Matrix-free infrared soft laser desorption/ionization

Infrared soft laser desorption/ionization was performed using a 2.94 µm Er : YAG laser and a commercial reflectron time-of-flight mass spectrometer. The instrument was modified so that a 337 nm nitrogen laser could be used concurrently with the IR laser to interrogate samples. Matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization and desorption/ionization on silicon with UV and IR lasers were compared. Various target materials were tested for IR soft desorption ionization, including stainless steel, aluminum, copper, silicon, porous silicon and polyethylene. Silicon surfaces gave the best performance in terms of signal level and low-mass interference. The internal energy resultant of the desorption/ionization was assessed using the easily fragmented vitamin B₁₂ molecule. IR ionization produced more analyte fragmentation than UV-MALDI analysis. Fragmentation from matrix-free IR desorption from silicon was comparable to that from IR-MALDI. The results are interpreted as soft laser desorption and ionization resulting from the absorption of the IR laser energy by the analyte and associated solvent molecules. Copyright © 2004 John Wiley & Sons, Ltd.     

Copper metallization for ULSL and beyond

The investigation of copper for use as an interconnection metal in the ultra large-scale integration (ULSI) era of silicon integrated circuits has accelerated in the past several years. The obvious advantages for using copper to replace currently used Al are related to its lower resistivity (1.7 μΩ-cm vs. 2.7 μω-cm for Al) and its higher electromigration resistance (several orders of magnitude higher compared with Al). The goal of this review is to examine the properties of copper and its applicability as the interconnection metal. A comparison of electromigration behavior of various possible interconnection metal in standard “bulk” state is made. This is followed by a review of the calculations made comparing (a) the RC (resistance × capacitance) time constants of various material systems and (b) the joule heating of the interconnection materials. A comparative study of various metal systems for the application as the interconnect metal is then made. These discussions will clearly establish the superiority of copper over other metals despite certain limitations of copper. We then review the properties, both physical and chemical, and materials science of copper. The concept of using alloys of copper with a minimal sacrifice on resistivity to gain reliability is also discussed. This is followed by the review of the deposition, pattern definition and etching. passivation, need of the diffusion barrier (DB) and adhesion promoter (AP), planarization and dual damascene process using chemical mechanical planarization, and reliability. This review shows that copper will satisfy the needs of the future integrated circuits and provide high performance and reliability as long as we provide an appropriate barrier to diffusion in the underlying devices and the dielectric.     

Monolithic Uncooled 8 × 8 Bolometer Arrays Based on Poly-SiGe Thermistor

This paper presents a monolithic uncooled 8 × 8 bolometer array with polycrystalline silicon-germanium (poly-SiGe) thermistors as active elements. The poly-SiGe films are deposited by ultrahigh vacuum vapor deposition (UHV/CVD) system and the dependence of the temperature coefficient of resistance (TCR) on annealing temperature has been investigated. To decrease the thermal conductance of the bolometer, the poly-SiGe thermistor was formed on a four leg suspended microbridge. The improved porous silicon micromachining techniques described here enable the integration of the bolometer array with the MOS readout circuitry. The measurements and calculations show that the mean responsivity is 1.07 × 10⁴ V/W with an uncorrected uniformity of 10.5% and a thermal response time of 10.5 ms, and the detectivity of 3.75 × 10⁸ cm Hz^1/2/W is achieved at a chopping frequency of 30 Hz and a bias voltage of 5 V.     

Early stages of silicon oxidation

Experiments have shown that the early stages of silicon oxidation proceed layer by layer, so that one layer is essentially complete before another develops. Other experiments show that the mechanism does not involve step growth, the most obvious mechanism. We use a new approach to modelling the growth to show that these two observations can be understood when there is a rate-determining step which depends strongly on the local oxide thickness. The rate in question might be the sticking probability, or the rate of incorporation of adsorbed oxygen species into the oxide network. Such mechanisms are possible when transport by an ionic species dominates, contrary to the situation for thicker films. Our modelling suggests the mechanisms are driven by the image interaction, as in earlier suggestions by Stoneham and Tasker, rather than an effect of the electric field central to the Mott-Cabrera mechanism.     

