Transistor Threshold Voltage Control via Nitrogen-Rich Barrier Layers
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Solution Overview
Problem
Conventional poly-silicon gates in semiconductor devices face performance issues due to boron penetration and depletion effects, and FinFETs struggle with adjusting threshold voltages using ion implantation, necessitating a method to form transistors with different threshold voltages.
Innovation Solution
A semiconductor device and method where different nitrogen concentrations in barrier layers and work function layers are achieved through multiple processing steps and patterned photoresist layers to create transistors with varying nitrogen ratios and thicknesses, allowing for distinct threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional poly-silicon gates are used in semiconductor devices, then the gate structure is simple and easy to manufacture, but boron penetration and depletion effects occur leading to inferior device performance
Solution Approach 1:
The gate electrode is constructed as a composite structure with multiple layers including a first work function layer (titanium nitride), a second work function layer (tantalum nitride), and a capping layer (tungsten). This composite gate structure eliminates boron penetration and depletion effects while achieving the desired work function, thereby resolving the technical contradiction between device performance and structural simplicity.
2Ease of operation
If ion implantation is used to adjust threshold voltage in FinFETs, then the process is simple, but threshold voltage adjustment is not effective in current FinFET architecture
Solution Approach 1:
The patent adjusts threshold voltage by changing the nitrogen concentration in the tantalum nitride barrier layer. By controlling the nitrogen-to-tantalum ratio (Ta:N) to be less than 1:1, the barrier layer's electrical properties are modified, enabling effective threshold voltage adjustment in FinFETs without relying on ion implantation. This resolves the contradiction by providing an effective adjustment method that works with FinFET architecture.
3Adaptability or versatility
If multiple processing steps are performed with patterned photoresist layers, then transistors with different threshold voltages can be formed, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies local quality by using patterned photoresist layers to selectively expose different gate trench regions to nitrogen-containing processing steps. This allows different nitrogen concentrations to be introduced into barrier layers of specific transistors, enabling the formation of high-threshold, low-threshold, and standard-threshold voltage transistors in the same device. The local application of nitrogen concentration variations achieves threshold voltage diversity while managing manufacturing complexity through targeted processing.
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
Enables the formation of N-type or P-type transistors with high, low, or standard threshold voltages by varying the nitrogen concentrations and thicknesses of work function and barrier layers, improving performance and adjustability in FinFET architecture.
Implementation Method 1
barrier layers in different nitrogen concentrations... so that each transistor may obtain different threshold voltages
Data Source
AI summary
A semiconductor device and a method of forming the same, the semiconductor device include a substrate, and a first transistor, a second transistor and a third transistor all disposed on the substrate. The first transistor includes a first channel, and a first barrier layer and a first work function layer stacked with each other on the first channel. The second transistor includes a second channel, and a second barrier layer and a second work function layer stacked with each other. The third transistor includes a third channel and a third barrier layer and a third work function layer stacked with each other on the third channel, wherein the first barrier layer, the second barrier layer and the third barrier layer have different nitrogen ratio. The first, the second and the third transistors have different threshold voltages, respectively.