Radiation-induced plasmons in St-SiO_2

1IntroductionOneofthemostweaknessesOfelectricdevicesbasedonSt-SiOZisthatthedevicesmaylacetheirfunctionsbecauseinterfaCe,t.t..[i]andpositivecharge[']arecreatedbyionizationradiationintheSt-SiO2.Overthepasty6ars,anumberOfmodelshavebeensuggestedtoexplaintheoriginsofillterfaCestateandpositivecharge.Rowever,theoXygenvarancymodel,whichwasproposedbyelectronspinresonance(ESR)formeasurementofpointdefects[3]1isinconsistentwiththebondstraingradientmodel,whichwassuggestedthroughXPS[4],intheexplansti…     

Si—SiO2及其在电离辐照下的等离激元

用ＸＰＳ分析技术对抗辐射加固与非加固的Ｓｉ－ＳｉＯ２进行了电离辐照前后Ｓｉ的一级等离激元（定位于Ｂ．Ｅ．１１６．９５ｅＶ）及ＳｉＯ２一级等离激元（定位于Ｂ．Ｅ．１２２．０ｅＶ）的研究。实验结果表明：存在一个由这两种等离激元组成的界面，在电离辐射的作用下，此界面区向ＳｉＯ２表面方向展宽，界面中心向ＳｉＯ２表面方向移动；两种Ｓｉ－ＳｉＯ２界面区中的ＳｉＯ２一级等离激元的浓度在正电场中辐照均随辐照剂量的增加而增加，而非加固样品中一级等离激元浓度在正电场中随辐照剂量的变化所产生的变动快于加固样品；在同一辐照剂量下加正电样品中等离激元浓度的变化远明显于不加电样品。     

电离辐射下双界面Si3N4/SiO2/Si的等离激元

用X光激发电子能谱(XPS)分析技术对Si3N4/SiO2/Si双界面系统经60Co电离辐照前后处于纯Si态的一级等离激元(定位于B.E. 116.95 eV)、处于SiO2态的一级等离激元(定位于B.E. 122.0 eV)和处于Si3N4态的一级等离激元(定位于B.E. 127.0 eV)进行了研究.实验结果显示:存在一个由Si3N4态等离激元和SiO2态等离激元构成的界面及由SiO2态等离激元和Si态等离激元构成的界面,在电离辐射的作用下,SiO2态-Si3N4态等离激元界面区中心向Si3N4态表面方向推移,同时SiO2态/Si3N4态等离激元界面区亦被展宽;电离辐照相当程度地减少位于SiO2态-Si态界面至Si衬底之间SiO2态的一级等离激元的浓度:同时偏置电场对SiO2/Si界面等离激元有显著作用.文中就实验现象以光电子能损进行了机制分析.     

Thermally Stimulated Current Measurements on Irradiated MOS Capacitors

Thermally stimulated current and high frequency C-V measurements have been used to study the properties of hole traps near the Si-SiO2 interface in irradiated silicon MOS capacitors. Pre-irradiation bias-temperature (BT) instabilities, both for negative and positive bias, were observed in non-ion-contaminated samples. The activation energy for BT instabilities for both polarities is ~1.0 eV independent of radiation hardness. Distributions of activation energies for trapped holes produced by Co60 irradiation are centered at ~0.85 and ~1.3 eV. The ~0.85 eV distribution occurs only if Na+ was previously present at the Si-SiO2 interface. The ~1.3 eV distribution consists of multiple overlapping distributions. Mechanisms that could lead to these distributions of activation energies are discussed.     

Vacuum Ultraviolet Radiation Effects in SiO2

Charging effects observed in MOS structures which have been exposed to sputtering plasmas or electron beam deposition suggest that Vacuum Ultraviolet (VUV) or soft X-radiation is important in producing these effects. Our experiments show that under positive gate bias VUV irradiation produces large positive charging effects for photon energies above 8.8 eV, the threshold for electron-hole pair creation in SiO2. This charging appears to be accompanied by an increase in interface state density. VUV radiation proves to be more useful than higher energy quanta or particles in studying radiation charging. This is true because one can control the depth of radiation absorption into the oxide. Etching experiments show that positive charge is induced near the Si-SiO2 interface even when radiation is absorbed near the gate electrode. This result is strong evidence in support of the hole transport and trapping model. We present evidence that under irradiation with positive bias, positive space charge is formed near both interfaces. We also show how a large positive space charge can be introduced into the oxide without a gate electrode.     

