Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

THE ANNEALING FEATURES OF Ta/Si MULTILAYER FILMS

The Ta/Si multilayers on (100) Si substrate have been studied over the annealing temper-ature range from 500 to 900℃ by X-ray diffraction and cross-section transmission electron microscopy. The periodicity of the multilayers becomes worse with increasing annealing tem-perature and disappears at 750℃. At 600℃, two kinds of modulation wavelength coexist because the size of several TaSi₂ grains is larger than the contracted original modulation wavelength. The films are contracted after annealing. The largest contraction, at least 40nm decreasing in thickness, occurs at 600℃. When the annealing temperature is lower than 600℃, h-TaSi₂ grains grow randomly and the growth is not affected by the substrate. At temperatures higher than 750℃, h-TaSi₂ grows preferentially in [001] direction parallel to [100] axis of Si substrate. The appearance of texture depends on whether the atomic diffusion is short range or long range at the corresponding annealing temperature.     

Study on optical anisotropy properties of SiO2 films with different thermal annealing temperatures

SiO2 films are deposited on Si substrates by an ion beam sputtering technique and continuously annealed in a quartz culture dish in air at various annealing temperature ranging from 20 to 750 ℃ with a step of 100 ℃ for a fixed time of 24 h. The effects of thermal treatment on optical anisotropy properties of SiO2 films are investigated by spectroscopic ellipsometry. When the annealing temperature is 550℃, the optical anisotropy properties of SiO2 film is minimum. The obtained results indicate that the optical anisotropy properties of SiO2 films can be improved by a proper thermal annealing process.     

Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method

Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.     

Effect of the annealing temperature on the long-term thermal stability of Pt/Si/Ta/Ti/4H–SiC contacts

The Pt/Si/Ta/Ti multilayer metal contacts on 4H–Si C are annealed in Ar atmosphere at 600°C–1100°C by a rapid thermal processor(RTP). The long-term thermal stability is evaluated by aging the annealed contact at 600°C in air. The contact's properties are determined by current–voltage measurement, and the specific contact resistance is calculated based on the transmission line model(TLM). Transmission electron microscope(TEM) and energy-dispersive x-ray spectrometry(EDX) are used to characterize the interface morphology, thickness, and composition. The results reveal that a higher annealing temperature is favorable for the formation of an Ohmic contact with a lower specific contact resistance, and causes the rapid degradation of the Ohmic contact in the aging process.     

Effect of Au/Ni/4H–SiC Schottky junction thermal stability on performance of alpha particle detection

Au/Ni/n-type 4H–SiC Schottky alpha particle detectors are fabricated and annealed at temperatures between 400℃ and 700℃ to investigate the effects of thermal stability of the Schottky contact on the structural and electrical properties of the detectors. At the annealing temperature of 500?C, the two nickel silicides(i.e., Ni_(31)Si_(12) and Ni_2Si) are formed at the interface and result in the formation of an inhomogeneous Schottky barrier. By increasing the annealing temperature,the Ni_(31)Si_(12) transforms into the more stable Ni_2Si. The structural evolution of the Schottky contact directly affects the electrical properties and alpha particle energy resolutions of the detectors. A better energy resolution of 2.60% is obtained for 5.48-MeV alpha particles with the detector after being annealed at 600℃. As a result, the Au/Ni/n-type 4 H–SiC Schottky detector shows a good performance after thermal treatment at temperatures up to 700℃.     

Effects of rapid thermal annealing on the morphology and optical property of ultrathin InSb film deposited on SiO2/Si substrate

Ultrathin InSb films on SiO2/Si substrates are prepared by radio frequency(RF) magnetron sputtering and rapid thermal annealing(RTA) at 300,400,and 500℃,respectively.X-ray diffraction(XRD) indicates that InSb film treated by RTA at 500℃,which is higher than its melting temperature(about 485℃),shows a monocrystalline-like feature.A high-resolution transmission electron microscopy(HRTEM) micrograph shows that melt recrystallization of InSb film on SiO2/Si(111) substrate is along the(111) planes.The transmittances of InSb films decrease and the optical band gaps redshift from 0.24 eV to 0.19 eV with annealing temperature increasing from 300℃ to 500℃,which is indicated by Fourier transform infrared spectroscopy(FTIR) measurement.The observed changes demonstrate that RTA is a viable technique for improving characteristics of InSb films,especially the melt-recrystallized film treated by RTA at 500℃.     

Effects of annealing temperature on the electrical property and microstructure of aluminum contact on n-type 3C–SiC

The 3C-SiC thin films used herein are grown on Si substrates by chemical vapor deposition. A1 contacts with differ- ent thickness values are deposited on the 3C-SiC/Si （100） structure by the magnetron sputtering method and are annealed at different temperatures. We focus on the effects of the annealing temperature on the ohmic contact properties and mi- crostructure of A1/3C-SiC structure. The electrical properties of A1 contacts to n-type 3C-SiC are characterized by the transmission line method. The crystal structures and chemical phases of A1 contacts are examined by X-ray diffraction, Raman spectra, and transmission electron microscopy, respectively. It is found that the A1 contacts exhibit ohmic contact behaviors when the annealing temperature is below 550 ℃, and they become Schottky contacts when the annealing tem- perature is above 650 ℃. A minimum specific contact resistance of 1.8 × 10-4 Ω cm2 is obtained when the A1 contact is annealed at 250 ℃.     

