Metal Gate Work Function Layer Doping for Threshold Voltage Separation
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Solution Overview
Problem
The semiconductor industry faces challenges in achieving a greater differential between threshold voltages of transistors due to limitations in etch selectivity between work function tuning layers and underlying layers during chlorine-based treatments, which affects the integration density and performance of electronic components.
Innovation Solution
A gate electrode with a doped work function tuning layer, such as titanium nitride, is used, where the tuning layer is doped with silicon or aluminum and includes oxygen bonds, allowing for increased etch selectivity during chlorine-based treatments to adjust the thickness of underlying layers and achieve a greater threshold voltage differential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chlorine-based treatment is used to reduce thickness of underlying layer for threshold voltage tuning, then threshold voltage differential can be adjusted, but etch selectivity between work function tuning layer and underlying layer is insufficient
Solution Approach 1:
The patent modifies the chemical composition parameters of the work function tuning layer by doping it with specific elements (such as tungsten, molybdenum, or titanium) and controlling the oxygen content. These parameter changes create a more pronounced chemical difference between the work function tuning layer and the underlying tantalum nitride layer, thereby enhancing etch selectivity during chlorine-based treatments while maintaining threshold voltage tuning capability.
Solution Approach 2:
The patent creates a composite work function tuning layer structure that combines multiple materials (e.g., tantalum nitride base layer with doped metal oxides). This composite structure provides both the desired work function characteristics for threshold voltage control and improved etch selectivity through the distinct chemical properties of the dopant materials, resolving the contradiction between tuning precision and etch differentiation.
2Manufacturing precision
If work function tuning layer thickness is reduced for threshold voltage adjustment, then threshold voltage differential increases, but etch selectivity control becomes more difficult
Solution Approach 1:
By changing the chemical composition parameters of the work function tuning layer through doping with specific metals and controlling oxygen concentration, the patent enhances etch selectivity without requiring significant thickness reductions. This allows for better control of the thin layer during chlorine-based treatments while achieving the desired threshold voltage separation.
Solution Approach 2:
The doped metal oxide layers act as intermediary materials between the gate dielectric and the underlying tantalum nitride layer. These intermediary layers provide the necessary etch selectivity enhancement and work function tuning, making the manufacturing process easier to control while achieving precise threshold voltage differentiation.
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 enhances the etch selectivity between the work function tuning layer and the underlying tantalum nitride layer, enabling greater flexibility in threshold voltage separation and improved performance of transistors by allowing for more precise tuning of threshold voltages.
Implementation Method 1
By adjusting the composition of the work function tuning layer, etch selectivity between the work function tuning layer and an underlying layer (e.g., a tantalum nitride layer) maybe increased during a chlorine-based treatment that reduces thicknesses of the underlying layer
Data Source
AI summary
A method includes depositing a first conductive layer over a gate dielectric layer; depositing a first work function tuning layer over the first conductive layer; selectively removing the first work function tuning layer from over a first region of the first conductive layer; doping the first work function tuning layer with a dopant; and after doping the first work function tuning layer performing a first treatment process to etch the first region of the first conductive layer and a second region of the first work function tuning layer. The first treatment process etches the first conductive layer at a greater rate than the first work function tuning layer.