纳米α-Al2O3磨料抛光单晶硅片光滑表面的形成机理

"将纳米α-Al2O3粉体配制成抛光液并冷冻成冰结抛光垫对单晶硅片进行了抛光,用原子力显微镜观察了抛光表面的微观形貌并测量了其表面粗糙度,采用透射电镜观察了单晶硅片抛光后的断面形貌．为进一步分析抛光过程中的化学作用机理,采用X射线光电子能谱分析了单晶硅片抛光后表面的化学成分．利用纳米压痕仪的划痕附件对单晶硅片进行了划痕测试,研究了抛光过程中的机械作用机理．结果表明纳米α-Al2O3磨料冰冻抛光单晶硅片时,在1 mm￡1 mm的范围内得到了微观表面粗糙度为0.367 nm的超光滑表面,亚表面没有任何损伤,材     

Study on sapphire removal for thin-film LEDs fabrication using CMP and dry etching

Mechanical grinding, chemical mechanical polishing (CMP) and dry etching process are integrated to remove sapphire substrate for fabricating thin-film light-emitting diodes. The thinning of sapphire substrate is done by fast mechanical grinding followed by CMP. The CMP can remove or reduce most of the scratches produced by mechanical grinding, recovering both the mechanical strength and wafer warpage to their original status and resulting in a smoother surface. The surface morphology and surface roughness on grinded and polished sapphire substrate are measured by using atomic force microscopy (AFM). The etch rates of sapphire by BCl₃-based dry etching are reported. Pattern transfer to the physical and chemical stability of sapphire is made possible by inductively coupled plasma (ICP) etch system that generates high density plasma. The patterning of several microns period in sapphire wafer by using a combination of BCl₃/Ar plasma chemistry and SiO₂ mask is presented. The anisotropic etch profile formed on sapphire wafer is obtained from scanning electron microscopy (SEM) images.     

Matching WMAP 3-year results with the cosmological Slingshot primordial spectrum

We consider a recently proposed scenario for the generation of primordial cosmological perturbations, the so called Cosmological Slingshot scenario. We first obtain a general expression for the Slingshot primordial power spectrum which extends previous results by including a blue pre-bounce residual contribution at large scales. Starting from this expression we numerically compute the CMB temperature and polarization power spectra arising from the Slingshot scenario and show that they excellently match the standard WMAP 3-year best-fit results. In particular, if the residual blue spectrum is far above the largest WMAP observed scale, the Slingshot primordial spectrum fits the data well by only fixing its amplitude and spectral index at the pivot scale k _p = 10⁻³ h Mpc⁻¹. We finally show that all possible distinctive Slingshot signatures in the CMB power spectra are confined to very low multipoles and thus very hard to detect due to large cosmic variance dominated error bars at these scales.     

附载CeO2的纳米γ-Al2O3合成及其悬浮液的分散稳定研究

以异丙醇铝和六水硝酸亚铈为铈源和铝源,采用溶胶-凝胶法制备了前驱体,并将前驱体在800℃下空气中焙烧2 h得到附载CeO2的高纯纳米γ-Al2O3.样品经X射线衍射(XRD)、透射电镜(TEM)、比表面积(BET)、化学成分和杂质含量分析,结果表明:合成的粉末为由γ-Al2O3和CeO2组成的混合物相,两者均属立方晶系,其中γ-Al2O3空间群为O7H-FD3M,CeO2空间群为Fm3m;晶粒平均粒径为15.7 nm,颗粒平均粒径约60～80 nm,粒子呈类球形,比表面积为159.01 m2·g-1;粒子纯度不低于99.97%,CeO2含量为24.22%.红外光谱(IR)测试结果显示,有Al-O-Ce键生成,表明CeO2与Al2O3并非简单混合.进一步通过对其悬浮液体系Zeta电位和吸光度的测定,研究了不同pH值条件、分散剂种类和用量以及氧化剂对其悬浮液分散稳定性的影响;采用超声波分散法,选择硝酸、氢氧化钾溶液作为pH调节剂,异丙醇胺作为分散剂,过氧化氢作为氧化剂,成功制备了长期存放不沉降的附载CeO2的纳米γ-Al2O3CMP浆料,确定了配制的优化工艺条件.     

