FinFET Metal Gate Work Function Tuning for Threshold Voltage Control
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Solution Overview
Problem
Existing FinFET devices face challenges in achieving precise control over the threshold voltage (Vt) of metal gates due to limitations in forming work function layers with varying thicknesses, which affects device performance and integration density.
Innovation Solution
A method is employed to form first and second work function layers with different thicknesses by converting a surface layer of the first work function layer into an oxide using a plasma process, followed by depositing a second work function layer, allowing for varying thicknesses in a single deposition process, thereby enabling distinct threshold voltages for different metal gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single deposition process is used to form work function layers, then the manufacturing process is simpler and more cost-effective, but it is difficult to achieve varying thicknesses required for different threshold voltages
Solution Approach 1:
The work function layer formation is segmented into multiple deposition steps within a single deposition process. The process deposits different materials (e.g., titanium nitride, tungsten silicon nitride, tantalum nitride) in sequence, with each material contributing to the overall work function and thickness profile. This allows varying thicknesses and compositions without requiring multiple separate deposition processes.
Solution Approach 2:
The deposition process utilizes parameter changes such as varying deposition rates, adjusting plasma power, changing gas flow ratios, and modifying deposition temperature during different stages of the same process. These parameter adjustments enable precise control over the thickness and composition of each work function layer component, achieving different threshold voltages while maintaining process integration.
2Manufacturing precision
If multiple deposition processes are used to form work function layers with different thicknesses, then precise threshold voltage control is achieved, but the manufacturing complexity and cost increase
Solution Approach 1:
Multiple deposition steps that would traditionally require separate deposition processes are merged into a single continuous deposition process. The process transitions between different materials and deposition conditions without breaking the vacuum or requiring process interruption, thereby achieving complex multi-layer work function structures with precise thickness control while maintaining manufacturing simplicity.
Solution Approach 2:
The single deposition process is designed to perform multiple functions: depositing different materials, controlling varying thicknesses, adjusting work functions, and forming different layer structures all within one process. This multi-functional approach eliminates the need for multiple specialized deposition processes, reducing manufacturing complexity while maintaining precision.
3Manufacturing precision
If the work function layer thickness is increased, then the threshold voltage control is improved, but the integration density decreases due to larger device footprint
Solution Approach 1:
The work function layer is formed as a composite structure with multiple materials (e.g., titanium nitride, tungsten silicon nitride, tantalum nitride) deposited in sequence. Each material contributes differently to the work function and thickness profile, allowing precise threshold voltage control through composition optimization rather than simply increasing overall thickness. This enables effective threshold control with minimized physical footprint.
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 allows for efficient and cost-effective formation of metal gates with different thicknesses, enhancing device performance and integration density by optimizing threshold voltage control without requiring multiple deposition processes.
Implementation Method 1
converting a surface layer of the first work function layer into an oxide using a plasma process
Implementation Method 2
depositing a second work function layer, allowing for varying thicknesses in a single deposition process
Data Source
AI summary
A method of forming a semiconductor device includes forming a first dummy gate structure and a second dummy gate structure over a fin; forming a first dielectric layer around the first dummy gate structure and around the second dummy gate structure; removing the first dummy gate structure and the second dummy gate structure to form a first recess and a second recess in the first dielectric layer, respectively; forming a gate dielectric layer in the first recess and the second recess; forming a first work function layer over the gate dielectric layer in the first and the second recesses; removing the first work function layer from the first recess; converting a surface layer of the first work function layer in the second recess into an oxide; and forming a second work function layer in the first recess over the gate dielectric layer and in the second recess over the oxide.