Extreme ultra violet (EUV) lithography is at the high volume manufacturing threshold. It is therefore important to address relevant technical and technological challenges on its roadmap. One of the crucial concerns is EUV mask metrology and inspection. While the technology matures it becomes possible to print increasingly fine features on wafer leading to tighter mask metrology and inspection requirements. This drives the needs for algorithmic advancement and development. The purpose of this project is to develop novel methods for inverse problem solving that can help to satisfy the industrial need for precise metrology and inspection of semiconductor structures.
In this project we focus on scatterometry, the industrial workhorse for mask and wafer metrology in the semiconductor industry, and on lensless imaging (ptychography), a possible solution for actinic (@λ = 13.5 nm) EUV mask inspection. We address a few relevant issues and discuss in detail novel methods and viewpoints that provide their satisfactory solution. The proposed solutions enrich the scatterometry/phase retrieval toolset and they are shown to outperform and advance the state-of-art methods.
By providing novel regression schemes, applying and discussing local and global sensitivity analysis methods to EUV scatterometry, and disclosing new phase retrieval/ptychographyc algorithms, we enable tighter metrology and inspection of EUV masks.
This study can be useful and of potential importance for the ones who work on EUV lithography and for the scatterometry/phase retrieval community.