Pre-breakdown in thin SiO2 films

The on-off fluctuations of the tunnel current in 5.6 nm SiO₂ films before dielectric breakdown are analyzed in detail. For this purpose, a low noise measurement system has been realized which allows detection of pre-breakdown phenomena and interruption of the stress before catastrophic failure occurs. A spectral analysis of these fluctuations is presented along with preliminary results of the experiments made possible, for the first time, by the new measurement system     

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.     

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.     

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.     

Avalanche-injected electron currents in SiO2 at high injection densities

Gated P⁺-N diodes in silicon were used to investigate the avalanche-injection of electrons into SiO₂ at high current densities. The acceptor concentration in the P⁺-region of the diodes was high in order to minimize surface depletion there by the relatively high positive gate voltage during the injection. Injection current densities up to 10 A/cm² were obtained. The oxide current vs. gate voltage characteristics are described quantitatively by a simple model in which the current is injection-limited. Hot electrons from the avalanche plasma in the junction lose energy by inelastic collisions and gain energy by drift in the surface potential. Both processes are assumed to occur in a layer of thickness equal to the surface depletion layer thickness in the P⁺-region. The temperature dependence of the injection current is ascribed to the temperature dependence of the energy loss term.     

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。     

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。     

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     

Electron and hole traps in SiO2 films thermally grown onSi substrates in ultra-dry oxygen

The densities of electron and hole traps in SiO₂ films, thermally grown on Si substrates in ultra-dry oxygen, were compared with those in SiO₂ films grown in pyrogenic steam (wet-oxide films). The results show that ultra-dry-oxide films have an undetectable density of electron traps that is less that 10¹¹/cm² , and little interface-states generation during carrier injection. However, hole traps in ultra-dry-oxide films are high, (2.6±0.1)×10¹²/cm² compared with (1.3±0.2)×10¹²/cm² in wet-oxide films, and these increase by a factor of two with post-oxidation anneal in ultra-dry Ar. The results of electron spin resonance measurements of E' centers in SiO₂ films are consistent with the results of electrical measurements. These suggest that there is a tradeoff correlation between the density of electron traps and hole traps, with respect to the amount of water- or hydrogen-related defects in SiO₂     

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     

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...     

SiO2 degradation with charge injection polarity

We have investigated gate oxide degradation in metal-oxide-semiconductor (MOS) devices as a function of high-field constant-current stress for charge injection from both gate and substrate. The two polarities are asymmetric: gate injection, where the substrate Si-SiO₂ interface is the collecting electrode for the energetic electrons, shows a higher rate of interface-state generation (ΔD_it) and lower charge-to-breakdown Q_bd. Thus the collecting electrode interface, which suffers primary damage, emerges as a critical degradation site in addition to the injecting electrode interface, which has been the traditional focus. Consistent with a physical-damage model of breakdown, we demonstrate that interfacial degradation is an important precursor of breakdown, and that the nature of breakdown-related damage is physical, such as trap-generation by broken bonds     

Effects of avalanche hole injection in fluorinated SiO2MOS capacitors

Significantly improved immunity to hot-hole damage of the SiO₂/Si structure is achieved by a shallow fluorine implantation into the poly-Si gate of MOS capacitors followed by a drive-in process. Compared to the nonfluorinated control, the fluorinated samples exhibit a dramatic reduction of both hole trapping probability and interface-trap generation under avalanche hole injection conditions. The degree of such an improvement increases monotonically as a function of the F implantation dose (up to 10¹⁶/cm² ). Significant decrease of the hole detrapping rate is also observed in fluorinated samples. Possible mechanisms are discussed     

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     

Thin-gate SiO2 films formed by in situ multiple rapidthermal processing

A reliable method of forming very thin SiO₂ films (<10 nm) has been developed by rapid thermal processing (RTP) in which in situ multiple RTP sequences have been employed. Sub-10-nm-thick SiO₂ films formed by single-step RTP oxidation (RTO) are superior to conventional furnace-grown SiO₂ on the SiO₂ /Si interface characteristics, dielectric strength, and time-dependent dielectric-breakdown (TDDB) characteristics. It has been confirmed that the reliability of SiO₂ film can be improved by pre-oxidation RTP cleaning (RTC) operated at 700-900°C for 20-60 s in a 1%HCl/Ar or H₂ ambient. The authors discuss the dielectric reliability of the SiO₂ films formed by single-step RTO in comparison with conventional furnace-grown SiO₂ films. The effects and optimum conditions of RTC prior to RTO on the TDDB characteristics are demonstrated. The dielectric properties of nitrided SiO₂ films formed via the N₂O-oxynitridation process are described     

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.     

Characterization of CuGaSe2 thin films grown by MOCVD

CuGaSe₂ thin films have been grown by metalorganic chemical vapor deposition (MOCVD), from three organometallic precursors. Samples of about 1-2 μm thick are codeposited onto Pyrex and Mo-coated soda lime glass. A large range of compositions was investigated and characterized. Stoichiometric CuGaSe₂ thin films are single-phased and their optical bandgap is about 1.68 eV. The features of the films are presented in relation with their composition. XRD spectra always exhibit a preferential orientation along the (112) plane. Secondary phases have been observed: Cu₂Se for Cu-rich films, CuGa₃Se₅ for Ca-rich films. Observation of the morphology reveals larger polyhedral grains for Cu-rich films becoming platelet-shaped and tilted for Ga-rich compounds. The optical properties are also sensitive to the compositional changes and related to the eventual presence of binary phases. The gap increases with the Ga-content. The CuGa₃Se₅, phase exhibit a gap of about 1.85 eV. All the samples have a p-type conductivity