Vaida Auzelyte

Extreme ultraviolet interference lithography at the Paul Scherrer Institut

We review the performance and applications of an extreme ultraviolet interference lithography (EUV-IL) system built at the Swiss Light Source of the Paul Scherrer Institut (Villigen, Switzerland). The interferometer uses fully coherent radiation from an undulator source. 1-D (line/space) and 2-D (dot/hole arrays) patterns are obtained with a transmission-diffraction-grating type of interferometer. Features with sizes in the range from one micrometer down to the 10-nm scale can be printed in a variety of resists. The highest resolution of 11-nm half-pitch line/space patterns obtained with this method represents a current record for photon based lithography. Thanks to the excellent performance of the system in terms of pattern resolution, uniformity, size of the patterned area, and the throughput, the system has been used in numerous applications. Here we demonstrate the versatility and effectiveness of this emerging nanolithography method through a review of some of the applications, namely, fabrication of metallic and magnetic nanodevice components, self-assembly of Si/Ge quantum dots, chemical patterning of self-assembled monolayers (SAM), and radiation grafting of polymers. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3116559]

Nanofabrication of Broad-Band Antireflective Surfaces Using Self-Assembly of Block Copolymers

We present a simple and cost-effective method for the fabrication of antireflective surfaces by self-assembly of block copolymers and subsequent plasma etching. The block copolymers create randomly oriented periodic patterns, which are further transferred into fused silica substrates. The reflection on the patterned fused silica surface is reduced to well below 1% in the ultraviolet, visible, and near-infrared ranges by exploiting subwavelength nanostructures with periodicities down to 48 nm. We show that by choosing the appropriate block copolymers and pattern transfer parameters the optical properties of the antireflective surface can be easily tuned, and the spectral measurements verify a significant reduction of the reflectivity by a factor of 10. The experiments, confirmed with simulations based on rigorous diffraction theory, also show that the tapered shape of the nanostructures gives rise to a graded index surface, resulting in a broad-band antireflective behavior.

Photoluminescence studies of SiGe quantum dot arrays prepared by templated self-assembly

The photoluminescence emission of SiGe quantum dot arrays prepared by templated self-assembly, combining extreme-ultraviolet interference lithography and molecular beam epitaxy, were studied. The PL spectra obtained from areas with ordered dots show a pronounced SiGe-quantum-dot–related signal. The corresponding no-phonon and assisted transversal optical phonon recombinations are well resolved due to the narrow-size distribution of the fabricated quantum dot arrays. Additionally, the dependence of the photoluminescence emission on dot size and Ge concentration is discussed as well as effects of laser power excitation.

Optical Sensing with Simultaneous Electrochemical Control in Metal Nanowire Arrays

This work explores the alternative use of noble metal nanowire systems in large-scale array configurations to exploit both the nanowires’ conductive nature and localized surface plasmon resonance (LSPR). The first known nanowire-based system has been constructed, with which optical signals are influenced by the simultaneous application of electrochemical potentials. Optical characterization of nanowire arrays was performed by measuring the bulk refractive index sensitivity and the limit of detection. The formation of an electrical double layer was controlled in NaCl solutions to study the effect of local refractive index changes on the spectral response. Resonance peak shifts of over 4 nm, a bulk refractive index sensitivity up to 115 nm/RIU and a limit of detection as low as 4.5 × 10−4 RIU were obtained for gold nanowire arrays. Simulations with the Multiple Multipole Program (MMP) confirm such bulk refractive index sensitivities. Initial experiments demonstrated successful optical biosensing using a novel form of particle-based nanowire arrays. In addition, the formation of an ionic layer (Stern-layer) upon applying an electrochemical potential was also monitored by the shift of the plasmon resonance.

Nanowire Development and Characterization for Applications in Biosensing

A nanowire is an extremely thin wire with a diameter on the order of a few nanometers and with lengths orders of magnitude larger than its diameter. The physical properties of nanowires at this scale are expected to deviate significantly from the bulk metal, due to confinement and surface effects. For example, the electrical conductivity of the wires changes considerably, due to the drastic increase in the surface-to-volume ratio, which can be exploited for sensing. Mechanical properties, such as the yield strength, are important parameters that need to be characterized for applications like flexible circuits. In order to study the nanowire properties one needs to arrange them on a surface in a controlled way.

Measuring resist-induced contrast loss using EUV interference lithography

In this paper the contrast behavior of photoresists upon EUV exposure is addressed. During a lithographic exposure, the intended shape undergoes contrast loss which can be divided into two portions. One part is assigned to exposure tool induced contrast loss (e.g. aberrations of the exposure optics, mechanical stability of the system), while the other part is due to chemical processes in the resist during exposure and development. Both contributors have to be decoupled from each other in order to solely analyze the resist contrast loss. The method presented here is based on an experimental evaluation of dense line/space patterns obtained from EUV exposures. For decoupling of the resist induced contrast loss from the exposure tool contrast, the aerial image has to be determined. As an alternative EUV exposure tool the EUV interference lithography (EUV-IL) beamline at Paul Scherrer Institute is applied for resist qualification. The theoretical description of the sinusoidal aerial image of the EUV-IL tool is presented as well as the experimental method applied to analyze resist patterns in terms of resist contrast. Finally, the results are compared with data obtained from ASMLs ADT EUV scanner.