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

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.

High-throughput surface patterning with wafer-sized stencils fabricated by a DUV/MEMS process

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

The endeavour to develop nanodevices demands for patterning methods in the nanometer scale. The continuous improvement in lithography methods based on deep UV (DUV), X-ray, or electron beam exposure allow for further progress in integrated circuit hardware manufacturing for the coming years. To bring nanodevices to the market, however, there is a need for fast, low-cost replication nanopatterning methods. In addition, an increased flexibility of the nanopatterning methods is important for the engineering of multimaterial and multifunctional nano/micro-electro-mechanical systems (NEMS/MEMS), such as polymer-based electronic and sensor devices, 3D microfluidic systems, and bio-analytical systems. The above-mentioned high-end patterning methods are all based on photolithography and etching, limiting the flexibility in substrate and material combinations. In addition, they have the drawback of the use of high-cost equipment. A series of alternative, complementary surface patterning methods are currently being developed that do not rely on photoresist exposure and thin-film etching steps, e.g. 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 , . We present here the advances towards a full-wafer (100 mm) DUV/MEMS-based nanostencil to allow high-throughput, large-area nanopatterning of mesoscopic structures (10^9 - 10^5 m). 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). Figure 1 shows the mid-process details of 200 nm DUV patterns after the RIE transfer into the 500-nm thick SiN layer. Patterning of nano-scale structures using stencils allows for a large choice of materials and surfaces to be nanopatterned, since it is a non-contact method and 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 applications (molecular electronics, nano-mechanical devices with a 90 MHz resonance frequency , as well as nano-scale Hall-sensor devices). Unconventional substrates for (Bio) MEMS and NEMS have also been applied such as highly ordered pyrolytic graphite (HOPG), polydimethylsiloxane (PDMS), and SU-8.

2004

DUV/MEMS based stencils for full-wafer scale, resistless, patterning of mesoscopic structures

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

Photoresist-based lithography has major limitations if applied to MEMS with mechanically fragile and chemically functionalized surfaces. As remedy, new alternative and complementary nanopatterning methods have been developed, such as thermo-mechanical indentation (nanoimprint lithography), local deposition of molecular layers (soft-lithography), and shadow-mask deposition (nano-stenciling). Nano-stenciling is a resistless pattering method based on direct, local deposition of material through a solid-state silicon nitride (SiN) membrane applicable on arbitrary surfaces. Patterning of mesoscopic structures (10^-9 – 10^-5 m) through focused ion beam (FIB) fabricated stencils has been demonstrated within a limited area. In order to increase area size and throughput of the nanostencil method we developed a 4” wafer-scale DUV/MEMS fabrication process. The mesoscopic patterns were first defined by a 4x reduced projection exposure using an ASML wafer stepper and transferred into the SiN layer by means of reactive ion etching. The membranes were released by wafer-through etching using KOH. Nano-scale structuring using stencil masks allows a large choice of materials and surface to be nanopatterned, as no etch-steps need to be applied. We have studied nanopatterns of various materials such as Al, Au, Bi and Cr for various mesoscopic experiments, on various surfaces such as silicon, oxides, but also on freestanding cantilevers and self-assembled monolayers (SAM). In the presentation we will show 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 90 MHz resonance frequency, as well as nano-scale Hall-sensor devices.

2004

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

High-throughput surface patterning with wafer-sized stencils fabricated by a DUV/MEMS process

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

2004

Ties between microsystem technology and nano-engineering

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

2004