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Journal ArticleDOI

Effect of different methods of oxidation on SiSiO2 interface state properties

01 May 1985-Applications of Surface Science (North-Holland)-Vol. 22, pp 983-991
Abstract: Three different methods of oxidation - thermal, TCE, and anodic — were applied to n-type (111) silicon 10 ohm cm resistivity samples. MOS test samples were fabricated and their interface state properties were characterized by C-V and AC field effect techniques. From C-V measurements the interface state density at mid gap was found to be less in TCE (2 × 1010 cm−2 eV−1) and anodic (1 × 1010 cm−2 eV−1) samples than in dry (5 × 1010 cm−2 eV−1) oxidized samples. The mobile charges were also less in TCE (2 × 1010 cm−2) and anodic (5 × 1010 cm−2) samples. Using the AC field effect technique, the frequency (2–100 kHz) and temperature dependence of field effect mobility, μFE, were studied. By applying Garrett's theory of frequency dependence of μFE, the relaxation times of interface states were found to vary from 30 to 3 μs in dry, 8 to 4 μs in TCE, and 4.5 to 1.5 μs in anodic samples in the temperature range 230 to 370 K. Using Rupprecht's theory of temperature dependence of relaxation times, thedominant energy levels, Ec - ET, were found to be shallower in TCE (0.04 eV) and anodic (0.06 eV) than in dry (0.1 eV) oxidized samples. The capture cross-section of these samples was found to be small, in the range 10−20 to 10−21 cm2. In TCE and anodic samples the shallow interface state levels indicate stronger interactions between silicon and oxygen atoms at the interface. The observed low densities of interface states and mobile charges in these samples also show improved passivation of silicon.

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Journal ArticleDOI
Abstract: A calculation method to treat the electronic structures of crystalline Si‐amorphous SiO2 interfaces with or without microstructural defects is developed based on semiempirical tight‐binding Hamiltonians and the Green’s function formulation, and applied for calculation of the energy level of the trap states between amorphous SiO2 and the Si substrate with (111) orientation. The major results are (i) the perfect interface does not have any states in the forbidden gap of Si although the Si‐O‐Si bonding angle at the interface is varied in the range between 120° and 180°, and neither does the interface with oxygen dangling bonds have any; (ii) trap states due to a Si dangling bond appear at about the middle of the Si band gap; and (iii) O‐vacancy and Si‐Si weak bonds at the interface produce trap states at the energy range higher than the midgap, whereas Si‐O weak bonds at the interface produces trap states at the energy range lower than the midgap. The energy level of these trap states varies with changing bo...

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203 citations


Journal ArticleDOI
K.H. Zaininger1, G. Warfield1Institutions (1)
Abstract: For the use of the MOS capacitance method in the study of surface properties, various approximations and assumptions, of a purely conceptual and of an experimental nature, are usually made. These are not always justified. In this paper the applicability of this capacitance method for surface studies is examined critically. It is shown that this method is limited in its applicability and accuracy, and that, in most cases, it yields only the gross features of the surface states. If there are traps distributed spatially throughout the oxide, only an effective surface state distribution can be found, and this effective distribution may be interpreted ambiguously as due either to traps right at the interface, throughout the oxide, or both. Because the MOS capacitance consists essentially of the oxide capacitance in series with the semiconductor capacitances there is a practical lower limit on the magnitude of the semiconductor capacitance which can be measured. Together with difficulties in interpreting measurements in the inversion layer regime, this leads to a restriction on that portion of the forbidden gap in which states may be investigated. MOS capacitors, produced by thermal oxidation of silicon in either wet or dry oxygen, were examined by this method. It was found that, within experimental accuracy, and within the range of surface potential that can be covered by these measurements, the total number of occupied traps usually varies linearly with surface potential if it is assumed that all the traps are located right at the interface. However, these results can also be explained if it is assumed that the oxide contains a high density of low lying trap sites which are essentially uniformly distributed spatially throughout the oxide. In some specimens a monoenergetic trap level 0.7 eV below the conduction band and located at the interface was found.

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125 citations


Journal ArticleDOI
Abstract: We report for the first time, the use of a focussed CO2 laser beam and a controlled oxygen atmosphere to induce localized oxidation on the surface of a silicon wafer. These thin oxide films have been compared by infrared spectrometry with thin furnace‐grown layers. We conclude that the laser‐grown oxides are compositionally similar to conventional layers, and can be described by the formula SiO2. In contrast the half‐width of the Si‐O stretching vibration at 1070 cm−1 was found to be consistently less than for furnace‐grown oxides. By fabricating simple Al‐SiO2‐Si‐Al diodes, the dielectric properties of the films have been studied.

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48 citations