Wafer Strain Removal via Laser Shield Tunnels
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Solution Overview
Problem
Wafers of silicon carbide (SiC) or gallium nitride (GaN) often warp and break during grinding, leading to poor productivity and non-uniform light emitting layer stacking, due to residual crystal strains in the peripheral portions of the wafers.
Innovation Solution
A method involving the use of a laser beam to create shield tunnels or grooves along the wafer's edge, either in an annular pattern or along a line, to remove the peripheral regions with crystal strains, thereby preventing warping during grinding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the front side or back side of a wafer is ground, then a mirror surface is formed, but warping and breakage occur due to residual crystal strains
Solution Approach 1:
The laser processing is performed before grinding to pre-remove or relax crystal strains in the peripheral portions of the wafer. This preliminary action prevents warping during subsequent grinding operations, allowing the wafer to maintain flatness and integrity while achieving the desired mirror surface finish.
Solution Approach 2:
The patent replaces purely mechanical grinding with a combined laser processing and grinding approach. The laser beam (optical energy) is used to selectively process peripheral regions and relieve crystal strains, substituting mechanical pre-treatment with a non-contact optical method that precisely targets strain-prone areas without causing mechanical damage.
2Productivity
If grinding is performed on wafers with crystal strains, then productivity is maintained, but warping occurs leading to non-uniform light emitting layer stacking
Solution Approach 1:
Laser processing is performed as a preliminary step before grinding to eliminate crystal strains that would cause warping. This allows the subsequent grinding and light emitting layer stacking to proceed without warping interference, ensuring uniform layer deposition while maintaining overall process efficiency through automation.
3Manufacturing precision
If laser processing is applied to remove crystal strains, then wafer flatness is improved, but additional processing time is required
Solution Approach 1:
The laser processing is applied selectively only to peripheral portions of the wafer where crystal strains are most problematic, rather than treating the entire wafer surface. This partial action approach removes sufficient strains to prevent warping while minimizing the additional processing time required, achieving a balance between flatness improvement and productivity.
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 method ensures that the wafers remain flat, allowing for uniform stacking of light emitting layers and preventing variations in the quality of optical devices like LEDs.
Implementation Method 1
a laser beam having such a wavelength as to be transmitted through the wafer is applied to the wafer from one side of the wafer, in positions located along a margin (edge) of the wafer and spaced a predetermined distance inward from the margin, so as to cause growth of fine holes and amorphous regions shielding the fine holes
Implementation Method 2
a laser beam having such a wavelength as to be absorbed in the wafer is applied to the wafer from one side of the wafer, along a line extending along a margin (edge) of the wafer and spaced a predetermined distance inward from the margin, so as to effect ablation and form a laser-processed groove along the margin of the wafer
Data Source
AI summary
A wafer is formed by slicing a single crystal ingot and removing crystal strains remaining in a peripheral portion of the wafer. In the crystal strain removing step, a laser beam having such a wavelength as to be transmitted through the wafer is applied to the wafer from one side of the wafer in positions located along the margin of the wafer and spaced a predetermined distance inward from the margin, to cause growth of fine holes and amorphous regions shielding the fine holes, over the range from one side to the other side of the wafer, whereby shield tunnels are formed in an annular pattern. Then, an external force is applied to the wafer along the shield tunnels so as to break the wafer in the region of the shield tunnels, thereby removing the peripheral wafer portion where the crystal strains are remaining.