Fast Surface States Research Articles

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 a 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.

The interface of plasma-anodized Hg1−xCdxTe

The process for forming plasma-anodized oxide on Hg1−xCdxTe with x = 0.215 and 0.290 and the properties of the interface are studied. The results of Auger electron spectroscopy and x-ray photoelectron spectroscopy surface analytical characterization and the electrical interface characterization are compared with respective data on the interface between Hg1−xCdxTe and its solution anodized native oxide. The plasma oxide exhibits a decreasing gradient of oxygen and an increasing gradient of unoxidized tellurium from the surface towards the bulk semiconductor. An accumulation of fluorine at the interface unique to the plasma oxide is observed. Metal-Insulator-Semiconductor (MIS) devices with the plasma-anodized interface have a relatively low concentration of positive fixed surface charge density, (1–3)×1011 cm−2, and fast surface state density per unit band gap of about 2×1011 cm−2 eV−1, measured at 77 K. The hysteresis in the capacitance-voltage characteristics of the MIS devices is negligible, indicating the near absence of slow-trapping effects which have been observed in anodic solution oxides. Photoconductors passivated with plasma oxide exhibit good responsivity and detectivity, indicating small surface recombination velocity and small interface trapping. A significant advantage of the plasma oxide is the excellent thermal stability of the interface. Devices such as MIS capacitors and photoconductors may be annealed in vacuum up to 95 °C for prolonged periods while retaining their properties.

Reduction of fast surface states on p-type GaAs

Native oxides and oxyfluorides were grown on GaAs by a glow discharge plasma process. Analysis of metal-insulator-semiconductor structures based on oxyfluoride dielectrics indicated vastly different interface properties compared to pure oxide dielectrics. Whereas oxide structures showed high densities of fast surface states, oxyfluorides showed no evidence of such effects.

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/SiO 2 interface and are thermally annealed independently of this reaction. A two step oxidation technique was used to investigate the electronic structure of the Si/SiO 2 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.

Phtovoltage Spectroscopy of Fast Surface States in Silicon MOS Structures

Phtovoltage Spectroscopy of Fast Surface States in Silicon MOS Structures

Gap states at the GaAs-natural oxide interface

The relaxation of surface conductivity changes during the application and after the removal of external electric fields was investigated for n-GaAs surfaces covered with natural oxide. The relaxation processes in the heterojunction system of the oxidized surface are governed by various excitation mechanisms between the depletion layer in the bulk and fast surface states at the GaAs-oxide interface. Analysis of the experimental results yields new data on the energetic distribution of the fast surface states which show that there is a set of empty states in the upper half of the bulk energy gap and a set of occupied states near the middle of the bulk energy gap.

Preparation of glow discharge amorphous silicon for passivation layers

a-Si films containing hydrogen were deposited by the decomposition of silane in a capacitively coupled r.f. plasma. The preparation conditions were examined in relation to the passivation of crystalline semiconductor devices. The substrate temperature during deposition should be between 280 and 300°C to ensure both the necessary stability against thermal effusion of hydrogen and an electrical resistivity which is high enough to avoud leakage currents. The mass density of such samples is almost equal to that of crystalline silicon and the influence of humidity is negligibly small. It was found that the breakthrough voltage of a p-n junction is markedly decreased after covering it with 0.2μm of a-Si produced by a glow discharge. This undesired reduction could be totally eliminated by the incorporation of a small percentage of oxygen into the a-Si layer. The fast surface states which limit the operation of charge-coupled devices could be compensated to a large extent by covering a device test structure with hydrogen-containing a-Si and subsequently annealing at 500°C.

Slow contamination and fast surface state effects SEM studies of Si phototransistors

The rate of growth of contamination films on the surface of Si phototransistors under examination in a scanning electron microscope was measured by multiple beam interferometry. The contamination film reduced the barrier electron voltaic effect current (i.e. the ″EBIC″ signal) by 10 to 20% after scanning a single line for an hour. The photovoltaic effect current of the transistors however was reduced by 90% after scanning the whole area of these devices for a few seconds. This is ascribed to the fact that bombardment-induced changes in surface electrical conditions strongly affect the carriers produced near the surface by photons but not the carriers produced at depths up to 2μm or more by the electron beam.

