EUV lithography is expected to be the most promising technology for semiconductor device manufacturing of the 7nm node and beyond. The EUV mask is a key element in the lithographic scanner optical path. The image border is a pattern free dark area around the die on the photomask serving as transition area between the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When printing a die at dense spacing on an EUV scanner, the reflection from the image border overlaps edges of neighboring dies, affecting CD and contrast in this area. This is related to the fact that EUV absorber stack reflects 1-3% of actinic EUV light. To reduce this effect several types of image border with reduced EUV light reflectance (<0.05%) have been proposed; such an image border is referred to as a black border (BB). In particular, an etched multilayer type black border was developed; it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border. However, wafer printing result still showed some CD change in the die influenced by the black border reflection. It was proven that the CD change was caused by DUV Out Of Band (OOB) light which is emitted from the EUV light source. In our previous study, a new types of multilayer etched BB called ‘Hybrid Black Border’ (HBB) had been developed and showed a good potential for DUV light suppression. OOB light reflection on HBB is ~3x lower than that of normal BB. Imaging performance was also demonstrated on NXE:3300 scanner system for N10 imaging structures of 16nm dense lines and 20nm isolated spaces. These results were compared to the imaging results obtained for a mask with the normal BB and 3x improvement was achieved; less than 0.2 nm CD changes were observed in the corners of the die. However, OOB light reflectance suppression was still not enough in short wavelength. In this study, we focused on OOB light reflectance reduction in short wavelength, and we developed a new HBB called ‘Advanced HBB’. We measured the OOB light reflectance of Advanced HBB by synchrotron radiation facility at PTB (Physikalisch- Technische Bundesanstalt, Germany). These results were compared to the results obtained from previous HBB. Then Advanced HBB achieved over 50% OOB light reflectance improvement in average wavelength 100nm to 270nm. Imaging performance also simulated in the edges and corners of the die. The CD-drop is expected to be more improved for Advanced HBB than previous HBB. As a result, it is expected the implementation of the Advanced HBB will help to mitigate the effects of possible increases of OOB light in the future higher power EUV sources.
EUV lithography is the most promising technology for semiconductor device manufacturing of the 10nm node and
beyond. The image border is a pattern free dark area around the die on the photomask serving as transition area between
the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When
printing a die at dense spacing on an EUV scanner, the reflection from the image border overlaps edges of neighboring
dies, affecting CD and contrast in this area. This is related to the fact that EUV absorber stack reflects 1-3% of actinic
EUV light. To reduce this effect several types of image border with reduced EUV reflectance (<0.05%) have been
proposed; such an image border is referred to as a black border. In particular, an etched multilayer type black border was
developed; it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border
(BB). However, wafer printing result still showed some CD change in the die influenced by the black border reflection. It
was proven that the CD shift was caused by DUV Out of Band (OOB) light from the EUV light source. New types of a
multilayer etched BB were evaluated and showed a good potential for DUV light suppression.
In this study, a novel BB called ‘Hybrid Black Border’ (HBB) has been developed to eliminate EUV and DUV OOB
light reflection by applying optical design technique and special micro-fabrication technique. A new test mask with HBB
is fabricated without any degradation of mask quality according to the result of CD performance in the main pattern,
defectivity and cleaning durability. The imaging performance for N10 imaging structures is demonstrated on
NXE:3300B in collaboration with ASML. This result is compared to the imaging results obtained for a mask with the
earlier developed BB, and HBB has achieved ~3x improvement; less than 0.2 nm CD changes are observed in the
corners of the die. A CD uniformity budget including impact of OOB light in the die edge area is evaluated which shows
that the OOB impact from HBB becomes comparable with other CDU contributors in this area. Finally, we state that
HBB is a promising technology allowing for CD control at die edges.
EUV lithography is the most promising technology for semiconductor device manufacturing of the 10nm node and beyond. The EUV mask is a key element in the lithographic scanner optical path. The image border is a pattern free dark area around the die on the photomask serving as transition area between the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When printing a die at dense spacing on an EUV scanner, the EUV light reflection from the image border overlaps edges of neighboring dies, affecting CD and contrast in this area. To reduce this effect an etched multilayer type black border was developed, and it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border (BB). However, wafer printing result still showed some CD change influenced by the black border reflection. It was proven that the CD shift was caused by DUV Out of Band (OOB) light which is emitted from EUV light source. New types of a multilayer etched BB were evaluated and showed a good potential for DUV light suppression. In this study, a novel black border called Hybrid Black Border has been developed which allows to eliminate EUV and DUV OOB light reflection. Direct measurements of OOB light from HBB and Normal BB are performed on NXE:3300B ASML EUV scanner; it is shown that HBB OOB reflection is 3x lower than that of Normal BB. Finally, we state that HBB is a promising technology allowing for CD control at die edges.
This paper discusses defectivity of a black border around the mask pattern of a reticle for extreme EUV lithography. An opaque image border is intended to overcome the limitation of the reticle masking blades of the scanner, in providing sufficiently sharp and accurate image delineation on wafer. The most commonly applied “black border” method for EUV reticles has the multilayer mirror removed in the image border area. A dedicated mask with such etched ML image border has been generated. It includes several modules of patterns, each surrounded by black border, so that each can be imaged separately with minimized background dose caused by its border. The printability of programmed defects within this image border has been assessed on an NXE3100 EUV scanner. Studied defect types include ML pedestals with and without absorber still on top. Especially the former must be totally avoided as such clear defect is very printable and can even erase parts of the pattern in neighboring dies.
EUV lithography is the most promising candidate for semiconductor device manufacturing of 1x nm half pitch and
beyond. For the practical use, EUV mask with a thin absorber could be adopted because of less shadowing effect. EUV
reflectivity from the thin absorber is about 1~3%. It would cause CD change on wafer especially at the exposure field
edge due to the leakage of the EUV light from neighboring exposure shots.1 To avoid this phenomenon, light shield
black border is needed at the edge of pattern area on mask. Stacked absorber type and ML-etched type of light shield
black border have been proposed in the past.2 The most important things for these black borders are that there is no
reflection of EUV light and no defect which affects pattern CD on wafer. ML-etched black border is considered to be
applied for early practical use from a viewpoint of manufacturability. Because CD degradation and defect increase might
happen due to 2nd litho and etch process on its main pattern area in manufacturing process of stacked absorber type.
In this paper, we will show several evaluation results regarding
ML-etched black border we have developed. It has a
good light shield performance for EUV and low DUV light reflection. Defect inspection in black border area can be
performed successfully by three kinds of inspection tools. As a result, most of the defects seemed not to be printable to
wafer. We also evaluated CD change, flatness change linked to mask IP shift and particle contamination on main pattern
area. What it comes down to is that there is no show-stopper for
ML-etched BB process for now.
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