γ射线作用下氧化铪基MOS结构总剂量效应研究

使用原子层淀积方法得到了7.8 nm厚度的HfO₂薄膜并通过直接溅射金属铝电极得到了Al/HfO₂/Si MOS电容结构,测量得到了HfO₂基MOS结构在60Co γ射线辐照前后的电容-电压特性,使用原子力显微镜得到了HfO₂薄膜在辐照前后的表面微观形貌,使用X射线光电子能谱方法测量得到了HfO₂薄膜在辐照前后的化学结构变化。研究发现,使用原子层淀积方法制备的HfO₂薄膜表面质量较高;γ射线辐照在HfO₂栅介质中产生了数量级为1012 cm-2的负的氧化层陷阱电荷;HfO₂薄膜符合化学计量比,介质内部主要的缺陷为氧空位且随着辐照剂量的增加而增加,说明辐照在介质中引入了陷阱从而导致MOS结构性能的退化。     

Physical and mechanical properties of silicon near the SiO2/Si interface

The influence of an oxide coating on the strength characteristics of single-crystal silicon surface layers is investigated by the microindentation method. It is shown experimentally that a strengthened layer with a thickness of 0.2–0.4 μm and a microhardness of 20–35 GPa, which is two or three times as much as the microhardness of bulk single-crystal silicon, is present near the SiO₂/Si interface. The thickness and microhardness of this layer depends on the growth conditions of the oxide. The formation of this layer is most probably caused by interstitial silicon atoms formed near the SiO₂/Si interface during silicon oxidation.     

氧化钛薄膜调控金属铜的表面等离子体共振特性研究

提出了一种利用氧化钛薄膜对金属铜薄膜表面等离子体共振特性调制的想法。实验中首先使用电子束蒸发制备一批同等厚度的氧化钛薄膜,再利用磁控溅射方法在氧化钛薄膜上沉积厚度为5～80 nm不等的金属铜薄膜。测试结果表明,氧化钛膜层对不同厚度的金属铜薄膜表面等离子体共振增强具有不同调制效果,金属铜薄膜厚度小于20 nm时,底层的氧化钛薄膜对Cu薄膜表面等离子体共振增强效果显著,且随着金属Cu膜层厚度增加表面等离子体共振峰发生蓝移,而当金属铜膜层的厚度超过20 nm时,共振增强效果因金属Cu薄膜消光能力的上升而开始减弱。     

Nanometric thinning of bonded silicon wafers using sacrificial anodic oxidation and investigated by X-ray reflectivity

X-ray reflectivity and atomic force microscopy are used to investigate silicon oxide ultra-thin films. Quantitative results are shown using a reflectivity simulation model based on kinematical X-ray theory. Changes in film thickness are discussed in relation to current density, voltage, charge and anodization time. The density and resistivity of silicon oxide are calculated and compared to that of thermal oxide. The electrical field existing in the layer during anodization is estimated. Surface roughness is also measured locally and averaged over the entire surface, producing a low value that meets microelectronic requirements. Thickness is carefully controlled. We show that ultra-thin silicon oxide films are of very high quality. Similar investigations are made on a twisted bonded silicon substrate obtained by the molecular bonding of two silicon wafers. It is shown that the silicon oxide is also of very good quality and can be used as a sacrificial silicon oxide in thinning down the upper silicon film. Controlled, accurate thinning is achieved down to a thickness of 10 nm, the level which is required for etching the dislocation network present at the bonding interface.     

Electrochemical and hydrothermal deposition of ZnO on silicon: from continuous films to nanocrystals

This article presents the study of the electrochemical deposition of zinc oxide from the non-aqueous solution based on dimethyl sulfoxide and zinc chloride into the porous silicon matrix. The features of the deposition process depending on the thickness of the porous silicon layer are presented. It is shown that after deposition process the porous silicon matrix is filled with zinc oxide nanocrystals with a diameter of 10–50 nm. The electrochemically deposited zinc oxide layers on top of porous silicon are shown to have a crystalline structure. It is also shown that zinc oxide crystals formed by hydrothermal method on the surface of electrochemically deposited zinc oxide film demonstrate ultra-violet luminescence. The effect of the porous silicon layer thickness on the morphology of the zinc oxide is shown. The structures obtained demonstrated two luminescence bands peaking at the 375 and 600 nm wavelengths. Possible applications of ZnO nanostructures, porous and continuous polycrystalline ZnO films such as gas sensors, light-emitting diodes, photovoltaic devices, and nanopiezo energy generators are considered. Aspects of integration with conventional silicon technology are also discussed.     

