Thin SiO2 films grown on silicon substrates were exposed to electron beam irradiation at energies from 100 eV to 2.5 KeV. Then, thermally stimulated exoelectron emission (TSEE) spectra were taken by heating the sample linearly to a maximum temperature of 600°C. We have compared the emission behavior from oxides grown on both n-typeand p-type, (100) and (111) silicon wafers. The TSEE spectra show emission peaks whichcan be categorized by their behavior into two groups. The β emission peaks are characteristic of emission from localized electron traps while the γ emission peaks result from the annealing of beam-induced defects. We have observed changes in the β peaks which appear to be associated with the concentration of dopants in the substrate material. In addition, we have identified a beam energy threshold near the oxygen Is binding energy for the creation of defects. This suggests that defect creation results froman electronic transition similar to electron stimulated desorption.

Electrically active traps were induced in the Si-SiO2 interfacial region by silicon ion bombardment. A Kaufman source was used to introduce 400 eV hydrogen ions into the oxide and the interface. The interaction of the hydrogen species with the traps was monitored by a comprehensive set of electrical measurements of the metal-oxide-silicon [MOS] structures.

The results of charge trapping and thermal annealing in X-ray irradiated SiO2 are presented. A comparative study is made between thermal oxide and SIMOX buried oxide behavior. At low dose (10 krad(SiO2)), X-ray induced charge trapping is found to be very different in thermal and SIMOX oxides. Results are interpreted in terms of a relatively large bulk trapping in SIMOX whereas thermal oxide behavior is dominatedby interface trapping. However, at high dose, both oxides behave similarly and are dominated by interface trapping. Etch-back experiments performed on SIMOX irradiated at 10krad (SiO2) and 1 Mrad (SiO2) reveal these two trapping regimes. Isochronal annealings have been performed up to 300°C on irradiated samples. Recovery data are interpreted assuming an energy distribution of trapped charge densities. Detrapping energies located at about 1.05 eV and 1.35 eV have been obtained in SIMOX whereas the thermal oxide exhibits a unique peak at 1.35 eV. Based on these data, SIMOX and thermal oxides are demonstrated to differ significantly.

The tunnelling front model has been used to obtain the spatial distribution of high-voltage, stress generated traps inside of MOS capacitors. It was found that the number of traps created by high voltage stress was proportional to the cube root of the fluence through the oxide during the stress. Measurement of the trap generation rate indicated that fewer traps were being created as higher amounts of charge were passed through the oxide. Further tests indicated that there was a voltage dependence to the trap generation which was independent of stress polarity.

Oxygen-vacancy defects (E') generated at the surface of buried SiO2 layers formed by O+ implantation during the separation by implantation of oxygen (SIMOX) process have been studied by electron spin resonance (ESR) at 4.2 K. The E' damage was generated during exposure to a dc Ar glow discharge that produces defects predominantly in a surface layer of ≈100 Å thick, reaching local volume densities at the surface up to 8 × 1019 cm−3. This glow discharge exposure, alternated with step-by-step etch back, allowed mapping of a defect generation sensitivity depth profile of the buried oxide (BOX) layer, revealing a fairly uniform sensitivity with a strong decline towards the BOX/substrate interface. Besides the usual E' γ signal, the E'δj center — a delocalized variant of the E' center — has been newly observed in the BOX. Reoxidation of the BOX was observed to reduce the E' sensitivity close to that of regular dry thermal oxide (≥ 29 times lower), while the E'γ signal could no longer be generated, again similar to conventional thermal oxide. These data suggest a revision of the model for the E' defect. In general, the results strongly suggest that the buried oxide contains excess Si, exceedingly so near the BOX/substrate interface.

An electron spin resonance study has been carried out on a-SiO2 films deposited from SiH4 and N2O gases using UV lamp induced chemical vapour deposition. Deposition pressures have been varied from 5 torr to 30 torr whilst the substrate temperature was maintained at 240°C. Bridging nitrogen (O3≡Si-N-Si≡O3) and oxygen-vacancy center defects are observed in small quantities (≈ 1016cm−3) whilst over coordinated N defects are observed in concentrations up to 1018 cm−3 dependent upon the deposition pressure. The concentration of these defects can be dramatically reduced either by depositing the a-SiO2 at high pressures (≈ 30 torr) or by post-deposition annealing at ≈ 600°C. Comparison with data on films produced by plasma enhanced chemical vapour deposition demonstrates that the mode of incorporation of nitrogen into the network depends critically upon the chemical species in the deposition reactor.

