As technology node of memory devices is approaching around 30nm, the process window is becoming much
narrower and production yield is getting more sensitive to tiny defects which used to be not, if ever, so critical. So it
would be very hard to expect the same production yield as now in near future.
It is possible to classify wafer defects into systematic and random defects. Systematic defects can be also divided
into design related and process related defects. Narrow process window, generally, is thought to be the source of
these systematic defects and we have to extend process window with Design for Manufacturing (DFM) and control
process variation with Advanced Process Control (APC) to ensure the production yield.
The sensitivity of random defects, however, has something to do with the smaller design rule itself. For example, the
narrower spaces between lines are subject to bridge defects and the smaller lines, to pinch defects.
Die to data base (DB) Design Based Metrology (DBM) has mainly been in use for detecting systematic defects and
feedback to DFM and APC so far. We are trying to extend the application of DBM to random defects control. The conventional defect inspection systems are reaching its highest limit due to the low signal to noise ratio for extremely small feature sizes of below 40nm. It is found that Die to DB metrology tool is capable of detecting small but critical defects with reliability.