Stealth Laser Dicing With Zigzag Cracks to Reduce Splash
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Solution Overview
Problem
During stealth laser dicing of semiconductor wafers, splash can occur, causing damage to circuitry and metal layers, particularly at die corners where scribe streets intersect, and existing methods often require high power that leads to excessive splash energy absorption by the substrate.
Innovation Solution
A multi-pass stealth laser dicing method is employed, where multiple laser pulses are applied with each pass forming offset cracks to create a zigzag-shaped crack pattern within the scribe street, reducing interaction between final-pass and preceding pass modified regions, thereby minimizing splash energy and allowing for lower power usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high power laser is used for stealth dicing, then dicing effectiveness is improved, but splash energy increases causing damage to circuitry and metal layers
Solution Approach 1:
The laser dicing process is divided into multiple passes, with each pass creating a portion of the final crack. The first pass creates an initial crack, and subsequent passes extend and refine it. This segmentation allows the total laser energy to be distributed across multiple lower-power pulses rather than one high-power pulse, reducing splash energy while achieving complete separation.
Solution Approach 2:
The first laser pass performs preliminary action by creating an initial crack and modified region before subsequent passes. This pre-formed crack structure reduces the energy required for following passes to complete the separation, as the crack propagation path is already partially established, thereby reducing overall splash energy.
2Object-affected harmful factors
If multiple laser passes are used to create offset cracks, then splash energy is reduced, but process complexity increases
Solution Approach 1:
The complex task of creating a clean cut with minimal splash is segmented into multiple simpler passes. Each pass has a specific function (initial crack creation, crack extension, crack refinement) and can be optimized independently. The control system manages this complexity through automated sequencing of the passes with predetermined offset parameters.
3Object-affected harmful factors
If offset cracks forming zigzag pattern are created, then interaction between modified regions is reduced, but manufacturing precision requirements increase
Solution Approach 1:
Instead of creating symmetric cracks along the scribe street centerline, the invention uses asymmetric offset positioning for each laser pass. The first pass creates a crack at one offset position, and subsequent passes create cracks at different offset positions, forming a zigzag pattern. This asymmetry ensures that the modified regions from different passes do not fully overlap, reducing interaction and splash energy.
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 effectively reduces splash-induced damage, increases die yields by enabling narrower scribe streets, and allows for more dies per wafer, while using lower power to achieve effective dicing.
Implementation Method 1
The laser energy melts the single crystalline semiconductor material and the related stress can form a crack
Implementation Method 2
an incident laser beam can interact with structures within the wafer resulting in splash
Data Source
AI summary
One example provides a method that includes directing a first laser beam at a surface of a semiconductor substrate along a scribe street thereof. The first laser beam is focused inside the substrate to form a first modified region, which is offset from a second modified region in a direction orthogonal to a scan direction of the first laser beam, and a first crack extending between the second modified region and the first modified region. A second laser beam is directed at the surface to form a third modified region, which is offset from the first and second modified regions, and a second crack extending from the first modified region to the surface. The first and second cracks form a zigzag-shaped crack within the substrate along the scribe street.