Electrical and structural properties of a stacked metal layer contact to n-InP

In this study, we found that the double metal contact structure in Pt/Al/n-InP diodes provides better rectification characteristics than conventional single-metal/n-InP Schottky diodes. The effective barrier height was measured to be 0.67 eV for a 400 °C-annealed Pt/Al/n-InP diode sample. The increase in the barrier height is attributed to the formation of Al₂O₃ at the metal/n-InP contact interface during thermal annealing. The formation of the phase Al₂O₃ phase was monitored by X-ray diffraction (XRD) analysis. The corresponding element profiles of Al and O were also confirmed at the metal/n-InP contact interface using secondary ion mass spectrum (SIMS) analysis. The lowering of the Schottky barrier height due to the inhomogeneity at the metal/n-InP junction is also discussed on the basis of the TE theory. The distribution of local effective Schottky barrier heights was explained by a model incorporating the existence of double Gaussian barrier heights, which represent the high barrier and low barrier of the full distribution in the temperature ranges of 83-198 and 198-300 K.     

Studies of the promising material CoSi2 on GaAs substrates

The thermal stability of CoSi₂ thin films on GaAs substrates has been studied using a variety of techniques. The CoSi₂ thin films were formed by depositing Co(500 Å) and Si(1800 Å) layers on GaAs substrates by electron-beam evaporation followed by annealing processes, where the Si inter-layer was used as a diffusion/reaction barrier at the interface. The resistivity of CoSi₂ thin films formed is about 30 cm. The Schottky barrier height of CoSi₂/n-GaAs is 0.76 eV and the ideality factor is 1.14 after annealing at 750° C for 30 min. The CoSi₂/GaAs interface is determined to be thermally stable and the thin film morphologically uniform on GaAs after 900° C/30 s anneal. The CoSi₂ thin films fulfill the requirements in GaAs self-aligned gate technology.     

Tayloring of the Schottky barrier height of Pt-Ir mixed silicide infrared detectors

 Pt-Ir silicide Schottky diodes were formed by e-beam evaporation of Pt and Ir onto p-Si(100) substrates in high vacuum with subsequent RTA-annealing at temperatures in the range of 300 to 500 °C. Rutherford Backscattering Spectrometry (RBS) and infrared photoresponse (PR) measurements were performed to determine the composition and the infrared electrooptical properties of the resulting films. Coevaporated Pt-Ir films are demixed during silicidation and form a PtSi layer at the interface to the silicon substrate. The Schottky barrier height is that of a pure PtSi film. Ir deposited prior to Pt exhibits Pt diffusion through the Ir layer. Only when the Ir film is reacted to IrSi by in situ annealing prior to Pt deposition, a mixed Ir-Pt silicide Schottky barrier is obtained. Infrared photoemission then yields intermediate Schottky barrier heights between those of PtSi and IrSi. From a detailed analysis of the photoemission characteristics, it is concluded that the intermediate barrier height is due to an area average of PtSi and IrSi grains which coexist at the Si interface. Received: 29 May 1996/Accepted: 12 August 1996     

Highly reproducible ideal SiC Schottky rectifiers: effects of surface preparation and thermal annealing on the Ni/6H-SiC barrier height

In this work, the effects of surface preparation and thermal annealing on the Ni/6H-SiC Schottky barrier height were studied by monitoring the forward I–V characteristics of Schottky diodes. The ideality factor n and the barrier height _B were found to be strongly dependent on the impurity species present at the metal/SiC interface. The physical mechanism which rules the Schottky barrier formation is discussed by considering the nature of the impurities left from the different surface preparation methods prior to metal deposition. In contrast, nickel silicide/SiC rectifiers (Ni₂Si/6H-SiC), formed by thermal reaction of Ni/6H-SiC above 600 °C, have an almost ideal I–V curve, independent of the surface preparation. Further improvement in the barrier height distribution can be obtained by increasing the annealing temperature to 950 °C. This behaviour is discussed in terms of the silicide phases and the consumption of a SiC layer during the thermal reaction. PACS 73.30.+y; 81.65.Cf; 81.05.Je     

CoSi2 formation in contact systems based on Ti-Co alloy with low cobalt content

The process of integrated-circuit contact formation based on Ti–Co alloy with low content of cobalt has been investigated. By AES and XRD it is shown that nitrogen doping of the alloy film during magnetron deposition and its subsequent annealing at 800–850°C allow simultaneously to obtain a CoSi₂ contact layer and a diffusion barrier layer on the basis of TiN. Electrical characteristics of Schottky barrier and ohmic contacts have been studied.     

