Doped Work Function Metal Gate Stack for Threshold Voltage Tuning
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Solution Overview
Problem
As the semiconductor industry continues to reduce minimum feature sizes to improve integration density, it faces challenges such as maintaining control over threshold voltage and ensuring reliable operation of field effect transistors (FETs).
Innovation Solution
The implementation of a gate stack structure with a pair of work function metal layers that generate dipoles, allowing for the tuning of threshold voltage in FETs. This structure includes a bottom work function metal layer with dopants, such as oxygen, and a top work function metal layer with different dopants, such as carbon, to achieve the desired electronegativity and effective work function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If minimum feature sizes are reduced to improve integration density, then more components can be integrated into a given area, but control over threshold voltage and reliable operation of FETs deteriorates
Solution Approach 1:
The gate electrode is segmented into multiple layers with different materials and functions. The lower gate electrode layer provides basic gate control, while the upper gate electrode layer with specific work function metal (titanium nitride) and dopants (oxygen, carbon) provides precise threshold voltage tuning. This segmentation allows independent optimization of each layer's properties to simultaneously achieve high integration density and reliable threshold voltage control.
Solution Approach 2:
Different regions of the gate electrode structure are assigned different local properties. The upper gate electrode layer has specific local quality characteristics including titanium nitride composition, oxygen dopants for desired electronegativity, and carbon dopants for adjusting effective work function. These localized quality adjustments enable precise threshold voltage control in miniaturized devices where overall device dimensions are reduced but functional requirements are maintained.
2Manufacturing precision
If work function metal layers are doped to tune threshold voltage, then precise control over FET operation is achieved, but device structure and manufacturing complexity increases
Solution Approach 1:
Multiple functions are merged into the upper gate electrode layer: it serves as both the primary gate control electrode and the work function tuning layer. The layer combines titanium nitride base material with oxygen dopants for electronegativity control and carbon dopants for effective work function adjustment. This merging eliminates the need for separate threshold voltage tuning structures, reducing overall device complexity while achieving precise threshold voltage control.
Solution Approach 2:
The effective work function of the gate electrode is tuned by changing compositional parameters of the upper gate electrode layer. Oxygen dopant concentration is adjusted to achieve desired electronegativity, and carbon dopant concentration is modified to fine-tune the effective work function. These parameter changes within the existing gate stack structure enable precise threshold voltage tuning without fundamentally altering the device architecture.
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 solution enables precise tuning of the threshold voltage of metal gate stacks, improving the reliability and performance of semiconductor devices by adjusting the dopant concentration in the work function metal layers.
Implementation Method 1
a pair of doped work function (WF) metal layers is formed over the gate dielectric layer. The pair of doped WF metal layers includes a bottom WF metal layer and a top WF metal layer. At least one of the top and bottom WF metal layers includes dopants, and the top WF metal layer is thicker than the bottom WF metal layer.
Implementation Method 2
At least one of the top and bottom WF metal layers includes dopants, and the top WF metal layer is thicker than the bottom WF metal layer. The doping process modifies the electrical properties of the metal layers to achieve desired work function values.
Data Source
AI summary
A semiconductor device includes a substrate, a gate stack, and epitaxy structures. The substrate has a P-type region. The gate stack is over the P-type region of the substrate and includes a gate dielectric layer, a bottom work function (WF) metal layer, a top WF metal layer, and a filling metal. The bottom WF metal layer is over the gate dielectric layer. The top WF metal layer is over and in contact with the bottom WF metal layer. Dipoles are formed between the top WF metal layer and the bottom WF metal layer, and the dipoles direct from the bottom WF metal layer to the top WF metal layer. The filling metal is over the top WF metal layer. The epitaxy structures are over the P-type region of the substrate and on opposite sides of the gate stack.