cvd basics

**Chemical Vapor Deposition (CVD)** — depositing thin films by chemically reacting gaseous precursors on a heated wafer surface. **Types** - **LPCVD** (Low Pressure): Uniform films, high temp (600-800C). Used for polysilicon, silicon nitride - **PECVD** (Plasma Enhanced): Lower temp (200-400C) using plasma energy. Used for SiO2, SiN passivation, BEOL dielectrics - **MOCVD** (Metal Organic): For III-V compound semiconductors (GaN, GaAs) - **ALD** (Atomic Layer Deposition): Self-limiting, one atomic layer at a time. Angstrom-level control. Essential for high-k gate oxides and ultra-thin films **Common Films** - SiO2 (TEOS-based): Interlayer dielectric - Si3N4: Etch stop layers, spacers, passivation - Polysilicon: Gate electrodes (legacy), hard masks - Tungsten (W-CVD): Contact plugs **Key Metrics** - Deposition rate, uniformity, step coverage (conformality) - Film stress, density, composition - Particle defects per wafer **CVD** is the workhorse deposition technique — virtually every layer in a modern chip involves at least one CVD step.