Optimal temperature for development of poly(methylmethacrylate)

The authors have investigated a range of poly(methylmethacrylate) (PMMA) development temperatures as low as $−70°C$ and characterized their effect on the resolution of PMMA as an electron resist. The results show that cooling, in addition to reducing the sensitivity of the commonly used positive-tone mode of PMMA, also increases the sensitivity of its less commonly used negative-tone mode. They have shown that the resolution-enhancing properties of cold development peak at approximately $−15°C$ as a result of these competing sensitivity changes. At lower temperatures, the high doses required to expose the resist produce significant cross-linking of the polymer, altering its solubility properties and sharply degrading the contrast. If the correct development temperature is used, however, sub-$10nm$ features are readily achievable in PMMA-based scanning electron-beam lithography.