Scatterometry based 65nm node CDU analysis and prediction using novel reticle measurement technique

Scatterometry was selected as CD metrology for the 65 nm CDU system qualification. Because of the dominant reticle residuals component in the 65 nm CD budget for dense lines, significant improvements in reticle CD metrology were required. SEM is an option but requires extensive measurements due to the scatterometry grating modules. Therefore a new technique was developed and called SERUM (Spot sensor Enabled Reticle Uniformity Measurements). It uses the on board exposure system metrology sensors to measure transmission that is converted to reticle CD. It has the advantage that an entire reticle is measured within two minutes with good repeatability. The reticle fingerprints correlate well to the SEM measurements. With the improvements in reticle CD metrology offered by SEM and SERUM the reticle residuals component no longer dominates the 65 nm budget for CDU system qualification.