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.
Recent development of the extremely light-weight micro pore optics based on the semiconductor MEMS (Micro Electro Mechanical System) technologies is reported. Anisotropic chemical wet etching of silicon (110) wafers were utilized, in order to obtain a row of smooth (111) side walls vertical to the wafer face and to use them as X-ray mirrors. To obtain high performance mirrors with smooth surfaces and a high aspect ratio, several modifications were made to our previous manufacturing process shown in Ezoe et al. (2005). After these improvements, smooth surfaces with rms roughness of the order of angstroms and also a high aspect ratio of 20 were achieved. Furthermore, a single-stage optic was designed as a first step to multi-stage optics. A mounting device and a slit device for the sample optic were fabricated fully using the MEMS technologies and evaluated.
Synchrotron radiation (SR) stimulated process, which has characteristics of high spatial resolution and low damage, is suitable for nano-processes. Si(111) surface after removal of native oxide by SR stimulated desorption was atomically flat with no damage. If the semiconductor surface is chemically modified and chemical bonds having a weak interaction with the substrate electronic states (a localized electronic state) are formed, for example, such as SiH2 and SiH3, they can be broken (etched) by the SR irradiations. Efficient site specific bone breaking, overwhelming the secondary electron effects, can be expected by a resonant excitations from a core electronic state to a dissociative valence electron state. The excitation energy and polarization tunability, which is unique characteristic of the SR process, will display its power in the nano-process applications which require the atom level control.