Comparison of lithographic performance between MoSi binary mask and MoSi attenuated PSM

Abstract

The mask error budget continues to shrink with shrinking DRAM half pitch and MPU gate size year by year. The ITRS roadmap calls for mask CDU to be cut in half by 2014[1]. Both mask maker and mask user must take advantage of various mask properties, OPC strategies and resolution enhancement techniques to drive improvements. Mask material selection impacts both lithographic performance and mask manufacturability. In turn mask material properties and manufacturing techniques impact our ability to meet the technology roadmap. Studies have shown the advantages of polarized light[2,3] as well as the impact of various mask materials on high NA lithography[4]. In this paper we select the recently introduced binary mask material made from a MoSi absorber called Opaque MoSi On Glass (OMOG) for comparison with the conventional 6% att. PSM and 20% att. MoSi PSM. Through simulation and wafer prints, we optimized mask feature from viewpoint of MEEF and maximum exposure latitude (EL). The MoSi att. PSMs suffer from higher MEEF, which is attributed to the negative effect of TE polarization for mask duty cycle of 50% for 50 nm half pitch and below. Therefore a lower mask duty cycle is required for att. PSM to bring the MEEF performance back to acceptable levels. Experimental results confirm simulation results. As a result of the lower mask duty cycle, the att. MoSi PSMs exhibit poor Sub Resolution Assist Feature (SRAF) printability. On the contrary, the MoSi binary mask delivers both acceptable MEEF and acceptable SRAF printing performance. Moreover, we found that the mask structure impact of OMOG to wafer CD is smallest among three masks. OMOG gives the best combination of lithographic performance and delivery compared to the MoSi att. PSMs.