Dual-tone Photoresist
Dual-tone photoresists have been developed years ago, allowing the printing of two lines in a single exposure imaging of a single line. Early demonstrations relied on crosslinking of the highest dose regions, rendering them insoluble in developer, while the lowest dose regions were normally insoluble already. Alternatively, a photobase generator may generate acid quenchers at high doses; the acid quenching counters their ability to render the photoresist soluble. The simplicity and cost-effectiveness of this approach make it compelling as a method of extending current photolithographic capability. However, due to its inherent edge-printing characteristic, loops will generally be formed, which will need to be addressed by other process steps. In addition, the expected acid or base diffusion may limit the resolution of this technique.
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