A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Adaptation of an STMS Structure as a Probe Type Structure <s> Ions of kiloelectron volt energies incident on a solid surface produce a number of effects: several atoms are sputtered off, several electrons are emitted, chemical reactions may be induced, atoms are displaced from their equilibrium positions, and ions implant themselves in the solid, altering its properties. Some of these effects, such as sputtering and implantation are widely used in semiconductor device fabrication and in other fields. Thus the capability to focus a beam of ions to submicrometer dimensions, i.e., dimensions compatible with the most demanding fabrication procedures, is an important development. The focused ion beam field has been spurred by the invention of the liquid metal ion source and by the utilization of focusing columns with mass separation capability. This has led to the use of alloy ion sources making available a large menu of ion species, in particular the dopants of Si and GaAs. The ability to sputter and to also induce deposition by causing breakdown of an adsorbed film has produced an immediate application of focused ion beams to photomask repair. The total number of focused ion beamfabrication systems in use worldwide is about 35, about 25 of them in Japan. In addition, there are many more simpler focused ion beam columns for specialized uses. The interest is growing rapidly. The following range of specifications of these systems has been reported: accelerating potential 3 to 200 kV, ion current density in focal spot up to 10 A/cm2, beam diameters from 0.05 to 1 μm, deflection accuracy of the beam over the surface ±0.1 μm, and ion species available Ga, Au, Si, Be, B, As, P, etc. Some of the applications which have been demonstrated or suggested include: mask repair, lithography (to replace electron beamlithography), direct, patterned, implantationdoping of semiconductors, ion induced deposition for circuit repair or rewiring, scanning ion microscopy, and scanning ion mass spectroscopy. <s> BIB001 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Adaptation of an STMS Structure as a Probe Type Structure <s> Two processes have been developed to enable both focused ion beam (FIB) repair of advanced masks and FIB device modification. Silicon dioxide- based films can be deposited by rastering a focused ion beam across a surface onto which a combination of siloxane and oxygen gases have been adsorbed. The deposited material exhibits sufficient dielectric strength to be used for FIB modification of devices. Applications of FIB dielectric deposition include: (1) Local passivation. (2) Backfilling vias to allow for probing buried metal layers without contacting exposed metal layers. (3) Electrical isolation between crossed metal lines. (4) Optically transparent films for phase shift mask repair. In the first half of this paper we discuss the gas delivery system, and the material and electrical characteristics of the films, as well as describing typical device modifications using FIB dielectric films. In the second half of the paper we describe a process for deposition of tantalum- containing films using a tantalum-based organometallic precursor for repair of clear defect on X-ray masks. Although FIB gold films are adequate for repair of gold-absorber, silicon-membrane X-ray masks, gold films are not acceptable in the fab line, and tantalum is preferred for repair of either tungsten or tantalum absorber X-ray masks. <s> BIB002 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Adaptation of an STMS Structure as a Probe Type Structure <s> In this paper the possibilities of focused ion beam (FIB) applications in microsystem technology are reviewed. After an introduction to the technology and the operating principles of FIB, two classes of applications are described. First the subject of FIB for microsystem technology inspection, metrology and failure analysis is outlined. A procedure for cross sectioning on samples is presented, as well as some examples of how this technique can be applied to study processing results. The second part of the paper is on the use of FIB as a tool for maskless micromachining. Both subtractive (etching) and additive (deposition) techniques are discussed, as well as the combination of FIB implantation of silicon with subsequent wet etching. We will show the possibility to fabricate three-dimensional structures on a micrometre scale, and give examples of recent realizations thereof. <s> BIB003 </s> A Review of Multimode Interference in Tapered Optical Fibers and Related Applications <s> Adaptation of an STMS Structure as a Probe Type Structure <s> A fiber-tip high-temperature sensor based on multimode interference is demonstrated both theoretically and experimentally. The temperature sensor presented can measure a broad temperature interval ranging from room temperature to 1089°C. An average sensitivity of 11.4 pm/°C is achieved experimentally. <s> BIB004
