Transistor Threshold Voltage Control via Work Function Modulation
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Solution Overview
Problem
In modern integrated circuits, achieving transistors with different threshold voltages is complicated by the need for various work function materials and doping processes, which can be affected by channel length and thermal budget, leading to difficulties in diffusion and stress relaxation.
Innovation Solution
The method involves forming semiconductor devices with distinct gate electrode structures in separate cavities, using a stack of layers including gate insulation, barrier, work function, and conductive materials, where the uppermost height of the work function material layers is less than the conductive materials, and the work function is modulated by treatment species, allowing for different threshold voltages without complicating the process flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different work function materials are provided in different regions to achieve different threshold voltages, then the threshold voltage differentiation is achieved, but the process flow is significantly complicated
Solution Approach 1:
The patent applies local quality by providing different work function material layers in different gate electrode regions. Specifically, a first work function material layer is provided in a first gate electrode region and a second work function material layer is provided in a second gate electrode region, where the work functions are different. This allows different threshold voltages to be achieved in different transistor regions while using a unified process flow, resolving the contradiction between threshold voltage differentiation and process complexity.
2Adaptability or versatility
If doping processes are used to provide different threshold voltages, then the threshold voltage adjustment is achieved, but the effectiveness is affected by channel length and thermal budget leading to diffusion and stress issues
Solution Approach 1:
The patent changes the parameter approach from doping concentration control to work function material selection. Instead of using doping processes that are sensitive to channel length and thermal budget, the invention directly controls threshold voltage by selecting different work function materials (e.g., titanium nitride, tantalum nitride, tungsten silicide) with predetermined work function values. This eliminates the diffusion and stress issues associated with high-temperature anneal processes while maintaining precise threshold voltage control.
Data Source
AI summary
A device includes a first transistor device having a first threshold voltage and including a first gate electrode structure positioned in a first gate cavity. The first gate electrode structure includes a first gate insulation layer, a first barrier layer, a first work function material layer formed above the first barrier layer, a second barrier layer formed above the first work function material layer, and a first conductive material formed above the second barrier layer. A second transistor device has a second threshold voltage different than the first threshold voltage and includes a second gate electrode structure positioned in a second cavity defined in the dielectric layer. The second gate electrode structure includes a second gate insulation layer, a second work function material layer, the second barrier layer formed above the second work function material layer, and a second conductive material formed above the second barrier layer.