1 / 42

Advanced Deposition Techniques in Semiconductor Fabrication

Explore the methods and critical issues of depositing materials in semiconductor fabrication, covering dielectrics, metals, semiconductors, and more. Learn about chemical vapor deposition, physical deposition, and sputtering processes used in creating layers such as SiO2, poly-silicon, and nitrides.

briones
Download Presentation

Advanced Deposition Techniques in Semiconductor Fabrication

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 12.0 Deposition

  2. Materials Deposited • Dielectrics • SiO2, BSG • Metals • W, Cu, Al • Semiconductors • Poly silicon (doped) • Barrier Layers • Nitrides (TaN, TiN), Silicides (WSi2, TaSi2, CoSi, MoSi2)

  3. Deposition Methods • Growth of an oxidation layer • Spin on Layer • Chemical Vapor Deposition (CVD) • Heat = decomposition T of gasses • Plasma enhanced CVD (lower T process) • Physical Deposition • Vapor Deposition • Sputtering

  4. Critical Issues • Adherence of the layer • Chemical Compatibility • Electro Migration • Inter diffusion during subsequent processing • Strong function of Processing • Even Deposition at all wafer locations

  5. CVD of Si3N4 - Implantation mask • 3 SiH2Cl2 + 4 NH3Si3N4 + 6 HCl + 6 H2 • 780C, vacuum • Carrier gas with NH3 / SiH2Cl2 >>1 • Stack of wafer into furnace • Higher temperature at exit to compensate for gas conversion losses • Add gases • Stop after layer is thick enough

  6. CVD of Poly Si – Gate conductor • SiH4Si + 2 H2 • 620C, vacuum • N2 Carrier gas with SiH4 and dopant precursor • Stack of wafer into furnace • Higher temperature at exit to compensate for gas conversion losses • Add gases • Stop after layer is thick enough

  7. CVD of SiO2 – Dielectric • Si0C2H5 +O2SiO2 + 2 H2 • 400C, vacuum • He carrier gas with vaporized(or atomized) Si0C2H5and O2 and B(CH3)3 and/or P(CH3)3 dopants for BSG and BPSG • Stack of wafer into furnace • Higher temperature at exit to compensate for gas conversion losses • Add gases • Stop after layer is thick enough

  8. CVD of W – Metal plugs • 3H2+WF6 W + 6HF • T>800C, vacuum • He carrier gas with WF6 • Side Reactions at lower temperatures • Oxide etching reactions • 2H2+2WF6+3SiO2 3SiF4 + 2WO2 + 2H2O • SiO2 + 4HF  2H2O +SiF4 • Stack of wafer into furnace • Higher temperature at exit to compensate for gas conversion losses • Add gases • Stop after layer is thick enough

  9. Chemical Equilibrium

  10. CVD Reactor • Wafers in Carriage (Quartz) • Gasses enter • Pumped out via vacuum system • Plug Flow Reactor Vacuum

  11. CVD Reactor • Macroscopic Analysis • Plug flow reactor • Microscopic Analysis • Surface Reaction • Film Growth Rate

  12. Macroscopic Analysis • Plug Flow Reactor (PFR) • Like a Catalytic PFR Reactor • FAo= Reactant Molar Flow Rate • X = conversion • rA=Reaction rate = f(CA)=kCA • Ci=Concentration of Species, i. • Θi= Initial molar ratio for species i to reactant, A. • νi= stoichiometeric coefficient • ε = change in number of moles

  13. Combined Effects Contours = Concentration

  14. Reactor Length Effects SiH2Cl2(g) + 2 N2O(g) SiO2(s)+ 2 N2(g)+2 HCl(g) How to solve? Higher T at exit!

  15. Deposition Rate over the Radius CAs r Thiele Modulus Φ1=(2kRw/DABx)1/2

  16. Radial Effects This is bad!!!

  17. Combined Length and Radial Effects Wafer 10 Wafer 20

  18. CVD Reactor • External Convective Diffusion • Either reactants or products • Internal Diffusion in Wafer Stack • Either reactants or products • Adsorption • Surface Reaction • Desorption

  19. Microscopic Analysis -Reaction Steps • Adsorption • A(g)+SA*S • rAD=kAD (PACv-CA*S/KAD) • Surface Reaction-1 • A*S+SS*S + C*S • rS=kS(CvCA*S - Cv CC*S/KS) • Surface Reaction-2 • A*S+B*SS*S+C*S+P(g) • rS=kS(CA*SCB*S - Cv CC*SPP/KS) • Desorption: C*S<----> C(g) +S • rD=kD(CC*S-PCCv/KD) • Any can be rate determining! Others in Equilib. • Write in terms of gas pressures, total site conc.

