Low-dose SIMOX wafers for LSIs fabricated with internal-thermal-oxidation (ITOX) process: electrical characterization

Electrical performance of separation by implanted oxygen (SIMOX) wafers manufactured by internal-thermal-oxidation (ITOX) process was evaluated. Breakdown behaviour of the buried oxide (BOX) layer was confirmed quantitatively to be dominated by Si islands therein, which were found to be reduced in size or eliminated by the ITOX process. By optimizing the oxygen dose and ITOX amount, a BOX breakdown field of about 8 MV/cm, comparable to those of thermally-grown oxide, was attained. The gate oxide integrity on an ITOX-SIMOX wafer was found to be superior to that of bulk Si wafers, indicating the wafer surface was improved by the high temperature annealing.     

Effect of annealing conditions on the formation of low-dose SIMOX structures implanted at 190 keV

The structure of low-dose SIMOX wafers as a function of annealing conditions has been studied using TEM. A set of samples were implanted at 190 keV with doses of 0.5, 0.83 and 1.8 × 10¹⁸cm^-2} oxygen followed by annealing treatment at different ramp rates (1^~ Cmin^-1 or 5^~ Cmin^-1), temperatures (1310 °C or 1350 °C), and holding times (0 or 5 h). The results show that a higher annealing temperature (1350 °C) with a longer holding time improves the quality of the top Si layers and the smoothness of the interfaces in low-dose SIMOX wafers. A slow thermal ramp rate results in sharp interfaces but leads to a high density of Si islands in the buried oxide (BOX) layer. Chemical etching experiment performed on the top Si layer of a low-dose SIMOX shows pipeline structure indicating the inhomogeneous chemical reactivity of the top Si layer. © 2001 Kluwer Academic Publishers     

低剂量 SIMOX圆片线缺陷和针孔的研究

用Secco法、Cu-plating法分别表征了低剂量SIMOX圆片顶层硅线缺陷、埋层的针孔密度。结果显示,低剂量SIMOX圆片的顶层硅缺陷密度低,但埋层质量稍差。通过注入工艺和退火过程的进一步优化,低剂量SIMOX将是一种有前途的SOI材料制备工艺。     

Electrochemical deposition of Ni and Cu onto monocrystalline n-Si(100) wafers and into nanopores in Si/SiO2 template

Nickel and copper were potentiostatically deposited onto monocrystalline n-Si (100) wafers and in nanoporous SiO₂/Si template from 0.5 M NiSO₄ + 0.5 M H₃BO₃ and 0.005 M CuSO₄ + 0.5 M H₃BO₃ solutions. Nanoporous SiO₂/Si template was formed by etching in dilute HF solution of ion tracks. The latter were produced by high-energy (380 MeV) Au⁺ ions bombardment of silicon oxide thermally grown on silicon (100) substrate. The deposition of metals was studied using cyclic voltammetry (CV), chronoamperometry; the structure and morphology of products were ex-situ investigated by SEM and XRD. The level of pores filling was controlled by deposition time. Electrodeposition occurred selectively into nanopores and the deposition on SiO₂ layer was excluded. It was found out that Ni and Cu electrodeposited into nanopores of SiO₂/Si system formed the same structures as at electrodeposition on the surface of monocrystalline n-Si—granules for Ni and scale-shaped particles for Cu deposits.     

Fabrication of hydroxyapatite with highly ordered macroporous frame by colloidal templating method

Three-dimensional, highly ordered macroporous frame of hydroxyapatite has been fabricated via a template-assisted colloidal processing technique. In the present method, colloidal template was first prepared with SiO₂ spheres by gravitational sedimentation, which was then infiltrated with hydroxyapatite precursor prepared by the sol-gel process. The resulting hydroxyapatite replicated the three-dimensionally ordered macroporous structure of SiO₂ template. Modified by H₂O₂, the SiO₂ spheres could be packed into better ordered templates. After removal of the template by immersing in NaOH solution, the well-ordered macroporous frame made from HA was obtained. The arrangement of the pore structure was hexagonal close-packed and pore sizes could be controlled by changing the sizes of SiO₂ spheres. The resulting highly ordered macroporous frame of hydroxyapatite could have potential applications in the biomedical field.     

Dielectric properties of (Ba,Ca)(Zr,Ti)O3/CaRuO3 heterostructure thin films prepared by pulsed laser deposition

(Ba_0.90Ca_0.10)(Zr_0.25Ti_0.75)O₃ (BCZT) thin films were grown on Pt/Ti/SiO₂/Si substrates without and with a CaRuO₃ (CRO) buffer layer using pulsed laser deposition (PLD). The structure and surface morphology of the films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At room temperature and 1 MHz, the dependence of dielectric constant and tunability of the films with electric field were investigated; the dielectric constant and tunability are 725 and 47.0%, 877 and 50.4%, respectively, for the BCZT film on Pt/Ti/SiO₂/Si substrates without and with the CRO buffer layer at 400 kV/cm. The tunability of the BCZT/CRO heterostructure thin films on Pt/Ti/SiO₂/Si substrates was higher than that of the BCZT thin films on Pt/Ti/SiO₂/Si substrates. The high constant likely results from the oxide electrode (CRO).     

