Epitaxial Wafer Fabrication Reducing Surface Defects
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Solution Overview
Problem
The existing epitaxial wafer fabrication methods face challenges in reducing surface defect density due to lattice mismatch and growth defects, which affect the quality of epitaxial wafers, particularly in silicon carbide-based substrates.
Innovation Solution
A method involving a pre-growth step with a buffer layer formed at a higher temperature and lower growth speed, followed by a subsequent growth step at a lower temperature and higher speed, to reduce lattice mismatch and surface defects, with controlled C/Si ratio and flux of reactive gases, allowing for continuous epitaxial growth without interruption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single-step epitaxial growth process is used, then the fabrication time is short, but the surface defect density is high due to lattice mismatch and growth defects
Solution Approach 1:
The single-step epitaxial growth process is divided into multiple sequential growth steps with different conditions. Each step targets specific defect reduction: initial growth at lower temperature for lattice matching, intermediate growth for defect elimination, and final growth for surface quality. This segmentation allows comprehensive defect control without excessive total fabrication time.
Solution Approach 2:
The method performs preliminary epitaxial growth under optimized conditions before final wafer completion. The initial growth steps prepare the crystal structure with proper lattice matching and defect reduction, creating a foundation that prevents subsequent defect formation during faster final growth stages.
2Productivity
If high growth speed is used throughout the epitaxial process, then the fabrication time is reduced, but the surface defect density increases due to growth defects
Solution Approach 1:
The growth speed is dynamically adjusted throughout the epitaxial process rather than maintained at a constant high rate. The process starts with lower growth speeds for initial crystal formation and lattice matching, then progressively increases speed as the crystal structure stabilizes, achieving both high productivity and low defect density.
Solution Approach 2:
Multiple growth parameters including temperature, pressure, and growth speed are changed systematically across different growth steps. The method optimizes the combination of these parameters at each stage to balance growth speed and defect reduction, rather than prioritizing speed alone throughout the entire process.
3Manufacturing precision
If low growth temperature is used, then the surface defect density is reduced, but the growth speed decreases
Solution Approach 1:
The epitaxial growth process uses periodic alternation between different temperature regimes. Lower temperatures are applied periodically during critical initial stages for defect reduction, while higher temperatures are used in later stages to accelerate growth. This periodic temperature variation resolves the trade-off between precision and speed.
Solution Approach 2:
The method performs preliminary growth at lower temperatures to establish proper crystal structure and reduce surface defects before transitioning to higher temperature fast growth. This preliminary low-temperature action creates a defect-free foundation that allows subsequent high-speed growth without compromising surface quality.
4Manufacturing precision
If multiple separate processing steps including polishing are used, then the surface quality is improved, but the fabrication complexity and time increase
Solution Approach 1:
The method merges the epitaxial growth process with surface quality improvement functions that would traditionally require separate polishing steps. By optimizing growth conditions and sequences, the epitaxial layer is formed with inherently low defect density and high surface quality, eliminating or reducing the need for additional mechanical processing steps.
Solution Approach 2:
The epitaxial growth process itself is designed to produce high-quality surfaces without requiring external polishing operations. The controlled growth conditions and multi-step sequence enable the material to self-organize into a low-defect structure, making the process self-sufficient for surface quality improvement.
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 significantly reduces surface defect density to 0.5 or less per cm², enabling high-quality epitaxial wafers with reduced fabrication time and cost, and eliminates the need for separate polishing processes.
Implementation Method 1
a buffer layer being formed on the substrate in a pre-growth step
Implementation Method 2
reduce lattice mismatch and surface defects
Implementation Method 3
a gas/liquid/solid silicon composite is transferred to a surface of a single crystal silicon wafer (or substrate) to be thermally decomposed
Implementation Method 4
an epitaxial wafer is fabricated by laminating silicon onto a single crystal silicon wafer through continuous growth of a single crystal structure
Data Source
Figure 1(a)~1(c)
Figure 2~3
Figure 4~5
AI summary
Disclosed is an epitaxial wafer (300B) including a substrate (110), and an epitaxial structure (210B) disposed on the substrate (110), wherein the epitaxial structure (210B) includes a first epitaxial layer (212B), a second epitaxial layer (214B) disposed on the first epitaxial layer (212B), and a third epitaxial layer (216) disposed between the first epitaxial layer (212B) and the second epitaxial layer (214B), the third epitaxial layer (216) having a first doping concentration around a first boundary adjacent to the first epitaxial layer (212B) and a second doping concentration different from the first doping concentration around a second boundary adjacent to the second epitaxial layer (214B).