Structural properties of fluorinated SiO2 thin films

Fluorinated SiO₂ (SiOF) films, prepared by plasma enhanced chemical vapour deposition from SiH₄, N₂O and CF₄ precursors, have been analysed by infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) to extract chemical and structural information. Notwithstanding XPS reveals that fluorine concentrations are quite low (less than 4 at.%), the analysis of the Si–O–Si vibration modes in the IR spectra indicates that CF₄ addition involves a deeper modification of the film structure, than the simple formation of Si–F bonds. In particular, by increasing the F concentration in the oxides, the stretching frequency of the Si–O–Si bonds increases, while the bending frequency decreases. On the basis of the central force model, both observations are consistent with the occurrence of a Si–O–Si bond angle relaxation phenomenon, the importance of which increases with the fluorine concentration in the films.     

Contact potential measurements on thin SiO2 films

Contact potential measurements by the Kelvin method were performed in vacuum on silicon wafers whose thermal oxide film was etched into the shape of a wedge. A given position along the oxide corresponded directly to a given depth and by scanning a reference electrode stripe across the wafer, information about the distribution of the oxide charge through the thickness was obtained. It was found that the oxide charge was positive and concentrated within a few hundred angstroms of the SiSiO₂ interface.     

Photo-CVD process for ultra thin SiO2 films

In this paper we first report the use of very low deposition rate photo-induced chemical vapor deposition process, (below 0.05 nm/min). This photo-CVD process is adequate to grow very thin and ultra thin layers of SiO₂. Details on the design of the reaction chamber, reactive gases and process parameters to obtain the desired deposition regime are presented. Dependence of deposition rate on pressure in the chamber and gas flow ratio is discussed. Deposited layers were characterized using I–V and C–V techniques.     

Pre-breakdown noise in electrically stressed thin SiO2 layers of MOS devices observed with C-AFM

A conductive atomic force microscope (C-AFM) has been used to analyse the degradation stage (before breakdown, BD) of ultrathin (<6 nm) films of SiO₂ at a nanometer scale. Working on bare gate oxides, the conductive tip of the C-AFM allows the electrical characterization of nanometric areas. Due to the extremely small size of the analysed areas, several features, which can be masked by the current that flows through the overall test structure during standard electrical tests, are observed. In particular, switching between different conduction states and sudden changes of conductivity have been measured during ramped voltage tests, which have been related to the trapping and detrapping of single electronic charges in the defects generated during the electrical stress. This phenomenon, which has been observed during constant voltage stresses in the form of random telegraph signals, has been associated to the pre-breakdown noise measured in poly-gated structures. The C-AFM has also allowed to directly measure the I–V characteristics of the fluctuating spot.     

Spin synthesis of monolayer of SiO2 thin films

The highly ordered monolayer of submicron size silica (SiO₂) particles (235 nm) is developed on p-silicon by using three-step spin-coating in colloidal suspension, which has significant potential in various applications. The influence of three-step spin speeds, spinning time, acceleration time between different steps, concentration of SiO₂ particles in the solution, solution quantity, and the ambient humidity (relative humidity) on the properties of monolayer SiO₂ are studied in order to achieve a large area monolayer film. A relatively high surface coverage and uniform monolayer film of SiO₂ particles in the range of 85%-90% are achieved by appropriate control of the preparative parameters. We conclude that this method can be useful in industrial applications, because of the fabrication speed, surface coverage and cost of the process.     

SiO2薄膜光学常数物理模型

SiO2薄膜是光学薄膜领域内常用的重要低折射率材料之一。在文中研究中,通过测量薄膜的椭偏参数,使用非线性最小二乘法反演计算获得薄膜的光学常数。采用离子束溅射和电子束蒸发两种方法制备了SiO2薄膜,在拟合过程中,基于L8（22）正交表设计了8组反演计算实验,以评价函数MSE为考核指标。实验结果表明:对IBS SiO2薄膜拟合MSE函数影响最大的为界面层模型,对EB SiO2薄膜拟合MSE函数影响最大的为Pore模型。同时确定了不同物理模型对拟合MSE函数的影响大小和反演计算过程模型选择的次序,按照确定的模型选择次序拟合,两种薄膜反演计算的MSE函数相对初始MSE可下降35%和38%,表明拟合过程模型选择合理物理意义明确。文中提供了一种判断薄膜物理模型中各因素对于薄膜光学常数分析作用大小的途径,对于薄膜光学常数分析具有指导意义。     

High-field-induced degradation in ultra-thin SiO2 films

Very thin thermal oxides are shown to exhibit a failure mode that is undetected by conventional breakdown tests. This failure mode appears in the form of excessive leakage current at low field and is induced by high-field stresses. The stress-induced oxide leakage is permanent and stable with time and thermal annealing. It becomes the dominant failure mode of thin oxides because it always precedes destructive breakdown. Experimental results and theoretical calculations show that the leakage current is not caused by positive charge generation and accumulation in the oxide. It is proposed that the oxide leakage originates from localized defect-related weak spots where the insulator has experienced significant deterioration from electrical stress. The leakage conduction mechanism appears to be thermally assisted tunneling through the locally reduced injection barrier, and the model seems to be consistent with both I-V measurements at temperatures from 77 K to 250°C and theoretical calculations     

