Ti/Si和Ti/O/Si界面相互作用的研究

本文利用XPS、UPS和AES等分析技术,对不同清洁处理的Ti/Si(111)界面进行了研究.在超高真空(～4 × 10~(-10)mbar)中,高纯Ti(99.99％)淀积在Si(111)表面上.Ti/S界面产生相互作用.Ti2p和Si2p芯能级产生化学位移,利用电子组态变化的观点解释了所观测到的化学位移.具有氧玷污的Ti 蒸发源,淀积在Si(111)表面上,没有观察到界面相互作用.如果在Si(111)表面存在极薄的氧化层,则在界面处首先形成 Ti的氧化物.文中讨论了氧玷污对界面互作用的影响.     

过渡金属Ni,Pd,Pt硅化物/Si(111)界面的电子态

本文用薄片模型和经验的紧束缚方法给出了 Ni,Pd,Pt过渡金属硅化物/Si(111)界面电子态的理论结果.与Si-Ni,Si-Pd和Si-Pt的UPS实验结果符合较好.     

Pd/a-Si:H界面的光电子能谱研究

本文利用光电子能谱(XPS、UPS)技术研究了Pd淀积层与离子注入制备的a-Si∶H层组成的系统.本工作分析了Pd/a-Si∶H的界面键合状态及组分分布的变化对价带谱与芯能级谱的影响,并与Pd/C-Si系统的结果进行了比较.结果表明:Pd/a-Si∶H界面具有与Pd/C-Si界面相似的电子结构;但是,Pd原子在a-Si∶H中具有较大的扩散速率,因此,处于更富Si的环境中。     

原位XPS分析Al2O3作为势垒层的Er2O3/Si结构

在超高真空条件下,通过脉冲激光沉积(PLD)技术制作了Er2O3/Al2O3/Si多层薄膜结构,原位条件下利用X射线光电子能谱(XPS)研究了Al2O3作为势垒层的Er2O3与Si界面的电子结构.XPS结果表明,Al2O3中Al的2p芯能级峰在低、高温退火前后没有变化;Er的4d芯能级峰来自于硅酸铒中的铒,并非全是本征氧化铒薄膜中的铒;衬底硅的芯能级峰在沉积Al2O 3时没有变化,说明Al2O3薄膜从沉积到退火不参与任何反应,与Si界面很稳定;在沉积Er2O3薄膜和退火过程中,有硅化物生成,表明Er2O3与Si的界面不太稳定,但随着Al2O3薄膜厚度的增加,其硅化物中硅的峰强减弱,含量减少,说明势垒层很好地起到了阻挡扩散的作用.     

关于Ge/GaAs(110)界面的费米能级钉扎

采用饱和的平板模型及半经验的紧束缚方法计算了吸附Ge原子的GaAs(110)表面在不同覆盖度情况下的电子态密度.结合以前对Ge/GaAs(110)界面系统电子态的理论与实验研究工作,提出Ge/GaAs(110)界面的费米能级钉扎位置主要决定于GaAs表面层与Ge吸附层之间的电子电荷转移.     

CeO2高K栅介质薄膜的制备工艺及其电学性质

研究了CeO2作为高K(高介电常数)栅介质薄膜的制备工艺,深入分析了衬底温度、淀积速率、氧分压等工艺条件和利用N离子轰击氮化Si衬底表面工艺对CeO2薄膜的生长及其与Si界面结构特征的影响,利用脉冲激光淀积方法在Si(100)衬底生长了具有(100)和(111)取向的CeO2外延薄膜;研究了N离子轰击氮化Si衬底表面处理工艺对Pt/CeO2/Si结构电学性质的影响.研究结果显示,利用N离子轰击氮化Si表面/界面工艺不仅影响CeO2薄膜的生长结构,还可以改善CeO2与Si界面的电学性质.     

