Identifying And Monitoring Effects Of Lens Aberrations In Projection Printing

Abstract

Basic studies of projection printed images are presented to identify the types of patterns which are most susceptible to residual aberrations and to establish test structures which may be used to monitor the presence of critical types of residuals. These effects are explored by including arbitrary lens optical path difference (OPD) aberration functions in a twodimensional optical image simulation program associated with SAMPLE. The lens aberration function is expressed either in Zernike polynomials or a series expansion. The intensity is calculated from Hopkin's transmission cross -coefficient formulation with a self -checking algorithm. A catalog of results is presented here for the dominant primary aberrations of coma and astigmatism for a fixed maximum OPD of 0.4 A,. Contact holes are shown to be much more susceptible to astigmatism than coma and the traditional checkerboard test pattern is verified as a sensitive diagnostic pattern. An alternative structure consisting of thin lines with a short break is shown to be even more sensitive to astigmatism and useful for distinguishing it from coma. A further improvement in sensitivity is obtained through the use of small nonprintable defect -like features in proximity to regular features which coherently interact with the blurred image of the feature. A test target of this type is recommended for monitoring coma.Best Focus + 0.5 ¡m N X O COMA -0.20 (0.75,0), OPD in 0.0X

Demonstration of 12 nm Resolution Fresnel Zone Plate Lens based Soft X-ray Microscopy

“…7 shows the modulation plotted as a function of the grating spatial frequency. The theoretical modulation curve for a 100 nm thick Mo/Si test object at 1.75 nm wavelength was calculated using the SPLAT program [25] for the partially coherent, hollow-cone illumination employed in the experiment, and is included in Fig. 7.…”

“…For a zone plate lens used at high magnification and ignoring the spherical aberration correction term, NA MZP is equal to λ/(2∆r MZP ) [22], where ∆r MZP is the outermost (smallest) zone width of the MZP. For the partially coherent illumination [23,24] utilized here, k 1 ≅0.4 and thus the theoretical resolution is 0.8∆r, as calculated using the SPLAT computer program, a 2-D scalar diffraction code which evaluates partially coherent imaging [25]. The spatial resolution achieved to date has been limited by the ability to fabricate very small zone width with the required placement accuracy.…”

<title>Exact computation of scalar 2D aerial imagery</title>

“…Many aerial image simulators employ what has become known as the "Hopkins Model" 3 . Consider a typical microlithographic imaging system, comprised of a (finite) source, condenser optics, a semitransparent mask to be imaged, objective optics, and a silicon wafer in the image plane.…”

Review of computational lithography modeling: focusing on extending optical lithography and design-technology co-optimization

“…Berkeley developed a full simulation package that included image formation simulation and is termed SAMPLE [4] . The first commercial simulation software called PROLITH [5] was offered by Mack (now marked by KLA-Tencor Inc.) and followed shortly by SPLAT [6] from the Berkeley ' s group. All these software are upgraded to vector imaging as time progress.…”