General CVD Precursor Considerations

Volatility

• vapor pressure - simple molecules with high vapor pressure are rare
• determined by molecular weight and molecularity (degree polymerized) - result of structure and bonding
• control - temperature, valving

Stability, Reactivity, and Safety

• bond strength, bond dissociation energy - affects process temperature and film composition (purity)
• thermal stability in storage and delivery into the reactor
• reactivity of the precursor and byproducts towards other substances (including biological objects like us)

Single-Source Precursor

• providing more than one element into the film
• simpler delivery system
• uniform elemental distribution at atomic level possible
• limited composition range

Common Precursors

• hydrides: MH_x -
        SiH₄, GeH₄, AlH₃(NMe₃)₂, NH₃, PH₃ ...
 
• halides: MX_y -

TiCl₄, TaCl₅, MoF₆, WF₆, ...
 
• metal-organics -

metal alkyls: AlMe₃, AliBu₃, Ti(CH₂tBu)₄ ....
metal alkoxides: Ti(OiPr)₄, [Cu(OtBu)]₄ ....
metal dialkylamides: Ti(NMe₂)₄, Cr(NEt₂)₄ ....
metal diketonates: Cu(acac)₂, Pt(hfac)₂ ....
metal carbonyls: Fe(CO)₅, Ni(CO)₄ ....
others: complexes with alkene, allyl, cyclopentadienyl, ..... ligands
many precursors have mixed ligands

Supplier of CVD Chemicals

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| Hsin-Tien Chiu | Home of CVD | CVD Essentials | Fundamental CVD Steps | CVD Applications |

E-mail: htchiu@chiuserv.ac.nctu.edu.tw