Ties between Microsystems Technology and Nano-Engineering

Our research is centered on the engineering of structures at the mesoscopic length scale. Patterns between the micrometer and nanometer bridge molecules and biological cells to microelectronics and microsystems, and further to the macroworld, and vice versa. Standard photo-resist based lithography and micro/nano-fabrication methods, however, reach limits when applied to advanced micro- and nano-electromechanical systems (MEMS/NEMS). New alternative nanopatterning methods, such as local vacuum deposition through nanostencils, scanning probe methods, as well as nanostrucuturing with focused ion beam (FIB), are therefore being further developed in our lab. Some of our research activities, which cover the mesoscopic length scale that can bridge the “Top-Down” engineering methods and the “Bottom-Up” self-organization strategies, will be presented in this talk.

Ties between microsystem technology and nano-engineering

Jürgen Brugger, Schahrazede-Lila Mouaziz, Johannes Steen, Marc Antonius Friedrich van den Boogaart

The continuous improvements in conventional lithography methods for integrated circuit hardware allow further device shrinkage deep into the sub-micron dimensions. Two major drawbacks of these high-end patterning methods based on photoresist technologies are i) their high process costs and ii) their limited process versatility. Increased flexibility, however, becomes important for the engineering of advanced nano/micro-electro-mechanical systems (NEMS/MEMS), such as ultra-thin solid-state membrane or cantilever devices, polymer-based devices, micro/nanofluidics, and bio-analytical systems. Often standard lithography methods cannot be applied on unconventional materials, because the surfaces to be structured are either mechanically unstable and/or (bio-) chemically functionalized. Bottom-up methods relying on self-assembling strategies are making tremendous progress to form ordered structures with nanometer precision, but they still lack control on a larger scale. The key aspect in the near future is to find new ways to tie top-down and bottom-up methods together, and to connect structures across the nano/micro gap so that the improved effects relying on nanometer dimensions can be efficiently scaled-up. Recently, a series of new, alternative surface patterning methods related to MEMS technology have been developed, such as molecule delivery via DipPen/NADIS lithography or soft-lithography, thermo-mechanical indentation by Nanoimprint lithography, or local deposition via nanostencils. Due to their versatility and multiple length-scale capabilities they have great potential to form bridges between nano and micro-world. We will present some examples of our contribution to the field of MEMS and Nanotechnology, such as large area nanostencil based on a DUV/MEMS membrane, NEMS devices, functional SAM layers for MEMS, self-assembled nanowire sensors, nanoscale Hall-probe on surface released polymer cantilevers, and focused ion beam (FIB) and focused electron beam (FEB) nanofabrication. Some of these examples are presented in detail during TNT’04.

2004

Full-wafer stencils fabricated by a DUV/MEMS process for high-throughput patterning of mesoscopic structures

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

Photoresist-based lithography has major limitations when applied to micro-electro-mechanical systems (MEMS) with mechanically fragile and/or chemically functionalised surfaces. As a remedy, alternative, complementary nanopatterning methods have been developed, e.g. thermo-mechanical indentation (nanoimprint lithography), local printing of molecular layers (soft lithography), and shadow-mask deposition (nanostencil patterning). The nanostencil method is a resistless patterning method based on direct, local deposition of material on an arbitrary surface through a solid-state silicon nitride (SiN) membrane. In addition, the method offers the possibility of simultaneous deposition of micrometer and nanometer scale structures. Patterning of such mesoscopic structures (10^9 - 10^5 m) through stencils fabricated by MEMS processes in combination with focused ion beam (FIB) milling has been demonstrated within a limited area. In order to produce larger membranes enabling increased throughput of the nanostencil method, we developed a 100-mm wafer-scale (deep-UV) DUV/MEMS fabrication process. The mesoscopic patterns were first defined by a 4× reduced projection exposure using an ASML wafer stepper and then transferred into a SiN layer by means of reactive ion etching (RIE). The membranes were released by wafer-through etching using potassium hydroxide (KOH). Patterning of nano-scale structures using stencils allows for a large choice of materials and surfaces to be nanopatterned since no etch steps need to be applied. We have studied the nanopatterning of metals (Al, Au, Bi, and Cr) on various surfaces (silicon, oxides, freestanding SiN cantilevers, and self-assembled monolayers (SAM)) for different mesoscopic experiments. We will present details on the DUV/MEMS process and the application of the full-wafer stencil for specific applications such as templates for molecular electronics, nano-mechanical devices with a 90 MHz resonance frequency, as well as nano-scale Hall-sensor devices.

