Dual Work Function Metal Gate Structure via Selective 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, and metal gate electrodes are complex to fabricate, especially in forming dual metal layers with disparate work functions for PMOS and NMOS devices.
Innovation Solution
The method involves forming a metal layer with an initial work function and adjusting it by doping with fluorine or carbon to achieve distinct work functions for PMOS and NMOS regions, using techniques like ion implantation to produce Gaussian concentration profiles, allowing for the formation of dual metal gate electrodes from a single metal layer, thereby simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If polysilicon gate electrodes are used with very thin gate insulating layers, then the device can be scaled down, but voltage drops and high gate resistance occur due to gate depletion effect
Solution Approach 1:
The patent changes the material parameter of the gate electrode from polysilicon to metal (such as tungsten, titanium, tantalum, molybdenum, ruthenium, nickel, or niobium), fundamentally altering the electrical properties to eliminate gate depletion effects and enable operation with very thin gate insulating layers while maintaining low gate resistance and stable voltage characteristics
Solution Approach 2:
The patent employs composite material structures including metal gate electrodes combined with high-k gate dielectrics, and uses metal compounds, alloys, nitrides, silicides, and oxides to create gate electrode structures that optimize both electrical performance and compatibility with thin insulating layers
2Reliability
If separate metal layers are formed for PMOS and NMOS gates to achieve disparate work functions, then device performance is optimized, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by selectively doping different regions of a single metal layer with different materials (phosphorus for NMOS regions, boron for PMOS regions) to create locally distinct work functions, allowing optimization of both PMOS and NMOS device performance from one unified gate structure
Solution Approach 2:
The patent merges the formation of PMOS and NMOS gate electrodes into a single metal layer deposition and doping process, combining what would traditionally require separate metal layers and multiple fabrication steps into one integrated process flow
3Adaptability or versatility
If doped polysilicon gate electrodes are used, then work function can be adjusted, but gate resistance increases and stability issues occur with high-k gate dielectrics
Solution Approach 1:
The patent changes the fundamental material parameter from polysilicon to metal, which inherently provides lower gate resistance and better stability with high-k dielectrics while maintaining the ability to adjust work function through selective doping with phosphorus or boron in different regions
Solution Approach 2:
The patent replicates the work function adjustment capability of doped polysilicon in metal gate structures by using selective ion implantation or diffusion of dopants into metal layers, copying the functional advantage of work function tunability while eliminating the detrimental effects of polysilicon gate depletion
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 enables the creation of semiconductor devices with dual metal gate electrodes that are compatible with both PMOS and NMOS devices, reducing manufacturing complexity and cost by allowing work function adjustments without the need for multiple metal layer depositions, while ensuring compatibility and performance criteria are met.
Implementation Method 1
adjusting the work function of at least some selected portion of the metal layer by doping it with fluorine... fluorine doping may be accomplished by any one of a number of methods including ion implantation
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.