Study of EUV reticle storage effects through exposure on EBL2 and NXE

A parallelism was found between reticle lifetime experiments undertaken on TNO’s EBL2 platform and wafer printing on the ASML NXE EUV scanner installed at imec. EBL2 mimics reticle impact due to exposure of ten thousand wafers in NXE representative conditions in about one day. In-situ X-ray Photoelectron Spectroscopy (XPS) has shown that high-dose EUV exposure removes surface carbon and reduces ruthenium oxide to ruthenium. Repeating XPS after a period of reticle storage, revealed regrowth of such contamination layer and re-oxidation of ruthenium. This learning based on EBL2 explains a small but significant trend noticed in critical dimension measurement results on wafer through a batch of wafers exposed on NXE, in such that reticle storage effects are gradually undone upon exposure of the first wafers following reticle entry into vacuum.