Multistrata Subsurface Laser-Modified Microstructure With Backgrind-Assisted Controlled Fracture for Defect-Free Ultrathin Die Fabrication

We report the development of multistrata subsurface IR (1.342 μm) nanosecond pulsed laser die singulation [stealth dicing (SD)] on high backside reflectance (up to 82%) Si wafers. We study the microstructural properties and formation mechanisms of the subsurface Si dislocation belt layer with respect to laser scanning speed, pulse laser energies, and interstrata distances. We optimize and exploit the multistrata interactions between generated thermal shock waves and the preceding dislocation belt layers formed to initiate frontal crack fractures that separate out the individual dies from within the interior of the wafer. A new partial-SD before grinding (p-SDBG) integration scheme based upon the tandem use of three-strata SD for controlled crack fracture toward the frontside of the wafer followed by static loading from backgrinding to complete full kerf separation is demonstrated. The optimized three-strata SD process and p-SDBG integration scheme can be used to compensate for the high backside reflectance wafers to produce defect-free eight die stacks of 25-μm-thick mechanically functional and 46-μm-thick electrically functional 2-D NAND memory dies.