Polarized Raman spectroscopy study of NiSi film grown on Si(001) substrate

We report on the growth of NiSi film on Si(001) substrate with an orientation of NiSi[200]//Si[001]. Polarized Raman spectroscopy was used to assign the symmetry of the NiSi Raman peaks. Raman peaks at 213 cm⁻¹, 295 cm⁻¹, and 367 cm⁻¹ are assigned to be A _g symmetry and peaks at 196 cm⁻¹, and 254 cm⁻¹ are B _3g symmetry.     

X-ray photoelectron spectroscopy study of NiSi formation on shallow junctions

The influence of boron (B)/arsenic (As) on X-ray photoelectron spectroscopy (XPS) study of NiSi formation on shallow junctions is investigated in this paper. The Ni-silicide film was formed after 30 s soak anneal at 450 °C on ultra shallow p+/n or n+/p junctions. The atomic ratio of Ni/Si profile in depth was probed by XPS and the results show that a uniform NiSi layer forms on B-doped p+/n junction while a non-uniform, Ni-rich silicide layer forms on As-doped n+/p junction. It does not agree with the results of other independent phase identification methods such as X-ray diffraction, Rutherford backscattering spectroscopy, and Raman scattering spectroscopy, which all demonstrate the formation of NiSi on both n+/p and p+/n junctions. Comparing the raw binding energy spectra of Ni and Si for each silicide film, the similar spectra for Ni signals are revealed. But the Si signals with an obviously smaller intensity is found to be responsible for the apparent Ni rich silicide formation on As-doped n+/p junction. It indicates that As atoms in the silicide film can affect the sputtering yield of Ni and Si, while no noticeable effect is observed for B atoms. More As atoms than B atoms segregation into the silicide layer is indeed verified by secondary ion mass spectroscopy. And micro-Raman scattering spectroscopy further confirms that the degree of crystallinity for NiSi on n+/p junction is inferior to that on p+/n junction.     

Formation of Interfacial Layers in LaAlO3/Silicon during Film Deposition

We have studied the interracial reactions between amorphous LaAlO3 thin films and Si substrates, using high- resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It has been shown that the interracial layer between LaAlO3 film and Si substrate chemical states show that the ratio of La 4d3/2 to Al 2p is SiLaxAlyOz. The depth distributions of La, Si and Al of the interfacial layer remains unchanged with the depth compared to that of the LaAlO3 film. Moreover, the Si content, in the interracial layer gradually decreases with increasing thickness of the interracial layer. These results strongly suggest that the Al element is not deficient in the interracial layer, as previously believed, and the formation of a SiLaxAlyOz interracial layer is mainly due to the diffusion of Si from the substrate during the LaAlO3 film deposition. With the understanding of the interracial layer formation, ones can control the interface characteristics to ensure the desired performances of devices using high-k oxides as gate dielectrics.     

Silicidation in Ni/Si thin film system investigated by X-ray diffraction and Auger electron spectroscopy

Silicide formation induced by thermal annealing in Ni/Si thin film system has been investigated using glancing incidence X-ray diffraction (GIXRD) and Auger electron spectroscopy (AES). Silicide formation takes place at 870 K with Ni₂Si, NiSi and NiSi₂ phases co-existing with Ni. Complete conversion of intermediate silicide phases to the final NiSi₂ phase takes place at 1170 K. Atomic force microscopy measurements have revealed the coalescence of pillar-like structures to ridge-like structures upon silicidation. A comparison of the experimental results in terms of the evolution of various silicide phases is presented.     

