Semi-Polar Nitride Epitaxy with Inclined Defect-Blocking Posts
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Solution Overview
Problem
Current techniques are inadequate for suppressing lattice defects in epitaxial growth layers formed over non-c-plane oriented substrates, particularly semi-polar oriented GaN, where diagonally running defects persist due to lattice mismatch and limited effectiveness of existing defect reduction methods.
Innovation Solution
A patterned mask with 'window' openings or etched trenches, along with inclined posts, are used to block diagonally and vertically running defects by optimizing their dimensions based on the angle between the surface normal and the c-axis direction, ensuring effective defect suppression during growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lateral overgrowth technique is used on semi-polar substrates, then vertical defects are suppressed, but diagonally running defects persist and reduce effectiveness
Solution Approach 1:
The patent applies local quality by creating mask structures with specific geometric configurations (inclined posts and trenches) that are optimized for semi-polar orientations. These local structural modifications provide directional defect blocking tailored to the specific crystallographic orientation, making the defect suppression technique adaptable to semi-polar substrates while maintaining effectiveness against diagonally running defects.
Solution Approach 2:
The patent introduces inclined posts and trenches that extend in multiple dimensions rather than simple planar masks. By adding the dimensional aspect of inclination angles matching the semi-polar orientation, the mask structures can intercept defects propagating at diagonal angles, thereby resolving the limitation of conventional lateral overgrowth on non-c-plane substrates.
2Reliability
If mask thickness is increased to block defects, then defect suppression improves, but growth rate and productivity decrease
Solution Approach 1:
The patent segments the defect blocking function into multiple inclined posts or trenches distributed across the substrate. Instead of using a single thick mask layer that would completely block growth, multiple thinner segmented structures provide cumulative defect blocking while allowing growth to proceed through the spaces between segments, thereby maintaining productivity while achieving reliable defect suppression.
Solution Approach 2:
The inclined posts and trenches act as intermediary structures that selectively intercept defects while permitting growth material to pass through. These intermediary elements provide a compromise solution by blocking harmful defects without completely obstructing the growth pathway, thus maintaining both defect suppression and growth rate.
3Ease of manufacture
If simple planar masks are used, then manufacturing is simple, but they fail to block diagonally running defects in semi-polar layers
Solution Approach 1:
The patent employs asymmetric inclined posts and trenches with specific orientation angles that do not exhibit simple planar symmetry. These asymmetric structures are designed to match the diagonal defect propagation angles in semi-polar substrates, providing effective defect blocking while remaining manufacturable through standard lithography and etching processes with appropriate pattern design.
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
Significantly reduces lattice defects in nitride-based epitaxial growth layers by blocking defects tilted according to the substrate orientation, enhancing the quality of the growth material and reducing defect density.
Implementation Method 1
A mask is formed over the template layer, and a thickness of the mask is selected to be greater than or equal to the product of a width of the window openings times a cotangent of an angle between the surface normal and the c-axis direction for the semi-polar layer. The growth material is epitaxially grown over the template layer and the mask.
Implementation Method 2
etched trenches in the template layer or substrate, with vertical dimensions according to the product of the trench opening width times the cotangent of the angle between the surface normal and the c-axis direction for the semi-polar layer provides significant blocking of all diagonally running defects during growth.
Implementation Method 3
The growth material is epitaxially grown over the template layer and the mask
Data Source
AI summary
A structure method for producing same provides suppressed lattice defects when epitaxially forming nitride layers over non-c-plane oriented layers, such as a semi-polar oriented template layer or substrate. A patterned mask with “window” openings, or trenches formed in the substrate with appropriate vertical dimensions, such as the product of the window width times the cotangent of the angle between the surface normal and the c-axis direction, provides significant blocking of all diagonally running defects during growth. In addition, inclined posts of appropriate height and spacing provide a blocking barrier to vertically running defects is created. When used in conjunction with the aforementioned aspects of mask windows or trenches, the post structure provides sign0ificant blocking of both vertically and diagonally running defects during growth.