Replacement Metal Gate Threshold Voltage Adjustment via Lanthanum Oxide and Titanium Nitride
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Solution Overview
Problem
Current RMG processes for 20 nm technology nodes face challenges in reliable threshold voltage adjustment due to high leakage currents and time-dependent dielectric breakdown, particularly affecting n-type field effect transistors, which complicate the integration of additional metal layers.
Innovation Solution
A simplified RMG process involving the conformal formation of a lanthanum oxide margin adjusting layer and a titanium nitride metal capping layer, followed by an n-type work function metal layer, to enhance threshold voltage margin and reduce susceptibility to time-dependent dielectric breakdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Al diffusion is used to adjust threshold voltage in gate stack, then threshold voltage adjustment is achieved, but high leakage currents occur resulting in time dependent dielectric breakdown
Solution Approach 1:
A titanium nitride intermediary layer is introduced between the aluminum gate metal and the high-k dielectric layer. This intermediary layer acts as a diffusion barrier that prevents aluminum atoms from migrating into the dielectric, thereby eliminating leakage currents and TDDB while still allowing the aluminum layer to provide threshold voltage adjustment through controlled diffusion at the titanium nitride interface.
Solution Approach 2:
The gate metal stack is segmented into multiple functional layers: an aluminum layer for threshold voltage adjustment, a titanium nitride intermediary layer for diffusion barrier and work function adjustment, and a capping layer for protection. This segmentation allows each layer to perform its specific function independently, resolving the conflict between Vth adjustment and reliability.
2Manufacturing precision
If nWF metal layers are used to adjust Vth, then threshold voltage adjustment is achieved, but device complexity increases due to additional metal layers and selective removal processes
Solution Approach 1:
The titanium nitride layer performs multiple functions simultaneously: it serves as a diffusion barrier for aluminum, provides work function adjustment, acts as an adhesion layer, and functions as part of the gate electrode structure. This multi-functionality eliminates the need for separate nWF metal layers and selective removal processes, thereby reducing device complexity while maintaining Vth adjustment capability.
Solution Approach 2:
The diffusion barrier function and work function adjustment function are merged into a single titanium nitride layer, eliminating the need for separate functional layers. This merging simplifies the overall gate stack structure and reduces the number of patterning and etch steps required.
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 approach achieves additional threshold voltage margin and improved gate stack reliability with reduced leakage currents, simplifying the post-gate patterning process and enhancing the overall performance of n-type and p-type field effect transistors.
Implementation Method 1
conformally forming a margin adjusting layer in a first gate trench
Implementation Method 2
forming a metal capping layer on the margin adjusting layer
Implementation Method 3
annealing the Si capping layer
Data Source
AI summary
A methodology for enabling a gate stack integration process that provides additional threshold voltage margin without sacrificing gate reliability and the resulting device are disclosed. Embodiments include conformally forming a margin adjusting layer in a gate trench, forming a metal capping layer on the margin adjusting layer, and forming an n-type work function (nWF) metal layer on the metal capping layer.