Laser Processing Method for Crack-Free High-Speed Wafer Scribing
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Solution Overview
Problem
High repetition frequency pulsed laser beams used in semiconductor and optical device wafer processing can cause cracks due to heat accumulation, and materials with short absorption edges pose challenges for efficient ablation with wavelengths shorter than their absorption edge.
Innovation Solution
A laser processing method that adjusts pulse width based on the wavelength of the pulsed laser beam relative to the workpiece's absorption edge, plotted on a graph to prevent crack generation and ensure efficient ablation, even at high repetition frequencies and with wavelengths longer than the absorption edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the repetition frequency of the pulsed laser beam is increased to 20 kHz or more to improve productivity, then processing efficiency is improved, but cracks are generated due to heat accumulation
Solution Approach 1:
The patent applies parameter changes by adjusting the pulse width of the laser beam based on the repetition frequency. Specifically, when the repetition frequency is 20 kHz or more, the pulse width is set to 100 ps or less to prevent heat accumulation. This dynamic adjustment of the pulse width parameter allows high-speed processing while maintaining device quality by controlling the energy deposition rate.
2Productivity
If the wavelength of the pulsed laser beam is set shorter than the absorption edge to improve ablation efficiency, then processing efficiency is improved, but it becomes difficult to use for materials with short absorption edges such as sapphire
Solution Approach 1:
The patent applies parameter changes by adjusting the pulse width based on the ratio of laser wavelength to material absorption edge. When the wavelength is shorter than the absorption edge (wavelength/absorption edge < 1), the pulse width is set to 10 ps or less to achieve efficient ablation. This allows the use of wavelengths that would otherwise be unsuitable, expanding material compatibility while maintaining high ablation efficiency.
3Use of energy by moving object
If the pulse width is extended to improve energy delivery, then ablation efficiency is improved, but heat accumulation increases causing crack generation
Solution Approach 1:
The patent applies parameter changes by establishing a relationship between pulse width and repetition frequency to optimize energy delivery while preventing heat accumulation. When repetition frequency is high (20 kHz or more), pulse width is reduced to 100 ps or less. This ensures that each pulse delivers sufficient energy for effective ablation while the short duration prevents thermal diffusion and accumulation between pulses.
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
Prevents crack generation and maintains high processing efficiency by suppressing heat accumulation and enabling ablation of materials with short absorption edges using wavelengths longer than their absorption edge.
Implementation Method 1
applying a pulsed laser beam having an absorption wavelength (e.g., 532 nm, 355 nm, or 266 nm) to the wafer along the streets to thereby form a laser processed groove on the wafer along each street by ablation
Implementation Method 2
the use of the pulsed laser beam having an absorption wavelength to the workpiece is desirable for the improvement in processing efficiency
Data Source
AI summary
A laser processing method of applying a pulsed laser beam having a repetition frequency of 20 kHz or more to a workpiece to thereby process the workpiece. The relation between the wavelength of the pulsed laser beam and the pulse width generating no cracks is determined by experiment on the basis of the absorption edge of the workpiece, thereby setting the processing conditions. The relation between various set values for the wavelength and the limits of the pulse width is plotted to prepare a graph having a vertical axis representing the wavelength and a horizontal axis representing the pulse width. The pulsed laser beam is applied in the region below a curve obtained by connecting the limits of the pulse width at the various set values for the wavelength.