Aging study in advanced photomasks:Impact of EFM effects on lithographic performancewith MoSi binary and 6 attenuated PSM masks

摘要

As mask dimensions continue to shrink to meet the ITRS roadmap and with the extension of 193 nm immersion lithography, the masks are affected by electromagnetic field at high NA. Absorber degradation is regularly reported under long term 193 nm exposures in the subwavelength diffraction regime. The damage mechanism known as Electric Field induced Migration of chrome (EFM) partly contributes to the lifetime reduction of advanced masks. The EFM results in a progressive alteration of the Critical Dimension (CD), CD uniformity (CDU) degradation and assist features. This study evaluates the impact and the rate of absorber degradation due to an intensive ArF irradiation on assist features and its influence on the through pitch process window for sub-45 nm technology nodes. Lithographic performance is characterized after cumulative reticle aging stages. The aging test exposures are carried out directly on 193 nm scanner to duplicate the production environment. The analysis of printed wafers is correlated to advanced mask inspection (AIMS™). This paper reports results on irradiation damage sensitivity on two types of reticles: conventional 6% attenuated PSM and new binary material OMOG (Opaque MoSi On Glass) reticle. Test patterns have been generated with and without a set of Optical Proximity Corrections (OPC) model calibration structures based on 45nm down to 28nm half-pitch design. The combination of metrology measurements used in this work between printed wafers and reticles enables to define accurately the impact of mask damage caused by EFM effects on various test patterns and CD evolution and highlight some trends about advances masks aging phenomenon.