Investigation On Extreme Ultraviolet Lithography Mask

Extreme Ultraviolet Lithography (EUVL) is a leading candidate for next generation lithography technology, with wavelengths of 13.0nm, and is expected to support multiple technology generation from 65nm to 30nm. Experts from industry consider that mask technology is one of the most difficult challenges for EUVL. Masks for EUVL used in reflection, are fundamentally different from conventional masks which are applied in optical lithography. Because the exposure wavelength is in EUV region and the critical dimension (CD) is on the order of several tens nanometer, the flatness, roughness and defects of the mask substrate and the multilayers on blank must meet the rigorous expectations.By analyzing reflective properties of multilayers, the peak reflectivity, bandwidth and centroid wavelength as a function of roughness, period thickness and thickness ratio were obtained. Illumination uniformity errors at wafer plane due to the mask were analyzed, resulted a formula for estimating the error. According to total illumination uniformity error allowed for mask, requirements for multilayer peak reflectivity and bandwidth and centroid wavelength were proposed. This requirements are very close to ITRS2001's .Angular distribution of atoms sputtered from targets is researched. The emluator to imitate IBSD system is established by adopting cosine distribution. By some experimental researches on IBSD system and regression analyzing, the exponent of cosine distribution is determined and the emluator are completed for quantificationally simulation. Based on simulation results, uniformity is improved from 5.7% to 4.5% onφ140mm by rectifying targets position. Finally, the key design parameters of coating system was obtained, this system can meet ITRS requirements on uniformity of film thickness.Dispersed SiO2 spheres with the diameter of 230nm were fabricated on silicon wafer to simulate defects on mask substrate. Substrate with defects were coated with Mo/Si multilayers to investigate the smoothing properties. Experimental results show that multilayers could smooth defects, but not enough for blank fabrication. Therefore, ion-assisted polishing should be employ during thin film deposition process. In addition, some inspection technologies for defects are simply discussed.