High aspect ratio silicon nanomoulds for UV embossing fabricated by directional thermal oxidation using an oxidation mask

Abstract

Nanomoulding is simple and economical but moulds with nanoscale features are usually prohibitively expensive to fabricate because nanolithographic techniques are mostly serial and time-consuming for large-area patterning. This paper describes a novel, simple and inexpensive parallel technique for fabricating nanoscale pattern moulds by silicon etching followed by thermal oxidation. The mask pattern can be made by direct photolithography or photolithography followed by metal overetching for submicron- and nanoscale features, respectively. To successfully make nanoscale channels having a post-oxidation cross-sectional shape similar to that of the original channel, an oxidation mask to promote unidirectional (specifically horizontal) oxide growth is found to be essential. A silicon nitride or metal mask layer prevents vertical oxidation of the Si directly beneath it. Without this mask, rectangular channels become smaller but are V-shaped after oxidation. By controlling the silicon etch depth and oxidation time, moulds with high aspect ratio channels having widths ranging from 500 to 50 nm and smaller can be obtained. The nanomould, when passivated with a Teflon-like layer, can be used for first-generation replication using ultraviolet (UV) nanoembossing and second-generation replication in other materials, such as polydimethylsiloxane (PDMS). The PDMS stamp, which was subsequently coated with Au, was used for transfer printing of Au electrodes with a 600 nm gap which will find applications in plastics nanoelectronics.

Fabrication of high-aspect-ratio polymer nanochannels using a novel Si nanoimprint mold and solvent-assisted sealing

“…The bottom part of the silicon mold turned out to be wider compared to the top part after the LOCOS process. This was mainly due to the isotropic oxidation at the corner of the silicon nanoridge, and it affected the size of the top part of the formed nanochannel after nanoimrpinting (Chen et al 2007). If needed, aspect ratio higher than 1:5.5 can also be achieved by reducing the pattern widths on the photomask or by carefully controlling the LOCOS process time.…”

“…If needed, aspect ratio higher than 1:5.5 can also be achieved by reducing the pattern widths on the photomask or by carefully controlling the LOCOS process time. Figure 3c shows that the resulting sidewalls of the silicon nanoridges had low surface roughness owing to the anisotropic KOH etching along the silicon crystalline geometry when compared with other Si etching technique such as deep reactive ion etching (DRIE) (Chen et al 2007;Liang et al 2007). Generally, DRIE leaves sidewalls with corrugation or scallop shapes, because of the nature of the process sequence that is cycled between etching and passivation phases (Nilsson et al 2003).…”

“…Although extremely well-defined nanostructures can be easily obtained using these techniques, the fabrication cost is high. Alternatively, methods such as edge lithography have been developed for NIL stamp fabrication, which utilizes selective removal or deposition of materials at the edges of lithographically defined microscale features (Grabiec et al 2004;Haneveld et al 2006;Zaborowsk et al 2006;Zhao et al 2008;Liang et al 2007;Chen et al 2007). For example, Grabiec et al demonstrated the use of local oxidation of silicon (LOCOS) for NIL stamp fabrication (Grabiec et al 2004).…”

NEMS by Sidewall Transfer Lithography

“…Further applications include field emission electrodes [39,40] and quantum dots [41][42][43]. Silicon stamps for nanoimprint lithography have also been extensively explored [44][45][46][47][48][49][50][51].…”

Wafer-scale fabrication of high-aspect ratio nanochannels based on edge-lithography technique

“…Here we presented a top-down fabrication technique for wafer-scale and high aspect ratio nanochannel preparation. Edge lithography, [25][26][27] a MEMS technique compatible fabrication approach, was utilized to define aluminium nanogaps, instead of chromium ones 27 due to the better etching controllability of the aluminium etchant. High aspect ratio nanochannels were then fabricated by deep reactive ion etching (DRIE) with so-prepared aluminium patterns as the etching mask.…”