Stealth Wafer Dicing After Laser Ablation of Scribe-Street Metal
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Solution Overview
Problem
Metal bridging during stealth dicing of semiconductor wafers with surface metallization prevents effective singulation of semiconductor device dies, as the metal layer can form bridges between dies, hindering the crack propagation necessary for die separation.
Innovation Solution
Applying a dicing tape over the metal layer on scribe streets and using a laser to ablate the metal layer before performing stealth dicing, adjusting the laser power and focal depth to create metal-free regions, thereby preventing metal bridging and ensuring successful singulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If stealth dicing is used to singulate semiconductor device dies, then the singulation process is non-mechanical and avoids mechanical stress, but metal bridging occurs when metal is present over the scribe street areas, preventing effective singulation
Solution Approach 1:
The patent applies preliminary action by performing laser ablation of the metal layer before the stealth dicing process. The laser removes metal from the scribe street areas in advance, creating metal-free zones that will not interfere with subsequent crack propagation during stealth dicing. This preliminary removal of the harmful metal element ensures that the later singulation process can proceed effectively without metal bridging.
Solution Approach 2:
The patent applies the extraction principle by removing the metal layer from the scribe street areas using laser ablation. The laser energy selectively vaporizes and ejects the metal material, extracting it from the region where it would otherwise prevent effective singulation. This extraction of the problematic metal element allows the stealth dicing process to function properly.
2Manufacturing precision
If laser energy is focused at various depths in the semiconductor wafer to melt the single crystalline semiconductor material, then crack propagation is enabled for singulation, but metal bridging can occur that prevents effective singulation
Solution Approach 1:
The patent applies preliminary action by performing laser ablation of the metal layer before the stealth dicing process. The laser removes metal from the scribe street areas in advance, creating metal-free zones that will not interfere with subsequent crack propagation during stealth dicing. This preliminary removal of the harmful metal element ensures that the later singulation process can proceed effectively without metal bridging.
Solution Approach 2:
The patent converts the harmful effect of metal presence into a beneficial process by using the laser's interaction with metal to achieve selective removal. The laser energy that would normally be absorbed by metal (causing heating and potential bridging) is instead used to vaporize and remove the metal completely from the scribe streets, transforming the potential problem into the solution.
3Productivity
If a saw blade is used to saw scribe streets between semiconductor device dies, then mechanical separation is achieved, but rough edges are created on the separated dies
Solution Approach 1:
The patent applies mechanics substitution by replacing the mechanical sawing process with a thermal field-based laser process. Instead of using a physical saw blade that mechanically cuts through the material (creating rough edges), the patent uses laser energy to melt and vaporize material, followed by stress-induced crack propagation. This non-mechanical approach produces smooth edges without the mechanical trauma inherent in sawing.
Solution Approach 2:
The patent utilizes phase transitions in the material response to laser energy. The laser heating causes localized melting of the semiconductor material, and the subsequent rapid cooling and stress release causes crack propagation through phase change and thermal stress mechanisms. This phase transition-based separation produces clean, smooth edges compared to mechanical cutting.
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 method effectively prevents metal bridging, allowing for smooth and complete separation of semiconductor device dies without the rough edges associated with mechanical sawing, enhancing the efficiency and reliability of the singulation process.
Implementation Method 1
The laser beam scans across the scribe streets and ablates the metal layer in the scribe streets
Implementation Method 2
The energy laser energy melts the single crystalline semiconductor material and the related stress can form a crack
Data Source
AI summary
In a described example, a method includes: applying a dicing tape over a metal layer covering a portion of a surface of scribe streets on a device side of a semiconductor wafer that includes semiconductor device dies formed thereon separated from one another by the scribe streets; and placing the semiconductor wafer with the device side facing away from a laser in a stealth dicing machine. A power of a laser beam is adjusted to a first power level. The laser beam is focused through the non-device side of the semiconductor wafer to a first focal depth in the metal layer. The laser beam scans across the scribe streets and ablates the metal layer in the scribe streets. The method continues by singulating the semiconductor device dies using stealth dicing along the scribe streets in the stealth dicing machine.