Takayuki Takano

Micropore x-ray optics using anisotropic wet etching of (110) silicon wafers

To develop x-ray mirrors for micropore optics, smooth silicon (111) sidewalls obtained after anisotropic wet etching of a silicon (110) wafer were studied. A sample device with 19 microm wide (111) sidewalls was fabricated using a 220 microm thick silicon (110) wafer and potassium hydroxide solution. For what we believe to be the first time, x-ray reflection on the (111) sidewalls was detected in the angular response measurement. Compared to ray-tracing simulations, the surface roughness of the sidewalls was estimated to be 3-5 nm, which is consistent with the atomic force microscope and the surface profiler measurements.

Large Arrays of TES X‐ray Microcalorimeters for Dark Baryon Search

Arrays of transition edge sensor (TES) X‐ray microcalorimeters can provide a high energy resolution and a large area necessary for future dark baryon search missions such as DIOS (Diffuse Intergalactic Oxygen Surveyor). In the current design, the energy resolution of 2 eV at 0.3–1.5 keV and the geometrical area of 1 cm2 are required for DIOS. As an R&D study, we fabricated a 16×16 Ti/Au bilayer TES array without an absorber, and achieved the energy resolution of 4.4±0.2 eV at 5.9 keV. Considering the recent experimental results on so‐called excess noise, we investigated a detailed design of the TES array for DIOS. We concluded that we need a at least 20×20 pixel array consisting of 250 μm‐square TESs and 500 μm‐square mushroom‐type Bi/Au absorbers. We discussed technical issues to manufacture such a large format array.

Fabrication of a needle array using a Si gray mask for x-ray lithography

The authors fabricated a gray mask for x-ray lithography using a silicon-on-insulator wafer by employing microelectronic mechanical system fabrication technologies. Generally, when a three-dimensional (3D) resist structure is fabricated using x-ray lithography, an x-ray mask is rotated or scanned to adjust the exposure time of x ray irradiating the resist. However, the authors maintain that 3D resist structure can be made not only by manipulating the x-ray exposure time but also it could be accomplished rather more effectively by making basic changes in the very structure of x-ray masks. Here they present a procedure for making such a mask. Moreover, the use of such a mask could simplify the x-ray lithography process and make it operator friendly. The structure proposed here is known as gray mask and comprises of Si x-ray absorber on SU-8 membrane. Such a structure, unlike stencil mask structure, allows the formation of pattern with isolated features. The x-ray gray mask was evaluated on a beam line BL-4 ...

Evaluation of the soft x-ray reflectivity of micropore optics using anisotropic wet etching of silicon wafers

The x-ray reflectivity of an ultralightweight and low-cost x-ray optic using anisotropic wet etching of Si (110) wafers is evaluated at two energies, C K(alpha)0.28 keV and Al K(alpha)1.49 keV. The obtained reflectivities at both energies are not represented by a simple planar mirror model considering surface roughness. Hence, an geometrical occultation effect due to step structures upon the etched mirror surface is taken into account. Then, the reflectivities are represented by the theoretical model. The estimated surface roughness at C K(alpha) (approximately 6 nm rms) is significantly larger than approximately 1 nm at Al K(alpha). This can be explained by different coherent lengths at two energies.

Demonstration of fabricating a needle array by the combination of x-ray grayscale mask with the lithografie, galvanoformung, abformung process

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.

Fabrication and evaluation of a grayscale mask for x-ray lithography using MEMS technology

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 mi- crostructures on a polymethylmethacrylate PMMAsheet 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 pro- cess. It is well known that the absorbers of an x-ray mask can be made into 3-D 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 lithog- raphy XRL using a beam line BL-4 in the synchrotron radiation facility TERAS of National Institute of Advanced Industrial Science and Technol- ogy 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-m width also referred as 20-m lines could be processed to achieve a halberd-like shape. Thus, the effectiveness of the grayscale mask in adjusting to the varying thick- nesses of absorber was confirmed by XRL experiments. Moreover, we showed that the final shape of PMMA resist structures after XRL was predictable by calculations.

Design and Fabrication of a MEMS X-ray Optic using Anisotropic Wet Etching of Si Wafers

In this paper, we report on the development of X-ray optics using anisotropic wet etching of silicon wafers. Both X-ray mirrors and an optics mount are fabricated fully using the MEMS technologies

Fabrication of a Si stencil mask for the X-ray lithography using a dry etching technique

We fabricated a Si stencil X-ray mask only in a dry process without electroplating and chemical etching. An X-ray absorber of thickness 30 µm with vertical sidewalls was able to be fabricated. In addition, we succeeded in demonstration of the X-ray lithography in the beam line BL-4 of the synchrotron radiation facility TERAS of AIST. Line and space patterns of line width 2 - 200 µm were transcribed plainly on the surface of a PMMA sheet. It was confirmed that the edge of PMMA microstructures was sharp. There is a possibility that this Si stencil mask can be applied as an X-ray mask for the deep X-ray lithography.

A Micromachined X-Ray Collector for Space Astronomy

A novel micromachined X-ray collector using anisotropically etched Si (111) planes as X-ray mirrors for future astronomical missions is reported. Mirrors, fabricated using dynashock-type ultrasonic waves, have very smooth surfaces with an rms roughness of nm or less. After the etching, mirror chips were cut from the wafer with a dicing machine and adhered to a mount formed by deep reactive ion etching, in order to collect parallel X-ray beam (0100 mm) on a tiny focus (phi 4 mm). The first light image was successfully obtained at Al Kalpha 1.49 keV in a ISAS 30 m-long beam line.

The first light of a single-stage MEMS x-ray optic

The first light of a ultra-lightweight and low-cost micro-pore X-ray optic utilizing MEMS (Micro Electro Mechanical Systems) technologies is reported. Our idea is to use silicon (111) planes appeared after anisotropic wet etching of silicon wafers. As a first step to Wolter type-1 optics, a single-stage optic with a focal length of 750 mm and a diameter of 100 mm was designed for energies below 2 keV. The optic consists of 218 mirror chips for X-ray reflection and an optic mount for packing these chips. Design parameters and required fabrication accuracies were determined with numerical simulations. The fabricated optic satisfied these accuracies and its imaging quality was measured at the ISAS X-ray beam line at Al Kα 1.49 keV. A focused image was successfully obtained. The measured image size of ~4 mm was consistent with the chip sizes. The estimated X-ray reflectivity also could be explained by micro-roughness of less than 3 nm and geometrical occulting effect due to large obstacle structures on the reflection surface.