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High yield dicing of anodically bonded silicon glass wafers by pressure induced fracture

This paper describes a technique that uses applied force to dice anodically bonded silicon–glass wafers with high yields. The chips are suspended to the wafer by anchors; when pressure is applied to a chip, stress concentrates at the narrow anchors, which then fracture and release the chip from the wafer. Anchor fracturing has been used to dice crystalline and non-crystalline materials but its application to dicing constructs of various materials has remained challenging because of the disparity with which fractures propagate in different materials and in their interfaces. The technique we present here makes it possible to fracture composite materials (silicon and glass anodically bonded) by eliminating any material interface from the fracturing regions—i.e. the anchors. The approach was tested using two types of anchors fabricated in anodically bonded silicon–glass wafers: in one type, the silicon–glass interface expanded most of the anchor (coincident anchors) but such an interface was inexistent in the other type (non-coincident anchors). The study determined dicing yields—i.e. percentage of chips not damaged by the fracture of the anchors—of ~40% and 100% for test structures with coincident and non-coincident anchors, respectively. The presence of a silicon–glass interface in the suspending anchors often resulted in fractures propagating away from the anchors, and ultimately in damage to the suspended chips. This technique provides an inexpensive, robust and simple alternative to currently available dicing methods for the glass–silicon wafer pairs frequently used in wafer-level packaging of MEMS.

 

source: iopscience

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