carrier gas

Carrier gas is an inert gas used to transport precursor vapors from their source to the deposition chamber in CVD and ALD processes. **Common gases**: Nitrogen (N2) and argon (Ar) most common. Helium occasionally for thermal properties. **Mechanism**: Carrier gas flows through or over heated liquid/solid precursor source, picks up precursor vapor, and delivers it to chamber. **Bubbler delivery**: Carrier gas bubbles through liquid precursor. Precursor concentration depends on bubbler temperature, pressure, and carrier flow rate. **Flow control**: Mass flow controllers (MFCs) precisely meter carrier gas flow. Precursor delivery rate controlled indirectly through carrier flow and source temperature. **Inertness**: Carrier gas must not react with precursor or deposit on surfaces. Must be ultra-high purity. **Dilution effect**: Carrier gas dilutes precursor concentration in chamber. Affects deposition rate and uniformity. **Purge function**: In ALD, carrier gas also serves as purge gas between precursor pulses, removing unreacted species. **Chamber pressure**: Carrier gas contributes to total chamber pressure. Process pressure set by combination of gas flows and pumping speed. **Thermal role**: Carrier gas can assist heat transfer in some chamber configurations. **Purity requirements**: Parts-per-billion purity. Inline purifiers remove residual moisture and oxygen.