We demonstrated fabricating a needle array of polycarbonate (PC) and polymethyl methacrylate (PMMA) by using a 3-D LIGA (lithografie, galvanoformung, abformung) process. The diameter of the bottom of the needle was about 50 µm, and the height was 135 µm. Although the LIGA process is commonly applied for making structures with vertical sidewalls, the use of an x-ray grayscale mask in the LIGA process has made it possible to fabricate needle-shaped structures. The x-ray grayscale mask was composed of a Si x-ray absorber and an SU-8 membrane. The sidewall of the x-ray absorber was diagonally processed by Si tapered-trench-etching technology such that the transmission intensity of x rays could be changed locally. The x-ray lithography experiment was executed by using this x-ray grayscale mask on a beamline BL-4 in the TERAS synchrotron radiation facility at National Institute of Advanced Industrial Science and Technology (AIST). By using this facility, a PMMA resist master with three-dimensional (3-D) structures was made. A Pt layer was then sputter-deposited as a seed layer on the PMMA resist master, and a Ni mold was fabricated by electroforming technology. In addition, a needle array of PC and PMMA was produced by hot embossing technology. Self-assembled monolayers (SAMs) of a release agent were required on the surface of the mold pattern to achieve a complete molding. Thus, we succeeded in extending the LIGA process to three dimensions by the use of an x-ray grayscale mask.
We have succeeded in fabricating a needle array of polycarbonate by using a three-dimensional LIGA process. The diameter of the bottom of the needle was about 50 μm, and the height was 135 μm. Although a usual LIGA process has been employed to form structure only with vertical sidewalls, it has now become possible to fabricate needle shape structure by employing a technology that combines X-ray gray mask with the LIGA process. The X-ray gray mask was composed of Si X-ray absorbers and a SU-8 membrane. The sidewall of the X-ray absorber was diagonally processed by Si tapered-trench-etching technology where the transmission intensity of X-rays could be varied locally. An X-ray lithography experiment was executed by using the X-ray gray mask on a beamline BL-4 in TERAS synchrotron radiation facility at AIST. Using this technology a PMMA resist master with three-dimensional structures was made. A Pt layer was sputter deposited as a seed layer on the PMMA resist master, and a Ni mold was fabricated by an electroforming technology. In addition, needle arrays of polycarbonate (PC) and of polymethyl methacrylate (PMMA) were produced by hot embossing technology. Thus, we succeeded in extending the LIGA process to a three-dimensional process capability by employing X-ray gray mask.
We propose a new fabrication method of an x-ray grayscale mask using micro-electro-mechanical-systems (MEMS) technologies, and also report on successful fabrication of three-dimensional (3D) microstructures on a polymethylmethacrylate (PMMA)sheet by using only a single x-ray exposure. We showed that silicon can be diagonally etched by optimizing the etching condition in a reactive-ion-etching (RIE) process. It is well known that the absorbers of an x-ray mask can be made into 3D shapes. Here, we describe how this process can be extended to fabricate an x-ray grayscale mask by using a tapered-trench-etching technique. With such a mask, we carried out experiments on x-ray lithography (XRL) using a beam line BL-4 in the synchrotron radiation facility TERAS of National Institute of Advanced Industrial Science and Technology (AIST). The dose energy used for the exposure was 150 mA·h, and the subsequent resist development was done by a GG developer at room temperature for 16 h. The sidewalls in the upper part of the PMMA resist structure were inclined and rounded. In particular, the shape of the PMMA resist structure of the lines with 20-μm width (also referred as 20-μm lines) could be processed to achieve a halberd-like shape. Thus, the effectiveness of the grayscale mask in adjusting to the varying thicknesses of absorber was confirmed by XRL experiments. Moreover, we showed that the final shape of PMMA resist structures after XRL was predictable by calculations.
We proposed a new fabrication method of an X-ray gray mask using MEMS technologies, and we also succeeded in
fabricating three-dimensional microstructures on a PMMA sheet by using only a single X-ray exposure. Silicon can be
diagonally etched by optimizing the etching condition in a RIE process. We thought X-ray absorbers of an X-ray mask
were processed to three-dimensional shape, and a gray mask for the X-ray lithography was fabricated by using a tapered-trench-
etching technique. Then, we experimented on the X-ray lithography using the beamline BL-4 in the synchrotron
radiation facility TERAS of AIST. The total dose energy was 150 mAxh and the development was performed at the room
temperature for 16 h using a GG developer. Sidewalls in the upper part of the PMMA resist structure were inclined and
rounded. Especially, the shape of the PMMA resist structure of the line width 20 μm was able to be processed to shape
like the target. Thus, the effectiveness of the gray mask that adjusted the thickness of absorber was confirmed by X-ray
lithography experiments. Moreover, we experimentally showed that the final shape of PMMA resist structures after the
X-ray lithography was predictable by the calculation.
