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Characterization of Laser Recast Profile and Height for Laser Dicing Process

Laser dicing for semiconductor wafer singulation, in one form, is a careful process of burning a path along the saw streets, while a wafer is mounted on dicing tape. The high temperature of the laser melts the substrate material, resulting in a by-product known as laser recast, or slag, which builds up along the sides of the cutting path. A protective coating is applied before dicing to protect the circuitry but may leave some recast along the edges of the die. This recast is generally harmless but may interact with later packaging steps. Though the usual laser recast does not affect die performance, it could cause failures in certain die packaging, especially when there are some laser recast outliers (e.g., higher than usual recast accumulation) at a random location. Before the laser recast can be further reduced with certain verification, an appropriate methodology needs to be developed for the characterization of the recast profile and height. This paper describes an innovative method utilizing different but readily available metrology tools to quantitatively analyze the laser recast produced by a laser dicing process. Each of them can be used to determine the laser recast level of a dicing process and to justify whether the process is optimized in terms of the laser recast reduction.