Effects of rapid thermal annealing on crystallinity and Sn surface segregation of Ge_(1-x)Sn_x films on Si(100) and Si(111)

Germanium-tin films with rather high Sn content(28.04% and 29.61%) are deposited directly on Si(100) and Si(111)substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge_(1-x)Sn_x films is investigated by x-ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). The x-ray diffraction(XRD) is also performed to determine the crystallinities of the Ge_(1-x)Sn_x films. The experimental results indicate that root mean square(RMS) values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400℃. The diameter of the Sn three-dimensional(3 D) island becomes larger than that of an as-grown sample when the annealing temperature is 700℃. In addition, the Sn surface composition decreases when annealing temperature ranges from 400℃ to 700℃. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600℃. The present investigation demonstrates that the crystallinity of Ge_(1-x)Sn_x/Si(111) has no obvious advantage over that of Ge_(1-x)Sn_x/Si(100) and the selection of Si(111) substrate is an effective method to improve the surface morphologies of Ge_(1-x)Sn_x films. We also find that more severe Sn surface segregation occurs in the Ge_(1-x)Sn_x/Si(111) sample during annealing than in the Ge_(1-x)Sn_x/Si(100) sample.     

Effects of Ag on Electrical Properties of Ag/Ni/p-GaN Ohmic Contact

Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 × 10^-4 Ωcm^2 is obtained at annealing temperature of 550^o C.     

Cu/SiO2/Si(111)体系中Cu和Si的扩散及界面反应

室温下利用磁控溅射在p型Si(111)衬底上沉积了Cu薄膜. 利用X射线衍射和卢瑟福背散射分别对未退火以及在不同温度点退火后样品的结构进行了表征. 在此基础上，研究了Cu/SiO₂/Si(111)体系的扩散和界面反应. 实验结果表明：当退火温度高于450℃时出现明显的扩散现象，并且随着温度的升高，体系扩散现象会更加显著. 当退火温度低于450℃时没有铜硅化合物生成，当温度达到500℃时才有铜硅化合物生成. 关键词： 薄膜 扩散 界面反应 硅化物     

Si-W/Si/SiO2/Si(100)的横截面电子显微镜研究

本文用横截面电子显微镜法分析了Si-W/Si/SiO₂/Si(100)在440—1000℃退火后的晶化过程,以及各个界面的变化情况.发现Si-W合金膜中,WSi₂并未优先在表面、界面处形成晶核.当退火温度不高于700℃时,反应在合金膜内发生,表面、界面起伏和缓.退火温度高达800—1000℃时,界面、表面出现原子扩散,造成剧烈的界面起伏;表面则出现小的热沟槽,Si/SiO₂界面也出现高分辨电子显微镜才能观察到的起伏.表面、界面的原子迁移的动力来源于晶界与表面、界面张力.由于SiO₂中Si—O键很稳定,不易发生Si和O在界面处的互扩散,所以Si/SiO₂界面起伏很小. 关键词：     

Surface morphology and reaction at Cu/Si interface—Effect of native silicon suboxide

Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu₃Si and Cu₄Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites.     

Formation of copper islands on a native SiO2 surface at elevated temperatures

A combination of in situ X-ray photoelectron spectroscopy analysis and ex situ scanning electron- and atomic force microscopy has been used to study the formation of copper islands upon Cu deposition at elevated temperatures as a basis for the guided growth of copper islands. Two different temperature regions have been found: (I) up to 250 °C only close packed islands are formed due to low diffusion length of copper atoms on the surface. The SiO₂ film acts as a barrier protecting the silicon substrate from diffusion of Cu atoms from oxide surface. (II) The deposition at temperatures above 300 °C leads to the formation of separate islands which are (primarily at higher temperatures) crystalline. At these temperatures, copper atoms diffuse through the SiO₂ layer. However, they are not entirely dissolved in the bulk but a fraction of them forms a Cu rich layer in the vicinity of SiO₂/Si interface. The high copper concentration in this layer lowers the concentration gradient between the surface and the substrate and, consequently, inhibits the diffusion of Cu atoms into the substrate. Hence, the Cu islands remain on the surface even at temperatures as high as 450 °C.     

Fabrication of quantum wires by selective intermixing induced in GaAs/AlGaAs quantum well heterostructures by SiO2 capping and subsequent annealing

Results are presented demonstrating that selective intermixing of GaAs/AlGaAs quantum well heterostructures by SiO₂ capping and subsequent annealing can be spatially localized with a length scale compatible with the observation of lateral quantum confinement effects. Patterning of a 400 nm-thick SiO₂ encapsulation layer deposited by rapid thermal chemical vapor deposition into arrays of wires was performed using high resolution electron beam lithography and subsequent reactive ion etching. After high temperature (850°C) annealing, photoluminescence experiments indicate the creation of double barrier quantum wires when small trenches (< 100 nm) are etched in the SiO₂ film at a period greater than 800 nm. Signatures of the formation of one-dimensional subbands are observed both in photoluminescence excitation spectroscopy and linear polarization anisotropy analysis. A mechanism involving the ability of the stress field generated during annealing at the SiO₂ film edges to pilot the diffusion of the excess gallium vacancies which are responsible for the enhanced interdiffusion under SiO₂ is suggested to account for the high lateral selectivity achievable with this novel process.     

