Dummy Gate is the sacrificial polysilicon gate structure used in the gate-last (RMG) process — serving as a placeholder during FEOL processing (spacer formation, S/D implant, silicidation) and later removed and replaced with the real high-k/metal gate stack.

What Is a Dummy Gate?

• Material: SiO₂ (thin dummy oxide) + poly-Si or amorphous-Si (gate body).
• Purpose: Defines the transistor channel length, spacer offset, and S/D geometry.
• Removal: Wet etch (NH₄OH for poly-Si, HF for dummy oxide) after CMP planarization exposes the gate top.
• Result: An empty trench (gate cavity) lined by spacers -> ready for high-k/metal gate deposition.

Why It Matters

• Process Compatibility: All existing FEOL modules (implant, anneal, salicide) work as-is with the dummy gate.
• Critical Etch: Dummy gate removal must be perfectly selective to spacer and channel — any damage to the channel is fatal.
• Scaling: Dummy gate height and profile directly determine the replacement gate trench geometry.

Dummy Gate is the theatrical understudy — performing all the rehearsals (high-temperature processing) so the star (real metal gate) can make a fresh, undamaged appearance for the final show.