Yuichiro Ezoe

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.

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

Mems open the way to ultra-lightweight and low-cost x-ray optics

Grazing-incidence x-ray optics are widely used in biological diagnostics, nuclear physics, and space research. However, the usable grazing-incidence angle is small, less than several degrees at 1keV. Therefore, to collect photons from weak sources in x-ray astronomy, multiple mirrors with smooth surfaces, comparable to the x-ray wavelength, are prepared one by one. The number of mirrors ranges from a few to thousands; fabricating all these mirrors is costly and labor intensive and, as the number of mirrors increases, the telescope becomes heavy and more expensive to launch. To drastically decrease these fabrication and launching costs for future missions, new ideas are necessary. How can we decrease the telescope weight? One solution is to shrink it. If we shrink the size of the mirrors in the telescope by a factor of A, the mirror weight decreases by A. To keep the same effective area, we have to increase the mirror number by A. Consequently, the telescope weight will decrease by A. This is the basic idea of so-called micro-pore optics. The limit of this size reduction comes from x-ray diffraction, which is determined by the x-ray energy and the distance between the mirrors. Micro-pore optics have μmto mm-scale through holes and use their side walls as x-ray mirrors. Our approach is to use the semiconductor micro-structure fabrication technologies (microelectro-mechanical systems, or MEMS) for micro-pore optics. We use anisotropic wet etching and deep reactive ion etching (D-RIE) to obtain reflection planes and accurately defined optic shapes, respectively. Figure 1 illustrates the concept of MEMS x-ray optics. We etch silicon (110) wafers in KOH solution, to fabricate smooth silicon (111) planes vertical to the wafer face that we use as x-ray mirrors. Because the crystal plane is limited in a certain direction, we Figure 1. MEMS x-ray optics consist of silicon wafer mirror chips arranged on a pair of optic mounts.

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.

Research and development of MEMS x-ray optics

Development of a new light-weight and low-cost micro pore optics is reported. Utilizing anisotropic chemical wet etching of MEMS (Micro Electro Mechanical System) technology, a number of smooth sidewalls are obtained at once. These sidewalls are potential X-ray mirrors. As a first step of R&D, basic characters of sidewalls such as surface roughness and X-ray reflectivity are experimentally studied. Rms-roughness of 10 ~ 20Å is confirmed in a KOH-etched wafer. Furthermore, the X-ray reflection is for the first time detected at Mg Kα 1.25 keV. Based on the obtained results, numerical simulations of four-stage MEMS X-ray optics are performed for future satellite mission.

Recent development of micropore optics using MEMS technologies

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.