Nano-FET Gate Structures With Dual Capping Layers for Threshold Uniformity
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Solution Overview
Problem
As semiconductor devices continue to shrink in size, challenges arise in maintaining uniformity and reducing threshold voltage variation in nanostructure field-effect transistors (nano-FETs), affecting device performance.
Innovation Solution
A method is employed to form a first capping material around the work function material of a nanosheet in a nano-FET, followed by a second capping material that wraps around the first capping material, preventing their merger and ensuring a uniform thickness, thereby reducing threshold voltage variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single capping material is used around the work function material, then the manufacturing process is simpler, but the uniformity of thickness and threshold voltage variation are worsened
Solution Approach 1:
The single capping material layer is segmented into two distinct capping material layers (first capping material and second capping material) with different properties. The first capping material provides initial coverage while the second capping material ensures uniform thickness and prevents merging, thereby resolving the contradiction between manufacturing simplicity and thickness uniformity.
Solution Approach 2:
The patent uses composite capping structures with two different capping materials having complementary properties. The first capping material (e.g., silicon nitride) provides mechanical strength and adhesion, while the second capping material (e.g., silicon oxide) provides planarity and uniform thickness control, together achieving better overall performance than a single material could provide.
2Device complexity
If the capping material layers are allowed to merge, then the manufacturing process is simpler, but the threshold voltage variation increases
Solution Approach 1:
The second capping material acts as an intermediary layer between the first capping material layers of adjacent nanosheets. This intermediary layer prevents direct merging of the first capping materials while maintaining structural integrity, thereby preventing threshold voltage variation caused by unintended material interaction.
Solution Approach 2:
The patent applies different capping materials at different locations with specific functions: the first capping material provides initial protection and adhesion close to the work function material, while the second capping material provides uniform thickness control and prevention of merging in the regions between adjacent nanosheets, achieving local optimization for overall device reliability.
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 improves the performance of nano-FETs by enhancing uniformity and reducing threshold voltage variation, leading to better device performance.
Implementation Method 1
a first capping material is formed around the work function material of one nanosheet, and a second capping material is formed around the first capping material
Data Source
AI summary
A semiconductor device includes nanosheets between the source/drain regions, and a gate structure over the substrate and between the source/drain regions, the gate structure including a gate dielectric material around each of the nanosheets, a work function material around the gate dielectric material, a first capping material around the work function material, a second capping material around the first capping material, wherein the second capping material is thicker at a first location between the nanosheets than at a second location along a sidewall of the nanosheets, and a gate fill material over the second capping material.