XPS STUDIES OF IRRADIATED HARD AND SOFT Si—SiO_2

The interracial structure of hard and soft oxides grown by dry oxidation on<100> n-type silicon substrates is examined using high resolution mild X-ray photoelectron spectroscopy (XPS) before and after irradiation. Substantial differences in silicon of silica state (B.E. 103.4 eV), silicon of transitional state (B.E. 101.5 eV), surplus oxygen (B.E. 529.6 eV) and negative two-valence oxygen (B.E. 531.4 eV) are observed between the two kinds of samples. The XPS spectra strongly depend on the conditions of irradiation for soft samples, but do not as remarkablely as soft samples for hard samples. The effects of irradiation doses on XPS are greater than that of irradiation bias fields. Some viewpoints of irradiation induced hole electron pair are proposed to explain the results.     

Radiation-Induced Defects in SiO2 as Determined with XPS

Device quality gate oxides (~ 850 ?) grown on Si (100) substrates are irradiated with 0 - 20 eV electrons during in situ XPS measurements. These structures have been thinned stepwise to 25 to 60 ? using a relatively benign wet-chemical depth-profiling procedure. An analytical method based on oxide/substrate intensity ratios is used to deduce the product of the atomic number density (D) and the electron mean free path (?) as a function of depth for these structures. Samples showing a wide variety of hole trapping efficiencies were examined. Si+3 species are formed in the region of the Si/SiO2 interface and are observed during the course of their relaxation and annihilation. These formation results are correlated with the presence of strained Si-O-Si bonds at the interfaces. Radiation hard and soft structures show different strained bond distributions in the interfacial region. The direct observation of bond cleavage and bond strain gradients in these samples is used to extend silica devitrification models to explain the generation of fixed oxide charge and interface states. This bond strain gradient (BSG) model is shown to be consistent with a variety of experimental EPR and electrical observations of hole- and electron-trap generation by ionizing radiation.     

电子束在MOS结构中的能量沉积与辐照效应

根据电子输运“双群理论”计算出电子在Ｓｉ－ＳｉＯ２材料中的能量沉积。用与硅等２效的外推电离室测定了１．０ＭｅＶ和１．５ＭｅＶ的电子束在ＭＯＳ电容芯片中的吸收剂量。用Ｘ光电子谱、俄歇谱、深能级瞬态谱和Ｃ－Ｖ方法测量分析了ＭＯＳ电容Ｓｉ－ＳｉＯ２材料化学结构，界面态密度和Ｃ－Ｖ曲线在辐射前后的变化，根据理论和实验结果，从辐射剂量学的角度分析讨论了电子能量沉积，电离缺陷和辐射效应间的关系，并提出一个关于     

Defect Structure and Irradiation Behavior of Noncrystalline SiO2

Various phenomena occuring during ionizing or particle irradiation of vitreous silica and Si-SiO2 interface structures are explained. Densification and changes in bond polarizability are due to the basic trend of maximizing ?-bonding between Si and O atoms with minimum bond strain. Hole trapping in SiO2, as exhibited, e.g., in irradiated MOS devices, is an intrinsic property of the Si-O bond. Irradiation generates trivalent Si and non-bridging O defects. These interact with impurities, especially SiOH and SiH groups, as well as with interstitial H. These defects determine the radiation behavior of vitreous silica and Si-SiO2 interfaces, as well as the stability of MOS devices.     

Study of Ionizing Radiation Damage in MOS Structures Using Internal Photoemission

The effects of ionizing radiation in large-geometry MOS structures were studied by use of internal photoemission techniques. Barrier heights at both the silicon-silicon dioxide and the silicon dioxide-metal (chromium and aluminum) interfaces were measured before and after irradiation in a Co60 gamma cell. It was determined that the measured barrier energy heights may be considerably reduced by radiation-induced oxide charge. The internal photoemission technique also provided significant information concerning the effects of impurities in the oxide and the related radiation hardness of the oxide layer. Oxide layers doped with chromium ions showed significant electron trapping at two discrete energy levels (3.4 and 3.8 eV). Samples exhibiting the 3.4 eV level showed great radiation hardness, while those with only the 3.8 eV peak were very radiation soft. The information obtained, using the internal photoemission technique, has provided considerable insight into the mechanisms and fabrication processes associated with radiation-hardened MOS devices.     

