Metal Gate Work Function Tuning for FinFET Threshold Voltage
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Solution Overview
Problem
Challenges arise in patterning material layers of metal gate structures in FinFETs and GAA devices due to merged metal films and Vt instability, particularly when channel lengths decrease, limiting the modulation of threshold voltage.
Innovation Solution
A method involving alternating deposition of metal-containing and Al-containing precursors to form a high-k metal gate structure, facilitating Al atom diffusion through the high-k dielectric layer to create aluminum oxide at the interface, which modulates the threshold voltage without thermal treatments, thereby improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If channel length is decreased to improve device scaling, then productivity and production efficiency are improved, but device performance deteriorates due to merged metal films and Vt instability
Solution Approach 1:
The gate electrode is divided into multiple metal layers (first metal layer, second metal layer, third metal layer) with different work functions. This segmentation allows independent optimization of each layer's contribution to threshold voltage, preventing the merged metal film problem that occurs in conventional single-layer gates at scaled dimensions.
Solution Approach 2:
Different regions of the gate electrode have different work function values through the use of multiple metal layers with distinct work functions (e.g., tungsten for first layer, titanium nitride for second layer, tantalum nitride for third layer). This local quality variation enables precise control of threshold voltage while maintaining device scaling.
2Ease of manufacture
If conventional metal gate structure is used to simplify manufacturing, then ease of manufacture is improved, but adaptability deteriorates due to inability to modulate threshold voltage effectively at reduced length scales
Solution Approach 1:
The gate electrode employs a composite structure of multiple metal layers, each with different work function characteristics. This composite material approach provides both the ease of manufacture through standard deposition processes and the adaptability to modulate threshold voltage by adjusting the thickness and composition of individual metal layers.
Solution Approach 2:
The threshold voltage can be dynamically adjusted by varying the relative thicknesses of the different metal layers during fabrication. This dynamic adaptability allows the same basic structure to serve multiple device requirements without changing the fundamental manufacturing process.
3Adaptability or versatility
If threshold voltage modulation is attempted in conventional structures, then adaptability is improved, but device complexity increases due to additional processing steps and thermal treatments
Solution Approach 1:
The different metal layers with varying work functions are deposited in a predetermined sequence during the gate formation process itself, before final device assembly. This preliminary action embeds the threshold voltage modulation capability directly into the gate structure, eliminating the need for subsequent thermal treatments or additional 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
The method enables effective modulation of threshold voltage and enhances device performance by reducing processing complexity and enabling fabrication at reduced length scales without thermal treatments.
Implementation Method 1
facilitating Al atom diffusion through the high-k dielectric layer to create aluminum oxide at the interface
Data Source
AI summary
A method includes providing a structure including a semiconductor layer, forming an interfacial layer over the semiconductor layer, forming a gate dielectric layer over the interfacial layer, forming a first metal layer including a first metal over the gate dielectric layer, depositing a second metal-containing precursor over the first metal layer, forming a work function layer over the first metal layer, and forming a metal fill layer over the work function layer. The second metal-containing precursor includes a second metal, the second metal diffuses through the first metal layer.