Metal Gate Barrier Layer Engineering for Threshold Voltage Uniformity
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Solution Overview
Problem
As semiconductor technology advances, the weak corner turn on (WCTO) effect becomes a problem in metal gate transistors with short channel lengths, leading to uneven threshold voltage reduction due to inadequate aluminum atom diffusion to the bottom corner of the metal gate, resulting in higher threshold voltages in shorter channel length transistors compared to longer ones.
Innovation Solution
A semiconductor structure with a metal gate featuring a conformal N-work function metal layer and an engineered underlying barrier layer, which allows more aluminum atoms to diffuse to the bottom corner of the metal gate by varying the thickness of the barrier layer and forming a stair profile, ensuring consistent threshold voltage reduction across different channel lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conformal barrier layer is used in metal gate transistors, then the manufacturing process is simple, but aluminum atom diffusion to the bottom corner is inadequate, causing uneven threshold voltage reduction
Solution Approach 1:
The barrier layer is engineered with non-uniform thickness, being thinner at the bottom corner region and thicker at other areas. This local variation in barrier layer properties enables enhanced aluminum atom diffusion specifically at the bottom corner, resolving the uneven threshold voltage reduction while maintaining overall process simplicity
Solution Approach 2:
The solution introduces a vertical dimension variation in the barrier layer thickness rather than maintaining a uniform planar structure. By creating a stair profile with different thickness levels, the patent enables controlled aluminum diffusion pathways that address the corner region deficiency without complicating the overall manufacturing approach
2Manufacturing precision
If the barrier layer thickness is varied to enhance aluminum diffusion, then threshold voltage reduction becomes consistent, but the manufacturing process complexity increases
Solution Approach 1:
Rather than making the entire barrier layer complex, only the bottom corner region has varied thickness. The rest of the barrier layer maintains standard conformal deposition, thus achieving improved aluminum diffusion and threshold voltage uniformity without substantially increasing overall device complexity
Solution Approach 2:
The barrier layer is engineered with the desired thickness profile before aluminum deposition occurs. This preliminary structuring of the barrier layer ensures that aluminum atoms have the correct diffusion pathways prepared in advance, achieving consistent threshold voltage reduction without requiring complex post-processing steps
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively addresses the WCTO effect by ensuring consistent aluminum atom distribution and threshold voltage reduction across transistors with varying channel lengths, improving the performance of both long and short channel length metal gate transistors.
Implementation Method 1
allows more aluminum atoms to diffuse to the bottom corner of the metal gate
Data Source
AI summary
The present disclosure provides a semiconductor structure includes a semiconductor layer having a first surface, and an interlayer dielectric (ILD) defining a metal gate over the first surface of the semiconductor layer. The metal gate includes a high-k dielectric layer, a barrier layer, and a work function metal layer. A thickness of a first portion of the barrier layer at the sidewall of the metal gate is substantially thinner than a thickness of the barrier layer at the bottom of the metal gate. The present disclosure provides a method for manufacturing a semiconductor structure. The method includes forming a metal gate trench in an ILD, forming a barrier layer in a bottom and a sidewall of the metal gate trench, removing a first portion of the barrier layer at the sidewall of the metal gate trench, and forming a work function metal layer conforming to the barrier layer.