For some measurement environments it is beneficial to be able to utilise a sensor which has a single-ended or probe type structure which potentially can offer sensing with a high spatial resolution. As a further development of the STMS in BIB004 , a multimode fiber tip based on the STMS fiber structure has also been proposed, to form a probe type sensor, in effect one half of a complete STMS structure which also relies on reflection from the tip. Figure 7 presents the schematic diagram of experimental setup for fabricating the tapered MMF tip structure. remains straight with the help of a constant applied tension. In this experiment, the position of the laser beam can be adjusted flexibly by using gold-coated mirrors on a one-dimensional (1D) motorized translation stage, while the opening and closing of its shutter can be controlled through a LabView program. When the output power of CO2 laser is fixed at 15 W, the CO2 laser beam irradiation can produce a tapered MMF. For some measurement environments it is beneficial to be able to utilise a sensor which has a single-ended or probe type structure which potentially can offer sensing with a high spatial resolution. As a further development of the STMS in BIB004 , a multimode fiber tip based on the STMS fiber structure has also been proposed, to form a probe type sensor, in effect one half of a complete STMS structure which also relies on reflection from the tip. Figure 7 presents the schematic diagram of experimental setup for fabricating the tapered MMF tip structure. The fabrication process used the same optical setup and laser parameters as the STMS structure fabrication above, but now one end of the structure was fixed vertically on a support and to the other end a constant tension was applied by a 30 g weight. With the help of the constant tension provided by the weight, when the middle of the MMF section was exposed to the CO2 laser beam with an average output power of 15 W, tapering occurred because of the tension applied to the fiber. Because of the tension, the fiber taper breaks uniformly at a point The fabrication process used the same optical setup and laser parameters as the STMS structure fabrication above, but now one end of the structure was fixed vertically on a support and to the other end a constant tension was applied by a 30 g weight. With the help of the constant tension provided by the weight, when the middle of the MMF section was exposed to the CO 2 laser beam with an average output power of 15 W, tapering occurred because of the tension applied to the fiber. Because of the tension, the fiber taper breaks uniformly at a point forming a tip. For the purpose of improving the reflection of the tip, some additional material is coated on the fiber end. A thermal evaporator is used to coat a circa 40 nm thickness of gold on the tapered MMF tip. It is worth noting that the gold film on the SMS fiber structure such as MMF long waist and conical transitional region, should be partially removed by the application of a gold-etching solvent which contains iodine and potassium. Finally, we obtain a tapered MMF tip structure with its end coated with a thin gold film, as shown in Figure 8 . In addition, the microscope image of the fabricated tapered MMF tip is shown in Figure 9 . The fabrication process used the same optical setup and laser parameters as the STMS structure fabrication above, but now one end of the structure was fixed vertically on a support and to the other end a constant tension was applied by a 30 g weight. With the help of the constant tension provided by the weight, when the middle of the MMF section was exposed to the CO2 laser beam with an average output power of 15 W, tapering occurred because of the tension applied to the fiber. Because of the tension, the fiber taper breaks uniformly at a point forming a tip. For the purpose of improving the reflection of the tip, some additional material is coated on the fiber end. A thermal evaporator is used to coat a circa 40 nm thickness of gold on the tapered MMF tip. It is worth noting that the gold film on the SMS fiber structure such as MMF long waist and conical transitional region, should be partially removed by the application of a gold-etching solvent which contains iodine and potassium. Finally, we obtain a tapered MMF tip structure with its end coated with a thin gold film, as shown in Figure 8 . In addition, the microscope image of the fabricated tapered MMF tip is shown in Figure 9 . While the CO2 laser technique described above can be used to fabricate a tip, it does not allow the tip parameters to be determined very precisely or repeatably. Focused ion beam (FIB) technology BIB001 BIB002 BIB003 can also be used to fabricate the fiber tip. FIB technology can support the micro-operations required to form the tip with high precision, such as localized milling and metal coating deposition. In order to achieve a good manufacturing accuracy in nanoscale on fiber tips, therefore, an FIB system (Helios 600, FEI Inc., Hillsboro, OR, USA) was employed to flat cut the tapered MMF tip, which can greatly increase the reflectivity of the fiber tip. Firstly, to avoid charging during FIB milling, a gold layer with thickness of circa 50 nm was deposited on the tapered MMF tip surface by employing an electron beam evaporator. A FIB beam with a size smaller than 30 nm can be obtained through adjusting the accelerating voltage and current into optimal values (30.0 kV and 93 pA. Thus, the tapered MMF tip end shape can be controlled with precision. After FIB milling, the remained gold layer on the tapered MMF tip surface was removed totally by gold-etching solvent, which contained iodine and potassium iodine. Then, another 40 nm thickness of gold, to be used as mirror, was coated on the tapered MMF tip end to increase the reflectivity. From a comparison of tapered MMF tip structures with and without FIB milling, we found that the FIB milling process can provide an improvement of a circa 40 dB for the reflectivity. Thus, it is demonstrated that the FIB milling technology is an appropriate approach to improve the capability of TOF-based MMF devices.