Thickness of SiO2 thin film on silicon wafer measured by dispersive white-light spectral interferometry

We present a white-light spectral interferometric technique for measuring the thickness of SiO₂ thin film on a silicon wafer. The technique utilizes a slightly dispersive Michelson interferometer with a cube beam splitter and a fibre-optic spectrometer to record channelled spectra in two configurations. In the first, a standard configuration with two identical metallic mirrors, the recorded channelled spectrum is fitted to the theoretical one to determine the effective thickness of the beam splitter made of BK7 optical glass. In the second configuration one of the mirrors is replaced by SiO₂ thin film on the silicon wafer and the recorded channelled spectrum is fitted to the theoretical one to determine the thin-film thickness. We consider multiple reflection within the thin-film structure, use the optical constants for all the materials involved in the set-up, and confirm very good agreement between theory and experiment. The technique is applied to four samples with various SiO₂ film thicknesses. PACS 07.60.Ly; 68.55.Jk; 78.20     

Spectral interferometry and reflectometry used to measure thin films

A new method for a precise measurement of the oscillatory part of phase change on reflection (interferometric phase) from a thin-film structure is presented. The method, which is based on phase retrieval from the spectral interferograms recorded at the output of a slightly dispersive Michelson interferometer, is combined with reflectometry. The interferometric phase of the thin-film structure is measured precisely using a reference sample of known phase change on reflection. The spectral reflectance of the thin-film structure is also measured in the interferometer. The feasibility of the method is confirmed in processing the experimental data for SiO₂ thin film on a silicon wafer of known optical constants. Four samples of the thin film are used and their thicknesses are determined. We confirm very good agreement between the thicknesses obtained from the interferometric phase and reflectance measurements. PACS  07.60.Ly; 68.55.Jk; 78.20.Bh     

The effect of silicon substrate on thickness of SiO2 thin film analysed by spectral reflectometry and interferometry

Techniques of spectral reflectometry and interferometry are used for measuring small changes in thickness of SiO₂ thin film grown by thermal oxidation on different silicon substrates. A slightly dispersive Michelson interferometer with one of its mirrors replaced by a thin-film structure is used to measure the reflectance and interferometric phase of the thin-film structure at the same time. The experimental data are used to determine precisely the thickness of the SiO₂ thin film on silicon wafers of two crystallographic orientations and different dopant concentrations. We confirmed very good agreement between the experimental data and theory and revealed that the thin-film thickness, which varies with the type of silicon substrate, depends linearly on the wavelength at which minimum in the spectral reflectance occurs. Similar behaviour was revealed for the interferometric phase.     

The refractive index of homogeneous SiO<Subscript>2</Subscript> thin films

The effect of the through-thickness inhomogeneity of SiO₂ films on their refractive index is studied. The SiO₂ films, deposited by tetraethoxysilane pyrolysis on plane-parallel oriented crystalline quartz substrates and on silicon plates, were etched layer-by-layer in Pliskin’s solution. The refractive index and the geometric thickness of films were calculated from the measured ellipsometric angles after each etching. The determination errors of the refractive indices as functions of the film thickness, which result from the measurement errors of the polarization angles and substrate parameters, are numerically analyzed. For SiO₂ films thicker than 20nm, no effect of inhomogeneity is found. The refractive indices of thinner films were observed to depend on the thickness. The reasons for such dependences are discussed.     

Silicon based polytetrafluoroethylene electrets: Preparation and corona charging characteristics

In this paper, silicon based planar technology and high performance fluorocarbon polymer polytetrafluoroethylene (PTFE) are combined to achieve PTFE thin film electrets on wafer. The PTFE film is fabricated onto SiO₂ substrates and Pt substrates using spin coating and annealing processes, and its electret effect is demonstrated using negative corona charging method. PTFE electrets with different surface morphology exhibit different charge storage capability. Maximally, surface potential of ?396 V is achieved on Pt substrates and ?361 V is achieved on SiO₂ substrates. The average retain rate of surface potential over 240 h is 90.6% for Pt substrates and 76.3% for SiO₂ substrates. The proposed method presents the primary step toward integrated electrostatic devices.     

