Fullerene derivative based spin-on-carbon hard masks for advanced lithographic applications

Spin-on-Carbon (SoC) hardmasks are an increasingly key component of the microchip fabrication process. Progress in lithographic resolution has made the adoption of extremely thin photoresist films necessary for the fabrication of “1x nanometre” linewidth structures to prevent issues such as resist collapse during development. While there are resists with high etch durability, ultimately etch depth is limited by resist thickness. A possible solution is the use of a multilayer etch stack. This allows for considerable increase in aspect ratio. For the organic hard mask base layer, a carbon-rich material is preferred as carbon possesses a high etch resistance in silicon plasma etch processes. A thin silicon topcoat deposited on the carbon film can be patterned with a thin photoresist film without feature collapse, and the pattern transferred to the underlying carbon film by oxygen plasma. This produces high aspect ratio carbon structures suitable for substrate etching. In terms of manufacturability it is beneficial to spin coat the carbon layer instead of using chemical vapor deposition, but the presence of carbon-hydrogen bonds in typical spin-on-carbon leads to line wiggling during the etch (a significant problem at smaller feature sizes). We have developed a fullerene based SoC and reported on material characterization. The materials low Ohnishi number provides high etch durability and the low hydrogen level allows for high resolution etching without wiggling. Here recent advances in material development and work towards commercialization of the materials are presented and the use of the materials in etch stacks is demonstrated