Alicyclic polymers for 193 nm resist applications: Lithographic evaluation

Photoresist compositions designed for 193 nm lithography were formulated from a series of cycloaliphatic co- and terpolymers of 2-methylpropyl bicyclo[2.2.1]hept-5-ene-2-carboxylate (trivial name, carbo-tert-butoxynorbornene), bicyclo[2.2.1]hept-2-enecarboxylic acid (trivial name, norbornene carboxylic acid), 8-methyl-8-carboxytetracyclo[4,4,0.1,(2,5)1(7,10)]dodec-3-ene (trivial name, methyltetracyclododecene carboxylic acid), 5-norbornene-2-methanol, and maleic anhydride, which were synthesized by free radical, Pd(II)-catalyzed addition and ring-opening metathesis polymerization techniques. The cycloaliphatic polymer backbones provide etch resistance, mechanical properties, and stability to radiation. The lithographic function is provided by carefully tailored pendant groups, which include an acid functionality that is masked by protecting groups that undergo acid-catalyzed thermolysis, as well as polar groups that influence the adhesion, wettability, and dissolution properties of the polymer. The polymers are soluble in common organic solvents and have glass transition temperatures ranging from less than 60 degrees C to higher than 250 degrees C depending on the specific structure and mode of polymerization. The polymers are as transparent at 193 nm as the corresponding acrylics. The dry etch resistance of these polymers varies with the formulation, but the polymers etch more slowly than APEX-E, a commercial deep UV photoresist under conditions typically used to pattern polysilicon. Upon exposure and baking, the resists have demonstrated high sensitivities (3-15 mJ/cm(2)), and 0.16 mu m features have been resolved.