稀土铒离子注入多孔硅的发光

稀土离子Er注入多孔硅中.在350keV能量,1×1012~1×1015/cm2剂量范围内,注入后的多孔硅仍保持明亮的可见光发射.退火后,在近红外区测到1.54μm附近Er3+的特征发射.其发射强度比硅单晶对照样品明显增强,实验表明这增强作用来源于多孔硅的表面发光层.电化学制备过程中在表面层中带入的O、C、F等多种杂质可能是Er3+发光增强的原因.     

发光多孔硅表面微结构及其晶格畸变的实验研究

用电化学方法制备了不发光多孔硅和发光多孔硅,用X射线双晶衍射对两类多孔硅表面进行了微结构分析和晶体质量表征,实验表明两类多孔硅的微结构间存在着很大差别。不发光多孔硅表面对X射线的双晶衍射摇摆曲线可解叠成两个峰,它们分别来自样品多孔层和单晶硅衬底,而发光多孔硅对X射线的双晶衍射摇摆曲线呈高斯对称分布,不可解叠。发光多孔硅比不发光多孔硅表面晶体质量差,且电化学腐蚀越严重,表面晶体质量下降也越严重。     

非晶硒化镉和辉光放电非晶硅对锁模激光的瞬态响应

用对撞锁模Nd:YAG激光器产生的超短光脉冲对非晶硒化镉和辉光放电非晶硅的瞬态响应进行研究,并用多重俘获传导模型分析光生载流子的弛豫过程.     

Photoluminescence and electroluminescence from porous silicon

The properties and origins of the red, blue and infrared photoluminescence bands of porous silicon are reviewed and discussed in the light of the models that have been proposed to explain the experimental and theoretical results. The red band is due to quantum confinement possibly supplemented by surface states; the blue band is linked to the presence of silicon dioxide; the infrared band is correlated with dangling bonds and bandgap luminescence in large crystallites. The fabrication and characterization of light-emitting devices made of porous silicon are reported and discussed with respect to critical issues such as the device stability, efficiency, modulation speed, emission wavelength, and compatibility with microelectronic processing.     

光束传播法分析硅交叉波导光开关的光学效应

运用光束传播法对硅交叉波导全内反射光开关中的光学效应进行了详细分析。结果表明：１）光学表面衰减波和泄漏波所引发的光遂道效应对开关特性有重要影响；２）反射端功率的相对大小于与反射区界面位置密切相关，其起因是古斯－汉欣位移；３）合理考虑这些因素的影响可以大大降低器件对折射率变化的要求。     

The effect of constraints on the initial steps of adsorption of nitrogen atoms on the silicon surface as modeled by the cluster [Si9H12 + N]

The effect of constraints on the initial steps of the incorporation of nitrogen on silicon has been assessed by calculations with the [Si₉H₁₂ + N] model cluster using density functional theory with the hybrid functional B3LYP, and two basis sets that differ significantly in size. The relative stability of the various stationary points is dependent on the type of constraints imposed on the cluster. Constrained calculations have predicted the structure with the nitrogen symmetrically bonded to the dimer silicons as the global minimum, however, if no constraint is imposed and the whole cluster is optimized, as done in this work, a structure with the nitrogen inserted between the dimer and the first layer and bonded to three silicon atoms is predicted to be the most stable one by about 17 kcal/mol by either the doublet or quartet route. The whole process is very exothermic and reaction barriers in the intermediate steps are easily overcome. Calculations with the smaller basis do not essentially change the major conclusion about the relative stability of the various stationary points. The most stable structure and frequency calculations are consistent with a planar NSi₃ moiety and its asymmetrical stretching frequency.