Materials for and performance of multilayer lithography schemes

The 45-nm node will require the use of thinner photoresists, which necessitates the use of multilayer pattern transfer schemes. One common multilayer approach is the use of a silicon-rich anti-reflective hardmask (Si BARC) with a carbon-rich pattern transfer underlayer (spin-on carbon, or SOC). The combination of the two layers provides a highly planar platform for a thin resist, and provides a route to etch substrates due to the alternating plasma etch selectivities of the organic resist, inorganic Si BARC, and organic SOC. Yet such schemes will need to be optimized both for pattern transfer and optics. Optimizing optics under hyper-NA immersion conditions is more complicated than with standard (that is, NA < 1) lithography. A rigorous calculation technique is used to evaluate and compare standard lithography to a hyper-NA case using a multilayer stack. An example of such a stack is shown to have reasonable lithographic performance.