Air Gap in Semiconductor Isolation for Narrow Channel Effect
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Solution Overview
Problem
The narrow channel effect in field effect transistors, caused by boron diffusion into the element isolation insulating film and fixed charges within it, leads to fluctuations in transistor characteristics and increased power consumption, especially in memory chips with small gate widths.
Innovation Solution
Incorporating an air gap between the element isolation insulating film and the channel region to prevent boron diffusion and reduce fixed charges, thereby stabilizing the channel and minimizing stress-induced mobility changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an oxide film is used as element isolation insulating film, then element isolation is achieved, but boron diffusion into the oxide film causes threshold voltage fluctuations and narrow channel effect
Solution Approach 1:
The element isolation insulating film is segmented into multiple layers: a first oxide film layer in contact with the channel region, a second oxide film layer above it, and an air gap between them. This segmentation prevents boron diffusion while maintaining isolation functionality.
Solution Approach 2:
An air gap is introduced as an intermediary layer between the oxide film and the channel region. This air gap acts as a barrier that prevents boron diffusion and reduces fixed charge effects, thereby stabilizing transistor characteristics.
2Productivity
If channel width is reduced to increase transistor density, then productivity improves, but narrow channel effect increases causing threshold voltage fluctuations
Solution Approach 1:
The insulating film is divided into multiple layers with an air gap, creating a segmented structure that specifically addresses narrow channel effects in small-width transistors while maintaining high transistor density.
Solution Approach 2:
The physical state of the insulating film is changed by introducing an air gap (gas phase) between solid oxide layers. This parameter change eliminates boron diffusion paths and reduces fixed charge effects that cause threshold voltage fluctuations in narrow channel transistors.
3Productivity
If oxide film heating is applied for processing, then manufacturing progress is achieved, but film stress changes cause channel mobility fluctuations
Solution Approach 1:
The multi-layer oxide structure with air gap segments the stress distribution, allowing controlled stress management during heating processes while maintaining channel mobility stability.
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 suppresses the narrow channel effect, reduces threshold voltage fluctuations, and decreases power consumption by stabilizing transistor characteristics and carrier mobility, while also reducing layout dependency and stress on the semiconductor substrate.
Implementation Method 1
Incorporating an air gap between the element isolation insulating film and the channel region to prevent boron diffusion
Implementation Method 2
reduce fixed charges, thereby stabilizing the channel
Implementation Method 3
the oxide film composing the element isolation insulating film generates a film stress depending on the history of a heating process
Data Source
AI summary
According to one embodiment, a semiconductor device includes an element isolation insulating film, a gate electrode film, source/drain regions, a channel region, and an air gap. The element isolation insulating film partitions an element arrangement area on one main face side of a semiconductor substrate. The channel region is disposed near a surface of the semiconductor substrate below the gate electrode film. The air gap is disposed at a region of the element isolation insulating film contacting with the channel region.