Laser Machining High-Hardness Substrates Inhibiting Cutting Line Displacement
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Solution Overview
Problem
High-hardness substrates like single-crystal sapphire are difficult to cut precisely using laser machining methods, as repeated formation of modified regions can lead to displacement from the planned cutting line, resulting in oblique chip cross-sections and defects.
Innovation Solution
A laser machining method where a focused laser beam is applied at multiple distances from one surface of the substrate, using a first machining method from one end to the central portion and a second method from the opposite end, to form modified regions, reducing beam scattering and minimizing damage to electronic devices on the rear surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If modified regions are formed multiple times by changing depth in high-hardness substrates, then cutting capability is improved, but displacement from planned cutting line occurs causing chip shape defects
Solution Approach 1:
The substrate surface is divided into multiple regions (first region from one end to center, second region from other end to center) and modified regions are formed in each region separately using bidirectional machining. This segmentation prevents cumulative displacement that would occur with unidirectional repeated machining, thereby maintaining chip shape accuracy while achieving precise cutting through multiple depth passes.
2Productivity
If laser beam output is increased to improve cutting efficiency, then productivity is improved, but damage to electronic devices on rear surface increases
Solution Approach 1:
The laser beam output is adjusted according to the depth of modified region formation. When forming modified regions at greater depths, higher laser output is applied to maintain cutting efficiency, while at shallower depths lower output is used to minimize thermal damage to electronic devices on the rear surface. This localized adjustment of laser parameters optimizes both productivity and device safety.
3Manufacturing precision
If modified regions are formed at multiple distances from substrate surface, then cutting capability is improved, but laser beam scattering increases
Solution Approach 1:
Instead of forming modified regions from shallow to deep distances which causes cumulative laser scattering, the method forms modified regions in reverse order - first at greater distances from the substrate surface where scattering has minimal cumulative effect, then progressively at shallower distances. This inversion of the formation sequence reduces overall laser beam scattering while maintaining the ability to form modified regions at multiple depths for improved cutting capability.
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 inhibits displacement of modified regions from the planned cutting line, reducing chip shape defects and ensuring precise cutting of substrates like semiconductor wafers with electronic elements.
Implementation Method 1
irradiation of a focused laser beam is applied to plural distances from one surface of a substrate
Implementation Method 2
a laser beam is condensed by a field lens optical system and irradiation of the laser beam is conducted to the inside of the substrate so that a modified region having a low strength compared with the one before the irradiation is formed
Data Source
AI summary
Provided is a laser machining method in which, when modified regions are formed plural number of times by changing the depth in the thickness direction of a substrate, displacement of the formed modified regions from a planned cutting line is inhibited. Specifically provided is a laser machining method for cutting a substrate (10) into chips. Modified regions are formed at a deep distance (d1) inside the substrate from the entrance surface of a laser beam by first scanning (a) in which the substrate is scanned with the laser beam along a planned cutting line (21a) in the X direction of the substrate and second scanning (b) in which the substrate is scanned with the laser beam along a planned cutting line (21b) in the Y direction. Modified regions are again formed at a shallow distance (d2) (d1>d2) inside the substrate by third scanning (c) in which the substrate is scanned with the laser beam along the planned cutting line (21a) in the X direction and fourth scanning (d) in which the substrate is scanned with the laser beam along the planned cutting line (21b) in the Y direction. The third scanning is performed by scanning from a U end portion at the periphery to the center and scanning from a D end portion at the periphery to the center.