微加工中的聚焦离子束直接写入技术

概述了聚焦离子束直接写入、离子研磨、离子注入及离子沉积技术。介绍了利用聚焦离子束技术在镀金硅片上研磨出的图案及制作出的各种纳米结构。聚焦离子束诱导沉积技术为将在各种科学工程领域应用的多种微结构的实现提供了可能,如聚焦离子束真空封装技术,它可被用来真空封装MEMS器件。     

聚焦离子束在光纤探针制备技术中的应用

本文概述了利用聚焦离子束制备用于近场光学显微镜光纤探针的方法,讨论了探针的锥型刻蚀、孔径控制和特殊结构加工等;论述了聚焦离子束的工作原理和在光纤探针高精度加工方面的优势。利用此技术制备的光纤探针的锥型和针尖孔径精确可控,并具有高光洁度,高通光效率等特点。     

Monte Carlo simulation for the sputtering yield of Si3N4 thin film milled by focused ion beams

The sputtering yield of the Si3N4 thin film is calculated by Monte Carlo method with different parameters. The dependences of the sputtering yield on the incident ion energy, the incident angle and the number of Gallium (Ga) and Arsenic (As) ions are predicted. The abnormal sputtering yield for As at 90 keV occurs when the incident angle reaches the range between 82°and 84°.     

Mosfet fabrication using ion beam nitridation

Ion beam nitridation has been suggested as an alternative to the conventional local oxidation process which is used in the fabrication of most metal-oxide-semiconductor (MOS) integrated circuits. The implantation of 2 keV nitrogen ions in doses of up to 8 x 10¹⁷ cm^-2 results in the formation of a silicon nitride layer approximately 10 nm thick. Herein we describe the electrical characteristics of n-channel silicon gate metal-oxide-semiconductor-field-effect-transistors (MOSFETs) fabricated using this modified local oxidation process, and compare them to devices fabricated simultaneously but using the conventional local oxidation technology. The effective device channel lengths and widths are determined from the electrical characteristics of devices with mask (ideal) dimensions of 4, 6, 8 or 10 μm. The ion beam nitrided devices exhibit a significant reduction in the lateral oxidation effect. A 1.3 μm increase in channel width relative to conventional processing is observed for the ion beam nitrided devices with a 690 mm thick field oxide. On the other hand, fixed oxide charge densities are found to increase by a factor of about two due to the nitrogen implantation, and device channel mobilities are reduced by about 25%.     

Materials modification using intense ion beams

Pulsed intense ion beams have been developed for applications including surface modification and alloying, and thin-film and nanopowder synthesis. Rapid thermal processing with ions is quite promising for large-scale commercial use, due to the high specific ion energy deposition (joules per cubic centimeter) without reflection, and to the relative efficiency and low cost of the pulsed power ion-beam drivers compared to other high-kinetic energy alternatives. We discuss in this paper the basis for the use of ions in materials processing and the methods of beam formation and impingement on material to be treated, and give examples of recent and ongoing work in materials processing.     

Gain-coupled distributed-feedback GaInAs-GaAs laser structuresdefined by maskless patterning with focused ion beams

First-order periodic gain modulation in GaInAs-GaAs laser structures has been realized by maskless focused ion-beam implantation. The structures were implanted with Ga⁺-ions at an ion energy of 130 keV and a line dose of 1*10⁷ 1/cm. The periodicity of the gratings was designed for laser operation at 77 K and room temperature. With optical pumping we have observed single-mode laser operation due to the distributed feedback effect at wavelengths between 849 mn and 944 mn at 77 K (grating periods between 124 and 140 nm) and between 954 nm and 1005 mn at room temperature (grating periods between 140 and 148 nm)     

GaAs MESFET fabrication using maskless ion implantation

A 2000-Å-diameter focused-ion beam from a Au-Si liquid-metal-alloy ion source was used to implant the doped regions of GaAs metal-semiconductor gate field-effect transistors. An Al stopping layer on the wafer was used to trap the Au ions. The 140-keV Si⁺⁺beam component was deflected under computer control to implant 8 × 50 µm active channel regions and 16 × 50 µm contact regions. The devices were metallized using conventional lithography. DC electrical characteristics of the 1.5-µm-gate-length devices are comparable to those of conventionally processed devices of identical geometry.     

