Extreme Ultraviolet-Printability and Mechanistic Studies of Engineered Hydrogen Silsesquioxane Photoresist Systems

Abstract

Hydrogen silsesquioxane (HSQ) photoresist has shown extremely high-resolution performance for electron-beam lithography and interference lithography and can be a potential photoresist candidate for extreme ultraviolet lithography (EUVL). To optimize this system for sub-10 nm patterning, it is important to understand the EUV- and electron-induced chemistry underpinning the functionality of this resist material. Here, we present an EUV-printability study on HSQ photoresist at resolutions of 16 and 22 nm combined with a mechanistic study on EUV- and electron-induced desorption of HSQ films. First, patterning results showed that the simple HSQ cages require a high EUV dose and an aggressive developer to print dense features. EUV- and electron-induced desorption experiments revealed that hydrogen and silane are the dominant species fragmented from HSQ, indicating dehydrogenation and redistribution pathways as the cross-linking mechanism. Quantum chemical calculations suggested that neutral dissociation is the dominant mechanism in HSQ cross-linking at low energies, i.e., below its ionization threshold, whereas dissociative ionization contributes significantly at higher energies. A distinct structure is observed at about 8 eV and a clear peak at about 11 eV, indicating a significant contribution through dissociative electron attachment at these energies. Based on these results, an engineered HSQ system is designed by adding silanol or carbinol (R-CH3OH) groups to the partially cross-linked HSQ cages to increase its tetramethylammonium hydroxide (TMAH) developer and EUV sensitivity. Finally, 2.38% v/v TMAH is used to develop a 16 nm printed dense line-space with a line-edge roughness of 6.4 nm but requiring an EUV dose of over 100 mJ/cm(2).