The Study on the Real Defect on EUV Blankmask and Strategy of EUV Mask Inspection

Study of Real Defects on EUV Blanks and a Strategy for EUV Mask Inspection Sungmin Huh , Abbas Rastegar , Stefan Wurm , Kenneth Goldberg , Iacopo Mochi , Toshio Nakajima , Masahiro Kishimoto , Mitsuhiko Komakine S E M A T E C H 255 Fuller Road, Suite 309, Albany, N Y 12203 U S A 2-400, Lawrence Berkeley National Laboratory, Berkeley, C A 94720 A G C Electronics America , 257 Fuller Road, Albany N Y 12203 ABSTRACT The availability o f defect-free masks remains one of the key challenges for inserting extreme ultraviolet lithography ( E U V L ) into high volume manufacturing, yet little data is available for understanding native defects on real masks. In this paper, two E U V mask blanks with known native buried phase defects were characterized with a Lasertec M7360 (266 nm wavelength), atomic force microscope ( A F M ) , and S E M A T E C H ' s actinic inspection tool (AIT), which is an EUV-wavelength microscope. The results show that there are various kinds of native defects on the mask blank. Not surprisingly, the surface height and measured E U V intensity profile of real blank defects can differ significantly from Gaussian-shaped defects. A l l defects found by the M7360 were observable in the A I T , yet many do not perturb the intensity enough to be printable in isolation. This paper shows that defects come in various sizes and types and clarifies what must be done to learn more about real defect printability to achieve defect-free mask blanks. Keywords: E U V , mask, phase defect, Confocal D U V inspection, actinic inspection INTRODUCTION Over the past year, leading-edge chip manufacturers have shifted their interest towards the insertion of extreme ultraviolet lithography ( E U V L ) . This emphasis is increasing the pressure to resolve defect-free blanks, which remains one o f the key challenges impeding E U V L insertion into high volume manufacturing ( H V M ) . The success o f the industry's mask blank defect reduction effort critically depends on the timely availability o f inspection tools that can precisely and reliably find ever smaller defects. S E M A T E C H ' s Mask Blank Development Center ( M B D C ) has provided the world's best defect inspection capability starting in 2003 with the Lasertec M l 3 5 0 tool and continuing with the second generation tool, the M7360, in 2006. Both tools have deep ultraviolet ( D U V ) light sources for defect detection: 488 nm wavelength for the M l 3 5 0 and 266 nm wavelength for the M7360. However, to meet high volume manufacturing requirements for sub-32 nm half-pitch (HP) patterning, the industry needs a blank inspection tool to determine printability in the E U V wavelength (13.5 nm). S E M A T E C H operates and funds an EUV-wavelength microscope (the S E M A T E C H actinic inspection tool [AIT] at Lawrence Berkeley National Lab [ L B N L ] ) and a state-of- the-art Lasertec M7360 to support the development of inspection tools and reticle blanks to eventually meet H V M requirements. In this paper, two E U V mask blanks with known native buried phase defects were characterized with a Lasertec M7360 (266 nm wavelength), atomic force microscope ( A F M ) , and AIT. Our results show that there are various kinds of native defects on the mask blank. Not surprisingly, the surface height and measured E U V intensity profile of real blank defects can differ significantly from the intensity drop of Gaussian-shaped defects. A l l defects found by the M7360 were observable in the A I T , yet many do not perturb the intensity enough to be printable in isolation. This paper shows defects come in many sizes and types and clarifies what must be done to learn more about real defect printability to achieve defect-free mask blanks.