GaN Substrate Off-Angle Control for Device Uniformity
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Solution Overview
Problem
Current nitride semiconductor light emitting devices face challenges in achieving desired device characteristics due to off-angle variations on GaN wafers, limiting the usable surface area for device fabrication.
Innovation Solution
A method of fabricating single crystal gallium nitride substrates by cutting ingots along predetermined planes with specific off-angle orientations, followed by polishing and grinding to create substrates with controlled off-angles, ensuring a minimum off-angle at the edge and a monotonic change across the surface, thereby expanding the usable surface area for nitride semiconductor devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional GaN wafers are used with existing polishing methods, then manufacturing process is simple, but off-angle variations are not less than desired range limiting usable surface area
Solution Approach 1:
The substrate surface is divided into multiple regions (first region with minimum off-angle at edge, second region with monotonic off-angle change, third region with maximum off-angle). This segmentation allows different areas to serve different functional purposes, maximizing the usable surface area while maintaining controlled off-angle characteristics in each region.
Solution Approach 2:
Different regions of the substrate are given different off-angle characteristics tailored to their specific functions. The first region near the edge has minimum off-angle suitable for certain device structures, the second region has monotonic off-angle change for uniform device performance, and the third region has maximum off-angle for other specific applications. This local optimization resolves the contradiction between usable area and precision.
2Manufacturing precision
If off-angle is minimized across the substrate surface, then device uniformity improves, but edge regions lose beneficial off-angle characteristics
Solution Approach 1:
The substrate is designed with spatially varying off-angle characteristics where the minimum off-angle is positioned at the edge region rather than being uniformly distributed. This allows edge regions to maintain their beneficial properties while the overall substrate provides controlled off-angle variation for device uniformity.
Solution Approach 2:
The substrate surface is segmented into functional regions with different off-angle characteristics. The first region at the edge maintains minimum off-angle for specific device structures, while other regions have progressively different off-angles, allowing both edge functionality and overall uniformity to coexist.
3Manufacturing precision
If single crystal ingots are cut along multiple predetermined planes, then substrate off-angle control improves, but fabrication process complexity increases
Solution Approach 1:
The ingot is divided into multiple slices along predetermined planes that are inclined at different angles. Each slice is then processed to create regions with specific off-angle characteristics. This segmentation approach systematically achieves precise off-angle control across different substrate regions.
Solution Approach 2:
The ingot is prepared in advance by growing single crystal material with controlled orientation, and then cutting along predetermined planes before the substrate fabrication stage. This preliminary action establishes the off-angle distribution pattern early in the process, simplifying subsequent substrate processing while maintaining precision.
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 allows for the production of nitride semiconductor devices with improved surface morphology and uniformity, enhancing the yield and performance of semiconductor devices by maintaining a non-zero off-angle across the substrate, which is crucial for epitaxial growth and device uniformity.
Implementation Method 1
The ingot of single crystal gallium nitride is grown by vapor phase epitaxy in a direction of a predetermined axis.
Implementation Method 2
Each substrate has a mirror polished primary surface.
Data Source
AI summary
A method of fabricating a single crystal gallium nitride substrate the step of cutting an ingot of single crystal gallium nitride along predetermined planes to make one or more signal crystal gallium nitride substrates. The ingot of single crystal gallium nitride is grown by vapor phase epitaxy in a direction of a predetermined axis. Each predetermined plane is inclined to the predetermined axis. Each substrate has a minor polished primary surface. The primary surface has a first area and a second area. The first area is between an edge of the substrate and a line 3 millimeter away from the edge. The first area surrounds the second area. An qaxis perpendicular to the primary surface forms an off-angle with c-axis of the substrate. The off-angle takes a minimum value at a first position in the first area of the primary surface.