Yasushi Mizuno

Impact of realistic source shape and flexibility on source mask optimization

Abstract. Source mask optimization (SMO) is widely used to make state-of-the-art semiconductor devices in high-volume manufacturing. To realize mature SMO solutions in production, the Intelligent Illuminator, which is an illumination system on a Nikon scanner, is useful because it can provide generation of freeform sources with high fidelity to the target. Proteus SMO, which employs co-optimization method and an insertion of validation with mask three-dimensional effect and resist properties for an accurate prediction of wafer printing, can take into account the properties of Intelligent Illuminator. We investigate an impact of the source properties on the SMO to pattern of a static random access memory. Quality of a source made on the scanner compared to the SMO target is evaluated with in-situ measurement and aerial image simulation using its measurement data. Furthermore, we discuss an evaluation of a universality of the source to use it in multiple scanners with a validation and with estimated value of scanner errors.

Portable phase measuring interferometer using Shack-Hartmann method

A real-time inspection is useful and effective to optimize lens aberrations of excimer-exposure sytem, which can expose patterns less than 100 nm. We have developed a portable i.e., compact and lightweight phase measuring interferometer (P-PMI), which can be attached to a stage of the exposure system during real-time monitoring the aberration of the projection lens mounted on the exposure system. Measured repeatability of the wavefront measurement is ab out 0.1 mλ and tool-to-tool difference is 0.6mλ. Measured wavefront during adjusting a projection lens agree dwell with a simulated result. LWA was successfully optimized using P-PMI data.

Illumination optics for source-mask optimization

Source Mask Optimization (SMO) 1 is proposed and being developed for the 32 nm generation and beyond in order to extend dose / focus margin by simultaneous optimization of the illuminator source shape and a customized mask. For several years now, mask optimization techniques have been improving. At the same time, the flexibility of the illuminator must also be improved, leading to more complex illumination shapes. As a result, pupil fill is moving from a parametric model defined by sigma value, ratio, clocking angle, subtended angle and/or, pole balance, to a freeform condition with gray scale defined by light intensity in the illuminator. We have evaluated an intelligent illuminator in order to meet requirements of SMO. Then we have confirmed controllability of the pupilgram.

Integrated projecting optics tester for inspection of immersion ArF scanner

Immersion lithography has been intensively developed to print features, such as isolated lines and isolated spaces, which are smaller than 35 nm, with good depth of focus at a vacuum wavelength of 193 nm. Because the wavelength of the light in a liquid is reduced from the vacuum wavelength, the numerical aperture, i.e. the resolution (lambda/2NA) can be improved by a factor of the index of refraction of the liquid. At the end of 2005, Nikon scanner achieved 47nm L and S pattern. In order to utilize daily this performance of the immersion lithography apparatus with well-defined resolution enhancement technique in factory to its maximum content, optical parameters such as lens aberration, illuminator NA, pupil-fill annular ratio, and polarization status are to be measured and controlled more accurately than ever. To meet that need, an integrated projecting optics tester (iPot) for an in-situ inspection of wavefront aberration with calibration method to achieve high accurate measurement has been developed. The performance meets the required 47nm L&S pattern while the numerical aperture of immersion projection lens is larger than 1. The deviation between the averaged absolute value of the Zernike coefficient was 0.0022 lambda (0.42 nm). The deviation of the averaged absolute value of the coefficient in the scanned field is 0.0010 lambda (0.19 nm). Measured ratio of specific polarization (RSP) values of H and V polarized illuminated sections are 0.974 and 0.973, respectively. Projection lens with the low birefringence designed value is consistent with the measured value of RSP and the wavefront illuminated by linear polarizing light.

Illumination pupilgram control using an intelligent illuminator

Nikon’s Intelligent Illuminator, a freeform pupilgram generator, realizes a high flexibility for pupilgram control by using more than 10,000 degrees-of-freedom for pupilgram adjustment. In this work, an Intelligent Illuminator was integrated into an ArF scanner, the Nikon NSR-S621D. We demonstrate the pupilgram setting accuracy by direct correlation between on-body measured pupilgram and desired target pupilgram. We show that the Intelligent Illuminator is used for fine tuning of the pupilgram to match optical proximity effect (OPE) characteristics. We experimentally confirmed that a global source optimization software realized an improvement of lithographic process window without changing OPE characteristics by using optimized pupilgram made by Intelligent Illuminator.