具有SiO2/SiNX/SiO2 复合绝缘层的有机薄膜晶体管

We have investigated a SiO_2/SiN_x/SiO_2 composite insulation layer structured gate dielectric for an organic thin film transistor(OTFT) with the purpose of improving the performance of the SiO_2 gate insulator. The SiO_2/SiN_x/SiO_2 composite insulation layer was prepared by magnetron sputtering.Compared with the same thickness of a SiO_2 insulation layer device,the SiO_2/SiN_x/SiO_2 composite insulation layer is an effective method of fabricating OTFT with improved electric characteristics and decrease...     

Annealing effects in the PECVD SiO2 thin films deposited using TEOS, Ar and O2 mixture

In this work, we present the results obtained on the characterization of silicon oxide thin films deposited by plasma enhanced chemical vapor deposition (PECVD) using a mixture of tetraethylorthosilicate (TEOS), oxygen and argon. The electrical characteristics of the implemented MOS capacitors, after the annealing process (600°C), showed an increase in the break-down strength as well as the effective charge density.     

Low electric field breakdown of thin SiO2 films understatic and dynamic stress

A comprehensive study of Time-Dependent Dielectric Breakdown (TDDB) of 6.5-, 9-, 15-, and 22-nm SiO₂ films under dc and pulsed bias has been conducted over a wide range of electric fields and temperatures. Very high temperatures were used at the wafer level to accelerate breakdown so tests could be conducted at electric fields as low as 4.5 MV/cm. New observations are reported for TDDB that suggest a consistent electric field and temperature dependence for intrinsic breakdown and a changing breakdown mechanism as a function of electric field. The results show that the logarithm of the median-test-time-to failure, log (t₅₀), is described by a linear electric field dependence with a field acceleration parameter that is not dependent on temperature. It has a value of approximately 1 decade/MV/cm for the range of oxide thicknesses studied and shows a slight decreasing trend with decreasing oxide thickness. The thermal activation E_a ranged between 0.7 and 0.95 eV for electric fields below 9.0 MV/cm for all oxide thicknesses. TDDB tests conducted under pulsed bias indicate that increased dielectric lifetime is observed under unipolar and bipolar pulsed stress conditions, but diminishes as the stress electric field and oxide thickness are reduced. This observation provides new evidence that low electric field aging and breakdown is not dominated by charge generation and trapping     

CMOS-compatible silicon devices on thin SiO2 membranes

A novel method of fabricating low power silicon-based devices on thermally insulating membranes for use in sensing applications is presented. The devices can be operated at temperatures of ~250°C with power consumption not exceeding 25mW     

Transport process in thin SiO2 films with an embedded 2-D array of Si nanocrystals

This work deals with the electrical characteristics and physical properties of novel dielectric systems based on silicon nanocrystals embedded in SiO₂ matrices. In particular, the transport phenomena of 10 nm thick SiO₂ capacitors with an embedded thin layer (5 nm) of LPCVD Si nanocrystals, located at different tunneling distances from the oxide–substrate interface, are studied. An original model based on an elastic tunneling phenomenon, which allows an efficient evaluation of the main structural characteristics of Si dots, is proposed.     

Excess currents induced by hot hole injection and FN electroninjection in thin SiO2 films

The behavior of excess currents induced by Fowler-Nordheim electron injection stress (FN electron injection) has been investigated for 6.0-nm oxides. Excess currents are induced by FN electron injection in 6.0-nm oxides together with positive charges being induced in it. To clarify the role of hole injection in FN electron injection, the behavior of excess currents induced by substrate hot hole injection has also been investigated in 6.0-nm oxides. The leakage behavior after hot hole injection is the same as FN electron injection. The excess currents induced both by the FN electron injection and by the substrate hot hole injection are due to trap-assisted tunneling and field enhancement at the cathode due to the positive trapped charge. The charge centroid of the positive charges induced by both stresses are located 3.0 nm from the Si/SiO₂ interface which is at the center of 6.0-nm oxide. The excess currents induced by hot hole injection and FN electron injection are caused by traps in SiO₂ films produced by injected holes from the anode     

不同沉积方式SiO2薄膜的自然时效特性

SiO2薄膜是光学薄膜领域内常用的重要低折射率材料之一。文中采用不同沉积技术在Si基底上制备了SiO2薄膜,并研究了它们光学特性的自然时效特性。采用不同贮存时间的椭偏光谱表征SiO2薄膜的光学特性,随着时间的增加,EB-SiO2薄膜和IAD-SiO2薄膜的物理厚度和光学厚度随着增加,但IBS-SiO2薄膜随着减小,变化率分别为1.0%,2.3%和-0.2%。当贮存时间达到120天时,IBS-SiO2薄膜、EB-SiO2薄膜和IAD-SiO2薄膜的物理厚度和光学厚度趋于稳定。实验结果表明,IBS-SiO2薄膜的光学特性稳定性最好,在最外层保护薄膜选择中,应尽可能选择离子束溅射技术沉积SiO2薄膜。     

