Pd-Si薄膜固相反应的透射电子显微镜研究

本工作利用透射电子显微术研究了Pd-Si薄膜固相反应的初始生成相及生成相Pd₂Si与(111)取向Si衬底的取向关系随Pd膜厚度、退火温度等因素的变化规律。实验结果表明:在衬底保持室温的条件下,Pd沉积到Si(111)上时也能够生成一层外延的Pd₂Si,其厚度足以在常规的选区电子衍射中产生明显的信号。在170℃退火时,Pd-Si反应即可持续到生成200nm厚的外延的Pd₂Si。在Pd膜厚度为400nm的条件下,Pd₂Si与Si(111)衬底的取向关系为[0001]_(Pd2Si)轴织构。 关键词：     

A leed-aes study of thin Pd films on Si(111) and (100) substrates

A system Pd (deposit)-Si (substrate) has been studied by LEED and AES. Pd₂Si formed on Si(111) became epitaxial after a short time of annealing at a temperature between 300 and 700°C, while the Pd₂Si formed on Si(100) did not, in both cases the surfaces of the Pd₂Si being covered with a very thin Si layer. A sequence of superstructures (3√3 × 3√3), (1 × 1), and (2√3 × 2√3) was observed successively in Pd/Si(111) as the annealing temperature was increased. A (√3 × √3) structure was obtained by sputtering the 3√3 surface slightly. It was found that the √3 structure corresponds to Pd²Si(0001)-(1 × 1) grown epitaxially on Si(111), and that the 3√3 structure comes from the thin Si layer accumulated over the silicide surface, while the 2√3 and 1 structures arise from a submonolayer of Pd adsorbed on Si(111). Superstructures observed on a Pd/Si(100) system are also studied.     

AES and factor analysis study of silicide growth at the Pd/c-Si interface

We have measured the evolution of a palladium/silicon interface under consecutive annealing periods, performed at 200°C in UHV conditions. The interface was analyzed by means of Auger electron spectroscopy combined with factor analysis applied in a sequential way. We found that silicide appears only after annealing and evolves until all the palladium is consumed. A silicon compound different from silicide, identified as Pd_xSi with x<2 is found at the interface Pd/Si and Pd₂Si/Si, before and after annealing respectively.     

Formation of palladium silicide by rapid thermal annealing

The formation of palladium silicide Pd₂Si by rapid thermal annealing of Pd layers on silicon has been studied as a function of annealing time (1–60s) in the temperature range 350–500 °C. It is shown that the results found for conventional furnace annealing (long duration, low temperature) can be extrapolated for rapid thermal annealing (shorter time, higher temperature) when taking into account the exact time dependence of the short temperature cycle. The growth rate is essentially diffusion limited and the activation energy is close to 1.1±0.1 eV. Silicide resistivity of about 30–40 cm was obtained for 200–400 nm thick Pd₂Si layers formed at 400 °C for a few seconds.     

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.     

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.     

Preparation and crystallization of Pb(Zr0.95Ti0.05)O3 thin films deposited by radio-frequency magnetron sputtering with a stoichiometric ceramic target

0.95 Ti_0.05)O₃ (PZT 95/5) thin films of perovskite structure were prepared on various substrates by the radio-frequency magnetron sputtering with a stoichiometric ceramic target. The crystal structure of the films showed a strong dependency on the crystal structure of the substrates. After conventional-furnace annealing at 750 °C, crack-free and transparent epitaxial PZT 95/5 films were successfully obtained on SrTiO₃(100) substrates, and highly oriented films on LaAlO₃(012). The films on r-sapphire exhibit slightly preferred orientation along both the (040) and (122) axes of the orthorhombic PZT 95/5 phase. The films on YSZ(100) consist principally of the perovskite PZT 95/5 phase with random orientation with a small portion of unknown phase. However, the formation of the perovskite PZT 95/5 phase was not observed in the films on Si(110) or (111)Pt-coated Si substrates. The crystallization of the perovskite PZT 95/5 on these substrates could be improved by rapid thermal annealing (RTA). Single perovskite phase was obtained in the films on (111)Pt/Si which had RTA at 750 °C for 1 min. No tangible loss of Pb from the films occurred during either the sputtering or annealing. Received: 17 April 1997/Accepted: 18 November 1997     