The energy position of electrically active centers in the oxide layer of SIMOX structures

Silicon-on-insulator (Si-SiO₂) structures fabricated using the SIMOX technology were studied by measuring high-frequency capacitance-voltage characteristics. Based on these data, the energy position of electrically active centers in the oxide layer of SIMOX structures is estimated.     

Synthesis, characterization and catalytic activity of ordered macroporous silicas functionalized with organosulfur groups

Hybrid three-dimensionally ordered macroporous (3DOM) SiO₂-SO₃H materials with different S/Si ratio have been prepared by colloidal crystal templating method. The process involved preparation of 3DOM SiO₂-SH materials by co-condensation of (3-mercaptopropyl)triethoxysilane and tetraethoxysilane via sol-gel transformation, and following oxidation of -SH group to -SO₃H group by H₂O₂. Materials were characterized by scanning electron microscopy (SEM), Fourier transform infra-red spectrometer (FTIR), thermogravimetric analysis (TGA), and nitrogen adsorption measurement. SEM observation shows that the macropores are highly ordered with a typical “surface-templated” structure. The surface area of 3DOM SiO₂-SH material is 25.1 m²/g and SiO₂-SO₃H material is 18.6 m²/g. Catalytic activity test shows that 3DOM SiO₂-SO₃H materials possess a high activity for the esterification of acetic acid and n-butanol, and the activity is increased with the amount of sulfur in the materials. This study provided significant results for developing new application of 3DOM materials.     

Influence of the nature of oxide matrix on the photoluminescence spectrum of ion-synthesized silicon nanostructures

The photoluminescence of various Si ion implanted oxide layers annealed at high-temperature has been studied in the range of 350-1500 nm. The set of investigated oxide materials includes thermal SiO₂, deposited SiO₂, Si_0.9Ge_0.1O₂, GeO₂ films on silicon substrate, and sapphire wafers. The results are discussed in terms of generation and modification of the defect centers and nanoclusters formation taking into account several factors related to composition and structure of the original oxide matrices.     

低能低剂量注水形成SOI结构材料的研究

采用无质量分析器的离子注入机，以低能量低剂量注水的方式替代常规SIMOX注氧制备SOI材料，测试结果表明，此技术成功地制备了界面陡峭，平整，表层硅单晶质量好的SOI结构材料，在剂量一定的条件下，研究不同注入能量对SOI结构形成的影响，使用剖面透射电镜技术（XTEM）和二次离子质谱技术（SIMS）等测试方法对注入样品和退火后样品进行分析，结果表明，表层硅厚度随注入能量增大不断增大；埋层二氧化硅厚度相对独立，仅在超低能（50keV)低剂量情况下厚度出现明显降低；埋层质量（包括界面平整度，硅岛密度等）与注入能量变化相关。     

Room temperature transformations induced in SiO2 layers by chemical compounds: I

Transformations in the structure and the composition of SiO₂ films as a result of the action of some organic compounds at room temperature were studied by various methods. Secondary ion mass spectrometry (SIMS) showed that hydrogen-containing species were removed from the SiO₂ layers (which were prepared by the thermal oxidation of silicon wafers) after a prolonged exposure to diethyl ether vapour. Electron microscopy and electron diffraction studies showed that the exposure led to the development of a crystalline phase in the SiO₂ layer. SIMS and transmission electron microscopy measurements both supported the view that the transformation from an amorphous structure to a denser more crystalline phase took place as a result of an interaction between molecules of diethyl ether and the SiO₂ surface. The removal of hydrogen-containing species seems to be a condition for this kind of transformation.In a recent short note¹ we have presented some preliminary results concerning amorphous-to-crystalline phase transformations in SiO₂ films which were prepared by the thermal oxidation of silicon wafers and which were treated at room temperature with various (mainly organic) compounds.Electron microscopy and electron diffraction studies clearly revealed the presence of a crystalline phase. Of the compounds investigated diethyl ether seemed to be the most active in inducing this type of transformation.In the following, more results will be given of investigations performed with the aim of understanding the phenomena and an explanation of the transformation mechanism will be offered.     

氢氧复合注入对SOI-SIMOX埋层结构影响的研究

实验研究了氢、氧复合注入对注氧隔离技术制备SOI（Silicon On Insulator)材料埋层结构的影响。用截面透射电子显微镜和二次离子质谱技术分析了退火前后材料的微结构变化。研究表明，氢离子的注入有利于注氧隔离制备的SOI材料埋层的增宽。进一步的结果表明，室温氢离子注入导致的增宽效应比高温注入明显。     

Thermodynamic and kinetic properties of indium- implanted silicon III: High temperature diffusion in oxidizing atmospheres

To a first approximation, indium diffusion in silicon is characterized by the same diffusion coefficient in an oxidizing atmosphere as in an inert atmosphere.Chemical etching of oxidized wafers has revealed unusual etch patterns and a bimodal stacking fault distribution for samples implanted at 10¹² ions cm^-2.The segregation between silicon and SiO₂ markedly favours silicon. However, in the first stages of oxidation indium can be incorporated in the SiO₂ layer because of the high growth rate of the oxide compared with the low indium diffusivity. After that, the “snowplough” effect gives rise to indium accumulation at the silicon surface.     

