High Throughput and Improved Edge Straightness for Memory Applications Using Stealth Dicing

This paper describes the throughput and edge straightness achieved by singulating memory wafers using a dicing method called Stealth Dicing (SD). Conventional SD faces the problem that, when the laser beam is focused in a region deep inside the silicon wafer, the beam is blurred, and its power density decreases owing to spherical aberration caused by a refractive index mismatch between air and the wafer material, and as a result, the throughput decreases. In this study, we used a phase-only Spatial Light Modulator (SLM) to improve the spherical aberration, and we evaluated how the total amount of aberration correction affected the processing performance. In addition, we evaluated the processing capability using three laser wavelengths (1064 nm, 1080 nm and 1099 nm) which have different transmittances in silicon. The edge straightness at these wavelengths changed with the aberration correction and was 1 μm or less in the case of under correction. The crack length decreased in the case of under correction. Thus, there was a trade-off between the aberration correction and crack growth. By applying the SD method with optimized aberration correction using 1099 nmwavelength laser light to dice memory wafers, the throughput was improved by two-times compared with Blade Dicing, and high manufacturability for volume production can thus be anticipated.