SiC Substrate Mask Design for Defect Blocking and Warpage Reduction
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Solution Overview
Problem
The challenge lies in forming high-quality silicon carbide (SiC) substrates with few crystal defects, as the lattice constant and thermal expansion coefficient differences between silicon and SiC lead to stress and warpage issues during epitaxial growth, making it difficult to achieve large-diameter substrates with minimal defects.
Innovation Solution
A substrate configuration with multiple layers of silicon carbide films and strategically positioned masks, where the thickness and width of the masks are optimized to satisfy specific relationships (e.g., T1<tan(54.6°)×W1 and D1≧tan(54.6°)×W1), allowing for accurate blocking of crystal defects and reducing stress, thereby enhancing the quality of the SiC film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single crystal ingot of SiC is formed by sublimation, then crystal quality can be improved, but it is very difficult to form a substrate having a large diameter and few crystal defects
Solution Approach 1:
The patent divides the substrate formation process into two stages: first forming a small-diameter single crystal ingot by sublimation with high crystal quality, then using it as a seed for epitaxial growth to expand into a large-diameter substrate. This segmentation allows each stage to optimize for its specific purpose without compromise
Solution Approach 2:
The patent performs preliminary sublimation growth to create a high-quality single crystal seed before performing the main epitaxial growth step. This preliminary action ensures that the crystal structure is already optimized before scaling up to large diameters
2Area of stationary object
If cubic SiC is epitaxially grown directly on a Si substrate, then large diameter substrates can be formed, but lattice constant and thermal expansion coefficient differences cause crystal defects and warpage
Solution Approach 1:
The patent introduces an intermediary layer (such as SiO2 or Si3N4) between the Si substrate and the 3C-SiC epitaxial layer. This intermediary acts as a buffer that reduces the direct interaction between the mismatched Si and SiC lattices, thereby decreasing dislocation density and improving crystal quality while allowing large diameter growth
Solution Approach 2:
The patent modifies the growth parameters by using an intermediary layer that changes the interface conditions between Si substrate and SiC film. This parameter change in the interface structure allows for reduced stress and improved crystal quality during epitaxial growth
3Reliability
If an oxide film is formed on the growth base substrate to reduce crystal defects, then defect reduction can be achieved, but the oxide film generates stress causing substrate warpage
Solution Approach 1:
The patent applies the oxide film only in specific local regions rather than uniformly across the entire substrate. By controlling the spatial distribution and thickness of the oxide layer, it provides defect reduction where needed while minimizing overall stress accumulation that causes warpage
4Reliability
If the thickness of the oxide film is increased to reduce crystal defects, then defect blocking can be improved, but substrate warpage due to film stress increases
Solution Approach 1:
The patent optimizes the oxide film thickness to a specific parameter range that provides sufficient defect blocking capability while maintaining acceptable stress levels. By precisely controlling the thickness parameter, it achieves the minimum required value for defect reduction without exceeding the threshold that causes significant warpage
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 crystal defects and stress in the SiC film, resulting in a substrate with improved quality and reduced warpage, suitable for high-voltage semiconductor applications.
Implementation Method 1
a method in which cubic SiC is epitaxially grown directly on a Si substrate has been proposed
Implementation Method 2
the mask has a first mask provided between the silicon substrate and the first cubic silicon carbide film and a second mask provided between the first cubic silicon carbide film and the second cubic silicon carbide film
Data Source
AI summary
A substrate with a silicon carbide film includes a Si substrate, and a SiC film and a mask stacked on the Si substrate. The SiC film has a first SiC film provided on the upper side of the Si substrate and a second SiC film provided on the upper side of the first SiC film. The mask has a first mask provided on the Si substrate and including an opening (first opening) and a second mask provided on the first SiC film and including an opening (second opening). The width W1 (μm) of the first opening and the thickness T1 (μm) of the first mask satisfy the following relationship: T1<tan(54.6°)×W1.