Hf Gate Insulator Sidewall Barrier for Threshold Stability
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Solution Overview
Problem
The challenge in semiconductor devices is the diffusion of elements introduced into Hf-based gate insulating films, which leads to reduced concentration and effectiveness in threshold voltage reduction, especially as channel width decreases, due to diffusion into silicon oxide device isolation regions.
Innovation Solution
Incorporating a sidewall insulating film made of silicon nitride or silicon oxynitride between the gate insulating film and the device isolation region to prevent diffusion of rare earth elements or alternative elements, maintaining their concentration and effectiveness in reducing threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal gate electrode is used to suppress depletion phenomenon, then the depletion problem is solved, but the absolute value of threshold voltage becomes large
Solution Approach 1:
The patent applies different materials to different regions: polysilicon gate electrode in the active region for proper threshold control, and metal gate electrode in the non-active region for depletion suppression. This local differentiation allows each region to optimize its specific function without compromising the other.
Solution Approach 2:
The gate electrode is segmented into two distinct parts: a first gate electrode made of polysilicon and a second gate electrode made of metal. This segmentation enables independent optimization of threshold voltage (polysilicon) and depletion suppression (metal) in different spatial zones.
2Manufacturing precision
If element for threshold reduction is introduced into Hf-based gate insulating film, then threshold reduction is achieved, but element diffuses into device isolation region
Solution Approach 1:
A barrier insulating film is introduced as an intermediary layer between the Hf-based gate insulating film containing the threshold reduction element and the device isolation region. This barrier film prevents diffusion of the element into the isolation region while allowing the threshold reduction effect to persist in the active region.
Solution Approach 2:
The patent extracts the threshold reduction element (rare earth element or aluminum) from the gate insulating film at the interface with the device isolation region by introducing a barrier insulating film, thereby preventing its diffusion into the isolation region while maintaining its beneficial effects in the active region.
3Length of moving object
If channel width is reduced for miniaturization, then device size is reduced, but threshold reduction effect is weakened due to element diffusion
Solution Approach 1:
The barrier insulating film acts as a mediator that prevents element diffusion even in narrow channel structures. This allows miniaturization to proceed while maintaining stable threshold voltage control, as the barrier film confines the threshold reduction element within the active region.
Solution Approach 2:
The barrier insulating film is formed beforehand to prevent element diffusion before miniaturization effects become problematic. This preliminary protective measure ensures that even as channel width is reduced, the threshold reduction effect remains stable due to prevented element loss.
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 effectively maintains the threshold voltage reduction effect across varying channel widths, improving semiconductor device performance by preventing element diffusion and ensuring consistent operation.
Implementation Method 1
Incorporating a sidewall insulating film made of silicon nitride or silicon oxynitride between the gate insulating film and the device isolation region to prevent diffusion of rare earth elements or alternative elements
Data Source
AI summary
A device isolation region is made of a silicon oxide film embedded in a trench, an upper portion thereof is protruded from a semiconductor substrate, and a sidewall insulating film made of silicon nitride or silicon oxynitride is formed on a sidewall of a portion of the device isolation region which is protruded from the semiconductor substrate. A gate insulating film of a MISFET is made of an Hf-containing insulating film containing hafnium, oxygen and an element for threshold reduction as main components, and a gate electrode that is a metal gate electrode extends on an active region, the sidewall insulating film and the device isolation region. The element for threshold reduction is a rare earth or Mg when the MISFET is an n-channel MISFET, and the element for threshold reduction is Al, Ti or Ta when the MISFET is a p-channel MISFET.