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Microelectronics Processing Physical Vapor Deposition

Microelectronics Processing Physical Vapor Deposition. Issues. Vacuum basics Vacuum Technology basics Some vacuum systems Evaporation Sputter deposition Metallization. Vacuum basics. Kinetic theory of gases At relatively low pressures Not too low temperatures

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Microelectronics Processing Physical Vapor Deposition

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  1. Microelectronics ProcessingPhysical Vapor Deposition Microelectronics processing - E. Finkman

  2. Issues • Vacuum basics • Vacuum Technology basics • Some vacuum systems • Evaporation • Sputter deposition • Metallization Microelectronics processing - E. Finkman

  3. Vacuum basics • Kinetic theory of gases • At relatively low pressures • Not too low temperatures • Molecules described as rigid balls • Constant velocity • Elastic collisions • Redistribution of kinetic energy Microelectronics processing - E. Finkman

  4. Vacuum basics Ideal gas law PV = nRT (1) P - pressure V - volume T - temperature n - number of moles R - gas constant Microelectronics processing - E. Finkman

  5. Vacuum basics Ideal gas law PV=nRT (1) P - pressure V - volume T - temperature N - number of moles R - gas constant 1 R=kBNAV kB= 1.38x10-23 J/molec K NAV= 6x1023 molec/mol Microelectronics processing - E. Finkman

  6. Vacuum basics The average molecular speed vav= (8kBT/M)1/2 (2) M – molecular weight The average time between collisions tav= 1/(21/2 Nd2vav )(3) d – molecular diameter N – number density of molecules (per unit volume) Microelectronics processing - E. Finkman

  7. Vacuum basics The average distance between collisions (the Mean Free Path -  )  = 1/(21/2Nd2) (4) Thus, if  is larger than the dimension of the chamber, the particles will travel without collisions! Thus, if  is larger than the dimension of the chamber, the particles will travel without collisions! Microelectronics processing - E. Finkman

  8. Vacuum basics In order to increase the mean free path we have to reduce N reduce P Microelectronics processing - E. Finkman

  9. Vacuum basics Microelectronics processing - E. Finkman

  10. Vacuum basics Microelectronics processing - E. Finkman

  11. Vacuum basics Microelectronics processing - E. Finkman

  12. Vacuum basics - Conclusions - I When the gas flows through a system with Dimensions V1/3>> , flow is viscous. When P is lowered,  increases If  exceeds system dimensions, the flow becomesmolecular. Reducing P Molecular flow No collision between source and target (less contamination) Microelectronics processing - E. Finkman

  13. Vacuum basics - Conclusions - II Surface and film contamination is determined by the background pressure of the chamber, or by the ratio between the partial pressure of the desired species and that of the background molecules in the chamber. Example: what is the value of P for flow through a tube 5 cm in diameter to be molecular? Microelectronics processing - E. Finkman

  14. Vacuum Technology basics S – Pumping speed (volume per unit time, l/sec) Q – Flow to the pump (mass per unit time, ) Q = PS The lowest pressure achievable by a given pump: P = Q/S Microelectronics processing - E. Finkman

  15. Vacuum Technology basics • P = Q/S • This equation holds when gas is inserted to the chamber • A leak: • Gas flows intentionally into the chamber • Imperfect seal (air leaks in from the outside) • Outgasing from chamber walls Microelectronics processing - E. Finkman

  16. Vacuum Technology basics The effect of tubes, orifices, restrictions are measured in terms of the conductance C = Q/P P = P1 –P2 Two obstacles in series, C1and C2: C-1 = C1-1+ C2-1 Tubes, constrictions, valves, and other components reduce system conductance. Microelectronics processing - E. Finkman

  17. Typical Vacuum System 1 5 4 2 6 3 Microelectronics processing - E. Finkman

  18. Rotary pumps Microelectronics processing - E. Finkman

  19. Rotary pump with gas ballast Microelectronics processing - E. Finkman

  20. Root pump Microelectronics processing - E. Finkman

  21. Sorption pumps ~800m2/cm3 Microelectronics processing - E. Finkman

  22. High vacuum pumps: Diffusion pump Gaede 1913 Microelectronics processing - E. Finkman

  23. Diffusion pump disadvantage • Diffusion pumps are based on boiling oil. • Oil can be transported to the chamber by • back-streaming, causing contamination • to the processed semiconductor. • Partial solutions: • Use low vapor pressure oil • Insert a cold trap over the pump Microelectronics processing - E. Finkman

