Wafer Laser Cutting with Selective Polarization for Die Strength
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Solution Overview
Problem
As semiconductor wafer thickness decreases, traditional mechanical saws become less effective, and laser cutting emerges as a more advantageous method. However, laser singulation faces challenges in achieving a balance between process throughput and die quality, primarily due to laser-induced defects such as micro-cracks and chip-outs.
Innovation Solution
The method involves selectively controlling and utilizing the polarization of the incident laser beam. By alternating between S-polarized and P-polarized laser light, the process optimizes cutting characteristics and anneals defects, thereby enhancing wafer strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser cutting is used to singulate thin wafers, then cutting capability and throughput are improved, but laser-induced defects such as micro-cracks and chip-outs increase, reducing die quality
Solution Approach 1:
The patent applies periodic action by alternating between two different laser polarization states (first and second polarization states) during the cutting process. This periodic switching allows the laser to periodically anneal previously processed areas while simultaneously cutting, thereby reducing cumulative thermal stress and preventing defect formation without sacrificing cutting throughput
Solution Approach 2:
The patent changes the polarization state parameter of the laser beam between two distinct states. By switching between these polarization states, the laser can modify its interaction with the semiconductor material - one state optimized for cutting efficiency and the other for defect annealing - thus resolving the contradiction between throughput and quality
2Productivity
If high-power laser is used for rapid material removal, then process throughput is improved, but laser-induced defects and stress increase, reducing wafer strength
Solution Approach 1:
The patent converts the harmful thermal stress and defects caused by high-power laser cutting into beneficial annealing effects. By using alternating polarization states, previously processed areas are periodically reheated in a controlled manner that allows stress relief and defect repair, thus transforming the harmful thermal effects into beneficial strengthening mechanisms
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 the wafer while maintaining top die strength, thus improving the overall quality of laser-cut semiconductor wafers.
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
irradiating the irradiation region of the semiconductor wafer with laser light having a first polarization state, and subsequently irradiating the irradiation region of the semiconductor wafer with laser light having a second polarization state
Data Source
AI summary
A method of cutting a semiconductor wafer by selectively controlling and utilising the polarization of incident laser beam or beams that includes 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.