Takahiro Onoue

Development of fiducial marks on EUV blanks for defect mitigation process

We have developed two types of fiducial marks (FMs) which are going to be used for defect mitigation process of EUV masks. Those FMs were prepared either on substrate by conventional lithography process or on multilayer (ML) by focused ion beam (FIB). The position accuracy of those FMs was evaluated in advanced electron beam writer, and the FMs prepared on ML showed excellent position repeatability of less than 2nm in 3sigma. Teron 610 blank inspection showed good position repeatability of defects lower than 100nm in maximum. We have developed FIB process for preparing FMs, which gives no defect adder being larger than 70nm. Thus, the fiducial mark process on ML by FIB would be preferable, and will be developed further.

Inspection and compositional analysis of sub-20 nm EUV mask blank defects by thin film decoration technique

EUVL requires a high yield of low-defect density reflective mask blanks, one of the top two critical technology gaps for the commercialization of this technology. One of the major sources of mask blank defects is the top of the substrate due to substrate quality, cleaning residue, and handling- or storage-induced defects. SEMATECH’s current inspection tool, the Lasertec 7360, can detect defects down to 37 nm on quartz substrates in dense scan mode. Defects below 40 nm on these substrate are difficult to detect, which challenges the quantification and characterization, and hence the determination of defect sources. SEMATECH developed a thin film decoration technique to quantify sub-40 nm defects and analyze composition to pinpoint defect sources. The technique involves oblique angle deposition in an ion beam deposition system, which decorates the particle. The decoration of particles is optimized by depositing enough thin film so that defects can be detected by the Lasertec7360 and yet keeping the film thin enough to employ several metrology techniques to efficiently analyze defect composition. The challenges involved with the metrology of such embedded defects and the impact of oblique angle deposition will be discussed. A theoretical model of defect decoration that can successfully simulate the thin film deposition on top of the defects will be provided. The effect of angle, deposition rate, and deposition time to quantify the decoration effect will also be presented.

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.