Si-SiO2 System Research Articles

Total reflection and surface scattering of soft X-rays on the Si-SiO2 system and hexagonal BN crystal

Reflection spectra for different grazing angles and reflectivity angular dependences of the Si-SiO2 system with different dioxide thicknesses have been measured in the energy range 40-850 eV, including the Si L2.3 and O K absorption edges. The angular dependences have been used for the dielectric constant determination. By turning a BN hexagonal crystal and using s-polarized radiation a strong reflectivity dependence on the crystal orientation has been detected. Indicatrices of the surface roughness scattering have been recorded for the BNhex crystal surface. The statistical properties of the roughness have been investigated by means of perturbation theory. These measurements were obtained using synchrotron radiation, and the interest in the specific properties of this radiation for such measurements is emphasized.

Fowler-Nordheim tunnelling injection in the Si-SiO2 system treated with argon plasma

The bulk positive charge in SiO2 layers (420-620 AA) generated by RF-soft Ar plasma has been studied by the high-field Fowler-Nordheim injection technique. It is proposed that the reduction in barrier height (0.4-0.5 eV) observed is a result of this plasma-created charge, which is located in the vicinity of the injecting gate electrode. Using both current-voltage and current-time characteristics, present a new experimental method for determining the effective density of trapped charge. It has been found that after plasma treatment the trapped charge increases to a value of 5*1011 cm-2 and 15*1011 cm-2 for plasma exposure times of 5 and 20 min respectively. The charge centroid does not depend on the plasma exposure time or oxide thicknesses used. The plasma-generated positive charge is associated with the E' centres resulting from the plasma breaking of strained Si-O bonds.

ESR Investigation of the SiSiO2 System

The defect structure of the SiSiO2 systems subjected to various annealing and ultrasound treatments is studied by ESR at 20 and 115 K. ESR spectra of phosphorus atoms and PA centers are detected. The correlation between the densities of these defects in differently treated SiSiO2 systems is investigated. These' data are found to support the model of PA centers as vacancy complexes. [Russian Text Ignored.]

Electrical characterization of defects created in the Si-SiO2 system by ionizing radiation

This paper reviews some of the electrical characterization methods used to determine electrically active defect densities produced by ionizing radiation exposure of the Si-SiO2 system. The electrical characterization methods discussed are the charge-capacitance method, the conductance method, and the charge pumping method. Interface trap and fixed oxide charge densities are separated by use of the interface trap charge neutral point. The controversy in the literature about the location in silicon bandgap energy of this charge neutral point is addressed, and it is shown that it is located at midgap to a good approximation. The comparative advantages and limitations of the three measurement methods for radiation studies are discussed.

Properties of the fluorine-implanted Si-SiO 2 system : G. S. Virdi, C. M. S. Rauthan, B. C. Pathak and W. S. Khokle. Solid-St. Electron.34(8), 889 (1991)

Properties of the fluorine-implanted Si-SiO 2 system : G. S. Virdi, C. M. S. Rauthan, B. C. Pathak and W. S. Khokle. Solid-St. Electron.34(8), 889 (1991)

Interactions of silicon point defects with SiO2 films

Interactions of point defects with SiO2 films play a central role in integrated circuit fabrication processes. In this work, a model is developed for the Si-SiO2 system that considers the segregation of excess silicon between the oxide and the silicon substrate and diffusion and reaction of that excess silicon in SiO2. The model is able to explain a broad range of experimental observations under both oxidizing and nonoxidizing conditions in a consistent manner including: the variation of interstitial supersaturation with oxidation rate in steam and dry O2 ambients, oxidation enhanced and retarded diffusion results in 〈100〉 and 〈111〉 silicon, the large interstitial supersaturation resulting from the nitridation of SiO2, the reduction of SiO2 in argon and the corresponding decrease in interstitial concentration, contradictory calculations of effective interstitial diffusivity, and the greatly reduced effective recombination velocities for nitrided oxides relative to capped oxides.

ESR Study of Porous Silicon

ABSTRACTA detailed ESR study has been performed on porous silicon on both <100> and <111> p-type silicon substrates prepared using anodization in HF under a range of conditions and the results are correlated with the light emission properties. It is found that the ESR spectra are dependent upon the orientation of the samples. The ESR defect centers are identified to be the Pb centers or Pbo centers of the Si-SiO2 system from the g-value anisotropy maps. The variation of the spin density Ns with annealing conditions has also been studied for samples annealed either in nitrogen or oxygen ambient at 200°C for various time intervals. It is concluded that the increase or decrease of Ns are due to the generation or elimination of the Pb or Pbo centers in conjunction with the oxidation process during annealing. From PL study of these samples, it is found that there is no simple correlation between the spin density and the PL intensity. However, a blue shift in the PL peak position was observed both in samples after a post-annealing etch in HF solution, and in samples annealed in oxygen without a post-annealing etch. This blue shift supports the quantum confinement model of light emission from porous silicon.

