Direct formation of graphene layers on top of SiC during the carburization of Si substrate

We grow graphene film on silicon substrates having various orientations by simple heating in the presence of carbon source gas. We observed that a 3C-SiC (111) film would form upon carburizing silicon with carbon deposited from a carbon source because it is well lattice-matched with Si (110) (less than 2%). Graphene grew on the buffer layer of 3C-SiC (111). The surface consists of hexagonal arrays that can act as a template for graphene growth. This simple and inexpensive method of forming graphene on silicon wafer in situ is compatible with silicon technology.     

氢化非晶硅叠层薄膜对单晶硅表面钝化研究

采用等离子体增强化学气相沉积法生长的单层本征氢化非晶硅薄膜对单晶硅片进行钝化,结果表明增加氢稀释比有利于减少薄膜中的缺陷,增强钝化效果,过量的氢稀释比会导致非晶硅在硅片表面的外延晶化生长,降低钝化效果。退火导致非晶硅晶化程度增加,降低了钝化效果,同时退火提升了薄膜的质量,改变了H键合方式,增强了钝化效果。因此,单层氢化非晶硅只有在合适的氢稀释比和退火温度才可以获得最佳钝化效果。为了提高非晶硅薄膜对硅片的钝化效果,采用具有高低氢稀释比的叠层本征非晶硅薄膜对硅片进行钝化。因此将高氢稀释比沉积的非晶硅薄膜叠层生长于低氢稀释比的薄膜之上,避免非晶硅在硅片表面的外延生长。在退火过程中,高氢稀释比薄膜中的氢扩散到低氢稀释比薄膜中,有效地钝化了非晶硅中和单晶硅表面的悬挂键,改善了非晶硅/硅片的界面质量,叠层钝化后硅片的少子寿命为7.36 ms,隐含开路电压为732 mV。     

纳米多孔SiO2薄膜的制备与红外光谱研究

以正硅酸乙酯为原料,采用溶胶-凝胶法,结合旋转涂胶、超临界干燥工艺在硅片上制备了纳米多孔SiO2薄膜。XRD表明薄膜为无定形态;SEM显示薄膜具有多孔网络结构,其SiO2粒子直径为10~20nm。利用FTIR研究了薄膜的结构,纳米多孔SiO2薄膜含有Si—O—Si与Si—OR结构,呈疏水性;该SiO2薄膜热处理后因含有Si—OH基团而呈吸水性;用三甲基氯硅烷对热处理SiO2薄膜进行修饰可使其呈疏水性,修饰后的薄膜在N2中温度不高于450℃可保持其疏水性与多孔结构。     

X-ray study of the wetting behaviour of CCl4 on Si/SiO2 surfaces

The complete wetting of an uncoated silicon wafer covered with a native oxide layer by saturated vapour of carbon tetrachloride was studied by using the x-ray reflectivity-technique. Differential heating of the substrate relative to a liquid reservoir was used to examine the disjoining pressure as a function of film thickness. The measurements were done at the temperaturesT=308K andT=318K of the reservoir. The observed film thicknesses varied between 26Å and 345Å depending on the temperature difference. A model for explaining the measured film thickness as a function of the temperature difference in terms of van der Waals forces is presented. It is based on the non-retarded interaction and includes terms of higher order in the film thickness. Microscopic constants like the Hamaker constant were determined and compared with reported values.     

Probing simultaneously the volume and surface structure of nanospheres adsorbed at a solid-liquid interface by GISANS

We demonstrate in this paper the possibilities offered by Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of solid/liquid interfaces. We present experimental results obtained by Specular Neutron Reflectivity (SNR) and GISANS on a model system made of silica nanospheres adsorbed on a silicon wafer by electrostatic interactions both at solid/air interface and solid/liquid interfaces. At the solid/liquid interface, we demonstrate that grazing incidence scattering enables to discriminate the surface and the bulk scattering. The surface structure factor derived from GISANS shows that the nanospheres are organized as a repulsive liquid system, with a surface fraction occupation consistent with values obtained by SNR. This original setup highlights a direct correlation between the structure of the silica nanospheres in solution and their organization on the surface: due to the strong electrostatic repulsions between spheres, their organization at the surface is close to the projection in 2D of the 3D organization of the nanospheres in solution.     

Nanosphere dispersion on a large glass substrate by low dose ion implantation for localized surface plasmon resonance

Dispersing nanospheres on a large glass substrate is the key to fabricate noble metal nanostructures for localized surface plasmon resonance through dispersed nanosphere lithography. This article reports that by modifying the glass surface with low dose ion implantation and successively dip coating the surface with poly(diallyldimethyl ammonium chloride) (PDDA), polystyrene or silica nanospheres can be dispersed on a large glass substrate. Investigation shows that several kinds of ions, such as silicon, boron, argon, and arsenic, can improve the nanosphere dispersion on glass, attributed to the ion bombardment-caused silicon increment. Ion implantation imposes no surface roughness or optical loss to the glass substrate, thus this method is suitable for localized surface plasmon resonance application. Experiments show silicon ion implantation can best disperse the nanospheres. For the gold nanostructures obtained by obliquely evaporating 30 nm of gold film onto the polystyrene nanospheres, which are dispersed on a silicon ion implanted glass substrate, a localized surface plasmon resonance sensitivity of 242 nm/RIU is achieved.     