X-ray spectral analysis of the interface of a thin Al<Subscript>2</Subscript>O<Subscript>3</Subscript> film prepared on silicon by atomic layer deposition

The extent and phase chemical composition of the interface forming under atomic layer deposition (ALD) of a 6-nm-thick Al₂O₃ film on the surface of crystalline silicon (c-Si) has been studied by depthresolved, ultrasoft x-ray emission spectroscopy. ALD is shown to produce a layer of mixed Al₂O₃ and SiO₂ oxides about 6–8 nm thick, in which silicon dioxide is present even on the sample surface and its concentration increases as one approaches the interface with the substrate. It is assumed that such a complex structure of the layer is the result of interdiffusion of oxygen into the layer and of silicon from the substrate to the surface over grain boundaries of polycrystalline Al₂O₃, followed by silicon oxidation. Neither the formation of clusters of metallic aluminum near the boundary with c-Si nor aluminum diffusion into the substrate was revealed. It was established that ALD-deposited Al₂O₃ layers with a thickness up to 60 nm have similar structure.     

Growth of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> films on the Si(111) surface covered by a thin SiO<Subscript>2</Subscript> layer

Magnetite polycrystalline films are grown by variously oxidizing a Fe film on the Si(111) surface covered by a thin (1.5 nm) SiO₂ layer. It is found that defects in the SiO₂ layer influence silicidation under heating of the Fe film. The high-temperature oxidation of the Fe film results in the formation of both Fe₃O₄ and iron monosilicide. However, the high-temperature deposition of Fe in an oxygen atmosphere leads to the growth of a compositionally uniform Fe₃O₄ film on the SiO₂ surface. It is found that such a synthesis method causes [311] texture to arise in the magnetite film, with the texture axis normal to the surface. The influence of the synthesis method on the magnetic properties of grown Fe₃O₄ films is studied. A high coercive force of Fe₃O₃ films grown by Fe film oxidation is related to their specific morphology and compositional nonuniformity.     

关于热生长SiO2薄膜厚度的测量

在半导体硅器件的研究工作中,需要准确地测量和控制SiO₂薄膜的厚度。由于干涉原理,SiO₂薄膜在白光照射下呈现颜色。但薄膜厚度与颜色相应的单色光的波长并不成简单的函数关系。本文叙述了用干涉显微镜测量热生长SiO₂薄膜厚度的方法。由测量结果得到SiO₂薄膜的折射率以及SiO₂和硅界面及空气和硅界面反射相移之差。并且测量了一组标准样品的薄膜厚度,列出了薄膜厚度与干涉颜色的对应关系。所得结果与从Rollet数据所推算的结果大致符合。样品厚度还包括了Rollet数据中所未包括的范围(3300—4200?)。     

Effects of thickness on the infrared optical properties of Ba<Subscript>0.9</Subscript>Sr<Subscript>0.1</Subscript>TiO<Subscript>3</Subscript> ferroelectric thin films

Using infrared spectroscopic ellipsometry (IRSE), the optical properties of the Ba_0.9Sr_0.1TiO₃ (BST) ferroelectric thin films with different film thicknesses on Pt/Ti/SiO₂/Si substrates prepared by a modified sol-gel method have been investigated in the 2.5–12.6 m wavelength range. By fitting the measured ellipsometric parameter ( and ) data with a three-phase model (Air/BST/Pt) and the classical dispersion relation for the BST thin films, the optical constants and thicknesses of the thin films have been obtained. The average thickness of the single layer decreases with increasing film thickness. The refractive index of the BST films decreases with increasing thickness in the wavelength range 2.5–11 m, and increases with increasing thickness in the wavelength range 11–12.6 m. However, the extinction coefficient of the BST films monotonously decreases with increasing thickness. It is closely associated with the crystallinity of the thin films, the crystalline size effect and the influence of the interface layer. The absorption coefficient of the BST films with different thicknesses decreases with increasing thickness. PACS 77.55.+f; 78.20.Ci; 78.30.Am; 81.70.Fy; 81.40.Tv     

N掺杂SiO2纳米薄膜的制备及其磁性

利用射频磁控反应溅射技术,制备了氮掺杂的SiO₂纳米薄膜.发现N掺杂SiO₂体系纳米薄膜具有铁磁性.较小的氮化硅颗粒均匀分布在氧化硅基质中有利于磁有序的形成.基底温度为400℃时,样品薄膜具有最大的饱和磁化强度和矫顽力,分别为35 emu/cm³和75 Oe.薄膜的磁性可能产生于氮化硅和氧化硅的界面.理论计算表明,N掺杂SiO₂体系具有净自旋.同时,由氮化硅和氧化硅界面之间的电荷转移导致的轨道磁矩也会对样品的磁性有贡献 关键词： 2薄膜')" href="#">N掺杂SiO₂薄膜 射频磁控反应溅射 界面磁性 基底温度     

Wettability and crystalline orientation of Cu nanoislands on SiO<Subscript>2</Subscript> with a Cr underlayer

