Highly cross-linked polysilanes were recently investigated in an attempt to improve drawbacks of bottom antireflective coatings (BARCs) composed of loosely cross-linked polysilanes that are used for deep ultraviolet (UV) lithography. A highly cross-linked structure was prepared by thermally crosslinking poly (phenylmethylsilane-co-methylhydrosilane-co-methysilyne) with m-diethynyl benzene during baking after coating. Resist profiles are achieved on it without producing a foot or leaving residue at the bottom of the resist. The refractive indices at the KrF excimer laser wavelength (248 nm) are n = 1.93 and k = 0.32. The reflection is reduced 0.9% regardless of variation in the thickness of the substrate. Highly cross-linked polysilanes improve the melting of loosely cross-linked polysilanes during BARC etching. They also improve the surface roughness of loosely cross-linked polysilanes after substrate (SiO2) etching. The etch selectivity of the highly cross-linked polysilane BARC/resist during BARC etching is 2.1, which is higher than that of organic BARC/resist (similar to1). The etch resistance of the highly cross-linked polysilane during substrate etching is 1.1 times greater than that of the resist. Highly cross-linked polysilanes can not only be etched with high selectivity against resist but can also be superior etch mask for substrate etching.