Imaging optics setup and optimization on scanner for SMO generationprocess

Source & Mask Optimization1 (SMO) is a promising candidate to realize further reduction of k1 factor to achieve 22nm feature lithography and beyond. To make the SMO solutions feasible all imaging-related parameters should be closer to the designed parameters used in SMO process. In this paper, we discuss how we realize this in the imaging system setup on the scanner. The setup process includes freeform pupilgram generation, pupilgram adjustment and thermal aberration control. For each step the important factors are speed and accuracy.

Polarization properties of state-of-art lithography optics represented by first canonical coordinate of Lie group

The polarization characteristics of the state-of-art of optical lithography equipment are approximately ideal, i.e., in general only small polarization changes are induced by optical elements. Because of that, the polarization matrices of the optics are close to the unit element, which can be represented using the first canonical coordinate of a Lie group. The four-matrix basis of real general linear group of degree two is classified from a geometrical point of view. The complex versions of the four matrices are added to the four real matrices to obtain the basis of Lie ring of two-dimensional complex linear group, which is sufficient for physically possible polarization transformations. Each geometrical basis matrix generates non-Jones space of easy to understand individual optical phenomena. We propose a new physical polarization representation of projection optics for microlithography, which has eight real parameters, suitable for conventional pupil representation, with individual real optical characteristics applicable to optical elements. Pupil maps of a simulated projection lens whose polarization aberration and diattenuation induced by compensated intrinsic birefringence of CaF2 lens elements, are shown using the representation.

On board polarization measuring instrument for high NA excimer scanner

We developed an instrument for monitoring the polarized illuminator of the ArF scanner. A rotatable retarder and a rotatable analyzer were incorporated in the instrument for polarimetry. The instrument measures polarization state of the polarized illuminator in sufficient accuracy. Stokes parameter of the illumination light incorporated in the ArF scanner was successfully obtained. The measured result showed that the polarization state of the illumination light was controlled well. The instrument is as small and light-weighted as can be installed on board.

Effect of azimuthally polarized illumination imaging on device patterns beyond 45nm node

For an ultra-high numerical aperture (NA), such as that exceeding 0.9, the p-polarized component of light that has passed through a region at the limit of the NA of a high-NA lithography tool, degrades contrast because of the so-called vector imaging effect, and is therefore detrimental to the formation of optical images. Polarized illumination removes the effect of the p-polarized light component and provides illumination light composed of s-polarized light. The higher the NA, the greater are the benefits of polarized illumination. Therefore, in lithography at the 45-nm node and below, polarized illumination is viewed as an indispensable technology. We explore the applicability of polarized illumination to device manufacturing processes at the 45-nm node and beyond, with a focus on the utilization of azimuthally polarized illumination, which enables one mask exposure. The data used in this research were obtained through imaging simulations and experiments using a dry lithography tool equipped with a 0.92-NA projection lens. In imaging simulations using a lithography simulator, the application of azimuthally polarized illumination improved image contrast in resists by approximately 20% for half pitch (HP) 65-nm dense patterns. As a result, device patterns showed enhanced robustness with respect to exposure dose error; extended process windows; and reduced mask error enhancement factor (MEEF), line edge roughness (LER), and line end shortening (LES). This paper examines the results of experiments conducted using imaging simulations and lithography tools on other product device like patterns (besides special patterns in which benefits can clearly be expected, including dense (L/S) patterns), and reports the results.

The impact of realistic source shape and flexibility on source mask optimization

Source mask optimization (SMO) is widely used to make state-of-the-art semiconductor devices in high volume manufacturing. To realize mature SMO solutions in production, the Intelligent Illuminator, which is an illumination system on Nikon scanner, is useful because it can provide generation of freeform sources with high fidelity to the target. Proteus SMO, which employs co-optimization method and an insertion of validation with mask 3D effect and resist properties for an accurate prediction of wafer printing, can take into account the properties of Intelligent Illuminator. We investigate an impact of the source properties on the SMO to pattern of a static-random access memory. Quality of a source made on the scanner compared to the SMO target is evaluated with in-situ measurement and aerial image simulation using its measurement data. Furthermore we discuss an evaluation of a universality of the source to use it in multiple scanners with a validation with estimated value of scanner errors.