Selective Etching of Gate Stack Layers for Threshold Voltage Spread
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Solution Overview
Problem
Metal-Oxide-Semiconductor (MOS) devices face challenges in creating a sufficient threshold voltage spread due to the poly depletion effect, which increases the effective gate dielectric thickness and makes it difficult to form an inversion layer, especially in Fin Field-Effect Transistors (FinFETs), where the poly depletion effect reduces the selectivity between metal layers and affects the threshold voltage consistency.
Innovation Solution
Doping aluminum into the titanium nitride work function tuning layer increases the etching selectivity between the tantalum nitride barrier layer and the titanium nitride work function tuning layer, allowing for reduced thickness loss during etching and maintaining the threshold voltage spread by selectively thinning the barrier layer, thereby minimizing the adverse impact on work function tuning layers in adjacent transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the barrier layer is thinned to adjust threshold voltage, then the threshold voltage spread is improved, but the work function tuning layer thickness is reduced due to lack of selectivity
Solution Approach 1:
The patent changes the chemical composition parameter of the work function tuning layer by doping aluminum into the titanium nitride layer. This parameter change increases the etching selectivity between the barrier layer and the work function tuning layer, allowing the barrier layer to be thinned while preserving the work function tuning layer thickness, thus resolving the contradiction between improving threshold voltage spread and maintaining layer thickness
Solution Approach 2:
The patent applies local quality by creating a work function tuning layer with non-uniform aluminum doping concentration. The aluminum doping concentration varies across different regions of the layer, with higher doping in specific areas to enhance etching selectivity locally where needed, while maintaining appropriate work function characteristics in other regions
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 approach effectively maintains a significant spread between threshold voltages of transistors, ensuring adequate differences for various circuit requirements while reducing the adverse reduction in threshold voltage spread, even when etching the barrier layer, by enhancing etching selectivity and minimizing the thickness loss of work function tuning layers.
Implementation Method 1
Doping aluminum into the titanium nitride work function tuning layer increases the etching selectivity between the tantalum nitride barrier layer and the titanium nitride work function tuning layer
Implementation Method 2
removing the first portion of the first work function tuning layer; thinning the first portion of the barrier layer
Data Source
AI summary
A method includes forming a gate dielectric comprising a portion extending on a semiconductor region, forming a barrier layer comprising a portion extending over the portion of the gate dielectric, forming a work function tuning layer comprising a portion over the portion of the barrier layer, doping a doping element into the work function tuning layer, removing the portion of the work function tuning layer, thinning the portion of the barrier layer, and forming a work function layer over the portion of the barrier layer.