Sub-10 nm silicon nano-structures based on block copolymer lithography and high selectivity cryogenic temperature dry etching

D.L. Olynick, Z. Liu, S. Cabrini, X. Gu, T.P. Russell, V. Ishchuck, I.W. Rangelow
Lawrence Berkeley National Laboratory, US

Keywords: block copolymer lithography, RIE, plasma etching, silicon, nanowires

Summary:

We use cryogenic plasma etching, down to sub-10 nm scale towards production of densely packed silicon wires, hole and fins from various block copolymer derived masks. With careful micron and deep nanoscale etching we show that cryogenic temperature etching can provide extreme selectivity and anisotropy at the nanoscale even with soft masks. Selectivity is enhanced while maintaining pattern verticality because resist etch rates decrease as temperature is lowered Using this process, Si pattern transfer is achieved with no intermediate hard mask and very thin PS masks (13 and 6 nm) created from BCP lithography using PS-b-P2VP. Higher selectivity can be achieved with a chromium hard mask. Aspect ratios of greater than 12:1 were achieved and limited by silicon wire collapse during etching. Temperature control was also important in the chromium etching to prevent migration of the PDMS spheres created after etching the PS from a PS-PDMS BCP pattern. Simulation work shows the role of oxygen and ion angular distribution in the silicon profile evolution.