Lithography immersion

The above equation indicates that resolution of immersion is R/n, where R is resolution without immersion. Therefore X/n is called the effective wavelength. Table 3.4 shows the resolution and effective wavelength in immersion lithography. 

Normal CA resists shown in Chapter 2 are available for immersion lithography. However, significant improvements to immersion lithography are also expected when the refractive index (RI) of the resist is increased beyond the current average value of 1.65. Specifically, theoretical calculations have shown that an increase in the RI of the polymeric resist, to a value around 1.9-2.0, will result in an increase in the exposure latitude, contrast, and mask error enhancement factor (MEET), R(ACD f /ACD, ., i,). A. Whittaker et ai 10,11 have reported that the design and S3mthesis of novel polymers with increased RI achieved 193 resist formulations. An essential part of the discovery process is the use of quantitative structure-property relationship (QSPR) models to predict the RI of small molecules and polymers.  

Candidates of high-RI model compounds are shown in Table 3.5. RI values in this table were estimated from the QSPR model. Those compoimds were reacted with methacryloyl chloride in the presence of a base to yield the corresponding methacrylamide, thiomethacrylates, and methacrylate. The synthesized methacrylate of high RI compounds was copolymerized 

Predicted RI Values at 193 run for Target Model Compounds Identified by QSPR Models 

MTP = 2-methyl-l-(lH-l,2,4-triazol-l-yl)propane-l-one, IMP = S-thiophene-2-yl-2-methylpropane thioate, TMPT = S-l,3-thiazol-2-yl-2-methylpropane thioate, MTMP = S-(5-methyl-l,3,4-thiazole-2-yl)-2-methylpropane thioate, TEMP = 2-(thiophene-2-yl) ethyl-2-methylpropanoate. 

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Positive-type resist compositions, (I), were prepared by Ishiduka et al. (1) containing adamanthyl, 7-butyolactonc, and a perfluoroalcohol component for use in liquid immersion lithography. Perfluoro acetal and ketal, (II), monomers... 

Poly(2-acrylamido-2-methyl-l-propanesulfonic acid and isopropylhexafluor-oalcohol), (IV), was prepared by Khojasteh et al. (4) and used as a top antireflective coating and barrier layer for immersion lithography. 

In current semiconductor fabrication, photolithography with 193 nm UV irradiation is able to pattern features that are 37 nm wide. However, the rapid miniaturization of ICs demands improvements in photolithography in order to sharpen the line resolution at size regimes far below 37 nm (Figure4.30). Although immersion lithography has been suggested as a candidate for sub-50-nm line resolution, there... 

Fluoropolymers have received much attention for applications in various fields because of their excellent properties (1) such as high thermal stability, high chemical stability, low adhesion, biological suitability, low frictional resistance, and transparency at vacuum ultraviolet (VUV) region (2). Because of the sufficient transparency at 157 nm, fluoropolymers are used as a polymer for F2 and F2 immersion lithography for semiconductor industry (2). Polymethacrylates containing bi- and/or tri-alicyclic structures, which are major polymers in ArF resist (3), are too absorptive at 157 nm and cannot be used as a polymer in F2 and F2 immersion resist (2). 

Besides the use in F2 and F2 immersion lithography, fluoropolymers are used in various fields. Fluoropolymer is one of the candidate for a polymer for MEMS, and fabrication of fluoropolymers by ultra-short pulsed lasers (9), and synchrotron radiations (10) has been studied. Polymer outgassing as well as the micro- and nano-fabrication depends on the polymer radiolysis. It is important for the micro- and nano-fabrication to investigate outgassing characteristics which is obvious outcome in the polymer radiolysis. 

For further enhancement of the resolution at 193 nm, immersion lithography employing water as an optical element between the last lens and resist has emerged recently as a new technology in competition with 157 nm lithography. In immersion lithography the effective exposure wavelength is reduced by the refractive index of the immersion fluid (193/1.44= 134 nm for 193 nm water immersion). 

SEMATECH (2003) 2nd Immersion Lithography Workshop, July 11,2003, San Jose,CA CD available from International SEMATECH, Austin, TX... 

Today, in the regime of hyper-numerical-aperture imaging and immersion lithography, polarization effects have become very dominant. Understanding these effects and designing around them have relied enormously on the theories of Fresnel and Young. 

The roots of immersion lithography date back to the invention of immersion microscopy by Ernst Abbe (1840 1905) in 1878, since he sought ways to increase the resolving power of optical... 

The basis of the imaging performance similarities and differences in terms of resolution and depth of focus, respectively, between immersion and dry lithography can be derived as follows. The nonparaxial scaling equations (applicable in systems with high angles of incidence) for resolution in dry and immersion lithographies are given by " ... 

Lin, The K3 coefficient in non paraxial lambda/NA scaling equations for resolution, depth of focus, and immersion lithography, J. Microlith. Microfab. Microsyst. 1(1), 7 (2002) New lambda/ NA scaling equations for resolution and depth of focus, Proc. SPIE 4000, 759 (2000). 

Similarly, the nonparaxial scaling equations for depth of focus in dry and immersion lithographies are given by... 

From Eqs. (13.32)-(13.35), resolution in dry and immersion lithographies are equal for the same wavelength and NA, while the DOF of immersion hthography is greater than that of dry hthography by a factor that is at least as great as the refractive index of water (which is 1.44 at X 193 nm at standard atmospheric tempera-... 

The main difference between dry and immersion lithography is the fact that the exposure is done in air in dry lithography and in a liquid (water) in immersion lithography. To prevent the leaching of resist components into the immersion water, topcoats are often used. It should be mentioned that topcoats do not prevent water from leaching into the resist film. The topcoat layer is removed after the exposure and PEB steps, but before development. 

Figure 13.52 Depth of focus performance of dry and water immersion (wet) lithography at NA 0.85. Note the significant enhancement in depth of focus obtained with immersion lithography (--l jLm) relative to dry lithography (. 06 jLm) for NA 0.85. (Photo courtesy of ASML.)...

Figure 13.54 Evolutionary tree of defects in an immersion lithography cluster. Actual defects on wafers are indicated in bold.

Okoroanyanwu, R. Kirsch, R. Wirtz, M. Grundkowski, and W. Grundke, Defect metrology in water immersion lithography, Semiconductor Fabtech (Nov. 2007). 

De Bisschop, A. Erdman, and A. Rathsfeld, Simulation of the effect of a resist surface bound air bubble on imaging in immersion lithography, Proc. SPIE 5754, 243 253 (2004). 

In general, the single-exposure techniques rely on the use of either hyper-NA >1.0 as implemented in immersion lithography (see Chapter 13) or exposure wavelength reduction as implemented in EUV lithography (see Chapter 14) and electron-beam lithography (see Chapter 15). These techniques may be complemented with reticle-based resolution-enhancement techniques such as phase-shifting masks and the like. 

Fig. 9.4 (a) 32 nm line and space structures (X-SEM graphs) generated by means of 193 nm immersion lithography, and (b) 60 nm structures generated by means of... 

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