Low energy electron loss spectroscopic study of Pd-Si(111) system

Effect of Pd deposition on a clean Si(111) surface was studied by ELS and AES methods for submonolayer [1 ML = 7.8 × 10¹⁴atomscm^-2forSi(111)] to several tens of monolayers. ELS spectra showed that the electronic nature of Pd-Si bonding for ? 1 ML of Pd coverage is different from Pd₂Si formed for ? 3 ML. Namely, it was shown that some critical thickness for Pd on Si(111) exist for inducing interfacial intermixing reaction at room temperature.     

Study of the structural and magnetic characteristics of epitaxial Fe3Si/Si(111) films

The results of the structural and magnetic studies of the epitaxial structure prepared during the simultaneous evaporation from two iron and silicon sources on an atomically pure Si(111)7 × 7 surface at a substrate temperature of 150°C have been presented. The epitaxial structure has been identified as a single-crystal Fe₃Si silicide film with the orientation Si[111]‖Fe₃Si[111] using methods of the X-ray structural analysis, transmission electron microscopy, and reflection high-energy electron diffraction. It has been established that the epitaxial Fe₃Si film at room temperature has magnetic uniaxial anisotropy (H _a = 26 Oe) and a relatively narrow uniform ferromagnetic resonance line (ΔH = 11.57 Oe) measured at a pump frequency of 2.274 GHz.     

Pd adsorption on Si(1 1 3) surface: STM and XPS study

Pd-induced surface structures on Si(1 1 3) have been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In the initial process of the Pd adsorption below 0.10 ML, Pd silicide (Pd₂Si) clusters are observed to form randomly on the surface. By increasing the Pd coverage to 0.10 ML, the clusters cover the entire surface, and an amorphous layer is formed. After annealing the Si(1 1 3)-Pd surface at 600 °C, various types of islands and chain protrusions appears. The agglomeration, coalescence and crystallization of these islands are observed by using high temperature (HT-) STM. It is also found by XPS that the islands correspond to Pd₂Si structure. On the basis of these results, evolution of Pd-induced structures at high temperatures is in detail discussed.     

Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

The kinetics of Ni₂Si growth from pure Ni and from Ni_0.93V_0.07 films on (111) and (100) silicon has been studied by the combination of He⁺ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4–5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.     

Characterization of ultrathin nickel layers on Si(111) using RHEED and RBS

Ultrathin nickel layers (0–40 Å) on Si(111) were characterized using reflection high energy electron diffraction (RHEED) in conjunction with high-resolution Rutherford backscattering spectrometry (RBS). RBS shows that Ni, when deposited on Si(111) at 300 K, reacts with the Si to form clusters with an average composition close to Ni₂Si, until the clusters coalesce into a continuous layer. RHEED measurements show that the microstructure of this layer also matches the Ni₂Si composition: the film consists mainly of very fine-grained Ni₂Si crystallites (∼ 15 Å grain size) which are randomly oriented. Additional Ni deposition results in the accumulation of an unreacted fine-grained Ni layer on top of the silicide film.     

Structure analysis of thin iron-silicide film from φ-scan RHEED Patterson function

The atomic structure of thin iron silicide film, grown epitaxially on the Si(111) surface, has been analyzed by means of the three-dimensional RHEED Patterson function analysis. The iron-silicide-terminated surface with (2 × 2) periodicity has been prepared by a solid-phase epitaxy method. 2 ML of Fe were deposited on the Si(111)-(7 × 7) surface and annealed at 500°C. Three-dimensional Patterson function was calculated from series of φ-scanned RHEED intensity distributions converted to the k-space. The resulting model of γ-FeSi₂ structure consists of two silicide layers faulted to each other with three relaxed Si adatoms above the H₃ site.     

