Although sub-diffraction-limit-resolution optical imaging has been attained via superlenses in the UV regime, the corresponding resist profile in general exhibits a very poor contrast, far below the minimum requirement for photolithography. Here, it is experimentally demonstrated thin flat silver superlenses, engineered through refining interfacial roughness to reduce scattering loss, capable of resolving grating features of sub-50 nm resolution with a high contrast of about 2.2. The seed layer effect on the superlens performance at a wavelength of 365 nm has been probed through both experimental and analytical methods. The performance of Ag, Ag/Ni and Ag/Ge superlenses agrees well with theoretical predications. The results show that a smooth interface is a key factor for realizing high performance superlensing, while damping losses become dominant when the roughness is reduced to less than 2 nm. This work verifies that a superlens is a potential tool for sub-diffraction limit nano-photolithography.