Replacement Gate Structure for Enhanced Conductivity
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Solution Overview
Problem
The scaling of replacement gate electrodes in semiconductor devices reduces the volume of high conductivity metal, leading to increased resistance, which adversely affects the performance of field effect transistors by causing signal delay and voltage loss.
Innovation Solution
A method is employed where a gate dielectric layer and a work function material layer are patterned to leave conductive material in the gate cavity, ensuring the conductive material occupies the full width of the replacement gate structure, while the work function material is only present in proximity to semiconductor material portions, reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the replacement gate electrode is scaled down to match the shrinking transistor dimensions, then the device size is reduced, but the volume of high conductivity metal is reduced leading to increased resistance
Solution Approach 1:
The patent applies local quality by using different materials with different properties in different regions of the gate electrode. The work function material (e.g., TiN) is used only in proximity to the channel region where it is needed for threshold voltage control, while high conductivity metal (e.g., Cu, Al, or W) is used in the remaining portions of the gate cavity where low resistance is the priority. This spatial differentiation of material properties resolves the contradiction by allowing the gate to have both the work function characteristics needed for device operation and the conductivity needed for low resistance, even as the overall gate dimensions are scaled down.
2Manufacturing precision
If the work function material layer is scaled down to maintain optimal work function values, then the work function control is maintained, but the volume occupied by high conductivity metal is reduced causing increased overall resistance
Solution Approach 1:
The patent segments the gate electrode into functionally distinct regions: a work function material region adjacent to the channel for threshold voltage control, and high conductivity metal regions in the remaining gate cavity for low resistance. This segmentation allows each material to be optimized for its specific function without compromising the other, resolving the contradiction between maintaining precise work function control and ensuring low overall resistance in scaled devices.
Solution Approach 2:
The patent applies local quality by using different materials with different properties in different regions of the gate electrode. The work function material (e.g., TiN) is used only in proximity to the channel region where it is needed for threshold voltage control, while high conductivity metal (e.g., Cu, Al, or W) is used in the remaining portions of the gate cavity where low resistance is the priority. This spatial differentiation of material properties resolves the contradiction by allowing the gate to have both the work function characteristics needed for device operation and the conductivity needed for low resistance, even as the overall gate dimensions are scaled down.
3Ease of manufacture
If high resistance gate electrode is used in scaled devices, then the manufacturing process is simpler, but the performance is degraded due to signal delay and voltage loss
Solution Approach 1:
The patent uses composite materials by combining work function material and high conductivity metal in a single gate electrode structure. This composite approach allows the gate to simultaneously provide threshold voltage control (through the work function material) and low resistance for fast signal transmission (through the high conductivity metal), resolving the contradiction between manufacturing simplicity and performance in scaled devices.
Data Source
AI summary
After formation of a gate cavity straddling at least one semiconductor material portion, a gate dielectric layer and at least one work function material layer is formed over the gate dielectric layer. The at least one work function material layer and the gate dielectric layer are patterned such that remaining portions of the at least one work function material layer are present only in proximity to the at least one semiconductor material portion. A conductive material having a greater conductivity than the at least one work function material layer is deposited in remaining portions of the gate cavity. The conductive material portion within a replacement gate structure has the full width of the replacement gate structure in regions from which the at least one work function material layer and the gate dielectric layer are removed.