SPATIAL DENSITY OF LINES EXPOSED IN POLY(METHYLMETHACRYLATE) BY ELECTRON-BEAM LITHOGRAPHY

In this article we report the experimental investigation of the density of patterns exposed with electron beam lithography (EBL). A linear relationship was found between the minimum width of poly(methylmethacrylate) (PMMA) walls and the given resist thickness (height of the walls). Below the minimum width, PMMA walls become wavy or fail due to the internal stresses caused by PMMA swelling during development. Previous research pertaining to proximity effects at feature sizes and spacing below the 0.25 mum range is limited. We have experimentally investigated proximity effects in very-high-density gratings in the pitch range from 50 to 330 nm. The relationship between electron beam dose and grating pitch, where proximity effects during electron beam lithography play a major role, was achieved. By fitting the experimental results with a triple Gaussian model, the contributions of the different electron distributions in proximity effects were determined. It was found that fast secondary electrons dominate the proximity effects in the range we studied and they limit the density of patterns fabricated by EBL.