Epitaxial Layer Overgrowth for Dislocation Trapping
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Solution Overview
Problem
Current methods for fabricating semiconductor heterostructures with lattice-mismatched materials struggle to effectively constrain dislocation defects, limiting the size of the area that can be applied and requiring repetitive lithography and epitaxial steps, which is inefficient and not applicable to all heteroepitaxial systems.
Innovation Solution
The use of aspect ratio trapping (ART) and epitaxial layer overgrowth (ELO) techniques, where a first semiconductor layer is formed within a masking layer opening, with controlled vertical and lateral growth rates, and subsequent layers are grown to trap dislocation defects and facilitate coalescence, allowing for reduced defect densities and improved material integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If substrate patterning and epitaxial lateral overgrowth techniques are used, then dislocation defect densities are greatly reduced, but repetitive lithography and epitaxial steps are required which reduces productivity
Solution Approach 1:
The patent applies preliminary action by performing substrate patterning with openings of specific aspect ratios before epitaxial growth. The mask layer is patterned in advance to define regions where dislocations will be trapped during subsequent growth, eliminating the need for repetitive lithography steps while maintaining defect reduction effectiveness.
Solution Approach 2:
The substrate is segmented into multiple regions through patterned mask layers with different opening aspect ratios. This segmentation allows different areas to serve different functions: high aspect ratio openings trap dislocations while lower aspect ratio regions allow defect-free growth, enabling simultaneous defect management across the wafer without repetitive processing.
2Manufacturing precision
If epitaxial lateral overgrowth is used to eliminate defects, then defect-free regions are achieved, but the area to which the technique applies is limited requiring repetition of steps
Solution Approach 1:
The patent employs asymmetric mask openings with different aspect ratios (width-to-depth ratios) to create zones with different defect-trapping characteristics. High aspect ratio openings effectively trap dislocations, while adjacent lower aspect ratio openings permit lateral overgrowth to expand defect-free regions. This asymmetric design allows defect management and area expansion to occur simultaneously across different regions of the same wafer.
Solution Approach 2:
Different regions of the substrate are assigned different local qualities through the mask pattern: some regions have high aspect ratio openings optimized for dislocation trapping, while other regions have lower aspect ratio openings optimized for lateral overgrowth and area expansion. This local differentiation allows each region to perform its specialized function while contributing to the overall defect reduction and area coverage goals.
3Speed
If increased lateral growth rate of gallium nitride is used, then epitaxial lateral overgrowth is enhanced, but this increased growth rate has not been demonstrated in all heteroepitaxial systems reducing adaptability
Solution Approach 1:
The patent changes the critical parameter from growth rate dependence to aspect ratio geometry. Instead of relying on increased lateral growth rates that are material-specific, the invention uses the geometric aspect ratio of mask openings as the controlling parameter. This parameter change makes the technique universally applicable to all heteroepitaxial systems regardless of their specific growth rate characteristics, while still achieving effective dislocation trapping and lateral overgrowth.
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 enables the formation of semiconductor devices with reduced dislocation defects, enhancing their functionality and performance by effectively constraining dislocation defects and allowing for larger area applications, particularly in lattice-mismatched materials systems.
Implementation Method 1
A first layer, which includes a second semiconductor material lattice-mismatched to the first semiconductor material, is formed within the first opening. The first layer has a thickness sufficient to extend above a top surface of the masking layer.
Implementation Method 2
A second layer, which includes the second semiconductor material, is formed on the first layer and over at least a portion of the masking layer. A vertical growth rate of the first layer is greater than a lateral growth rate of the first layer and a lateral growth rate of the second layer is greater than a vertical growth rate of the second layer.
Data Source
AI summary
Methods and structures are provided for formation of devices, e.g., solar cells, on substrates including, e.g., lattice-mismatched materials, by the use of aspect ratio trapping and epitaxial layer overgrowth. A method includes forming an opening in a masking layer disposed over a substrate that includes a first semiconductor material. A first layer, which includes a second semiconductor material lattice-mismatched to the first semiconductor material, is formed within the opening. The first layer has a thickness sufficient to extend above a top surface of the masking layer. A second layer, which includes the second semiconductor material, is formed on the first layer and over at least a portion of the masking layer. A vertical growth rate of the first layer is greater than a lateral growth rate of the first layer and a lateral growth rate of the second layer is greater than a vertical growth rate of the second layer.