pFET Gate Work-Function Stack With Al-C Layer for Threshold Tuning
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Solution Overview
Problem
Existing transistors face challenges in achieving optimal work function tuning for p-type transistors, particularly in FinFETs and Gate-All-Around (GAA) transistors, which affect the threshold voltage and overall performance.
Innovation Solution
The introduction of an aluminum-and-carbon containing work-function layer is inserted between the high-k dielectric layer and the p-type work-function layer, enhancing the overall work function and reducing the threshold voltage of p-type transistors by forming dipoles with the high-k gate dielectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a p-type work-function layer (e.g., TiN) is used in the gate of p-type transistors, then the gate structure is formed, but the work function is insufficient to achieve optimal threshold voltage
Solution Approach 1:
The patent applies composite materials by combining an aluminum-and-carbon containing layer with a p-type work-function layer (such as TiN). This composite structure creates a work-function layer with enhanced properties, where the aluminum-and-carbon layer contributes to increasing the overall work function beyond what the p-type layer alone can achieve, thereby optimizing the threshold voltage for p-type transistors
Solution Approach 2:
The patent changes the work function parameter by introducing an aluminum-and-carbon containing layer that forms dipoles with the high-k gate dielectric layer. This dipole formation modifies the electrical characteristics and increases the work function of the gate structure, enabling optimal threshold voltage control for p-type transistors
2Reliability
If the work function is increased to reduce threshold voltage, then transistor performance improves, but additional process steps are required
Solution Approach 1:
The patent segments the work-function layer into multiple functional components: an aluminum-and-carbon containing layer that forms dipoles with the high-k dielectric, and a p-type work-function layer (such as TiN). This segmentation allows each layer to perform its specific function - the aluminum-and-carbon layer provides work function enhancement through dipole formation, while the p-type layer provides baseline work function - resulting in a composite structure that achieves optimal threshold voltage control
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 approach effectively increases the work function and reduces the threshold voltage of p-type transistors by up to 250 mV, improving transistor performance.
Implementation Method 1
enhancing the overall work function and reducing the threshold voltage of p-type transistors by forming dipoles with the high-k gate dielectric layer
Data Source
AI summary
A method includes forming a dummy gate stack over a semiconductor region, forming a source/drain region on a side of the dummy gate stack, removing the dummy gate stack to form a trench, with the semiconductor region being exposed to the trench, forming a gate dielectric layer extending into the trench, and depositing a work-function tuning layer on the gate dielectric layer. The work-function tuning layer comprises aluminum and carbon. The method further includes depositing a p-type work-function layer over the work-function tuning layer, and performing a planarization process to remove excess portions of the p-type work-function layer, the work-function tuning layer, and the gate dielectric layer to form a gate stack.