N-type Work Function Metal Layer Oxidation Control
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Solution Overview
Problem
N-type work function metal layers in FinFET devices are susceptible to oxidation, affecting the threshold voltage of NMOS devices due to oxygen absorption from the environment and the capping layer, leading to instability in the work function.
Innovation Solution
A method involving the formation of a substrate structure with a high-k dielectric layer, a capping layer, and multiple N-type work function metal layers, where the second N-type work function metal layer has a higher Ti/Al atomic ratio than the first, reducing oxygen absorption and stabilizing the work function by forming the layers in a way that prevents oxygen absorption, such as using TiN or TiSiN as the capping layer and TiAl or TiSiAl as the first N-type work function metal layer, and TixAly or TixNzAly as the second N-type work function metal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single N-type work function metal layer is used, then the manufacturing process is simple, but the work function is unstable due to oxidation
Solution Approach 1:
The single N-type work function metal layer is segmented into multiple layers with different Ti/Al atomic ratios. The first layer has a lower Ti/Al ratio (0.5-2.0) and the second layer has a higher Ti/Al ratio (2.0-5.0), creating a gradient structure that prevents oxidation while maintaining manufacturing feasibility through sequential deposition processes
Solution Approach 2:
The patent uses composite material structure by combining different TiAl-based metal layers with varying compositions. The first layer uses TiAl with lower Ti content and the second layer uses TiAl with higher Ti content, creating a composite work function metal stack that provides both oxidation resistance and electrical performance
2Object-affected harmful factors
If the Ti/Al atomic ratio is increased to reduce oxidation, then oxidation resistance improves, but the work function changes affecting threshold voltage
Solution Approach 1:
Different regions of the work function metal stack have different Ti/Al atomic ratios tailored to specific functions. The first layer (lower Ti/Al ratio) is optimized for work function control and electrical performance, while the second layer (higher Ti/Al ratio) is optimized for oxidation resistance, with each layer having localized properties suited to its role
Solution Approach 2:
The patent systematically changes the Ti/Al atomic ratio parameter across different layers to achieve both oxidation resistance and proper work function. By controlling the Ti/Al ratio in the first layer to be lower (0.5-2.0) and in the second layer to be higher (2.0-5.0), the patent optimizes both chemical stability and electrical characteristics
Data Source
AI summary
A method for manufacturing a semiconductor device includes providing a substrate structure including a substrate, a high-k dielectric layer on the substrate, a capping layer on the high-k dielectric layer, forming a first N-type work function metal layer on the capping layer, forming a second N-type work function metal layer on the first N-type work function metal layer, and forming a metal electrode layer on the second N-type work function metal layer. The second N-type work function metal layer has a Ti/Al atomic ratio greater than the Ti/Al atomic ratio of the first N-type work function metal layer. The second work function metal layer having a higher Ti/Al atomic ratio will not absorb appreciable oxygen from the atmosphere, so that oxygen will not be available to the first work function metal layer, thereby reducing the oxidation level of the first work function metal layer.