Ion beam modification of silicide-silicon interfaces

We have modified the contact interface between Pd₂Si and n-Si by ion implantation and investigated the effect of the implantation on Schottky barrier height and rate of silicide formation by electrical current-voltage measurements and Rutherford backscattering spectroscopy. Various ions, As. P, B. O and Si at 50 keV and up to a dose of 5 × 10¹⁴ ions/cm² were implanted into Si wafers before the Pd-deposition to form Pd₂Si. In the case of As and P, the implantation showed a large erect on the subsequent Pd₂Si formation; the formation is enhanced in the as-implanted samples, but it is retarded if an annealing at 600°C precedes the Pd-deposition. Silicide formation was found generally to help reduce the implantation damage (with or without the 600°C annealing) and showed improvements on the electrical characteristics of the contact interface. Consumption of the entire implanted region by silicide formation is found necessary for obtaining a good diode performance. In the case of As implantation, a lowering of the Schottky barrier height of Pd₂Si has been observed.     

Differential evaluation of the Hall effect in silicon with oxygen-related donors

Three kinds of samples were used to form Co suicides by thermal annealing: firstly, a Co film of about 370 Å thick, evaporated on a (100) single crystal Si (Si ^c /Co); secondly, an evaporated boron-containing Si (Si ^e (B)) layer on the top of the first sample (Si ^c /Co/Si ^e (B)). The last sample is in the Co film of the first sample we deposited a Si^e(B) layer (Si ^c /Co/Si ^e (B)/Co). A laterally uniform CoSi₂ layer can be formed from the second and the third samples by annealing at 450 °C. In the first sample, the CoSi₂ can be formed only at temperatures above 500 °C and the disilicide is laterally less uniform than in the second and third samples. The Schottky barrier heights of the three samples derived from the forward and reverse I–V characteristics show that the barrier height is 0.01–0.02eV higher in the uniform case than in the nonuniform case.     

Pt interlayer effects on Ni germanosilicide formation and contact properties

Ni and Ni(Pt) germanosilicide formation and their contact properties on n-type epitaxial Si_0.84Ge_0.16 have been studied in this work. It is revealed that compared to NiSi, NiSiGe has enhanced phase stability but worse morphology stability. It is also found that Pt incorporation in germanosilicidation improves the morphology of the germanosilicide film. The Schottky contact characteristics of NiSiGe and Ni(Pt)SiGe on n-SiGe were evaluated by current–voltage (I–V) technique at room temperature. NiSiGe/n-SiGe contact shows a Schottky barrier height (SBH) of 0.65 eV with little difference from that of NiSi/n-Si contact. However, the contact shows a reduced SBH with a markedly increased ideality factor and leakage current when annealing temperature increases to 650 °C, indicating thermal degradation of the contact quality. Pt incorporation increases the SBH to 0.73 eV. In addition, its diode parameters such as SBH, ideality factor, and reverse leakage show better conformity during the whole annealing temperature range (from 450 to 650 °C). Therefore, it is concluded that Pt interlayer between Ni and SiGe can modulate the barrier height of Ni germanosilicide and improve its contact properties.     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜     

Barrier lowering and leakage current reduction in Ni-AlGaN/GaN Schottky diodes with an oxygen-treated GaN cap layer

We report on the effect of oxygen annealing for GaN surface on the Schottky barrier configuration and leakage current in Ni-AlGaN/GaN Schottky barrier diodes. After oxygen annealing, their turn-on voltage and reverse-bias leakage current characteristics are significantly improved due to a reduction in the Schottky barrier height (SBH) and suppression in the surface states respectively. Interface state density extracted from the Terman method was reduced by 2 orders of magnitude. X-ray photoelectron spectroscopy measurements show that the oxygen annealing induces Ga₂O₃ on the GaN surface. The formation of Ga₂O₃ reduces the interface state density as well as lowers the SBH through the modification of hybridized metal induced gap states.     

