Using Lasers to Dice Thin Silicon Wafers

BY DELPHINE PERROTTET, Kali DUNNE, Gillian WALSH, AND Billy DIGGIN, XSIL LTD.

Mechanical saw dicing is the conventional technology used for dicing thick silicon wafers. However, below 100 μm, abrasive saws encounter issues — primarily low die strength and decreasing machining speed. Singulation of die mounted on die-attach film (DAF) also proves challenging for traditional methods. Laser-based technologies offer efficient solutions for thin wafers on DAF. With the increased percentage of thin wafers in high-volume applications and the decrease of wafer thickness (several manufacturers have roadmaps to reduce from 75 μm down to 25 μm and thinner), interest in laser solutions is growing significantly.

Laser-based Dicing System

For thin wafers, laser dicing demonstrates high throughput and provides higher yield than traditional methods. However, additional processes are essential to address die strength and contamination. The first step is to coat the wafer for protection. The wafer is then laser diced. After dicing, the wafer is cleaned to remove the coating and debris. The last step is an etching process, which increases die strength.

Coating

Coating provides effective protection against debris and contamination. This resist solution is dispensed onto the wafer surface then spread over the entire surface by virtue of a spinning process that rotates the wafer at high speed until the coating is dry.

As running cost is one of the main concerns of chip manufacturers, a low-cost product has been selected for coating. It is a non-ionic, water-soluble coating, which is dispensed and spin-coated inside the integrated wash station.

For a 300-mm thin silicon wafer, the volume of coating used will be 50

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