Semiconductor Wafer Laser Cutting with Selective Polarization Switching
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Solution Overview
Problem
Current laser cutting methods for semiconductor wafers face challenges in achieving balanced throughput and die quality, particularly in thin wafers, due to high stress-induced defects and uneven fracture strength between the front and back sides, which are not adequately addressed by existing post-treatment methods.
Innovation Solution
The method involves selectively controlling the polarization state of the laser beam between linear perpendicular, linear parallel, circular, and elliptical polarization states to optimize cutting and annealing processes, using a laser-cutting apparatus with a polarizing component and drive system to move the wafer relative to the irradiation region, enhancing absorption and reducing defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser cutting is used to increase throughput, then productivity improves, but die strength deteriorates due to high stress-induced defects
Solution Approach 1:
The patent applies parameter changes by switching the polarization state of the laser beam between linear perpendicular, linear parallel, circular, and elliptical polarization states. This changes the physical parameters of the laser light to optimize both cutting efficiency and defect reduction, thereby improving die strength while maintaining throughput
Solution Approach 2:
The patent employs periodic action by alternately irradiating the wafer with laser light of different polarization states. The method involves switching between at least two different polarization states during the cutting process, creating a periodic variation in laser light properties that reduces stress-induced defects while maintaining cutting speed
2Productivity
If high power laser is used to improve cutting speed, then productivity improves, but manufacturing precision deteriorates due to increased defects
Solution Approach 1:
The patent changes the polarization state parameter of the laser light to optimize the balance between cutting speed and quality. By switching between different polarization states (linear perpendicular, linear parallel, circular, elliptical), the method maintains high cutting speed while reducing the generation of micro-cracks and chip-outs that would compromise manufacturing precision
3Strength
If conventional post-treatment methods are used to improve die strength, then strength improves, but productivity deteriorates due to additional processing steps
Solution Approach 1:
The patent merges the cutting process with the defect reduction process by integrating polarization state switching directly into the laser cutting operation. This combination eliminates the need for separate post-treatment steps, as the periodic switching of polarization states during cutting simultaneously achieves both cutting and defect mitigation, thereby maintaining productivity while improving die strength
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 significantly increases the back-side die strength of semiconductor wafers while maintaining throughput, allowing for improved cutting efficiency and reduced defects by optimizing laser light absorption and ablation characteristics.
Implementation Method 1
Laser removal of the semiconductor material occurs due to a rapid temperature increase of a relatively small area in which the laser beam is focused, which causes local material to melt, explosively boil, evaporate and ablate.
Implementation Method 2
a selectively actuatable optical polarizing component for switching a polarization state of the laser light directed to the irradiation region between a first polarization state and a second, different, polarization state
Data Source
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AI summary
A method of cutting a semiconductor wafer by selectively controlling and utilising the polarization of incident laser beam or beams, comprising irradiating the semiconductor wafer with laser light having a first polarization state, and subsequently irradiating the semiconductor wafer with laser light having a second polarization state, the second polarization state being different from the first polarization state.