| Popis: |
The laser stealth dicing system is a unique wafer processing system to enable high-throughput and debris-free wafer dicing. In the laser stealth dicing system, a focused pulsed laser forms a modification layer and cracks inside a silicon wafer. During pulsed laser radiation and wafer scanning, cracks formed in the previous shot interfere with a focusing laser pulse on a defocus plane. As a result, a part of interacted laser beam scatters, generating back-side splash defects on the device layer. An asymmetric beam shaping of defocused spot becomes necessary to minimize the splash defects. At the same time, the focused spot should maintain sufficiently small focused spot size to generate a modified layer inside the silicon wafer. This paper presents a concept of an innovative focusing spot shaping with an asymmetrical pupil phase filter which is individually optimized for both defocused and focused spots. We optimized the phase filter to generate a threedimensionally- asymmetrical focused spot which deforms defocused spot with a near diffraction-limited focal spot size. The through-focus spot shaping technique is enable to minimize splash defects and improve the yield of the laser wafer dicing process. |
