Fluoropolymers lithography

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. 

Outgassed Species from Fluoropolymers for F2 lithography on Exposure to 157 nm... 

As described in detail later, the polymers for use in 157 nm lithography universally contain fluorine because only fluoropolymers provide low enough absorption at 157 nm. The acid group of choice is hexafluoroisopropanol, which has a pKa similar to that of phenol, as mentioned earlier. Several platforms are available (Fig. 41) 1) tetrafluoroethylene-norbornene,2) 2-trifluoromethyl-acrylate-norbornene, 3) 2-trifluromethylacrylate-styrene, 4) 2-trifluoromethy-lacrylate-vinyl ether, 5) all-norbornene, 6) methacrylate, and 7) cyclopolymers. 

Fluoropolymers for 157 nm lithography can be categorized into two groups 1) polymers containing F in the backbone, typically prepared by copolymerization involving tetrafluoroethylene (TFE) and 2) polymers containing F in the side chain (Fig. 83). NBHFA has been copolymerized with NBTBE,NBHFA... 

The absorpticHi of organic polymers at 157 nm is dominated by the C (2p) electrons. An early audition of a large number of both organic and inorganic polymers indicated that fluorinated hydrocarbon polymers and sUoxane polymers were the most promising polymer platforms to achieve adequate transparency and plasma etch resistance [17]. This pioneering work has spurred tremendous efforts to develop transparent and etch resistant fluoropolymers for 157 run lithography. 

To avoid the negative properties of PDMS and variations of PDMS, researchers have investigated the use of fluoropolymers as mold materials in soft lithography. Fluoropolymer elastomeric moltb have lowered surface energies, tunable modulus, chemical stability, transparency to visible light, and solvent resistance. Rolland et have developed photocurable... 

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