Stability of across field line variation (ACLV) is crucial in advanced semiconductor manufacturing. Degraded signatures
cause deterioration of transistor parameters and yield loss. After having contained haze issues, the IC industry is now
confronting a new reticle degradation mechanism. It has been reported, that targeting energy is changing with the
number of exposures and later on a rapid increase of ACLV is observed. Although effective monitoring and correction
methods have been introduced, the root cause of this type of reticle degradation has not been fully elucidated.
Our AIMSTM, SEM and optical CD measurements on reticle demonstrated consistency with wafer CD measurements and
clearly show that pattern distortions on wafers originate from the front side of the reticle. The results indicate the
transmission loss to be gradually distributed over the reticle surface causing CD variations. In the most acute case,
changes in the center area could be detected by the reticle inspection tool. Dependency of degradation rate on percentage
of the clear field on the reticle and reticle type was observed.
Finally, using a variety of analytical techniques including AFM, ion and gas chromatography, TOF-SIMS, Auger and
TEM we have been able to identify the root cause of this problem. Our experimental results do show that the structural
degradation of the absorber film is the primary cause for CD change. Possible mechanisms behind this effect are