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chemical vapor deposition Cvd

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chemical vapor deposition

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chemical vapor deposition Cvd

  1. 1. CVD
  2. 2. MOS Transistor
  3. 3. CVD Thin Film Growth 1 2 3 4 5 6
  4. 4. Atmospheric Pressure CVD
  5. 5. Atmospheric Pressure CVD
  6. 6. Atmospheric Pressure CVD Horizontal type Barrel type
  7. 7. Atmospheric Pressure CVD
  8. 8. Low Pressure CVD
  9. 9. Low Pressure CVD
  10. 10. Laser Enhanced CVD
  11. 11. Plasma Enhanced CVD
  12. 12. Plasma Enhanced CVD
  13. 13. Plasma Enhanced CVD
  14. 14. Thin Film Deposition• Quality – composition, defect density, mechanical and electrical properties • Uniformity – affect performance (mechanical , electrical) Thinnin g leads to ↑ R Voids: Trap chemicals lead to cracks (dielectric) large contact resistance and sheet resistance (metallization) AR (aspect ratio) = h/w ↑ with ↓ feature size in ICs.
  15. 15. Examples Poor step coverage with increasing AR Thinning causes metal resistance to increase, generates heat and lead to failure
  16. 16. Chemical Vapor Deposition Flat on the susceptor Cold wall reactor Methods of Deposition: Chemical Vapor Deposition (CVD):APCD, LPCVD, HDPCVD Physical Vapor Deposition (PVD: evaporation, sputtering) Atmospheric Pressure : APCVD Cold wall reactors (walls not heated - only the susceptor) Low pressure: LPCVD – batch processing. Hot wall reactor
  17. 17. Atmospheric Pressure Chemical Vapor Deposition Transport by forced convection By diffusion through boundary layer Diffusion through the B. L Desorption of by products Transport of byproducts by forced convection @ the surface (4): decomposition, reaction, surface migration attachment etc. (3) May be desorption which depends on a sticking coefficient  (4) Growth rate for Si deposition N=5•1022 cm-3 Mole fraction of the incorporating species in the gas phase. Partial pressure Total concentration in the gas phase CT = 1 * 1019 cm-3 5 * 1022 V = 0.14 µm/min PG @ 1 torr Ptotal = 1 atm = 760 torr adsorption transport reaction Steady state Steps in deposition As in Deal-Grove model for oxidation
  18. 18. Growth Kinetics Determined by the Smaller of ks or hG Two limiting cases 1) Surface reaction ks << hG Control: fast transport slow reaction Yk N C v S T = 2) Mass transfer or gas phase diffusion hG << ks Yh N C v G T = Fast reaction and slow transport. Temperature uniformity more important than the gas flow  wafers vertically  poly-Si Put wafers flat to ensure flow uniformity @ the Si surface. Epitaxy APCVD SiO2 (111) Si shows slower v – fewer attachment sites than in (100) Si Ea ≈ 1.6 eV for all Si sources  H desorption from the Si surface. With H2 as a gas carrier Light mass heavy Limited by transport Both are linear with time (t) SiH4 the fastest growth kS limited deposition is VERY temp sensitive. hG limited deposition is VERY geometry (boundary layer) sensitive
  19. 19. Boundary Layer – Diffusion to the Surface Gas moves with the constant velocity U. Boundary layer (caused by friction ) increases along the susceptor, mass transfer coefficient hG decreases, gas depletion caused by consumption of the reacting species (concentrations decrease) Growth rate decreases along the chamber • Use tilted susceptor • Use T gradient 5-25°C • Gas injectors along the tube • Use moving belt Deposition of alloys DIFFICULT – various reactions, kinetics (species, precursors) Use PVD rather than CVD B.L. viscosity gas density

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