Defocus tolerance

Organic-based polymeric photoresists, whose contrasts are on the order of 2, require a value of (CMTF)resist of about 0.6. In order to achieve higher resolution, one would need to increase NA, decrease X or both. However such changes in the system NA or in the wavelength of the exposing radiation can be achieved only at the expense of defocus tolerance and increased lens complexity. An alternative approach would be to use a resist system with a contrast value substantially greater than that of conventional photoresists. 

Figure 5. Defocus tolerance versus resolution-limit characteristics, simulated results (6).

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