Generation kinetics of oxide charges and surface states during oxidation of silicon

A simple model to account for the generation kinetics of oxide charges and surface states during oxidation of silicon is presented. In the model, oxide charges and surface states are generated by a reaction between silicon and oxygen within the mono-molecular layer of the Si/SiO₂ interface and are thermally annealed independently of this reaction. A two step oxidation technique was used to investigate the electronic structure of the Si/SiO₂ interface and it was found that centers of fast surface states are located within 1.4–2.0 Å of the interface and that the centroid of oxide charges is located at about 8 Å from the interface. These results agreed with the model.     

A new model for the thermal oxidation kinetics of silicon

A model is presented which reasons that the thermal oxidation of silicon is surface reaction limited, and that the reaction rate is controlled by the viscous flow of newly forming oxide to accommodate the volume expansion that occurs when silicon oxidizes. The SiO₂ must form at silicon lattice sites and therefore epitaxially. This thermody-namically unstable epitaxial structure reconfigures and this reconfiguration results in an increase of the average viscosity of the oxide. The continual increase of average oxide viscosity accounts for the continual decrease in oxidation rate with time. A mathemat-ical analysis based on this model is used to derive the simple power law x = at^b relating oxide thickness, x, to oxidation time, t which has been shown previously to model phe-nomenologically all of the extant dry oxidation data.¹ The physical significances of the coefficient a and exponent b are obtained by the interpretation of the x vs t data in the literature in terms of this mathematical analysis.     

Effects of HCl and Cl2 additions on silicon oxidation kinetics

The growth kinetics of SiO₂ films (100-18000Å) on [100], 2Ωcm silicon have been investigated between 900-1100?C with additions of 0-9 vol.% HC1 or 0-2 vol.% Cl₂ to the dry oxygen ambient. The thickness-time data could best be fitted numerically to a mixed linear-parabolic equation that included a correction for fast initial growth. Equivalent amounts of chlorine (e.g., 2 vol.% HC1 or 1 vol.% Cl₂) produced completely different effects on the rate of SiO₂ growth. The quantitative effects of halogen additions were studied in greatest detail at 900?C. At that temperature, the parabolic rate constant increased linearly with the HC1 concentration. At the same time, the linear rate constant remained constant. Both rate constants did change when Cl₂ was used as an additive. The effect of HC1 additions on the parabolic rate constant reaches a maximum around 1000?C. Possible mechanisms for the halogen effects are discussed,← and it is seen that the gas phase reaction 4 HC1 + 0₂ → 2 H₂O + 2 Cl₂ is not reflected in the growth kinetics.     

Effect of γ irradiation on the photoluminescence kinetics of porous silicon

The effect of γ irradiation on the photoluminescence decay dynamics in porous silicon is investigated. Growth of the photoluminescence intensity and decrease of the decay time in irradiated porous silicon are explained by a lowering of the barriers to recombination of spatially separated electrons and holes via tunneling. The γ irradiation of porous silicon leads to a greater dispersion of the decay time. Fiz. Tekh. Poluprovodn. 33, 1462–1464 (December 1999)     

Interface charges beneath laser-annealed insulators on silicon

Laser annealing of a thermally grown, silicon-dioxide layer reduces an initially high fixed-charge density. Similar annealing of a silicon-nitride-covered silicon water does not markedly improve the interface characteristics. Laser melting and recrystallization of polycrystalline silicon above a thermally grown oxide does not appreciably increase the interface charges at the underlying silicon-dioxide/single-crystal-silicon interface.     

Effect of oxidation on orientation-dependent boron diffusion in silicon

The orientation dependence of boron diffusion in silicon has been investigated, with emphasis on the effect of surface oxidation. It is demonstrated that the presence of an oxide is not sufficient to cause enhanced diffusion in (100) silicon, but the oxide must be growing. Also, the segregation effect has been shown to be the dominant means of transport of boron atoms to the growing oxide, but the segregation coefficient does not appear to be strongly orientation dependent. The difference in surface lattice densities for the different orientations is unlikely to be directly responsible for the observed anisotropy, but the resulting difference in bond densities may be in part responsible, as suggested by the temperature variation of the effect.     

Oscillatory kinetics of anodic oxidation of silicon – influence of the crystallographic orientation

This work describes the oscillatory kinetics of the anodic oxide growth on silicon with crystallographic orientations (1 1 1) and (1 0 0). Although the oscillations are observed for two orientations if the experimental variables are properly chosen, their shape, amplitude and period are essentially different. It is shown that the oscillations are caused by a continuous growth of thin oxide layers at the sample surface and their peeling off.An analysis of the morphology of the samples and their kinetics of growth shows that the oscillatory anodization kinetics is a self-organizing phenomenon emerging as a result of collective interactions in the electrolyte/Si system. These interactions are influenced by the crystallography of silicon. The case of (1 1 1) Si shows the presence of the correlation links in a sequence of individual oscillations nearly two times longer than in the case of (1 0 0) Si . These differences are attributed to different mechanisms of the pore formation in (1 1 1) and (1 0 0) silicon wafers.     

