Dual Work Function Metal Gate via Single Layer Doping
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Solution Overview
Problem
Conventional semiconductor devices face challenges with polysilicon gate electrodes when using very thin gate insulating layers, experiencing voltage drops, high gate resistance, and stability issues due to the gate depletion effect, while metal gate electrodes are difficult to fabricate and require complex processing.
Innovation Solution
The method involves forming a metal layer with a specific work function and adjusting it by doping with fluorine or carbon to achieve different work functions for NMOS and PMOS gate electrodes, using techniques like ion implantation to produce a Gaussian dopant profile, allowing for the formation of dual metal gate electrodes from a single metal layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polysilicon gate electrodes are used with very thin gate insulating layers, then the manufacturing process is simple and easy to deposit, but voltage drops and high gate resistance occur due to gate depletion effect
Solution Approach 1:
The patent changes the material parameter from polysilicon to metal (such as tungsten, titanium, tantalum, molybdenum, ruthenium, nickel, or niobium), fundamentally altering the electrical properties to eliminate gate depletion effects while maintaining compatibility with thin gate insulating layers
Solution Approach 2:
The patent employs composite metal gate structures combining multiple metal layers with different work functions, where a first metal layer provides a first work function and a second metal layer provides a second work function, enabling simultaneous optimization for both PMOS and NMOS devices
2Reliability
If metal gate electrodes are used to replace polysilicon, then gate depletion effects are eliminated, but fabrication becomes difficult and processing complexity increases
Solution Approach 1:
The patent divides the metal gate structure into multiple layers, each with specific thickness and work function characteristics, allowing independent optimization of each layer's properties to achieve overall device performance while simplifying the deposition process
Solution Approach 2:
The patent applies different work function characteristics to different regions of the gate electrode by using metals with specific work functions in specific locations, enabling simultaneous optimization for PMOS and NMOS devices within the same gate structure
3Adaptability or versatility
If dual metal gate electrodes with different work functions are formed using separate metal layers, then PMOS and NMOS devices can be optimized, but multiple depositions and etching steps are required
Solution Approach 1:
The patent merges the formation of dual work function gates into a single deposition process by using a stack of metal layers where each layer contributes a different work function characteristic, eliminating the need for separate deposition and etching steps for each metal gate type
Solution Approach 2:
The patent creates a universal gate structure that serves both PMOS and NMOS devices simultaneously, where the stacked metal layer configuration provides the necessary work function range for both device types without requiring separate processing streams
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 simplifies the manufacturing process by eliminating the need for multiple metal layer depositions and etching steps, providing flexible work function adjustment and improved stability, while minimizing processing complexity and costs.
Implementation Method 1
adjusting it by doping with fluorine or carbon to achieve different work functions for NMOS and PMOS gate electrodes
Implementation Method 2
using techniques like ion implantation to produce a Gaussian dopant profile
Data Source
AI summary
A semiconductor device and related methods of manufacture are disclosed in which dual work function metal gate electrodes are formed from a single metal layer by doping the metal layer with carbon and/or fluorine.