Semiconductor Device Work Function Layer Threshold Voltage Control
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Solution Overview
Problem
The challenge in semiconductor devices is to achieve high performance and integration while maintaining effective operating characteristics, particularly in MOSFETs, where scaling down leads to difficulties in achieving varying threshold voltages and controlling work function layers, resulting in spatial limitations and increased gate resistance.
Innovation Solution
The semiconductor device incorporates transistors with different threshold voltages by varying the thickness of work function layers and barrier layers, and using a high-k dielectric layer with a work function control element, allowing for precise control of threshold voltages and reduced transistor sizes, which enables higher integration and improved electrical characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If MOSFETs are scaled down to achieve high integration, then device density increases, but threshold voltage control and operating characteristics deteriorate
Solution Approach 1:
The patent applies local quality by implementing different work function layer configurations for different transistor types (NFET and PFET) and different threshold voltage requirements (low-Vt and high-Vt). Specifically, NFETs receive a titanium nitride work function layer while PFETs receive a tungsten nitride work function layer, allowing each transistor type to be optimized independently for its specific electrical characteristics and threshold voltage requirements, thereby maintaining reliable threshold voltage control despite device scaling
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the composition, thickness, and material properties of the work function layers and barrier layers. The work function layer thickness is controlled within 1-5 nm, and barrier layer thickness within 2-10 nm, with specific material compositions (e.g., titanium nitride, tungsten nitride, tantalum nitride) selected to achieve precise threshold voltage control across different transistor types and operating conditions, enabling reliable operation at scaled dimensions
2Manufacturing precision
If work function layers are added to control threshold voltage, then threshold voltage precision improves, but device complexity and manufacturing steps increase
Solution Approach 1:
The patent applies segmentation by dividing the gate electrode structure into distinct functional layers: a work function layer (1-5 nm thick) for threshold voltage control, a barrier layer (2-10 nm thick) for preventing metal diffusion, and a metal layer for gate conductivity. This segmentation allows each layer to be independently optimized and controlled, achieving precise threshold voltage control while maintaining a systematic manufacturing approach that manages complexity through modular structure design
Solution Approach 2:
The patent implements universality by designing a multi-functional gate electrode structure where the work function layer simultaneously controls threshold voltage, the barrier layer prevents metal diffusion into the dielectric, and the combined structure serves as the gate electrode. This multi-functionality reduces the need for separate components and processes, managing device complexity while achieving precise threshold voltage control through an integrated structure
3Reliability
If barrier layers are placed between dielectric and metal layers, then metal diffusion prevention improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies composite materials by combining the barrier layer (made from titanium nitride, tungsten nitride, or tantalum nitride) with the adjacent dielectric and metal layers to form an integrated gate electrode structure. The barrier layer's specific material properties (low diffusion coefficient, appropriate work function) are leveraged to prevent metal diffusion into the dielectric, while the composite structure is designed to be tolerant of typical deposition process variations, managing manufacturing precision requirements through material selection rather than extreme process control
Data Source
AI summary
A semiconductor device includes a substrate having an active region, and first to third transistors on the active region of the substrate, each of the first to third transistors including a dielectric layer on the substrate, a metal layer on the dielectric layer, a barrier layer between the dielectric layer and the metal layer, and a work function layer between the dielectric layer and the barrier layer, wherein the barrier layer of the third transistor is in contact with the dielectric layer of the third transistor, and wherein a threshold voltage of the second transistor is greater than a threshold voltage of the first transistor and less than a threshold voltage of the third transistor.