FinFET Work Function Layer Thickness Control
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Solution Overview
Problem
Conventional methods for adjusting threshold voltages in FinFETs are inadequate, as they cannot easily be tuned using ion implantation, and polysilicon gates face issues like boron penetration and depletion, leading to inferior performance.
Innovation Solution
A method involving the use of novel etching chemicals, specifically radical oxygen such as dilute ozone and hydrogen peroxide, to form semiconductor devices with different work function layers, allowing for precise control of work function thickness and surface oxidation to achieve uniform and compact surfaces, thereby enabling precise adjustment of threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If ion implantation is used to adjust threshold voltage in conventional planar metal gate transistors, then threshold voltage can be adjusted, but this method cannot be easily applied to FinFET architecture
Solution Approach 1:
The patent changes the parameter of threshold voltage adjustment from ion implantation to work function layer thickness control. By depositing work function layers of different thicknesses (5-20 nm range) in different transistor regions, the threshold voltage is tuned without requiring ion implantation, making it compatible with FinFET architecture while maintaining adjustability
Solution Approach 2:
The patent applies local quality by creating different work function layer thicknesses in different transistor regions (e.g., higher threshold voltage regions vs. lower threshold voltage regions). This allows each region to have optimized local characteristics suitable for its specific function while using the same FinFET fabrication process
2Ease of manufacture
If conventional polysilicon gate is used, then gate electrode can be formed, but boron penetration and depletion effect occur which reduces gate capacitance and driving force
Solution Approach 1:
The patent uses composite materials by combining metal layers (such as titanium nitride, tantalum nitride, or tungsten) with high-K dielectric materials. This composite gate structure replaces conventional polysilicon, eliminating boron penetration and depletion effects while maintaining ease of formation through standard deposition processes, thereby improving gate capacitance and driving force
Solution Approach 2:
The patent changes the material parameter from polysilicon to metal-based work function layers. This material substitution eliminates the chemical issues (boron penetration) and physical limitations (depletion effect) of polysilicon while maintaining compatibility with high-K dielectric gate insulators, thus improving overall gate performance
3Productivity
If photoresist layers are removed using conventional cleaning methods, then photoresist can be removed, but residue polymers remain and work function layer surface is not uniform
Solution Approach 1:
The patent uses strong oxidants (ozone or hydrogen peroxide) to completely oxidize and remove photoresist residue polymers from the work function layer surface. This oxidation process achieves both high cleaning efficiency and uniform surface quality, eliminating the trade-off between productivity and manufacturing precision in the cleaning process
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 method allows for the precise control of threshold voltages in FinFETs, minimizing inaccuracy between center and edge voltages to less than 5 mV, enabling the formation of transistors with high, low, or standard threshold voltages, and improving the surfacing and cleaning ability of work function layers.
Implementation Method 1
those photoresist layers are removed through a wet cleaning process by using a cleaning agent of radical oxygen, such as dilute ozone (DIO3) and/or hydrogen peroxide (H2O2). In this way, the residue polymers, such as CxHyFz composition, generated while patterning the work function layer are easily removed via the cleaning processes
Implementation Method 2
the work function layers may also obtain preferable surfacing, since a slight amount of the work function layers may also be oxidized to generate a uniform and compact surface
Data Source
AI summary
A method of forming a semiconductor device includes following steps. First of all, a first work function layer is formed on a substrate. Next, a first patterned photoresist layer is formed on the first work function layer. Then, the first work function layer is partially removed by using the first patterned photoresist layer as a mask to form a patterned first work function layer. Subsequently, the first patterned photoresist layer is removed by providing radical oxygen.