Wafer-scale Nanopatterning Research Articles

Fabrication of ultrahigh-aspect-ratio and periodic silicon nanopillar arrays using dislocation lithography and deep reactive-ion etching

The aspect ratio of nanostructures determines the mechanical sensitivities and responses, such as hydrodynamic and oscillating flow detection. Nanopillar arrays with ultrahigh aspect ratio were fabricated using deep reactive-ion etching (DRIE) based on the optimized parameters in this study. Wafer-scale nanopatterning was achieved using dislocation lithography with normal photolithography machine instead of e-beam or EUVL. The wafer-scale Cr masks with 300, 500, and 700 nm line arrays were successfully patterned on silicon, providing etching mask for the fabrication of nanopillar arrays with a high aspect ratio. The important limitation of undercut during DRIE was solved by modifying the process parameters and using double masks composed of photoresist and Cr. Finally, the aspect ratio of the silicon nanopillar array reached 120 with smooth surface and vertical sidewalls. The methodology can provide a general approach for fabricating complex 3D periodic nanostructures that can be applied to various fields of multifunctional detection applications to increase detection probability and sensitivity.

Wafer-scale nanopatterning using fast-reconfigurable and actively-stabilized two-beam fiber-optic interference lithography.

A fast-reconfigurable and actively-stabilized fiber-optic interference lithography system is demonstrated in this paper. Employment of fiber-optic components greatly enhances the flexibility of the whole system, simplifies its optical alignment, and suppresses the interference of mechanical vibrations. Active stabilization is implemented in the system and evaluated through modeling and experiment. We demonstrate 3-inch-diameter wafer-scale patterning of 240-nm-period grating lines with a sub-50-nm linewidth and an aspect ratio over 3. Two-dimensional patterns of different geometries and dimensions are also demonstrated to show the versatility of our system. Step-and-repeat exposure is demonstrated with independently controlled patterning fields of 2×2cm2 large.

Effective Synthesis of Highly Oxidized Graphene Oxide That Enables Wafer-scale Nanopatterning: Preformed Acidic Oxidizing Medium Approach

Demand for rapid and massive-scale exfoliation of bulky graphite remains high in graphene commercialization and property manipulation. We report a procedure utilizing “preformed acidic oxidizing medium (PAOM)” as a modified version of the Hummers’ method for fast and reliable synthesis of graphene oxide. Pre-mixing of KMnO4 and concentrated H2SO4 prior to the addition of graphite flakes enables the formation of effectively and efficiently oxidized graphene oxide (EEGO) featured by its high yields and suspension homogeneity. PAOM expedites diffusion of the Mn-oxidants into the graphite galleries, resulting in the rapid graphite oxidation, capable of oxidizing bulky graphite flakes (~0.8 mm in diameter) that can not be realized by the Hummers’ method. In the scale-up tests, ten-time amount of graphite can be completely exfoliated by PAOM without need of extended reaction time. The remarkable suspension homogeneity of EEGO can be exploited to deposit ultra-flat coating for wafer-scale nanopatterning. We successfully fabricated GO optical gratings with well-defined periodicity (300 nm) and uniform thickness (variation <7 nm). The combination of the facile and potent PAOM approach with the wafer-scale patterning technique may realize the goal for massive throughput graphene nanoelectronics.

Employing refractive beam shaping in a Lloyd's interference lithography system for uniform periodic nanostructure formation

Uniform periodic structure formation over a large sample area has been challenging in laser interference lithography (LIL) mainly due to the Gaussian intensity distribution inherent to a laser beam. In this work, refractive beam shaping devices are applied in a Lloyd's interferometer to create a flat-top light field (2.8% intensity variation over an area of 20 × 20 cm2) for wafer-scale nanopatterning. Around 10−2 variation in fill factors are obtained for all the reported one dimensional and two dimensional periodic structures across a 2-in. wafer, which is 1 order of magnitude lower than the values obtained for the samples exposed to a Gaussian light field. The proposed LIL system also allows gradual light field transitions from the Gaussian, super-Gaussian, and flat-top to the inverse-Gaussian by simply adjusting the spot size of the laser incident to the beam shaper. The authors believe that the proposed LIL system can be applied for a variety of applications that benefit from the nature of periodic nanostructures.

Polymer-confined colloidal monolayer: a reusable soft photomask for rapid wafer-scale nanopatterning.

We demonstrate the repeated utilization of self-assembled colloidal spheres for rapid nanopattern generations. Highly ordered micro-/nanosphere arrays were interlinked and confined by a soft transparent polymer (polydimethylsiloxane, PDMS), which can be used as light-focusing elements/photomasks for area-selective exposures of photoresist in contact. Because of the stiffness of the colloidal spheres, the photomasks do not encounter feature-deformation problems, enabling reliable production of highly uniform patterns over large areas. The geometrical feature of the patterns, including the size, pitch, and even the shape, can be finely tuned by adjusting the mask design and exposure time. The obtained patterns could be used as deposition or etching mask, allowing easy pattern transfer for various applications.

