Pattern Transfer of Nanomasks Based on Diblock Copolymers Self-Assembling through Reactive Ion Etching

We investigate the pattern transfer on oxide substrates of lithographic masks with nanometer dimensions. The nanomasks are realized through the Lithography based on block CoPolymers self-assembling (LCP). LCP is low cost, VLSI compatible and allows the formation of controlled and highly dense nanofeatures at wafer scale. The pattern transfer to a hard mask is an important step for many applications, and it is usually pursued by dry etch. However it is critical step due to the small size and chemical instability of the copolymer which acts as the resist. In this work a process of dry etch based on reactive ion etching is studied. The chemistry used is CF4 diluted with N2. The dilution is found to optimize the oxide/copolymer etch selectivity, thanks to the polymerization effect of the CFx radicals on the mask. The experimental data are discussed in the framework of a model which takes into account the impinging fluxes of the plasma components (i.e. neutral fluorine, carbon-fluorine particles and ions) for different distributions of the fragmentation products. The etching rate is followed for planar and nanopatterned oxides and the results compared in terms of the visibility contribution for the attachment and desorption of the etchant species.