Lithographic comparison of assist feature design strategies

Subresolution assist features, when used in conjunction with off-axis illumination, have shown great promise for reducing proximity effects while improving lithographic process window. However, these patterns result in an increased emphasis on the mask manufacturing process, primarily in the areas of mask writing and inspection. In choosing a design strategy, one must be careful to account for the mask making capabilities, such as write tool grid size and linearity, along with the lithographic effect of errors in the mask making process. In addition to mask errors, stepper lens aberrations and expected process variations can also have a large influence on design rules. Generally, design tradeoffs must be made to balance the impact of these for the best overall lithographic performance.