Design,fabrication and optical characterization of cerium oxide-magnesium fluoride double layer antireflection coatings on monocrystalline silicon substrates

Theoretical and experimental studies of a double layer antireflection coating deposited onto silicon wafers have been carried out. Magnesium oxide and cerium oxide fabricated by physical vapor deposition method have been applied as low- and high-refractive index materials. MgF₂–CeO₂–Si structures exhibited the reflectivity below 3% in the wavelength window from 0.5 μm to 1.2 μm. Theoretical simulations of spectral characteristics of the reflectivity of these coatings have been performed. A good correlation between experimental data and theoretical curves has been observed with the assumption that a thin SiO₂ layer of a thickness of 16 nm is formed onto Si substrates.     

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO₂ (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO₂ = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO₂ = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO₂ = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.     

硅离子注入引入纳米晶对SIMOX材料进行总剂量辐射加固

本研究工作采用硅离子注入和高温退火工艺对SIMOX材料的BOX层进行总剂量辐射加固.辐射实验结果证明了该加固方法的有效性.PL谱和HRTEM图像显示了硅离子注入及退火工艺在材料的BOX层中引入了Si纳米晶,形成电子陷阱能级,有效俘获电子,从而提高了材料BOX层的抗总剂量辐射能力.     

Turn-off current variation in drain-offset polysilicon thin film transistors

Bottom gate drain-offset polysilicon thin film transistors (poly-Si TFTs) were fabricated on SiO₂ coated Si wafers. After completing gate oxide deposition, we exposed the wafers to air in a clean room. Poly-Si films were deposited on the gate oxides for the active layer of the drain offset poly-Si TFTs with changing the air-exposure time. Threshold voltage shift to positive value and turn-off current raise with increasing the air-exposure time were observed. In this paper, we focused on evaluating the causes of the turn-off current raise with the air-exposure time. The carbons piled up at the poly-Si/SiO₂ interface were observed by a SIMS measurement, which is considered to be the origin of negative charges. The concentration of the carbon was remarkably increased by expanding the air-exposure time. The existence of the negative charges in the oxide was also found by a capacitance-voltage measurement. We conclude that the carbons originated from the air in the clean room are the main cause of the threshold voltage and turn-off current variation in the drain-offset poly-Si TFTs.     

The problems of native SiO2 layer removing for epitaxial growth of YSZ film on Si

The preparation processes of epitaxially grown YSZ (Yttrium stabilized ZrO₂) buffer layers on silicon (100) wafers were investigated. The “etching” procedure, at which the thin (∼5 nm) SiO₂ native amorphous layer from the Si surface was reduced to volatile SiO by deposition of a few nm thick Zr layer and subsequent annealing at low pressure, was monitored by mass spectrometer. The subsequent YSZ layer was deposited by evaporation or RF sputtering technique and examined by XRD and TEM observations. The results show that the epitaxy of YSZ layer is strongly influenced by efficiency of amorphous SiO₂ reduction at Si surface.     

Evolution of SiO2/Ge/HfO2(Ge) multilayer structure during high temperature annealing

Use of germanium as a storage medium combined with a high-k dielectric tunneling oxide is of interest for non-volatile memory applications. The device structure consists of a thin HfO₂ tunneling oxide with a Ge layer either in the form of continuous layer or discrete nanocrystals and relatively thicker SiO₂ layer functioning as a control oxide. In this work, we studied interface properties and formation kinetics in SiO₂/Ge/HfO₂(Ge) multilayer structure during deposition and annealing. This material structure was fabricated by magnetron sputtering and studied by depth profiling with XPS and by Raman spectroscopy. It was observed that Ge atoms penetrate into HfO₂ layer during the deposition and segregate out with annealing. This is related to the low solubility of Ge in HfO₂ which is observed in other oxides as well. Therefore, Ge out diffusion might be an advantage in forming well controlled floating gate on top of HfO₂. In addition we observed the Ge oxidation at the interfaces, where HfSiO_x formation is also detected.     

Structure and optical properties of ordered mesoporous copper oxide–silica composite films

In this study, ordered mesoporous copper oxide–silica (CuO–SiO₂) composite films with CuO/SiO₂ molar ratio ≤6% have been prepared. Small-angle X-ray diffraction and transmission electron microscopy investigations show that the mesoporous CuO–SiO₂ composite films have a hexagonally ordered pore array nanostructure. Wide-angle X-ray diffraction analysis reveals that the copper oxide and silica in the composite films are non-crystalline. The non-crystalline CuO in the mesoporous composite films has an obvious blue-shift phenomenon of the absorption edge. The calculated band gap energy for CuO is 3.2?eV, which is much higher than its bulk counterparts (1.21–1.5?eV).