Effects of rapid thermal annealing on the morphology and optical properity of ultrathin InSb film deposited on SiO2/Si substrate

Ultrathin InSb thin films on SiO₂/Si substrates are prepared by radio frequency (RF) magnetron sputtering and rapid thermal annealing (RTA) at 300, 400, and 500℃, respectively. X-ray diffraction (XRD) indicates that InSb film treated by RTA at 500℃, which is higher than its melting temperature (about 485℃), shows a monocrystalline-like feature. High-resolution transmission electron microscopy (HRTEM) micrograph shows that melt recrystallization of InSb film on SiO₂/Si(111) substrate is along the (111) planes. The transmittances of InSb films decrease and the optical band gaps redshift from 0.24 eV to 0.19 eV with annealing temperature increasing from 300℃ to 500℃, which is indicated by Fourier transform infrared spectroscopy (FTIR) measurement. The observed changes demonstrate that RAT is a viable technique for improving characteristics of InSb films, especially the melt-recrystallized film treated by RTA at 500℃.     

Thermal stability and chemical bonding states of AlOxNy/Si gate stacks revealed by synchrotron radiation photoemission spectroscopy

Annealing-temperature dependence of the thermal stability and chemical bonding states of AlO_xN_y/SiO₂/Si gate stacks grown by metalorganic chemical vapor deposition (MOCVD) using new chemistry was investigated by synchrotron radiation photoemission spectroscopy (SRPES). Results have confirmed the formation of the AlN and AlNO compounds in the as-deposited samples. Annealing the AlO_xN_y samples in N₂ ambient in 600-800 °C promotes the formation of SiO₂ component. Meanwhile, there is no formation of Al-O-Si and Al-Si binding states, suggesting no interdiffusion of Al with the Si substrate. A thermally induced reaction between Si and AlO_xN_y to form volatile SiO and Al₂O is suggested to be responsible for the full disappearance of the Al component that accompanies annealing at annealing temperature of 1000 °C. The released N due to the breakage of the Al-N bonding will react with the SiO₂ interfacial layer and lead to the formation of the Si₃-N-O/Si₂-N-O components at the top of Si substrate. These results indicate high temperature processing induced evolution of the interfacial chemistry and application range of AlO_xN_y/Si gate stacks in future CMOS devices.     

Crystallization and surface morphology of Au/SiO2 thin films following furnace and flame annealing

A crystallization and surface evolution study of Au thin film on SiO₂ substrates following annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in a high vacuum (10⁻⁷ mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. Au thin films can be crystallized on SiO₂ substrates by both furnace and flame annealing. Annealing arranges the Au crystallites in the (1 1 1) plane direction and changes the morphology of the surface. Both, slow and rapid annealing result in a good background in the XRD spectra and hence clean and complete crystallization which depends more on the temperature than on the time of annealing. The epitaxial temperature for the Au/SiO₂ system decreases in the range of 350-400 °C. Furnace and flame annealing also form crystallized gold islands over the Au/SiO₂ surface. Relaxation at high temperatures of the strained Au layer, obtained after deposition, should be responsible for the initial stages of clusters formation. Gold nucleation sites may be formed at disordered points on the surface and they become islands when the temperature and time of annealing are increased. The growth rate of crystallites is highest around 360 °C. Above this temperature, the layer melts and gold diffuses from the substrate to the nucleation sites to increase the distance between islands and modify their shapes. Well above the eutectic temperature, the relaxed islands have hexagonally shaped borders. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above 360 °C is 0.2 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system. Epitaxial Au(1 1 1) layers without formation of islands can be prepared by furnace annealing in the range of 300-310 °C and by flame annealing of a few seconds and up to 0.5 min.     

溶胶-凝胶法Er2O3薄膜的结构和光学特性

针对稀土Er掺杂Si光源中Er离子掺杂浓度低的问题,采用溶胶-凝胶（Sol-gel）法在Si(100)和SiO2/Si(100)基片上旋涂法制备Er₂O₃光学薄膜,Er离子浓度与以前掺杂方法相比提高了2个数量级.900 ℃热处理获得单一立方结构的Er₂O₃薄膜材料.光致发光（PL）特性研究表明在654 nm波长的激光泵浦下,Er₂O₃薄膜材料获得了1.535 μm的发光峰,并具有较小的温度猝灭1/5.在SiO₂/Si(100)基体上制备的Er2O3薄膜材料的光致发光强度比Si(100)基体上制备的薄膜提高2-3倍.研究结果表明具有强光致发光特性的Er₂O₃薄膜是一种有前景的硅基光源和放大器材料.