TiAl Metal Gate Stack for FinFET Threshold Voltage Tuning
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Solution Overview
Problem
The challenge in scaling transistor gate structures for smaller devices is the limited adjustment in threshold voltage due to decreased spacing between transistors, making it difficult to tune the threshold voltage effectively in n-type finFETs.
Innovation Solution
The formation of gate stacks with titanium-aluminum (TiAl) layers having different aluminum concentrations (Al/Ti ratios) is proposed, where a bilayer or trilayer structure is used, with TiAl layers having a low Al/Ti ratio acting as an oxygen getter to trap oxygen atoms and maintain transistor reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the transistor gate structure is scaled down to manufacture smaller devices, then device size is reduced, but the adjustment range of threshold voltage becomes limited due to decreased spacing between transistors
Solution Approach 1:
The gate structure is segmented into multiple work function layers (first work function layer and second work function layer) with different materials and properties. This segmentation allows independent optimization of each layer's thickness and composition to achieve the desired threshold voltage tuning range without increasing overall gate structure spacing.
Solution Approach 2:
The patent employs composite material structures including titanium nitride (TiN), tungsten nitride (WN), and other metal nitride combinations in the work function layers. These composite material systems provide enhanced threshold voltage controllability through material composition ratios and thickness variations, enabling effective tuning despite reduced device dimensions.
2Manufacturing precision
If the work function layer thickness is adjusted to tune threshold voltage, then threshold voltage control is achieved, but the adjustment capability is limited by the decreased spacing between transistors in scaled devices
Solution Approach 1:
Different regions of the gate structure have different material compositions and thicknesses. The first and second work function layers have distinct local properties (different materials, different thicknesses) that are optimized for specific functions, enabling precise threshold voltage control within the constrained gate spacing.
Solution Approach 2:
The patent utilizes multiple parameters including material composition ratios, layer thicknesses, and material types to control threshold voltage. By varying these parameters independently in different work function layers, the system achieves precise threshold voltage tuning without requiring increased gate structure spacing.
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 achieves a significant reduction in threshold voltage (about 57%) and an increase in saturation current (about 16%) for n-type finFETs, while maintaining the performance of p-type transistors and ensuring reliable transistor operation.
Implementation Method 1
TiAl layers having a low Al/Ti ratio acting as an oxygen getter to trap oxygen atoms
Data Source
AI summary
The present disclosure describes a method for the formation of gate stacks having two or more titanium-aluminum (TiAl) layers with different Al concentrations (e.g., different Al/Ti ratios). For example, a gate structure can include a first TiAl layer with a first Al/Ti ratio and a second TiAl layer with a second Al/Ti ratio greater than the first Al/Ti ratio of the first TiAl layer.