抗辐射加固与非加固工艺制备Si/SiO_2电离辐照的XPS深度剖析

采用氩离子刻蚀XPS分析方法对抗辐射加固与非加固工艺制备的Si/SiO_2系统进行电离辐照深度剖析。实验结果表明:在辐照剂量及偏置电场相同条件下辐照,非加固样品的界面区比加固样品界面区宽;同一工艺生长的SiO_2,衬底杂质浓度低的样品其界面区窄于衬底杂质浓度高的样品;辐照样品的Si过渡态密度最高位滞后于未辐照样品的;同时,加固样品Si过渡态及剩余氧的密度最高位出现慢于非加固样品的;衬底杂质浓度高的样品其Si过渡态及剩余氧的密度最高位的出现快于衬底杂质浓度低的样品的;此外含剩余氧的过渡层要比含Si过渡态的过渡层薄。最后根据实验结果,对Si/SiO_2三层模型进行了修正。     

Characterization of Annealing of Co60 Gamma-Ray Damage at the Si/Si02 Interface

The annealing of Co60 gamma-ray damage at the Si/SiO2 interface is a well behaved phenomenon. Based on the characterization of annealing over a temperature range of 25° to 300°C, a physical model is developed. This model suggests that the annealing of the radiation damage occurs in two phases: first, the Qf-like trapped positive charges are converted to acceptor-like fast-states, and second, the fast-states are gradually annihilated. Both of these phases occur at an accelerated rate at a given temperature in presence of hydrogen. The densities of trapped positive charges and fast-states reach saturation levels which depend on the level of radiation (dose rate), and the temperature. The tolerance level of an IC to radiation exposure depends on these saturation levels. The experimental results also indicate that the positive charges are trapped at the Si/SiO2 interface even if a negative gate-bias is applied during irradiation. Furthermore, it is unambiguously observed that once the holes are trapped at the interface, they do not move along the interface even under applied biases, but they move only toward Si where they become acceptor-like fast-states.     

鼻咽癌放射治疗时野外组织器官剂量的研究

本文借助非均匀组织等效似人体模型,模拟鼻咽癌放射治疗,研究了＾６０Ｃｏγ射线和电子直线加速器产生的６ＭＶＸ射线对野外组织器官的受照剂量。结果表明,离照射野越近组织器官受照剂量越高,加眼晶体、垂体、甲状腺等,但睾丸的受照剂量明显高于腹部;＾６０Ｃｏγ射线照射时野外组织器官的剂量明显高于６ＭＶＸ射线;＾６０Ｃｏγ射线照射时,在耳前野野外挡铅可使眼晶体、视网膜受照剂量下降２０％,睾丸表面挡铅可使睾丸受照     

Gamma Total Dose Effects on ALS Bipolar Oxide Sidewall Isolated Devices

Advances in bi-polar technology that increase device performance through the use of oxide sidewall isolation have revived concerns about total dose radiation effects. Extensive Cobalt 60 tests of Texas Instruments ALS devices were conducted and comparative results of "walled" and "nested" emitter devices are included. It was determined that inversion at the Si-SiO2 interface between the isolation oxide and residual EPI material was the source of IIH leakage. Controls were established to improve gamma total dose tolerance.     

Molecular-dynamics simulation of threshold displacement energies in zircon

Molecular-dynamics simulations were used to examine the displacement threshold energy (E_d) surface for Zr, Si and O in zircon using two different interatomic potentials. For each sublattice, the simulation was repeated from different initial conditions to estimate the uncertainty in the calculated value of E_d. The displacement threshold energies vary considerably with crystallographic direction and sublattice. Based on the present simulations and previous experimental studies, this work recommends E_d values of 75, 75 and 60 eV for Zr, Si and O, respectively, to be used in Monte Carlo simulations of irradiation damage profile in zircon.     

Si/SiO2系统的总剂量辐射损伤及辐射感生界面态的能级分布

对比了目前常用的三种用54HC电路制作工艺制作的MOS电容的总剂量辐射实验结果,并从微观氧化物电荷、界面态的感生变化及其界面态的能量分布变化等角度,研究了在不同制作工艺条件下,54HC电路Si/SiO2系统总剂量辐射损伤特性.     

Molecular dynamics simulation of fluorine ion etching of silicon

Formation of precursors and desorption of etching products by fluorine ion irradiation were studied using molecular dynamics (MD) simulation. When F atoms impact sequentially on a Si substrate, a mixed layer of F and Si atoms is formed on the surface. When the incident energy is below 30 eV, the fluorine coverage reaches steady state after 1.0×10¹⁶ atoms/cm² irradiation. The ratio of F to Si in the mixed layer is about 1:1. At an incident energy of 15 eV, the mixed layer at steady state consists of 4.5 ML of fluorine with a depth of 20 Å and the main etching products are SiF₃ and SiF₄. At 30 eV incident energy, the mixed layer at steady state is 6.5 ML with a depth of 40 Å and the main etching products are SiF₂ and SiF₃. When F atoms were irradiated onto a Si substrate heated at 1000 K, a significant reduction of F coverage was observed due to diffusion of F atoms.