Generation of Various Complex Patterned Structures From a Single Ellipsoidal Dot Prepattern by Capillary Force Lithography

Abstract

Parallel nanometer-scale patterning techniques such as edge lithography, [1] nanoimprint lithography (NIL), [2][3][4] soft lithography, [5,6] and combined lithography, referred to as capillary force lithography (CFL), [7][8][9][10][11] have recently attracted considerable attention because of high resolution and high reproducibility. These techniques replicate a pattern from a master mold prefabricated on a solid substrate by conformal contact without complicated equipment, leading to the fabrication of high-resolution patterns (sub-100 nm features) over large areas with high throughput. However, the widespread application of these techniques is hindered by the fact that the master mold generally needs to be prepared by electron-beam lithography via an expensive and time-consuming process.[12]We report a novel method for creating many different complex structures from a single prepattern that is either prepared from a master mold or stamped onto a solid substrate by patterning with a poly(dimethylsiloxane) (PDMS) replica mold. We show that various metal patterns including ellipses, dots, rings, chains of dots (or rings), ribbons, and wavy lines with various feature sizes can be generated from a single pattern of isolated ellipsoidal dots by simply varying the residual polymer film thickness and the reactive ion etching (RIE) time. Such periodic structures are difficult to fabricate with other methods, and their fabrication with such methods is very time-consuming. The flexibility of generating various types of pattern shapes from a single prepattern makes this approach very attractive, and it has the significant additional advantage of low cost and high efficiency because it is free of sophisticated processing. This technique enables the fabrication of large-area periodic patterns with features of various shapes and sizes, and might enable the industrial production of nanoelectronic devices, micro-/nanoelectromechanical systems (MEMS/NEMS), biochip/sensors, and micro-/nanofluidic systems. [13][14][15][16][17] Figure 1 shows the fabrication scheme for creating patterned gold nanoarrays using patterning with a PDMS replica, known as CFL. A highly uniform gold layer (∼40 nm thick) is deposited by electron beam evaporation onto a silicon wafer coated with a ∼3 nm thick chromium adhesion layer. Different types of metal or semiconductor templates can be prepared, provided that the different target layers can be deposited onto a substrate. Such hard metal masking layers can be used repeatedly as patterned molds. A thin film of polystyrene (PS, 20000 g mol -1) is spin-coated as a residual layer onto the gold surface. When the PDMS mold is placed on the PS surface and heated above the glass transition temperature (T g ), capillary forces drive the polymer into the void space of the patterns to conform to the surface topology of the mold, resulting in a negative copy of the mold. Reactive ion etching (RIE) with a gas mixture of O 2 (40 sccm) and CF 4 (60 sccm) plasma is then performed on the PS replica at a chamber pressur...

Fabrication of Flexible Binary Amplitude Masks for Patterning on Highly Curved Surfaces

“…Techniques such as capillary force lithography (CFL) [63][64][65] exploit capillary forces to mold a polymer melt into the relief features of a patterned stamp. This procedure closely follows the earlier reported micromolding in capillaries (MIMIC) transfer process that exploits capillary wetting to fill a channel system with a liquid prepolymer that is subsequently cured (leaving a microstructured polymer feature on the substrate on removal of the mold).…”

Simulations of novel nanostructures formed by capillary effects in lithography

“…Capillary force, as one of the predominant forces at the nanometer size-scale, can be used not only to expedite micro-and nano-scale imprint lithography, but also to enable the formation of interesting and useful features on the lithographic products with details finer than those of the original molds [1][2][3][4][5][6][7][8]. These techniques take advantage of interfacial tension and wettability to control both the rate and the extent of the rising capillary and the resulting meniscus curvature.…”

“…For example, Bruinink et al [3,4] have reported a technique of using the edge of a meniscus formed by capillary force lithography (CFL) as a mold of making second-generation stamps with increased resolution. Moreover, it has also been shown in CFL experiments that ring-like structures can be made taking advantage of the height variations of menisci formed in cylindrical capillaries [5,6]. However, it should be noted that only linear or ring-like structures have been reported to date; few experimental results have been reported with different cross-sectional geometries, even as simple as triangles or rectangles.…”

Two‐Photon Excited Fluorescence Enhancement for Ultrasensitive DNA Detection on Large‐Area Gold Nanopatterns

“…Figure 1 is a schematic representation of enhanced two-photon excited fluorescence (TPEF) DNA detection using large-area metal nanopatterns. To prepare a desired substrate, capillary force lithography (CFL) [22,23] was employed to fabricate metal nanopatterns with various feature sizes over a large, patterned area (2.7 mm  2.7 mm). We used the versatility of CFL to generate patterns of gold metal dots of diameter (D) 110 or 150 nm, with a period (S) of 250 nm.…”

“…[11,15] It is noteworthy that the feature diameter of the gold dots can be further controlled by varying the reactive ion etching (RIE) time. [22] Various feature diameters (110-150 nm) of gold patterns can be prepared from a single dot (D ¼ 100 nm) pre-pattern by varying the RIE time from 10 to 20 s. The resulting gold patterns are defect-free over the entire area of 2.7 mm  2.7 mm, which is large enough to show a perfect, homogeneous spectral effect across the entire patterned substrate (see the Supporting Information, Figure S1). …”