Laser Beam Shaping for Semiconductor Wafer Singulation
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Solution Overview
Problem
Laser singulation of semiconductor wafers is constrained by the need for precise control over feeding speed and pulse repetition frequency, which limits throughput due to non-uniform irradiance profiles and varying scribe depths caused by Gaussian laser beams.
Innovation Solution
A laser system with a beam-shaping device using aspherical lenses to redistribute the irradiance of a Gaussian laser beam, creating a more uniform irradiance profile and allowing for higher feeding speeds without compromising scribe depth uniformity, achieved through the use of a combination of beam expanders and focusing devices to modify the aspect ratio of the laser output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the laser beam width is made small to exceed the material ablation threshold, then the irradiance is sufficient for laser singulation, but the feeding speed is constrained by the maximum possible distance between consecutive laser pulses
Solution Approach 1:
The patent changes the irradiance distribution parameter from Gaussian to top-hat profile using beam shaping optics. This allows the beam to maintain sufficient irradiance for ablation while distributing energy more uniformly across a wider area, enabling faster feeding speeds without compromising singulation quality.
Solution Approach 2:
The patent introduces a new dimension to the laser beam profile by transforming the radial symmetry of Gaussian beams into a flattened top-hat distribution. This dimensional transformation of the irradiance profile allows simultaneous achievement of adequate irradiance and increased processing speed.
2Productivity
If the pulse repetition frequency is increased to increase feeding speed, then the average power is higher, but the pulse energy drops rapidly exceeding a certain threshold
Solution Approach 1:
The patent changes the temporal-energy distribution by redistributing spatial irradiance. The top-hat profile allows higher pulse repetition frequencies without pulse energy degradation because the uniform energy distribution prevents localized overheating and maintains consistent ablation efficiency at higher frequencies.
3Productivity
If the feeding speed is increased to improve throughput, then the productivity increases, but the scribe depth becomes non-uniform due to Gaussian irradiance distribution
Solution Approach 1:
The patent transforms the irradiance profile parameter from Gaussian to top-hat distribution. This change ensures uniform energy deposition along the scribe line at higher feeding speeds, maintaining consistent scribe depth and morphology without the trough-like variations characteristic of Gaussian beams.
Solution Approach 2:
The patent applies homogeneity by creating a uniform top-hat irradiance distribution across the beam profile. This homogeneous energy distribution ensures that all portions of the scribe line receive equal irradiance, resulting in uniform scribe depth and improved manufacturing precision at higher throughput.
4Illumination intensity
If the laser beam is focused to a small width, then the irradiance exceeds the ablation threshold, but the distance between consecutive pulses must be within a maximum possible distance
Solution Approach 1:
The patent transforms the beam profile from a narrow focused Gaussian spot to a wider top-hat distribution. This dimensional change in the irradiance profile allows the laser to maintain effective irradiance over a larger area, increasing the permissible distance between consecutive 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
The solution enables more efficient use of laser energy, increases device density on semiconductor wafers, and enhances throughput by maintaining consistent scribe depths and reducing irradiance wastage, thus overcoming the constraints of conventional laser systems.
Implementation Method 1
a beam-shaping device having a plurality of aspherical lenses to redistribute irradiance of the laser beam
Implementation Method 2
aspherical lenses to redistribute irradiance of the laser beam
Implementation Method 3
Laser singulation is contingent on delivering irradiance (i.e. fluence or energy) to the semiconductor wafer that exceeds its material ablation threshold
Implementation Method 4
delivering irradiance that exceeds its material ablation threshold
Data Source
AI summary
An apparatus 101 for singulating an object is disclosed. The apparatus 101 comprises a laser 103 configured to emit a laser beam 105 with a Gaussian irradiance profile, as well as a beam-shaping device 115 configured to reshape the Gaussian irradiance profile of the laser beam 105 emitted from the laser 103. In particular, the beam-shaping device 115 has a plurality of aspherical lenses 117, 119 to redistribute irradiance of the laser beam 105, so as to reduce variation of the irradiance in an effective irradiation spectrum of the laser beam 105 for singulating the object. By redistributing the irradiance of the laser beam 105, irradiation energy may be more efficiently delivered to the semiconductor wafer 102 for laser singulation, compared with conventional laser beams with Gaussian irradiance profiles which are non-uniform. A method of singulating an object is also disclosed.