Silicon Substrate Edge Crack Reduction via Stepped Dielectric Film
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Solution Overview
Problem
Silicon substrates used for nitride-based semiconductor devices face issues such as increased dislocation density and stress due to lattice and thermal expansion mismatches, leading to crack formation and brittleness during epitaxial growth and cooling processes.
Innovation Solution
A silicon wafer with a dielectric film on its edge portion, either nitride or oxide, is used to reduce stress by growing a second nitride semiconductor thin film with a polycrystalline or amorphous structure on the edge, while maintaining a single-crystal nitride film on the main portion, thereby reducing crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a silicon substrate is used instead of a sapphire substrate, then thermal conductivity is improved and warping is reduced, but dislocation density increases due to lattice constant mismatch
Solution Approach 1:
The patent applies local quality by creating a stepped structure where the peripheral portion has a different height than the main surface. This allows the edge portion to have distinct structural characteristics that accommodate stress and reduce dislocation propagation, while the main surface maintains optimal conditions for high-quality nitride semiconductor growth.
Solution Approach 2:
The silicon substrate is segmented into two distinct regions: a main surface for growing high-quality nitride semiconductor and a peripheral portion with stepped structure. This segmentation allows each region to serve its specific function - the main surface for device fabrication and the peripheral portion for stress management and dislocation control.
2Ease of manufacture
If a nitride thin film is grown on a silicon substrate, then manufacturing cost is reduced, but stress is generated due to thermal expansion coefficient mismatch
Solution Approach 1:
The stepped structure creates a local quality difference between the main surface and peripheral portion. The peripheral portion's stepped configuration provides stress relief by creating a gradual transition zone that accommodates thermal expansion mismatch, reducing interface stress while maintaining cost-effective silicon substrate usage.
3Productivity
If a silicon substrate with large diameter is used, then productivity is improved, but plastic deformation occurs due to applied stress at higher temperatures
Solution Approach 1:
The substrate is divided into a main surface area for large-diameter production and a peripheral stepped portion for stress management. This segmentation allows large diameter substrates to be used for improved productivity while the stepped peripheral structure prevents plastic deformation by providing stress relief zones.
Solution Approach 2:
The stepped peripheral portion provides local structural quality that accommodates thermal stress in large-diameter substrates. This local modification allows the overall substrate to maintain its large diameter for high productivity while preventing deformation through the stress-absorbing stepped edges.
4Loss of time
If the silicon substrate is cooled to room temperature, then the growth process is completed, but cracks are generated and grown at edge portions due to thermal shock
Solution Approach 1:
The stepped peripheral structure serves as a pre-designed stress buffer that cushions against thermal shock during cooling. By having this structural feature in place before cooling begins, the substrate can withstand thermal contraction stresses without generating cracks at the edges, protecting the overall integrity during the cooling process.
5Reliability
If a dielectric film is formed on the edge portion, then crack propagation is reduced, but manufacturing complexity increases
Solution Approach 1:
The dielectric film is applied locally only to the stepped peripheral portion rather than the entire substrate surface. This localized application provides crack resistance where it is most needed at the edges while minimizing the increase in manufacturing complexity by avoiding unnecessary processing of the main surface area.
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 lowers interface stress and reduces deformation and crack generation in the silicon substrate, allowing for larger diameter substrates and improved nitride semiconductor thin film growth without significant substrate damage.
Implementation Method 1
A crack reducing portion is formed on the silicon edge portion... This approach lowers interface stress and reduces deformation and crack generation in the silicon substrate
Implementation Method 2
growing a second nitride semiconductor thin film with a polycrystalline or amorphous structure on the edge, while maintaining a single-crystal nitride film on the main portion
Data Source
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AI summary
Crack formation and propagation in a silicon substrate may be reduced by forming a crack reducing portion. The silicon substrate includes a silicon main portion and a silicon edge portion formed around the silicon main portion. The crack reducing portion is formed on the silicon edge portion of the silicon substrate such that directions of crystal faces in the crack reducing portion are randomly oriented.