Effect of oxidation-induced positive charges on the kinetics of silicon oxidation

The oxidation kinetics of silicon is investigated using two-step oxidation in dry O₂. It is found that in an initial state of second oxidation the growth rate of the oxide is different from the oxide's equilibrium growth rate and that the difference in these growth rates is due to the difference in the linear growth rates in these two stages. To explain the difference in the growth rates at the two stages, a model which accounts for the effect of oxide charges on the kinetics of the oxidation of Si is presented. In this model, negatively-charged oxidant species are prevented from reaching the Si/SiO₂ interface by the oxide field near the interface caused by the positive charges generated by the oxidation.     

Surface charges and surface potential in silicon surface inversion layers

The effect of interface charges on the channel conductance in MOS transistors has been investigated. It has been found that, by measuring the conductance as a function of temperature, it is possible to determine both the "fixed" interface charge which is independent of the surface potential and the charge trapped in surface states whose occupancy is a function of the surface potential. The characteristics of the two charge components are discussed. It appears that neither a continuous nor a delta-function energy distribution alone is adequate to describe the observed surface-state density.     

Standardized terminology for oxide charges associated with thermally oxidized silicon

Standarized terminology for oxide charges associated with the thermally oxidized silicon system is presented. This terminology is recommended by a committee established by the Electronics Division of the Electrochemical Society and the IEEE Semiconductor Interface Specialists Conference. All engineers and scientists concerned with oxide charges in silicon semiconductor applications are urged to adopt this terminology.     

Saturation capacitance of thin oxide MOS structures and the effective surface density of states of silicon

The capacitance vs voltage curve of thin oxide (30–40 Å) MOS structures in strong accumulation was studied. The results were interpreted in terms of equivalent surface density of state masses, which was found to be 0·2 m₀ for the silicon valence band and 0·06 m₀ for the conduction band, for both 111 and 100 surfaces. The experimental density of state masses were shown to be much lower than the bulk values. Equivalent density of states masses were calculated from a surface quantization model and in this case agreement with the experiments was obtained for the valence band only.     

Analysis of charges and surface states at the interfaces of semiconductor-insulator-semiconductor structures

A method for determining the energy spectrum of charges and surface-state densities at the interfaces of semiconductor-insulator-semiconductor structures was developed; the method is based on the analysis of capacitance-voltage characteristics. The method was experimentally tested with Si-SiO₂-Si structures prepared by direct bonding of both mirror-polished smooth wafers and wafers with a regular mesoscopic relief pattern at the inner surface of the wafers to be bonded. The density of surface states is lower at the surfaces with a regular relief pattern than that at the surfaces without the surface relief.     

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.     

Thin oxide films of silicon by high pressure oxidation

High pressure oxidation of silicon was performed at an oxidation temperature range of 650 to 800°C for thin oxide films with about 300 å thickness. The index of refraction was dependent on an oxidation temperature but independent of the oxidation pressure as 1.475 at 750°C. The dielectric breakdown strength of the oxide film was measured by the voltage ramping,method. The fixed oxide charge about 1.0 × 10¹¹ cm^?2 was also measured from the high frequency C-V measurement. The pulse scanning C-V measurement technique was used to measure the minority carrier generation rate in the depleted surface. The surface generation velocity was slightly dependent on the oxidation temperature and indicated that the fast surface states increased with decreasing oxidation temperature.     

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.     

Nonplanar oxidation and reduction of oxide leakage currents at silicon corners by rounding-off oxidation

We report that, based on the curvature radius at the convex corner of a trenched Si surface and electric field intensification, sacrificial thermal oxidation before gate oxide formation is very effective to round off the convex corner. We call it a rounding-off oxidation. From a simple one-dimensional model that considers both stress generation during Si oxidation and Stress relaxation by oxide viscous flow, it is foreseen that oxidation in a diluted oxidizing ambient and/or at a higher oxidation temperature reduces the stress in the oxide films. Experimentally, we report that the rounding-off oxidation with the above condition effectively rounds off the convex Si corner and decreases the thin gate oxide leakage currents and that the addition of a few percent of H2O to the dry oxygen rounding,off oxidation ambient is also effective. The relation between the sacrificial rounding-off oxidation and the time-dependent dielectric breakdown of thin gate oxides formed at the convex corner is also shown.     

Room temperature plasma oxidation mechanism to obtain ultrathin silicon oxide and titanium oxide layers

Scaling rules for sub-micrometric MOS devices have led to the necessity of ultrathin dielectric films and high-k dielectric layers. In this paper we present first results of room temperature plasma oxidation to obtain ultrathin layers of SiO₂ and TiO₂. The oxidation process in O₂ and N₂O shows a power law dependence with time and inverse proportionality with pressure. The oxidation rate is inversely proportional to pressure for both high and medium resistivities substrates. An oxidation model is proposed to explain this behavior. Ellipsometric and C–V characterization show complete oxidation of titanium verifying that a dielectric layer is formed.     

