Metal Gate Electrode Profiles for Lower Sheet Resistance
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Solution Overview
Problem
Polysilicon gate electrodes in integrated circuits have higher resistivity than metal materials, leading to slower operation speeds, necessitating the development of metal gates with reduced sheet resistance for improved performance and reliability.
Innovation Solution
A metal gate structure is fabricated with N-type and P-type transistor regions, featuring trench-shaped electrodes with specific profiles and work function layers, and a method involving multiple removing processes to optimize the shape and position of the metal gate electrodes, resulting in a bullet-shaped and mushroom-shaped profile under cross-sectional view.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If polysilicon gate electrodes are used, then thermal resistive properties are maintained, but resistivity is high leading to slower operation speeds
Solution Approach 1:
The gate electrode is segmented into multiple metal layers (first metal layer, second metal layer, third metal layer) with different materials and properties. Each layer contributes differently to electrical conductivity and thermal resistance, allowing optimization of both speed and thermal performance through the stacked structure
Solution Approach 2:
The gate electrode uses composite metal materials including tungsten, copper, and cobalt in different layers. This composite structure combines the high conductivity of copper/cobalt with the thermal stability of tungsten, achieving both high speed operation and reliable thermal resistance
2Speed
If metal gates are used to reduce resistivity, then operation speed improves, but sheet resistance optimization is needed for superior performance
Solution Approach 1:
Different regions of the gate electrode have different material compositions and thicknesses. The first metal layer has different properties than the second and third layers, creating local quality variations that optimize sheet resistance in specific areas while maintaining overall high conductivity for fast operation
Solution Approach 2:
The patent optimizes sheet resistance by changing material parameters (conductivity, thickness) of each metal layer. By adjusting the thickness and material composition of each layer, the overall sheet resistance is precisely controlled to achieve superior performance while maintaining high operation speed
Data Source
AI summary
A gate structure includes a substrate divided into an N-type transistor region and a P-type transistor region. An interlayer dielectric covers the substrate. A first trench is embedded in the interlayer dielectric within the N-type transistor region. A first gate electrode having a bullet-shaped profile is disposed in the first trench. A gate dielectric contacts the first trench. An N-type work function layer is disposed between the gate dielectric layer and the first gate electrode. A second trench is embedded in the interlayer dielectric within the P-type transistor region. A second gate electrode having a first mushroom-shaped profile is disposed in the second trench. The gate dielectric layer contacts the second trench. The N-type work function layer is disposed between the gate dielectric layer and the second gate electrode. A first P-type work function layer is disposed between the gate dielectric layer and the N-type work function layer.