titanium silicide (tisi2)

**Titanium Silicide (TiSi₂)** is the **first-generation contact silicide** — used from the early VLSI era through the 250nm node, offering low resistivity in its C54 phase but suffering from a narrow-line effect that made it unsuitable for sub-250nm gate widths. **What Is TiSi₂?** - **Phases**: C49 (high-$ ho$, ~60 $muOmega$·cm, forms first) and C54 (low-$ ho$, ~15 $muOmega$·cm, desired phase). - **C49 -> C54 Transition**: Requires nucleation at grain boundaries. On narrow lines, fewer grain boundaries = fewer nucleation sites = C54 doesn't form. - **Narrow-Line Effect**: On gates < 250 nm wide, TiSi₂ stays in the high-resistivity C49 phase. **Why It Matters** - **Historical Pioneer**: The first widely adopted silicide in CMOS manufacturing. - **Replaced**: Superseded by CoSi₂ (no narrow-line effect) at the 180nm node and later by NiSi. - **Legacy**: Still used in power devices and some specialty processes where gate widths are large. **TiSi₂** is **the grandfather of contact silicides** — the first low-resistance self-aligned contact material that served the industry until its narrow-line limitation forced retirement.