Rapid thermal oxidation of porous silicon for surface passivation

Rapid thermal oxidation with dry oxygen has been carried out on porous silicon (PS) films formed by electrochemical etching. The purpose of the paper was to investigate the surface passivation capability of the oxidized PS layers and to understand the oxidation mechanism. Rutherford back scattering (RBS) and X-ray photoemission spectroscopy (XPS) analyses confirmed the formation of a stoichiometric quasi-silicon dioxide. Besides, elastic recoil diffusion analysis (ERDA) demonstrated that a high concentration of hydrogen is still present in the PS film even after oxidation. RTO resulted in a good surface passivation effect at high temperature (>1000°C) as seen by internal quantum efficiency analysis. However, lifetime in bulk silicon is affected by the RTO process.     

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.     

Gate oxide reliability improvement related to dry local oxidation of silicon

Gate oxide reliability can be effectively improved by using dry field oxidation instead of the conventional wet one. The obtained improvement is suggested to occur because of a better oxide quality in the active region border due to the absence of the characteristic defects induced by wet local oxidation.     

Correlation between reliability and oxidation temperature for ultra-dry ultrathin silicon oxide films

The correlation between time-dependent dielectric breakdown lifetime and oxidation temperature of 800–950°C for 3.5 and 5.0 nm thick silicon oxide films as gate insulators was investigated. To obtain ideal gate oxide films with few hydrogen-related defects and precise thickness distribution that extremely influence the lifetime, metal-oxide semiconductor diodes with the films used in the evaluation were produced by our continuous ultra-dry process. The films oxidized at 850°C showed the largest lifetimes irrespective of thickness. The enhancement, however, was confirmed only in the diodes selecting the oxidesilicon substrate interfaces as the anode-side, where the lifetime is mainly dominated. Interestingly, a similar relationship was observed in their density characteristics. This suggests that the condition near the oxide-silicon substrate interfaces is probably improved by the 850°C oxidation due to microscopic structural changes.     

Improvement of poly-silicon hole induced gate oxide failure by silicon rich oxidation

This paper depicts the improvement of poly-silicon (poly-Si) holes induced failures during gate oxide integrity (GOI) voltage-ramp (V-Ramp) tests by replacing plasma enhanced oxidation with silicon rich oxidation (SRO), which is cap oxide on transfer gate serving as a hard mask to selectively form salicide. The SRO was found to be capable of completely removing salicide block etching induced poly-Si holes. With this SRO film deposited on poly-gate, the higher density silicon in cap oxide fills the interface of poly-Si grains and repairs the poly-Si film damaged by source–drain (S/D) implantation. The plasma-induced damage (PID) effect is observed and SRO can also suppress this PID effect and, thus, enhance GOI process margin. This is because PID may be enhanced during plasma poly-Si etching and S/D implantation, which induces the under-layer latent defects and deteriorates the adhesion between poly-grains and oxide. The SRO refraction index, which is 1.56 in this study with maximum silane (SiH₄) in cap oxide furnace, was found to play an important role on eliminating poly-holes. In-line SEM inspections show that poly-Si holes happen at open area such as the GOI test patterns of large bulk area and of poly-Si edge. Therefore, in-line defect inspections, which usually check only cell area, fail to find poly-Si holes. Hence, the in-line GOI monitor is proposed to detect such “hidden” defects. In this paper, we found SRO can successfully eliminate poly-Si holes, which lead to GOI failures, with minimum productivity loss and negligible process costs. Since GOI monitor by V-Ramp test is implemented to detect such reliability failure, wafer-level reliability control is recommended to proactively monitor and improve GOI performance. In order to achieve more stringent reliability targets as technology marches to the 0.10 μm era, we introduce the concepts of build-in reliability to facilitate qualifications and to incorporate related/prior reliability concerns for developing advanced processes.     

On an analytical solution for two-dimensional diffusion of silicon self-interstitials during oxidation of silicon

An analytical solution for two-dimensional diffusion of silicon self-interstitials during the oxidation of silicon is presented. The lateral effect of oxidation enhanced diffusion of boron in silicon is explained by the solution, because the increment of diffusivity is proportional to the incremental concentration of interstitials. Agreement between theoretical and experimental increments of the diffusivity is excellent.     

Shallow boron junctions implanted in silicon through a surface oxide

The partial-ion-channeling tail in the atomic distribution profile of low-energy boron implants into     

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.     

A television IF acoustic surface wave filter on bismuth silicon oxide

A brief account is given of a television IF acoustic surface wave filter made on bismuth silicon oxide. The potential advantages of this substrate material are pointed out, the filter design techniques used are explained, and the device construction is described. Measured responses of filters for two television systems are given.     

Tunnel oxide prepared by thermal oxidation of thin polysilicon filmon silicon (TOPS)

A textured tunnel oxide, TOPS, prepared by thermally oxidizing a thin polysilicon film on a Si substrate is reported. Due to the rapid diffusion of oxygen through the grain boundaries of the thin polysilicon into Si substrate and the enhanced oxidation rate at the grain boundaries, a textured Si-SiO₂ interface is obtained. The textured interface results in localized high fields and enhances electron injection into TOPS. TOPS exhibits a higher electron injection efficiency, a better immunity to the electron trapping and interface state generation under high-field operation, and a higher asymmetric injection polarity than the normal oxide