Photomask Defect Inspection and Metrology for Semiconductor Lithography Technology

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Semiconductors are the indispensable components of a wide range of products, such as smartphones and electrical appliances, and this award contributes to the creation of new knowledge in photomask inspection and metrology for the semiconductor industry. The availability of the interferometry inspection technology helps enhance the lithography manufacturing resolution, promote miniaturization and increase the performance and reduce the cost of electronic devices. In semiconductor manufacturing processes, photomasks with holes and transparencies that allow light to shine through in a defined pattern are an enabling technology for lithography. Photomask defects, such as unwanted patterns, contaminations and substrate flaws, become increasingly important sources of inaccuracies in the lithography processes and patterning. This award supports fundamental research to develop new measurement principles in photomask inspection, metrology, design and manufacturing. The project's inspection technique and simulation methods enable the determination of photomask quality. The method identifies photomask defects, creates defect models and compensates for lithography manufacturing errors. As a result, this research provides photomask manufacturers with significant time and cost savings by automating the photomask defect analysis process, which benefits the photomask, lithography machine tool and semiconductor manufacturing industries and, thus, the U.S. economy. This project provides interdisciplinary research experience for students, broadens participation of underrepresented groups in research through a precision metrology internship program, and influences engineering education through a course in Mechanical Measurements and Precision Machine Tools. As the photomask industry progresses towards smaller and smaller technology nodes, the need for more aggressive inspection becomes critical. Photomask inspection involves checking the correctness of the fabricated photomasks used for semiconductor device fabrication. The projected images of the defective photomask appear as irregularities, such as, line widths that are narrower or wider than designed, line-edge roughness of the patterns and distortions that may significantly alter the mechanical and electrical properties of what is being fabricated. This problem becomes more pronounced since photomask complexity rises with the complexity of new semiconductor chips. This research fills a critical knowledge gap in inspection technology and fundamental identification of photomask defects by using knife-edge diffraction interferometry (KEDI) and artificial neural network models. Through insights obtained from rigorous simulation tools and experimental results, the research team determines that the printability of lithography photomask defects can be quantitatively characterized prior to lithography operation and the simulation model can be extended to compensate for image distortions that occur during sub-wavelength lithography using printed structures smaller than the wavelength of light.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.