J.A. van Kan

ION BEAM LITHOGRAPHY AND NANOFABRICATION: A REVIEW

To overcome the diffraction constraints of traditional optical lithography, the next generation lithographies (NGLs) will utilize any one or more of EUV (extreme ultraviolet), X-ray, electron or ion beam technologies to produce sub-100 nm features. Perhaps the most under-developed and under-rated is the utilization of ions for lithographic purposes. All three ion beam techniques, FIB (Focused Ion Beam), Proton Beam Writing (p-beam writing) and Ion Projection Lithography (IPL) have now breached the technologically difficult 100 nm barrier, and are now capable of fabricating structures at the nanoscale. FIB, p-beam writing and IPL have the flexibility and potential to become leading contenders as NGLs. The three ion beam techniques have widely different attributes, and as such have their own strengths, niche areas and application areas. The physical principles underlying ion beam interactions with materials are described, together with a comparison with other lithographic techniques (electron beam writing a...

Three-dimensional nanolithography using proton beam writing

We report the utilization of a focused mega-electron-volt (MeV) proton beam to write accurate high-aspect-ratio structures at sub-100 nm dimensions. Typically, a MeV proton beam is focused to a sub-100 nm spot size and scanned over a suitable resist material. When the proton beam interacts with matter it follows an almost straight path. The secondary electrons induced by the primary proton beam have low energy and therefore limited range, resulting in minimal proximity effects. These features enable smooth three-dimensional structures to be direct written into resist materials. Initial tests have shown this technique capable of writing high aspect ratio walls of 30 nm width with sub-3 nm edge smoothness.

A novel micro-machining method for the fabrication of thick-film SU-8 embedded micro-channels

In this paper, a novel method to realize embedded micro-channels is presented. The presented technology is based on a direct write technique using proton beams to pattern thick-film SU-8. This proton micro-machining method allows the production of high aspect ratio and complex three-dimensional micro-structures in polymers with aspect ratios of over 100 and 20 using poly(methylmethacrylate) (PMMA) and SU-8 respectively. As the SU-8 is used as a structural material, its mechanical properties have to be characterized. For a start, the Youngs modulus of the proton beam exposed SU-8 is determined using a stylus-type load-deflection method. The second part of this paper describes the underlying theory and method used by the author to determine the Youngs modulus of the proton beam exposed SU-8. Measurements of the SU-8 micro-structures show that the Youngs modulus is dependent on the proton beam exposure dose. An exposure dose of 9.5 nC mm-2 results in an average Youngs modulus value of 4.254 GPa.

Fabrication of high aspect ratio 100nm metallic stamps for nanoimprint lithography using proton beam writing

We report a way of fabricating high-quality void-free high-aspect-ratio metallic stamps of 100nm width and 2μm depth, using the technique of proton beam writing coupled with electroplating using a nickel sulfamate solution. Proton beam writing is a one-step direct-write process with the ability to fabricate nanostructures with high-aspect-ratio vertical walls and smooth sides, and as such has ideal characteristics for three-dimensional (3D) stamp fabrication. Nanoindentation and atomic force microscopy measurements of the nickel surfaces of the fabricated stamp show a hardness and side-wall roughness of 5GPa and 7nm, respectively. The fabricated 100nm 3D stamps have been used to transfer test patterns into poly(methylmethacrylate) films, spin coated onto a silicon substrate. Proton beam writing coupled with electroplating offers a process of high potential for the fabrication of high quality metallic 3D nanostamps.

Erbium-doped waveguide amplifiers fabricated using focused proton beam writing

Buried channel waveguides were fabricated in Er3+–Yb3+ codoped phosphate glasses using focused proton beam writing. Proton ion doses in the range of 1014–1015 ions/cm2 and 2.0 MeV energy were used. The waveguides were located 38 μm below the substrate surface and are in excellent agreement with the transport and range of ions in matter simulation. The waveguide properties were measured, and the fluorescence spectra and optical gain of the waveguides were characterized. The maximum net gain of the waveguide amplifiers at 1.534 μm wavelength was measured to be ∼1.72 dB/cm with 100 mW pump power at 975 nm wavelength.