Influence of backside implantation on the impurity concentration in the Si-SiO2 system

La concentration des impuretes non voulues a grande mobilite dans ce systeme peut etre diminuee par une implantation d'ions dans la couche de Si avant le processus d'oxydation

Comparison of the effects of ionizing radiation at twelve dose rates from 0.0015 to 100 rad(Si)/s

Evidence is presented that two competing failure mechanisms exist in the Si-SiO2 system with one mechanism dominating at low dose rates and the other at high. Much lower dose failures than expected were discovered at low dose rates (<0.1 rad(Si)/s) and very low dose rates (∼0.001 rad(Si)/s) in commercial SGS 4007 CMOS devices. These failure doses plotted versus dose rate have a bell-shaped curve, rather than the expected straight line (decreasing with increasing dose rate), indicating that a different failure mechanism is dominant at low dose rates than at high.

Electrical damage to silicon devices due to reactive ion etching

The damage, due to reactive ion etching in CF4+O2 plasma, has been investigated by I-V and C-V techniques using silicon devices such as Au/n-Si Schottky contacts, p+-n diodes and MOS structures. The forward characteristics of a Schottky diode and an exposed junction diode are significantly degraded due to RIE. The amount of damage increases with increasing RF voltage. Considerable recovery occurred when various post RIE treatments were used for the lower RF voltage RIE etching. Almost no recovery upon annealing is found for the higher voltage etching, which suggests the formation of more complex, defect sites at the higher etching voltages. MOS capacitors as well as MOSFETS were used to investigate the damage effects of RIE in Si-SiO2 systems.

The charge and trap generation in thin SiO2layers under low energy ion bombardment

Abstract Charge and trap generation in thin thermal SiO2 layers on silicon under 1.5 keV Ar+ ion bombardment has been investigated by internal photoemission techniques. The long-range perturbation of inner Si-SiO2 interface separated by 200 nm oxide from ion penetration layer was observed. Positive charge and Coulombic electron trap formation near the semiconductor surface have been associated with hole transport through oxide layer and their interaction with Si-SiO2 interfacial defects. A new neutral-type electron trap generation in oxide bulk has been registered under ion bombardment or hole injection. This effect was attributed to hole-induced break of strained Si-O bonds produced during Si-SiO2 system formation or by oxide radiation damage.

A new growth enhancement in thin SiO2 formed by rapid isothermal oxidation of silicon

Rapid growth of thin SiO2 (&amp;lt;100 Å) on silicon is observed following annealing in argon. The growth enhancement is active for a short time following argon anneals, and does not depend on oxide thickness in the sub-100-Å regime. Also, the enhancement may be reset many times, by annealing, for a growing oxide film. Growth kinetics of the enhancement are different than those of the often discussed initial growth regime enhancement. The anneal time required to produce enhanced growth is a factor of 10 less than that required to reduce interface trap density. Study of the phenomenon at time scales not accessible through furnace processing is made possible by the use of a rapid isothermal processor. The annealing process alters the Si–SiO2 system in some way, as yet undetermined, that affects the growth of the oxide in the thin regime. In this paper, we present the results of in situ anneal induced growth enhancement during rapid thermal oxidation of n-type (100) silicon. These results should shed a new light on dry thermal oxidation of silicon.

Alternative Quasi‐Classical Transport Equations. III. Charge Transport in MIS Systems with Inclusion of Diffuse Surface Scattering and Quantum Size Effects

AbstractOn the basis of the results of two preceding parts in this paper new expressions for the current density, the conductivity, and the local and effective mobility in the channel of a MIS field effect transistor are presented. For the first time in these expressions the following two different effects of the interface are taken into account simultaneously: (i) the vanishing of the wave functions at the interface as a quantum mechanical effect and (ii) incomplete specular reflection at the interface. Numerical results are given for the SiSiO2 system both, in the constant field approximation and for self‐consistent potentials in the range of surface fields between 2 × 104 and 3 × 105 V cm−1. The main new result is that the decrease of the mobility due to surface scattering is reduced by wave function effects giving so a much better agreement with experimental data of other authors. Problems of the influence of temperature and the consideration of an energy dependent relaxation time are discussed.

Ozone cleaning of the Si-SiO2 system

The cleaning of monocrystalline silicon substrates and thin thermally grown SiO2 layers on silicon by electrochemically produced ozone has been investigated. In both cases organics are removed very effectively. In comparison with other dry cleaning methods no radiation damage occurs.

Point-defect generation during oxidation of silicon in dry oxygen. I. Theory

In this paper, we consider how oxidation in dry O2 influences the point-defect densities in silicon. By using relationships based on the continuity equations in the oxide and applying a proposed set of boundary conditions to the oxidizing Si-SiO2 system, we derive an analytic expression for the supersaturation of interstitials during oxidation. The analysis results in an expression having the experimentally observed sublinear dependence on oxidation rate without requiring any assumptions of nonlinearity. In addition, through observations of the dependence of the linear rate constant in the linear-parabolic model of oxidation on ambient oxygen pressure, it is possible to predict how the interstitial supersaturation will vary with oxidation rate at a given temperature. A companion paper [J. Appl. Phys. 59, 2551 (1986)] compares the predictions of the model with experimental results.