Asymmetric distribution of surface second harmonic generation for thin silver films deposited on Si(111)

The asymmetric distributions of surface optical second harmonic generation (SHG) through azimuthally angular scans of (111) silicon wafers on which thin silver films were deposited, have been detected with different polarizations of output beams. On account of the inversion symmetry of silicon crystals, the SHG for the Ag/Si system is mainly contributed by the silver film and the silicon surface. In this work, we found that the interface strain implies an asymmetric intensity variation of SHG with respect to the surface azimuthal angles as an ultra thin Ag film is deposited on silicon wafers. This asymmetric behavior is prominent as the deposited silver layer is heated so that the continuous film aggregates to become granular nanoparticles. Similar changes of the surface asymmetric SHG are observed for a bare Si wafer imposed upon by an external force.     

X-ray diffraction imaging investigation of silicon carbide on insulator structures

A new process was recently developed to manufacture silicon carbide on insulator structures (SiCOI). The process consists of several steps: (i) hydrogen implantation into an oxidised SiC wafer, (ii) bonding the oxidised surface of this wafer to an oxidised silicon substrate and (iii) high temperature splitting of a thin SiC film from the SiC wafer at the depth of the maximum hydrogen concentration and further annealing of the splitted film. The defect generation occurring during this process was investigated by synchrotron radiation X-ray diffraction topography, with special emphasis on to the last two steps. Various X-ray topographic techniques were used to characterise the lattice defects inside the SiC wafer, to quantify the strong lattice distortion near the edges of the splitted SiC film and to reveal SiC film regions lost during the splitting process. Moreover, we show that the strain fields of dislocations, observed in the silicon substrate after high temperature splitting and annealing of the splitted structure, induce a corresponding deformation in the thin SiC overlayer, despite the presence of the sandwiched oxide film. The defect density is much lower in the central region of the SiCOI structure. Received: 29 June 2001 / Accepted: 8 November 2001 / Published online: 20 March 2002     

Silicon nano-wires fabricated by thermal evaporation of silicon wafer

Thin silicon nano-wires (SiNWs) with a diameter of 10–20 nm were fabricated by a simple thermal evaporation of silicon wafer at 1523 K. The gold produced by an electrochemical method was covered on the wafer surface as catalyst. It was found that the SiNWs are amorphous and its Raman peak shifted down maybe due to the effect of laser heating and quantum confinement. Finally, a temperature gradient growth model is suggested to explain the growth direction of SiNWs.     

Fabrication of silicon wafer with ultra low reflectance by chemical etching method

A pyramid and nanowire binary structure of monocrystalline silicon wafer was fabricated by chemical etching. Much lower reflectance of silicon wafer with this structure was obtained compared with that of single pyramid or nanowaire arrays. The morphology, reflectivity and etching thickness of this structure were studied, as well as the influence on them caused by etching time and thickness of silver film. An average reflectance of 0.9% was obtained under optimized condition. The formation mechanism of silicon nanowires was explained by experimental evidence.     

Adsorption and manipulation of carbon onions on highly oriented pyrolytic graphite studied with atomic force microscopy

Carbon onions produced by DC arc discharge method were deposited on highly oriented pyrolytic graphite (HOPG) surface and their adsorption and manipulation was studied using an atomic force microscopy (AFM). Well-dispersed adsorption of carbon onions on HOPG surface was obtained and aggregations of onions were not observed. The van der Waals interaction between the onion and HOPG surface and that between two onions, were calculated and discussed using Hamaker's theory. The manipulation of adsorbed onions on HOPG surface was realized using the AFM in both the raster mode and the vector mode. The controllability and precision of two manipulation modes were compared and the vector mode manipulation was found superior, and is a useful technique for the construction of nano-scale devices based on carbon onions.     

Bending vibrations of semiconductor wafers with local heat sources

Experimental and theoretical analysis of temperature fields generated by the pulsed current heating of metallization paths on a semiconductor wafer surface is performed. It is shown that any step change in the heating power causes bending vibrations of the wafer. Within the safety margins for semiconductor device operation, the vibration amplitude is proportional to the step amplitude. The damping factor for the entire wave packet is found (Γ=1103 s^?1), and frequency components of acoustic radiation excited in a 300-µm-thick silicon wafer are determined.     

