We constructed an extreme ultraviolet microscope (EUVM) system for actinic mask inspection that consists of
Schwarzschild optics and an X-ray zooming tube. This system was used to inspect finished extreme ultraviolet lithography (EUVL)
masks and Mo/Si coated substrates of ULE glass. And we have fabricated programmed phase defects on the blanks used for
inspection. The EUVM was able to resolve a programmed line-pit defect with a width of 40 nm and a depth of 10 nm, and also with a
width of 70 nm and a depth of 2.0 nm. However, a 75-nm-wide 1.5-nm-deep pit defect was not resolved. Also, the EUVM was able to
resolve a programmed hole-pit defects with widths ranging from 35 nm to 170 nm and depths ranging from 2.5 nm to 2.2 nm.
However, 20-nm-wide 1.5-nm-deep hole-pit defects were not resolved. These results agree with the simulation results perfectly. Thus,
in this study, one critical dimension of a pit defects was experimentaly estimated to be a width of 20 nm and a depth of 2.0 nm.
A key requirement for the success of EUV lithography is a high volume supply of defect-free Mo/Si multilayer (ML)-
coated mask blanks. The process of fabricating mask blanks is particularly sensitive to particle contamination because
decoration by the deposition of the reflective stack on sub-lithographic (< 22 nm) particles can create larger, printable
One possible source of added defects is the mask substrate fixturing method, which, in the Veeco ion beam deposition
(IBD) system used to deposit our ML coatings, must allow tilt and rotation of a vertically oriented substrate. As
commonly practiced, an electrostatic chuck (ESC) is used instead of a mechanical clamping fixture to avoid transferring
particles to the front surface of the mask by mechanical clamping and declamping operations. However, a large number
of particles can be introduced to the backside of the mask by electrostatic clamping. Up to now, there has been little
concern about such backside particles, except for relatively large particles (> 1 micron) that may affect out-of-plane
distortion of the mask in an EUV lithography tool. As the cleanliness of the EUV masks and mask blank fabrication
approaches perfection, however, there is more concern that particles transferred from the backside to the frontside of the
mask may be a significant issue. Such transfer may occur in the deposition chamber, in the substrate cassette, or in the
transfer module and may be indirect.
In this paper, we present data from characterizing the amount, size, shape, composition, and location of the backside
particle defects generated by electrostatic clamping, using a particle counter and scanning electron microscope (SEM),
and compare results for a pin-type e-chuck, which has a small contact area, with the standard flat e-chuck. The key
result is a 10X to 30X reduction in the total number of backside particles for the pin chuck. Also, preliminary data
indicates that the pin chuck stays cleaner under service conditions than the flat chuck. The exact elemental composition
of the defects is sensitive to the clamping method and type of backside Cr coating. In general, for the flat chuck, Al
defects, attributed to particles from the alumina chuck surface, are dominant. For the pin chuck, Si,Cr,N,O defects from
the mask surface are mainly observed.
The availability of defect-free mask blanks is one of the most significant challenges facing the
commercialization of extreme ultraviolet lithography (EUVL). The SEMATECH Mask Blank Development Center
(MBDC) was created to drive the development of EUVL mask blanks to meet the industry's needs. EUV mask defects
come from two primary sources: the incoming mask substrate and defects added during multilayer deposition. For
incoming defects, we have both an in-house advanced cleaning capability and an advanced in situ defect smoothing
capability. This smoothing system utilizes combinations of ion beam deposition and etch to planarize any remaining
incoming substrate defects. For defects added in the multilayer deposition process, we have an aggressive program to
find, identify, and eliminate the defects. This paper summarizes progress in smoothing substrate defects and eliminating
ever smaller multilayer-added defects. We will show the capability of our smoothing process to planarize our existing
population of bump and pit type defects and discuss how quickly this can be done. We will also discuss how many
defects are added by the planarization process. In addition, we will show 54 nm sensitivity defect data for multilayer-coated
EUV mask blanks.
Recent rapid progress in the technologies of extreme ultraviolet lithography (EUVL) is ensuring that EUVL will be a primary candidate for the next generation lithography beyond 32-nm node. However, realization of defect-free reflective mask blank is still counted as one of the most critical issues for high volume production in EUVL. Asahi Glass Company (AGC) has developed comprehensive technologies for manufacturing EUVL mask blanks from figuring and polishing glass substrate to cleaning, multilayer coating, and evaluating its performances by making use of our long and wide experience in providing high quality processed glass substrates and coatings for electronic devices. In this paper, we will present the current status of each aspect of EUVL mask blank development in AGC toward the specifications required for high volume production. In the effort to meet the specifications, we have introduced a number of key technologies that can be divided into three regions, which are materials, glass processings, and evaluations. We have developed state-of-the-art processes and tools for manufacturing EUV mask blanks, such as a new polishing technique for extremely flat substrate, a new cleaning recipe and tool for low-defect substrate, and a newly developed deposition tool for ultra-low defect and higher EUV reflective coating with our new optical thin film materials for multilayer coating. Furthermore, in order to clarify their performances, we also introduced a wide variety of evaluation techniques such as flatness and roughness measurement of substrate, a defect inspection, and EUV reflectometry as well as defect analysis techniques which help us eliminate printable defects in EUVL mask blanks.