Alicyclic backbone polymers

Synthesis and Evaluation of Alicyclic Backbone Polymers for 193 nm Lithography... 

By chain backbone is understood the polymer chain proper without side groups and branches. For instance, all vinyl polymers have two atoms per structural unit in the chain backbone. If an aromatic ring is part of the backbone, Z is counted as follows o-phenylene, Z = 2 m-phenylene, Z = 3 p-phenylene, Z = 4. For alicyclic rings the same rule is applied. 

Polymers for use in 193 nm lithography are co-, ter-, and tetra-polymers of 1) methacrylates, 2) norbornenes, 3) norbornene-maleic anhydride, 4) nor-bornene-sulfur dioxide, and 5) vinyl ether-maleic anhydride (Fig. 39). While 1), 3), 4), and 5) are prepared by radical polymerization, all-norbornene polymers 2) are synthesized by transition-metal-mediated addition polymerization [166-168].Norbornenes (Fig.40) are sluggish to undergo radical [168,169] and cationic [170] polymerizations. Their ring-opening metathesis polymerization (ROMP, Fig. 40) [ 171 ] has never produced worthy resist polymers. The C=C double bonds introduced in the ROMP polymer backbone must be hydrogenated to reduce the 193 nm absorption and the ROMP polymers tend to have low Tg. However, the major problem for the ROMP polymers was their unacceptable swelling in aqueous base development. While polymethacrylate systems contain etch-resistant alicyclic structures in the ester side chain, norbornene-based systems carry the alicyclic unit in the backbone. Essentially all the 193 nm re-... 

While ring-opening polymerization of camphorsultam was attempted futilely to prepare a new polymer containing a bicyclic structure and a new acidic sulfonamide group in the backbone [115b], radical cyclopolymerization was exploited in the synthesis of 193 nm alicyclic polymers (Fig. 79). Transannular polymerization to form polynortricyclene bearing tert-butyl ester was utilized in radical copolymerization with MA (Fig. 79) [275]. Radical cyclopolymer-... 

The second platform of ester-protected positive resists designed for ArF lithography is the alicyclic polymer platform,which was first developed at the University of Texas at Austin,and involves resists in which the alicyclic units with pendant ester-protecting groups, acidic groups, and adhesion-promoting groups constitute the backbone of the polymer. Resist polymers of this platform... 

The acrylate platform is characterized by the presence of pendant aliphatic and alicyclic units with acid labile groups on an acrylate backbone. These resist polymers have high transparency at 193 nm, excellent adhesion properties, and high... 

The weakest bond in a polymer chain determines the overall thermal stability of the polymer molecule. The aliphatic carbon-carbon bond has a relatively low bond energy (see Table 5.1). Oxidation of alkylene groups is also observed during prolonged heating in air. Thus the weak links to be avoided are mostly those present in alkylene, alicyclic, unsaturated, and nonaromatic hydrocarbons. On the other hand, the functions proven to be desirable are aromatic (benzenoid or heterocyclic) ether, sulfone, and some carboxylic acid derivatives (amide, imide, etc.). Aromatic rings in the polymer chain also give intrinsically stiff backbone. 

The etch resistance of common acrylic polymers is poor but can be improved without reducing 193-nm optical transparency by the attachment of alicyclic pendant groups to the backbone. For example, a 1 1 copolymer of tert-butyl methacrylate and adamantyl methacrylate (108) exhibits a nearly twofold reduction in plasma etch rate compared to the ert-butyl methacrylate homopolymer. Figure 15b provides examples of alicyclic ester groups that have been assessed (109-111). 

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