Formation and electron-beam annealing of implantation defects in a thin-film Si-SiO2 heterostructure

Technical Physics - The radiation-induced defects in a 20-nm-thick SiO2 film on a silicon wafer are studied by optically stimulated electron emission. Accelerated (12-keV) silicon ions is found to...     

Characterization of heat-assisted magnetic probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments.     

Controlling the transmission of ultrahigh frequency bulk acoustic waves in silicon by 45° mirrors

In this paper, we present a feasible microsystem in which the direction of localized ultrahigh frequency (∼1 GHz) bulk acoustic wave can be controlled in a silicon wafer. Deep etching technology on the silicon wafer makes it possible to achieve high aspect ratio etching patterns which can be used to control bulk acoustic wave to transmit in the directions parallel to the surface of the silicon wafer. Passive 45° mirror planes obtained by wet chemical etching were employed to reflect the bulk acoustic wave. Zinc oxide (ZnO) thin film transducers were deposited by radio frequency sputtering with a thickness of about 1 μm on the other side of the wafer, which act as emitter/receptor after aligned with the mirrors. Two opponent vertical mirrors were inserted between the 45° mirrors to guide the transmission of the acoustic waves. The propagation of the bulk acoustic wave was studied with simulations and the characterization of S₂₁ scattering parameters, indicating that the mirrors were efficient to guide bulk acoustic waves in the silicon wafer.     

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.     

Structural and spectroscopic analysis of hot filament decomposed ethylene deposited at low temperature on silicon surface

The deposition of decomposed ethylene on silicon wafer at lower temperature using hot filament chemical vapor deposition (HFCVD) method was applied to compose thin film of carbon and its compounds with silicon and hydrocarbon structures. The films were analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy with elemental microanalysis by energy dispersive X-ray spectrometer. The structure and morphology of the early stage of the film deposition was analyzed. The obtaining of SiC as well as diamond-like structure with this method and catalytic influence of chemical admixtures on the film structure and properties are discussed.     

Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

Effect of PECVD SiN_x/SiO_yN_x–Si interface property on surface passivation of silicon wafer

It is studied in this paper that the electrical characteristics of the interface between Si O_y N_x/Si N_x stack and silicon wafer affect silicon surface passivation. The effects of precursor flow ratio and deposition temperature of the Si O_y N_x layer on interface parameters, such as interface state density Ditand fixed charge Qf, and the surface passivation quality of silicon are observed. Capacitance–voltage measurements reveal that inserting a thin Si O_y N_x layer between the Si N_x and the silicon wafer can suppress Qfin the film and Ditat the interface. The positive Qfand Ditand a high surface recombination velocity in stacks are observed to increase with the introduced oxygen and minimal hydrogen in the Si O_y N_x film increasing. Prepared by deposition at a low temperature and a low ratio of N_2O/Si H_4 flow rate, the Si O_y N_x/Si N_x stacks result in a low effective surface recombination velocity(Seff) of 6 cm/s on a p-type 1 ?·cm~(–5) ?·cm FZ silicon wafer.The positive relationship between Seffand Ditsuggests that the saturation of the interface defect is the main passivation mechanism although the field-effect passivation provided by the fixed charges also make a contribution to it.     

A novel anti-shock silicon etching apparatus for solving diaphragm release problems

This paper presents a novel anti-shock bulk silicon etching apparatus for solving a universal problem which occurs when releasing the diaphragm (e.g.\ SiNx), that the diaphragm tends to be probably cracked by the impact of heating-induced bubbles, the swirling of heating-induced etchant, dithering of the hand and imbalanced etchant pressure during the wafer being taken out. Through finite element methods, the causes of the diaphragm cracking are analysed. The impact of heating-induced bubbles could be the main factor which results in the failure stress of the SiNx diaphragm and the rupture of it. In order to reduce the four potential effects on the cracking of the released diaphragm, an anti-shock bulk silicon etching apparatus is proposed for using during the last etching process of the diaphragm release. That is, the silicon wafer is first put into the regular constant temperature etching apparatus or ultrasonic plus, and when the residual bulk silicon to be etched reaches near the interface of the silicon and SiNx diaphragm, within a distance of 50--80~\mu m (the exact value is determined by the thickness, surface area and intensity of the released diaphragm), the wafer is taken out carefully and put into the said anti-shock silicon etching apparatus. The wafer's position is at the geometrical centre, also the centre of gravity of the etching vessel. An etchant outlet is built at the bottom. The wafer is etched continuously, and at the same time the etchant flows out of the vessel. Optionally, two symmetrically placed low-power heating resistors are put in the anti-shock silicon etching apparatus to quicken the etching process. The heating resistors' power should be low enough to avoid the swirling of the heating-induced etchant and the impact of the heating-induced bubbles on the released diaphragm. According to the experimental results, the released SiNx diaphragm thus treated is unbroken, which proves the practicality of the said anti-shock bulk silicon etching apparatus.