Ultraviolet radiation has been used to anneal out extrinsic defects in several types of deposited a-SiO2 films. The UV light was obtained from a new krypton UV-VIS-IR lamp with a spectral range of 170 nm <λ<3μ This “cold” annealing was performed on a-SiO2 films, with various thicknesses up to 400 nm. The films were deposited by various techniques, ultraviolet induced chemical vapour deposition (UVCVD), plasma enhanced vapour deposition (PECVD) and spin-on-glass (SOG). Fourier Transform Infra-Red spectroscopy (FTIR) and Electron Spin Resonance (ESR) were used to characterize the effect of the radiation. In the case of UVCVD and SOG a-SiO2 films, it is shown that the UV radiation removes the Si-H bonds and reduces significantly the amount of C-H and C-H3 groups. In both these films, an important reduction in the amount of adsorbed water and Si-OH groups is observed, together with an increase in the number of Si-O bonds. In PECVD films made with tetraethylorthosilicate (TEOS) vapour and O2 as precursor gases, we find evidence for an important reduction in the amount of C and the number of Cn Hy related defects. The UV treatment is effective even at temperatures as low as 100 °C, which suggests that it could constitute a much needed low temperature annealing step.

It has been observed that the low-level, pre-tunneling currents through thin gate oxides increased after the oxides had been stressed at high voltages. The number of traps inside of the oxide generated by the stress has been shown to increase as the 1/3 power of the fluence that had passed through the oxide during the stress. The increases in the low-level, pre-tunneling currents have been shown to be proportional to the number of stress generated traps in the oxide and not to the fluence during the stress. The voltage dependences of the excess low-level leakage currents were stress and measurement polarity dependent. Attempts have been made to fit the voltage dependences of the excess low-level currents to Fowler-Nordheim tunneling, Frenkel-Poole conduction or Schottky barrier lowering. The increase in the portion of the low-level, pre-tunneling current that was not dependent on stress/measurement polarity sequence was best fit using Schottky emission currents. The model that has been developed to describe the increases in the low-level currents has centered on trap-assisted currents through the oxides.

In this work, we report the effects of an ammonia plasma nitridation on the charge trapping properties of thin SiO2 films in correlation with their nitrogen and hydrogen contents. Electron traps characteristics were determined by die avalanche injection technique. Hydrogen contents were measured by Elastic Recoil Detection analysis (ERDA). Nitrogen depth profiles were obtained with Auger spectroscopy. It is shown that the bulk electron trapping properties are essentially controlled by the specificity of hydrogen and nitrogen incorporation in the SiO2 films during the ammonia plasma process. For short nitridation times, an increase of hydrogen related electron trap densities is observed in good agreement with hydrogen ERDA measurements. However hydrogen concentration never exceeds 3 at% and can be scaled down by a short time post-nitridation anneal in oxygen, to a level comparable indeed inferior to that of a non-nitrided oxide. For heavy nitridation, an additional electron trap is detected which could be associated to the presence of nitrogen in the bulk of SiO2.

Energy filtering has been applied to electron diffraction patterns to obtain electron scattering intensity data of single energy collected using a scanning transmission electron microscope. For amorphous materials, the technique permits reconstruction of radial distribution functions from elastically scattered electron intensity data; amorphous silica thin films have been analyzed in the present experiments. The radial distribution functions are characterized in terms of interatomic distances and are compared to neutron scattering results in the form of total correlation functions.

New defects were revealed in PECVD SiOxNyHz thin layers upon VUV-illuminations with a deuterium (De) lamp. The ESR signal measured after a 8-hour illumination reached a saturated amplitude one or two decades higher than the dark ESR signal. The dark ESR signal level was recovered after a 3-hour anneal at 380°C. In addition to the silicon dangling bonds already identified in the dark ESR, the bridging nitrogen dangling bonds and over-coordinated nitrogen were identified after VUV-radiations. The relative densities of the various kinds of defect are given as a function of the O/O+N oxynitride composition.

In the present work structural and electrical properties of thin films, deposited by PECVD from He-diluted S1H4+NH3+N2O gas mixtures, have been studied. Film compositions have been analyzed by NRA, RBS and hydrogen content has been determinated by ERDA while Infrared spectroscopy has been used to evaluate the local bonding configurations. Electrical properties have been measured in metal-insulator-metal structures by I-V ramp. From the results obtained, the oxynitride films show suitable properties for application as gate insulator in amorphous silicon thin film transistor.

