Minoru Sakamoto

Improvement of total quality on EUV mask blanks toward volume production

Total quality on EUV mask blanks have to be improved toward future volume production. In this paper, progress in EUV blank development and improvement in flatness, bow and ML blank defects as critical issues on EUV blanks were reported. Steadily progress in flatness improvement was made in the past five years by improving polishing processes. A LTE substrate with a high flatness of 78 nm PV in 142 mm square area was achieved in average. Annealing process was developed to make small bow of less than 600 nm after ML coating. It was confirmed that annealed ML blank has stable performance in bow and centroid wavelength values through mask making process. Small bow of less than 300 nm was successfully demonstrated using annealing process and a CrN back side film with high compressive stress. Low defects of 0.05 defects/cm2 at 70 nm SiO2 sensitivity inspected by a Lasertec M1350 was demonstrated on a multilayer (ML) blank with a LTE substrate as best. Small defects over 50 nm in a M7360 were effectively reduced by improvement of polishing process consisting of local polish, touch polish and cleaning.

Development of new chrome blanks for 65-nm node and beyond

For advanced reticle fabrication, a resist thinning technique continues a promising trend of the resolution enhancement. To bring out thin resist performances, a new chrome absorber has been developed for the second layer of 193nm att-PSM. The new chrome absorber is thinner and has a higher dry-etch rate than our current products, such as NTAR5. This new chrome absorber can utilize a super thin resist application because of a reduction in dry-etching time. Additionally, a technique of film stress reduction was also developed to reduce placement shift by film stress relaxation. The new chrome absorber with super thin resist (TF blanks) exceeds current products in the mask-making metrics of resolution and CD performance. This performance will meet the requirements of 65nm-node and beyond.

Improvement of defects and flatness on extreme ultraviolet mask blanks

Abstract. We have improved flatness and defects on an extreme ultraviolet (EUV) blank, which are critical issues for implementing EUV lithography. A high flatness of less than 30 nm on a glass substrate and low defects over 22 nm sphere-equivalent-volume-diameter (SEVD) on a multilayer (ML) blank are required for 22 nm half-pitch process. Flatness quality was improved to an average of around 50 nm and 30 nm as best, through more precise polishing process. Defect quality of single digit over 60 nm was achieved by improvement of fabrication process. New defect inspection was started for further defect reduction using a Teron Phasur. It was confirmed that there are lots of real phase defects with low height of less than 2 nm on a ML blank captured by the Teron. Small defects over 25 nm SEVD have been dramatically reduced to 20 defects mainly by various improvements of fabrication processes. A gap in flatness and defects between actual quality and the requirement is getting small, and both the qualities will be improved further for near future production.