FinFET Threshold Voltage Control via Work Function Modulation
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Solution Overview
Problem
The reduction in channel length of FinFET devices leads to variations in threshold voltage, causing performance issues due to the short-channel effect, where some transistors become activated while others remain off, requiring costly compensation circuits to manage power and space efficiently.
Innovation Solution
The method involves determining the threshold voltage of a first transistor gate with a specific length and adjusting the process parameters for transistors with varying gate channel lengths to ensure their threshold voltages fall within a predetermined range, using techniques such as modulating the work function material thickness, type, or adding/halting the formation of halo layers to maintain uniformity across devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the channel length of FinFET devices is reduced to improve operating speed and increase device density, then the switching speed and density are improved, but the threshold voltage varies significantly causing short channel effects where transistors cannot be properly controlled
Solution Approach 1:
The patent applies different work function material thicknesses to different gate channel length regions. Specifically, gates with longer channel lengths have thinner work function material layers, while gates with shorter channel lengths have thicker work function material layers. This local differentiation compensates for the short channel effect in shorter gates while maintaining proper threshold voltage in longer gates, thereby resolving the threshold voltage control issue without sacrificing the benefits of reduced channel length.
2Power
If multiple fins are used in parallel to increase current flow and drive strength, then the drive strength is increased, but the device complexity and manufacturing process difficulty increase
Solution Approach 1:
The patent changes the work function material thickness parameter as a function of gate channel length. By controlling this single parameter (thickness) to vary across different gate regions, the patent achieves compensation for short channel effects without requiring fundamental changes to the multi-fin device architecture. This approach maintains the drive strength benefits of multiple fins while avoiding the need for complex additional manufacturing steps.
3Productivity
If transistors with different gate channel lengths are formed in close proximity to increase density, then the device density is increased, but the threshold voltage uniformity deteriorates requiring costly compensation circuits
Solution Approach 1:
The patent performs preliminary compensation by varying the work function material thickness during the manufacturing process itself, before the devices are assembled into circuits. By pre-adjusting the threshold voltages of different gate length transistors through controlled material deposition, the patent eliminates the need for post-fabrication compensation circuits. This preliminary action maintains high device density while achieving threshold voltage uniformity through process integration rather than additional circuitry.
Data Source
AI summary
At least one method, apparatus and system are disclosed for controlling threshold voltage values for a plurality of transistor devices. Determine a first threshold voltage of a first transistor gate comprising a first gate channel having a first length. Determine a second length of a second gate channel of a second transistor gate. Determining a process adjustment of the second gate based on the second length for providing a second threshold voltage of the second transistor gate. The second threshold voltage is within a predetermined range of the first threshold voltage. Provide data relating to process adjustment to a process controller for performing the process adjustment.