Work Function Gate Layer With Oxygen Barrier Doping for MOSFET Scaling
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Solution Overview
Problem
The challenge of preventing parasitic capacitance among gate stacks in MOSFETs due to reduced spacing during device scaling, which affects device performance in CMOS fabrication.
Innovation Solution
Incorporating a work function layer doped with barrier elements, such as TiN, TaN, WN, or TiAlN, to prevent oxygen diffusion and maintain the integrity of the work function layer, combined with a replacement polysilicon gate technique to form functional gate structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gate length and spacing are reduced to scale down MOSFETs, then device integration density is improved, but parasitic capacitance among gate stacks increases
Solution Approach 1:
A barrier layer is introduced as an intermediary between adjacent gate stacks. This barrier layer acts as a mediator to reduce the parasitic capacitance coupling between neighboring gates, allowing the gate stacks to be placed closer together while maintaining electrical isolation. The barrier layer material (such as silicon nitride or silicon oxide) has low dielectric constant properties that specifically target the reduction of parasitic capacitance without affecting the primary gate function.
Solution Approach 2:
The harmful parasitic capacitance effect is extracted and isolated by introducing a dedicated barrier layer structure. Instead of relying solely on the inherent properties of the gate stack materials, a separate functional layer is extracted from the gate structure to specifically address the parasitic capacitance problem, allowing the main gate functionality to remain intact while the barrier layer handles the capacitance reduction.
2Reliability
If work function layer is used to adjust threshold voltage, then device performance is improved, but oxygen diffusion into the work function layer causes threshold voltage instability
Solution Approach 1:
A barrier layer is positioned between the work function layer and the ambient environment (or between adjacent gate stacks) to act as an oxygen barrier. This intermediary layer prevents oxygen diffusion into the work function layer, thereby stabilizing the work function layer's composition and maintaining consistent threshold voltage. The barrier layer material is selected to have high resistance to oxygen permeation.
Solution Approach 2:
The barrier layer is formed prior to or concurrently with the work function layer deposition to preemptively block oxygen diffusion pathways. By establishing the oxygen barrier before the work function layer is fully formed or exposed to oxygen-containing environments, the composition stability of the work function layer is preserved from the outset, preventing threshold voltage drift during subsequent processing or device operation.
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
Reduces parasitic capacitance and maintains consistent threshold voltage, enhancing device performance and reliability in scaled MOSFETs.
Implementation Method 1
a plurality of barrier elements are formed on or under a top surface of the second portion of the work function layer. The plurality of barrier elements block oxygen from diffusing into the work function layer during the formation of the gate electrode.
Data Source
AI summary
The present disclosure provides a method of manufacturing a semiconductor device. The method includes: forming a transistor region in a substrate; forming a gate dielectric layer over the transistor region; forming a diffusion-blocking layer over the gate dielectric layer; forming a first portion of a work function layer over the diffusion-blocking layer; forming a second portion of the work function layer over the first portion of the work function layer; forming a plurality of barrier elements on or under a top surface of the second portion of the work function layer; and forming a gate electrode over the work function layer, wherein the plurality of barrier elements block oxygen from diffusing into the work function layer during the formation of the gate electrode.