Chantal Khan Malek

Applications of LIGA technology to precision manufacturing of high-aspect-ratio micro-components and -systems: a review

The by far leading technology for manufacturing MEMS devices is Si-micromachining with its various derivatives. However, many applications of microsystems have requirements on materials basis, geometry, aspect ratio, dimensions, shape, accuracy of microstructures, and number of parts that cannot be fulfilled easily by mainstream silicon-based micromachining technologies. LIGA, an alternative microfabrication process combining deep X-ray lithography, plating-through-mask and molding, enables the highly precise manufacture of high-aspect-ratio microstructures with large structural height ranging from hundreds to thousands of micrometers thick. These tall microstructures can be produced in a variety of materials with well-defined geometry and dimensions, very straight and smooth sidewalls, and tight tolerances. LIGA technology is also well suited for mass fabrication of parts, particularly in polymer. Many microsystems benefit from unique characteristics and advantages of the LIGA process in terms of product performance. The LIGA technology is briefly reviewed. The strengths of the manufacturing method and its main fields of application are emphasized with examples taken from various groups worldwide, especially in micromechanics and microoptics.

Laser processing for bio-microfluidics applications (part I)

This paper reviews applications of laser-based techniques to the fabrication of microfluidic devices for biochips and addresses some of the challenges associated with the manufacture of these devices. Special emphasis is placed on the use of lasers for the rapid prototyping and production of biochips in particular for applications in which silicon is not the preferred material base. Part I of this review addresses applications and devices using UV lasers for laser ablation and surface treatment of microchannels, in particular in polymers.

Room temperature, water-based, microreactor synthesis of gold and silver nanoparticles

Synthesis of gold and silver nanoparticles at room temperature using a polydimethylsiloxane (PDMS) microreactor has been reported. The reactions have been performed using aqueous metal salt solutions and borohydride reducing agent with tri-sodium citrate as the capping agent. Effect of concentration of reducing agent on the optical properties of the nanoparticles has been investigated. The nanoparticles were characterised by UV-Vis absorption spectroscopy and transmission electron microscopy. The UV-Vis absorption spectra show a blue shift in the spectra with increasing concentration of the reducing agent, which indicates reduction in the size with increased amount of the reducing agent. The sizes of the nanoparticles are uniformly smaller in the microreactor synthesis as compared to those in the conventional batch synthesis, under similar reaction conditions. The microreactor synthesis is very fast and improves the monodispersity with excellent reproducibility.

Diffraction properties of a 0.24-μm period multilayer laminar amplitude grating in the soft x-ray region

We report on the fabrication of a laminar multilayer amplitude grating, characterization in the soft x-ray region, and modeling of its properties. Holographic lithography was used to produce a 0.24-μm spatial period grating on a triode sputtered Mo/C multilayer mirror. The pattern was transferred into the multilayer mirror by reactive ion etching in an SF 6 plasma after an intermediate lift-off step. The position and relative efficiency of the different orders of a grating etched down to the silicon substrate were measured at the Cu L αβ line (1.33 nm). The results were interpreted in the framework of a scalar kinematic diffraction theory.

Semitransparent soft x-ray multilayer mirrors

We report on the conception, fabrication, and characterization of a multilayer beamsplitter for use at oblique incidence in the soft x-ray range. Thin film deposition, conventional patterning, and anisotropic etch techniques are used to produce the self-supporting silicon carbide carrier film. Large-area Mo/C multilayer beamsplitters (1 cm2) were fabricated. Experimental results on the reflection and transmission at 1.33 nm are presented and compared with theoretical calculations. The role of the supporting film and the flatness of the structure are addressed. Our process is compared with existing approaches from the literature.

Fabrication of high-resolution multilayer reflection zone plate microlense for the soft x-ray range

The fabrication of linear, circular, and elliptical reflective zone plate lenses by a multistep process using microfabrication technologies is reported. The diffractive elements were generated by electron-beam lithography on a Mo/C multilayer mirror obtained by means of the triode sputtering technique. The patterns were transferred anisotropically into the multilayer mirror by reactive ion etching in a fluorinated plasma. An intermediate metallic mask made by the lift-off process was used for the transfer process. The groove depth could be monitored by following the reflectivity ofthe structure with a helium-neon laser during etching. Linear, circular (with 0.4-μm outer zones), and elliptical Fresnel zone plates (with 0.8-μ.m outer zones) were produced. Test patterns with a 50-nm top and 90-nm bottom resolution were produced. The groove profile and dimensional control were also investigated.

The effect of concentration in the patterning of silica particles by the soft lithographic technique

Soft lithography provides remarkable surface patterning techniques to organize colloidal particles for a wide variety of applications. In particular, micromolding in capillaries (MIMIC) has emerged as a patterning method in the nanometer to micrometer scale in a single step by using templating and directing nanoparticles via capillary forces in the channel. The present work reports the results of the micropatterning of monodispersed silica particles of ~338 ± 2 nm size in ethanol medium, using MIMIC on silicon substrates. The effect of the concentration of silica particles on the patterning has been investigated. The patterns are well aligned and completely filled at 2 wt% concentration of silica particles.

Fabrication And Test Of Soft X-Ray Multilayer Diffraction Gratings

Holographic lithography was used to produce a 0.36 μm spatial period grating on top of a Mo/C layered synthetic microstructure. The pattern was transferred to the multilayer mirror by reactive ion etching. The performance of the device has been evaluated at the Cu.Lα,β3 wavelength ( 1.33 nm ). A simple theoretical model explains the main features of the diffraction efficiency of the soft X-ray highly dispersive multilayer mirror.

Fabrication and performance of linear multilayer gratings in the 44-130 angstrom wavelength range

Two types of linear multilayer gratings have been investigated with special attention on the influence of the fabrication method on performance. Rh/C and Mo/Si systems have been realized for use above the carbon K-edge at 43.6 A and the silicon L3 edge at 125 A, respectively. We analyzed in detail the performance of the multilayer coatings in relation with their structural behavior. Mo/Si amplitude gratings were manufactured by suppressing the soft X-ray reflectivity of the multilayer mirror in selective areas with gold coating and lift off process. This method provides a well-defined 3 micron period Au grating. The soft X-ray reflectivity of the multilayer alone reached a maximum of 45 percent at normal incidence, whereas it was measured around 12.5 percent after Au grating deposition. Up to 13 grating orders were detected in the grating scan and detector scan showing the very good quality of these structures. A more unusual method was applied to manufacture Rh/C multilayer gratings. A carbon grating was first patterned on a silicon substrate and the multilayer was deposited at the end of the process. Measured reflectivity around 60 A in conventional 0 - 20 scan shows a reduction of the performances by a factor three. This is probably due to the surface roughness of the carbon grating prior to the multilayer deposition.

Selected examples in nano–sciences and nano–technologies at FEMTO–ST

This paper contributes selected examples based on the research and development of sub–micrometric and nanoscale structures at FEMTO–ST. In particular, exploitation of bandgap materials such as lithium niobate is a specialty of the institute and is applied in active photonic and phononic devices. Another area of active research concerns instrumentation at the microscale and nanoscale. More recently, biomolecular engineering and nanobiocharacterisation have been developed for nanobiotechnology and biosensors.