The use of high lens numerical aperture for improving the resolution of a lithographic lens requires a high incident angle
of exposure light in resist, which induces vectorial effects. As a result, high NA lithography has become more sensitive
to vectorial effects, and a vectorial fingerprint with higher accuracy has become necessary for effective image forming
simulation. We successfully obtained true polarization characteristics of single optics by separating the effect of
measurement optics, arranged serially, in the measurement optical path. Accuracy of the separated polarization
characteristics of two test birefringent optics on a testbench for principle verification was calculated to be better than
0.01 nm of OPE simulation error.
High lens numerical aperture for improving the resolution of a lithographic lens requires a high incident angle of
exposure light in resist, which induces the vectorial effect. As a result, the vectorial effect has become more sensitive and
vectorial fingerprint with higher accuracy has been required for effective image forming simulation. We successfully
obtained true polarization characteristics of projection optics without the effect of measurement optics for more accurate
image forming simulation. Accuracy of the result of separating Jones matrix of projection optics and that of
measurement optics are presented.
In hyper-NA imaging, the vector properties of the light become important. Therefore, to characterize and to fully exploit
the state-of-the-art lithographic apparatus, reconstruction of polarization matrices in the pupil plain of a projection lens
has become indispensable. We will present a reconstructed Jones matrix of a benchtest projection optic. The
reconstruction method is based on the concept of the first canonical coordinate of the Lie group, which conjures up a
geometrical approach. The Jones matrix of this benchtest immersion projection lens is successfully reconstructed using
the data obtained by an on-body tool called iPot. A reconstructed polarized wavefront and polarized wavefront measured
by iPot agree very well. This newly developed methodology is essential to capturing the nature of light transformations
in the hyper-NA projection lenses. It is of fundamental importance to quantifying the properties of the state-of-the-art
projection lenses used in lithography.
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.
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.
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.
At the end of last century, the name of “quantum lithography” has been emerged. This exciting approach was proposed for making a resolution two times higher than that of the conventional optics without changing a wavelength and a numerical aperture. For those who want optical lithography to last long, this has been thought to be a great technology. However, an applicability of the proposed method to the current exposure system i.e., reduced projection exposure system has not yet been examined clearly. We have investigated the proposed quantum lithography to apply into the current exposure system using reticle. For simplicity, coherent illumination i.e. sigma is zero condition is used for calculation. Our quantum lithography compatible to mask exposure system explains probability of one and two photon absorption on the image plane i.e. on wafer. We have shown that the half-wavelength quantum lithography using conventional mask exposure system is impossible because diffraction at the mask makes biphoton into two photon. We have found that there is still super-resolution quantum lithography using mask exposure, however, there is little possibility of quantum lithography practically today because biphoton light source is as dark as stars. To realize quantum lithography practically, further development of not only biphoton light source but also two-photon absorption resist is indispensable.
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.