Avalanche‐Induced Hot Electron Injection and Trapping in Gate Oxides on p‐Si

Hot electron trapping in gate oxides can lead to threshold drifts in short channel MOSFET's. Therefore, factors affecting the efficiency of hot electron trapping have been investigated by rf‐bias aging of MOS capacitors followed by flatband voltage measurements. It was found that avalanche‐injection electron current levels of >5 μA cm−2 produce excessive amounts of hot electron trapping; currents of <4 μA cm−2 were preferred for oxide characterization. A relatively small amount of hot electron trapping produced an enormous density of fast surface states. The observed flatband shifts would, therefore, contain significant contributions from surface states. The total flatband shift due to hot electron injection and trapping increased with higher p‐Si substrate doping levels and with increasing oxide thickness . Eectron beam irradiation (5–30 μC cm−2) followed by a 450°C, anneal did not significantly change the hot electron trapping behavior of the gate oxide. Possible implications of these results on the generic reliability of VLSI devices are discussed.

Photoelectrical method of determination of fast surface states density in MIS structures

Photoelectrical method of determination of fast surface states density in MIS structures

An investigation of the interface state density in metal-silicon nitride-silicon structures

MNS capacitors were submitted to a series of alternating voltage pulses, and measurements were performed at different stages of this cycling. The interface state parameters at the SiSi 3N 4 interface were evaluated using the conductance method; the surface potential ψ S was obtained from a measurement of the high-frequency capacitance. Experimental results are explained by the formation, during cycling, of new fast surface states located at the SiSi 3N 4 interface.

Determination of capture cross section and surface-states concentration profile using the surface-acoustic-wave convolver

Energy distribution of surface states and majority-carriers capture cross section is determined using the surface-acoustic-wave (SAW) convolver. The semiconductor is placed a small distance above the SAW delay line, with a uniform air gap between the two media. A fast rise time dc pulse is applied across the semiconductor-delay line structure, and the resulting change in the SAW propagation loss is observed. The transient response of the SAW propagation loss represents the emission or trapping of majority carriers from surface states. From this transient response, the capture cross section and the concentration profile of the surface states are determined. The results obtained agree with the already known distribution of fast surface states; it is constant at the middle of the gap and increases towards the conduction band, whereas the capture cross section is constant in the middle of the gap and decreases toward the conduction band. This new SAW technique is simple, sensitive, and requires no contact to the semiconductor surface.

Transistor Surface Effects Responsible for Anomalous Third-Order Intermodulation Distortion in Undersea Cable Telephone System

Anomalous intermodulation distortion has been observed in the SG submarine cable repeater amplifier. The anomalous distortion was found to be dependent upon the crystal orientation in the SG bipolar transistor. This fact suggested that transistor surface effects might be responsible for the anomalous distortion. To test this hypothesis, computer models of the transistor with surface effects were used to compute the third-order modulation coefficient M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> - Surface effects in the collector-base junction alone were modeled by a junction-controlled mos capacitor with fast surface states. The mos capacitor model then was added to a modified Gummel-Poon transistor model to simulate surface effects in the complete transistor. It was found that intermodulation contributed by the surface effects was dominant in the case of 〈111〉 orientation, and the behavior of the computed intermodulation was similar to the observed behavior. This paper describes the transistor modeling and the intermodulation computations developed in testing the hypothesis. The principal conclusion confirms that the anomalous distortion from the SG transistor is due to surface effects, in particular, to a high surface-state density.

The interface between Hg 1− xCd xTe and its native oxide

The results of a study of the electrical properties of the interface between Hg 1− x Cd x Te with x = 0.21 and its native oxide at 77°K are presented. The native oxide is formed by anodic oxidation and results in an interface with reproducible properties. The surface charge, the surface mobility and the effective lifetime are obtained from galvanomagnetic measurements and are related to the semiconductor bulk parameters, the oxide thickness and the annealing conditions. The surface state charge and the metal-semiconductors work function difference are obtained from the shift of the flat band voltage of metal-oxide-semiconductor (MOS) capacitor characteristics. The interface between Hg 1− x Cd x Te and its native anodic oxide is characterized by a density of fast surface states of the order of 5 × 10 11cm −2 (eV −1) near the middle of the bandgap. The density of states increases towards the band edges to the order of 10 13cm −2 (eV −1). The measured flat band voltage is approximately −0.5 V for an oxide thickness of 500 Å and for an n-type semiconductor with an electron carrier concentration in the range 1–3 × 10 15 cm −3 at 77°K. The fixed oxide surface state charge is positive for both p-type and n-type semiconductors and is of the order of 6 × 10 11 charges per cm −2. The surface properties, the significance and the reproducibility of the results are evaluated.

