A new methodology to specify via and contact layer reticles for maximizing process latitude

It is well known that shrinking k1 factors are making via and contact layers more difficult to print with acceptable latitude and low defectivity. A typical method for improving the common process window is to use embedded attenuated phase shifting masks (EAPSM). However, even with the improved resolution offered by this technology, small deviations in reticle contact size are producing increasingly severe patterning problems - at the extreme, missing contacts. In this study, we conducted an investigation of a production reticle causing repeating wafer defects that passed the reticle manufacturer’s outgoing inspection. We have examined this reticle using a new inspection algorithm that measures reticle contact energy. This technique successfully detected slightly undersized contacts directly corresponding to the coordinates of the repeating wafer defects. However, the reticle contact energy inspection also detected numerous undersized contacts that were not detected by wafer SEM inspection. We have produced and printed to wafer a test reticle with programmed over and under sized contacts in order to create a new reticle specification to detect defective contacts before they are shipped to the wafer fab.