Yoon Jong Han1,3, Dongmin Jeong2,3, Jinho Ahn1,2,3*

1 Division of Nanoscale Semiconductor Engineering, 2 Division of Materials Science and Engineering, 3 EUV-IUCC (Industry University Collaboration Center)

Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, Korea

P14

INTRODUCTION

❑ High-numerical aperture (High-NA) EUV lithography

⚫ For resolution capability of sub-3 nm technology node, 0.55 NA EUV platform and anamorphic optics

system is required

➢ Light cones overlapping problem occurs due to the incident and reflected light in high-NA system

➢ Anamorphic optics (4X/8X) system, which uses different demagnification factors for x and y directions,

will be applied at 0.55 NA system for solving overlapping problems of light cones

➢ To enable sub-3 nm node a novel EUV mask materials and structure is required for 0.55 NA

anamorphic optics EUV system

<Light cones overlapping problems> <Illustration of anamorphic optics for high-NA EUVL>

※ Ref. Jan van Schoot. et al., EUV lithography scanner for sub 9 nm resolution,

International symposium on EUVL, Washington (2014)

❑ High-k material absorber in high-NA system

⚫ Conventional TaBN mask has low contrast in high-NA system

➢ Mask 3D effects such as non-telecentricity (nTC) and best focus shift,

severely occur in a thick absorber. Non-telecentricity is the pattern

shift through focus and best focus shift is the variation of best focus

depending on pattern pitch ratio

➢ Conventional TaBN mask is not sufficient for high-NA system since

the imaging properties is degraded by severe mask 3D effects

➢ By research on novel absorber material and structure, EUV mask

absorber thickness should be reduced to mitigate mask 3D effects

EXPERIMENT

<Optical constants of materials at 13.5 nm

(from CXRO database)>

➢ Using Ni as absorber material, imaging properties evaluation and absorber structure design is

performed by PROLITH 2019b simulation tool (KLA)

<Image contrast of conventional TaBN

mask for high-NA EUVL><Schematic of conventional TaBN absorber(left) and

high-k material absorber(right) structure>

<Simulation conditions for patterning 10 nm half-pitch L/S pattern>

⚫ As Ni shows high extinction coefficient compared to TaBN, mask 3D effects is expected to be mitigated

through thin absorber thickness

RESULTS & DISCUSSION

❑ Design of multi-stack Ni absorber EUV mask structure

<Normalized image log slope(NILS) depending on Ni

absorber thickness>

⚫ Ni shows about 40% higher extinction coefficient than that of TaBN at 13.5 nm wavelength

⚫ Compared to conventional TaBN absorber, high-k absorber shows improved imaging properties at the thinner

thickness and is expected to mitigate mask 3D effects

⚫ As Ni dry etching with plasma is difficult due to its crystallinity, absorber structure with spacer layers is designed

<Crystallinity of Ni absorber>

※ Ref. Philipsen, Vicky, et al. "Single element and metal alloy novel EUV mask absorbers

for improved imaging." International Conference on Extreme Ultraviolet Lithography 2017

❑ Imaging properties evaluation of multi-stack Ni absorber

<Comparison of imaging properties(NILS) and mask 3D effects(nTC, best focus shift)>

⚫ 4 layers stack absorber is designed as Ni 10.5 nm/ CrN 5.0 nm/ Ni 10.5 nm/ CrN 5.0 nm

⚫ Although CrN of low extinction coefficient is inserted into the absorber, comparable NILS and 17% mitigated

avg. nTC compared to Ni-pure absorber is shown

⚫ Compared to conventional 50nm TaBN absorber, the absorber shows comparable NILS value and mitigated

mask 3D effects, 49% reduction of avg. nTC and 61% reduction of best focus range

❑ Imaging properties depending on spacer materials

⚫Spacer layer is set to 3 nm and simulation of 4

layers stack absorber of 31 nm thickness is

performed

⚫ The absorbers with candidate spacer materials

show comparable NILS with 50 nm TaBN absorber

⚫ For wet cleaning process, CrN is selected as

spacer due to its high adhesion with absorber &

capping layer

<NILS depending on spacer materials>

❑ Imaging properties depending on total CrN spacer layer thickness

⚫As total thickness of CrN spacer increases, imaging

properties degrades due to its smaller extinction

coefficient

⚫Absorber imaging properties degrades rapidly above

10 nm thickness of CrN,

⚫Considering imaging properties, total 10 nm thickness

of CrN spacer is selected

SUMMARY & CONCLUSION

⚫ As imaging performance of conventional TaBN mask is limited due to severe mask 3D effects in high NA

EUV platform, a novel advanced EUV mask is studied

⚫ Due to its high extinction coefficient, Ni shows enough imaging properties at thin thickness

➢ Absorber structure considering not only mask performance but also dry etching and wet cleaning

processes

➢ Ni/ CrN / Ni/ CrN multi-stack absorber (Ni 10.5 nm/ CrN 5.0 nm/ Ni 10.5 nm/ CrN 5.0 nm)

➢ Ni absorber and CrN spacer is optimized which has wet cleaning compatibility and dry etching

process

➢ Multi-stack Ni absorber of 31 nm thickness shows mitigated mask 3D effects by thin thickness and

also has enough imaging properties

Sample

Result

RemarkBefore(nm)

After(nm)

Delta(nm)

CrN 21.7 21.3 0.4slightest variation

Ni/CrN/Ni/CrN 32.1 31.1 1.0slightest variation

Ru

⚫ As a result of the CrN experiment, high adhesion of CrN and Ru is shown by a small variation of 0.4 nm

⚫ Multi-stack Ni absorber blank mask also shows only slightest variation, and it is confirmed that the mask

structure has compatibility with wet cleaning process

<Schematic of cleaning sample, CrN (left),

Ni/CrN/Ni/CrN (right)><Result of wet cleaning process>

SC-1 ( NH4OH:H2O2:H2O = 1:1:5 ) @ 60C°, 15min 3 trials

❑ Wet cleaning process compatibility

7-11 June 2020, Online2020 EUVL Workshop

<NILS depending on total spacer layer thickness>