Metal Gate Diffusion Barrier Layers for Stable Threshold Voltage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As integrated circuits downscale, the close proximity of nearby transistors leads to threshold voltage shifts due to aluminum diffusion between devices, degrading FET properties, particularly in 3D FETs where metal gate films play a crucial role in defining work function and threshold voltage.
Innovation Solution
Incorporating a diffusion barrier layer at the surface of aluminum-containing work function adjustment material layers to prevent aluminum diffusion into adjacent FETs, using Ti-rich, Ta-rich, or Si-doped layers to suppress aluminum migration and maintain device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If aluminum-containing work function adjustment material layers are used to define gate properties, then work function and threshold voltage control is improved, but aluminum diffusion into adjacent FETs occurs causing threshold voltage shifts
Solution Approach 1:
A diffusion barrier layer is introduced as an intermediary between the aluminum-containing work function adjustment material layer and adjacent FETs. This barrier layer (comprised of Ti, Ta, W, Mo, or their nitrides/oxides) mediates the interaction by blocking aluminum diffusion while allowing the work function adjustment material to perform its intended function of defining gate properties and threshold voltage.
Solution Approach 2:
The gate structure is segmented into multiple functional layers: the work function adjustment material layer for electrical property control, and a separate diffusion barrier layer for protecting against aluminum migration. This segmentation allows each layer to independently perform its specific function without interfering with the other.
2Length of moving object
If transistor dimensions are downscaled to increase integration density, then device miniaturization is achieved, but aluminum diffusion effects are amplified due to closer proximity
Solution Approach 1:
The diffusion barrier layer serves as a protective intermediary that becomes increasingly critical as transistors are downscaled. By placing this barrier between adjacent miniaturized devices, the patent prevents aluminum diffusion effects from being amplified by the reduced spacing, thereby maintaining device performance in scaled technologies.
Solution Approach 2:
The diffusion barrier layer is applied in advance during the gate structure formation process, before aluminum diffusion can occur. This preliminary protective action prevents the harmful diffusion effect from manifesting, allowing continued downsscaling without suffering from aluminum migration issues.
3Reliability
If metal gate films are used to define work function and threshold voltage, then FET performance is improved, but aluminum diffusion between nearby FETs degrades device reliability
Solution Approach 1:
The diffusion barrier layer acts as a mediator that protects the aluminum-containing work function adjustment material from diffusing into adjacent FETs. This intermediary layer (composed of Ti, Ta, W, Mo, or their compounds) allows the metal gate films to maintain their performance-enhancing properties while preventing the harmful metal migration that would otherwise degrade device reliability.
Solution Approach 2:
The gate structure employs a composite material approach, combining the work function adjustment material (aluminum-containing) with a diffusion barrier material (Ti, Ta, W, Mo or their nitrides/oxides). This composite structure leverages the electrical properties of the aluminum-containing layer while using the barrier layer to prevent its harmful migration, achieving both performance and reliability.
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
The diffusion barrier layer effectively isolates nearby FETs from aluminum diffusion, maintaining stable threshold voltages and improving device reliability and performance by preventing performance degradation due to metal migration.
Implementation Method 1
Incorporating a diffusion barrier layer at the surface of aluminum-containing work function adjustment material layers to prevent aluminum diffusion into adjacent FETs
Data Source
AI summary
A semiconductor device includes a gate structure disposed over a channel region and a source/drain region. The gate structure includes a gate dielectric layer over the channel region, one or more work function adjustment material layers over the gate dielectric layer, and a metal gate electrode layer over the one or more work function adjustment material layers. The one or more work function adjustment layers includes an aluminum containing layer, and a diffusion barrier layer is disposed at at least one of a bottom portion and a top portion of the aluminum containing layer. The diffusion barrier layer is one or more of a Ti-rich layer, a Ti-doped layer, a Ta-rich layer, a Ta-doped layer and a Si-doped layer.