Ultrahigh vacuum-compatible fabrication and electrical characterization systems for environmentally sensitive metal oxide semiconductor capacitors

We describe an integrated, ultrahigh vacuum system for metal oxide semiconductor (MOS) device fabrication and characterization. This system is advantageous for electrical property measurements on electronic devices with environmentally sensitive materials and is especially important as device dimensions approach the nanoscale. Without exposure to atmosphere, MOS capacitors were fabricated by evaporatively depositing gate metal on molecular-beam-epitaxy (MBE) grown dielectrics through a shadow mask in an UHV electrode-patterning chamber. Finished devices were transferred in UHV to an in situ UHV electrical characterization probe station. We obtained excellent agreement between air-ambient ex situ and in situ probe station measurements with less than 0.3% systemic error for frequencies from 20 Hz to 1 MHz. We have successfully measured MOS capacitors with sensitivity to a density of interface states of 1x10(10) states cm(-2) eV(-1). These measurements show 0.5% systematic error for measurement frequencies from 20 Hz to 1 kHz and less than 0.1% from 1 kHz to 1 MHz. The integrated system presented here is one where complex, MBE-grown MOS heterostructures can be synthesized and tested rapidly to explore new field-effect-device physics and functionality.     

用于分布反馈光栅的纳米压印模板制作

高质量、低成本的压印模板的获得是采用纳米压印技术制作分布反馈光栅的难点,本文采用双层金属掩模及liftoff金属剥离方法制作了适用于紫外压印技术的石英基压印模板.首先,采用电子柬光刻技术在镀钛的石英基片表面直写出DFB光栅的光刻胶图形,接着,在其表面溅射一层金属镍并进行金属剥离得到与光刻胶相对的图形,最后采用电感耦合等...     

Characterization of nanoscale recording mark on Ge2Sb2Te5 film

We have fabricated nanoscale recording marks on Ge(2)Sb(2)Te(5) (GST) films with conductive atomic force microscope (AFM). GST films were deposited on glass or polyimide film with thickness of 150-200nm by the rf-sputtering method. Through current-voltage (I-V) spectroscopy, good cantilevers for fabrication and characterization of nanoscale marks on GST were selected. A fresh and highly conductive tip showed voltage-switching characteristic in the I-V curve, where the threshold voltage was approximately 1.6V. Nanoscale dot and wire arrays of crystalline phases were successfully obtained by varying sample bias voltage from -10 to 10V. With highly conductive tips, nanowires having full-width at half-maximum of approximately 20nm could be fabricated, whereas nanowires could not be fabricated with bias voltage below -2V. The width of the nanoscale mark was increased by repetition of AFM lithography even with same applied voltage and lithography speed. For a thicker nanowire, the width measured in current-image (C-image) was observed to be approximately 2 times of that measured in topography-image (T-image). This result supports that current sensing provides an image of phase-changed GST area with higher resolution than topography sensing.     

A chamber attached to the SEM for fracturing and coating frozen biological samples

A chamber for introducing, fracturing and coating frozen biological samples has been developed as an attachment to the sepcimen chamber of a scanning electron microscope. Together with a eucentric-tilt cold-stage, this chamber constitutes a complete system for viewing fractured biological surfaces of the type normally only seen by replica techniques. An air-lock on the chamber accepts a transfer module to allow insertion of the frozen sample without frost build-up. Fracturing is carried out with a precisely adjustable cooled knife under a 10--100X binocular microscope. The sample can tilt and rotate while being coated with carbon or metals evaporated from rechargeable sources introduced through the air-lock. Cooling in the chamber is provided by a cylindrical copper tank filled with liquid nitrogen. The chamber has its own LN2 trapped high vacuum system. After preparation the sample can be placed directly into the SEM through an isolation valve. The cold-stage utilizes a Joule-Thomson refrigerator. The sample can be kept below 103 K at all times though there are provisions for heating it in the fracturing and cold-stage positions. A system of controls, sensors and interlocks simplifies the operation of the system.     

Cryosputtering—a combined freeze-drying and sputtering method for high-resolution electron microscopy

Preparing cellular structures for visualization by high-resolution scanning electron microscopy (SEM) is a multi-step process which includes fixation, dehydration, drying and metal coating. Drying and metal coating are limiting for high-resolution work. Commonly, the dried samples are exposed to the air before they are inserted into a metal coating apparatus, thereby exposing them to moisture and the accompanying risk of rehydration, which may cause changes in the supramolecular structure. We have modified a freeze-dryer to accommodate a magnetron sputtering head, in order to sputter-coat the frozen-dried samples while still in the drying chamber in the cold, a process we call cryosputtering. A layer of 1·5 nm of tungsten was cryosputtered onto whole mounts of cytoskeletons from detergent-extracted human glioma cells or fibroblasts and the specimens were examined by high-resolution SEM and transmission electron microscopy (TEM). To reduce the effects of backstreaming oil from the vacuum system, a turbomolecular pump backed by a two-stage rotary vane pump was connected to the drying-coating chamber. This pump system provides a high vacuum, making it possible to dry the specimens at — 90°C/183 K, thus reducing the risk for recrystallization of water. Furthermore, the high vacuum minimizes the negative effects of contaminants, which can be deposited onto the specimen surface and affect the quality of the metal coat formed during sputtering.     

