Measurement of EUV scattering from Mo/Si multilayer mirrors N. Kandaka, T. Kobayashi, T. Komiya, M. Shiraishi, T. Oshino and K. Murakami Nikon Corp. 3 rd EUVL Symposium Nov. 2-4 2004 (Miyazaki, JAPAN)
Outline - Introduction - Sample substrates before and after depositing Mo/Si multilayer - Reflectivity and angular scattering distribution - Summary June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 2
Introduction(1) Numerous EUV multilayer mirrors will be be employed in in EUV lithography system. Illumination Optics Mask Mask Stage Target Condenser Mirror Projection Optics Laser EUV Source Wafer Stage Wafer June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 3
Introduction(2) In EUV multilayer-coated reflective optics, not only surface roughness of mirror substrates, but roughness caused by multilayer deposition significantly affects its performance. (1) We observed the surface roughness of Mo/Si multilayer coatings deposited by ion beam sputtering. Surface profiles were measured by AFM before and after coating multilayer. Power spectral density (PSD) was calculated to evaluate surface roughness. (2) We measured EUV reflectivity and angular distribution of scattering. June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 4
Sample substrates & multilayer deposition -- We prepared 3 polished fused silica substrates (sample A, A, B and C). -- Mo/Si multilayers were deposited on on the substrates by by ion beam sputtering. Mo/Si multilayers Number of pairs: 50pairs Layer period: ~7.1 nm (Mo: ~2.5nm, Si: ~4.6nm) June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 5
AFM images (1x1µm) of sample substrates Sample:A Before deposition After deposition 0.136nmRMS 0.112nmRMS Sample:B 0.155nmRMS 0.117nmRMS June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 6
AFM images (1x1µm) of sample substrates Sample:C 0.285nmRMS 0.161nmRMS June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 7
PSDs of sample surfaces After Sample:A Before 10µm 1µm 100nm 10nm Sample:A Sample:C 100nm Before After June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 8 Sample:A 300nm Sample:B After Before -- Substrate roughness in in the the region of of structure size size of of less less than than 100 100 nm nm were reduced by by Mo/Si multilayer deposition by by ion ion beam sputtering. -- Sample B and and C have high high roughness in in the the region of of structure size size of of more than than 300 300 nm nm and and 100nm respectively.
EUV reflectivity of Mo/Si multilayers Sample A Sample B Sample C Peak reflectivity Sample A: 67.7% Sample B: 67.1% Measured EUV reflectivity Sample C: 65.7% Measured at Photon Factory BL-12A (KEK) Angle of incidence : 14 deg June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 9
Measurement of EUV angular scattering distribution Intensity 2θ 2θ Reflected beam SR-ring Monochromator detector (Photomultiplier) λ= 13.4nm scattering slit Sample Measured Measured at at Photon Photon Factory Factory BL-12A BL-12A (KEK) (KEK) Wavelength Wavelength :: 13.4 13.4 nm nm Angle Angle of of incidence incidence :: 14 14 deg deg June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 10
EUV angular scattering distribution -- The The scattering intensities of of samples B and and C were were higher higher than than that that of of sample A at at less less than than 3 degrees and and 8 degrees respectively. -- 3 degrees and and 8 degrees correspond to to 100nm 100nm and and 300nm 300nm in in the the structure size size of of surface roughness. Sample A 300nm 2.6) Sample B Sample C 100nm 7.7) June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 11
Scattering from a single surface λ: wavelength R: the normal incidence reflectivity - Equation (1) is the Born approximation for scattering from a single surface *. - In the case of small roughness, near normal incidence and small scattering angle, scattering from a multilayer is approximated by equation (1) *. * E. Gullikson Proc. SPIE 3331 pp72-80 June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 12
June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 13 Scattering from multilayer - Optical path difference of reflected beams are same as wavelength (=13.4 nm ) d * cos θ d * cos( θ+α) θ α High reflectivity - Optical path difference of scattered beams are different from wavelength (=13.4 nm) Scattered intensity will be lower than that calculated by using equation (1)
Calculation of angular scattering distribution direct beam The angular distribution of scattered EUV light deduced from PSD by using equation (1) 1/Io di/dω Measured angular distribution of EUV light. Scattering Angle (deg) Calculation which take account of the effect of optical path difference June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 14
Calculation of angular scattering distribution 1/Io di/dω 1000 100 10 1 0.1 0.01 0.001 direct beam 0.1 1 10 100 Scattering Angle (deg) The measured EUV angler scattering distribution and the calculated EUV angler scattering distribution agreed well. Calculated from PSD Measured data June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 15
Scattering on rough surface Incidence beam Reflected beam 14 14 θ Scattering angle is is depend on on the spatial frequency of of roughness 14 14 θ scattered L=d sin(14+θ) d cos(14) =d (0.242(cosθ-1)+0.970sinθ) 0.970 d sinθ approx. =λ (=13.4nm) d June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 16
Scattering loss of reflectivity Scattering loss: The total value of scattering intensity integrated throughout the whole range of solid angles Total scattering loss Dependence of the scattering loss on the region of spatial frequency of roughness June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 17
The loss of EUV reflectivity due to scattering By By adding the the scattering loss loss to to the the peak reflectivity, the the total total intensity became the the same for for all all samples. Measured peak reflectivity Scattering loss 68~68.5% Scattering loss June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 18
Summary -- EUV angler scattering distribution and the surface profile of of substrate (PSDs) agreed well. -- By calculating the total scattered EUV intensity, the scattering loss of of the reflectivity was estimated for each sample. June. 28. 2004 3rd EUVL Symposium Nov. 2-4 2004 (Miyazaki JAPAN) Slide 19