Hexagonal contact holes patterning at 32 nm pitch: influence of the stack and of the etching process on AEI performances

For further scaling of capacitors in 6F² DRAM cell, this study explores the feasibility of using 0.33 Numerical Aperture (NA) EUV lithography to pattern hexagonal contact holes with a minimum center-to-center (C2C) distance of 32nm. The patterns are printed onto a Chemically Amplified Resist (CAR) with a Dark Field (DF) mask and subsequently etched into a TiN layer. Key performance metrics include post-etch Critical Dimension (CD) control, across-wafer CD Uniformity (CDU) control, Local CD Uniformity (LCDU) reduction, and Failure-Free Latitude (FFL) enlargement. First, the impact on the aforementioned etch performances of the materials’ properties within the stack are investigated. We focus on layers thickness, layers density and surface roughness. Next, we explore the impact of the etching conditions on the after etch performance metrics. Among others, we investigate the carbon layer opening step with an emphasis on minimization of etch byproducts’ redeposition to prevent holes clogging, which can deteriorate LCDU and FFL. Finally, we present preliminary results from wafers exposed using the TWINSCAN EXE:5000 High NA EUV scanner, a state-of-the-art tool available at the ASML-imec HNA EUV Lithography Lab.