CeO_2高K栅介质薄膜的制备工艺及其电学性质

研究了 Ce O2 作为高 K (高介电常数 )栅介质薄膜的制备工艺 ,深入分析了衬底温度、淀积速率、氧分压等工艺条件和利用 N离子轰击氮化 Si衬底表面工艺对 Ce O2 薄膜的生长及其与 Si界面结构特征的影响 ,利用脉冲激光淀积方法在 Si(10 0 )衬底生长了具有 (10 0 )和 (111)取向的 Ce O2 外延薄膜 ;研究了 N离子轰击氮化 Si衬底表面处理工艺对 Pt/ Ce O2 / Si结构电学性质的影响 .研究结果显示 ,利用 N离子轰击氮化 Si表面 /界面工艺不仅影响 Ce O2 薄膜的生长结构 ,还可以改善 Ce O2 与 Si界面的电学性质     

Ag在Si(111)面上吸附的理论研究

本文用集团模型和电荷自洽的推广的休克尔方法,对 Ag在Si(111)面上覆盖度较高的情况作了研究.得到了 Ag集团在 Si(111)面上稳定的吸附构型和与一些UPS实验结果符合得较好的电子态密度.对Ag在Si(111)面形成的凝聚相也进行了讨论.     

磁控溅射纳米PtSi薄膜表面和界面特征

采用磁控溅射方法在p—Si(111)衬底上淀积5nmPt膜，退火后形成PtSi薄膜，利用原子力显微镜和高分辨电子显微镜观察了PtSi薄膜的表面和界面特征。实验结果表明，工艺条件影响PtSi薄膜的微观组织结构和表面形貌，随着衬底温度增加，薄膜表面由柱晶状团簇变为扁平状团簇，薄膜显微结构由多层变为单层，衬底加热有利于形成界面清晰、结构完整、成分单一的PtSi薄膜。     

Pt/Ti/Si三元固相反应生长PtSi过程的实验研究

采用离子溅射方法在硅衬底上淀积Pt/Ti/Si多层结构,研究了不同退火温度(500℃和800℃)、相同退火时间(30 min)固相反应形成PtSi薄膜的工艺.通过XRD、AES等测试方法,研究了原子的互扩散和反应过程.结果表明,在500℃退火时,由于Pt-Ti-O-Si过渡层的存在,使得Pt和Si反应不够充分,生成物中有部分Pt2Si存在,而800℃退火时,由于过渡层Ti与Si反应生成TiSi2,消耗了大量的Si,使得Pt与Si反应也不够充分.根据上述实验,给出了Pt/Ti/Si三元固相反应在不同退火温度下应采取的工艺务件.     

Characterization of hafnium oxide grown on silicon by atomic layer deposition: Interface structure

Ultra-thin films of hafnium oxide deposited on Si(1 0 0) substrates by means of atomic layer deposition using tetrakis(diethylamino)hafnium as the hafnium precursor are characterized. These films and interface structures are probed using Fourier transform infrared spectroscopy along with Z-contrast imaging and electron energy loss spectroscopy (EELS) of a scanning transmission electron microscope. The interface structure of HfO₂/Si(1 0 0) is further investigated using angle resolved X-ray photoelectron spectroscopy to probe the core level orbitals (Hf 4f, Si 2p, O 1s) at high resolution. The interfacial differences are also examined by probing the Hf 4f bonding with normal incidence XPS in thin and thick films. The XPS studies show that the binding energies remain unchanged with film depth and that there is no apparent signature of silicate structure in the as-deposited films. EELS spectra taken at the interface and XPS measurements suggest the interface is mainly silicon oxide. Two different cleaning methods used show difference only in the thickness of the silicon oxide interlayer.     

