NA/σ optimization strategies for an advanced DUV stepper applied to 0.25-μm and sub-0.25-μm critical levels

Beeck, Maaike Op de; Ronse, Kurt G.; Ghandehari, Kouros; Jaenen, Patrick; Botermans, Harry; Finders, Jo; Lilygren, John A.; Baker, Daniel C.; Vandenberghe, Geert; Bisschop, Peter De; Maenhoudt, Mireille; hove, Luc Van den

doi:10.1117/12.275973

Cited by 9 publications

(2 citation statements)

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“…F=rcR"2/(1-R), (2) 8=2,rJs/A.+z1b, (3) As -2dfla cosa. (4) In these equations, I is the incident light intensity, 8 is the phase shift, 1q is extra phase shift on reflection from the etalon surface, A. is the laser wavelength, d is the etalon gap, F is the etalon finesse, a iS the refractive index of gas filing the gap, and a is the incident angle.…”

Section: Fwhm Spectral Measurements With Etalon Spectrometermentioning

confidence: 99%

Novel metrology for measuring spectral purity of KrF lasers for deep-UV lithography

Ershov¹,

Padmabandu²,

Tyler³

et al. 1999

SPIE Proceedings

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The use of higher NA lenses of next generation 248 nm microlithography systems sets tight requirements on the spectral purity of the laser, especially because these lenses are not chromatically corrected. Present day KrF excimer lasers are equipped with etalon-based spectrometers that can measure the laser linewidth at full-width-at-half-maximum (&FWHM), at nearly every pulse. Both, experience and analysis have shown that the AX FWHM may not be the optimum measure of laser spectral purity, and that a better characterization would be the width of the line that contains 95% ofthe laser energy, AX iflt Therefore, the lithographer is at risk of losing the image quality if the line shape, characterized by is outside its limit, even if the laser signals that the AXFW is within limits. In this paper, we describe the results of our development of new generation spectrometers that are capable of making simultaneous, high resolution AX FWHM and L\X95% measurements of laser line shape. The measurements can be done on a pulse-to-pulse basis or with averaging over an exposure window. Several different configurations and their comparable analysis are presented. These new spectrometers are compact, and can be integrated with a deep UV laser or used as a portable field service tool. Despite the small size, the spectrometers have a resolution of about 0. 1 pm when measuring FWHM values and about 0.3 pm when measuring 95% integral values. The implementation of these new metrology tools provides the lithographer with a correct measure of the laser spectral purity during exposure and during process optimization.

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Section: Fwhm Spectral Measurements With Etalon Spectrometermentioning

confidence: 99%

Novel metrology for measuring spectral purity of KrF lasers for deep-UV lithography

Ershov¹,

Padmabandu²,

Tyler³

et al. 1999

SPIE Proceedings

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“…It appears that the DOF increases towards the coherent limit [8,9], although no comprehensive study has appeared on this aspect. In the field of lithography, an optimum value for the imaging NA and σ is found based on a desired DOF and a particular mask pattern [10,11], even introducing novel metrics for DOF [12]. Von Waldkirch et al [13,14] investigated the influence of partial coherence on the DOF for a retinal projection display.…”

Section: Introductionmentioning

confidence: 99%

Impact of partial coherence on the apparent optical transfer function derived from the response to amplitude edges

2017

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We present an investigation of the impact of partial coherence on optical imaging systems with the focus on whole slide imaging (WSI) systems for digital pathology. The investigation is based on the analysis of the edge response of the optical system, which gives rise to an apparent optical transfer function (OTF) that can be linked to two elementary complex functions Q and U. The function Q is directly related to the transmission cross coefficient (TCC) and can be identified with the performance function first introduced by Kintner and Sillitto. The function U depends on the TCC in a more involved way. When there are no aberrations the Q-function corresponds to the real part of the apparent OTF and the U function to the imaginary part of the apparent OTF. Close to the incoherent limit the effect of the U function is a mere shift of the edge compared to the fully incoherent case. We propose a new expression for the dependence of the depth of focus (DOF) on spatial frequency and on the partial coherence factor σ, and validate it by simulation. Partial coherence effects are investigated experimentally on a WSI system with a compact LED-based Köhler illumination unit with variable condenser NA. This unit incorporates a top hat diffuser for providing a reasonably uniform illumination field, with variations below 10% across the imaged field of view. The measurements of the apparent through-focus OTF derived from edges on a custom resolution chart for different σ were substantially in agreement with the simulations. Finding an optimal value for σ is not straightforward as lateral resolution and the level of edge ringing improve with increasing σ, whereas edge contrast and DOF improve with decreasing σ. We assess that the trade-off for the particular application of WSI systems for digital pathology is optimized for a σ value in the range of 0.55-0.75.

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Photolithography

Bandelier¹,

Charley²,

Lagrange³

2013

Lithography

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NA/σ optimization strategies for an advanced DUV stepper applied to 0.25-μm and sub-0.25-μm critical levels

Cited by 9 publications

References 0 publications

Novel metrology for measuring spectral purity of KrF lasers for deep-UV lithography

Novel metrology for measuring spectral purity of KrF lasers for deep-UV lithography

Impact of partial coherence on the apparent optical transfer function derived from the response to amplitude edges

Photolithography

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