Novel UV-USP Laser Grooving and Plasma Dicing Separation Schemes for Next Generation Advanced Packaging

Zero defect in semiconductor packaging is key especially for high demanding reliability applications (automotive, spatial...) combined with high performance technologies (Silicon ultra lowK wafers 40nm and beyond). The most complex challenge is the Chip Package Interconnect which requires an optimized and controlled singulation process to prevent weaknesses occurring during the process (ILD crack/ delamination, side wall crack, metal burrs, humidity propagation and die strength weakness). Laser grooving prior mechanical dicing offers a good seal ring protection of the chips, ie use of a laser to perform ablation and remove the sawing street contents (dielectric / metallization / patterns) in order to make a clean `path' for the mechanical sawing step afterward. Degradation of the blade condition is also reduced with this approach. This article describes the interactions between laser grooving process and the lLD BEOL delamination prevention by applying a perfect U shape profile.Laser Grooving process selection is a complex combination of different requirements: (i) U shape profile geometry tradeoff to guarantee integrity of BEOL layers during mechanical dicing, while keeping a high level of miniaturization of the sawing street not to increase wafer cost. (ii) Laser technology and process to match the required U-shape geometry minimizing redeposition of residues (recast), avoid pitting (voids) and absorb the heterogenous content of a scribe line with a minimum level of energy applied. This is achieved thanks to an accurate selection of the laser source (wavelength, beam size), accuracy of the beam position (lens optical system), ablation method (multi pass) and process parameter optimization (power, speed, frequency...). (iii) Advanced characterization technics are required to ensure the required quality criteria are matched, like 3D profilometer, FIB cross sections, SEM controls, AOI and 3 points die strength.STMicroelectronics is deploying this quality driven mindset to high volume manufacturing environment in all BE manufacturing plants. Emerging technologies like ultrafast laser wavelength or replacement of mechanical dicing by plasma dicing are next steps of interest further enhanced the robustness of more and more fragile wafer FE technologies.

Advanced packaging has a challenge on its hands in dealing with reliability issues caused during singulation. Specifically, in the case of Wafer Level Chip Scale packaging (WLCSP) where the sawn die edge is the package edge and is exposed. WLCSP manufactured on the newer nodes are based on Ultra-low K dielectric material. This material is inherently porous and mechanically fragile. During the singulation step, there is a likelihood of creating chipping and delamination. Rudolph have developed a comprehensive approach to detecting defects generated at the laser grooving and saw process steps. There are two recommended approaches. The first approach is an inspection approach that is focused on detecting the defects after it has occurred. The second, a more sophisticated approach is to attempt to pre-empt occurrence of defects. In the first approach-die seal ring inspection, algorithms have been developed around the die seal ring to ensure the die integrity. These algorithms not only include the capability to detect the defect but also measure the defect size, defect position and frequency of defects. All of this is done while minimizing false defects that are typically found due to street and reticle artifacts that are often falsely detected as chipping. This enables customers to perform advanced disposition to ensure the optimal balance between shipping good die and preventing the shipment of potential reliability fails. The second approach — Kerf metrology and Saw control comprises of Fault detection and classification (FDC) to record equipment data during the singulation processes and inspection equipment to detect surface defects such as chips, delamination and cracks. The combination of FDC to monitor equipment performance and the ability to correlate Metrology/Inspection performance data enables customers to not only detect defects but preemptively eliminate them. Poorly singulated dies can now be analyzed all the way back to the process equipment signals. Once these signals are identified they can be monitored to prevent or alert operators of possible excursions. These analytics will help customers define and ramp robust processes, justify consumable costs and ultimately lead to a better understanding of this difficult and challenging process. Finally, specific YMS capabilities exist to align and analyze the collected equipment and process data.