Takanori Katoh

High aspect ratio micromachining Teflon by direct exposure to synchrotron radiation

Micromachining Teflon was achieved by direct exposure to synchrotron radiation and the microstructures made had the smallest surface detail down to 20 μm with structural height of more than 200 μm, that is, aspect ratio on the order of 10. The quality of micromachining Teflon by this process was found to be critically dependent on photon flux of the synchrotron radiation. Analysis of the mass distribution of gaseous species formed upon this process suggested that photochemical processes rather than pyrolytic processes may still dominate.

Direct writing for three-dimensional microfabrication using synchrotron radiation etching

This paper presents rapid three-dimensional microfabrication technologies for PTFE by direct writing with the TIEGA process, a LIGA-like process which replaces hard X-ray lithography with synchrotron radiation (SR) direct photo-etching. The etching rates of this process are of the order of 6-100 /spl mu/m/min, depending on the photon flux of the SR light. An X-ray lathe has been modified into an SR etching lathe to form cylindrical, helical, pyramidal, ellipsoidal, and other nonplanar objects. A metallic wire covered with a PTFE sheet is rotated and/or moved while being irradiated with SR through a mask. Moreover, direct writing without using any masks has been developed, by combining a scanning stage with a high degree of freedom under an He atmosphere, for creating any microstructure. The capabilities of these technologies and initial fabrication results are described here.

Synchrotron radiation ablative photodecomposition and production of crystalline fluoropolymer thin films

Deposition of crystalline thin films of polytetrafluoroethylene (PTFE) was carried out on Si(100) substrates by synchrotron irradiation of a PTFE target in vacuo. In situ mass spectrometric analysis of gaseous species evolved during the irradiation shows that, different from the laser ablation of PTFE for the deposition, the SR‐induced reactions should be ablative photochemical decomposition (APD) rather than photothermal unzipping decomposition, yielding saturated fluorocarbons rather than monomers as the main gaseous products. Detection of a trace of CF3 in the deposited films by XPS and FTIR was consistent with our APD mechanism. In our processing, an increase in the target temperature made great improvements including considerable enhancement of the deposition rates, reduction of the CF3 component, and achievement of the crystalline features closer to the PTFE target, whereas an increase in the substrate temperature made the film surface rough.

Synchrotron Radiation Micromachining of Polymers to Produce High-Aspect-Ratio Microparts

Synchrotron radiation (SR) direct micromachining of polymers was developed and high-aspect-ratio microparts of polytetrafluoroethylene (PTFE) were made. The limitation of critical dependence on the photon flux was eliminated by processing PTFE at a temperature of 200–250°C, so that the process was greatly simplified and the aspect-ratios were improved with reducing the smallest surface detail to less than ten microns and achieving the largest structural height of one thousand microns. The decomposition mechanism was discussed with a comparison between the SR micromachining and laser ablation.

Micromachining of crosslinked PTFE by direct photo-etching using synchrotron radiation

Micromachining of crosslinked PTFE (polytetrafluoroethylene) using synchrotron radiation direct photo-etching method has been demonstrated. High aspect-ratio microfabrication was carried out. The etching rate of crosslinked PTFE was higher than that of non-crosslinked PTFE. Through the etching rate measurements of various samples, it was found that synchrotron radiation etching rate of crosslinked PTFE only depends on the degree of crosslinking, neither molecular weight nor crystallinity. The effect of molecular motion on etching process was discussed from temperature dependence data on etching rate. Furthermore, the surface region of synchrotron radiation irradiated sample was investigated by Fourier transform infrared spectroscopy and the experimental result showed that the modification induced by synchrotron radiation proceeded before desorption.

Deposition of Teflon-polymer thin films by synchrotron radiation photodecomposition

Abstract Thin films of Teflon-polymers such as PTFE (polytetrafluoroethylene), FEP (polytetrafluoroethylene-co-hexafluoro-propylene) and PFA (polytetrafluoroethylene-co-perluoroalkoxy vinyl ether) were deposited on Si(100) substrates by synchrotron radiation (the critical wavelength of 1.5 nm) etching of their corresponding starting materials in vacuo. Analysis of the deposited films has been carried out with X-ray photoelectron spectroscopy (XPS), Fourier transfer infrared (FTIR) spectroscopy as well as X-ray diffraction (XRD) and their surface morphologies were observed under scanning electron microscopy (SEM). For the deposition of the Teflon-polymer films, the processing with the synchrotron radiation photo-etching was compared with that using laser ablation and significant differences between them are discussed.

Focusing Hard X-Ray with a Single Lens

We show that a 10 keV X-ray has been focused into 3.4–8.4 µm at a focal length F=0.4–1.5 m with a single refractive lens and such X-ray microbeams can be generated in array. For the beam from a synchrotron radiation source, which typically had a diameter =100 µm, transmissions of our lenses were measured to be T=54–85%. X-ray imaging of a copper mesh was carried out with a magnification of about 5 in one dimension and the imaging resolution was evaluated to be 0.9 µm. Our lenses have performed well under a flux of 1.1×1011 photonss-1mm-2, showing no visible damage due to the X-ray exposure.

Surface modification of polytetrafluoroethylene by synchrotron radiation

Abstract Surface modification of polytetrafluoroethylene (PTFE) films by the irradiation using synchrotron radiation (SR) below the melting temperature was studied. The changes in chemical structures, surface compositions and thermal properties of the SR-irradiated PTFE were examined by solid-state 19F NMR, X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC), respectively. In order to investigate the degree of modification as a function of depth from the irradiated surface, some PTFE thin films were stacked in layers under vacuum and then they were irradiated with SR. It was found that crosslinking reaction was induced by SR-irradiation in the solid-state within 50 μm from the exposed surface and chain scission was dominant at deeper layers.

3-dimensional micromachining of PTFE using synchrotron radiation direct photo-etching

In order to fabricate highly functional microdevices for MEMS, three-dimensional (3D) micromachining that can form certain round or curved structures is required. Recently, a high aspect ratio micromachining process using synchrotron radiation (SR) direct photo-etching of polymers without any process gases, the so called TIEGA (Teflon included etching galvanicforming), has been developed. The etching rate is of the order of 10-100 /spl mu/m/min. Therefore, the processing for a 1000 /spl mu/m-depth microstructure takes about 10 minutes, much shorter than that required for the deep X-ray lithography (LIGA) process. Moreover, it is free from problems of sticking due to the surface tension of the developer, the rinsing process etc., as SR etching is a completely dry process. Due to the high processing speed and smoothness of the etched surfaces, SR etching might have a potential for 3D micromachining by combining a scanning stage with a high degree of freedom. It is expected that microstructures formed by SR etching will be applied not only to highly functional mircodevices, but also in the biomedical field, due to the material characters of PTFE. In this paper, we propose SR etching as a new approach to form 3D microstructures of PTFE and describe results of preliminary experiments for 3D micromachining.

Low-Resistivity Highly Transparent Indium-Tin-Oxide Thin Films Prepared at Room Temperature by Synchrotron Radiation Ablation

High-transparency, low-electrical-resistivity indium-tin-oxide (ITO)thin films were prepared on quartz substrates using synchrotron radiation ablation at room temperature. The films had a low resistivity (ρ=1.3×10-4 Ωcm) and high-transparency properties in the visible region (T = 83% at 550 nm). X-ray diffraction patterns indicate that the crystalline ITO film was obtained by room-temperature deposition.