Plasma-Enhanced CVD (PECVD) is a thin film deposition technique that uses plasma to activate chemical reactions at lower temperatures than thermal CVD — enabling dielectric deposition on temperature-sensitive structures and achieving tunable film properties through plasma conditions.

How PECVD Works

1. Precursor gases flow into chamber (e.g., SiH4 + N2O for SiO2; SiH4 + NH3 + N2 for SiN). 2. RF plasma (13.56 MHz or 2.45 GHz) dissociates gases into reactive radicals and ions. 3. Radicals adsorb and react on heated wafer surface (200–400°C). 4. Film grows — by-products pumped away.

vs. Thermal CVD (LPCVD)

Common PECVD Films

• PECVD SiO2: ILD dielectric, passivation. Deposited with SiH4 + N2O or TEOS + O2.
• PECVD SiN (Si3N4): Passivation, diffusion barrier, etch stop. SiH4 + NH3 + N2.
• PECVD SiON: Tunable refractive index between SiO2 and Si3N4. ARC layer.
• PECVD a-Si: Polysilicon precursor, TFT backplanes.
• PECVD Low-k (SiCOH): Ultra-low-k (k~2.7) ILD for Cu interconnects.

Stress Tuning

• LF power (380 kHz) increases ion bombardment → compressive stress.
• HF power (13.56 MHz) reduces bombardment → tensile stress.
• Dual-frequency PECVD: Independent stress tuning from -500 MPa to +500 MPa.
• Application: Tensile SiN capping over NMOS for electron mobility enhancement.

Key Equipment

• Applied Materials Producer, Novellus Sequel (now Lam Research): Batch PECVD.
• Tokyo Electron Livas: Single-wafer cluster PECVD for tight uniformity.

PECVD is indispensable in back-end-of-line processing — its low-temperature operation makes it the only practical method for depositing dielectrics over completed transistors and metal interconnects.