Contrast transfer function limiting resolution

X = 180°, and reappear inverted. The resolution limit of the image is normally taken to be the point just before the first zero in this contrast transfer function [85]. At optimum focus this is close to the point to point resolution calculated in Section 3.1, at about 0.5(Cs The appearance of the image will change in a complicated manner with very small changes in focus. 

An alternative readout system is a scanning differential phase-contrast microscope with a split detector as shown in Figure 16.5. The optical configuration is compact and easy to align. The memory medium, in which the data bits have been recorded, is located at the focus of an objective lens. The band limit of the optical transfer function (OTF) is the same as that of a conventional microscope with incoherent illumination. The resolution, especially the axial resolution of the phase-contrast microscope, is similar to that obtained by Zemike s phase-contrast microscope. The contrast of the image is much improved compared to that of Zernike s phase-contrast microscope, however, because the nondiffracted components are completely eliminated by the subtraction of signals between two detectors. The readout system is therefore sensitive to small phase changes. 

The resolution of the resist patterning is a function of the resist contrast and the optical diffraction effects produced by the mask aligner. For a description of Fraunhofer and Fresnel diffraction effects which limit resolution as a function of the optical modulation transfer function of the mask aligner, see Campbell [12] and Mack [13], In general, a shorter wavelength is key to achieve smaller feature sizes, for example, deep UV is able to generate features in... 

FIGURE 1.10 Transfer function calculated for optimum contrast (a) Reproduction of the phase shift sin % from Scherzer (1949) in case of optimum contrast, usually improperly called the extended Scherzer plateau (at 870 A defocus position for the high-resolution transmission electron microscopy used), (b) Effect of defocus on cos %. (Adapted from N. Uyeda et al. Molecular image resolution in electron microscopy. J. Appl. Phys. 43, 5181-5189 (1972). With permission.) (c) Scherzer plateau calculated for Philips CM 20 (200 kV, Cj = 1.2 mm). (From O. Scherzer. The theoretical resolution limit of the electron microscope. J. Appl. Phys. 20, 20-29 (1949). With permission.)... 

---