Tungsten Gate Cap Structure for Lower MBC MOSFET Gate Resistance
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Solution Overview
Problem
Multi-gate metal-oxide-semiconductor field effect transistors (MOSFETs), specifically multi-bridge channel (MBC) transistors, face high gate contact resistance due to the lack of a metal fill layer, which affects their performance and efficiency.
Innovation Solution
A tungsten gate cap layer is deposited over the recessed gate stack layers in the MBC transistors, reducing gate contact resistance by about one order of magnitude and improving on-current by 3% to 5%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MBC transistor structure is used without metal fill layer, then device complexity is reduced and manufacturing is simplified, but gate contact resistance increases significantly
Solution Approach 1:
The gate structure is segmented into multiple functional layers: work function layers (TiN, TaN) for electrical properties and a tungsten gate cap layer for low resistance. This segmentation allows each layer to optimize its specific function, resolving the contradiction between simplicity and low contact resistance.
Solution Approach 2:
The gate structure uses composite materials combining different metal properties: TiN/TaN work function layers provide appropriate work functions for n-type and p-type devices, while the tungsten gate cap layer provides extremely low electrical resistance. This composite approach achieves low gate contact resistance without excessive complexity.
2Reliability
If gate structure volume is increased to include metal fill layer, then gate contact resistance decreases, but device dimensions increase and scaling is limited
Solution Approach 1:
The tungsten gate cap layer is applied locally only where needed for low resistance contact, rather than filling the entire gate volume. This localized application reduces resistance without significantly increasing overall gate structure volume, maintaining scalability.
Solution Approach 2:
The invention changes the material parameter (electrical resistivity) by introducing tungsten with extremely low resistivity into the gate structure. This parameter change achieves low contact resistance without requiring large volume increases, enabling continued device scaling.
3Productivity
If work function layers alone are used in gate structure, then device complexity is minimized, but on-current is insufficient due to high contact resistance
Solution Approach 1:
The invention merges the electrical properties of work function layers (TiN/TaN) with the low resistance properties of tungsten in a unified gate structure. This combination achieves both appropriate work function for device operation and low contact resistance for high on-current.
Solution Approach 2:
The composite gate structure combines TiN/TaN work function layers with tungsten gate cap layer, achieving both sufficient on-current through proper work function and low gate contact resistance through tungsten's excellent electrical conductivity.
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
The implementation of the tungsten gate cap layer significantly reduces gate contact resistance and enhances the performance of MBC transistors by improving on-current, addressing the limitations of conventional MBC transistors.
Implementation Method 1
A tungsten gate cap layer is deposited over the recessed gate stack layers in the MBC transistors
Data Source
AI summary
The present disclosure provides a semiconductor device and a method of forming the same. The semiconductor device includes a first channel members being vertically stacked, a second channel members being vertically stacked, an n-type work function layer wrapping around each of the first channel members, a first p-type work function layer over the n-type work function layer and wrapping around each of the first channel members, a second p-type work function layer wrapping around each of the second channel members, a third p-type work function layer over the second p-type work function layer and wrapping around each of the second channel members, and a gate cap layer over a top surface of the first p-type work function layer and a top surface of the third p-type work function layer such that the gate cap layer electrically couples the first p-type work function layer and the third p-type work function layer.