Annealing and measurement temperature dependence of W2B5-based rectifying contacts to n-GaN

The thermal stability and measurement temperature dependence of Schottky contact characteristics on n-GaN using a W₂B₅/Ti/Au metallization scheme was studied using current-voltage (I-V), scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) measurements. The elemental profile obtained from samples annealed at 350 °C showed some titanium diffusion into the gold layer but little other difference from the as-deposited wafer. Annealing at 700 °C produced significant diffusion of titanium. The Schottky barrier height increased with anneal temperature up to 200 °C, reaching a maximum value of 0.65 eV, but decreased at higher annealing temperatures. The reverse breakdown voltage from diodes fabricated using the W₂B₅-based contacts showed a similar dependence. The reverse current magnitude was larger than predicted by thermionic emission alone. The barrier height showed only minor changes with measurement temperature up to 150 °C.     

Cobalt-induced polycrystalline silicon film growth

Cobalt (Co)-induced crystalline silicon (Si) growth was investigated. The Co catalyst reacted to dc magnetron sputtered Si at 600 °C forming a Co silicide layer. The polycrystalline Si (poly-Si) was epitaxially grown above the Co silicide template, which has a small lattice misfit to Si. Annealing followed to improve the Si crystallinity. X-ray diffraction was performed to trace Co silicide phase formation and transition. The Co-rich silicide phase transitioned to CoSi₂ by annealing. The crystallinity of Si films was identified using reflection absorption Fourier transform-infrared spectroscopy, which detected unique peaks at 689 and 566 cm⁻¹ after the annealing process. The thin poly-Si film was used to fabricate a Schottky diode to prove the electronic quality. A good quality Si thin film was achieved by the metal-induced Si growth.     

掺Mo对NiSi薄膜热稳定性的改善

报导了在镍薄膜中掺入少量Mo提高了镍硅化物的热稳定性.结果表明，经650— 800℃快速热 退火形成的Ni(Mo)Si硅化物薄膜电阻值较低，约为2．4(Ω／□).XRD分析表明薄膜中只存在 NiSi相，而没有NiSi₂生成.由吉布斯自由能理论分析表明在Ni薄膜中掺人5．9 ％Mo对改善 Ni硅化物热稳定性起到至关重要的作用.经650—800℃快速热退火后的 Ni(Mo)Si／Si肖特基 二极管电学特性良好，势垒高度Φ_B为0．64—0．66eV，理想因子接近于1，更 进一步证明掺少量的Mo能够改善NiSi薄膜的热稳定性. 关键词： 镍硅化物 快速热退火 x射线衍射分析 卢瑟福背散射     

Band structure and valence-band offset of HfO2 thin film on?Si?substrate from photoemission spectroscopy

Synchrotron radiation photoemission spectroscopy and optical transmission spectrum measurements have been performed on an HfO₂ thin film grown on a Si(100) substrate to determine the band structure of the HfO₂/Si stack. The result shows a valence-band offset of 2.5 eV and a conduction-band offset of 2.2 eV for the HfO₂/Si interface. The Schottky barrier height between Au and HfO₂ is obtained from current density–voltage measurement. The characterization reveals that the dominant conduction mechanism in the region of low field under gate injection is Schottky emission. The energy-band diagram of an Au–HfO₂–Si MOS stack was obtained from these results.     

