Projection optics

Vergnole, S., Delage, L., Reynaud, R, 2004, Accurate measurement of differential chromatic dispersion and contrast in an hectometric fibre interferometer in the frame of GHANA project. Optics Comm, submitted... 

Even though projection optics embodies the inherent limitation of pattern transfer just mentioned, this technique has become a dominant approach in high-resolution work. A key reason for this success is the ability of projection printing to use reduction refraction optics with high numerical apertures. The resolving power of projection systems can be approximated by ... 

The factors that contribute to limit resolution in projection optics are well known (2) and are manifested in the form of a degradation in the free space image as the exposure systems are operated near their diflEraction limit. To some extent, this lens-generated degradation of image quality can be compensated by designing resist systems with a nonlinear dissolution response to dose. 

Figure 2.5. The intensity function or aerial image of a mask is ideally a square wave. However, projection optics operating near their diffraction limit degrade this square wave into a sinusoid with a small direct current dc) term. When this intensity function is imposed on the contrast-enhancement lithographic material, bleaching occurs most rapidly in the high-intensity areas such that the transmitted intensity function that exposes the resist is modified and thus leads to improved contrast.

Figure 3.5. Micralign 500 projection optics system. Reproduced from Per-kin-Elmer Users Manual.)...

S)ly(phenylenevinylene)s, 290 iazopiperidinedione, photolysis, 89/ All-reflecting 1 1 projection optical system, 117/... 

Usually, manufacturers of the projection optics for steppers destined for manufacturing of VLSI try to use the optics having minimal NA. 

A premixed one-dimensional flame produced by a flat flame burner of the McKenna design is often used for temperature calibrations at combustion temperatures. Figure 14.5 shows a typical setup, in which the beam projection optics and the detector are mounted on either side of fhe burner. Multiple passes can also be used to increase the absorbance by placing mirrors on each side of fhe burner (not shown). A fine wire... 

There are six basic elements of optical lithography, i.e., (i) an exposure source, (ii) an illumination optics system, (iii) a photomask or reticle and its pellicle, (iv) a projection optics system, (v) a wafer stage, and (vi) a photoresist-coated wafer. As shown in Fig. 13.3, the source provides the exposure radiation that, with the aid of the illumination optics, illuminates the photomask and transfers... 

The illumination system comprises a series of relay optics and uniformizing optics that project the radiation from the source through the photomask to the entrance pupil of the projection optics of the lithographic lens, where it forms an image of the illumination source (see Fig. 13.8). This type of illumination system is referred to as Kohler illumination. The fraction of the pupil filled by the illuminator source s image determines the degree of coherence in the projection... 

The radiation traversing the entire chain of illuminator and projection optics forms an aerial image of the mask that is projected onto the resist-coated wafers. A fast shutter within the illuminator assembly exposes the photoresist to the image for a very short period of time, on the order of a few tenths of a second. The integrated energy of each exposure must he repeatable to within 1%, such that the illumination of the reticle is fairly uniform (<+l%) over a large area, a feat it accomplishes with the aid of a number of methods, including the use the of fly s eyes and rods. " ... 

The exposure optics system comprises the set of optics (mirrors and lenses) that delivers the aerial image of the mask to the resist-coated wafer on the exposure stage. There are two categories of such systems. Contact and proximity optics systems are the simplest and the least expensive of the systems, but are not well suited for high-volume IC manufacture because of their high level of defectivity. The other system, the projection optics system, is predominantly used in modern semiconductor manufacturing. Both systems rely on the entire mask, or at least a portion of it, to be imaged simultaneously. 

Given the susceptibility of fused silica to laser-induced damage, particularly at high fluences at 193-nm wavelength, it is not used in the illuminator lenses. Rather, at present, calcium fluoride is used in most 193-nm illumination systems for elements where fused silica s lifetime has been projected to be unacceptably short. Also, when necessary, optical coatings that are laser resistant and can function as antireflection coatings are coated on fused silica lenses to protect them from surface damage. Typically, fused silica lenses are used in the projection optics where fluences are much lower than in the illuminator lenses. ... 

Murakami, T. Oshino, H. Kondo, H. Chiha, H. Komatsuda, K. Nomura, and H. Iwata, Devel opment status of projection optics and illumination optics for EUVl, Proc. SPIE 6921, 69210Q... 

The EUV exposure system comprises the plasma source (for generating the plasma that in turn emits EUV photons), the source collection optics (comprising the condenser and illumination optics), and the projection optics. A schematic of an EUV exposure tool is shown in Eig. 14.8. 

Condenser optics have short lifetimes their optics specifications are less stringent than those for the projection optics. The condenser optical components are considered consumable and are replaced on a regular basis. In contrast, projection optics have extremely tight specifications and are difficult and time consuming to fabricate and to align. 

Hollenshead and L. Klehanoff, Modeling extreme ultraviolet/H20 oxidation of ruthenium optic coatings, J. Vac. Sci. Technol. B 24,118 130 (2006) Y. Gomei, H. Takase, T. Aoki, Y. Kakutani, and M. Niihe, Scaling law in acceleration test of extreme ultraviolet lithography projection optics mirror contamination, J. Vac. Sci. Technol. B 23, 2848 2851 (2005) A.N. Broers, W.W. Molzen, J.J. Cuomo, N.D. Wittels, Electron beam fabrication of 80A metal structures, Appl. Phys. Lett. 29, 596 598 (1976). 

Second, because contamination resulting from carbon deposition depends on the local intensity of the EUV radiation at the surface of the mirror, it is possible that certain parts of the mirror surface in the projection optics may experience a local reduction in reflectivity that is larger than that occurring at other locations. The result is apodization of the projection optics, which can cause CD variation across the chip that is printed with EUV lithography. ... 

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