FinFET Metal Gate WFM Tuning for Precise Threshold Voltage
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Solution Overview
Problem
The semiconductor industry faces challenges in manufacturing self-aligned contact structures over source/drain regions in nanometer technology process nodes, particularly in achieving precise control over threshold voltages for FinFETs and metal gate structures.
Innovation Solution
The method involves forming a work function adjustment material (WFM) layer with varying thicknesses and materials for different FinFETs and p-channel FETs, allowing for precise adjustment of threshold voltages through the fabrication process of metal gate structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional metal gate structure fabrication is used, then manufacturing process is simpler, but threshold voltage control precision deteriorates
Solution Approach 1:
The gate structure is segmented into multiple functional layers: a base metal gate layer and an additional work function adjustment material layer. This segmentation allows independent optimization of each layer's thickness and material properties to achieve precise threshold voltage control while maintaining manufacturing feasibility.
Solution Approach 2:
The work function adjustment material layer is applied selectively with varying local thicknesses in different regions of the gate structure. This local quality variation enables precise threshold voltage tuning for specific transistor types (n-channel vs p-channel) and voltage requirements (low-voltage vs ultra-low-voltage) without redesigning the entire gate structure.
2Manufacturing precision
If uniform conductive layer thickness is used, then manufacturing process is simpler, but threshold voltage adjustment precision deteriorates
Solution Approach 1:
The conductive layer structure transitions from a static uniform thickness design to a dynamic variable thickness design. The work function adjustment material layer is formed with different thicknesses in different regions, enabling dynamic threshold voltage adjustment while using standard fabrication techniques like selective etching and deposition.
Solution Approach 2:
The thickness parameter of the work function adjustment material layer is varied to change the electrical properties of the gate structure. By controlling the layer thickness from thin to thick in different regions, precise threshold voltage adjustment is achieved without changing the fundamental fabrication process parameters.
3Reliability
If thicker conductive layers are used, then etching damage is reduced, but device performance deteriorates
Solution Approach 1:
Instead of using uniformly thick conductive layers throughout, the solution applies partial thickness - a thin base layer for structural integrity and etching protection, plus an additional work function adjustment layer only where needed for threshold voltage control. This partial action approach minimizes etching damage while maintaining optimal device performance.
Solution Approach 2:
The work function adjustment material layer acts as an intermediary between the base metal gate layer and the contact structures. It provides the necessary etching protection and electrical property adjustment without requiring the base conductive layers to be excessively thick, thus maintaining device performance while preventing etching damage.
Data Source
AI summary
A semiconductor device includes first-type-channel field effect transistors (FETs) including a first first-type-channel FET including a first gate structure and a second first-type-channel FET including a second gate structure. The first first-type-channel FET has a smaller threshold voltage than the second first-type-channel FET. The first gate structure includes a first work function adjustment material (WFM) layer and the second gate structure includes a second WFM layer. At least one of thickness and material of the first and second WFM layers is different from each other.