Chemical Vapor Deposition

1. Chemical Vapor Deposition This presentation is partially animated. Only use the control panel at the bottom of screen to review what you have seen. When using your mouse, make sure you click only when it is within the light blue frame that surrounds each slide.

2. Introduction to Chemical Vapor Deposition A) Chemical Vapor Deposition CVD Types CVD Uses CVD Process General CVD Reactor Concept General CVD Process Advantages General CVD Process Applications B) Dealing with Engineering Science of CVD Reactions Transport Processes Laminar Flow Boundary Layer Concept Other Susceptor to Flow Axis Options Thermodynamics Reaction Kinetics C) Operational Overview Polycrystaline Silicon Silicon Dioxide Nitride Films

3. Chemical Vapor Deposition Current Options LPCVD APCVD Atmospheric Pressure CVD Low Pressure CVD PECVD Plasma Enhanced CVD

4. Polycrystalline Silicon Chemical Vapor Deposition CVD Applications Customized Surfaces Epitaxial Layers Insulator Conductors CVD Silicon dioxide Barriers Silicon Nitride

5. r g r = Growth Rate of Film g Chemical Vapor Deposition CVD Process Input Flow Rate Arrival Flow Rate Growth Rate Film Surface Reaction Surface Reaction Rate Substrate

6. CVD Reactor Concept Reaction Chamber Susceptor Controlled Thermal Environment Controlled Pressure Environment

7. General CVD Process Applications Epitaxial Films Enhance performance of Discreet and Integrated Bipolar Devices Allow Fabrication of RAM’s and CMOS in Bulk Substrate Dielectrics Insulation between Conducting Layers Diffusion and Ion Implant Masks Capping Dopant Films Extracting Impurities Passivation to Protect Structures from Impurities Moisture Scratches Polysilicon Conductors Gate Electrodes Conductors for Multilevel Metalizations Contacts for Shallow Junction Devices General CVD Process Advantages Excellent Step Coverage Large Throughput (100 A/min film growth) Low Temperature Processing (450 to 1000 C) Applicable to any Vaporization Source Technology (Laser CVD for direct Writing)

8. Transport Processes Turbulent Flow No, to Many Particles. Molecular Flow No, to Low a Throughput B) Dealing with Engineering Science of CVD Reactions Transport Processes Thermodynamics Reaction Kinetics Laminar Flow ( Only One Left, Make Do) Set Conditions For Laminar Flow ( Low Reynolds Number Value)

9. Tube Diameter Gas Density Gas Viscosity D µ R = D V ( ) # Reynolds Number Linear Velocity

10. % ' 0 . 33 " $ Reagent’s Gas Phase Coefficient of Thermal Diffusion Laminar Flow Conditions Diameter and velocity in tens of cm and cm/s will give Reynolds numbers in laminar flow regime Reagent Partial Pressure 5 1.67 R = 1.76 x 10 ( D /R) (1/ T ) ( T/ y ) (Z) P) $ Growth Boundary Layer Thickness

11. X X X X 1 2 3 4 X X X X 4 1 Under developed flow pattern at this position along susceptor 2 3 Velocity Gradient Profiles at Discrete Points along Flow Axis Input Reactant Gas Flow Boundary layer develops along susceptor flow axis Susceptor Distance Above Susceptor Graphic Exaggerated for Visual Effect

12. X X X X 4 1 Under developed flow pattern at this position along susceptor 2 3 Velocity Gradient Profiles at Discrete Points along Flow Axis Trends in Gradients Velocity Values Increase Along Susceptor Increase Above Susceptor Temperature Values Increase Along Susceptor Decrease Above Susceptor Reactant Concentration Value Decrease Along Susceptor Increase Above Susceptor

13. A) Input gas flow B) Input gas flow C) Input gas flow D) Input gas flow E) Input gas flow Other Susceptor to Flow Axis Options Design Factors Include Flow Direction and Wafer Angle

14. K.E. Spear th 7 Conference on CVD 1979 Electrochemical Society Vol 79 Thermodynamics CVD Phase Diagram Give range of input conditions for CVD that could produce specific condensed phases. . Presented as Function of Temperature or Pressure vs Mole Fraction Boron codeposit only in High Boron Mole Fractions in input stream 0.01 Atm 1.0 Atm o 1400 C Boron codeposition favored at higher pressures. o 1200 C TiB Phase 2 TiB2 &B Phase o 1000 C H/HCl = 0.95 0.6 Reactant Gas Mole Fraction B/(Ti + B) Use Graphic for Educational Value Only