Enzyme inhibition-based biosensor for the electrochemical detection of microcystins in natural blooms of cyanobacteria

An electrochemical biosensor for the detection of microcystin has been developed based on the inhibition of the protein phosphatase 2A (PP2A) by this cyanobacterial toxin. The enzyme has been immobilised by entrapment using a poly(vinyl alcohol) azide-unit pendant water-soluble photopolymer (PVA-AWP). Electrode supports and immobilisation conditions have been optimised by colorimetric assays, the highest immobilisation yields being obtained with screen-printed graphite electrodes and the 1:2 PP2A:PVA ratio. Catechyl monophosphate (CMP), α-naphthyl phosphate (α-NP) and 4-methylumbelliferyl phosphate (4-MUP) have been used as phosphorylated substrates to monitor the protein phosphatase activity by electrochemical methods, the former providing the highest chronoamperometric currents at appropriate working potentials (+450 mV versus Ag/AgCl). Incubation with standard microcystin solutions has demonstrated the inhibition of the immobilised enzyme, proportional to the toxin concentration. The standard inhibition curve has provided a 50% inhibition coefficient (IC₅₀) of 83 μg L⁻¹, a limit of detection (LOD; 35% inhibition) of 37 μg L⁻¹, and 100% inhibition at about 1000 μg L⁻¹. Real samples of cyanobacterial blooms from the Tarn River (Midi-Pyrénées, France) have been analysed using the developed amperometric biosensor and the toxin contents have been compared to those obtained by a conventional colorimetric protein phosphatase inhibition (PPI) assay and high-performance liquid chromatography (HPLC). The results clearly justify the use of the developed amperometric biosensor as screening method for microcystin detection.     

Electrochemical characterization of surface complexes formed on Cu and Ta in succinic acid based solutions used for chemical mechanical planarization

Open-circuit potential measurements, cyclic voltammetry and Fourier transform impedance spectroscopy have been used to study pH dependent surface reactions of Cu and Ta rotating disc electrodes (RDEs) in aqueous solutions of succinic acid (SA, a complexing agent), hydrogen peroxide (an oxidizer), and ammonium dodecyl sulfate (ADS, a corrosion inhibitor for Cu). The surface chemistries of these systems are relevant for the development of a single-slurry approach to chemical mechanical planarization (CMP) of Cu lines and Ta barriers in the fabrication of semiconductor devices. It is shown that in non-alkaline solutions of H₂O₂, the SA-promoted surface complexes of Cu and Ta can potentially support chemically enhanced material removal in low-pressure CMP of surface topographies overlying fragile low-k dielectrics. ADS can suppress Cu dissolution without significantly affecting the surface chemistry of Ta. The data analysis steps are discussed in detail to demonstrate how the D.C. and A.C. electrochemical probes can be combined in the framework of the RDE technique to design and test CMP slurry solutions.     

纳米氧化铈的制备及其抛光性能的研究

采用溶胶-凝胶法制备了纳米CeO2粉体,并采用XRD、TOF-SIMS对其进行了表征。结果表明平均晶粒度在13.3nm,粒度分布均匀。进而研究了纳米CeO2在玻璃基片抛光中的抛光性能。ZYGO形貌仪表明,抛光后其表面平均粗糙度值(Ra)可降低到0.6nm左右。原子力显微镜(AFM)在5μm×5μm范围内测得基片表面粗糙度Ra值为0.281nm,表面光滑,划痕等表面微观缺陷明显改善。     

Polishing behavior of PS/CeO2 hybrid microspheres with controlled shell thickness on silicon dioxide CMP

Organic-inorganic composite microspheres with PS as a core and CeO₂ nanoparticles as a shell were synthesized by in situ decomposition reaction of Ce(NO₃)₃ on the surfaces of PS microspheres prepared through soap-free emulsion polymerization. The shell thickness of the composite microspheres could be turned by varying the concentration of Ce(NO₃)₃ in the reaction solution. The whole process required neither surface treatment for PS microspheres nor additional surfactant or stabilizer. The as-synthesized PS/CeO₂ composite microsphere samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Oxide chemical mechanical polishing (CMP) performance of the PS/CeO₂ composite abrasives with different shell thickness was characterized by atomic force microscopy (AFM). The results indicated that the as-prepared core-shell structured composite microspheres (220-260 nm in diameter) possessed thin shell (10-30 nm) composed of CeO₂ nanoparticles (particle diameter of 5-10 nm), and the final CeO₂ contents of the composite microspheres ranged from 10 to 50 wt%. A possible mechanism for the formation of PS/CeO₂ composite microspheres was discussed also. The CMP test results confirmed that the novel core-shell structured composite abrasives are useful to improve oxide CMP performance. In addition, there is an obvious effect of shell thickness of the composite abrasives on oxide CMP performance.