  24. Cryogenic Pump Turbo Molecular Pump High vacuum pumps: cryogenic pump • High pumping speed • High throughput for H2O • Momentary power loss is • detrimental. • Large capacity • Need regeneration Microelectronics processing - E. Finkman

  25. Cryogenic Pump Turbo Molecular Pump High vacuum pumps: turbo-molecular pump • High speed rotation • blades. • Require backing • pump. • Produces vibration. Microelectronics processing - E. Finkman

  26. Pumping speed (l/sec) Pressure (torr) Speed versus pressure comparison –clarify pump choice Microelectronics processing - E. Finkman

  27. Evaluation of vacuum pumps Microelectronics processing - E. Finkman

  28. Measurement of Pressureand LeakDetection Microelectronics processing - E. Finkman

  29. Pressure Gauges Microelectronics processing - E. Finkman

  30. Mechanical Gauges Bourdon Gauge Diaphragm Gauge Microelectronics processing - E. Finkman

  31. Reference point in measuring Pressure Microelectronics processing - E. Finkman

  32. A mechanical Gauge Capacitance gauge: the deflection of a membrane Is measured as a change in capacitance Microelectronics processing - E. Finkman

  33. Thermocouple Gauge • A filament is heated by a constant DC current (20 to 200mA) • The filament is exposed to the gas • The heat in the filament is transported to the gas • As the pressure decreases, the temperature increases • We measure the temperature of the filament (by a thermocouple) • The pressure is obtained by an output voltage (V<20 mV DC) • Pressure range: 2 Torr – 10-3 Torr • With an industrial D/A converter, range extended to 103 – 10-3 Torr • Pirani sensor: the filament is a thermal resistor Microelectronics processing - E. Finkman

  34. Hot Cathode ion Gauge Refined by Bayard-Alpert – 1950 Range: 10-2 – 10-10 Torr Microelectronics processing - E. Finkman

  35. Cold cathode Vacuum Gauge Microelectronics processing - E. Finkman

  36. Leaks and leak testing Microelectronics processing - E. Finkman

  37. Places likely to leak • O-rings seals • metal gaskets • electrical feedthroughs • shut-off valves with through leaks, • internal welds/brazes on utility pipes • chamber welds Microelectronics processing - E. Finkman

  38. Reasons for poor vacuum • high vacuum pump failing • high solvent concentration in pump oil • poor quality oil in a mechanical pump • sample outgassing • outgassing from new chamber fixturing • increased vapor pressure due to heating • venting to air during humid weather • helium permeation through rubber or plastic components Microelectronics processing - E. Finkman

  39. Residual Gas Analysis - Principle Mass separation Quadrupole mass spectrometer Microelectronics processing - E. Finkman

  40. Residual Gas Analysis - Principle Lorentz force law F =q(E+vXB( Newton’s 2nd law F=ma Mass spectrometry m/q=E+vXB Microelectronics processing - E. Finkman

  41. Physical Vapor Deposition:1. Evaporation Schematic diagram of evaporation equipment • Types of evaporation sources: • Filament evaporation; • Electron beam source. Microelectronics processing - E. Finkman

  42. Evaporation geometry for system using planetary substrate hoder Microelectronics processing - E. Finkman

  43. The evaporation rate in g/sec is estimated to be Where AS the source area in cm 2, m is the gram-molecular mass, T the temperature in K, and Pe the vapor pressure in torr. Source evaporation rate Problem alloying! Microelectronics processing - E. Finkman

  44. The Contact Hole Filling Problem: The atoms are coming in straight line from a “point source”, i.e. their incidence on the sample is nearly perpendicular. The hole filling problem looks like this: The actual situation may look slightly better, due to a small sticking coefficient, which is the ratio of the number of atoms that “stick” on the surface relative to the number of incident atoms: SC = Freacted/Fincident . But this effect is usually not so dramatic. Evaporation – Why is not being used in present day Si technology? Microelectronics processing - E. Finkman

  45. -V (DC) (glow discharge) Cathode shield Schematic diagram of DC powered sputter deposition equipment Vacuum ground DC Sputter deposition ~-100-1000V Microelectronics processing - E. Finkman

  46. DC Sputter systemPlasma structure and voltage distribution Al, W, Ti, silicides, other metals Microelectronics processing - E. Finkman

  47. Basic properties of plasma Microelectronics processing - E. Finkman

  48. Basic properties of plasma Microelectronics processing - E. Finkman

  49. Processes in sputter deposition Microelectronics processing - E. Finkman

  50. Sputtering yield in a DC system Microelectronics processing - E. Finkman

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