Direct observation of internal void-formation in Stealth Dicing

Abstract

Stealth Dicing (SD) technology is an innovative laser dicing method, developed by Hamamatsu Photonics K. K., for semiconductor silicon wafers. In the advanced dicing process, a pulsed laser beam in the near-infrared region focused in a transparent wafer generates local modification regions, which become origins of cracks for separation. Owing to the non-contact and internal process, SD process has many advantages such as a completely dry process, high throughput, high quality, less kerf losses, and low running costs. The phenomenon of advanced dicing technology has not been sufficiently elucidated, and therefore many SD parameters have not been optimized although there are affect to dicing results. In this study, the laser modification phenomenon of SD in a Si wafer was investigated to focus on the actual phenomena. Firstly, the cleaved cross-section observation and nondestructive observation before cleaving has been conducted. Secondly, the subsurface time-resolved measurement have been proposed to observe SD mechanisms. Finally, in-situ observation of SD laser processing inside a Si wafer has been conducted to discuss the laser energy absorption phenomena. In addition, a few distinctive phenomena, including fine void structure with dislocation mapping, dynamics of transient absorption phenomenon inside the Si wafer after laser irradiation, and nanosecond-scale spreading of the laser shutoff phenomenon at SD laser focusing point, are confirmed.