Reverse transfer of nanostencil patterns using intermediate sacrificial layer and lift-off process
Schematic representation of the stencil lithography process.
Formation of a nanowire pattern connecting two large pads (nanobridge) by the normal nanostencil lithography. The narrow slit connecting two large openings in the stencil is composed of two freestanding cantilevers.
Reverse nanostencil lithography process. (a) Growth of -thick thermal on the Si substrate. (b) Evaporation of -thick Cr onto the substrate through the stencil. (c) Formation of the primary Cr pattern on the layer. (d) Dry and wet etching of the layer using the Cr pattern as an etch mask. (e) Secondary deposition of -thick Cr on the entire substrate. (f) Formation of the reversed Cr pattern by lift-off in a BHF solution.
Evolution of the pattern structure during the reversing process: (a) after dry etching of the layer, (b) after the additional wet etching, and (c) after the deposition of the second Cr.
Reversing behavior of a Cr stencil pattern. (a) The primary Cr pattern on the layer formed by the stencil deposition and (b) the reversed Cr pattern on Si.
Various types of the Cr pattern on Si formed by the reverse nanostencil process.
SEM images of (a) the nanobridge structure in a SiN stencil and (b) the Cr pattern obtained from it by the reverse nanostencil process. The beneficial effect of pattern blurring is schematically shown in (c). Due to the pattern blurring during the stencil deposition, the final Cr bridge pattern is narrower than the original SiN bridge in the stencil.
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