Abstract
When a permeable nanosecond pulse laser which is focused into the inside of a silicon wafer is scanned in the horizontal direction, a belt-shaped high dislocation density layer is formed at an arbitrary depth in the wafer. Applying tensile stress perpendicularly to this belt-shaped modified layer, silicon wafer can be separated easily into individual chip without creating any damage to the wafer surface comparing with the conventional blade dicing method, because the cracks that spread from the modified layer up and down progress to the surface. This technology is called "stealth dicing" (SD), and attracts attentions as a novel dicing technology in semiconductor industries. In order to clarify the formation mechanism of modified layer, we paid attention to an experimental result that the absorption coefficient varies with temperature. We analyzed a coupling problem composed of focused laser propagation in a silicon single crystal, laser absorption, temperature rise, and heat conduction. Simple thermal stress analysis was also conducted based on those results. As a result, formation mechanism of the modified layer could be explained clearly. Temperature dependence of absorption coefficient is the most important factor of the modified layer formation.
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