Replacement Gate Work-Function Metals for Threshold Voltage Tuning
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Solution Overview
Problem
Current transistor manufacturing processes for FinFETs and GAA transistors face challenges in achieving optimal work-function layers for both n-type and p-type transistors, leading to variations in threshold voltages and increased manufacturing costs due to the need for different materials and processes.
Innovation Solution
The use of ruthenium and/or molybdenum as work-function metals in both n-type and p-type transistors, allowing for shared processing steps and the formation of mid-gap work functions, with additional work-function layers tuning the threshold voltages, enabling the production of transistors with varying threshold voltages without excessive cost increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If different work-function materials (TiAl for n-type, TiN for p-type) are used in replacement gates, then optimal threshold voltage control is achieved for each transistor type, but manufacturing complexity and cost increase due to separate processing steps
Solution Approach 1:
The patent applies universality by using a single work-function material (tantalum) that can serve both n-type and p-type transistors. The same material deposition process is used for both transistor types, eliminating the need for separate TiAl and TiN processing steps. This multi-functional approach maintains threshold voltage control while simplifying the manufacturing process.
Solution Approach 2:
The patent employs parameter changes by adjusting the thickness of the tantalum work-function layer to achieve different threshold voltages for n-type and p-type transistors. Instead of changing materials, the invention varies the physical parameter (layer thickness) of the same material to tune the electrical properties, thereby maintaining manufacturing simplicity while achieving precise voltage control.
2Manufacturing precision
If separate work-function materials are deposited for n-type and p-type transistors, then precise threshold voltage tuning is achieved, but manufacturing cost increases
Solution Approach 1:
The invention uses a universal tantalum-based work-function material system that replaces the need for separate TiAl and TiN deposition processes. This single material system performs the function of multiple materials, reducing material costs and processing expenses while maintaining the ability to tune threshold voltages through thickness control.
Solution Approach 2:
The patent achieves threshold voltage tuning by varying the thickness parameter of the tantalum work-function layer rather than using different materials. This approach eliminates the need for multiple material deposition processes, reducing manufacturing costs while preserving precise voltage control capability through simple thickness adjustment.
3Device complexity
If a single work-function material is used for both n-type and p-type transistors, then manufacturing complexity is reduced and processing steps are shared, but threshold voltage control precision may be compromised
Solution Approach 1:
The patent resolves this contradiction by using parameter changes - specifically, varying the thickness of the tantalum work-function layer to achieve different threshold voltages. For n-type transistors, a thinner tantalum layer provides lower work function, while for p-type transistors, a thicker layer provides higher work function. This maintains precise voltage control while using a single material system.
Solution Approach 2:
The invention employs composite material structures, combining tantalum work-function layers with high-k dielectric gate insulators. This composite approach allows the tantalum layer to provide work-function control while the high-k dielectric provides gate control, enabling precise threshold voltage tuning through the combined structure even when using a single work-function material for both transistor types.
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 reduces manufacturing complexity and cost by allowing common processing steps for both transistor types while enabling precise tuning of threshold voltages, facilitating the production of transistors with diverse performance requirements.
Implementation Method 1
depositing a first work-function layer over the gate dielectric layer, wherein the first work-function layer comprises a metal selected from the group consisting of ruthenium, molybdenum, and combinations thereof
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, forming a gate dielectric layer extending into the trench and on the semiconductor region, and depositing a fist work-function layer over the gate dielectric layer. The work-function layer comprises a metal selected from the group consisting of ruthenium, molybdenum, and combinations thereof. The method further includes depositing a conductive filling layer over the first work-function layer, and performing a planarization process to remove excess portions of the conductive filling layer, the first work-function layer, and the gate dielectric layer to form a gate stack.