Front end wafer Scanning Infra Red Depolarization (SIRD) measurement correlation to back end wafer backside finishing

Scanning Infra Red Depolarization (SIRD) is a well established and accepted method for semiconductor Front End (FE) wafer substrate quality measurement. It often used as process control tool, defect monitoring/ screening and also quality management at FE. The method can indicate wafer internal stress (lattice structure slipline control, wafer fracture risk indication) level as well as wafer backside surface defects (pin mark etc) and surface treatment uniformity. There seems no or limited papers relevant to correlation of SIRD to BE application. Nevertheless, this technical paper, intended to explore if there is any correlation of FE SIRD measurement to Back End (BE) interest, particularly on wafer backside roughness. For interest of BE packaging aspect, wafer backside roughness, is having influence to glue adhesive adhesion properties (particularly wetting and level of `mechanical anchoring´ between the 2 adhesion surfaces) at Die Attach (DA) process. This also impact Reliability performance especially in Thermal Cycles (TC) and High Temperature Storage (HTS) in package level. The correlation established, can give indication of incoming wafer back behavior response to adhesive adhesion performance, consistency (can be assess through Hot Die Shear test (HDS) at 260deg C) and hence, finally the Package Reliability consistency without introducing additional process control at BE. It can also be wafer incoming quality control gate, when come to critical application, e.g. Automotive application relevant to safety, if necessary. This is not only cost effective where no extra measurement step at BE, FE not compatible wafer to BE, can be quarantined at BE wafer incoming for further deposition without wasting resources to proceed packaging assembly and testing. This can also be pro-active prevention of low robustness package (hard be screened out in manufacturing as 100% reliability/ stress test to production parts is just not possible and practical!) assembled to custome- , and create a potential risk of field failure during application. After comparing several measurement method and parameter, Ra value with laser beam measurement showing medium to strong correlation to SIRD. Low SIRD and small `Delta in SIRD´ in a wafer, also yield good HDS failure mode. Initial commendation for wafer SIRD to be below 3 and delta in SIRD below 3 as well for BE incoming wafer control. Despite this correlation exercise is conclusive, however still seen several areas of interest to further study and elaborate to further complete the correlation topic.