Mask Critical Dimension Specification Considering Process Sensitivity of Mask Error in Extreme Ultraviolet Lithography

Abstract

A systematic approach for critical dimension (CD) specification that considers the process window is devised. The concept of modified exposure latitude (EL) is introduced to exclude mask-related error terms. Process window calculation based on modified EL can be used to estimate required the mask CD specification considering mask CD uniformity and mean to target (MTT) error simultaneously. With this calculation, line and space (L/S) and contact array patterns in the 32 nm node are sufficient for a binary mask and 0.25 numerical aperture (NA). High NA and off-axis illumination (OAI) should be adopted in the 22 nm node. It is believed that an appropriate process margin for the 16 nm node can be further realized using phase shift mask (PSM) in addition to higher NA and OAI. Also, depth of focus (DOF), which satisfies CD uniformity in International Technology Roadmap for Semiconductor (ITRS), is estimated from the process window in each node. On the basis of this analysis, 0.23 µm in the 32 nm node, 0.11 µm in the 22 nm node, and 0.09 µm in the 16 nm node in DOF can be acquired for L/S. Furthermore, 0.15 µm in the 32 nm node, 0.075 µm in the 22 nm node, and 0.05 µm in the 16 µm node in DOF can be acquired for semi-dense contact array.