衬底表面处理对原子层沉积方式生长铂金薄膜的影响

在这篇文章中,我们利用原子层沉积(ALD)的方式在硅衬底上生长铂金(反应源是(CH₃C₅H₄Pt(CH₃)₃)和氧气)。将经过氢氟酸处理和氧气处理的两种类型硅衬底进行生长对比实验来探究衬底表面处理对原子层沉积方式生长铂金薄膜的影响。相对于经氧化处理的硅衬底来说,在氢氟酸处理的硅衬底上淀积铂金薄膜有较长的滞后时间且生长过程不同。此外,即使在原子层沉积铂金薄膜实验之前利用氢氟酸处理硅衬底以去除天然氧化层,淀积实验完成后在铂金和硅衬底界面处仍有一层中间氧化层。文章解释了导致这种差异性的原因。     

Atom probe tomography of Ni silicides: First stages of reaction and redistribution of Pt

The silicide formation and the redistribution of Pt after deposition and after a heat treatment at 290 °C of Ni_1−xPt_x films on Si have been analysed by atom probe tomography assisted by femtosecond laser pulses. Two phases with different composition were found to form during deposition at room temperature: a NiSi layer with a relatively constant thickness of approximately 2 nm and a particle of Ni₂Si. The shape of the Ni₂Si particle is in accordance with nucleation followed by lateral growth formation. After heat treatment, two silicide phases Ni₂Si and NiSi were found together with the Ni_1−xPt_x solid solution. The redistribution of Pt at the Ni_1−xPt_x/Ni₂Si interface is a clear illustration of the snowplow effect. A segregation of Pt at the Ni₂Si/NiSi interface has been observed and is attributed to interfacial segregation. The effect of the redistribution of Pt on the silicide formation is discussed.     

Visible light emitting Si/SiO2 superlattices

Six-period superlattices of Si/SiO₂ have been grown at room temperature using molecular beam epitaxy. With this mature technology, the ultra-thin (1–3 nm) Si layers were grown to atomic layer precision. These layers were separated by 1 nm thick SiO₂ layers whose thickness was also well controlled by using a rate-limited oxidation process. The chemical and physical structures of the multilayers were characterized by cross-sectional TEM, X-ray diffraction, Raman spectroscopy, Auger sputter-profile, and X-ray photoelectron spectroscopy. The analysis showed that the Si layer is free of impurities and is amorphous, and that the SiO₂/Si interface is sharp (0.5 nm). Photoluminescence (PL) measurements were made at room temperature using 457.9 nm excitation. The PL peak occurred at wavelengths across the visible range for these multilayers. The peak energy position E was found to be related to the Si layer thickness d by E (eV) = 1.60+0.72d⁻² in accordance with a quantum confinement mechanism and the bulk amorphous-Si band gap.     

Aluminum—Silicon Schottky barriers and ohmic contacts in integrated circuits

Experimental observations (electrical characteristics and in depth Auger analysis) have been made of the interface behavior in aluminum-silicon contacts. The barrier heights of these contacts (φbnfor n-type, φbpfor p-type silicon) are sensitive to heat treatments (HT) that are a part of normal integrated circuit processing. If oxide layers (≃20 Å) are present in the Al-Si interface, φbncan be as low as 0.45 eV and φbpas high as 0.75 eV. One can obtain reproducible barrier heights φbp≃ 0.7 eV and φbp≃ 0.5 eV by HT at T ≤ 300deg;C. As the temperature of HT is increased (up to ≃ 550deg;C) φbncan reach ≃ 0.9 eV and φbpdrop to < 0.35 eV. The HT at higher temperatures are accompanied by changes in the Al and Si profiles across the interface region. Two mechanisms have been found to be responsible for the changes in barrier height: 1) the removal of positive charges from the oxide, and 2) metallurgical reactions between the Al and Si. These two mechanisms have been separated and their individual behaviors qualified.     

The C 1<Emphasis Type="Italic">s</Emphasis> core level spectroscopy of carbon atoms at the surface SiC/Si(111)-4° layer and Cs/SiC/Si(111)-4° interface

Photoemission studies of the electronic structure of the Cs/nano-SiC/Si(111)-4° nanointerface are for the first time carried out with the use of synchrotron radiation in the photon energy range 120–450 eV. The in situ experiments are conducted in the case of submonolayer Cs coating of the surface of an epitaxial SiC layer grown on the vicinal surface Si(111)-4° by a new method of substrate-atom substitution. Modification of the valence-band spectra and the C 1s and Si 2p core levels is studied. The appearance of Cs-induced surface states, with binding energies of 1.2 and 7.4 eV, and a sharp change in the spectrum of the C 1s core level with the appearance of two additional modes are found. The evolution of the spectra shows that the Cs/nano-SiC/Si(111)-4° interface is formed due to charge transfer from Cs adatoms to surface atoms at terraces and steps of the vicinal surface. It is found that the structure of the C layer is nontrivial and involves energetically different carbon states.     