Cu thin films were grown by sputter deposition on SiO₂ substrates with a Cr underlayer that is known to improve the adhesion between Cu and SiO₂. The initial stage of Cu growth was investigated using transmission electron microscopy. Results showed that non-wetting spherical Cu nanoislands were formed with a random crystalline orientation on Cr/SiO₂, and evolved into a randomly oriented polycrystalline thin film. These results were then compared with our previous results on the initial growth of Cu on SiO₂ with and without a Ti underlayer. A quantitative model was proposed to explain the difference in dependence of the wettability of microscopic nanoislands and that of the adhesion of macroscopic thin films on interfacial interactions and surface energies. PACS 61.46.+w; 68.35.Md; 68.35.Np     

The film thickness dependent thermal stability of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>:Ag thin films as high-temperature solar selective absorbers

The monolayer Al₂O₃:Ag thin films were prepared by magnetron sputtering. The microstructure and optical properties of thin film after annealing at 700 °C in air were characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and spectrophotometer. It revealed that the particle shape, size, and distribution across the film were greatly changed before and after annealing. The surface plasmon resonance absorption and thermal stability of the film were found to be strongly dependent on the film thickness, which was believed to be associated with the evolution process of particle diffusion, agglomeration, and evaporation during annealing at high temperature. When the film thickness was smaller than 90 nm, the film SPR absorption can be attenuated until extinct with increasing annealing time due to the evaporation of Ag particles. While the film thickness was larger than 120 nm, the absorption can keep constant even after annealing for 64 h due to the agglomeration of Ag particles. On the base of film thickness results, the multilayer Al₂O₃:Ag solar selective thin films were prepared and the thermal stability test illustrated that the solar selectivity of multilayer films with absorbing layer thickness larger than 120 nm did not degrade after annealing at 500 °C for 70 h in air. It can be concluded that film thickness is an important factor to control the thermal stability of Al₂O₃:Ag thin films as high-temperature solar selective absorbers.     

同步辐射光激励的二氧化硅薄膜刻蚀研究

利用热氧化法在硅晶片上生长SiO₂薄膜，结合光刻和磁控溅射技术在SiO₂薄膜表面制备接触型钴掩模，通过掩模方法在硅表面开展了同步辐射光激励的表面刻蚀研究，在室温下制备了SiO₂薄膜的刻蚀图样.实验结果表明：在同步辐射光照射下，通入SF₆气体可以有效地对SiO₂薄膜进行各向异性刻蚀，并在一定的气压范围内，刻蚀率随SF₆气体浓度的增加而增加，随样品温度的下降而升高；如果在同步辐射光照射下，用SF₆和O₂的混合气体作为反应气体，刻蚀过程将停止在SiO₂/Si界面，即不对硅刻蚀，实现了同步辐射对硅和二氧化硅两种材料的选择性刻蚀；另外，钴表现出强的抗刻蚀能力，是一种理想的同步辐射光掩模材料. 关键词： 同步辐射刻蚀 接触型钴掩模 二氧化硅薄膜     

First nucleation steps during deposition of SiO2 thin films by plasma enhanced chemical vapour deposition

The initial nucleation stages during deposition of SiO₂ by remote plasma enhanced chemical vapour deposition (PECVD) have been monitored by XPS inelastic peak shape analysis. Experiments have been carried out on two substrates, a flat ZrO₂ thin film and a silicon wafer with a native silicon oxide layer on its surface. For the two substrates it is found that PECVD SiO₂ grows in the form of islands. When the SiO₂ particles reach heights close to 10 nm they coalesce and cover completely the substrate surface. The particle formation mechanism has been confirmed by TEM observation of the particles grown on silicon substrates. The kinetic Monte Carlo simulation of the nucleation and growth of the SiO₂ particles has shown that formation of islands is favoured under PECVD conditions because the plasma species may reach the substrate surface according to off-perpendicular directions. The average energy of these species is the main parameter used to describe their angular distribution function, while the reactivity of the surface is another key parameter used in the simulations.     

Structure, morphology and optical properties of SiO2−x thin films prepared by plasma-assisted pulsed laser deposition

The amorphous silicon oxide SiO_2−x thin films were prepared by the plasma-assisted pulsed laser deposition (PLD) method. X-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS-NIR scanning spectrophotometry and ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of obtained thin films. The influences of substrate temperatures, oxygen partial pressures and oxygen plasma assistance on the compositions of silicon oxide (SiO_2−x) thin films were investigated. Results show that the deposited thin films are amorphous and have high surface quality. Stoichiometric silicon dioxide (SiO₂) thin film can be obtained at elevated temperature of 200 °C in an oxygen plasma-assisted atmosphere. Using normal incidence transmittance, a novel and simple method has been proposed to evaluate the value of x in transparent SiO_2−x thin films on a non-absorbing flat substrate.     