2004

New photoplastic fabrication techniques and devices based on high aspect ratio photoresist

Grégoire Genolet

This thesis deals with the development of microfabrication technologies based on photoplastic structuring by lithographic and molding techniques. These technologies, combined with an original releasing method, allow for the simple fabrication of pseudo three-dimensional, soft, photoplastic microstructures with features and shapes that are difficult to obtain with standard micro-machining. The photoplastic material used is the SU-8 photoresist, a material that is used increasingly in the growing field of micro-electro-mechanical systems (MEMS). Photoplastic SU-8 microstructure fabrication is based on a combination of multi-layer spin-coating, molding and photolithographic processing of the resist on a prestructured silicon substrate. The final product is obtained by release of the structure from the substrate. This thesis describes several SU-8 microstructures which have been developed with an emphasis on atomic force microscopy (AFM) and scanning-near field optical microscopy (SNOM) probes. Scanning probe microscopy is a well-established technique for surface analysis, but batch-fabricated, low-cost probes still remain a challenging issue. Using a polymer for the cantilever facilitates the realization of mechanical properties that are difficult to achieve with classical silicon technology. The design, fabrication and testing of single lever and cassettes of multiple single-lever probes are presented and demonstrates the potential for fabrication structures with complicated shape and features. The fabrication process for SU-8 AFM probes is a simple batch process in which the integrated tips and the levers are defined in one photolithography step. Tip radii of curvature smaller than 15 nm have been obtained. The cantilever thickness depends on the spin-coating parameters, hence it can be very well controlled over a full wafer. Photoplastic cantilevers with thicknesses ranging from 1 to 6 μm have been produced. Imaging soft, condensed matter with photo-plastic levers, which uses laser beam deflection sensing, exhibits a resolution that compares well with that of commercially available silicon cantilevers. Lateral resolution of 5–6 nm has been estimated from imaging DNA-plasmid molecules. A vertical resolution of the order of 0.1 nm has been found. A similar fabrication technique was also developed to fabricate photo-plastic tips for SNOM that are to be attached to optical fibers. This technique allows optical apertures to be integrated at the end of the well-defined tip directly by probe fabrication, without the need for any post-processing for the aperture formation. Sub-100 nm aperture have been fabricated using this technique. Simple fabrication, as well as topographical and optical imaging demonstrate the potential of photoplastic-based probes for both AFM and SNOM applications, as well as for future combined probes development. In addition, the fabrication of functional microstructures by using SU-8 processing needs to be combined with other microfabrication techniques. Simple releasing of the molded structures from the substrate is especially of great importance. A sacrificial layer technique based on electrochemical etching enhancement has been developed and combined with the fabrication of the different photoplastic SU-8 probes presented. This technique allows the fast releasing of large microstructures and has been demonstrated by releasing other SU-8 photoplastic microfabricated devices.

EPFL2001

Full-wafer stencils fabricated by a DUV/MEMS process for high-throughput patterning of mesoscopic structures

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

2004

New photoplastic fabrication techniques and devices based on high aspect ratio photoresist

Grégoire Genolet

EPFL2001

Ties between microsystem technology and nano-engineering

Jürgen Brugger, Schahrazede-Lila Mouaziz, Johannes Steen, Marc Antonius Friedrich van den Boogaart

2004