Structural and phase transformations during initial stages of copper condensation on Si(001)

Auger-electron spectroscopy, electron-energy loss spectroscopy, low-energy electron diffraction, and atomic-force microscopy are employed to investigate the growth mechanism, composition, structural and phase states, and morphology of Cu films (0.1–1 nm thick) deposited on a Si(001)-2 × 1 surface at a lower temperature of Cu evaporation (900°C) and room temperature of a substrate. The Cu film phase is shown to start growing on the Si(001)⁻² × 1 surface after three Cu monolayers (MLs) are condensed. It has been revealed that atoms of Cu and Si(001) are mixed, a Cu₂Si film phase is formed, and, thereafter, Cu₃Si islands arise at a larger coating thickness. Annealing of the first Cu ML leads to reconstruction of the Si(001)-1 × 1-Cu surface layer, thereby modifying the film growth mechanism. As a consequence, the Cu₂Si film phase arises when the thickness reaches two to four MLs, and bulk Cu₃Si silicide islands begin growing at five to ten MLs. When islands continue to grow, their height and density reach, respectively, 1.5 nm and 2 × 10¹¹ cm⁻² and the island area is 70% of the substrate surface at a thickness of ten MLs.     

China rose petal as biotemplate to produce two-dimensional ceria nanosheets

China rose petal was used as robust biotemplate for the facile fabrication of novel ceria nanosheet with a thickness of about 7 nm via a continuous infiltration process. The presence of well-resolved peaks ([111], [200], [220], and [311]) for the products revealed the formation of the fluorite-structured CeO₂. The detailed characterization by field-emission scanning electron microscope (FESEM), field-emission transmission electron microscope (FETEM), and atomic force microscopy (AFM) exhibited the biomorphic structure of polycrystalline ceria film with the nanoparticle size of ca. 6.98 nm. Based on the surface chemistry and biochemistry processes, a possible mechanism for the formation of CeO₂ nanosheets is proposed. Furthermore, nitrogen adsorption–desorption measurement and photoluminescence spectrum (PL) were employed to characterize the samples. The ceria nanosheet showed the existence of mesopores (pores 2–4 nm diameter) on its surface and a broad emission ranging from 350 to 500 nm in photoluminescence spectrum. X-ray photoelectron spectroscopy analysis (XPS) confirmed that the mesoporous nanosheets possessed more surface vacancies than the bulk CeO₂; hence these hierarchical CeO₂ layers appear to be potential candidates for catalytic applications.     

Structural and electrical characterization of the nickel silicide films formed at 850 °C by rapid thermal annealing of the Ni/Si(1 0 0) films

Nickel di-silicide formation induced by RTA process at 850 °C for 60 s in the Ni/Si(1 0 0) systems are investigated as a function of the initial Ni film thickness of 7-89 nm using XRD, RBS, SEM, X-SEM and AFM. Based on the XRD and RBS data, in the silicide films of 400-105 nm, NiSi and NiSi₂ silicide phases co-exist, indicating that Ni overlayer is completely transformed to NiSi and NiSi₂ silicide phases. SEM reveals that these films consist of large grains for co-existence of NiSi₂ and NiSi phases, separated from one another by holes, reflecting that NiSi₂ grows as islands in NiSi matrix. These films have low sheet resistance, ranging from 1.89 to 5.44 Ω/□ and good thermal stability. For thicknesses ≤ 80 nm RBS yields more Si-rich silicide phases compared to thicker films, whereas SEM reveals that Si-enriched silicide islands with visible holes grow in Si matrix. As the film thickness decreases from 400 to 35 nm, AFM reveals a ridge-like structure showing a general trend of decreasing average diameter and mean roughness values, while sheet resistance measurements exhibit a dramatic increase ranging from 1.89 to 53.73 Ω/□. This dramatic sheet resistance increase is generated by substantial grain boundary grooving, followed by island formation, resulting in a significant phase transformation from NiSi₂-rich to Si-rich silicide phases.     

Formation of ultrathin magnetic cobalt films on the Si(111)7 × 7 surface

The phase composition, electronic structure, and magnetic properties of ultrathin cobalt films (no thicker than 20 ?) applied on a Si(111)7 × 7 surface at room temperature are studied by high-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism. It is shown that, as the cobalt thickness increases, first interface cobalt silicide and then an island (discontinuous) film of silicon-in-cobalt solid solution form on the silicon surface. A metal cobalt film starts growing after the deposition of a ∼7-?-thick Co layer. It is found that the ferromagnetic ordering of the system, which is characterized by surface magnetization, sets in after the deposition of a ∼6-?-Co layer at the stage of Co-Si solid solution formation.     