Focused ion beams for lithography and direct doping in VLSI device fabrication

We review the possible applications of focused ion beams to the lithography and doping stages in the fabrication of microelectronic devices. Topics discussed include ion sources, system performance, ion beam lithography and direct implantation doping. Emphasis is placed on a comparison between electron and ion beams for direct write lithography. Wafer throughput for both techniques is analysed in terms of equipment limitations and resist properties. For direct implantation doping, the effects of the ion beam profile are discussed and wafer throughput is considered. We conclude that, due to throughput limitations, ion beams are not appropriate for either lithography or direct doping for VLSI device fabrication.     

Transistor fabrication using diffusion barriers produced by electron beams

Diffusion barriers produced directly by electron-beam-initiated chemical reactions have been used to fabricate planar bipolar transistors without the use of normal oxidation or etching processes. Electrical characteristics of the transistors are comparable with conventional devices.     

聚焦厄米-高斯光束对两种粒子的捕获

基于广义惠更斯-菲涅耳原理和瑞利散射理论, 推导了聚焦厄米-高斯光束的光强和作用在瑞利微粒上辐射力 的解析表达式,主要研究聚焦厄米-高斯光束对折射率不同的两种粒子的俘获情况,以及光 束阶数m和n对俘获效果 的影响。研究发现,聚焦厄米-高斯光束在焦平面上呈现出矩形阵列分布的(m +1)×(n+1)个亮斑,这种光束选取合适的 光束阶数可以实现在亮斑处阵列分布的捕获(m+1)×(n+1)个高折射率粒子,同时在暗区俘获 m ×(n+1)个低折射率粒子。 此外,光束阶数越大,辐射力越大,越容易俘获两种类型粒子。因此,选择合适的光束阶数 ,可以实现两种不同折 射率的瑞利微粒的稳定捕获。所得结果可以应用在生物技术和纳米技术等领域。     

Formation of nanosize structures on a silicon substrate by method of focused ion beams

The results of experimental studies of modes in which nanosize structures are formed on a silicon substrate by method of focused ion beams are presented. Dependences of the diameter and depth of the nanosize structures on the ion beam current and time of exposure to the ion beam at a point are obtained. It is demonstrated that the main factor determining the rate of ion-beam milling is the ion beam current. The results of the study can be used in the development of technological processes for the fabrication of components for nanoelectronics and nanosystems engineering.     

A new edge-defined approach for submicrometer MOSFET fabrication

A novel technique employing vertical (anisotropic) dry etching for fabricating edge-defined submicrometer MOSFETs is described, and preliminary results are presented. Three basic process techniques are employed: formation of an edge-defined submicrometer element, pattern transfer of the element into an underlying doped polysilicon gate layer, and passivation of the FET using a sidewall oxide. The submicrometer element formation technique is limited to linewidths in the 0.1 µm to 0.4 µm range. Characterization of MOSFETs, having physical channel lengths ∼0.1 µm to 0.15 µm and believed to be the world's smallest MOSFET's reported to date, is discussed.     

Elementary scattering theory of the Si MOSFET

A simple one-flux scattering theory of the silicon MOSFET is introduced. Current-voltage (I-V) characteristics are expressed in terms of scattering parameters rather than a mobility. For long-channel transistors, the results reduce to conventional drift-diffusion theory, but they also apply to devices in which the channel length is comparable to or even shorter than the mean-free-path. The results indicate that for very short channels the transconductance is limited by carrier injection from the source. The theory also indicates that evaluation of the drain current in short-channel MOSFETs is a near-equilibrium transport problem, even though the channel electric field is large in magnitude and varies rapidly in space     

Fabrication of silicon micro-mould for polymer replication using focused ion beam

Focused ion beam sputtering was used to fabricate microscale moulds of circular conical structures in silicon. As scan strategy, a continuous slicing method (CSM) modified from a two-dimensional (2D) slice-by-slice approach combined with a spiral scan was tested experimentally. With carefully chosen ion beam conditions and processing parameters, moulds were fabricated as a function of the ion dose for specific dwell times. Using the fabricated moulds, polymeric polydimethylsiloxane (PDMS) and polyurethane acrylate (PUA) microstructures were replicated and compared with the mould dimensions. Using PUA, the resolution of the polymer structure was examined on a nanoscale. In addition, mould-making failure due to both beam overlap and the field of view (FOV) is discussed. Finally, micro-lenses of different sizes were fabricated successfully.     

