Chemical and Structural Investigation of High-Resolution Patterning with HafSOx

High-resolution transmission electron microscopy (TEM) imaging and energy-dispersive X-ray spectroscopy (EDS) chemical mapping have been used to examine key processing steps that enable sub-20-nm lithographic patterning of the material Hf-(OH)(4-2x-2y)(O-2)(x)(SO4)(y) qH(2)O (HafSOx). Results reveal that blanket films are smooth and chemically homogeneous. Upon exposure with an electron beam, the films become insoluble in aqueous tetramethylammonium hydroxide [TMAH(aq)]. The mobility of sulfate in the exposed films, however, remains high, because it is readily exchanged with hydroxide from the TMAH(aq) solution. Annealing the films after soaking in TMAH(aq) results in the formation of a dense hafnium hydroxide oxide material that can be converted to crystalline HfO2 with a high electron: beam dose. A series of 9 nm lines is written with variable spacing to investigate the cross-sectional shape of the patterned lines and the residual material found between them.