Research On Wafer Backside Discolor Issue

During the semiconductor inline inspection, engineers always foundwafer backside discolor. Single wafer scraped for the backside discolor andcan’t been fabrication-out, even backside had peeling defect, which couldcause more wafers scraped for defect issue. This dissertation shows us themechanism of discolor firstly, which is caused by the worse uniformity ofthe films’ thickness (SEM cut data gives us the best evidence). Then itdescribes the film’s structures detail, and chooses the chemical based ontheir chemical properties. At last it gives us the best solution: using49%HF to handle the SiO2&Si3N4and using100:1HNO3: HF to handle thePoly-silicon if they are damaged.For the handling time, if wafers backside have peeling defect, orcause wafer defocus or overlay out of spec or cause rapid thermal annealtool’s alarm, we have to handle the wafer at front end of line slightly, thenhandle again at backend of line (We can’t remove all backside films, whichhave special function to free of damage during the process). If they can’timpact other wafers or the following process, we propose to handle thewafer at the last time of fabrication-out. At the same time, make sure thedissociated ions are dissolved and let wafer free of crystal defect.This dissertation also summary the root cause of wafer backsidediscolors. Single wafer handling tool’s chemical leakage, e-chuck positionabnormal and wafer cross are major reasons of wafer backside discolors.Single wafer handling tool leakage has relationship with suck-back valve;e-chuck position abnormal, which is caused by longer life time parts, candamage wafer backside film combined with the polymer striper’s chemicaletching. All these three reasons can cause wafer backside discolor. At last,this dissertation gives the better solutions for discolor reduction: add inline monitor and inspection, add offline monitor, enhance monitor and do cycletest to catch tools’ abnormal at the first time. It also gives the suggestionsto modify tool’s configuration and prevent action. All these actions canreduce the probability of wafer backside discolors. But it’s a big challengefor us to handle the wafer backside discolor which use new materials.