LIGA技术基础研究

阐述了LIGA技术的组成及特点.对LIGA工艺掩膜、X射线光刻、电铸及塑铸等进行了工艺原理分析.用一次成型法制作了以聚酰亚胺为衬基、以Au为吸收体的X射线光刻掩膜.简单介绍了这种掩膜的制作工艺过程,并用这种掩膜在北京电子对撞机国家实验室进行了同步辐射X射线光刻,得到了深度为500μm,深宽比达8.3的PMMA材料的微型电磁马达联轴器结构.给出掩膜和X射线光刻照片.同时,对Au、Ni等金属材料的厚膜电铸进行了工艺研究.     

Development of a vacuum-compatible hydrodynamic spindle using an ionic liquid as a lubricant

The importance of beam machining and extreme ultraviolet lithography technologies in the area of precise and fine machining used for high-density optical discs, integrated circuits and patterned media of hard disc drives (HDDs) is rapidly increasing.In this paper, a very simple vacuum-compatible rotary spindle is proposed that uses an ionic liquid as a lubricant with a very low vapor pressure. The usefulness of the proposed spindle lubricated by an ionic liquid was experimentally confirmed by measuring the partial pressures of outgassed products during rotation of the spindle in the vacuum chamber, measuring the accuracy of movement of the rotary table and machining circular grooves by an electron beam in a scanning electron microscope (SEM). It was found that the proposed spindle could be used in vacuum, and the partial pressures of outgassed products were almost the same as those of a clean, empty vacuum chamber. In addition, it was confirmed that by using the proposed spindle, circular grooves with diameters of 200 and 400 μm, 450 nm width and 40 nm depth could be machined on a photoresist surface coated on a silicon wafer in vacuum of an SEM.     

Differential alternating current chip calorimeter for in situ investigation of vapor-deposited thin films

Physical vapor deposition can be used to produce thin films with interesting material properties including extraordinarily stable organic glasses. We describe an ac chip calorimeter for in situ heat capacity measurements of as-deposited nanometer thin films of organic glass formers. The calorimetric system is based on a differential ac chip calorimeter which is placed in the vacuum chamber for physical vapor deposition. The sample is directly deposited onto one calorimetric chip sensor while the other sensor is protected against deposition. The device and the temperature calibration procedure are described. The latter makes use of the phase transitions of cyclopentane and the frequency dependence of the dynamic glass transition of toluene and ethylbenzene. Sample thickness determination is based on a finite element modeling of the sensor sample arrangement. In the modeling, a layer of toluene was added to the sample sensor and its thickness was varied in an iterative way until the model fit the experimental data.     

ZSX100e型X射线荧光光谱仪真空系统故障的诊断方法

本文较全面的概括了ZSX100e型X射线荧光光谱仪真空系统的故障,并分析了故障原因。根据仪器分光室、样品准备室的真空系统工作原理和交互过程,从真空泵使用及性能判断、分光室和样品准备室的密封部件、探测器工作气体气路、探测器窗膜、自动芯线清洗装置、气体密度稳定器等几个方面归纳出不同情况下仪器真空系统故障的诊断方法。     

Low pressure mode combined with OsO4 vapor fixation and sputter-coating for the preservation of delicate aerial hyphae and conidia in the ESEM

