Extreme Ultraviolet-Printability and Mechanistic Studies of Engineered Hydrogen Silsesquioxane Photoresist Systems
Ashish Rathore, Ivan Pollentier, Maicol Cipriani, Harpreet Singh, Danilo De Simone, Oddur Ingólfsson, Stefan De Gendt
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/cm2.