Study of nickel silicide formation on Si(1 1 0) substrate

Nickel silicide formation on Si(1 1 0) and Si(1 0 0) substrate was investigated in this paper. It is confirmed that nickel monosilicide (NiSi) starts to form after 450 °C annealing for Si(1 0 0) substrate, but a higher annealing temperature is required for NiSi formation on Si(1 1 0) substrate, which is demonstrated by X-ray diffraction (XRD) and Raman scattering spectroscopy. The higher formation temperature of NiSi is attributed to the larger Ni₂Si grain size formed on Si(1 1 0) substrate. Ni silicided Schottky contacts on both Si(1 0 0) and Si(1 1 0) substrates were also fabricated for electrical characteristics evaluation. It clearly reveals that the rectifying characteristics of NiSi/n-Si(1 1 0) Schottky contacts is inferior to that of NiSi/n-Si(1 0 0) Schottky contacts, which is attributed to a lower Schottky barrier height and a rougher contact interface. The formation kinetics for nickel silicide on Si(1 1 0) substrate is also discussed in this paper.     

Formation of the Co/Si(110) interface: Phase composition and magnetic properties

The formation of the Co/Si(110)16 × 2 interface and its magnetic properties are studied by high-energy-resolution photoelectron spectroscopy using synchrotron radiation and magnetic linear dichroism in the photoemission of core electrons. It is shown that a cobalt coating less than 7 Å thick deposited on the silicon surface at room temperature results in the formation of an ultrathin (1.7 Å) interfacial cobalt silicide layer and a layer of silicon-cobalt solid solution. The ferromagnetic ordering of the interface is observed at an evaporation dose corresponding to 6–7 Å in which case a cobalt metal film begins to grow on the solid solution layer. During 300°C-annealing of the sample covered by a nanometer-thick cobalt layer, the metal film gradually disappears and four silicide phases arise: metastable ferromagnetic silicide Co₃Si and three stable nonmagnetic silicides (Co₂Si, CoSi, and CoSi₂).     

Formation of zero-dimensional hole states during molecular-beam epitaxy of Ge on Si (100)

The characteristic features of electronic spectra in Ge/Si (100) heterostructures obtained by molecular-beam epitaxy are investigated by capacitance spectroscopy. It is observed that the self-organization of a Ge film into an island film when the effective germanium thickness exceeds six monolayers is accompanied by the appearance of hole bound states, which can be attributed to size quantization and the Coulomb interaction of carriers in the array of Ge quantum dots. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 2, 125–130 (25 July 1998)     

Thin PTCDA films on Si(0 0 1): 1. Growth mode

We have studied the interface and thin film formation of the organic molecular semiconductor 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA) on clean and on hydrogen passivated Si(0 0 1) surfaces. The studies were made by means of high resolution X-ray photoelectron spectroscopy (HRXPS), near edge X-ray absorption fine structure (NEXAFS), low energy electron diffraction (LEED), and atomic force microscopy (AFM). On the passivated surface the LEED pattern is somewhat diffuse but reveals that the molecules grow in several ordered domains with equivalent orientations to the substrate. NEXAFS shows that the molecules are lying flat on the substrate. The Si 2p XPS line shape is not affected when the film is deposited so it can be concluded that the interaction at the interface between PTCDA and the substrate is weak. The evolution of the film formation appears to be homogeneous for the first monolayer with a nearly complete coverage of flat lying molecules based on the XPS attenuation. For layer thickness of 0.5-2 monolayers (ML) the molecules start to form islands, attracting the molecules in between, leaving the substrate partly uncovered. For thicker films there is a Stranski-Krastanov growth mode with thick islands and a monolayer thick film in between. For the clean surface the ordering of the film is much lower and angle resolved photoelectron spectroscopy (ARPES) of the molecular orbitals have only a small dependence of the emission angle. NEXAFS shows that the molecules do not lie flat on the surface and also reveal a chemical interaction at the interface.     

