UHV RHEED system for in-situ studies of sputtered films

An all-metal, bakeable, ultra-high vacuum reflection high-energy electron diffraction (UHV RHEED) system has been developed for in-situ studies of films during deposition on surfaces by processes such as r.f. sputtering, where pressures in the region of the specimen may be as high as 3–4 Pa. The design separates the 50 kV gun vacuum from that of the specimen chamber with a single differential pumping aperture, which also serves as the beam-defining aperture. The electron optics enable a focussed spot of about 50 μm to be produced on the detector at a distance of 50 cm from the end of the magnetic lens housing, with adequate current for RHEED studies. The RHEED system has been installed in an UHV r.f. magnetron sputter-deposition chamber and has been successfully applied to (i) monitor, in the presence of the sputter discharge, the surface of a chemically cleaned n-type Si(100) wafer and (ii) study the subsequent growth of Pt films on the silicon surface under different conditions of sputtering pressure and r.f. power.     

Influence of processing variables on the structure and properties of ZnO films

Zinc oxide films of high optical quality have been deposited onto both silica and silicon substrates using reactive sputtering, pulsed laser deposition, and an aqueous solution based technique. Films have been characterized with respect to crystalline phase and phase stability, surface morphology, and optical response by means of X-ray diffraction, Raman spectroscopy, atomic force microscopy, optical transmission and ellipsometry measurements. All films studied were of the wurtzite phase, fine-grained, and exhibited varying degrees of c-axis orientation with respect to the substrate normal depending upon deposition conditions. Films showed some degree of residual tensile stress which was inferred from the E₂ Raman line shift relative to the single-crystal frequency. The wurtzite phase was found to be stable to temperatures near 800 °C, but at higher temperatures, reaction with silica led to evolution of Zn₂SiO₄ at the interface. Variations in Raman line intensities upon post-deposition annealing have been correlated with oxidation of excess zinc in the lattice.     

In-situ ellipsometry on sputtered dielectric and magneto-optic thin films

A four-gun magnetron sputtering chamber incorporating in-situ real-time spectroscopic ellipsometric analysis was used to grow magneto-optic memory structures. Data were taken at 44 wavelengths simultaneously from 410 nm to 750 nm, allowing the study of SiC/TbFeCo/SiC depositions on quartz in real time. These data were used to determine the sputter rates, optical constants, and the thicknesses of the films. The SiC data were taken at 1 min time intervals during growth, and the TbFeCo deposition was monitored continuously. Data were taken during the deposition of the entire structure without subjecting the sample to destructive analysis techniques or an oxidizing or reactive atmosphere.     

Sputter deposition of ZnS:Mn/SrS:Ce multilayered thin film white phosphor

A full color thin film electroluminescent (TFEL) display can be fabricated by using color filters in combination with a high efficiency ‘white’ phosphor, such as a thin film multilayered stack of ZnS:Mn and SrS:Ce (denoted ZnS:Mn/SrS:Ce). To date, deposition of these multilayers has been limited to vacuum evaporation techniques and atomic layer epitaxy, both of which require different substrate temperatures for growth of high quality ZnS:Mn and SrS:Ce. This repeated thermal cycling during multilayer deposition can adversely affect electroluminescent (EL) performance and manufacturability. Sputter deposition of ZnS:Mn and SrS:Ce produces high quality phosphors for a wider range of substrate temperatures. We have determined a common set of radio frequency (rf) sputter deposition parameters for ZnS:Mn and SrS:Ce that result in high performance, multilayered white phosphors for use in TFEL devices. The EL performance of our samples is comparable to the best performance reported for evaporated multilayered samples. The major improvement is that the rf sputtered ZnS:Mn and SrS:Ce layers were deposited at the same substrate temperature. We report on the effects of sputter deposition parameters on the resultant composition and morphology of ZnS:Mn and SrS:Ce thin films and multilayers. Their EL performance was evaluated and correlated to composition and morphology.     

