Work Function Alloy Layer Tuning for Multi-Vt FinFETs
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Solution Overview
Problem
Existing methods for achieving multiple threshold voltages in FinFET devices are complex, time-consuming, and costly, particularly due to the need for multiple work function layer depositions and patterning, which are not compatible with smaller critical dimensions.
Innovation Solution
A semiconductor device with a work function alloy layer having multiple portions with different contents of an element, achieved through wet etching with varying conditions, allowing for distinct threshold voltages without additional work function layer depositions, enabling efficient fabrication of FinFET devices with improved scalability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple work function layer depositions and patterning are used to achieve multiple threshold voltages, then distinct threshold voltages can be obtained, but the fabrication process becomes complex, time-consuming, and costly
Solution Approach 1:
The patent applies parameter changes by varying the composition of a single work function alloy layer across different regions. Specifically, the alloy layer contains varying concentrations of metal elements (such as titanium, aluminum, and nitrogen) in different portions, which directly changes the work function parameter. This allows different threshold voltages to be achieved through compositional gradients rather than through multiple discrete layer depositions and patterning steps, thereby simplifying the fabrication process while maintaining the ability to produce distinct threshold voltages.
2Reliability
If multiple work function layer depositions and patterning are used to achieve multiple threshold voltages, then distinct threshold voltages can be obtained, but the fabrication time and cost increase
Solution Approach 1:
The patent merges multiple work function layer depositions into a single work function alloy layer formation step. Instead of depositing separate work function layers and then patterning them, the invention forms one continuous alloy layer with spatially varying composition. This consolidation of multiple steps into a single step significantly reduces fabrication time and process complexity while still achieving the desired multiple threshold voltages through the alloy's compositional variation.
3Reliability
If conventional work function layer methods are used, then multiple threshold voltages can be achieved, but compatibility with smaller critical dimensions is lost
Solution Approach 1:
The patent applies local quality by creating spatial variations in the composition of the work function alloy layer. Different regions of the alloy layer have different metal element concentrations (e.g., varying titanium or aluminum content), which locally adjusts the work function to achieve different threshold voltages. This local compositional control is compatible with smaller critical dimensions because it avoids the resolution limitations of photolithographic patterning and relies instead on atomic-layer deposition techniques that can precisely control composition at the nanoscale.
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 simplifies the fabrication process, reduces costs, and maintains compatibility with smaller dimensions, providing FinFET devices with multiple threshold voltages while minimizing complexity and expense.
Implementation Method 1
wet etching with varying conditions
Data Source
AI summary
A semiconductor device includes a plurality of fin structures disposed over a substrate and a work function alloy layer disposed over each fin structure of the plurality of fin structures. The plurality of fin structures includes a first fin structure and a second fin structure. A content of a first element in a first portion of the work function alloy layer, which portion is disposed over the first fin structure, is different from a content of the first element in a second portion of the work function alloy layer, which portion is disposed over the second fin structure.