reaction temperature

Reaction temperature is the temperature at which CVD chemical reactions proceed efficiently to deposit high-quality films on the wafer surface. **Thermal CVD**: Reactions are thermally activated. Higher temperature generally increases rate (Arrhenius relationship). Typical range 400-850 C. **PECVD**: Plasma provides activation energy, allowing reactions at 200-400 C. Temperature still affects film properties. **ALD**: Operates in temperature window. Too low = condensation or slow kinetics. Too high = precursor decomposition (loss of self-limiting behavior). **Temperature regimes**: **Surface-reaction-limited**: Rate depends on temperature, not gas delivery. Good uniformity. LPCVD operates here. **Mass-transport-limited**: Rate depends on gas delivery, not temperature. APCVD often here. **Film quality dependence**: Higher temperature generally produces denser, more stoichiometric films with fewer impurities (less hydrogen). **Stress effects**: Film stress changes with deposition temperature. Important for device engineering. **Thermal budget**: Total thermal exposure affects previously formed structures. Limits maximum temperature for later process steps. **Uniformity**: Temperature uniformity across wafer critical for thickness and property uniformity. **Measurement**: Thermocouple in chuck, pyrometer, or embedded temperature sensors.