Arc plasma jet cleaning of the silicon surface before CoSi2/Si contact formation

Cleaning of the silicon surface before Co film deposition is a key procedure in the synthesis of silicide (CoSi₂) and, hence, in the production of the metal-semiconductor contact. This study deals with a new method of surface cleaning using arc plasma jet treatment (APJT) at atmospheric pressure. The results show that cleaning of the Si surface using APJT (Ar/CCIF₃) improves the Schottky barrier contact parameters in comparison with conventional wet HF final cleaning and additional cleaning using in situ Ar-ion-beam sputter etching. Moreover, substantially longer time of wafer exposure to air between final cleaning and metal deposition is acceptable. Auger electron spectroscopy shows that APJT removes oxygen from the Si surface.     

Properties of Fe/Si heterostructure grown by MOCVD

An Fe film was grown on an Si(100) substrate by metalorganic chemical vapor deposition (MOCVD) using thermal decomposition of iron pentacarbonyl, Fe(CO)₅. The X-ray diffraction and cross-sectional high resolution electron microscopy (HREM) show that the Fe deposited film is a single crystal Fe film on Si(100). Single crystal Fe/Si Schottky barrier diodes exhibit good rectification.     

Study of Ni/Si(1 0 0) solid-state reaction with Al addition

The characteristics of Ni/Si(1 0 0) solid-state reaction with Al addition (Ni/Al/Si(1 0 0), Ni/Al/Ni/Si(1 0 0) and Al/Ni/Si(1 0 0)) is studied. Ni and Al films were deposited on Si(1 0 0) substrate by ion beam sputtering. The solid-state reaction between metal films and Si was performed by rapid thermal annealing. The sheet resistance of the formed silicide film was measured by four-point probe method. The X-ray diffraction (XRD) was employed to detect the phases in the silicide film. The Auger electron spectroscopy was applied to reveal the element profiles in depth. The influence of Al addition on the Schottky barrier heights of the formed silicide/Si diodes was investigated by current-voltage measurements. The experimental results show that NiSi forms even with the addition of Al, although the formation temperature correspondingly changes. It is revealed that Ni silicidation is accompanied with Al diffusion in Ni film toward the film top surface and Al is the dominant diffusion species in Ni/Al system. However, no Ni_xAl_y phase is detected in the films and no significant Schottky barrier height modulation by the addition of Al is observed.     

Temperature dependent electrical characteristics of Sn/p-Si Schottky diodes

Current-voltage and capacitance-voltage characteristics of Sn/p-Si Schottky diodes measured in the temperature range 80-320 K are presented and analysed. Anomalous strong temperature dependencies of the ideality factor and apparent barrier height were obtained. There was also a considerable difference between the apparent barrier heights obtained from current-voltage and capacitance-voltage characteristics. These anomalies are explained by the domination of the current by a high level of thermionic-field emission, and by the presence of deep levels near the Sn/Si interface, which yield a reduction of free hole concentration and a significant temperature dependence of the charge stored near the metal-semiconductor (MS) interface. The evaluation of temperature dependence of forward current for thermionic-field emission resulted in the following parameters: characteristic energy E₀₀ = 9.8 meV, Schottky barrier height at zero bias Φ_b0 = 0.802 eV, bias coefficient of barrier height β = 0, and effective Richardson constant A* = 37.32 A cm⁻² K⁻².     

Performance comparison of Pt/Au and Ni/Au Schottky contacts on AlxGa1-x N/GaN heterostructures at high temperatures

In contrast with Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts,this paper systematically investigates the effect of thermal annealing of Au/Pt/Al 0.25 Ga 0.75 N/GaN structures on electrical properties of the two-dimensional electron gas in Al 0.25 Ga 0.75 N/GaN heterostructures by means of temperature-dependent Hall and temperature-dependent current-voltage measurements.The two-dimensional electron gas density of the samples with Pt cap layer increases after annealing in N 2 ambience at 600℃ while the annealing treatment has little effect on the two-dimensional electron gas mobility in comparison with the samples with Ni cap layer.The experimental results indicate that the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts reduce the reverse leakage current density at high annealing temperatures of 400-600℃.As a conclusion,the better thermal stability of the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts than the Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts at high temperatures can be attributed to the inertness of the interface between Pt and AlxGa1-xN.