  20. Rate Limiting Steps • Adsorption • rA=rAD= kADCt (PA- PC /Ke)/(1+KAPA+PC/KD+KIPI) • Surface Reaction • (see next slide) • Desorption • rA=rD=kDCt(PA - PC/Ke)/(1+KAPA+PC/KD+KIPI)

  21. Surface Reactions

  22. Deposition of Ge Ishii, H. and Takahashik Y., J. Electrochem. Soc. 135,1539(1988).

  23. Silicon Deposition • Overall Reaction • SiH4 Si(s) + 2H2 • Two Step Reaction Mechanism • SiH4 SiH2(ads)+ H2 • SiH2 (ads)  Si(s) + H2 • Rate=kadsCt PSiH4/(1+Ks PSiH4) • Kads Ct = 2.7 x 10-12 mol/(cm2 s Pa) • Ks=0.73 Pa-1

  24. Silicon Epitaxy vs. Poly Si • Substrate has Similar Crystal Structure and lattice spacing • Homo epitaxy Si on Si • Hetero epitaxy GaAs on Si • Must have latice match • Substrate cut as specific angle to assure latice match • Probability of adatoms getting together to form stable nuclei or islands is lower that the probability of adatoms migrating to a step for incorporation into crystal lattice. • Decrease temp. • Low PSiH4 • Miss Orientation angle

  25. Surface Diffusion

  26. Monocrystal vs. Polycrystalline PSiH4=? torr

  27. Dislocation Density • Epitaxial Film • Activation Energy of Dislocation • 3.5 eV

  28. Physical Vapor Deposition • Evaporation from Crystal • Deposition of Wall

  29. Physical Deposition - Sputtering • Plasma is used • Ion (Ar+) accelerated into a target material • Target material is vaporized • Target Flux  Ion Flux* Sputtering Yield • Diffuses from target to wafer • Deposits on cold surface of wafer

  30. DC Plasma • Glow Discharge

  31. RF Plasma Sputtering for Deposition and for Etching RF + DC field

  32. Target Al Cu TiW TiN Gas Argon Deposited Layer Al Cu TiW TiN Poly Crystalline Columnar Structure Sputtering Chemistries

  33. Deposition Rate • Sputtering Yield, S • S=α(E1/2-Eth1/2) • Deposition Rate  • Ion current into Target *Sputtering Yield • Fundamental Charge

  34. Sheath RF Plasma Plasma rf Sheath • Electrons dominate in the Plasma • Plasma Potential, Vp=0.5(Va+Vdc) • Va = applied voltage amplitude (rf) • Ions Dominate in the Sheath • Sheath Potential, Vsp=Vp-Vdc • Reference Voltage is ground such that Vdc is negative

  35. Floating Potential • Sheath surrounds object • Floating potential, Vf • kBTe=eV • due to the accelerating Voltage

  36. Plasma Chemistry • Dissociation leading to reactive neutrals • e + H2 H + H + e • e + SiH4  SiH2 + H2 + e • e + CF4  CF3 + F + e • Reaction rate depends upon electron density • Most Probable reaction depends on lowest dissociation energy.

  37. Plasma Chemistry • Ionization leading to ion • e + CF4  CF3- + F • e + SiH4  SiH3+ + H + 2e • Reaction depend upon electron density

  38. Plasma Chemistry • Electrons have more energy • Concentration of electrons is ~108 to1012 1/cc • Ions and neutrals have 1/100 lower energy than electrons • Concentration of neutrals is 1000x the concentration of ions

  39. Oxygen Plasma • Reactive Species • O2+eO2+ + 2e • O2+e2O + e • O + e  O- • O2+ + e  2O

  40. Plasma Chemistry • Reactions occur at the Chip Surface • Catalytic Reaction Mechanisms • Adsorption • Surface Reaction • Desorption • e.g. Langmuir-Hinshelwood Mechanism

  41. Plasma Transport Equations • Flux, J

More Related