Interface States In MOS Structures Research Articles

Comparison of the generation of interface states in MOS structures due to /sup 60/Co and VUV irradiation accompanied with photoinjection of electrons

The buildup of interface states in MOS structures with differently annealed oxides is studied under vacuum ultraviolet (VUV) and /sup 60/Co irradiation. A larger creation of interface states is observed if photoinjection of electrons is applied simultaneously with the VUV irradiation. The presence of electrons at the Si/SiO/sub 2/ interface favors the generation and explains the larger amount of interface states after /sup 60/Co irradiation. After VUV irradiation the interface state density increases in n-samples to a specific saturation value which is reached earlier if the gate voltage is made more positive or samples are exposed to photoinjection. This is due to the increase of the radiation peak which is located in the upper half of the silicon gap. The impact of post oxidation annealing on interface state generation is investigated due to VUV and /sup 60/Co irradiation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analytic approach to the a.c. conductance method for rapid characterization of interface states in MOS structures

Nicollian and Goetzberger's well known integral expression for the equivalent parallel conductance due to interface states G p / ω has been given a simple analytical representation which is valid under the condition that interface potential fluctuation parameter σ > 1.5. Previous methods of conductance analysis based upon numerical and/or graphical construction are provided with alternative analytic relations. The earlier parametric numerical relations like ξ p, f w, f D and ln( ξ +/ ξ −) vs σ are described very well by analytic expressions in this paper. A new relation is presented to determine interface state time constant from the width of conductance peak. A new method is presented to determine dependence of σ on interface band bending from G p / ω vs bias measurements at just two frequencies. The expedient method of Nicollian, Goetzberger and Lopez utilises the same two curves to determine distribution of interface state density N ss and capture cross section σ p across the band gap. Therefore using the present new method for σ determination and other analytical relations for N ss and σ p determination, the expediency of their method is greatly enhanced. Complete conductance analysis for rapid characterization of the interface is shown to become now a simple straight forward affair, and the amount of data required is also substantially reduced.

Defect structure and generation of interface states in MOS structures

The correlation between the defect structure of the SiO 2 and the generation of interface traps upon avalanche injection of electrons and holes in MOS capacitor was investigated. Using samples with widely varying densities of intrinsic and H 2O-related trapping centers, and with different oxide thicknesses and gate electrodes it was established from experiments around room temperature that a one to one correlation between the densities of captured carriers and generated interface states exists as long as only a single type of carrier is involved. If simultaneously the second type of carrier is injected the picture becomes more complex. We confirm reports by other authors that at reduced temperatures (typically 77 K) two steps may be distinguished in the generation process, one of which is thermally activated. In this case the “yield” of interface states drops to values distinctly below one, even after warm up. In many cases the energy distribution of the states shows characteristic features: at E = E v + 0.45 eV for electron injection in samples with H 2O related traps, at E = E v + 0.75 eV for hole injection. Samples exhibiting these features always show the occurrence of slow states.

Accurate Determination of Capture Time Constant of Interface States in MOS Structures

Accurate Determination of Capture Time Constant of Interface States in MOS Structures

Evaluation of interface states in MOS structures by DLTS with a bipolar rectangular weighting function

A method is presented for determining the interface-state distribution in MOS structures by deep-level transient spectroscopy (DLTS) with a bipolar rectangular weighting function which has the better signal-to-noise ratio (S/N) than the ordinary DLTS using a dual-channel boxcar averager. Experimental results are given for electron traps at the Si-SiO2 interface and compared with those obtained from the ordinary DLTS method. Experimental requirements for the present method to evaluate the interface-state distribution are also discussed.

Photoionization cross section and density of interface states in MOS structures

We have measured the electron photoionization cross section and the interface state density in MOS capacitors of two different oxide thicknesses. In both cases good agreement is obtained between optical and nonoptical measurements of the interface state density, and an increase of the state density toward the conduction band is observed. The photoionization cross section increases monotonically with photon energy and also with trap energy increasing from midgap to the conduction band. This behavior is quite different from that observed for bulk states.

Optically active interface states in MOS structures

The results of studies of the interface states in clean n-type MOS capacitors by the low-temperature photocapacitance technique are reported. Energy distribution of the interface states density and photoionization cross-section are determined from the analysis of the photocapacitance kinetic. It is shown that the energy distribution of the interface state density can be described by the Gaussian distribution with maximum at about 0.7 eV below the conduction band edge and standard deviation of about 0.1 eV. The photoionization cross-section of these states can be described by the Lucovsky relationship. The maximum of the photoionization cross-section vs photon energy was equal to about 5 × 10 −20/( E c − E ss ) cm 2 for a given energy of the interface states E ss . From the comparison of the photocapacitance and quasi-static C-V measurements the existence of two types of interface states is suggested: “optically active states” with density decreasing towards the band edges, and “optically inactive states” with density increasing towards the band edges. No photocapacitance associated with “optically inactive states” was observed.

