><ul><ul><li>Active detection of CS location – </li></ul></ul><ul><ul><ul><li>quench arc when CS reaches edge </li></ul></ul></ul>
  25. 25. Heat Removal <ul><li>Total power P = V arc I arc </li></ul><ul><ul><li>V arc ~20-40 V </li></ul></ul><ul><ul><li>I arc ~ 50-1000 A </li></ul></ul><ul><ul><li>P > 1 kW </li></ul></ul><ul><li>Distribution </li></ul><ul><ul><li>~1/3 in cathode </li></ul></ul><ul><ul><li>~2/3 in anode </li></ul></ul><ul><ul><li>Substrate: </li></ul></ul>
  26. 26. Heat Removal from Cathode <ul><li>Cool cathode important to </li></ul><ul><ul><li>minimize MP generation </li></ul></ul><ul><ul><li>Prevent cathode damage </li></ul></ul><ul><li>In best case, C.S.’s rapidly moved around to give on average a uniform heat flux on cathode surface S=P/A </li></ul>
  27. 27. Heat Removal from Cathode, cont’d <ul><li>Then average surface Temp (far from C.S.) given by </li></ul>h c – contact heat transfer coefficient h w – heat transfer coefficient to water
  28. 29. Substrate Temperature Control <ul><li>T s critical in determining coating properties </li></ul><ul><li>Measure with IR radiation detector </li></ul><ul><li>T s determined by balance between heating and cooling processes </li></ul><ul><li>Often use heat flux from process to control T s </li></ul><ul><ul><li>Vary bias or arc current </li></ul></ul>
  29. 30. Macroparticle Control <ul><li>3 Approaches </li></ul><ul><ul><li>Ignore </li></ul></ul><ul><ul><ul><li>Get good results (e.g. with tool coatings) despite (or because of?) MPs </li></ul></ul></ul><ul><ul><li>Minimize MP Production/Transmission </li></ul></ul><ul><ul><li>Remove MPs </li></ul></ul>
  30. 31. Minimize MP Production/Transmission <ul><li>Choose refractory cathode material </li></ul><ul><ul><li>“ Poison” (i.e. nitride) cathode surface </li></ul></ul><ul><ul><ul><li>Operate at ‘higher’ N 2 background pressure </li></ul></ul></ul><ul><li>Low cathode temperature </li></ul><ul><ul><li>direct cooling </li></ul></ul><ul><ul><li>lower current (  lower deposition rate) </li></ul></ul><ul><li>Place substrates where plasma flux max, MP flux min </li></ul>
  31. 33. Macroparticle Removal <ul><li>Filtered Vacuum Arc Deposition </li></ul><ul><ul><li>Use magnetic field to bend plasma beam around an obstacle which blocks MP transmission </li></ul></ul>
  32. 34. VENETIAN BLIND
  33. 35. Two quarter-torus filtered arcs at Tel Aviv University
  34. 38. Filtered Arc – Advantages and Disadvantages <ul><li>Advantages </li></ul><ul><ul><li>High quality, very smooth coatings </li></ul></ul><ul><ul><li>‘ almost’ MP free </li></ul></ul><ul><ul><li>Can achieve higher deposition rate than other ‘high quality’ techniques </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Usually poor plasma transmission </li></ul></ul><ul><ul><ul><li>Material utilization efficiency low </li></ul></ul></ul><ul><ul><li>Much slower than unfiltered arc deposition </li></ul></ul><ul><ul><li>Bulky equipment </li></ul></ul>
  35. 39. Other Arc Modes <ul><li>Hot Anode Vacuum Arc </li></ul><ul><ul><li>Crucible anode </li></ul></ul><ul><li>Hot Refractory Anode Vacuum </li></ul>
  36. 40. 10  m
  37. 41. III. How can we coat the inside of:
  38. 42. Approach 1: Ignore MPs
  39. 43. Approach 1: Ignore MPs <ul><li>Cavity serves as vacuum chamber and anode </li></ul><ul><li>Various techniques for magnetically controlling c.s. motion </li></ul>
  40. 44. Approach 2: Miniature Filter: Example – Welty Rect. Filter
  41. 45. Approach 2: Miniature Filter: Another Example <ul><li>Progress in Use of Ultra-High Vacuum Cathodic Arcs for Deposition of Thin Film Superconducting Layers </li></ul><ul><li>J.Langner, M.J.Sadowski, P.Strzyzewski, R.Mirowski, J.Witkowski, S.Tazzari, L.Catani, A.Cianchi, J.Lorkiewicz, R.Russo, T.Paryjczak, J.Rogowski, J.Sekutowicz </li></ul><ul><li>Presentation 28 Sept at XXXIII-ISDEIV in Matsue, Japan </li></ul><ul><li>Showed use of a cylindrical “Venetian Blind” filter to deposit Nb inside cavity! </li></ul>
  42. 46. Approach III. Beilis “black-body” HRAVA deposition device
  43. 47. Interior Coatings - Considerations <ul><li>Use cavity as vacuum chamber </li></ul><ul><ul><li>Need complicated end seal to allow for electrical connections (main arc and trigger), cooling water, in some cases motion </li></ul></ul><ul><ul><li>Cooling can be applied directly to outside of tube </li></ul></ul><ul><li>Fitting everything into cavity – difficult! </li></ul><ul><li>Integrity, lifetime? </li></ul><ul><li>Triggering – not shown </li></ul>
  44. 48. Summary and Conclusions <ul><li>VAD uses inherent properties of cathode spot plasma jets to rapidly deposit dense, high quality coatings </li></ul><ul><li>Successful implementation requires “plasma engineering” to: </li></ul><ul><ul><li>Confine cathode spots on desired surface </li></ul></ul><ul><ul><li>Remove process heat </li></ul></ul><ul><ul><li>Control macroparticle contamination </li></ul></ul>
  45. 49. Summary and Conclusions, cont’d <ul><li>Several approaches exist for efficiently and rapidly coating interior of RF cavities </li></ul><ul><ul><li>But with technical difficulties </li></ul></ul>

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