For full commercialization, extreme ultraviolet lithography (EUVL) technology requires the availability of EUV mask blanks that are free of defects. This remains one of the main impediments to the implementation of EUV at the 22 nm node and beyond. Consensus is building that a few small defects can be mitigated during mask patterning, but defects over 100 nm (SiO2 equivalent) in size are considered potential “killer” defects or defects large enough that the mask blank would not be usable. The current defect performance of the ion beam sputter deposition (IBD) tool will be discussed and the progress achieved to date in the reduction of large size defects will be summarized, including a description of the main sources of defects and their composition.
Extreme ultraviolet lithography (EUVL) is the leading next generation lithography (NGL) technology to succeed optical
lithography at the 22 nm node and beyond. EUVL requires a low defect density reflective mask blank, which is
considered to be the most critical technology gap for commercialization of the technology. At the SEMATECH Mask
Blank Development Center (MBDC), research on defect reduction of EUV mask blanks is being pursued using the
Veeco Nexus deposition tool. Its defect performance is one of the factors limiting the availability of defect-free EUVL
mask blanks. SEMATECH has identified better understanding of the physics of the deposition process as one of the keys
to improving the defect performance of Nexus tools. SEMATECH is therefore undertaking an effort to model the
physics of the tool backed with an experimental program to characterize the process. The goal is to be able to predict
defect performance and defect improvement to direct new tool design. In this paper, we present the results of simulating
the deposition rate and uniformity of deposited multilayers and growth of the multilayer on a given defect profile.
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 53 nm sensitivity defect data for multilayer-coated EUV mask blanks.
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.
Mask blanks for extreme ultraviolet lithography (EUVL) are fabricated by depositing Mo/Si multilayer films on super polished substrates. These mask blanks must be nearly defect-free, and therefore particles occurring during the deposition process are a serious concern. Development of the next-generation ultra low defect deposition tool for fabricating EUVL mask blanks is crucial for the commercialization of the EUVL technology. ISMT initiated a project at the ISMT-N (Albany, NY) facility to provide an ion beam sputter deposition tool for multilayer deposition on 6” square format substrates to support the development and production of EUV mask blanks. The project has access to state-of-the-art metrology tools recently installed at the Albany facility and also has process development support from Lawrence Livermore National Laboratory (LLNL) and Veeco. The project goal is to work with suppliers, LLNL, Veeco, to baseline, perform defect and root cause analysis, and improve the current tool with an upgrade path to meet the final specification for EUV mask blanks. We will provide results on the quality of the mask blanks produced during the benchmarking phase of this tool; data will be presented for the EUV reflectivity, reflectance uniformity, centroid wavelength, and uniformity.