Characterization of linewidth variation for single- and multiple-layer resist systems

The advantages gained by the use of a multilayer resist system were examined by electrical linewidth measurements of polysilicon lines ranging in width from 0.7 to 1.0 µm. Multilayer resist was compared to single-layer resist and quantitative data was obtained regarding the theoretical advantages of reduced reflectivity, improved planarity, and thinner imaging resist inherent to a multilayer resist system. Two different thicknesses of single-layer resist revealed that a thinner imaging layer resulted in improvements of up to 15 percent for linewidth variation and 35 percent for depth of focus, Reducing reflections from the substrate from 33 to 3.5 percent led to improvements of up to 30 percent in linewidth variation and depth of focus. Introduction of a particular type of topography under the polysilicon led to a worsened linewidth variation and depth of focus, by up to 30%.