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To provide coherent x-ray sources for probing the dynamic structures of solid or liquid biological substances on the picosecond timescale, a high-aspect-ratio x-ray resonator cavity etched from a single crystal substrate with a nearly vertical sidewall structure is required. Although high-aspect-ratio resonator cavities have been produced in silicon, they suffer from unwanted multiple beam effects. However, this problem can be avoided by using the reduced symmetry of single-crystal sapphire in which x-ray cavities may produce a highly monochromatic transmitted x-ray beam. In this study, we performed nominal 100 µm deep etching and vertical sidewall profiles in single crystal sapphire using inductively coupled plasma (ICP) etching. The large depth is required to intercept a useful fraction of a stopped-down x-ray beam, as well as for beam clearance. An electroplated Ni hard mask was patterned using KMPR 1050 photoresist and contact lithography. The quality and performance of the x-ray cavity depended upon the uniformity of the cavity gap and therefore verticality of the fabricated vertical sidewall. To our knowledge, this is the first report of such deep, vertical etching of single-crystal sapphire. A gas mixture of Cl2/BCl3/Ar was used to etch the sapphire with process variables including BCl3 flow ratio and bias power. By etching for 540 min under optimal conditions, we obtained an x-ray resonant cavity with a depth of 95 µm, width of ~30 µm, gap of ~115 µm and sidewall profile internal angle of 89.5°. The results show that the etching parameters affected the quality of the vertical sidewall, which is essential for good x-ray resonant cavities.

We utilized the conventional planar fabrication technique and the electrochemical etching method to prepare porous Si layers in the p-type region of a p-n junction, which makes the study on the transverse transport property of this material possible. The junctions were fabricated by low energy ion implantation, with porous Si formed perpendicular to the junction and between two metal contacts. This structure confines currents to the direction parallel to the surface. Distinct photoconductivity and photovoltaic effects have been clearly revealed from the I-V curves.

Microwave remote plasma oxidation system was used to study the oxidation of SiGe samples at low temperatures. The extent of Ge segregation at oxide/SiGe interface was investigated by using SIMS depth profiles. By comparing the segregation factors, the Ge segregation in the samples oxidized by atomic oxygen at 500 °C was much less than that in the samples oxidized without plasma at 950 °C. The Ge segregation has been largely suppressed by atomic oxygen oxidation at lower temperature.