fluorinated silicon dioxide (fsg)

**FSG** (Fluorinated Silicate Glass) is an **early low-k dielectric material** — where fluorine atoms are incorporated into the SiO₂ matrix, reducing the dielectric constant from 3.9 to approximately 3.5 by weakening the Si-O bond polarizability. **What Is FSG?** - **Composition**: SiO₂ with ~3-6 atomic % fluorine substituting for oxygen. - **$kappa$**: ~3.5-3.7 (modest reduction from pure oxide). - **Deposition**: PECVD using SiF₄ or TEOS + fluorine source. - **Era**: Used at 180nm-130nm nodes as the first generation of low-k IMD. **Why It Matters** - **Gentle Introduction**: FSG was the industry's first step away from pure SiO₂, with minimal process changes needed. - **Stability**: Mechanically strong and moisture-resistant — much more robust than later ULK films. - **Replaced**: Superseded by SiCOH ($kappa approx 2.7$) at the 90nm node for better RC performance. **FSG** is **the first-generation low-k** — a conservative, reliable modification of SiO₂ that paved the way for more aggressive dielectric engineering.