Post deposition UV-induced O2 annealing of HfO2 thin films

UV-assisted annealing processes for thin oxide films is an alternative to conventional thermal annealing and has shown many advantages such as low annealing temperature, reducing annealing time and easy to control. We report in this work the deposition of ultra-thin HfO₂ films on silicon substrate by two CVD techniques, namely thermal CVD and photo-induced CVD using 222 nm excimer lamps at 400 °C. As-deposited films of around 10 nm in thickness with refractive indices from 1.72 to 1.80 were grown. The deposition rate measured by ellipsometry was found to be about 2 nm/min by UV-CVD, while the deposition rate by thermal CVD is 20% less than that by UV-CVD. XRD showed that the as-deposited HfO₂ films were amorphous. This work focuses on the effect of post deposition UV annealing in oxygen on the structural, optical and electrical properties of the HfO₂ films at low temperature (400 °C). Investigation of the interfacial layer by FTIR revealed that thickness of the interfacial SiO₂ layer slightly increases with the UV-annealing time and UV annealing can convert sub-oxides at the interface into stoichiometric SiO₂, leading to improved interfacial qualities. The permittivity ranges in 8–16, are lower than theoretical values. However, the post deposition UV O₂ annealing results in an improvement in effective breakdown field and calculated permittivity, and a reduction in leakage current density for the HfO₂ films.     

Total ionizing dose reliability of thin SiO2 in PowerMOSFET devices

This work shows an experimental study on the reliability of PowerMOSFET devices used in satellitar application. The total irradiated dose (TID) tolerance degree of a gate oxide as a function of its thickness and growth process has been investigated. Different oxide thin films, with thickness ranging from 25 nm to 35 nm, integrated in 30 V and 100 V N-channel STM PowerMOSFET vehicles, have been examined. The gate threshold voltage has been used to evaluate the degradation, in comparison to a predictive model. The attention is stressed onto non-ideality factors involving the gate degradation.     

GaAs MIS structures with SiO2 using a thin siliconinterlayer

The introduction of a pseudomorphic Si interlayer, about 1.0 nm thick, is found to dramatically improve the MIS characteristics of the SiO₂-GaAs system. Quasistatic and high-frequency capacitance/voltage data from such a novel capacitor structure on n -GaAs indicate that the surface of the GaAs is swept from inversion to accumulation. X-ray photoelectron spectroscopy and ion scattering spectroscopy confirm the presence of the Si layer and its complete coverage of the GaAs surface. The Si layer minimises the formation of any detrimental native oxides and thus controls the chemical nature of the GaAs surface. This approach has implications in the development of metal-insulator-semiconductor systems in general     

脉冲激光诱导TiO2/SiO2薄膜表面损伤性能实验

高功率的激光系统对光学元件的抗激光损伤性能的要求不断提高。主要研究薄膜在脉冲激光诱导作用下的损伤特性及其机理,实验采用YAG脉冲激光器对TiO2/SiO2薄膜样片进行1-on-1方式的激光诱导。实验结果表明:采用低能量激光诱导对薄膜的光学透过率影响不大。经低能量激光诱导后,薄膜的表面结构缺陷得以修复,表面结构趋于完整,变得均匀和细腻。脉冲激光诱导TiO2/SiO2薄膜样片,激光能量阶较小时,其损伤阈值随能量增加而增加,损伤阈值最大可增加1倍;激光能量阶较大时,其损伤阈值随能量增加而减小。     

Characterization of the hot-electron-induced degradation in thin SiO2 gate oxides

With decreasing oxide thickness, some of the established methods to characterize oxide degradation become inapplicable because of limited sensitivity and because of direct tunneling which gives rise to large leakage currents through the oxide. However, new techniques are emerging which could not previously be used on thicker oxides, such as stress-induced leakage current measurements, current noise measurements, hot-electron emission microscopy, ballistic electron emission microscopy and hot-carrier luminescence. Some of these techniques provide unprecedented information on the local current densities with high spatial resolution and can be used to study inhomogeneous degradation in thin oxides at low voltages where homogeneous hot-carrier degradation becomes energetically unfavorable. In Si/SiO₂/poly-Si structures, three different, homogeneous, hot-electron induced degradation processes have been identified, with threshold voltages at 12 V, 7.5 V and about 4 V. These are the generation of holes by impact ionization in the oxide, the injection of holes from the anode, and the release of hydrogen mostly from near the anode, respectively. The released hydrogen is very reactive and is responsible for the generation of many stress-induced defects. The existence of energy thresholds for homogeneous defect generation may limit the use of voltage acceleration for reliability evaluations.