Tailored Laser Pulse Bursts for Clean Semiconductor Link Severing
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Solution Overview
Problem
Conventional laser micromachining techniques face challenges in accurately processing semiconductor links due to over cratering caused by uneven passivation layers, leading to reduced reliability and quality of IC chips, and ultrafast lasers risk damaging the substrate with high peak power.
Innovation Solution
The use of tailored bursts of short or ultrashort laser pulses with adjustable amplitudes and pulse widths less than 1 nanosecond, allowing for precise processing of multiple layers with lower peak intensity and reduced heat affected zones, thereby minimizing damage to the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional nanosecond laser pulses with high peak power are used for link processing, then the laser can effectively sever the conductive link, but it causes over cratering in the passivation layer and damages the substrate
Solution Approach 1:
The laser pulse is segmented into a burst of multiple ultrashort pulses (e.g., 5-20 pulses) with individual pulse widths of 100 femtoseconds to 1 picosecond. This segmentation allows the total energy to be distributed across multiple lower-peak-power pulses, effectively severing the link while avoiding the over cratering and substrate damage caused by single high-peak-power nanosecond pulses.
Solution Approach 2:
The invention changes key laser parameters from conventional nanosecond pulses to ultrashort pulse bursts with pulse widths of 100 femtoseconds to 1 picosecond. The burst structure with adjustable envelope shapes (e.g., Gaussian, flat-top) and repetition rates (e.g., 100 MHz to 1 GHz) enables precise control of energy delivery, achieving clean link severing with minimal damage to surrounding structures.
2Object-affected harmful factors
If the passivation layer thickness is increased to protect the substrate, then substrate protection is improved, but the laser pulse cannot effectively penetrate to sever the link
Solution Approach 1:
The laser delivers energy through periodic ultrashort pulses within a burst sequence. The high repetition rate (100 MHz to 1 GHz) of these ultrashort pulses creates a periodic action that accumulates energy in the link material while allowing heat dissipation between pulses, enabling effective link severing through thicker passivation layers without substrate damage.
Solution Approach 2:
The ultrashort laser pulses induce rapid phase transitions (ablation) in the link material. The extreme peak power density of each ultrashort pulse causes instantaneous vaporization of the link material, creating a plasma channel that extends through the passivation layer to sever the link, while the short pulse duration prevents excessive heat diffusion to the substrate.
3Use of energy by moving object
If the laser pulse width is extended to nanosecond range for sufficient energy delivery, then total energy delivery is improved, but the heat affected zone expands causing more damage
Solution Approach 1:
The total laser energy is segmented into multiple ultrashort pulses within a burst, each with pulse widths of 100 femtoseconds to 1 picosecond. This segmentation delivers the required total energy while confining the heat affected zone to a minimal volume, as each ultrashort pulse deposits energy faster than heat can diffuse to surrounding areas.
Solution Approach 2:
The burst of ultrashort pulses provides continuous useful action through the high repetition rate (100 MHz to 1 GHz), delivering cumulative energy to the link material efficiently. The continuous nature of the burst ensures complete link severing while the ultrashort duration of each pulse maintains a small heat affected zone throughout the energy delivery process.
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 enhances processing quality by delivering more total laser energy with lower peak intensity, reducing the risk of over cratering and substrate damage, and improving the uniformity and reliability of IC chip processing.
Implementation Method 1
Laser micromachining processes include, for example, semiconductor memory link processing, material trimming, wafer/panel scribing, wafer/panel dicing, and via drilling
Implementation Method 2
The purpose of this final 'passivation' layer is to prevent the surface of the chip from reacting chemically with ambient moisture, to protect the surface from environmental particulates, and to absorb mechanical stress
Data Source
AI summary
A series of laser pulse bundles or bursts are used for micromachining target structures. Each burst includes short laser pulses with temporal pulse widths that are less than approximately 1 nanosecond. A laser micromachining method includes generating a burst of laser pulses and adjusting an envelope of the burst of laser pulses for processing target locations. The method includes adjusting the burst envelope by selectively adjusting one or more first laser pulses within the burst to a first amplitude based on processing characteristics of a first feature at a target location, and selectively adjusting one or more second laser pulses within the burst to a second amplitude based on processing characteristics of a second feature at the target location. The method further includes directing the amplitude adjusted burst of laser pulses to the target location.