Formation kinetics and structure of Pd2Si films on Si

Backscattering and X-ray techniques have been used to study properties of palladium silicide (Pd₂Si) formed by evaporating thin Pd layers on Si followed by heat treatment. The rate of formation of Pd₂Si in the temperature range of 200–275°C has been measured by 2-MeV ⁴He⁺ ion backscattering. The Pd₂Si layer is found to grow at a rate proportional to the square root of time for thicknesses ranging from approximately 200–4000 Å. The rate of growth is found to be independent of Si substrate orientation or doping type and the rate constant is found to fit a single activation energy of E_a = 1·5±0·1 eV over the temperature range measured. X-ray diffraction indicates the structure to be Pd₂Si with the basal plane roughly parallel to the substrate surface for films formed on 111, 110, 100 and evaporated (amorphous) silicon substrates. The degree of preferred orientation is markedly stronger on [111] Si. Ion channeling measurements confirm that in this case the c-direction of the Pd₂Si is parallel with the [111] direction in the underlying Si.     

Auger electron spectroscopy study of reactive ion etched silicon carbide

Reactive ion etching (RIE) of bulk 4H-SiC based on CHF₃-O₂ plasma was studied by varying the rf power and process pressure. The elements on the etched surface and the surface roughness were characterized by Auger electron spectroscopy and atomic force microscopy, respectively. It was found that the surface roughening is mainly caused by Al contamination and C rich layer (C residues) induced micromasking effect. The micromasking effect is in turn determined by the dc self-bias developed at the substrates. A threshold dc self-bias exists at around −320 to −330 V, beyond which no micromasking effect was observed. This observation is explained in terms of physical ion bombardment and sputtering in the RIE process.     

The specific contact resistance of Pd2Si contacts on n- and p-Si

The specific contact resistance ρ_c of Al and Pd₂Si contacts has been measured on p- and n-Si substrates of uniform resistivity. The variation of ρ_c with substrate resistivity is described by the following equations:

The specific contact resistance of Al contacts was found to be lower than the values of Pd₂Si contacts on p-Si. Pd₂Si contacts on both n- and p-Si, (111) orientation, become non-ohmic in the resistivity range $\text{0.020?0.10 Ω-}\text{cm}$.The data in this study are not sufficient to distinguish a variation in ρ_c with substrate orientation. Specific contact resistance values of Pd₂Si contacts on $\text{0.005 Ω-}\text{cm}\text{(100) n-}\text{Si}$ and $\text{0.010 Ω-}\text{cm}\text{(100) p-}\text{Si}$ were not significantly different from values expected for the (111) substrates.     

Measurement of As diffusivity in Ni2Si thin films

The lattice and grain boundary diffusion coefficients of As in 260 nm-thick Ni₂Si films were measured. The Ni₂Si layers were prepared via the reaction between a Si layer deposited by low pressure chemical vapor deposition and a Ni layer deposited by magnetron sputtering on a Si substrate covered with a SiO₂ film. As was implanted in the silicide. Its concentration profiles were measured using secondary ion mass spectroscopy before and after annealing (550-700 °C). 2D finite element diffusion simulations taking into account lattice diffusion and grain boundary (GB) diffusion were performed based on the microstructure of the samples. They were found to fit accurately the measured profiles and allowed to measure the diffusion coefficients for each temperature. Lattice diffusion is characterized by a pre-exponential factor D⁰v ∼ 1.5 × 10⁻¹ cm² s⁻¹ and an activation energy Qv ∼ 2.72 eV. In the case of GB diffusion P⁰ = sδD⁰gb = 9.0 × 10⁻³ cm³ s⁻¹ and the activation energy was found to be higher than for lattice diffusion with Qgb ∼ 3.07 eV. Existing data concerning diffusion in silicides and other materials is used to discuss these results. The diffusion of As in Ni₂Si could be reduced due to impurity segregation in GBs.     

Growth mechanism and optical properties of semiconducting Mg2Si thin films

Reactive deposition of magnesium onto a hot silicon substrate (200–500°C) does not result in any accumulation of magnesium or its silicide — the condensation coefficient of magnesium being zero. On the other hand, codeposition of magnesium with silicon at 200°C, using a magnesium-rich flux ratio, gives a stoichiometric Mg₂Si film. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited. The Mg₂Si layers are polycrystalline with a (111) texture. These stoichiometric silicide films still show a tendency to sublimate; whereas capping with an oxide results in extensive intermixing during annealing. The Mg₂Si films thus obtained exhibit optical transparency at sufficiently long wavelength, and an absorption edge. Extraction of the absorption coefficient from the data, and analysis of its energy dependence suggest an indirect bandgap of 0.74 eV, plus direct transitions at 0.83 and 0.99 eV.     

Processing of titanium films on silicon using a multiscanned electron beam

A multiscanned electron beam has been used to process titanium films thermally on single-crystal silicon. The redistribution of titanium and the composition of the processed films were studied by Rutherford backscattering. Oxygen contamination within the titanium is found to control the reaction rate. Processing conditions have been established which give stoichiometric TiSi2 layers and the removal of oxygen from the system. These results have been confirmed by Auger analysis and the surface texture has been examined using scanning electron microscopy.     