Pt-Ir silicide Schottky-barrier IR detectors

Schottky-barrier infrared detectors have been fabricated with silicide electrodes formed by sequential vacuum deposition of 5-10-Å-thick Pt and 10-20-Å-thick Ir layers on p-type Si substrates and subsequent thermal annealing. The barrier heights of the Pt-Ir Schottky diodes are 0.16-0.9 eV, compared with 0.22 eV for Pt-only diodes, and the detector cutoff wavelengths extend well beyond 6 μm. Furthermore, the Pt-Ir diodes exhibit higher detector quantum efficiency than either Pt-only or Ir-only diodes over a significant spectral range     

Tuning of the Platinum Silicide Schottky Barrier Height on n-Type Silicon by Sulfur Segregation

The Schottky barrier height $Phi_{B}$ of platinum silicide (PtSi) contacts on n-type silicon was tuned by sulfur segregation at the PtSi/Si interface. Sulfur was implanted prior to Pt deposition and segregated at the interface during PtSi formation. It was observed that the barrier height could be tuned by changing the sulfur dose. A minimum barrier height of 0.12 eV was obtained on n-type (100) Si substrates. Since PtSi naturally provides a small $Phi_{B}$ of 0.2 eV on p-type Si, it carries the potential to serve as the single metal source/drain contact metal in a CMOS integrated circuit with $Phi_{B}$ tuning on n-channel transistors.      

Direct Observation of Conductive Polymer Induced Inversion Layer in n‐Si and Correlation to Solar Cell Performance

Heterojunctions formed by ultrathin conductive polymer [poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate)—PEDOT:PSS] films and n‐type crystalline silicon are investigated by photoelectron spectroscopy. Large shifts of Si 2p core levels upon PEDOT:PSS deposition provide evidence that a dopant‐free p–n junction, i.e., an inversion layer, is formed within Si. Among the investigated PEDOT:PSS formulations, the largest induced band bending within Si (0.71 eV) is found for PH1000 (high PEDOT content) combined with a wetting agent and the solvent additive dimethyl sulfoxide (DMSO). Without DMSO, the induced band bending is reduced, as is also the case with a PEDOT:PSS formulation with higher PSS content. The interfacial energy level alignment correlates well with the characteristics of PEDOT:PSS/n‐Si solar cells, where high polymer conductivity and sufficient Si‐passivation are also required to achieve high power conversion efficiency.     

Hydrogenated amorphous silicon p–i–n solar cells deposited under well controlled ion bombardment using pulse‐shaped substrate biasing

We applied pulse‐shaped biasing (PSB) to the expanding thermal plasma deposition of intrinsic hydrogenated amorphous silicon layers at substrate temperatures of 200 °C and growth rates of about 1 nm/s. Fourier transform infrared spectroscopy of intrinsic films showed a densification with increasing deposited energy and a reduction in void content, whereas dual‐beam photoconductivity measurements showed an increase in Urbach energy above 4.8 eV/Si atom. From dark conductivity and photoconductivity measurements, we determined a maximum photoresponse of 2 × 10⁶ at 3 eV/Si atom, which decreased at higher deposited energies because of a higher dark conductivity as a result of a lower band gap. p–i–n solar cells with PSB applied during the intrinsic layer deposition showed initial energy conversion efficiencies of 7.4% at around 1 eV/Si atom. Decreasing open‐circuit voltage at >1 eV/Si atom can be related to a lower band gap, whereas the short‐circuit current drops at >4.8 eV/Si atom, predominantly because of hole collection losses as determined from quantum efficiency measurements. The reduced fill factor for >1 eV/Si atom was presumably related to a decrease in mobility‐lifetime product because of an increase in defect density. Copyright © 2011 John Wiley & Sons, Ltd.