PECVD (Plasma-Enhanced Chemical Vapor Deposition) uses plasma energy to enable film deposition at significantly lower temperatures than thermal CVD. Principle: RF plasma generates reactive species (radicals, ions) that drive chemical reactions at temperatures too low for thermal activation. Temperature: 200-400 C typical, compared to 600-800 C for LPCVD. Enables deposition after metallization. Plasma generation: RF power (13.56 MHz typical) applied between electrodes creates glow discharge in process gases. Common films: SiO2 (SiH4+N2O), SiN (SiH4+NH3/N2), SiC, SiCN, low-k dielectrics, amorphous silicon. Film properties: Generally lower density and more hydrogen incorporation than thermal CVD films. Tunable stress. Stress control: Film stress (tensile or compressive) adjustable via RF power, pressure, gas ratios. Important for strain engineering. Step coverage: Moderate. Not as conformal as LPCVD or ALD. Can be an issue for high-AR features. Equipment: Single-wafer chambers with parallel plate electrodes. Multi-station tools for throughput. Dual frequency: Low-frequency (100-400 kHz) + high-frequency (13.56 MHz) allows independent control of ion bombardment and plasma density. Applications: Passivation, ILD, etch stop layers, hard masks, MEMS.