Formation, electronic structure, and stability of film nanophases of transition metals on silicon

This paper is devoted to the study of the morphology, growth, electronic structure, and stability of ultrathin (0.03–3 nm) Co and Fe films on the Si(111) and Si(100) surfaces using Auger-electron spectroscopy, electron-energy loss spectrometry, low-energy electron diffraction, and atomic-force microscopy. It is shown that layer-by-layer growth of the metal with the formation of the film nanophase and the segregation of a submonolayer amount of Si on the film’s nanophase surface occurs during the process of layer-by layer growth of Co and Fe on Si(111)-7 × 7 and Si(100)-2 × 1 at room temperature after the growth of two-dimensional metal phases (the surface phase, the monolayer, and two metal monolayers). After these stages, the formation and growth of the bulk’s metal phase with the dissolution of silicon segregated before occur. It is shown that the upper layers of Si adjoining the surface phase, the monolayer, and two Co and Fe monolayers have respectively three different densities of the electron plasma that are higher than the density of the electron plasma in the volume of the silicon substrate. The nonmonotonous character of the morphological and chemical stability of Fe films with quantum-size thicknesses on Si(100) is discovered. After annealing, the film is first smooth, then it is nonuniform across its thickness; afterwards it is again smooth and then nonuniform across its thickness. In this case, the metal phase, different Fe silicides, and the bulk’s metal phase form successively in Fe films on Si(100) after annealing.     

电化学方法制备ZnO纳米颗粒掺杂类金刚石薄膜及其场发射性能研究

采用液相电化学沉积技术制备了ZnO纳米颗粒掺杂的类金刚石(DLC)薄膜, 研究了ZnO纳米颗粒掺杂对DLC薄膜场发射性能的影响. 利用X射线光电子能谱、透射电子显微镜、Raman光谱以及原子力显微镜分别对薄膜的化学组成、 微观结构和表面形貌进行了表征. 结果表明: 薄膜中的ZnO纳米颗粒具有纤锌矿结构, 其含量随着电解液中Zn源的增加而增加. ZnO纳米颗粒掺杂增强了DLC薄膜的石墨化和表面粗糙度. 场发射测试表明, ZnO纳米颗粒掺杂能提高DLC薄膜的场发射性能, 其中Zn与Zn+C的原子比为10.3%的样品在外加电场强度为20.7 V/μm时电流密度达到了1 mA/cm². 薄膜场发射性能的提高归因于ZnO掺杂引起的表面粗糙度和DLC薄膜石墨化程度的增加.     

Study of ultrathin iron silicide films grown by solid phase epitaxy on the Si(001) surface

Ultrathin films of iron silicide have been grown by high-temperature annealing of 0.14-to O.5O-nm-thick Fe films deposited on the Si(001) surface at room temperature. It has been found that annealing leads to the formation of nanoislands of iron silicide on the surface, so that their type depends on the thickness of the Fe film. High-energy electron diffraction and atomic force microscopy measurements have revealed that the deposition of Fe films less than 0.32 nm thick on the Si(001) surface stimulates epitaxial growth of both three-dimensional β-FeSi₂ and two-dimensional γ-FeSi₂ islands. It has been found that, for Fe coverages of more than 0.32 nm thick, a complete transition to solide phase epitaxy is observed only for two-dimensional β-FeSi₂ islands. The effect of prolonged annealing at 850°C on the morphology of the surface of the iron silicide film has been investigated.     

Oxygen distribution in nickel silicide films analyzed by time-of-flight secondary ion mass spectrometry

The oxygen distribution in Ni₂Si and NiSi films formed during a two-step silicidation process was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS mass spectra revealed that both silicon and nickel reacted with oxygen at the Ni₂Si surface. In addition, silicon nitride was formed at the surface by the reaction of silicon with nitrogen in the TiN capping layer during the first silicidation annealing. The amount of nitrogen at the NiSi surface varied with silicidation annealing temperature and with the formation conditions of the TiN capping layer. We also showed that a small amount of oxygen was penetrated into the NiSi film and strongly affected the level of junction leakage current in n⁺–p junctions in n-channel MOSFETs. The oxygen concentration in the NiSi film decreased with an increase in the amount of nitrogen at the NiSi surface.     

