As a result of repeated cleanings and exposure effects such as chrome migration or MoSi oxidation some
photomasks in the semiconductor fabs exhibit changes in critical dimension uniformity (CDU) over time.
Detecting these effects in a timely manner allows for better risk management and process control in
manufacturing. By monitoring changes in film reflectance intensity due to the various degradation mechanisms
it is possible to predict when they may begin to influence across chip line width variations (ACLV). By
accurately predicting the magnitude of these changes it is possible for semiconductor manufacturers to replace
the photomasks before they have an impact on yields. This paper looks at possible causes of CDU variations on
reticles during use and how this information might be used to improve or monitor reticle CDU changes over