Investigation of rapid thermal oxide/ silicon nitride passivation stack of n+ emitter

To anticipate the initial phosphorus diffusion parameters of silicon solar cells process fabrication, we report in this paper an overview of our experiments on silicon n⁺-emitters passivation by means of rapid thermal silicon oxide/silicon nitride stack. The process-induced changes have been evaluated and explained. We found that 900 °C and 80 s were the appropriate process parameters to grow 10 nm silicon oxide. Investigation of the effect of this oxidation on n⁺ multicrystalline silicon emitters revealed a large decrease (more than 25%) of the sheet resistance and around 12% increase of the junction depth. The experiments also revealed that the passivation effect of the optimal silicon oxide/silicon nitride stack is efficient only for higher emitter quality. In addition, we found that this stack reduces the surface reflection more than the optimal single silicon nitride layer.     

Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications

The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultrathin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultrahigh vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700 °C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape, and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO₂ shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO₂ interface with a low amount of suboxides. A minority charge carrier lifetime of 18 µs inside of the nanodots is determined.     

锐钛矿型TiO2(101)面原子几何及弛豫结构的第一性原理计算

采用平面波超软赝势方法计算了锐钛矿型TiO₂(101)面的表面能和表面原子弛豫结构.首先对TiO₂(101)面的6种不同的表面原子终止结构的体系总能量进行了计算,结果表明终止原子为两配位的O原子、次层为五配位的Ti原子的表面结构最为稳定.针对该表面研究了表面能和原子弛豫与模型中原子层数和真空厚度的关系,当原子层数为12层,真空厚度为0.4nm时,表面能收敛度小于0.01J/m².研究发现:表面上两配位的O原子向里移动约0.0012nm,五配 关键词： 第一性原理 2')" href="#">TiO₂ 表面结构 弛豫     

Analysis of semiconductor surfaces with very thin native oxide layers by combined immersion and multiple angle of incidence ellipsometry

In this paper the method of immersion and multiple angle of incidence ellipsometry is used for analyzing silicon and germanium single crystals covered with very thin native oxide layers under normal laboratory conditions. The method is applied at a wavelenght of 632.8 nm. If the values of the absorption index of both semiconductors are known with sufficient accuracy, the values of the refractive index of these semiconductor substrates, the refractive index and the thickness of the effective surface layers (a double layer consisting of the native oxide layer and the interface layer between the semiconductor and this native oxide film) can be determined with relatively high accuracy. These values are compared with those found by other researchers. The thickness and the refractive index of the native oxide layer on the silicon single crystal substrate are also evaluated taking into account the existence of the interface layer.     

Features of atomic and electronic structure of oxides on porous silicon surface according to XANES data

Based on synchrotron research of the fine structure main parameters of SiL _{2, 3} X-ray absorption edges (X-ray absorption near edge structure (XANES)) in porous silicon on boron-doped Si(100) wafers, the thickness of the surface oxide layer and the degree of distortions of the silicon-oxygen tetrahedron in this layer were estimated. The thickness of the oxide layer formed on the amorphous layer coating nanocrystals of porous silicon exceeds the thickness of the native oxide on the surface of Si(100) : P and Si(100) : B single-crystal (100) silicon wafers by several times. Distortion of the silicon-oxygen tetrahedron, i.e., the basic unit of silicon oxide, is accompanied by Si-O bond stretching and an increase in the angle between Si-O-Si bonds.     