High-resolution imaging of oxidized stepped silicon surfaces

The Si-SiO2 system has been the subject of extensive investigation due to its importance for MOS electronic devices. However, an understanding of the correlation between electronic processes, the structure of the Si-SiO2 interface, and the mechanism of oxidation is still lacking. This study is part of a broad research program that attempts to establish an atomistic model of the Si-SiO2 interface structure and mechanism of oxidation.In the experiment the p-type boron doped 7-17Ωcm Si wafers used for oxidation had a surface orientation 3° off [111] towards [10]. The wafers were cleaned before oxidation using the RCA procedures followed by immediate oxidation at 1000°C in dry O2 to various thicknesses ranging from 200Å to 1000Å. Cross-sections for TEM, with a normal parallel to the [10] direction of the Si substrate were prepared using standard procedures. These TEM specimens of thermally grown and native oxides were imaged with point to point resolution of 2.6Å using a JEM200CX electron microscope operating at 200 kV.

Temperature and field dependence of the generation of interface states in the Si-SiO2 system after high-field stress

We have studied the time dependence of the generation of interface states in the Si-SiO2 system after metal-oxide-semiconductor capacitors were stressed by a 7.4-MV/cm gate positive electric field for 8 h at 90 K. The interface state density increased logarithmically with time for temperatures between 180 and 300 K with fields between +2 and −2 MV/cm. An analysis based upon a distribution of formation energies is proposed to explain the logarithmic time dependence. We find that there are two peaks in this distribution. One peak at 0.7 eV is field independent while the other at 0.9 eV disappears when a zero or negative bias is applied.

Interface-state generation during avalanche injection of electrons from Si into SiO2

We have studied at both liquid-nitrogen temperature and room temperature the development of the interface states that are generated in the Si-SiO2 system when electrons are avalanche injected from the Si into the SiO2. Differences in development at the two temperatures indicate that the states are of two types. One appears immediately at liquid-nitrogen temperature and is probably identical with the states previously found to occur as the result of photoinjecting electrons through the interface. The other requires thermal energy to develop. These states may be associated with positive charge trapped at the interface and are probably related to those observed after radiation damage.

Interface state generation in the Si-SiO2 system by photoinjecting electrons from an Al field plate

We observe the generation of interface states in the Si-SiO2 system when electrons are internally photoinjected from an Al field plate and are swept through the oxide by a moderate electric field. Interface states appear immediately at 90 K. The rate of interface state generation caused by photoinjected electrons depends on the oxide thickness and the magnitude of the bias field. The generated interface state density is found to increase as Nss = AQs, where Q is the injected charge and s is generally in the range 0.5–0.7. The generation does not saturate after passage of a total charge of 0.35 C/cm2.

The effect of O2 plasma on properties of the SiSiO2 system

The radiation damage in a Si-SiO2 system exposed to O2 plasma in a planar reactor is investigated in dependence on the exposure time, the substrate temperature, and the pressure of O2. Capacitance-voltage (C-U) techniques and a static method are used to monitor charge trapping in the metal-oxide-semiconductor (MOS) capacitors. In all experiments a negative and a positive charging effect is observed as a result of plasma influence. Low and high temperature annealing is performed in order to eliminate radiation damage induced by the plasma. It is concluded that high temperature annealing is necessary prior to metallization to remove completely the radiation damage produced at substrate temperatures sufficiently above 20 °C. Metallized Si-SiO2 systems are also investigated and it is found that the metal layer gives a complete protection against the influence of the plasma. Strahlungsdefekte in Si-SiO2-Strukturen, die wahrend der Behandlung einer Struktur im Sauerstoffplasma eines Planarplasmareaktors entstehen, werden in Abhangigkeit von Bearbeitungszeit, Substrattemperatur und O2-Gasdruck untersucht. Auf dem plasmabehandelten Si-SiO2-System werden Metallpunkte aufgebracht und an den MOS-Kondensatoren C-U- und statische Q-U. Messungen durchgefuhrt. Positive und negative Ladungen im Dielektrikum werden als Folge der Plasmawirkung beobachtet. Zur Beseitigung der Strahlungsdefekte wird eine Temperung bei Hoch- und Niedertemperaturen durchgefuhrt. Ist die Substrattemperatur wahrend der Plasmabehandlung wesentlich hoher als 20 °C, dann ist zur vollkommenen Ausheilung der Defekte eine Hochtemperaturbehandlung vor der Metallisierung notwendig. Die Plasmabehandlung der mit Metallpunkten versehenen Strukturen zeigt, das das Metall als vollstandiger Schutz gegen einen Plasmaeinflus dienen kann.