InP Substrate Surface Cleanliness for Low-Defect Epitaxial Layers
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Solution Overview
Problem
Existing group III-V compound semiconductor substrates, such as indium phosphide and gallium arsenide, face issues with increased defects in epitaxial layers due to impurities and particles on the substrate surface, despite efforts to reduce sulfate ions and oxygen concentrations.
Innovation Solution
The development of group III-V compound semiconductor substrates with controlled particle sizes and the application of a protective film, particularly a surfactant-containing film, to maintain a clean surface and reduce light point defects in the epitaxial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a GaN layer is grown on a sapphire substrate, then the substrate provides mechanical support and thermal conductivity, but the lattice mismatch causes dislocation and threading defect generation
Solution Approach 1:
The patent introduces an AlN nucleation layer as an intermediate segment between the sapphire substrate and the GaN layer. This segmentation approach divides the direct GaN-sapphire interface into two separate interfaces (AlN-sapphire and AlN-GaN), allowing each interface to be optimized independently and reducing the direct lattice mismatch between GaN and sapphire
Solution Approach 2:
The patent employs temperature gradient methods during the growth process, using different temperatures for nucleation layer formation versus subsequent GaN layer growth. This parameter change allows optimization of defect reduction during nucleation while maintaining high-quality GaN crystal growth in later stages
2Volume of moving object
If the GaN layer is grown too thin, then the overall device size is reduced, but the layer cannot be grown uniformly across the substrate
Solution Approach 1:
The patent performs preliminary actions by first forming an AlN nucleation layer and performing in-situ surface preparation (such as oxygen plasma treatment) before growing the GaN layer. This preliminary action ensures that the substrate surface is properly prepared and activated, enabling uniform GaN nucleation and growth even at thin layer thicknesses
Solution Approach 2:
The patent applies local quality control by optimizing growth conditions specifically for the nucleation layer formation, using different parameters (temperature, pressure, gas flow) for the nucleation stage compared to the main GaN growth stage, ensuring uniformity is achieved where most critical
3Manufacturing precision
If oxygen is introduced during GaN layer growth to improve uniformity, then layer uniformity increases, but nitrogen vacancies are generated reducing electron mobility
Solution Approach 1:
The patent uses periodic action by implementing pulsed oxygen introduction during the growth process rather than continuous oxygen exposure. This allows periods of oxygen-assisted uniform growth followed by periods of pure nitrogen flow to prevent excessive oxygen incorporation that would create nitrogen vacancies and degrade electron mobility
Solution Approach 2:
The patent maintains continuous useful action by performing in-situ surface preparation and nucleation layer formation without breaking the vacuum or exposing the substrate to contamination. This continuous process ensures that the benefits of oxygen introduction for uniformity are maintained while minimizing interruptions that could lead to defect formation
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
The proposed solution effectively reduces defects in the epitaxial layers by minimizing particle and impurity adhesion, ensuring a cleaner substrate surface, thereby improving the quality of semiconductor devices.
Implementation Method 1
it has been conventionally known that when a GaN layer is grown on a sapphire substrate, dislocation and threading defects are generated due to a difference in a lattice constant between the sapphire substrate and the GaN layer
Implementation Method 2
subsequent surface treatment and nucleation layer formation are performed in an atmosphere containing oxygen
Data Source
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AI summary
An InP substrate that is a group III-V compound semiconductor substrate includes particles of greater than or equal to 0.19 µm in particle size at less than or equal to 0.22 particles/cm2 or particles of greater than or equal to 0.079 µm in particle size at less than or equal to 20 particles/cm2 on the main surface. An epilayer-attached InP substrate that is an epilayer-attached group III-V compound semiconductor substrate includes the InP substrate mentioned above and an epitaxial layer disposed on the main surface of the InP substrate, and includes LPDs of greater than or equal to 0.24 µm in circle-equivalent diameter at less than or equal to 10 defects/cm2 or LPDs of greater than or equal to 0.136 µm in circle-equivalent diameter at less than or equal to 30 defects/cm2 on the main surface in a case where the epitaxial layer has a thickness of 0.3 µm. Thus, a group III-V compound semiconductor substrate and an epilayer-attached group III-V compound semiconductor substrate are provided which can reduce defects of the epitaxial layer grown on the main surface.