Sematech Reduces Defects in EUV Mask Blanks

Sematech researchers have succeeded in reducing tool-generated defects from multilayer deposition of mask blanks used for extreme-ultraviolet (EUV) lithography, bringing the technology a step closer to high-volume manufacturing.

Mask blank defects generally are formed by decoration of substrate defects by the multilayer deposition process and by the deposition process itself. This has prevented the quality of mask blanks from keeping pace with roadmap requirements for the production of pilot line and high-volume manufacturing EUV reticles. Reducing the defects in the EUV mask blank multilayer deposition system is one of the most critical technology gaps the industry needs to address to enable cost-effective insertion of this technology at the 22-nm half-pitch. For successful introduction, integrated EUV blanks must meet a defectivity level of less than 0.003 defects per cm² at 25-nm sensitivity.

Following a two-year effort to improve deposition tool hardware, process parameters and substrate cleaning techniques, Sematech technologists deposited EUV multilayers with as few as eight defects per mask at 50-nm sensitivity (SiO₂ equivalent), including six substrate defects, one handling defect and one defect from the multilayer deposition process. This was achieved on a 40-bilayer film stack with a ruthenium cap and measured over the mask blank quality area of 132 x 132 mm.

In addition, the company developed novel cleaning processes to improve substrate cleaning yield on substrates, yielding an integrated process capable of manufacturing EUV mask blanks with less than 20 total defects at 45-nm sensitivity. The achievements in mask defect reduction and increase in yield for high-quality blanks are attributed to a significant improvement in substrate cleaning, handling and deposition.

Sematech is an international consortium of semiconductor device, equipment and materials manufacturers that helps its members and partners address the critical industry transitions, drive technical consensus, pull research into the industry mainstream, improve manufacturing productivity, and reduce risk and time to market.

For more information, visit: www.sematech.org