Effect of thermal oxidation on charge carrier transport in nanostructured silicon

The effect of short-time annealing in air on the conductivity of porous silicon in two different directions (parallel and orthogonal to the sample surface) is studied. The samples under study are produced by electrochemical etching of single-crystal silicon wafers with (100)-oriented surfaces. It is found that thermal oxidation of the resulting porous silicon layers has different effects on the conductivity measured normally and parallel to the sample surface. For the oxidized samples, the conductivity in the direction orthogonal to the surface is noticeably higher than the conductivity in the direction parallel to the surface. The results are interpreted in the context of the model of charge carrier transport with consideration for potential barriers at the boundaries of silicon nanocrystals.     

Effect of the charge state of defects on the light-induced kinetics of the photoconductivity of amorphous hydrated silicon

The photoconductivity and defect density in films of nondoped a-Si:H soaked with light (W=114 mW/cm², λ<0.9 μm) for 5 h were investigated. It is shown that σ_ph ~ t ^-γ and N _D ~ t ^β, where γ>β or γ⋍β, depending on the position of the Fermi level prior to light soaking, i.e., depending on the charge state of the defects: D ⁻ and D ⁰ or D ⁺ and D ⁰. It is also shown that the light-induced kinetics of σ _ph is affected by a transition of the defects into the D ⁰ state because of a corresponding shift of the Fermi level during light soaking. Fiz. Tekh. Poluprovodn. 32, 345–348 (March 1998)     

Advanced modeling of silicon oxidation

The reaction-diffusion (i.e. the linear-parabolic) mechanism, widely in use for modeling the thermal oxidation of silicon, can be rebutted on the following issues:• There is a poor fit of the linear-parabolic law or of its derivative X² +

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X =

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(t + τ) or

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dt//dx = 2X +

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with dry oxidation data.• The experimental P_H2O dependence of

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/

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and

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contradicts the basic assumptions of the reaction-diffusion model.• The model fails to explain all technically important phenomena, such as: the nature of the fixed oxide charge, Q_f, the orientation dependence, the cross-over effect, the cleaning effects, the weak spots, the bird's beak and other 2D and 3D effects.Thermal oxidation of silicon is much better described by the extended Jorgensen model, i.e. the classical ionic-transport model modified to include non-linear conduction.• This concept leads to an excellently fitting power-parabolic growth law: X² + AX^2-α = Bt or B dt/dX = 2X + (2 - α)AX^1-α which holds for the growth data for dry and wet oxidation, including the initial part of the dry growth curves.• It gives the correct P_H2O dependence of A and B. It fully accounts for the generation of fixed oxide charge while it easily explains the Deal annealing triangle.• The model has remarkable potential to explain the orientation and cross-over effects, the cleaning effect, the weak spots, bird's beak and other 2D and 3D effects.     

Low temperature oxidation of silicon

Oxidation of silicon in dry oxygen ambient at temperatures between 25°C to 500°C, with a point-to-plane corona discharge is studied. The oxidation rate for this case is a strong function of temperature and is found to increase significantly in comparison to the conventional thermal oxidation rate. For the thicker films, refractive index of the grown oxide layer approaches the value obtained for high-temperature thermally grown oxide     

Radiation-enhanced thermal oxidation of silicon

A technique of radiation-enhanced thermal oxidation of silicon is developed and implemented in process equipment. Test SiO₂ films are grown under exposure to 511-keV gamma-ray photons. Their electrical and radiation performance are evaluated. Basic mechanisms of radiation-enhanced oxide growth are proposed.     

Microwave plasma oxidation of silicon

The stringent requirements of the next generation of VLSI will force the temperature of IC processing to a lower regime. One of the most important areas is the formation of gate and field dielectrics. Dopant re-distribution, stacking fault and dislocation generation as well as bird's-beak problems can be eliminated or minimized by low temperature oxygen microwave plasma anodization. This paper describes our investigation in the low pressure, low temperature oxidation of silicon using this technique. Oxidation rate dependence on anodization current, time, orientation, plasma power and temperature are measured. Properties of the plasma oxide was characteristized by thickness uniformity, refractive index, infrared absorption and C-V measurement. Discussion on the species responsible for the oxidation, the transport mechanisms and the factors that could affect the kinetics of the growth are presented. We conclude that the technique looks promising for the future.     