Specimen preparation for high-resolution transmission electron microscopy using focused ion beam and Ar ion milling

We have developed a focused ion beam (FIB)-Ar ion-milling technique for high-resolution transmission electron microscopy. A micrometresized specimen was mounted on a cross section of metal foil of a few micrometres thick, using FIB microsampling. Following this, a 2 degrees wedgeshaped part was made in the specimen using FIB. Finally, the specimen was milled using an Ar ion beam to remove the FIB-damaged layers. We applied the FIB-Ar ion milling technique to a CeO(2)/Gd(2)Zr(2)O(7) multilayer specimen, resulting in the crystal lattice fringes of both layers being clearly observable in comparison to a specimen finished using a Ga ion beam at an accelerating voltage of 10 kV.     

Ultra-thin oxides on silicon fabricated using ultra-slow multicharged ion beams

We have used ultra-slow multicharged ions in ultra-high vacuum with a low partial pressure of O₂ to grow ultra-thin layers (0.3 to 2.0 nm) of SiO₂ on silicon. The advantage of using ultra-slow ions is that they interact with the surface only through their potential energy, not their kinetic energy, so they do not penetrate below the surface, avoiding implanted-induced damages to the substrate. This paper presents several analysis we have performed to qualify these ultra-thin SiO₂ layers, such as Fourier transform infrared spectroscopy–attenuated total reflection, Auger electron spectroscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry and surface charge analysis. The oxidation process was monitored in situ and in real time using visible light emitted during the irradiation, and the thickness of the SiO₂ layers could be controlled. We plan to used these ultra-thin SiO₂ layers in next generation MOS gate dielectric stack, as a buffer layer between the channel in silicon and a high-k dielectric.     

Space-charge waves of periodic-electrostatically focused electron beams

Space-charge wave propagation for periodic-electrostatically focused electron beams with nonuniform radial beam density distributions is the subject of this paper. The dispersion equation is obtained by solving a differential equation for the ac electric potential inside the electron beam and by matching the solution at the boundaries. An approximate analytic solution and a digital computer treatment are described. The reduced plasma frequency obtained is expressed in terms of the focusing parameters and is compared with that of a Brillouin beam. A study of the differential equation involved suggests that there are certain ranges of system parameters ("forbidden" zones) for which no wave propagation is possible, that is, no space-charge mode can be supported there.     

Linearly focused acoustic beams for acoustic microscopy

A linearly focused acoustic beam is investigated to be introduced into acoustic microscopy for characterising materials in the nonscanning version. The new acoustic beam enables us to detect acoustic anisotropies of materials to be measured successfully. For forming the acoustic beam, an acoustic sapphire lens with a cylindrical concave surface of 1.0 mm in radius is made and the acoustic field distributions are investigated at 200 MHz.     

Azimuthally periodic electrostatically focused electron ribbon beams

Methods of enhancing transmission of ribbon-shaped electron beams undergoing circular motion in azimuthally periodic cylindrical electrostatic lenses are treated. Lens forces add to the naturally occurring curvature focusing to achieve this increase in beam transmission. Three basic configurations, differing only in the method of applying lens voltages, are treated: symmetrical focusing, deflection focusing, and asymmetric focusing (including inner and outer electrode segmentation). Expressions for beam perveance and rippling are derived from the paraxial-ray equation for thin electron ribbons advancing along a two-dimensional curved optical axis. The stiffness of azimuthally periodic electrostatically focused electron ribbons (i.e., the immunity of the beam to transverse disturbing forces) also receives attention. Mathematical extensions of the analysis to ribbon beams undergoing helical motion are discussed, and numerical results applicable to selected values of lens parameters are presented. Experimental results for an azimuthally periodic lens, constructed to test the analysis, are discussed in light of the theory developed.     

Evaluation of focused O+ ion beams as a tool for making resist masks by reactive etching

A method of reactive etching is proposed in which focused 100-eV O⁺ ion beams are used for making organic-resist masks 12–24 nm thick with nanometer-sized apertures. Focused-ion-beam and ion-projection-lithography systems with an electrostatic immersion decelerating objective are considered. They are shown to provide an ultimate lateral resolution of ～14 or ～21 nm, respectively. Attainable etch rate is estimated. The potential usefulness of resist masks thus obtained is discussed in the context of quantum-computing devices containing quantum dots, quantum wires, and nanoscale conducting tracks.