SiC Epitaxial Layer Growth Temperature Segmentation
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Solution Overview
Problem
The challenge lies in manufacturing silicon carbide (SiC) semiconductor devices with low off angles (5 degrees or less) where crystal defects and surface roughness, such as bunching steps, occur due to reduced terrace width and increased surface energy, making it difficult to achieve a smooth epitaxial growth and expanding the process margin.
Innovation Solution
A method involving the growth of a first epitaxial layer at a high temperature to suppress crystal defects, followed by a second epitaxial layer at a lower temperature to reduce the height of bunching steps, thereby minimizing both crystal defects and surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the off angle of the substrate is decreased to reduce manufacturing costs, then the manufacturing cost is reduced, but the terrace width increases which raises the possibility of two-dimensional nucleation and crystal defects
Solution Approach 1:
The patent divides the epitaxial growth process into two distinct stages: a first growth stage at a higher temperature to form an initial epitaxial layer, and a second growth stage at a lower temperature to complete the epitaxial layer. This segmentation allows each stage to address specific requirements - the first stage suppresses two-dimensional nucleation by providing sufficient thermal energy for reactive species migration, while the second stage optimizes for other growth parameters, thereby resolving the contradiction between using low off-angle substrates and preventing crystal defects.
Solution Approach 2:
The patent changes the growth temperature parameter between two distinct stages. The first epitaxial growth is performed at a higher temperature (e.g., 1600-1700°C) to ensure adequate migration length for reactive species and suppress two-dimensional nucleation on wide terraces. The second epitaxial growth is performed at a lower temperature to optimize other aspects of layer formation. This parameter change enables the process to accommodate low off-angle substrates while maintaining low crystal defect density.
2Manufacturing precision
If the growth temperature is raised to increase the migration length of reactive species, then the crystal defects are reduced, but the bunching step occurs more significantly roughening the surface
Solution Approach 1:
The patent segments the epitaxial growth into two temperature stages: a first stage at higher temperature to suppress crystal defects through increased reactive species migration, and a second stage at lower temperature to minimize bunching step formation and surface roughening. This temporal segmentation of temperature conditions allows the process to achieve both low defect density and smooth surface morphology, resolving the contradiction between these two competing requirements.
Solution Approach 2:
The patent employs periodic variation in growth temperature during the epitaxial process. The temperature is periodically adjusted between a higher value during the first growth stage and a lower value during the second growth stage. This periodic temperature action enables the system to alternately prioritize defect suppression and surface smoothness, achieving both objectives in sequence within a single continuous growth process.
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 reduces the density of crystal defects and the height of bunching steps, enhancing the surface quality and process margin of SiC semiconductor devices, even with substrates having off angles of 5 degrees or less.
Implementation Method 1
causing a first epitaxial layer to grow on a main surface of a silicon carbide semiconductor substrate
Implementation Method 2
reactive species adhering to the crystal surface diffuse over the terrace
Implementation Method 3
causing a second epitaxial layer to grow on and in contact with an upper surface of the first epitaxial layer
Data Source
AI summary
A film of an epitaxial layer that allows the reduction in both the height of a bunching step and crystal defects caused by a failure in migration of reactive species on a terrace is formed on a SiC semiconductor substrate having an off angle of 5 degrees or less. A film of a first-layer epitaxial layer is formed on and in contact with a surface of the SiC semiconductor substrate having an off angle of 5 degrees or less. Subsequently, the temperature in a reactor is lowered. A second-layer epitaxial layer is caused to epitaxially grow on and in contact with a surface of the first-layer epitaxial layer. In the above-described manner, the epitaxial layer is structured with two layers, and the growth temperature for the second epitaxial layer is set lower than the growth temperature for the first epitaxial layer.