250-Å linewidths with PMMA electron resist

25-nm-wide lines and spaces have been fabricated in 22.5-nm-thick films of PdAu (40: 60) using electron-beam exposure and polymethylmethacrylate (PMMA) resist. A high-resolution scanning transmission electron microscopy (STEM) was used to expose the resist and the samples were mounted on 60-nm-thick Si 3N4 membrane substrates. Previously, the smallest metal structures formed with a resist process were 60 nm wide with spaces between the lines several times larger than the lines. The results presented here show that 25-nm lines can be fabricated with a center to center spacing of 50 nm.