退火对磁控溅射法制备半导体Mg2Si薄膜的影响

通过磁控溅射和氩气氛围退火,在Si(111)衬底上制备环境友好半导体Mg2Si薄膜,并采用XRD和SEM研究了退火对Mg2Si薄膜形成和微结构的影响。结果表明Mg2Si薄膜的质量取决于退火温度、退火时间和沉积的薄膜厚度。制备Mg2Si薄膜,400℃退火5h是最优退火条件。XRD和SEM结构表明Mg2Si是通过沉积的Mg和Si衬底原子的相互扩散形成的。退火减少薄膜缺陷,也影响薄膜的表明粗糙度。     

Barrier height control of Pd2 Si/Si schottky diodes using diffusion from doped Pd

The barrier height of metal-semiconductor contacts can be varied within wide limits by a suitable doping (Sb, Al) of the metal layer itself and application of a temperature treatment to the sandwich structure. As a result the doping elements are weakly diffused into the semiconductor surface. This leads to a change of the band bending and finally to a change of the barrier height. $\text{Pd}{}_2\text{Si}\text{n-}\text{Si}$ diodes with barrier heights q·φ_B between 0.5 and 0.8 eV were fabricated reproducibly by this method. The barrier height of undoped Pd₂Si/Si contacts equals 0.72 eV. The doping elements were introduced into the metal layer by partly covering the Pd-cathode of a DC-sputtering apparatus with Al or Sb, and subsequent sputtering of the composite cathode onto the silicon slices.The concentration of doping elements in the sputtered metal layer is given by the relation of the part of the cathode surface covered with the doping element to the whole cathode surface.     

Determination of existing stress in silicon films on sapphire substrate using Raman spectroscopy

Raman spectroscopy is used to determine built-in stresses in silicon on sapphire (SOS) devices. The method is direct, nondestructive and can be applied at various temperatures. For epitaxial silicon films on sapphire substrates a built-in stress of 7.0±0.3 kbar at room temperature and 8.7±0.3 kbar at liquid nitrogen temperature was measured.     

Interface studies of MBE-grown GaInAs/GaAsSb heterostructureslattice-matched to InP by Auger electron spectroscopy

The first interface study of an MBE-grown GaInAs/GaAsSb heterostructure lattice-matched to InP has been performed by Auger electron spectroscopy combined with ion sputtering. No surface segregation of Sb in the GaInAs/GaAsSb heterostructure was observed. The measured interface width of this heterostructure was found to be 2.2 nm by monitoring the Auger peak-to-peak height of the Sb MNN transition under 0.5 kV Ar⁺ ion sputtering     

FAPAS法制备稀土掺杂的Mg2Si

采用电场激活压力辅助合成（FAPAS）的方法,制备了稀土Sc、Y掺杂的Mg2Si热电材料,合成温度为1023-1073K,压力为50Mpa,所用时间约15min。所得试样结构均匀致密,平均晶粒尺寸约为1.5~2μm,微量的稀土元素不改变基体的组织形貌。掺杂2500ppmSc的式样有最大的绝对Seebeck系数,在408K达未掺杂式样的1.93倍,掺杂200ppmY的式样具有更好的电导率,在468K为未掺杂式样的1.69倍,而Sc掺杂式样具有更好的综合电性能。这两种掺杂试样的热导率分别为未掺杂试样的70%和84%。因此,这两个试样的热电优值-ZT得到了明显提高,分别在408K和468K时达到未掺杂试样的3.3倍和2.4倍。掺杂2500ppmSc的试样具有最大的ZT值为0.42,大于Y掺杂式样的0.4及未掺杂式样的0.25。Sc掺杂的式样在更低的温度区间有最佳的热电性能。     

A study of sputter deposited silicon films

Thermal annealing, oxidation, and impurity doping of room-temperature dc magnetron sputter deposited silicon films are examined. It was found that even with a fine grain structure, the films can be doped to the desired sheet resistances suitable for device applications, although the sheet resistances are higher (2 to 5 times) than those obtained from single crystal silicon. It was also found that pre-diffusion annealing decreases sheet resistance of boron-doped films, but increases the sheet resistance of phosphorus-doped films, this is correlated to the different behavior of boron and phosphorus at the grain boundaries. Oxidation rates are enhanced in both boron-doped and phosphorus doped films. Film thickness reductions of 11 to 31% after high temperature processes was observed. Effects of doping on the shrinkage in film thickness are presented.     

SiC MOSFETs with thermally oxidized Ta2Si stacked on SiO2 as high-k gate insulator

In this paper, we compare the electrical characteristics of MOS capacitors and lateral MOSFETs with oxidized Ta₂Si (O-Ta₂Si) as a high-k dielectric on silicon carbide or stacked on thermally grown SiO₂ on SiC. MOS capacitors are used to determine the dielectric and interfacial properties of these insulators. We demonstrate that stacked SiO₂/O-Ta₂Si is an attractive solution for passivation of innovative SiC devices. Ta₂Si deposition and oxidation is totally compatible with standard SiC MOSFET fabrication materials and processing. We demonstrate correct transistor operation for stacked O-Ta₂Si on thin thermally grown SiO₂ oxides. However the channel mobility of such high-k MOSFETs must be improved investigating the interface properties further.     