硅微粉氧化性质研究

考察了硅微粉在空气、水、聚乙二醇(PEG)以及PEG水溶液几种介质中的氧化行为,并分析比较了两种不同切割过程所产生的硅微粉屑的氧化情况。结果显示:200℃下干燥空气中硅微粉不发生明显氧化;在高于80℃的水中放置10d,硅微粉发生明显氧化,形成非晶SiO2。与水及水溶液相比,PEG能在一定程度上阻止硅微粉的氧化。另外,带锯切割中产生的硅微粉屑氧化严重,而多线切割中产生的硅微粉切屑无明显氧化。     

The effect of temperature gradient on silicon oxidation

A model for thermal oxidation of silicon in a nonuniform temperature field is suggested. Experimental data for temperature-gradient silicon oxidation are compared with analytical results. It was shown that growth rate depends on the temperature gradient direction, being higher for ∇T < 0.     

Low-energy ion beam oxidation of silicon

A low-energy oxygen ion beam with energy below 100 eV has been applied to the oxidation of unheated silicon substrates. Ultrathin (∼45 Å) FET-gate-quality oxides have been produced for the first time at room temperature using this technique. The high electrical quality of the oxides is demonstrated by the successful fabrication of n-channel MOSFET's.     

Effect of carbon on thermal oxidation of silicon and electrical properties of SiO2-Si structures

Growth of thermal oxide on silicon implanted with carbon at low energies is studied and electrical characteristics of the resulting SiO₂-Si structures are evaluated. After excluding the effect of surface damage on the oxide growth kinetics, it was determined that for the carbon implant doses up to 10¹⁴ cm⁻² the effect on oxide growth kinetics is limited. At higher carbon doses significant retardation of oxide growth was observed. A clear correlation between carbon dose and electrical characteristics of SiO₂-Si structures has also been established. In the case of each parameter of concern in this study its degrActation with increased carbon dose above 10¹⁴cm⁻², which corresponds to carbon concentration in silicon of the order of 10¹⁹ cm³, was observed. These effects may come to play during thermal oxidation of silicon wafers subjected prior to oxidation to the reactive ion etching in carbon containing gases such as CF₄, CHF₃, and others.     

Study on silicon surface oxidation of post-implant resist cleaning

Minimum substrate loss is required for resist strip of high dose, ultra shallow junction implant for source/drain extensions. Silicon surface oxidation of downstream plasma resist strip results in silicon recess of the source/drain extension regions. This paper reports the study of silicon surface oxidation for different resist strip plasma chemistries and the effect of plasma strip process parameters such as power, pressure and temperature on silicon surface oxidation. A good agreement was found between optical ellipsometry, XPS (X-ray photoelectron spectroscopy) and TEM (transmission electron spectroscopy) for thickness measurement of very thin (<20 Å) oxide grown on silicon surface due to plasma exposure. Selectivity of crust breakthrough and resist removal over silicon oxidation was also discussed in this paper along with dopant loss.     

Model of thermal oxidation of silicon at the volume-reaction front

A model of thermal oxidation of silicon, which interacts with an oxidizer at the volume-reaction front, is developed. The width of the reaction zone corresponds to the width of the transition layer with the violated stoichiometry (δ ≈ 7.5 Å). The oxidizer-diffusivity relaxation is taken into account from its value in stressed silicon dioxide to that in unstressed silicon dioxide, which is equal to the fused-quartz diffusivity. The relaxation is related to the structural reconstruction in amorphous silicon dioxide as it moves away from the reaction-zone boundary. The model describes well the thermal-oxidation kinetics of silicon in dry oxygen within a wide range of silicon dioxide thicknesses including the initial stage.     

Effects of deposition temperature on the oxidation resistance andelectrical characteristics of silicon nitride

A study was made of the effects of deposition temperature on the oxidation resistance and electrical characteristics of silicon nitride. It was found that silicon nitride below a certain limit thickness has no oxidation resistance. This threshold falls as the deposition temperature is lowered. 3-nm-thick silicon nitride deposited at 600°C has sufficient oxidation resistance For wet oxidation at 850°C, while 5 nm film deposited at 750°C has no oxidation resistance. The electrical characteristics also improve as the deposition temperature is lowered. 6-nm-thick silicon nitride deposited at 600°C shows a TDDB lifetime that is about two orders longer than that of 6-nm-thick silicon nitride deposited at 700°C. It was also found that the silicon nitride transition layer which is deposited at the initial stage of deposition influences the oxidation resistance and electrical characteristics of thin silicon nitride. It was concluded that lowering the deposition temperature reduces the influence of the transition layer and improves the oxidation resistance and electrical characteristics of thin silicon nitride