Low temperature processed hafnium oxide: Structural and electrical properties

In this work hafnium oxide (HfO₂) was deposited by r.f. magnetron sputtering at room temperature and then annealed at 200 °C in forming gas (N₂+H₂) and oxygen atmospheres, respectively for 2, 5 and 10 h. After 2 h annealing in forming gas an improvement in the interface properties occurs with the associated flat band voltage changing from −2.23 to −1.28 V. This means a reduction in the oxide charge density from 1.33×10¹² to 7.62×10¹¹ cm⁻². After 5 h annealing only the dielectric constant improves due to densification of the film. Finally, after 10 h annealing we notice a degradation of the electrical film's properties, with the flat band voltage and fixed charge density being −2.96 V and 1.64×10¹² cm⁻², respectively. Besides that, the leakage current also increases due to crystallization. On the other hand, by depositing the films at 200 °C or annealing it in an oxidizing atmosphere no improvements are observed when comparing these data to the ones obtained by annealing the films in forming gas. Here the flat band voltage is more negative and the hysteresis on the C–V plot is larger than the one recorded on films annealed in forming gas, meaning a degradation of the interfacial properties.     

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N₂⁺ ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N₂⁺ ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N₂⁺ ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si_xN_y on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N₂⁺ ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates.     

直流磁控溅射功率对ITO薄膜光学性能的影响

本实验的ITO薄膜样品是利用直流磁控溅射技术在玻璃基片上沉积而成的。通过改变溅射功率,研究不同溅射功率对ITO薄膜光学性能的影响。经各实验测试后发现：在实验给定的功率区间内,ITO薄膜的厚度随着溅射功率的增加而增加,其可见光透过率则随之降低。     

溅射气压对Li-W共掺杂ZnO薄膜性能的影响

通过RF磁控溅射在不同溅射气压环境中,在石英衬底上制备得到Li-W共掺杂Zn O薄膜(LWZO)。对样品进行X射线衍射(XRD)、扫描电镜(SEM)、透过率以及电阻率的测试。结果表明:适当溅射气压环境下,有助于提高LWZO薄膜的结晶质量;SEM结果显示随着溅射气压增加LWZO薄膜表面晶粒粒径更小,表面更平整;薄膜的透光率保持在85%左右。光致发光光谱表明:LWZO的光致发光由本征发光及缺陷发光组成,结晶度高以及择优取向好,本征发光强度强。同时,薄膜的最低电阻率也达到了6.9×10-3Ωcm。     

Preparation of Cr(N,O) thin films by RF reactive unbalanced magnetron sputtering

Chromium oxynitride thin films were deposited by radio-frequency (RF) reactive unbalanced magnetron sputtering at various O₂ flow rates onto Si(100) and glassy carbon substrates. The compositions of the thin films were analyzed by Rutherford backscattering spectroscopy. The thin films were found to contain up to 44 at.% oxygen. In Fourier-transform infrared spectra, a peak attributed to the Cr-N bond of CrN was observed, but no peak attributable to the Cr-O bond of Cr₂O₃ was found. The textures of the thin films were observed by transmission electron microscopy, which revealed that samples had a columnar structure. The hardness of the thin films was measured by nanoindentation. The hardness increased from 20 GPa to a maximum value of 31 GPa with increasing oxygen content.     

Numerical analysis of geometry effects for target re-deposition during low pressure hollow cathode magnetron sputtering

During low pressure ionized metal physical vapor deposition (PVD) of Cu seed layer for microprocessor interconnects, the re-deposited Cu film on the hollow cathode magnetron (HCM) target may fall off and damage the Cu film on the wafer. An analytical view factor model based on the analogy between metal sputtering and diffuse thermal radiation was used to obtain re-deposition profiles for HCM targets in low pressure (below 0.1 Pa) Cu ionized PVD. The model predictions indicate that there is an inherent non-uniformity in the re-deposition profile even for uniform sputtering over the entire HCM target. The predicted re-deposition profile agrees with experimental observations. Subsequent target redesign studies found that the non-uniformity in the re-deposition profile could be mitigated by using a conical sidewall between the top disk and the cylindrical sidewall or reducing the length of the cylindrical sidewall.