Epitaxial growth of zinc oxide by the method of atomic layer deposition on SiC/Si substrates

For the first time, zinc oxide epitaxial films on silicon were grown by the method of atomic layer deposition at a temperature T = 250°C. In order to avoid a chemical reaction between silicon and zinc oxide (at the growth temperature, the rate constant of the reaction is of the order of 10²²), a high-quality silicon carbide buffer layer with a thickness of ~50 nm was preliminarily synthesized by the chemical substitution of atoms on the silicon surface. The zinc oxide films were grown on n- and p-type Si(100) wafers. The ellipsometric, Raman, electron diffraction, and trace element analyses showed that the ZnO films are epitaxial.     

Formations and morphological stabilities of ultrathin CoSi2 films

In this paper we investigate the formations and morphological stabilities of Co-silicide fihns using 1-8-nm thick Co layers sputter-deposited on silicon （100） substrates. These ultrathin Co-silicide films are formed via solid-state reaction of the deposited Co films with Si substrate at annealing temperatures from 450 ℃ to 850 ℃. For a Co layer with a thickness no larger than i nm, epitaxially aligned CoSi2 films readily grow on silicon （100） substrate and exhibit good morphological stabilities up to 600 ℃. For a Co layer thicker than 1 nm, polycrystalline CoSi and CoSi2 films are observed. The critical thickness below which epitaxially aligned CoSi2 film prevails is smaller than the reported critical thickness of the Ni layer for epitaxial alignment of NiSi2 on silicon （100） substrate. The larger lattice mismatch between the CoSi2 film and the silicon substrate is the root cause for the smaller critical thickness of the Co layer.     

Electronic properties of electrolyte/anodic alumina junction during porous anodizing

The growth of porous oxide films on aluminum (99.99% purity), formed in 4% phosphoric acid was studied as a function of the anodizing voltage (23-53 V) using a re-anodizing technique and transmission electron microscopy (TEM) study. The chemical dissolution behavior of freshly anodized and annealed at 200 °C porous alumina films was studied. The obtained results indicate that porous alumina has n-type semiconductive behavior during anodizing in 4% phosphoric acid. During anodising, up to 39 V in the barrier layer of porous films, one obtains an accumulation layer (the thickness does not exceed 1 nm) where the excess electrons have been injected into the solid producing a downward bending of the conductive and valence band towards the interface. The charge on the surface of anodic oxide is negative and decreases with growing anodizing voltage. At the anodizing voltage of about 39 V, the charge on the surface of anodic oxide equals to zero. Above 39 V, anodic alumina/electrolyte junction injects protons from the electrolyte. These immobile positive charges in the surface layer of oxide together with an ionic layer of hydroxyl ions concentrated near the interface create a field, which produces an upward bending of the bands.     

Studies on the polycrystalline silicon/SiO_2 stack as front surface field for IBC solar cells by two-dimensional simulations

Interdigitated back contact(IBC) solar cells can achieve a very high efficiency due to its less optical losses. But IBC solar cells demand for high quality passivation of the front surface. In this paper, a polycrystalline silicon/SiO_2 stack structure as front surface field to passivate the front surface of IBC solar cells is proposed. The passivation quality of this structure is investigated by two dimensional simulations. Polycrystalline silicon layer and SiO_2 layer are optimized to get the best passivation quality of the IBC solar cell. Simulation results indicate that the doping level of polycrystalline silicon should be high enough to allow a very thin polycrystalline silicon layer to ensure an effective passivation and small optical losses at the same time. The thickness of SiO_2 should be neither too thin nor too thick, and the optimal thickness is 1.2 nm.Furthermore, the lateral transport properties of electrons are investigated, and the simulation results indicate that a high doping level and conductivity of polycrystalline silicon can improve the lateral transportation of electrons and then the cell performance.     

SEM/EDS study of metal-assisted oxide desorption

Strongly-enhanced desorption of a thick (100 nm) silicon oxide layer by the pre-sputtering of a thin germanium surface film was observed under high-temperature vacuum annealing conditions. High-resolution SEM imaging reveals that germanium nanoislands are first formed on the sample surface, and that these then act as nucleation centres for the formation of voids in the oxide, leading to a rapid desorption of the silicon oxide layer. EDS analysis of the silicon surface after oxide decomposition shows that the introduced germanium impurities are fully consumed in this desorption process.     

