Trench Gate Transistor Reliability via Offset Region Design
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Solution Overview
Problem
Transistors with extended source and drain regions to the vicinity of the gate electrode exhibit abnormal drain current characteristics due to electric field concentration at the trench corner, leading to hot carrier generation and reduced long-term reliability.
Innovation Solution
A semiconductor device configuration with a substrate, source and drain regions of a first conductivity type, a channel region of a second conductivity type, and low-concentration regions between the source and channel, and drain regions, where the sum of the length measurements of the underlying portion of the second low-concentration region from the trench corner is 0.1 μm or greater, preventing electric field concentration and hot carrier generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source region and drain region are extended to the vicinity of the bottom portion of the gate electrode, then on-resistance is reduced and transistor power is enhanced, but electric field concentration occurs at the trench corner causing hot carrier generation and reduced reliability
Solution Approach 1:
A low-concentration region is introduced as an intermediary structure between the high-concentration source/drain regions and the channel region. This intermediate region with gradually transitioning dopant concentration acts as a buffer that prevents abrupt electric field changes at the trench corner, thereby eliminating hot carrier generation while maintaining the extended source/drain configuration for low on-resistance
Solution Approach 2:
The dopant concentration parameter is changed gradually from the high-concentration source/drain regions through the low-concentration region to the channel region. This parameter transition prevents abrupt changes in electric field distribution, eliminating the electric field concentration at the trench corner that causes hot carrier generation, while preserving the beneficial low on-resistance characteristic
2Power
If source region and drain region are extended to the vicinity of the bottom portion of the gate electrode, then transistor power is enhanced, but breakdown voltage is reduced due to electric field concentration
Solution Approach 1:
The dopant concentration is changed gradually through the low-concentration region, creating a smooth transition that prevents abrupt electric field changes. This parameter gradient eliminates electric field concentration at the trench corner, thereby preventing breakdown voltage reduction while maintaining the extended source/drain configuration for high transistor power
3Reliability
If source region and drain region are extended to the vicinity of the bottom portion of the gate electrode, then on-resistance is reduced, but substrate current increases due to hot carrier generation
Solution Approach 1:
The low-concentration region serves as an intermediary that prevents hot carrier generation by eliminating abrupt electric field changes. Without hot carrier generation, substrate current is prevented while maintaining the extended source/drain configuration for low on-resistance
Solution Approach 2:
Gradual parameter change in dopant concentration through the low-concentration region prevents the conditions necessary for hot carrier generation. This eliminates the mechanism that would increase substrate current while preserving the low on-resistance benefit of extended source/drain regions
Data Source
AI summary
A trench gate transistor whose gate changes the depth thereof intermittently in the gate width direction, has a first offset region and a second offset region formed below the source and drain, respectively. The sum of length measurements of the underlying portion of the second offset region measured from the lower corner of the trench in a direction parallel to the substrate and in a direction perpendicular to the substrate is 0.1 μm or greater.