Proton beam writing of low-loss polymer optical waveguides

Proton beam writing is a direct-write micromachining technique capable of producing three-dimensional microstructures with straight and smooth sidewalls. Low-loss channel waveguides in SU-8, a chemically amplified negative tone resist, were fabricated using a focused submicron beam of 2.0 MeV protons with a dose of 30 nC/mm2 and a beam current of approximately 2 pA. Propagation losses of approximately (0.19±0.03) dB/cm were measured at 632.8 nm wavelength. Waveguides of arbitrary design can be easily fabricated using proton beam writing, making the technique ideal for the rapid prototyping of optical circuits.

Resist materials for proton micromachining

Abstract The production of high aspect ratio microstructures is a potential growth area. The combination of deep X-ray lithography with electroforming and micromolding (i.e. LIGA) is one of the main techniques used to produce 3D microstructures. The new technique of proton micromachining employs focused MeV protons in a direct write process which is complementary to LIGA, e.g. micromachining with 2 MeV protons results in microstructures with a height of 63 μm and lateral sub-micrometer resolution in PMMA resist. The aim of this paper is to investigate the capabilities of proton micromachining as a lithographic technique. This involves the study of different types of resists. The dose distribution of high molecular weight PMMA is compared with three other types of resist: First the positive photo resist AZ P4620 will be discussed and then PMGI SF 23, which can be used as a deep UV, e-beam or X-ray resist. Finally SU-8, a new deep UV negative type of chemically amplified resist will be discussed. All these polymers are applied using the spin coating technique at thicknesses of between 1 and 36 μm

Micromachining using focused high energy ion beams: Deep Ion Beam Lithography

Abstract The combination of deep X-ray lithography with electroforming and micromoulding (i.e., LIGA) has been shown to offer high potential for the production of high aspect-ratio microstructures. The LIGA technique, employing synchrotron light and a suitable X-ray mask, allows production of 3D microstructures in PMMA with aspect ratios around 100. Here we demonstrate that the novel technique of Deep Ion Beam Lithography (DIBL), a direct process utilizing a focused beam of MeV ions scanned in a predetermined pattern over a suitable resist material, can produce three dimensional microstructures with sub-micrometer feature sizes. Microstructures extending up to 100 μm from the substrate with aspect ratios approaching 100 can be produced. Multiple exposures at different ion energies allow production of multilayer structures in single resist layers of SU-8, a newly developed, chemically accelerated, negative tone, near UV, photoresist.

Fabrication of buried channel waveguides in photosensitive glass using proton beam writing

We report our results on the fabrication and characterization of buried, channel optical waveguides in photosensitive Foturan™ glass using a high energy proton beam. Waveguides were fabricated with varying fluence, and the propagation loss and refractive index change were measured. Near-field mode data measured at 632.8nm showed that waveguiding could be achieved for all fluences ranging from 1014to1016protons∕cm2. The maximum positive refractive index change of 1.6×10−3 was measured for the highest fluence. The waveguide propagation losses measured using the scattering technique were estimated to be in the range of 8.3–12.9dB∕cm, increasing with proton fluence.

Proton beam micromachining: a new tool for precision three-dimensional microstructures

Proton beam micromachining (PBM) is a novel technique for the production of high aspect-ratio three-dimensional (3D) microcomponents. PBM is a direct write process in which a focused beam of MeV protons is scanned in a pre-determined pattern over a suitable resist material (e.g. PMMA or SU-8) and the latent image formed is subsequently chemically developed. One strategy for full exploitation of the advantages offered by PBM is the conversion of the microstructures produced in the resist to metallic components by electrolytic plating. The metallic structures may then be used in a bulk production process, e.g. microstamping or micromolding. In this paper we describe the introduction of a beam blanking system to improve the quality of microstructures, and present data showing that electrolytic Ni plating of proton beam micromachined resist structures result in well defined and smooth metallic microstructures.