Two-dimensional photonic crystals of titanium dioxide are predicted to have many advantages over semiconductor photonic crystals, e.g., silicon and GaAs: in particular, low optical loss in the near infrared region used for optical communication, low thermal expansion, and a refractive index which is close to that of optical fibers. However, it is difficult to create micro-nano structures in titanium dioxide, since semiconductor micro-fabrication techniques cannot be applied to titanium dioxide. As the first step, we calculated the photonic band gap of titanium dioxide rod-slab on SiO2. Band gap percent against thickness of the rod-slab was also examined. Finally, we confirmed the most suitable structure for 2D photonic crystals. A deep X-ray lithography technique was employed to create a very deep and precise template. Liquid-phase deposition was then used to faithfully deposit a tightly packed layer of titanium oxide onto the template. Finally, the template was selectively removed to obtain a photonic nano-structure. A template for the most appropriate three dimensional structure was also fabricated using the method proposed by Yablonovitch. By employing the same method, we successfully obtained the 3D structure of TiO2.
Ablation from amorphous SiO2 (silica glass) was induced using ArF excimer laser. Threshold fluences of 2.5 J/cm2 was apparently necessary to commence ablation by a single pulse. Ablation was also observed after the number of pulses at below the threshold fluence. Microscopic structural change was examined with x-ray photoelectron spectroscopy, Raman spectroscopy, optical absorption spectroscopy in vacuum ultraviolet (vuv) region. A regular puckered four membered ring as well as Si3+ structure were introduced with irradiation. Repeat of flash heating and quenching by the pulse laser irradiation might generate regular puckered four membered rings and Si3+ species in silica glass. Increase of Si3+ concentration would reduce threshold fluence and number of pulse for ablation.
Relatively new modification methods for densification of sol- gel derived silica films using electronic excitations and water vapor were investigated. Dried silica gel films were found to be densified by vacuum ultraviolet irradiation and He+ ion implantation. The densification is deduced to be ascribed to dehydration and cleavage of the strained bonds through electronic excitations induced by the irradiations. The structure of the irradiated silica films is similar to that of silica glass densified under a high pressure. The exposure to water vapor at 80 degrees - 180 degrees Celsius is also effective in densification and dehydration of sol-gel silica films. These methods are expected to be valuable for fabrication of dense silica films at low temperatures. However, the silica films densified by the irradiations and the exposure are suggested to contain a strained network because a subsequent annealing above 300 degrees Celsius induced structural changes through a thermal relaxation.
A new type of polarizing undulator proposed and developed in the Electrotechnical Laboratory which produces high brilliant, quasi-monochromatic, wavelength-variable from the soft x-ray to infrared region, and polarized synchrotron radiation of any ellipticity was installed in the electron storage ring TERAS and NIJI-II. The synchrotron radiations emitted from these polarizing undulators were used for various research fields. In this review we report the radiation properties of the polarizing undulator, the development of magnetic circular dichroism instrument in VUV region for magnetic materials, the development of polarizing microscope for circular differential imaging, the absolute asymmetric synthesis study, and the others.
Photo-induced changes in structure of sol-gel derived SiO2 films were studied in order to explore a possibility of densification of sol-gel films at room temperature using energetic photons. Gel films which were produced on silicon substrates by dip-coating of sols prepared through hydrolysis of tetraethoxysilane were subjected to synchrotron radiation at room temperature. Structural changes of the gel films were investigated by ellipsometry and infrared spectroscopy. The radiation resulted in an increase in refractive index, a decrease in thickness of the films and a loss of OH groups. Increase in temperature of the films was less than 50 degree(s)C during the irradiation. The results indicate that ultraviolet lights induce densification of gel films through electronic excitation.
Second harmonic generation and the Bragg reflection gratings building up have attracted interest as novel nonlinear optical properties of SiO2:GeO2 fibers. The presence of optical absorption band centered at 5 eV is indispensable for emergence of these functions. In this article, we review a series of our recent works on optical properties of the 5 eV band and structural models for the responsible defects. A way to enhance concentrations of the defect is also shown.