引入纳米氧化层的CoFe/Pd双层膜结构中增强的垂直磁各向异性研究

制备了CoFe/Pd双层结构的界面处或CoFe层 内部引入纳米氧化层后的系列薄膜. 研究结果显示, 引入纳米氧化层后, 可以使薄膜的磁各向异性在退火后从面内转到垂直膜面方向. 并且对于在CoFe层内部引入纳米氧化层的这类样品, 其强烈的垂直磁性可以在相当宽的有效磁性层厚度范围内(1.2-2 nm)维持. 在保持垂直磁性的前提下, 这种特殊的双层膜结构中CoFe磁性层厚度比常规CoFe/Pd 多层膜中的CoFe层厚度至少多出1.4 nm. 本文的研究有助于制备出具有较高热稳定性的垂直磁性器件电极.     

Studies on morphology and molecular arrangement of pentacene on different substrates

Pentacene (C₂₂H₁₄) thin films with different thicknesses were fabricated to study the dynamic growth process and morphology of pentacene on different substrates. A discontinuous monomolecular layer was observed when a pentacene thin film is about 0.5 nm thick on native oxide silicon wafer. The terraced islands and dendritic structure gradually formed with increasing pentacene thin film thickness. The height of each layer is about 1.4 nm which corresponds well with the length of the long axis of the pentacene molecule at 1.45 nm. Experimental results show that the pentacene molecule is perpendicular to the silicon wafer surface with a slight tilted angle. However, the pentacene molecular orientation on a polymer pre-covered indium tin oxide coated substrate could not give any indication on the scale of nanometers. The surface roughness of substrates strongly influences pentacene molecular diffusion and the morphology of pentacene thin films.     

表面氧化钛涂层增强金刚石中浅层NV色心的荧光强度

本文利用原子层沉积技术在金刚石表面沉积了一层氧化钛涂层,该方法使得金刚石中的浅层(深度小于10 nm)NV~-色心的电荷态变得稳定,同时其荧光强度增强至大约原本的2倍.这种表面涂层技术能够为固态量子体系提供厚度可控的保护层或钝化层,同时又不损伤或腐蚀体系表面,有望成为一种固态量子体系钝化或封装的方法.     

Silicon surface passivation by static charge

A properly passivated silicon surface is chemically stable, and all interface properties are constant. The silicon dioxide layers fulfil the chemical stability requirements; however, their surface and interface charges have effect on the silicon surface potential barrier. Positive charge is usually assumed at the oxide-silicon interface, thus depletion or inversion layer develops in the case of p and accumulation in the case of n-type silicon.The surface of silicon dioxide can be charged macroscopically by corona charger or by conductive rubber stamp, microscopically by a tip of some scanning probe microscope (STM or AFM). The oxide surface usually retains the charges for a long time, however in the case of ultra-thin or other leaky oxide continuous charging it is necessary to keep the constant surface potential.The main purpose of this work is to summarize the possibilities of charging up the surface, the effect of the surface and interface charge on the surface properties of the silicon. The rearrangement of the surface charges will also be discussed.     

Combined AFM and Brewster-angle analysis of gradually etched ultrathin SiO2 - Comparison with SRPES results

Two surface sensitive techniques are employed to assess both structural and optical properties of an inhomogeneous Si(1 1 1)/silicon oxide multilayer system. Upon gradual etch-back of the native silicon oxide layer, structural changes of the respective interfaces were determined by contact-mode atomic force microscopy (CM-AFM); optical data were obtained by Brewster-angle analysis (BAA) at a single wavelength. It is shown, that the sensitivity of BAA leads to the identification of an additional strained sub-surface layer that was investigated by subsequent etching experiments and following optical analysis. Inclusion of this layer and its interfaces into a multilayer model allowed precise numerical evaluation of the respective oxide thicknesses in the range between 12 Å and 2 Å. These values, obtained by combination of BAA and AFM, are in excellent agreement with results obtained by synchrotron radiation photoelectron spectroscopy (SRPES). It is furthermore shown, that the thickness resolution limit of BAA (at constant nanotopographic roughness) is well below 1 Å. A limitation of BAA single-wavelength analysis is reached when the roughness variation, in terms of an effective layer and its thickness, exceeds the oxide thickness variation.