Surface Presentation

Chemical Vapour Deposition Presented by:Kashif Mairaj

( 601E03 )

University of the Punjab, Lahore, Pakistan. 11/30/08

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Contents • • • • • • • • • • • •

Introduction Basics of CVD General Requirements of CVD Types of CVD Chemical Reactions in CVD Step by Step Fundamentals CVD Reactors Applications Advantages Disadvantages Comparison Conclusion

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Introduction to CVD

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Basics of CVD • Chemistry of CVD • Thermodynamics of CVD • Kinetics of CVD • Transport of Gas 11/30/08

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Thermodynamics of CVD A+B

P

(CA.CB)/CP=K(T)/P2 ΔG=∆G° + RTlnK At Equilibrium ∆G°=-RTlnK “K” is found 11/30/08

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Kinetics of CVD

R = R0exp(-Ea/KT) 11/30/08

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General Requirements • Temperature of Substrate

• Energy Sources for CVD

• Precursors

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Types Of CVD • APCVD-Atmospheric Pressure CVD • LPCVD-Low Pressure CVD • MOCVD-Metallorganic CVD • OMCVD-Orgaometallic CVD • PECVD-Plasma Enhanced CVD • LACVD-Laser Assisted CVD • IICVD-Ion Induced CVD 11/30/08

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CVD Reaction Types • Pyrolysis • Reduction • Oxidation • Compound Formation • Disproportionation • Reversible Transfer 11/30/08

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Pyrolysis • AB(g) -- A(s) + B(g)

•

SiH4(g) --

Si(s) + 2H2(g)

at 650°C

• Use to Deposite Al, Ti, Pb, Mo, Fe, Ni, B, Zr, C, Si, Ge, SiO2, BN, Al2O3, MnO2, Si3N4 11/30/08

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An Example

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Reduction • AX(g) + H2(g) -- A(s) + HX(g) • Often lower temp than Pyrolysis • Reversible Ex: W deposition at 300°C

WF6(g) + 3H2(g) -- W(s) + 6HF(g) 300°C

at

Use to Deposit Al, Ti, Sn, Ta, Nb, Cr, Mo, Fe, B, Si, Ge, TaB, TiB2, SiO2, BP, Nb3Ge 11/30/08

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Oxidation •

AX(g) + O2(g) -- AO(s) + X(g)

• Ex: SiO2 deposition from silane and oxygen at 450°C

• SiH4(g) + O2(g) -- SiO2(s) + 2H2(g) Use to Deposit Al2O3, TiO2, SnO2, ZnO…… 11/30/08

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Compound Formation • AX(g) + NH3(g) -- AN(s) + HX(g) • AX(g) + H2O(g) -- AO(s) + HX(g) • Ex: Use of Ammonia gas • BF3(g) + NH3(g) -- BN(s) +3HF(g) 1100°C Use to Deposit TiN, TaN, AlN, SiC, Al2OKashif , SiO2 3, SnO 11/30/08 Mairaj2

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Disproportionation • 2AB(g) -- A(s) + AB2(g) Compounds involving elements with multiple states

Use to deposit

Al, C, GeSi, III-V Compounds

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Reversible Transfer • As4(g) + As2(g) + 3H2(g) -- 6GaAs(s) +6HCl(g) Driven)

(Entropically

Use to deposit GaInAs, AlGaAs, InP, FeSi2 11/30/08

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Step by Step Fundamentals

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CVD Reactors

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Applications • Coatings • • • •

To improve Wear resistance To enhance Corrosion resistance High temperature protection Erosion protection

• Semiconductors • Integrated circuits • Single crystal Growth 11/30/08

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Application • Dense Structural Parts • Optical Fibers • Composite (Ceramic matrix composites)

• Powder Production • Catalysts • Nanomacines

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Advantages of CVD • Gas Phase provides • • • • •

Uniform temperature within coating retort Uniform Concentration of deposited species Deposition rate is similar at all surfaces Variable shaped surfaces can be coated efficiently Give reasonable access of gases or powders in blind holes, screw threads, recesses and channels

• It is possible to form ductile CVD layers

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Disadvantages of CVD • CVD Process is carried out at relatively high • •

temperatures. Dimensional Tolerances limitation are important considerations. Some time reheating of the substrate after coating may be a problem.

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References • Books

• An Introduction to Surface Chemistry by Dr. Roger • •

• • • • •

Nix, Department of chemistry, University of London. Handbook of Tribology by Bharat Bhushan & B.k. Gupta Handbook of Chemical Vapour Deposition: principles, technologies and applications by H.O Pierson

Web Links www.timedomaincvd.com/cvd_fundamentals www.AZOM.com www.cvdtechnologies.co.uk/cvd http://chiuserv.ac.nact.edu

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