Yuliya Lisunova1 Utkur Mirsaidov1

1, National University of Singapore, Singapore, , Singapore

Liquid cell Transmission Electron Microscopy (TEM) has attracted a lot of research attention owing to its capacity to access materials properties and dynamics in liquids at a sub-nanometer resolution. In a standard configuration, it utilizes a sealed electron transparent silicon nitride membrane window to separate high-vapour liquid pressure from the vacuum environment. Recently, it has been shown fabrication of the nanofluidic channels directly onto the liquid cell window enabling to monitor the self-assembly dynamics in a dimensionally confined system [1]. Because of the manufacturing difficulty, the channel profile is of high sidewalls surface roughness and exceeds 100 nm which significantly limits its application. An improved technique of SiNx liquid cells nanostructuration is required to advance this field.
Here, we demonstrate the fabrication of dense high aspect ratio silicon nanopatterns of high resolution onto the liquid cell Si3N4 membrane window with the use of new electron beam lithography (EBL) resist, ‘SML’ (EM Resist Ltd.) and optimized deep reactive ion etch (DRIE) process parameters. Using SF6/C4F8 etch chemistry [2,3], we found an etch selectivity of SML to Si in the order of 1:4 and etch rate of 138 nm/min. Such etch chemistry is extremely useful for direct SML pattern transfer into silicon, without the hard-mask layer, thereby reducing the surface roughness of the substrate material. We achieved a dense silicon nanolines of a sub 20 nm half-pitch to a depth of 200 nm at 1.2 nm line edge roughness from SEM images. This new manufacturing process allows liquid cell TEM membranes fabrication of target dimension specific to their research at high accuracy and precision. We explore this technique for the prototyping of the active elements of the silicon electronics onto liquid cell membranes, for in-situ TEM imaging of wet chemical etching of the nanofins and elastocapillary interaction of the nanopillars.
[1] E. Mielle, S. Raj, Z. Baraissov, P.Král, and U. Mirsaidov. Dynamics of Templated Assembly of Nanoparticle Filaments within Nanochannels, Advanced Materials 29, 1702682 (2017)
[2] Y.Lisunova, M. Spieser, R.D.D. Juttin, F. Holzner, J. Brugger, High-aspect ratio nanopatterning via combined thermal scanning probe lithography and dry etching. Microelectronic Engineering 180, 20 (2017)
[3] C. Rawlings, M. Zientek, M. Spieser, Y. Lisunova, J.Brugger, U. Duerig, and A. W. Knoll, Fabrication of nanometer accurate 3D profiles using closed loop thermal Scanning Probe Lithography, in submission