Chemical Vapor Deposition Basics

Chemical Vapor Deposition (CVD)

• CVD is a deposition of material on a substrate using chemistry, where a chamber encloses the vapor and energy is provided to the system, typically thermally or radiatively.
• A precursor is a chemical that causes deposition on the substrate, typically a one or two-component chemical that reacts to form the desired material.
• The deposited layer requires a substrate, which can be a wafer or any other substrate, and it sits on a susceptor that holds the wafer during deposition.
• Susceptors must have certain characteristics, including cleanliness, to facilitate the deposition process.

Characteristics of CVD Films

• CVD is used to deposit high-quality films with very low contamination, which can be epitaxial and single crystalline.
• Epitaxy refers to growing single crystalline material on top of an existing single crystalline material, with perfect lattice-matching and large grains with no or few grain boundaries.

Applications of CVD

• CVD is used to grow device-grade semiconducting materials, such as high-mobility transistors in modern CMOS fabrication.
• CVD is used to grow heterojunctions, such as germanium on silicon or titanium dioxide on silicon, where the deposited layer has a different material than the substrate.
• CVD is used to grow high-quality thin films, not necessarily crystalline or epitaxial, such as polysilicon electrodes in CMOS.
• CVD is used to deposit dielectrics, such as silicon nitride and silicon oxide, on top of metal or directly on native substrates.

Advantages of CVD

• CVD can deposit a very wide range of materials, limited only by the ability to provide a suitable precursor.
• Chemists have developed ways to convert virtually every element into a CVD precursor.
• Gaseous precursors can be highly purified, providing an added advantage for CVD.