Printability and inspectability of programmed pit defects on the masks in EUV lithography

Printability and inspectability of phase defects in EUVL mask originated from substrate pit were investigated. For this purpose, PDMs with programmed pits on substrate were fabricated using different ML sources from several suppliers. Simulations with 32-nm HP L/S show that substrate pits with below similar to 20 nm in depth would not be printed on the wafer if they could be smoothed by ML process down to similar to 1 nm in depth on ML surface. Through the investigation of inspectability for programmed pits, minimum pit sizes detected by KLA6xx, AIT, and M7360 depend on ML smoothing performance. Furthermore, printability results for pit defects also correlate with smoothed pit sizes. AIT results for patterned mask with 32-nm HP L/S represents that minimum printable size of pits could be similar to 28.3 nm of SEVD. In addition, printability of pits became more printable as defocus moves to (-) directions. Consequently, printability of phase defects strongly depends on their locations with respect to those of absorber patterns. This indicates that defect compensation by pattern shift could be a key technique to realize zero printable phase defects in EUVL masks.