Nanopit smoothing by cleaning

摘要

Defect smoothing is a critical need for improving defects. There are different methods such as using a smoothing layer or multilayer deposition; however, smoothing processes tend to add defects of their own to the surface. This paper presents a novel pit smoothing method based on an anisotropic substrate etch process. Smoothing power is defined as a metric for comparing the smoothing capability of different smoothing processes. Defect smoothing by cleaning is a surface modification technique with a smoothing power <10 that does not add defects to the surface. This is demonstrated by comparing total defects on the mask blank and mask blank substrate for two processes: a standard ozone-based cleaning and a smoothing cleaning. The smooth/clean methods led to fewer defects on the blank and substrate surfaces than the standard clean while still meeting extreme ultraviolet (EUV) blank roughness requirements. Finally, it is shown that smoothed pits are still printable. Therefore, further improvements to the smoothing power of smooth/clean processes are needed. SEMATECH is currently working to improve smooth/clean processes for low thermal expansion material (LTEM) EUV substrates.