Laser Modification Zones for Wafer Dicing Stress Relief
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Solution Overview
Problem
The existing methods for separating semiconductor wafers into individual IC device die, such as those used in RFID tags, often result in stress-induced cracking due to the laser dicing process, leading to reliability issues and potential failure of the packaged devices under mechanical stress.
Innovation Solution
A method involving pre-grinding the backside of the wafer substrate and applying a laser to define secondary and main modification zones at specific focus depths, with the secondary zone located within active device boundaries, to minimize stress and facilitate controlled cracking during separation, thereby reducing the likelihood of die cracking when packaged in RFID tags.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser cutting is used to separate wafer into individual ICs, then cutting speed and precision are improved, but stress-induced cracking occurs in the die edges during packaging
Solution Approach 1:
The laser modification is segmented into two distinct zones: a primary modification zone extending from the back surface to a first depth, and a secondary modification zone extending from the back surface to a second depth greater than the first depth. This segmentation allows the stress to be distributed and controlled, preventing crack propagation while maintaining cutting efficiency.
Solution Approach 2:
Different modification depths are applied at different locations: the primary modification zone has a shallower depth while the secondary modification zone extends deeper. This local differentiation of modification quality creates a controlled stress distribution pattern that prevents edge cracking during subsequent packaging operations.
2Device complexity
If mechanical cutting is used to separate wafer, then equipment simplicity is maintained, but chipping occurs on the front-side or back-side of substrate
Solution Approach 1:
The patent replaces mechanical cutting with laser-based modification. Instead of using mechanical blades that cause chipping, a laser is used to create controlled modification zones in the substrate, enabling crack initiation and propagation along desired lanes without mechanical contact with the substrate surfaces.
3Ease of manufacture
If laser focuses into material to melt mono-crystalline silicon, then die separation is achieved, but polycrystalline re-crystallization induces stress creating cracks
Solution Approach 1:
The laser modification is performed in advance during wafer processing, creating the primary and secondary modification zones before die separation and packaging. This preliminary action prepares the material structure to control subsequent stress development and crack propagation during separation and packaging operations.
Solution Approach 2:
The dual-zone modification structure acts as a cushioning mechanism: the primary modification zone allows controlled crack initiation, while the secondary modification zone extends deeper to absorb and distribute stress, preventing uncontrolled crack propagation that would damage the die edges during packaging.
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 the stress on active device edges and minimizes cracking during the packaging process, enhancing the reliability and longevity of RFID tags by allowing for controlled separation and stress relief.
Implementation Method 1
a laser is applied to define a secondary modification zone in saw lanes; a laser is applied to the back-side of the wafer in the saw lanes to define a main modification zone
Implementation Method 2
the laser focuses into the material and melts the mono-crystalline silicon
Implementation Method 3
The material re-crystallizes as polycrystalline silicon
Implementation Method 4
pre-grinding the backside of a wafer substrate to a thickness; the back-side of the wafer is ground down to a depth so as to substantially remove the main modification zone
Implementation Method 5
To separate IC device die from one another, the protective foil is stretched
Data Source
AI summary
Consistent with an example embodiment, there is a method for preparing integrated circuit (IC) device die from a wafer substrate having a front-side with active devices and a back-side. The method comprises pre-grinding the backside of a wafer substrate to a thickness. The front-side of the wafer is mounted onto a protective foil. A laser is applied to the backside of the wafer, at first focus depth to define a secondary modification zone in saw lanes. To the backside of the wafer, a second laser process is applied, at a second focus depth shallower than that of the first focus depth, in the saw lanes to define a main modification zone, the secondary modification defined at a pre-determined location within active device boundaries, the active device boundaries defining an active device area. The backside of the wafer is ground down to a depth so as to remove the main modification zone. The IC device die are separated from one another by stretching the protective foil.