Pulsed laser deposition of BaGa<Subscript>2</Subscript>O<Subscript>4</Subscript>

This paper reports the first results obtained on monobarium gallate thin films grown on silicon and platinum coated substrates by pulsed laser deposition. The influence of oxygen background pressure and substrate (or post-annealing) temperature on the film properties was studied. The films were characterized by XRD, RHEED, AFM, photoelectron and electrical impedance spectroscopy. The structure analysis showed that the films crystallized into a hexagonal phase, most probably into (metastable) α-BaGa₂O₄. Depending on deposition conditions, films with different (from nearly epitaxial to polycrystalline) textures were obtained.     

Dispersive white-light spectral interferometry including the effect of thin-film for distance measurement

A spectral-domain white-light interferometric technique is used for measuring distances in a Michelson interferometer with a mirror represented by a thin-film structure (TFS) on a substrate. A fibre-optic spectrometer is employed for recording spectral interferograms that include wide wavelength range effects of dispersion in a cube beam splitter and multiple reflection within the TFS. Knowing the effective thickness of the beam splitter, its dispersion and parameters of the TFS and substrate, the positions of the second interferometer mirror are determined precisely by a least-squares fitting of the theoretical spectral interferograms to the recorded ones. We apply the technique to the beam splitter made of BK7 optical glass and to a uniform SiO₂ thin film on a silicon wafer. We compare the results of the processing that include and do not include the effect of the TFS.     

Electric and magnetic properties of CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript> bilayer thin films prepared by pulsed-laser deposition

CoFe₂O₄ (CFO) thin film with highly (111)-preferential orientation was first deposited on the silicon substrate by a pulsed-laser deposition, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) layers were deposited with different oxygen pressures to form the bilayer CFO/PZT nanocomposite thin films. X-ray diffraction showed that the PZT preferential orientation was strongly dependant on the oxygen pressure. The smooth film surface was obtained after depositing the CFO and PZT layers. The bilayer thin films exhibit good ferromagnetic and ferroelectric properties, and a low leakage current density of 0.004 μA/cm² at 50 kV/cm. The leakage current density curves show loops for the electric polarized field when the electric field reverses. PACS 77.84.Lf; 75.80+q; 81.05.Zx; 81.15.Fg     

Oxygen plasma and high pressure H<Subscript>2</Subscript>O vapor heat treatments used to fabricate polycrystalline silicon thin film transistors

Oxygen plasma and high pressure H₂O vapor heat treatment were applied to fabrication of n-channel polycrystalline silicon thin film transistors (poly-Si TFTs). 13.56 MHz-oxygen-plasma treatment at 250 °C, 100 W for 5 min effectively reduced defect states of 25-nm-thick silicon films crystallized by 30 ns-pulsed XeCl excimer laser irradiation. 1.3×10⁶-Pa-H₂O vapor heat treatment at 260 °C for 3 h was carried out in order to improve electrical properties of SiO_x gate insulators and SiO_x/Si interfaces. A carrier mobility of 470 cm²/V s and a low threshold voltage of 1.8 V were achieved for TFTs fabricated with crystallization at 285 mJ/cm². Received: 18 November 2002 / Accepted: 25 November 2002 / Published online: 11 April 2003 RID="*" ID="*"Corresponding author. Fax: +81-42/388-7109, E-mail: tsamesim@cc.tuat.ac.jp     

Controlling the orientation of ZnO nanorod arrays using TiO<Subscript>2</Subscript> thin film templates dip-coated by sol–gel

The oriented ZnO nanorod arrays have been synthesized on a silicon wafer that coated with TiO₂ films by aqueous chemical method. The morphologies, phase structure and the photoluminescence (PL) properties of the as-obtained product were investigated by field-emission scanning electron microscopy (FE-SEM), X-ray diffractometer (XRD), transmission electron microscope (TEM) and PL spectrum. The nanorods were about 100 nm in diameter and more than 1 μm in length, which possessed wurtzite structure with a c axis growth direction. The room-temperature PL measurement of the nanorod arrays showed strong ultraviolet emission. The effect of the crystal structure and the thickness of TiO₂ films on the morphologies of ZnO nanostructures were investigated. It was found that the rutile TiO₂ films were appropriate to the oriented growth of ZnO nanorod arrays in comparison with anatase TiO₂ films. Moreover, flakelike ZnO nanostructures were obtained with increasing the thickness of anatase TiO₂ films.