15. Boron-Carbon CVD Phase Diagrams BCl /CH = 4 -1 10 3 4 B C + B 4 -2 10 0 1600 C B C + C 4 B 1.0 Atm -3 10 B C 4 -4 10 Vapor Carbon -4 -3 -2 -1 -0 10 10 10 10 10 Partial Pressure for Methane Bernard Ducarroir J. Electrochem. Soc. 123 ,136, 1976 Use Graphic for Educational Value Only

16. Vanadium-Silicon-Hydrogen-Chloride CVD Phase Diagrams

18. Reaction Kinetics Titanium Diboron Deposition Arrhenius Plot Reaction Temperatures (2000 K to 1000 K) P = 0.263 Atm. 10.0 Input flow Rate = 462 cc /min 1.0 B/(B + Ti) = 0.66 Input Gases Cl/(Cl + H) = 0.33 TiCl 4 BCl 3 H 6.0 5.0 7.0 8.0 9.0 2 -1 1/T (x 10 / K) Besmann ,J. Electrochem. Soc. 124 , 790 (1979) Use Graphic for Educational Value Only

19. 10.0 (f) 1.0 (a) 1/T Higher Surface Reaction Rates Lower Surface Temperatures Arrhenius Rate Profiles Use Graphic for Educational Value Only

20. Arrhenius Isotherms (f) Surface Reaction Limiting Growth Rate 10.0 1.0 (a) Partial Pressure Reactant Gas Use Graphic for Educational Value Only

21. Operational Line for Deposition at Higher Pressure Desired Growth Rate Best Fit Model Behavior based On 5 Calibration Runs r g2 r g1 Current Growth Rate 1/ T 1/ T 2 1 New Operating Current Temperature Operating Temperature 1 / T ' & ) ln ( r / r ) ( q / k ) ( T T / T T + g2 g1 act 2 1 2 1

22. H Si H H H APCVD LPCVD o o 575 to 650 575 to 650 C C 25 PA to 130 PA 25 PA to 130 PA Si 100% Silane 20% to 30% Silane High Exposure Limit Si Si Pyrophoric Considerations Toxic ( 1 Atm but 90% N ) 2 Temperature At high temperatures get gas phase reactions that produce rough, loosely adhering deposits and poor uniformity. At low temperatures deposition rates are to slow for industrial situations. o Zone heating rear of furnace up to 15 C hotter. (Better film uniformity) Pressure (LPCVD) Four popular ways to alter pressure. Change gas flow rate but keep pumping speed constant. Change pumping speed with constant flow rate Change reacting gas or carrier gas with other held constant Change both gases but keep there ratio constant. C ) Operational Overviews Polycrystalline Silicon (Polysilicon)

23. 3 Low film density ( 2. 0 g/cm ) Silicon dioxide Low Temperature Loose adhering deposits on side walls of reactor. ( Particles that can contaminate the film. At high silane pressures allows for gas phase reactions. ( Promotes particle contamination and hazy films) Fair step coverage Deposition rate complex function of Oxygen concentration Easy chemical reaction. ( Low activation energy, 0.4 ev (10 kcal/mole) ) Film depends on gas phase transport of material to surface Low temperature allows production of films that will serve as insulation between aluminum levels in device.

24. Medium Temperature Silane Tetraethoxysilane TEOS OCH CH 2 3 H H H H H Si C Si C C H H C O O O H H H H H CH CH 2 3 650 to 750 C (LPCVD) 650 to 750 C 100 to 1000 std. cc / min NO 30 PA to 250 PA SiO SiO 2 2

25. High Temperature Nonlinear pressure dependence that is function of wafer position. Small amounts of Chlorine in films that tends to cause cracking in a poly layer) Reagent depletion problems Phosphorus doping is difficult. ( The phosphorus oxides are volatile at high deposition temperatures.) Excellent Uniformity

26. Cl H Si H Cl N H H H H N Si Cl Cl H Cl Cl Cl Cl H Si H Cl H Si H Cl N H H H Precursor Cl First Monolayer of Silicon Nitride Pad Silicon Dioxide Except for epi and parallel plate processes both sides of wafer are coated. Equipment Furnace with or without vacuum capability Plasma Chamber CVD is Crucial to Fabrication of IC's, Especially MOSFETS (The Bottom Line)