Metal Gate Etching Selectivity for Threshold Voltage Spread
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Solution Overview
Problem
The poly depletion effect in metal-oxide-semiconductor (MOS) devices leads to increased effective gate dielectric thickness, making it difficult to create an inversion layer, and conventional metal gate formation methods do not effectively maintain a sufficient threshold voltage spread between NMOS and PMOS devices.
Innovation Solution
Doping aluminum into a titanium nitride work function tuning layer to increase etching selectivity between a tantalum nitride barrier layer and the titanium nitride work function tuning layer, thereby reducing the loss in thickness of work function tuning layer and maintaining the spread between threshold voltages of transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional metal gate formation methods are used, then the process is simple, but the threshold voltage spread between NMOS and PMOS devices is insufficient
Solution Approach 1:
The gate structure is segmented into multiple functional layers: a barrier layer (tantalum nitride) and a work function tuning layer (titanium nitride with aluminum doping). This segmentation allows independent optimization of each layer's properties to achieve the desired threshold voltage spread while maintaining manufacturing feasibility.
Solution Approach 2:
Aluminum is selectively doped into the titanium nitride work function tuning layer to create local compositional variations. This local quality modification enables precise control of work function and threshold voltage characteristics in different regions, achieving the required voltage spread between NMOS and PMOS devices.
2Length of stationary object
If etching is performed to thin the barrier layer, then the gate dielectric thickness is reduced, but the work function tuning layer thickness is also lost
Solution Approach 1:
The barrier layer acts as an intermediary protective layer during the etching process. By carefully controlling the etch selectivity between the barrier layer and work function tuning layer, the barrier layer protects the underlying gate dielectric while allowing selective removal of excess work function tuning layer material.
Solution Approach 2:
The etching process parameters are optimized to achieve selective removal of materials based on their different etch rates. By controlling etch chemistry, power, and other parameters, the process selectively thins the barrier layer while minimizing loss of the work function tuning layer, achieving the desired gate dielectric thickness without excessive material loss.
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 solution maintains a significant threshold voltage spread between transistors, ensuring optimal performance in different circuits by reducing the thickness loss of work function tuning layers and barrier layers during etching processes.
Implementation Method 1
Doping aluminum into a titanium nitride work function tuning layer to increase etching selectivity between a tantalum nitride barrier layer and the titanium nitride work function tuning layer
Implementation Method 2
reducing the loss in thickness of work function tuning layer and maintaining the spread between threshold voltages of transistors
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.