Thin Film Deposition
Chemical Vapor Deposition (CVD)
LPCVD, PECVD, and the chemistry of depositing films from gases
CVD Fundamentals
CVD Fundamentals
In Chemical Vapor Deposition, gaseous precursors react on or near the wafer surface to form a solid film. The basic steps:
- Gas precursors are delivered to the chamber
- Precursors transport to the wafer surface (diffusion through a boundary layer)
- Precursors adsorb onto the surface
- Chemical reactions occur, forming the desired film
- Byproducts desorb and are pumped away
Key CVD variants:
- LPCVD (Low Pressure): 0.1–1 Torr, 600–900°C. Excellent uniformity and step coverage. Used for silicon nitride, polysilicon.
- PECVD (Plasma Enhanced): Uses plasma to enable reactions at lower temperatures (200–400°C). Critical for back-end processing where metals are already on the wafer.
- MOCVD (Metal-Organic): Uses metal-organic precursors. Key for III-V semiconductors (GaN, GaAs) in LEDs and power devices.
Analogy: Spray Painting
CVD is like spray painting, but at the molecular level. Instead of paint droplets, gas molecules arrive at the surface and chemically bond to it, building up a uniform coating layer by layer.
Knowledge Check
Knowledge Check
1 / 1Why is PECVD preferred over LPCVD for back-end-of-line processing?