Recent advancements in extreme ultraviolet (EUV) lithography have greatly enhanced the manufacturing of fine semiconductor nodes in high volume production (HVM). With the introduction of high NA (numerical aperture) EUV, further miniaturization is expected, and it is necessary to develop lithography technology to accommodate this. Chemically amplified resist (CAR) is widely used in HVM due to their stability and advantages as metal–free resists, and adapting CAR to the High–NA EUV era has important implications. Achieving high resolution in EUV involves a trade–off between resolution, line width roughness (LWR), and sensitivity. Reducing roughness is especially important because roughness can cause pattern defects. This paper aims to reduce CAR roughness and improve the trade–off. We investigated the reduction of roughness through a post–development treatment applied to EUV–exposed patterns. To examine the influence of this post–development treatment, we performed a power spectral density (PSD) analysis of LWR. Additionally, we compared the cross–sectional shape of resist patterns before and after treatment to understand the reactions occurring within the resist. The results showed that the LWR decreased by 13.1% for 44nm line/space (L/S) pitch and 4.0% for 28nm L/S pitch after the post–development treatment. Of particular interest, the use of additional processing demonstrated the potential to reduce low–frequency roughness, which is normally very challenging. These results show the potential for the application of CAR in next–generation lithography.
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. The traditional development process might be insufficient to achieve the requirements of ultra-high-resolution features with low defect levels. The aim of this paper is to establish a process to achieve a good roughness, a low defectivity at a low EUV dose, and capability for extremely-high-resolution for high numerical aperture (NA) and hyper-NA EUV lithography. A new development method named ESPERT™ (Enhanced Sensitivity develoPER Technology™) has been introduced to improve the performance of metal oxide-resists (MOR). ESPERT™ as a chemical super resolution technique effectively apodized the MOR chemical image, improving chemical gradient (higher exposure latitude (EL)) and reducing scums (fewer bridge defects). This new development method can also keep the resist profile vertical to mitigate the break defects. The performances of the conventional development and ESPERT™ were evaluated and compared using 0.33 NA EUV, 0.5 NA EUV, and electron beam (EB) exposures, for all line-space (LS), contact hole (CH), and pillar (PL) patterns. Using 0.33 NA EUV scanners on LS patterns, both bridge and break defects were confirmed to be reduced for all 32-nm-pitch, 28-nm-pitch, 26-nm-pitch LS patterns while reducing the EUV dose to size (DtS). In the electrical yield (1 meter length) test of breaks/bridges of 26-nm pitch structures, ESPERT™ reduced EUV dose while its combo yield was almost 100% over a wide dose range of 20mJ/cm². For CH patterns, in the case of 32-nm-pitch AEI (after etch inspection), EL was increased 7.5% up to 22.5%, while failure free latitude (FFL) was widened from 1-nm to 4-nm. A 16-nm-pitch LS pattern was successfully printed with 0.5 NA tool, while a 16-nm-pitch PL and an 18-nm-pitch CH patterns were also achieved with an EB lithography by ESPERT™. With ESPERT™, there was no pillar collapse observed for 12-nm half-pitch PL by 0.5 NA and 8-nm half-pitch PL by EB. With all the advantages of having a high exposure sensitivity, a low defectivity, and an extremely-high-resolution capability, this advanced development method is expected be a solution for high-NA EUV towards hyper-NA EUV lithography.
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.
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