Comparison of lithographic performance between MoSi binary mask and MoSi attenuated PSM
2009
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.
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