Toward 10nm DRAM with the single exposure patterning: optimization of the processes in 0.55NA EUV lithography

Abstract

The high resolution resulting from high-numerical aperture (HNA) extreme ultraviolet (EUV) lithography allows single exposures for the aggressive pitches of critical layers in memory with unprecedented quality. Here, we illustrate that HNA EUV can be used not only for printing the aggressive pattern but also for combining two critical layers in DRAM patterning, so that it is expected to dramatically reduce masks and process costs. The bit-line periphery (BLP) and the hexagonal (HEX) pillars (used for fabricating the store landing pad – SNLP of capacitors) can be exposed in a single exposure in which the HEX pillar pattern is the most critical. A new spin-on metal oxide resist (MOR) with dedicated processes have been introduced, which are adapted to the high-resolution conditions of the HNA tool. We work on pitches of 28 nm and 26 nm in DRAM, which are beyond the resolution limit of single patterning in the 0.33NA tool. High performance has been gained after the process optimization. Notably, we achieved large values of the HNA depth of focus in after etch inspection (AEI) results for pitch 28 nm HEX Pillars (60 nm) as well as the SNPL-BLP structure (52 nm) which considers the defectivity of the most critical areas. Printability of pitch 26 nm SNLP-BLP is promising. Results indicate the capability of sub-10 nm DRAM with a single exposure by utilizing HNA EUV lithography.