Double oxide deposition and etching nanolithography for wafer-scale nanopatterning with high-aspect-ratio using photolithography

We report a nanolithography technique for the high aspect-ratio nanostructure manufacturing using DODE (double oxide deposition and etching) process. Conventional microfabrication processes are integrated to manufacture nanostructure arrays with sub-100 nm of linewidth. This lithography method is developed to overcome resolution limits of photolithography. High aspect-ratio nanostructures with sub-100 nm of lindewidth were fabricated on wafer-scale substrate without nanolithography techniques. The DODE lithography process presented enabled to pave a way to overcome limitations of nanolithography processes and allowed to manufacture large-scale nanostructures using photolithography and thin film deposition and dry etching processes.

Tunable two-mirror interference lithography system for wafer-scale nanopatterning

We have designed and analyzed a novel (to the best of our knowledge) two-beam interference lithography system for large-area (wafer-level) nanopatterning with enhanced tunability of pattern periodicities. The tunable feature has been achieved by placing two rotational mirrors in the expanded beam paths at regulated angles for a desired period. Theoretical analyses show that the effective pattern coverage area greater than a 4 in. (10 cm) wafer scale is attainable with a 325 nm (30 cm coherence length) HeCd laser and 4 in. (10 cm) mirrors, while the pattern coverage area is restrained by the overruling effects between the optical coherence and mirror size. The experimental results also demonstrate uniform nanopatterns at varying periods (250-750 nm) on 4 in. (10 cm) substrates, validating the theoretical analyses. The tunable two-mirror interferometer will offer a convenient and robust way to prepare large-area nanostructures on a wafer scale with superior tunability in their pattern periodicities.

Wafer-Scale Nanopatterning and Translation into High-Performance Piezoelectric Nanowires

The development of a facile method for fabricating one-dimensional, precisely positioned nanostructures over large areas offers exciting opportunities in fundamental research and innovative applications. Large-scale nanofabrication methods have been restricted in accessibility due to their complexity and cost. Likewise, bottom-up synthesis of nanowires has been limited in methods to assemble these structures at precisely defined locations. Nanomaterials such as PbZr(x)Ti(1-x)O(3) (PZT) nanowires (NWs)--which may be useful for nonvolatile memory storage (FeRAM), nanoactuation, and nanoscale power generation--are difficult to synthesize without suffering from polycrystallinity or poor stoichiometric control. Here, we report a novel fabrication method which requires only low-resolution photolithography and electrochemical etching to generate ultrasmooth NWs over wafer scales. These nanostructures are subsequently used as patterning templates to generate PZT nanowires with the highest reported piezoelectric performance (d(eff) ∼ 145 pm/V). The combined large-scale nanopatterning with hierarchical assembly of functional nanomaterials could yield breakthroughs in areas ranging from nanodevice arrays to nanodevice powering.

Wafer-scale nanopatterning using electrodeposition

This work proposed and demonstrated a simple yet effective technique that can achieve wafer-scale nanopatterning using electrodeposition and standard microlithographic tools. The proposed technique shrinks the microscale features in the metal layer to the nanoscale and subsequently uses the same metal layer as the etch mask for pattern transfer. As a proof of concept, an array of trenches and holes with initial dimensions of around 700 nm over a 1×1 cm2 wafer area was used to achieve sub-100 nm features in the underlying substrate after the pattern transfer. In addition to the electrodeposition process, only standard i-line lithography, metal deposition and lift-off, and reactive ion etching were used in the experiment. The proposed technique can be extended to the patterning of a general nanoscale pattern except when the pattern density exceeds the resolution limit of the microlithographic tool. In this article, the authors also discuss the line-edge roughness, registration error, and pattern-dependent s...

Wafer Scale Nanopatterning and Nanomaterials Synthesis of Functional Nano Probes for Atomic Force Microscopy

AbstractThe key hurdle in nanoscience and nanotechnology is the large-scale integration of nanoscale materials with micron scale electronics and structures to form functional devices and sensors. We have developed an innovative bottom-up wafer scale fabrication method that combines nanopatterning and nanomaterials synthesis with traditional silicon micromachining technologies. We have achieved nano-micro integration through catalyst nanopatterning and registration at wafer scale and through effective nanocatalyst protection and release before and after microfabrication. Our wafer scale fabrication process has produced 244 carbon nanotube (CNT) probes per 4-inch silicon wafer with control over the CNT location, diameter, length, orientation, and crystalline morphology. CNT probes with diameters of 40-80 nm and lengths of 2-6 μm are found to be functional nano probes for atomic force microscopy (AFM) imaging. In this paper, we will address our nano probe design and fabrication considerations in detail. CNT tip locations and diameters are defined by e-beam lithography. CNT length, orientation, and crystalline quality are controlled by the plasma enhanced chemical vapor deposition (PECVD) method. With effective catalyst protection schemes, this fabrication process is very similar to the conventional approach for fabricating wafer-scale silicon AFM probe tips. Process control is feasible and the overall yield is greatly improved. Our method and technology can be easily adapted to many other nanomaterials (nanotubes and nanowires) synthesis and processes for their rational design, fabrication, and integration in their applications.