Switching Device Thermal Stress Mitigation via Metal Layer Expansion
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Solution Overview
Problem
The existing switching devices face issues with thermal stress leading to cracks in the first metal layer and increased resistance in the second region due to mismatched thermal expansion coefficients, and they also suffer from reduced breakdown voltage and high resistance when the grid-shaped trench is modified to prevent floating body regions.
Innovation Solution
The proposed switching device includes a semiconductor substrate with a first metal layer, a second metal layer, and an insulating protective film, where the second metal layer has a smaller linear expansion coefficient than the first metal layer, and a second conductivity type peripheral region is introduced in the ineffective range to connect with the body region, reducing thermal stress and ensuring breakdown voltage while maintaining low resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the grid-shaped trench is modified to prevent floating body regions, then breakdown voltage is maintained, but resistance in the second region increases
Solution Approach 1:
The patent applies local quality by creating a peripheral region with different trench characteristics than the central region. Specifically, the trench depth is reduced or trenches are omitted in the peripheral area where body regions are present, while maintaining full-depth trenches in the central switching region. This localized modification allows the peripheral body regions to remain electrically active and connected to the second region, reducing resistance without compromising the breakdown voltage in the main switching area.
2Reliability
If the second metal layer is filled in recesses to prevent gaps, then thermal stress is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by forming the recesses in the second metal layer during the initial metal layer formation process, before subsequent processing steps. The recesses are created with predetermined dimensions and positions that account for thermal expansion differences. This preliminary structuring allows the second metal layer to naturally accommodate thermal stress during operation without requiring additional corrective measures or complex multi-step manufacturing processes.
3Object-affected harmful factors
If contact holes are provided in all cell regions, then electrical connection is improved, but thermal stress concentration increases
Solution Approach 1:
The patent applies local quality by selectively providing contact holes only in specific cell regions rather than uniformly across all cell regions. Contact holes are placed in regions where electrical connection is critical, while omitting them in regions where thermal stress concentration would be problematic. This selective approach optimizes the balance between electrical connectivity and thermal stress distribution by adapting the contact hole pattern to the local functional requirements of different cell regions.
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 configuration effectively suppresses cracks in the first metal layer, ensures low resistance in the second region, and maintains high breakdown voltage by mitigating thermal stress and electric field concentration.
Implementation Method 1
a linear expansion coefficient of the second metal layer is smaller than a linear expansion coefficient of the first metal layer
Implementation Method 2
inner surfaces of the first trenches and inner surfaces of the second trenches are covered with a gate insulating film
Implementation Method 3
an upper surface of which is connected to a heat sink block by soldering
Data Source
AI summary
A switching device includes a semiconductor substrate having a first element range and an ineffective range. First trenches extend in a first direction across the first element range and the ineffective range. Second trenches are provided in each inter-trench region within the first element range and are not provided within the ineffective range. A gate electrode is disposed in the trenches. No contact hole is provided in an interlayer insulating film within the ineffective range. The first metal layer covers the interlayer insulating film. The insulating protective film covers a portion of the first metal layer on its outer peripheral side within the ineffective range. The second metal region is in contact with the first metal layer within an opening of the insulating protective film, and is in contact with a side surface of the opening.