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A new class of acid labile poly­(aryl acetal) polymers has been developed that can be used in photoresist formulations for next-generation microlithography techniques including extreme ultraviolet (EUV) or electron beam lithography. Example polymers have been synthesized by an optimized Suzuki polycondensation protocol. They are soluble in common photoresist solvents but are insoluble in water or aqueous bases that are used to develop positive photoresists. The structural design includes further elements that are aimed at improving photoresist resolution, stability, and etch resistance. Upon acid exposure, the acetal linkages are cleaved, and the polymers degrade into phenolic terphenyl fragments, which are readily soluble in a photoresist developer. Polymer degradation has been studied by NMR and LC-MS. Lithographic formulations have been developed and tested in line-and-space patterning experiments using EUV photolithography. Optimized resist formulations achieved 22 nm resolution with line width roughness values of 5.7 nm.

This paper discusses the continued evolution of Polymer-bound PAG [PBP] resists for sub-20nm lithography. Utilizing EUV wavelength, there has been enough progress in resolution and sensitivity to justify the use of these materials. PBP resists have shown that the principal demerit of acid diffusion can be overcome through attachment of the PAG anion to the lithographic polymer. Since the introduction of this chemically amplified resist approach, we have seen steady improvement in resolution, sensitivity, and LWR. Using a 0.30NA EUV tool with dipole, we can achieve 22nm hp resolution, with 12mJ dose, and 4.2nm LWR. Through rational PAG cation design, we have substantially reduced to a factor of 1/10th the PBP resist response to Out-of-Band Radiation compared to a TPS-based PBP. In this way, the resist can act as in situ spectral filter for unwanted longer wavelength exposure.

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