Epitaxial III-Nitride Substrate Crack Prevention via Axial Symmetry
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Solution Overview
Problem
The existing methods for slicing semiconductor substrates from epitaxially grown group III nitride semiconductor single crystals often result in cracks due to strain imbalance caused by impurity concentration differences and non-uniform crystal properties, particularly when attempting to slice large crystals.
Innovation Solution
A method involving the removal of a hollow cylindrical region from the crystal, maintaining axial symmetry to balance strain distribution, followed by slicing the solid columnar region, using techniques like grinding, ultrasonic processing, or electric discharge processing to prevent crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cylindrical grinding is performed to remove the outer peripheral edge before slicing, then crack prevention during slicing is improved, but the crystal may still develop cracks during the grinding process itself due to strain imbalance
Solution Approach 1:
The patent applies preliminary action by performing a first cylindrical grinding to remove the outer peripheral edge and reduce impurity concentration before the main slicing operation. This preliminary removal of the hollow cylindrical region prepares the crystal structure to prevent cracks during subsequent slicing, while the process itself is controlled to avoid creating new cracks by maintaining axial symmetry throughout the grinding operation.
Solution Approach 2:
The patent addresses asymmetry by explicitly maintaining axial symmetry during the grinding process. The hollow cylindrical region is removed in a manner that preserves the rotational symmetry of the crystal around its central axis, ensuring uniform strain distribution and preventing crack formation that would result from asymmetric material removal.
2Manufacturing precision
If the outer peripheral edge is removed to eliminate stained regions, then slicing quality is improved, but the strain balance in the crystal is disrupted causing cracks
Solution Approach 1:
The patent uses preliminary action by removing the hollow cylindrical region containing the outer peripheral edge and stained regions before slicing. This preliminary removal eliminates the sources of staining and impurities that would compromise slicing quality, while the process is designed to maintain axial symmetry to preserve strain balance.
Solution Approach 2:
The patent resolves the strain balance issue by maintaining axial symmetry during the removal process. The hollow cylindrical region is removed uniformly around the central axis, ensuring that strain is distributed evenly and the crystal's compositional stability is preserved despite the removal of the outer peripheral edge.
3Productivity
If large diameter crystals are grown to increase substrate area, then productivity is improved, but crack occurrence increases due to reduced dislocation density and uniform crystal properties
Solution Approach 1:
The patent applies preliminary action by removing the hollow cylindrical region from large diameter crystals before slicing. This preliminary step eliminates the outer peripheral regions where cracks are most likely to form in large crystals, enabling successful slicing of large diameter substrates that would otherwise be prone to cracking due to their uniform crystal properties and low dislocation density.
Solution Approach 2:
The patent uses the extraction principle by removing the hollow cylindrical region containing the outer peripheral edge and stained regions from the large diameter crystal. This extraction eliminates the vulnerable outer regions while preserving the high-quality inner regions, enabling the production of large area substrates without the crack problems that would otherwise occur.
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 effectively prevents crack formation during slicing, allowing for the production of high-quality semiconductor substrates with reduced strain and warp, suitable for large diameter substrates with low dislocation density.
Implementation Method 1
removing a hollow cylindrical region... by grinding
Implementation Method 2
removing a hollow cylindrical region... by ultrasonic processing
Implementation Method 3
removing a hollow cylindrical region... by electric discharge processing
Implementation Method 4
epitaxially growing a columnar group III nitride semiconductor single crystal
Implementation Method 5
growing a nitride semiconductor single crystal on a seed crystal substrate by vapor phase epitaxy
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3B
AI summary
[Problem] To provide a semiconductor substrate manufacturing method whereby a semiconductor substrate can be obtained by slicing an epitaxially grown III nitride semiconductor single crystal, while suppressing generation of cracks. [Solution] According to one embodiment of the present invention, a semiconductor substrate manufacturing method includes: a step for epitaxially growing a columnar III nitride semiconductor single crystal (2) on a main surface of a circular substrate (1); a step for removing a cylindrical region (4) on the outer circumferential side of the III nitride semiconductor single crystal (2), and leaving a columnar region (3) on the inner side of the cylindrical region (4) of the III nitride semiconductor single crystal (2); and a step for slicing the columnar region (3) after removing the cylindrical region (4). The cylindrical region (4) is removed such that the shape of the III nitride semiconductor single crystal (2) is constantly axisymmetrical with the center axis of the III nitride semiconductor single crystal (2) as a symmetric axis.