Mask blank material optimization impact on leading-edge ArF lithography

In this study, we investigate what kind of mask blank material is optimum for the resolution enhancement techniques (RET) of leading-edge ArF lithography. The source mask optimization (SMO) is one of the promising RET in 2Xnm-node and it optimizes mask pattern and illumination intensity distribution simultaneously. We combine SMO with the blank material optimization and explore the truly optimized SMO. This study consists of three phases. In the first phase, we evaluate maximum exposure latitude (Max.E.L.) and mask error enhancement factor (MEEF) of fictitious materials that have typical real (n) and imaginary (k) value of refractive index by 3D rigorous simulator as the basic analysis. The simulation result shows that there are two high lithographic performance combinations of n and k values; one is low-n/high-k and the other is high-n/low-k. In the second phase, we select actual blank material that has similar optical parameters with the result of the previous phase. The lithographic performance of the selected material is investigated more precisely. We find that the candidate material has good lithographic performance at the semi-dense pitch. In the final phase, we create a test mask of this candidate blank material and verify simulation result by experimental assessment. The exposures are performed on NA1.30 immersion scanner (Nikon NSR-S610C). The experimental result shows the improvement of Max.E.L. in head to head type pattern. This study will discuss the potential of blank material tuning for the ArF lithography extension.