Low-temperature diffusion of silicon atoms in the nickel-nickel silicide-silicon system

The diffusion of Si atoms from a silicon substrate through a layer of nickel monosilicide into a Ni film is investigated in the temperature interval 470–670°K by the method of radioactive isotopes. The distribution profile of Si in NiSi and Ni is derived. The GB-diffusion parameters of Si in NiSi are determined. It is shown that when T>570°K there is an increase in the thickness of the initial NiSi layer, and a kink appears on the in D=f(1/T) curve. The associated change in the activation energy of diffusion from 0.43 (470–570°K) to 0.72 eV (570–670°K) is explained by the formation of Ni-Si and Si-O type complexes. The diffusion of silicon atoms accompanied by complex-formation processes determines the evolution of the resistivity of the Ni-NiSi-Si contact.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 78–83, March, 1985.     

Micro-Raman spectroscopic investigation of NiSi films formed on BF<Subscript>2</Subscript><Superscript>+</Superscript>-, B<Superscript>+</Superscript>- and non-implanted (100)Si substrates

The micro-Raman spectroscopic technique was used to investigate vibrational properties of NiSi thin films formed on three different (100)Si substrates: non-implanted, 20 keV BF₂⁺-implanted, and 20 keV B⁺-implanted. Raman measurements were also performed on NiSi powder to identify various phonon modes associated with different selection rules of group theory. It was found that the Raman peaks for NiSi thin films formed on the BF₂⁺-implanted substrate were broader and shifted to lower frequencies compared to those for films formed on the other substrates. The broadening of the Raman peaks for these films, which also exhibit much improved thermal stability, is attributed to the small grains that probably result from the segregation of fluorine to grain boundaries and interfaces. It is further proposed that grain boundary segregation influences the stress in the silicide film, resulting in shifts in phonon peak positions. PACS 78.30.Am; 74.25.Kc; 68.35.Dv; 68.55.Ln; 66.30.Jt     

Reactive epitaxy of cobalt disilicide on Si(111)

A study of the mechanism governing the initial stages in silicide formation under deposition of 1–10 monolayers of cobalt on a heated Si(111) 7×7 crystal is reported. The structural data were obtained by an original method of diffraction of inelastically scattered medium-energy electrons, which maps the atomic structure of surface layers in real space. The elemental composition of the near-surface region to be analyzed was investigated by Auger electron spectroscopy. Reactive epitaxy is shown to stimulate epitaxial growth of a B-oriented CoSi₂(111) film on Si(111). In the initial stages of cobalt deposition (1–3 monolayers), the growth proceeds through island formation. The near-surface layer of a CoSi₂(111) film about 30 Å thick does not differ in elemental composition from the bulk cobalt disilicide, and the film terminates in a Si-Co-Si monolayer triad.     

等离子增强原子层沉积低温生长AlN薄膜

采用等离子增强原子层沉积技术在单晶硅基体上成功制备了AlN晶态薄膜, 利用椭圆偏振仪、原子力显微镜、小角掠射X射线衍射仪、高分辨透射电子显微镜、 X射线光电子能谱仪对样品的生长速率、表面形貌、晶体结构、薄膜成分进行了表征和分析, 结果表明, 采用等离子增强原子层沉积制备AlN晶态薄膜的最低温度为200 ℃, 薄膜表面平整光滑, 具有六方纤锌矿结构与(100)择优取向, Al_2p与N_1S的特征峰分别为74.1 eV与397.0 eV, 薄膜中Al元素与N元素以Al-N键相结合, 且成分均匀性良好. 关键词： 氮化铝 等离子增强原子层沉积 低温生长 晶态薄膜