Quenched‐In Bulk Defects and Interface States in MOS Structures Measured by Transient Capacitance Spectroscopy

The induced defects and interface states in MOS structures as a result of high temperature oxidation are investigated using a transient capacitance technique. Samples after dry oxidation at 1000 C were slowly cooled down to 700°C before pulling out. The densities of traps and interface states were shown to be two to five times lower for the slowly cooled samples than that for the fast cooled ones. The major bulk traps are at −0.26 and −0.49 eV, while the major interface state distribution resides at −0.6 eV. The carrier generation both in the bulk and at the interface is shown to be reduced on slow cooling. The results suggest that the interface states and the bulk traps are the consequence of quenched‐in impurities.

Abstract: Dynamic properties of interface states in MOS structures

Abstract: Dynamic properties of interface states in MOS structures

Evidence for multiphonon emission from interface states in MOS structures

Abstract Transient capacitance measurements on MOS structures give strong evidence for a temperature-dependent capture cross-section for electrons at the continuously distributed interface states. A theoretical model that explains this behavior is lattice-relaxation multiphonon emission.

Transient capacitance measurements of hole emission from interface states in MOS structures

The energy spectrum of MOS interface states and the capture cross section for holes have been measured in p-type silicon by transient capacitance spectroscopy. In MOS capacitors with interface state densities of &amp;lt;1010 cm−2 eV−1 near midgap, the density decreases with energy towards the valence-band edge over the measurement range of 0.17 &amp;lt;E−Ev&amp;lt;0.6 eV. The capture cross section for holes is of the order of 5×10−13 cm2 and is independent of temperature and energy. It appears that the measured distribution consists of acceptor states that extend from the conduction band into the lower half of the silicon forbidden band. The absence of a detectable signal from interface states in a valence-band tail implies that the capacitance transient for hole emission is outside the measurement range. A sharply peaked signal observed for electron (minority carrier) capture at high temperatures indicates that these states are present, but have an extremely low capture cross section for holes, ⩽10−23 cm2.

Interface States Induced by Amorphous SiO2 in MOS Structures

In order to understand physical origin of interface states in MOS structures, model calculations of the interface states are carried out. The model of the ideal Si–SiO 2 , interface is introduced. This model represents that the Si–SiO 2 interface is given as the boundary between two bonding-type materials and the intrinsic interface state is absent. It will be assumed that observed interface state is caused by the difference between real interface and the ideal one. The real boundary of MOS structures may be described approximately in terms of the crystalline Si and the amorphous SiO 2 with an ideal glassy structure. Based on the simple model of amorphous SiO 2 , the density of interface states is calculated semi-qualitatively. The obtained results suggest that the interface states induced by the amorphous SiO 2 do not give the observed density of the interface states and the amorphous state of SiO may take into account this density.

The effect of ion bombardment on the interface states in MOS structures: L Pranevychius and A Aulas, Proc of 11th Intern Conf on Phenom in Ioniz Gases, Prague 1973, 67

The effect of ion bombardment on the interface states in MOS structures: L Pranevychius and A Aulas, Proc of 11th Intern Conf on Phenom in Ioniz Gases, Prague 1973, 67

Interface states in MOS structures with 20–40 Å thick SiO 2 films on nondegenerate Si

MOS structures having different metal contacts on 20–40 Å thick SiO 2 films and non-degenerate Si have been investigated. These structures show large frequency dispersion of the measured admittance curves caused by carrier recombination in interface states. However, build-up of a Si inversion layer is not observed because the minority carriers are drained away by tunneling through the oxide into the metal. Interface state density distributions across the whole Si band gap are obtained by evaluating measured capacitance and conductance curves. Characteristic peaks of 0.12–0.30 eV half width are found for the metal contacts, Mg at 0.54 eV, Cu at 0.23 eV, Cr at 0.18 eV and 0.52 eV, and Au at 0.15 eV and 0.97 eV above the valence band edge. The position of a peak seems to be related to the valence of the metal. Interface states caused by Cr, Cu and Mg contacts are of acceptor type. Their capture cross-section obtained from conductance measurements varies between 10 −7 and 10 −18 cm −2. A rapid increase of the state density with decreasing oxide thickness or sample annealing indicates that the states are caused by metal diffusion through the oxide into the interface. An observed saturation of the state density at about 2 × 10 13 cm −2 V −1 is possibly due to a limited solubility of metal impurities in the oxide.