HKMG

HKMG stands for high-k metal gate, a technology used in CMOS semiconductor fabrication to replace the traditional silicon dioxide gate dielectric and polycrystalline silicon gate with a high-permittivity dielectric and a metal gate. The high-k dielectric allows a physically thicker oxide while preserving gate capacitance, which reduces leakage current and supports continued device scaling. The metal gate replaces poly-Si gates to improve threshold voltage control and eliminate poly-silicon gate depletion effects.

Typical high-k materials used in HKMG include hafnium oxide (HfO2) and zirconium oxide (ZrO2), while common metal gate materials include titanium nitride (TiN) and tantalum nitride (TaN). The metal gate work function is engineered to suit NMOS and PMOS devices, often requiring different materials or processing to achieve appropriate threshold voltages across the complementary pair.

The transition to HKMG became essential around the 45-nanometer technology node and has since been adopted in many advanced nodes by leading semiconductor manufacturers. The integration with high-k dielectrics and metal gates prompted changes to deposition, patterning, and annealing steps, including atomic layer deposition for the dielectric, metal gate deposition with subsequent planarity steps, and careful interface engineering to control reliability and performance.

Reliability considerations for HKMG include bias temperature instability, charge trapping, and interface state management, which have driven ongoing optimization in materials, processing, and device design. HKMG remains a foundational technology in modern CMOS, enabling continued scaling while mitigating leakage and improving performance.