Impact of EUV light scatter on CD control as a result of mask density changes

Krautschik, Christof G.; Ito, M.; Nishiyama, Iwao; Okazaki, Shinji

doi:10.1117/12.472302

Cited by 43 publications

(33 citation statements)

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“…Flare in ST-LITH is modeled as a constant image intensity added to the aerial image, reducing contrast. As Stearns et al 4 and Krautschik et al 5 have described, flare in EUV systems is actually the result of very high order aberration and is effectively lengthens the tails of the point spread function of the EUV optical system. The level of flare will vary as a function of local pattern density.…”

Section: Simulations Of Contact Printing With Euvmentioning

confidence: 96%

Novel design of att-PSM structure for extreme-ultraviolet lithography and enhancement of image contrast during inspection

et al. 2002

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Attenuated Phase Shift Masks (Att-PSM) have been actively investigated and developed for conventional optical lithography to enhance the lithographic performance. In this paper, Att-PSM for Extreme Ultraviolet Lithography (EUVL) is compared to binary EUVL masks through simulation. Additionally, a new structural design for EUVL Att-PSM that is intended to enhance the image contrast during the inspection is also presented. Aerial image simulation for 50 and 35-nm wide contact holes was performed using an internally developed optical projection lithography simulator. Analysis of phase shift and attenuation for various combinations of Att-PSM layers was also done using an internally developed simulator based on optical multilayer thin film theory. The results of aerial image simulation agree with previously published results in that Att-PSM for EUVL provide steeper edge profile and higher peak intensity compared to the binary EUVL mask. These enhanced aerial images provide greater exposure latitude and 28% to 80% greater depth of focus for Att-PSM compared to binary masks for printing contacts. The simulations were also used to set initial targets for phase and reflectance control of the PSM stack for 35-nm contacts. Mean reflectance between 3 and 6% and phase of 180±10° result in significantly larger DOF than for binary masks. The prototype structure simulated for an EUVL Att-PSM consists of an upper dielectric layer (SiON) and a lower metal layer (TaN or Cr) on top of Mo/Si multilayer mirror. With this dual layer scheme, satisfying the optical requirements (180° phase shift and 3~15% attenuation) is easier than with a single layer structure because accurate control of phase shift and attenuation is possible by controlling the thickness of both the upper and lower layers. Obtaining the desired phase shift and transmission using a single layer is difficult. The advantage of having a dielectric (SiON) top layer is that the thickness of dielectric layer can be optimized to enhance the image contrast at inspection wavelength (normally DUV) as well as to provide the desired phase shift at exposure wavelength (13.4-13.5nm). Another advantage of Att-PSM for EUVL is the reduced height of patterned structure on the multilayer mirror which provides a relative advantage in resolution by reducing the image blur caused by the shadowing effects of the taller absorber stack.

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Section: Simulations Of Contact Printing With Euvmentioning

confidence: 96%

Novel design of att-PSM structure for extreme-ultraviolet lithography and enhancement of image contrast during inspection

et al. 2002

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“…EUV flare can also lead to CD variations due to mask pattern density variations. 1 Mask Cr coverage and Cr density variations lead to localized variation in flare that in turn cause critical feature size variations. 1,2 Placing upper limits on the allowable flare in an exposure system is imperative for feature size dimensional control.…”

Section: Introductionmentioning

confidence: 99%

“…1 Mask Cr coverage and Cr density variations lead to localized variation in flare that in turn cause critical feature size variations. 1,2 Placing upper limits on the allowable flare in an exposure system is imperative for feature size dimensional control. 1 Flare for extreme ultraviolet (EUV) lithography is generally different from deep ultraviolet (DUV) lithography due to different scattering range and mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…1,2 Placing upper limits on the allowable flare in an exposure system is imperative for feature size dimensional control. 1 Flare for extreme ultraviolet (EUV) lithography is generally different from deep ultraviolet (DUV) lithography due to different scattering range and mechanism. EUV flare is simpler to understand than DUV flare because the flare for EUVL is only generated by the rough surfaces of projection optics, while DUV flare can be generated by many components in the lithography tool.…”

Section: Introductionmentioning

confidence: 99%

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Lithographic flare measurements of EUV full-field projection optics

et al. 2003

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We demonstrate direct flare measurements of 4-mirror projection optics in the Engineering Test Stand (ETS) using a conventional resist clearing method (the Kirk method). Two extreme ultraviolet (EUV) lithographic projection optics, one with higher flare than the other, have been characterized and the results compared. The measured results have also been compared to analytical calculations based on measured mirror roughness and the extended point spread function (PSF). Full-field flare across the 24 mm field width has been measured, and we have verified that flare is constant across the field for EUV lithography as predicted. Horizontal (H) and vertical (V) flare bias has been observed and the cause of the H-V flare bias has been investigated. The main cause has been identified to be anisotropic mirror polishing. Simulations with the 2 dimensional Power Spectral density (PSD) function have confirmed the experimental results.

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“…The application of this tool has been demonstrated with an example ALU circuit, involving 90,000 transistors. For this example, regression equations were extracted relating speed and leakage current to the minimum CD and imperfections in lithography, such as the optical proximity effect [I], Coma 121, lens aberrations [2], and flare [3]. Using these regression equations, the delay sensitivities to lithography imperfections have been analyzed under the condition where the leakage current remains bounded.…”

Section: Introductionmentioning

confidence: 99%

Simulation of circuit speed and leakage current in the presence of imperfect lithography

Milor¹,

Choi²,

Capodieci³

2003 5th International Conference on ASIC. Proceedings (IEEE Cat. No.03TH8690)

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In semiconductor manufacturing, profit is strongly influenced by yield (cos!, and speed (revenue). Shrinking the gate CD (Critical Dimension) improves chip speed but increases chip leakage current (subthreshold current), believed to reduce yield Lithography influences both chip speeds and leakage. We have developed a tool to simulate both chip speed and leakage current in the presence of gate CD variations caused by lithography. This tool has been applied to an ISCAS '95 benchmark circuit. Regression equations were extracted relating speed and leakage currefit to the minimum CD and various imperfections in lithography. In this example, it is revealed that the delay is sensitive to lens aberrations andflare in lithography, bul not the optical proximiry effect and Coma when the maximum total leakage current is below IuA.

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Impact of EUV light scatter on CD control as a result of mask density changes

Cited by 43 publications

References 0 publications

Novel design of att-PSM structure for extreme-ultraviolet lithography and enhancement of image contrast during inspection

Novel design of att-PSM structure for extreme-ultraviolet lithography and enhancement of image contrast during inspection

Lithographic flare measurements of EUV full-field projection optics

Simulation of circuit speed and leakage current in the presence of imperfect lithography

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