The newer generation of environmental scanning electron microscopes (ESEMs) allows samples to be viewed under a range of different vacuum conditions. No specific sample preparation protocols are required with the ESEMs, as fresh, unfixed samples are used and discarded later. We have worked out a method that preserves aerial hyphae on biltong that closely resemble fresh specimens and may be stored for viewing at a later date. Another advantage is that fixed samples are more resilient to the variable vacuum encountered in the ESEM. When biltong samples with fungal growth were first studied, we observed that vacuum-related artifacts were induced unless vacuum conditions and changes in pressure were carefully controlled. Damage readily occured in conidia and its delicate hyphae. Fresh, unfixed samples are very vulnerable to these artifacts. In addition, biltong proved to be a problematic study sample because of its high salt content, its hygroscopic nature as well as being laden with spices. To eliminate these artifacts, the preservation of specimens by OsO4 vapor fixation combined with a special sputter-coating technique is described. Previous studies confirmed that OsO4 vapor fixation is superior to traditional immersion fixation methods for the examination of hyphae and conidia of various fungi in a conventional SEM. However, both preparation methods induce sample shrinkage. We observed that OsO4 vapor fixation followed by Au coating under strictly controlled vacuum conditions induced fewer artifacts and gave the best images with minimum distortion in low pressure (LP) mode. The proposed method allows samples to be viewed both in ESEM and LP mode. There are however some disadvantages inherent to ESEM mode. Even when viewing fixed, coated samples, care should be taken to maintain a pressure of not lower than 0.2 Torr in the specimen chamber. It is critical that different samples have the same vacuum exposure history, as shrinkage and collapse were found to be directly related to the lowest pressure the samples were subjected to, both in the sputter coater chamber and in the electron microscope specimen chamber.     

Creating internal conductivity in dry biological SEM samples by a simple vapour treatment

Internal sample conductivity in scanning electron microscopy can be a valuable alternative to metal coating. Proton conductivity may be used for this purpose. Many solid materials with active hydrogen atoms, such as hydrogen‐ and ammonium‐salts, organic acids, and even ice, are protonic conductors or semiconductors. Here we present a method to generate proton conductivity in dry biological materials. A simple treatment with hydrogen chloride gas or hydrochloric acid vapour for a few minutes provides sufficient conductivity for many samples. After a removal of excess hydrogen chloride vapour with a vacuum desiccator, the objects may be examined in the SEM without metal coating. The use of internally conductive samples extends the range of easy‐to‐perform SEM preparation techniques. It is advantageous for material contrast imaging of uncoated samples, and it can be used in combination with metal coating to enhance conductivity on difficult samples with complex overlapping surfaces, where simple metal coating does not reliably eliminate charging problems.     

Scanning probe lithography for fabrication of Ti metal nanodot arrays

We report fabrication of Ti metal nanodot arrays by scanning probe microscopic indentation. A thin poly-methylmethacrylate (PMMA) layer was spin-coated on Si substrates with thickness of 70 nm. Nanometer-size pore arrays were formed by indenting the PMMA layer using a cantilever of a scanning probe microscope. Protuberances with irregular boundaries appeared during the indentation process. Control of approach and pulling-out speed during indentation was able to dispose of the protrusions. Ti metal films were deposited on the patterned PMMA layers by a radio-frequency sputtering method and subsequently lifted off to obtain metal nanodot arrays. The fabricated metal nanodot arrays have 200 nm of diameter and 500 nm of interdistance, which corresponds to a density of 4×10⁸/cm². Scanning probe-based measurement of current–voltage (I–V) behaviors for a single Ti metal nanodot showed asymmetric characteristics. Applying external bias is likely to induce oxidation of Ti metal, since the conductance decreased and volume change of the dots was observed. I–V behaviors of Ti metal nanodots by conventional e-beam lithography were also characterized for comparison.     

高分辨二次离子质谱超高真空样品台的研制

目前,微束类分析仪器的一次离子束斑越来越精细,直径已达到微米级甚至亚微米级,仪器真空度也已达到稳定的超高真空水平,因此,亟需研制一种与之相匹配的高分辨样品台,提高在超高真空环境下的分辨力及定位精度。新研制的样品台,通过置于真空腔体外部的高精度滑台驱动小型焊接波纹管的伸缩传递三维运动,解决了大尺寸焊接波纹管表面放气及承受较大大气压力的问题;通过使用适用于超高真空的材料和固体润滑、无动态密封,解决了高真空中摩擦偶件的润滑问题。实验数据表明：在40 mm行程范围内,运动平台三轴定位重复性为0.94、1.83、0.38 μm,分辨力为0.10 μm,并已成功地应用在1.19×10^-6 Pa超真空环境下。外置的高精度滑台不仅克服了真空电机在真空腔体内发热及绝缘材料放气的问题,而且不需要引入任何电子电气元件及导线,不会在分析腔室内产生电磁干扰,行程不受装置本身的限制。这些特性不仅可满足二次离子质谱仪的要求,也适用于具有高分辨、超高真空环境、无污染要求的其他分析测试仪器。     

Quasi in situ scanning force microscope with an automatic operated reaction chamber

We describe the design and performance of a quasi in situ scanning force microscope with an automatic operated reaction chamber. The design provides a repetitive hermetically sealed sample environment for successive processing. The reaction chamber is based on a combination of a flexure-guided cover, a piezo-positioning system and a force applicator system. An axial force seals the cover against the reactor enabling flow-through applications at low pressure, ambient pressure, or elevated pressure. The position stability of the sample relative to the probe is characterized and a full automated operation of the instrument is explored by the alignment of an ABC terblock copolymer thin film undergoing solvent vapor annealing in the presence of a high electric field. Due to the high electric field strength and the sharp scanning force microscope tip it is impossible to perform in situ scanning in the presence of the electric field.     