Properties of rare earth oxide films

We investigated the properties of rare earth oxide films produced by the vacuum evaporation of rare earth metallic films and their oxidation in an oxygen atmosphere; we also studied the silicon-rare earth oxide interface. The rare earth oxide films were characterized by good insulating properties: an electrical resistivity of more than 10 12 Ω cm, a dielectric permittivity of 7–20, a dielectric dissipation factor of 0.01 or less and a breakdown field strength of (2–6) × 10 6 V cm −1. The behaviour of the effective surface charge density curve at flat-band voltages for scandium, yttrium and lanthanum to lutetium was found to be identical with that of the thermal neutron capture cross section for these elements. The presence of a deep level located some 0.3–0.38 eV below the conduction band edge was observed in fast surface state spectra of Si/Ln 2O 3 structures (Ln  Sc, Y, La, Gd, Er). On heating an Si/Y 2O 3/Al structure at 423 K for 20 min with a gate voltage of +5 V we observed a shift in the capacitance-voltage curve of approximately 2.5 V towards more negative voltages; for the same conditions but with a gate voltage of −5 V the shift was about 1 V in the opposite direction.

Influence of ΦMS(T) in the determination of the Si-SiO2surface states

The determination of fast surface states at the Si-Si0 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system by the Gray-Brown low-temperature technique is carefully analyzed. Included in this analysis is the variation of the semiconductor work function with the temperature and the doping impurity partial ionization at low temperature. It is shown that particularly the influence of the semiconductor work function is very significant. For instance, we obtained for an Si-SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> system a number of surface states, with energy levels between 0.32 and 0.53 eV, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N_{fs} \simeq 8.5 \times 10^{9}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> or <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N_{fs} \simeq 1.0 \times 10^{11}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , the difference due to the influence of the semiconductor work function only.

High temperature annealing of mnos devices and its effect on si-nitride stress, interface charge density and memory properties

The effects of high temperature annealing in N2 and H2 ambients upon the following properties of MNOS devices have been investigated: Si-nitride stress, etch rate, index of refraction, fixed interface charge and fast surface state density, memory window and charge retention at elevated temperatures. The CVD Si-nitride and Si-oxynitride films were deposited at temperatures as low as 610°C with a NH3/SiH4 ratio of 1000:1, the heat treatments were performed in the temperature range from 640°C to 1130°C. A similar N2-annealing behavior was found for film stress and flatband voltage. The film stress increased with increasing annealing time and temperature while the interface charge density changed from high positive values (QN/q = 4 × 1012cm−2) after nitride deposition at 610°C to high negative values (QN/q = -4 × 1012cm−2) after annealing at 930°C, The fast interface state density increased while the charge retention time was drastically reduced. The changes of the properties by N2 annealing are mainly attributed to decomposition of SiH and NH bonds. Minor effects were obtained by annealing in H2 and the drastic changes caused by N2 annealing could be reversed to a great extent by subsequent H2 annealing. Finally the different effects of deposition and annealing temperature on the propertiesare discussed .

Characteristics of interface-doped MNOS memory devices

The results of an investigation of the characteristics of MNOS memory devices are given in which the interface between the oxide and nitride was doped with a few monolayers of various refractory metals. In particular, write speeds of the order of microseconds could be obtained along with retention times which could be extrapolated to many decades. No temperature dependence could be found for the decay of stored charge between 77 K and 300°C, indicating that retention is normally dominated by Fowler-Nordheim back tunneling from the interface. Long time exposure to high gate voltages and write/erase cycling in excess of 1000 cycles sharply reduces the achievable memory window, and is accompanied by the copious generation of fast surface states, at least in p-channel devices.

The effects of processing on radiation damage in SiO2

This paper briefly reviews the general interaction of radiation with thermally grown SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , both phenomenologically and atomistically. Radiation-induced trapped charge, the creation of fast surface states, and the all-important neutral electron traps are discussed. The types of radiation and their concomitant damage produced by the typical processes of ion implantation, reactive ion etching, and electron-beam lithography are outlined. The effect of these processes on the oxidized silicon system is treated, and process modification to minimize radiation damage is discussed.

Effect of high-temperature, postoxidation annealing on the electrical properties of the Si–SiO2 interface

The electrical properties of thin thermal SiO2 films were studied as a function of high-temperature, postoxidation annealing in various ambients. Surface charge measurements were made of SiO2–Si structures after annealing for different time intervals in a N2 ambient at temperatures ?925°C. The oxidation-induced fixed oxide charge rapidly decreased. A more gradually increasing charge was observed that is primarily attributed to fast surface states.