Work Function Modulation via Gas Treatment in Metal Gate Structures
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Solution Overview
Problem
The reduction in size of semiconductor devices leads to leakage current issues due to thin gate dielectric layers, and conventional methods like using high-k materials result in Fermi-level pinning and increased threshold voltage, making it difficult to control process stability and form continuous films with metal gate structures.
Innovation Solution
A method for modulating the work function of semiconductor devices with a metal gate structure involves forming stacked gate structures with patterned hard masks, using nitrogen-containing or oxygen-containing gases for gas treatments, and employing atomic layer deposition (ALD) for work function metal layers, gate dielectric layers, and barrier layers to achieve different threshold voltages without relying on ion implant tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the work function metal layer is reduced to modulate work function, then the work function modulation becomes more effective, but process stability control becomes difficult and continuous film formation becomes challenging
Solution Approach 1:
The patent changes the chemical state of the work function metal layer through gas treatment (oxidation or nitridation) rather than changing its physical thickness. This allows work function modulation while maintaining a constant, optimized metal layer thickness that ensures process stability and continuous film formation.
Solution Approach 2:
The patent introduces gas treatment (oxygen or nitrogen) as an intermediary process to modify the work function metal layer. This intermediary chemical treatment enables work function adjustment without directly manipulating the metal layer thickness, thus avoiding the instability issues associated with thin film deposition.
2Object-affected harmful factors
If high dielectric constant material is used to replace silicon oxide to form gate dielectric layer, then leakage current is avoided, but Fermi-level pinning is generated and threshold voltage increases
Solution Approach 1:
The patent introduces a metal gate structure with work function metal layers as an intermediary between the high-k dielectric and the channel. This metal gate acts as a buffer that prevents direct interaction between the polysilicon gate and high-k dielectric, thereby avoiding Fermi-level pinning while maintaining the leakage current benefits of high-k materials.
Solution Approach 2:
The patent uses a composite gate structure consisting of multiple metal layers (work function metal layers combined with other metal layers) to achieve both low leakage current and avoidance of Fermi-level pinning. The composite structure allows independent optimization of different functions within the gate stack.
3Manufacturing precision
If ion implant tuning is used to adjust threshold voltage, then threshold voltage adjustment is achieved, but manufacturing cost increases
Solution Approach 1:
The patent extracts the threshold voltage adjustment function from the ion implantation process and relocates it to the work function metal layer deposition and gas treatment processes. This eliminates the need for additional ion implantation steps, thereby reducing manufacturing cost while maintaining threshold voltage adjustability.
Solution Approach 2:
The patent performs work function metal layer deposition and gas treatment as preliminary actions during the standard fabrication process flow, before final device completion. This preliminary adjustment of threshold voltage through work function control eliminates the need for subsequent ion implantation tuning steps.
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 method allows for the modulation of work functions with improved process stability and reduced manufacturing costs, enabling the formation of semiconductor devices with varying threshold voltages while maintaining reliability and controlling the thickness of work function metal layers effectively.
Implementation Method 1
A first gas treatment is performed to the first work function metal layer of the first stacked gate structure exposed by the patterned hard mask layer. A gas used in the first gas treatment includes nitrogen-containing gas or oxygen-containing gas.
Data Source
AI summary
A method for modulating a work function of a semiconductor device having a metal gate structure including the following steps is provided. A first stacked gate structure and a second stacked gate structure having an identical structure are provided on a substrate. The first stacked gate structure and the second stacked gate structure respectively include a first work function metal layer of a first type. A patterned hard mask layer is formed. The patterned hard mask layer exposes the first work function metal layer of the first stacked gate structure and covers the first work function metal layer of the second stacked gate structure. A first gas treatment is performed to the first work function metal layer of the first stacked gate structure exposed by the patterned hard mask layer. A gas used in the first gas treatment includes nitrogen-containing gas or oxygen-containing gas.