Advanced development for contact-holes of metal-oxide resists

One of the key steps in the pattern formation chain of extreme ultraviolet (EUV) lithography is the development process to resolve the resist pattern after EUV exposure. A simple traditional development process might be insufficient to clear the holes in contact-hole (CH) patterns and often causes missing hole defects around target-CD. In prior papers, a new development method named ESPERT™ (Enhanced Sensitivity develoPER Technology™) has been introduced to improve the performance of metal oxide-resists (MOR) for line/space (L/S) and pillar patterns. ESPERT™ as a chemical super resolution technique effectively apodized the MOR chemical image, improving chemical gradient and reducing scums. In this work, this development technique was optimised for CH patterns to reduce both the local CD uniformity (LCDU) and to reduce the levels of missing contact holes at a lower exposure dose. This is made possible thanks to the capability of the updated version of ESPERT™ that can effectively remove the scums (resist residues) inside CH to extend the missing hole defect margins. The high development contrast of the new development technique results also in a much higher exposure latitude. Using 0.33 NA EUV scanners on 36-nmpitch hexagonal patterns, the new development enhanced exposure latitude (EL), failure free latitude (FFL), and failure free dose ranges at both ADI (after development inspection) and AEI (after etch inspection) for two diverse types of MORs. For instance, in the case of the reference MOR developed by ESPERT™, CHs were nicely transferred to a TiN layer, even for small CD holes of 14.7 nm. If compared to the data by conventional development, using the new method, the EL was increased from 16.0% to 49.1%, the FFL was extended from 2 nm to 6 nm, and the failure free dose range was increased from 13.3% to 72.2%. It was also possible to have EUV dose-to-size (DtS) of 28 mJ/cm² with EL of 49.9% at ADI, using the new development. With all those advantages, this new development method is expected to be the solution for CH pattern formation of negative tone MORs in EUV lithography.