FinFET Gate Work-Function Layers for Threshold-Voltage Tuning
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Solution Overview
Problem
The increasing demand for high-performance, high-speed, and multifunctional semiconductor devices necessitates finer patterns and three-dimensional channel structures, such as FinFETs, to overcome limitations in operating characteristics due to size reductions in planar metal oxide semiconductor FETs, while maintaining improved electrical characteristics and reliability.
Innovation Solution
A semiconductor device design featuring a substrate with active patterns, channel layers, and a gate structure that includes a multilayer work function electrode pattern with a work function adjusting layer having a higher oxygen concentration, allowing for the adjustment of threshold voltages through surface oxidation treatment, enabling transistors with varying threshold voltages on the same substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a planar metal oxide semiconductor FET structure is used, then manufacturing is simpler, but operating characteristics deteriorate due to size reductions
Solution Approach 1:
The patent transitions from a planar FET structure to a FinFET structure with a three-dimensional channel. The channel is formed by standing fins extending vertically from the substrate, adding a vertical dimension to the current flow path. This dimensional change increases the effective channel area and improves carrier transport while maintaining a compact footprint, thereby improving operating characteristics without sacrificing manufacturability.
Solution Approach 2:
The FinFET structure employs composite material layers including semiconductor fins (e.g., Si or SiGe), dielectric isolation layers, metal gate electrodes, and contact regions. The channel layers are formed from semiconductor materials with specific bandgap properties, while the gate dielectric uses materials with optimized permittivity. This composite structure enables precise control of electrical characteristics and improved device performance.
2Reliability
If threshold voltage is adjusted by changing gate electrode material, then transistor performance is optimized, but manufacturing complexity increases
Solution Approach 1:
The gate electrode is segmented into multiple functional layers: a first metal layer (e.g., TiN) providing base work function, a work function adjusting layer (e.g., TiON or TiAlON) for threshold voltage tuning, and a second metal layer (e.g., TaN or WN) for additional work function adjustment. This segmentation allows independent optimization of each layer's contribution to threshold voltage control while maintaining manufacturability through sequential deposition processes.
Solution Approach 2:
The patent adjusts threshold voltage by changing the chemical composition and stoichiometry of the work function adjusting layer, specifically controlling the oxygen concentration in the TiON layer. By varying the O:Ti ratio (e.g., 0.9-1.1), the work function of the gate electrode is precisely tuned, which directly controls the threshold voltage. This parameter-based control approach enables fine-grained adjustment without adding structural complexity.
3Reliability
If oxygen concentration in work function adjusting layer is increased, then threshold voltage is lowered, but layer composition control becomes more difficult
Solution Approach 1:
The work function adjusting layer is formed by performing an oxidation process on the first metal layer before depositing the second metal layer. This preliminary oxidation step introduces oxygen into the Ti layer, forming TiON with controlled oxygen concentration. By controlling the oxidation time, temperature, and oxygen pressure during this preliminary step, the oxygen concentration in the work function adjusting layer is precisely controlled, enabling reproducible threshold voltage adjustment.
Solution Approach 2:
Instead of using mechanical methods to control oxygen concentration (such as physical vapor deposition with oxygen plasma), the patent employs a chemical oxidation process where oxygen is introduced through controlled thermal oxidation. This chemical approach provides more precise and uniform oxygen incorporation into the metal layer, achieving better compositional control and more reliable threshold voltage adjustment.
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
The design allows for the fabrication of transistors with diverse threshold voltages, enhancing electrical performance and reliability by optimizing the gate structure's composition and oxygen concentration, thereby supporting advanced semiconductor device integration.
Implementation Method 1
allowing for the adjustment of threshold voltages through surface oxidation treatment
Data Source
AI summary
A semiconductor device is provided, the semiconductor device including: a first transistor and a second transistor on a substrate, wherein each of the first transistor and the second transistor includes an active pattern on the substrate, channel layers spaced apart from each other on the active pattern, and a gate dielectric layer and a gate electrode surrounding the channel layers, wherein the gate dielectric layer of the first transistor includes a first work function metal layer and a first work function adjusting layer on the first work function metal layer, and the gate electrode of the second transistor includes a second work function metal layer, the first and second work function metal layers include the same material, and the first work function adjusting layer includes an oxide of the same material, wherein a threshold voltage of the first transistor is lower than a threshold voltage of the second transistor.