Metal Gate Stack with TaC Barrier for Void-Free Replacement Gates
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Solution Overview
Problem
As semiconductor device dimensions shrink and gate length scales down, forming a void-free metal gate structure in the replacement-gate process becomes challenging due to electromigration, which can lead to deteriorated electrical characteristics and structural integrity of the gate electrode.
Innovation Solution
A metal gate electrode stack is formed with a wetting layer and a metal diffusion blocking layer to inhibit the diffusion of metal ions, ensuring a continuous void-free metal gate electrode by using materials like cobalt, titanium, or tantalum for the wetting layer and titanium nitride or tantalum nitride for the diffusion blocking layer, along with a work function layer and conductive barrier materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the replacement-gate process is used to form metal gate electrodes, then the polysilicon depletion effect is avoided, but void formation occurs due to electromigration when device dimensions are scaled down
Solution Approach 1:
A wetting layer is introduced as an intermediary between the metal gate electrode and the gate dielectric layer. This wetting layer improves the filling characteristics of the metal gate electrode and prevents void formation by facilitating complete deposition and adhesion to the gate dielectric surface, thereby resolving the void formation issue while maintaining the electrical performance benefits of metal gate electrodes.
Solution Approach 2:
The gate electrode structure is designed as a composite system comprising multiple materials: the metal gate electrode material (such as cobalt, titanium, or tantalum), the wetting layer material, and the gate dielectric layer. This composite structure combines the advantages of different materials to achieve both good electrical characteristics and void-free formation, overcoming the limitations of using a single material system.
2Productivity
If device dimensions are scaled down, then higher integration density is achieved, but electromigration causes void formation in metal gate structures
Solution Approach 1:
The wetting layer serves as a mediator that enables reliable metal gate electrode formation at scaled dimensions. By improving wetting and adhesion properties, it ensures complete filling of the gate trench even at smaller dimensions, preventing void formation and maintaining structural integrity despite the challenges posed by electromigration in miniaturized structures.
Solution Approach 2:
The invention changes the physical and chemical parameters of the gate electrode formation process by introducing the wetting layer, which modifies the surface properties and deposition characteristics. This parameter change enables void-free metal gate formation at scaled dimensions where conventional processes would fail due to electromigration-induced voids.
3Reliability
If metal ions diffuse into the gate dielectric layer, then electrical characteristics deteriorate, but preventing diffusion adds process complexity
Solution Approach 1:
The wetting layer acts as an intermediary barrier between the metal gate electrode and the gate dielectric layer. This layer not only improves filling characteristics but also serves as a diffusion barrier that prevents metal ions from migrating into the gate dielectric, thereby protecting electrical performance while adding only a single thin layer to the structure.
Solution Approach 2:
The wetting layer performs multiple functions simultaneously: it improves the filling characteristics of the metal gate electrode, prevents void formation, and acts as a diffusion barrier to prevent metal ion migration into the gate dielectric. This multi-functionality achieves multiple goals without proportionally increasing device complexity.
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 configuration enhances the filling characteristics of the metal gate electrode, preventing void formation and improving the reliability and structural integrity of the gate electrode by inhibiting metal ion diffusion, thus maintaining optimal electrical performance.
Implementation Method 1
A wetting layer and a metal diffusion blocking layer are sequentially formed on the gate dielectric layer to inhibit the diffusion of metal ions
Implementation Method 2
A wetting layer and a metal diffusion blocking layer are sequentially formed on the gate dielectric layer to inhibit the diffusion of metal ions
Data Source
AI summary
A method of making a semiconductor device includes forming first and second dummy gates over a substrate. The method includes removing the first and second dummy gates to define first and second openings. The method includes depositing a continuous gate dielectric layer in the first opening and the second opening. The method includes depositing a continuous capping layer on the gate dielectric layer, wherein the capping layer includes TaC. The method further includes depositing a continuous barrier layer on the capping layer, wherein the barrier layer includes TaC and a second material. The method includes depositing a first work function layer over the barrier layer in the first opening. The method includes depositing a second work function layer over the barrier layer in the second opening. The method includes depositing a continuous metal layer over each of the first work function layer and the second work function layer.