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Microelectronics Processing Oxidation

Microelectronics Processing Oxidation. Properties of SiO 2 Oxidation Process Functions of SiO 2 Equipment for Si Oxidation Mechanism of Si Oxidation. Factors affecting oxidation Doping Substrate Orientation Pressure Chlorine addition Dopant Redistribution Polysilicon Oxidation

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Microelectronics Processing Oxidation

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  1. Microelectronics Processing Oxidation

  2. Properties of SiO2 Oxidation Process Functions of SiO2 Equipment for Si Oxidation Mechanism of Si Oxidation Factors affecting oxidation Doping Substrate Orientation Pressure Chlorine addition Dopant Redistribution Polysilicon Oxidation Additional Oxidation Processes Content

  3. Thermal SiO2 Properties

  4. Thermal SiO2 Properties (cont.) (7) Amorphous material

  5. Oxidation Process • Oxidation Techniques • Thermal Oxidation • Rapid Thermal Oxidation • Thermal Oxidation Techniques • Wet Oxidation • Si (solid) + H20 SiO2 (solid) + 2H2 • Dry Oxidation • Si (solid) + O2 (gas) SiO2(solid)

  6. Conceptual Si Oxidation System • Thermal Oxidation • Heat is added to the oxidation tube during the reaction ..between oxidants and silicon - 900-1,200C temperature range - Oxide growth rate increases as a result of heat • Used to grow oxides between 60-10,000Å

  7. Thermal Oxidation Process • Wafers are placed in wafer load station • Dry nitrogen is introduced into chamber - Nitrogen prevents oxidation from occurring • Nitrogen gas flow shut off and oxygen added to chamber - Occurs when furnace has reached maximum temperature - Oxygen can be in a dry gas or in a water vapor state • Nitrogen gas reintroduced into chamber - Stops oxidation process • Wafers are removed from furnace and inspected • Dry Thermal Oxidation Characteristics • Oxidant is dry oxygen • Used to grow oxides less than 1000Å thick • Slow process - 140 - 250Å / hour

  8. Dry Thermal Oxidation Process • Thin Oxide Growth • Thin oxides grown (<150Å) for features smaller than 1 ..micrometer - MOS transistors, MOS gates, and dielectric components • Additional of chemical species to oxygen decreases ..oxide growth rate (only in special cases) • - Hydrochloric acid (HCI) - Trichloroethylene (TCE) - Trichloroethane (TCA) • Decreasing pressure slows down oxide growth rate

  9. Wet Thermal Oxidation • Wet Thermal Oxidation Characteristics • Oxidant is water vapor • Fast oxidation rate - Oxide growth rate is 1000-1200Å / hour • Preferred oxidation process for growth of thick oxides

  10. Goal of Oxidation Process The goal of oxidation is to grow a high quality oxide layer on a silicon substrate

  11. Functions of Oxide Layers (1) • Passivation • Physically protects wafers from scratches and particle ..contamination • Traps mobile ions in oxide layer

  12. Function of Oxide Layers (2) • Masking • During Diffusion, Ion Implantation, and Etching SiO2

  13. Function of Oxide Layers (3) • Insulating Material • Gate region - Thin layer of oxide - Allows an inductive charge to pass between gate metal and silicon

  14. Function of Oxide Layers (4) • Dielectric Material • Insulating material between metal layers - Field Oxide

  15. Function of Oxide Layers (5) • Dielectric Material • Tunneling oxide - Allows electrons to pass through oxide without resistance

  16. Functions and Thickness of Oxide Layers

  17. Projections for Si Technology

  18. Thermal Oxidation Equipment Oxidation occurs in tube furnace - Vertical Tube Furnace - Horizontal Tube Furnace

  19. Wet Thermal Oxidation Techniques Bubbler

  20. Wet Thermal Oxidation Techniques Flash System

  21. Wet Thermal Oxidation Techniques Dryox System

  22. Thickness of Si consumed during oxidation

  23. Kinetics of Si02 Growth - Oxide Growth Mechanism • Oxidant (O2) reacts with silicon atoms • Silicon atoms are consumed by reaction • Layer of oxide forms on silicon surface

  24. Oxide Growth Mechanism (1) • Linear Parabolic Model • Linear (first) Stage of Oxidation - Chemical reaction between silicon and oxidants at wafer surface - Reaction limited by number of silicon atoms available to react with oxidants - During the first 500Å of oxide growth, the oxide grows linearly with time - Growth rate begins to slow down as oxide layer grows

  25. Oxide Growth Mechanism (2) • Linear Parabolic Model • Parabolic Stage - Begins when 1,000Å of oxide has been grown on silicon - Silicon atoms are no longer exposed directly to oxidants - Oxidants diffuse through oxide to reach silicon - Reaction limited by diffusion rate of oxidant

  26. Deal-Grove Model (1)

  27. Deal-Grove Model (2)

  28. Deal-Grove Model (3)

  29. Deal-Grove Model (4)

  30. Deal-Grove Model (5)

  31. Deal-Grove Model (6)

  32. Deal-Grove Model (7)

  33. Deal-Grove Model (8)

  34. Deal-Grove Model (9)

  35. (a) (b) a) Interface reaction is the rate limiting step b) Limited by oxidant transport through the SiO2 rate Limiting cases in Si oxidation

  36. Deal-Grove Model Parameters

  37. Deal-Grove model (10) - Effect of temperature on the rate constants B, and B/A B(T)=Boexp(-EA/kT) (B/A)(T)=(B/A)oexp(-EA/kT)

  38. Values for the coefficients Do and EA Each of the coefficients B, and B/A has an Arrhenius relationship of the type: D=D0exp(-EA/kT)

  39. Diffusivities of some materials in silicon glass

  40. Examples

  41. Effect of Xi on Wafer Topography (1)

  42. Effect of Xi on Wafer Topography (2)

  43. Factors that Affect Oxidation

  44. High Doping concentration effect • Dopants in silicon • Dopants increase oxide growth rate - During Linear Stage of oxidation N-type dopants increase growth rate • Dopants cause differential oxidation - Results in the formation of steps - Affects etching process

  45. High Doping concentration effect

  46. Wafer Orientation • Oxide grows faster on <111> wafers - more silicon atoms available to react with oxidant • Affects oxide growth rate during Linear Stage Growth Rate Dependence on Si Substrate Orientation

  47. Origin of Substrate Orientation Effect

  48. (a) (b) Growth of SiO2 on <100> and <111> oriented Si wafers: (a) dry oxygen; (b) steam. Substrate Orientation Effect - Oxidation Charts

  49. Effect of High Pressure Oxidation • Atmospheric pressure - Slow oxide growth rate • An increase in pressure increase oxide growth rate • Increasing pressure allows temperature to be ..decreased - Oxide growth rate remains the same - For every 10atm of pressure the temperature can be reduced 30°C • Dry Thermal oxidation - Pressure in oxidation tube increased • Wet Thermal oxidation - Steam pressure introduced into oxidation tube

  50. Effect of High Pressure Oxidation

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