AES quantitative interpretation of the first stages of Pd2Si formation during Pd adsorption on Si(111) at room temperature

The quantitative analysis of the evolution of Pd and Si N(E) Auger peak amplitudes has been carried out as a function of Pd concentration on a Si(111) surface. Modelization of these evolutions has allowed us to conclude that the formation of the Pd₂Si silicide occurs from the beginning of Pd adsorption even at room temperature.     

On new two-dimensional structures produced on the Si (111) and Si (100) surface upon molecular-beam epitaxy of cobalt and silicon

Highly perfect epitaxial heterostructure CoSi₂ films have been grown on the surface of Si (111) and Si (100) single crystals by the method of molecular-beam epitaxy. The optimal regimes of the film growth with different thicknesses have been determined. It has been shown that short-term annealing of epitaxial films at T = 900–950 K leads to the formation of new CoSi₂/Si(111)-2 × 2 and CoSi₂/Si(100)−2 × 4 superstructures.     

In situ RHEED analysis of epitaxial Gd2O3 thin films grown on Si (001)

Epitaxial Gd₂O₃ thin films were successfully grown on Si (001) substrates using a two-step approach by laser molecular-beam epitaxy. At the first step, a ～0.8 nm thin layer was deposited at the temperature of 200 ^°C as the buffer layer. Then the substrate temperature was increased to 650 ^°C and in situ annealing for 5 min, and a second Gd₂O₃ layer with a desired thickness was deposited. The whole growth process is monitored by in situ reflection high-energy electron diffraction (RHEED). In situ RHEED analysis of the growing film has revealed that the first Gd₂O₃ layer deposition and in situ annealing are the critical processes for the epitaxial growth of Gd₂O₃ film. The Gd₂O₃ film has a monoclinic phase characterized by X-ray diffraction. The high-resolution transmission electron microscopy image showed all the Gd₂O₃ layers have a little bending because of the stress. In addition, a 5–6 nm amorphous interfacial layer between the Gd₂O₃ film and Si substrate is due to the in situ high temperature annealing for a long time. The successful Gd₂O₃/Si epitaxial growth predicted a possibility to develop the new functional microelectronics devices.     

Thickness dependent formation and properties of GdSi2/Si(100) interfaces

Epitaxial and polycrystalline orthorhombic GdSi₂ films were grown on Si(100) substrates by solid phase reaction between Si and Gd films at different thicknesses of the Gd film . The most important property of these GdSi₂/Si interfaces was defect formation. This was investigated by studying the properties of the Schottky barriers by means of current voltage and capacitance–voltage characteristics, deep level transient spectroscopy by double crystal X-ray diffractometry, and transmission electron microscopy. Epitaxial growth of the silicide layer ensured a relatively low interface defect density (about 10¹⁰ cm^-2), while the non-epitaxial growth induced defects of a much higher density (about 10¹² cm^-2). The defects generated during the silicide formation are located within a depth of about 10 nm from the GdSi₂/Si interface. PACS 68.55.-a; 73.40.-c; 81.15-zThis revised version was published in March 2005. References 10-17 were added in the online version (pdf file).     

On the Auger inverse sensitivity factors of In and Sb in InSb

The Auger inverse sensitivity factors α_i for In and Sb on a (111) In surface of an InSb crystal mounted on a 30° sample holder were determined as 0.56 ± 0.04 and 0.67 ± 0.05, respectively, by Auger Electron Spectroscopy (AES). These values were referenced to the clean Si 92 eV peak and differ significantly from those obtained for In and Sb when in their elemental form. Angular dependent variations in the α_i values were observed upon rotation of the sample about its normal.     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

LEED-AES study of the AuSi(100) system

The system Au/Si(100) has been studied using LEED and AES. Au films grow as Au(111) | Si(100) having six azimuthally rotated orientations at low deposition temperatures below 50°C after the formation of intermediate gold suicide layers. Crystalline gold silicide thin layers are formed on the Au(111) film after heat treatment at 100–400°C. Two types of suicide LEED pattern observed seem to have no correlation with crystallographic data reported on quenched alloy films. Heat treatment over 450°C leads to agglomeration of the film, producing a series of Au-induced superstructures. Heat treatment of the Au film over 1000°C regenerates the clean Si surface accompanied with many etch pits.