plasma frequency

Plasma frequency in CVD refers to the RF frequency used to generate and sustain the plasma, which fundamentally affects film properties and deposition behavior. **Standard frequency**: 13.56 MHz is the ISM (Industrial, Scientific, Medical) band standard. Most common in semiconductor processing. **High frequency (HF)**: 13.56 MHz and above (27 MHz, 40 MHz, 60 MHz). Lighter ions cannot follow field oscillation - reduced ion bombardment. Higher plasma density. **Low frequency (LF)**: 100-400 kHz. Heavy ions can follow field oscillations - increased ion bombardment energy. More energetic surface bombardment. **Dual frequency**: Modern PECVD uses both HF and LF simultaneously. HF controls plasma density and dissociation. LF controls ion bombardment energy. Independent tuning of chemistry and film properties. **Stress tuning**: LF power ratio controls film stress. Higher LF fraction = more compressive stress from increased ion bombardment. **Film density**: Higher ion bombardment (more LF) produces denser films with less hydrogen. **Frequency selection**: Choice depends on desired film properties, deposition rate, and uniformity requirements. **VHF**: Very high frequency (>30 MHz) used in some applications for higher plasma density and rate. **Impedance matching**: RF matching networks required to efficiently couple power to plasma at each frequency.