二氧化硅超薄膜的扫描隧道显微镜和扫描隧道谱研究

用超高真空热氧化方法在Si(111)清洁衬底上生长了二氧化硅超薄膜，并利用超高真空扫描隧道显微镜和扫描隧道谱技术对超薄膜的表面形貌和局域电学特性进行了研究。结果显示，在超薄范围二氧化硅呈层状生长，不同层的微分电导谱所测禁带宽度差别可以达到约3eV，形貌对二氧化硅带宽的影响小于膜厚的影响。     

Mobility study on RIE etched silicon surfaces usingSF6/O2 gas etchants

A methodology for the measurement of the inversion layer mobility on trench gate structures, which allows independent measurement of the sidewall and bottom surface mobilities, is described. Using this method, the inversion layer mobility has been experimentally studied for trenches formed using the SF₆/O₂ method on diffused base regions of power UMOSFETs. The effect of several post RIE surface treatments on the surface mobility is reported. The measured sidewall mobilities have been found to be comparable to those previously reported for other RIE etchants. These results are of interest for the design of devices using the trench gate (UMOS) technology     

Interface composition of atomic layer deposited HfO2 and Al2O3 thin films on InAs studied by X-ray photoemission spectroscopy

We present a synchrotron-based XPS investigation on the interface between InAs and Al₂O₃ or HfO₂ layers, deposited by ALD at different temperatures, for InAs substrates with different surface orientations as well as for InAs nanowires. We reveal the composition of the native Oxide and how the high-κ layer deposition reduces Oxide components. We demonstrate some of the advantages in using synchrotron radiation revealing the variation in Oxide composition as a function of depth into the subsurface region and how we can indentify Oxides even on nanowires covering only a small fraction of the surface.     

Infrared spectroscopy and X-ray diffraction studies on the crystallographic evolution of La2O3 films upon annealing

Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La₂O₃ films are promising for integration into future NVMs because they are expected to crystallize above 400 °C in the hexagonal phase (h-La₂O₃) which has a higher κ value than the cubic phase (c-La₂O₃) in which most of REOs crystallize. In this work, La₂O₃ films are grown on Si by atomic layer deposition using La(C₅H₅)₃ and H₂O. Within the framework of the h-La₂O₃ formation, we systematically study the crystallographic evolution of La₂O₃ films versus annealing temperature (200-600 °C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)₃ occurs. Vacuum annealing of sufficiently thick (>100 nm) La(OH)₃ layers induces clear changes in FTIR and GIXRD spectra: c-La₂O₃ gradually forms in the 300-500 °C range while annealing at 600 °C generates h-La₂O₃ which exhibits, as inferred from our electrical data, a desirable κ ∼ 27. A quick transformation from h-La₂O₃ into La(OH)₃ occurs due to H₂O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La₂O₃ formation.     

Monitoring of TiSi2 formation on narrow polycrystallinesilicon lines using Raman spectroscopy

Micro-Raman spectroscopy is used to monitor titanium silicide (TiSi₂) formation on narrow undoped polycrystalline silicon lines. Linewidths varying from 1.0 μm down to 0.35 μm, with silicidation by rapid thermal anneal (RTA) temperature ranging between 780°C and 1020°C were analyzed. Phase changes between C49 and C54-TiSi₂ phases were clearly observed. Results demonstrate that analysis of the C54-TiSi₂ Raman peak intensity allowed fast and nondestructive estimation of the process window for low resistivity C54-TiSi₂ formation. Comparison with sheet resistivity measurements showed that micro-Raman scattering provides a complimentary means to electrical analysis for the study of TiSi₂ formation     

Photoluminescence spectroscopy of sputtering Er-doped silicon-rich silicon nitride films

Er-doped silicon-rich silicon nitride (SRN) films were deposited on silicon substrate by an RF magnetron reaction sputtering system. After high temperature annealing, the films show intense photoluminescence in both the visible and infrared regions. Besides broad-band luminescence centered at 780 nm which originates from silicon nanocrystals, resolved peaks due to transitions from all high energy levels up to ~2H_(11/2) to the ground state of Er~(3+) are observed. Raman spectra and HRTEM measurements have been performed to investigate the structure of the films, and possible excitation processes are discussed.     

磁控溅射掺铒富硅氮化硅薄膜的光致荧光谱

Er-doped silicon-rich silicon nitride （SRN） films were deposited on silicon substrate by an RF magnetron reaction sputtering system. After high temperature annealing, the films show intense photoluminescence in both the visible and infrared regions. Besides broad-band luminescence centered at 780 nm which originates from silicon nanocrystals, resolved peaks due to transitions from all high energy levels up to 2H11/2 to the ground state of Er^3＋ are observed. Raman spectra and HRTEM measurements have been performed to investigate the structure of thefilms, and possible excitation processes are discussed.