Study of high-resolution electron-beam resists for applications in low-temperature lithography

The authors report on the application of PMMA, hydrogen silsesquioxane, and AZ nLOF 2070 for electron-beam lithography at temperatures ranging from room temperature down to 6 K. Here, the low temperature range is of particular interest with respect to deterministic quantum-device processing using in-situ cathodoluminescence lithography. With decreasing temperature all resist under investigation show a decrease in sensitivity. In addition, an anomaly is observed for positive-tone PMMA for which the sensitivity rises for temperatures below 30 K. This behavior is explained in terms of a modified chain-scission mechanism that takes into account the sublimation of CO. Furthermore, our studies reveal evidence for a strong influence of the formation of volatile reaction products on PMMA. Alongside swelling of the negative-tone PMMA, an overall increased etch resistance as compared to unexposed PMMA and a decrease in sensitivity of almost one order of magnitude could be observed. This leads us to the assumption that the network-formation in negative-tone PMMA is attributed to a carbonization process rather than cross-linking.