Stencil mask methodology for the parallelized production of microscale mechanical test samples

A new methodology to parallelize the production of micromechanical test samples from bulk materials is reported. This methodology has been developed to produce samples with typical gage dimensions on the order of 20-200 μm, and also to minimize the reliance on conventional focused ion beam fabrication methods. The fabrication technique uses standard microelectronic process methods such as photolithography and deep-reactive ion etching to create high aspect ratio patterned templates-stencil masks-from a silicon wafer. In the present work, the stencil mask pattern consists of a linear row of tensile samples, where one grip of each sample is integrally attached to the bulk substrate. Once fabricated, the stencil mask is placed on top of a pre-thinned substrate, and the pattern and substrate are co-sputtered using a broad ion beam milling system, which ultimately results in the transfer of the mask pattern into the substrate. The methodology is demonstrated using a Si stencil mask and a polycrystalline Ni foil to manufacture an array of metallic micro-tensile samples.     

屏蔽膜板随动式微细电铸技术基础研究

提出了屏蔽膜板随动式微细电铸技术，屏蔽阳极膜板随电沉积层的增加而微量移动，从而可以用厚度有限的屏蔽层制造出原理上高度不受限制的三维金属微结构。针对该工艺的特点研制了试验装置，利用紫外光刻制作的屏蔽阳极膜板开展了两种随动方式的研究，分别得到了侧壁陡直的微齿轮和具有倾斜轮廓的微十字结构。     

System for in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy and quartz crystal microbalance

We present a versatile chamber ("atmospheric corrosion cell") for soft x-ray absorption/emission spectroscopy of metal surfaces in a corrosive atmosphere allowing novel in situ electronic structure studies. Synchrotron x rays passing through a thin window separating the corrosion cell interior from a beamline vacuum chamber probe a metal film deposited on a quartz crystal microbalance (QCM) or on the inside of the window. We present some initial results on chloride induced corrosion of iron surfaces in humidified synthetic air. By simultaneous recording of QCM signal and soft x-ray emission from the corroding sample, correlation between mass changes and variations in spectral features is facilitated.     

MoSx/MoSx-Mo纳米多层膜的制备及其环境摩擦学特性

用直流磁控溅射在钢基体上交替溅射制备了MoSx/MoSx-Mo纳米多层膜。采用划痕仪测试薄膜与基体的结合力;采用SEM和XRD分析了纳米多层膜的形貌和显微结构;在球-盘式微摩擦试验机上测试了纳米多层膜在真空和潮湿空气中的摩擦学性能。结果表明,纳米多层膜的结合力优于纯MoS2膜。随着溅射沉积气压的升高,MoSx(002)面择优取向减弱,纳米多层膜的结合力下降。溅射气压0.24 Pa沉积的纳米多层膜在真空和潮湿空气中都呈现出最低的摩擦因数和磨损率,具有优异的环境摩擦磨损特性。     

同步辐射X射线光刻掩模镀金工艺的研究

介绍了利用北京正负对撞机(BEPC)同步辐射X射线光刻装置,进行LIGA工艺技术深结构光刻实验研究,详细论述了X射线光刻使用的掩模制备过程及掩模镀金工艺,在国内最早曝光出直径为400μm、厚为27～45μm的三维立体齿轮胶图形。     

A sample scanning system with nanometric accuracy for quantitative SPM measurements

A sample scanning device operating in a working volume of 30 x 30 x 18 microm with interferometer and capacitance-based controls of displacements, is described. The xy-stage uses plane mirror linear interferometers and fast phase-meters for control of displacements of precise ball-bearing stages driven by piezo flexure actuators. The stage operates with a full range bandwidth of 200 Hz, and an estimated accuracy (k = 2) of 3 nm + 1 x 10(-3) L, where L is the lateral displacement. A novel z-stage based on a kinematic coupling between two plates, the upper one being moved by three bimorph plates and the distance being measured by three capacitive sensor, is described. The tilt of the z-stage is kept within fractions of a microrad, leading to a full range estimated accuracy of 2 nm + 2 x 10(-3) h, where h is the vertical displacement. The control bandwidth is of about 1 kHz, thus allowing fast and accurate step-height measurements. In order to test the device used in a scanning probe microscope, micrometric patterned surfaces made using high resolution e-beam lithography and precise metal deposition on silicon are imaged. Results of pitch measurements are discussed and compared with those obtained using optical diffractometry.