Mask 3D Effects and Compensation for High NA EUV Lithography

Mask shadow compensation for EUV lithography has typically been performed using simple rule-based schemes during optical proximity correction (OPC). However, as feature sizes decrease, the required corrections get more complex as they become dependent on both feature size and type. Thus, OPC models that account for these 3D mask effects are becoming essential. These models become even more important for higher numerical aperture EUV systems due to larger angles of incidence on the mask and tighter process budgets for CD and overlay. This paper will focus on estimating these 3D mask effects and evaluate the extendibility of current available OPC models for some specific higher numerical aperture EUV systems. It is concluded that the current available 3D mask models are capturing the primary effects and it is believed that with further refinement they are likely extendable to meet the needs of future high-NA tools. Additionally, a combination of thinner mask absorber, tighter scanner focus control and/or larger optical magnification will likely be required to print sub-30nm pitch structures with higher numerical aperture EUV systems.