Thin films of highly transparent amorphous silicon oxynitride (a-SiOx Ny:H) were prepared by rf glow discharge decomposition of SiH4,NH3 and N2O gases, in a PECVD reactor provided with an in situ phase-modulated ellipsometer. The ratio [N2O]/ ([N2O] + [NH3]) was varied from 0 to 1 in a dilution with 5% of SiH4, keeping constant the total gas flow rate. From spectroscopic ellipsometric measurements, performed in the range 1.5–5.0 eV, the refractive index of the films was calculated applying the Bruggeman effective medium theory. The structural model used considers a three-component mixture layer, composed of void, silicon dioxide (glass) and silicon nitride (pyrolitic), on a c-Si substrate. The x and y composition parameters were calculated from the fitted relative volume fraction of each constituent, ranging from a-SiO2 N0:H to a-SiO0N1.33:H, which are in fair agreement with those obtained from XPS measurements. These results, along with data of FTIR spectra of the films show a clear correlation between the void fraction and the bonded hydrogen content of the films.

A technique has been developed to determine the density and distribution of spatially deep traps throughout an insulator. These traps were created and charged by a high voltage stressing pulse and allowed to discharge upon the removal of the pulse. During the transient following pulse removal, the currents were measured. A correlation from current to trap densities and from time of decay to location within the dielectric has been made. This method has been applied to gauge the differences between nitrided dielectrics and thermal oxides. We have found initial trap levels, before stressing, to be lower in silicon oxide devices than silicon oxynitride devices. However, trap levels increased faster in thermal oxides as the stress increased, and became larger than the levels found in nitrided oxides. Nitrided devices tended to resist additional trap formation. Current-voltage measurements have shown that nitrides developed higher leakage currents as the stress was increased than did thermal oxides.

In the PECVD SixNyHzOw the hydrogen is principally incorporated as N-H bonds. For O/(O+N) below 0.4, the %H is constant at 25%; from 0.4 to 1, it decreases to 4%. We show that a chemical ordered model is likely to describe the hydrogen incorporation in the amorphous network while a random bond model fails.

Development of aluminum gate thin-film transistors (TFT) is described. This TFT is fabricated based on an aluminum oxide insulator technology, in which aluminum is anodically oxidized to form Al2O3. The use of aluminum is effective in reducing the delay of the gate busline of the display panels due to its low resistivity. The Al2O3 films formed by an anodic oxidation, block the growth of hillocks during TFT fabrication which is one of the biggest issues of aluminum metallization. With this technology it is possible to design and fabricate TFT/LCD panels larger than 30 inches and with more than 1000 scan lines.

Amorphous insulator/amorphous silicon structures show, under bias-stress conditions, a drift of the electrical characteristics. In the present work, in order to discriminate the main source of instability in amorphous silicon dioxide/amorphous silicon Thin-Film Transistors, the determination of both threshold voltage and flat-band voltage has been performed after bias-stressing the devices with different gate voltages and at different temperatures. Flat-band voltage was determined by the space-charge photomodulation technique. From the close correlation observed between the two quantities, we conclude that the predominant instability mechanism is represented by change in the gate insulator charge at and near the insulator/semiconductor interface. Time evolution of the threshold voltage shifts has been investigated as a function of stress bias and temperature. The data are explained in terms of a new model based on the dispersive charge injection (hopping of electrons via localised states) into the first 2–3 nm of the gate insulator adjacent to die semiconductor layer (transitional region). Possible origin of the transitional region can be related to the reduction of the gate insulator induced by activated hydrogen, as suggested by photoemission experiments performed with synchrotron radiation on SiO2 bombarded with low energy (100 eV) H-ions.

Nitrogen-rich amorphous silicon-nitride films a-Si1−xNx:H were prepared by glow-discharge decomposition of gas mixtures of ammonia and silane. With increasing nitrogen content the spin density, Ns, decreases from 4×1018cm−3 (x = 0.55) to 3×1017cm−3 (x = 0.67). These films were used as a gate dielectric in amorphous silicon TFTs. The TFTs are characterized by measurements of the transfer characteristics and by a transient current spectroscopy (TCS). Nitrogen-rich dielectrics with Ns<1018cm−3 have little influence on the transfer characteristic, however, they tend to have a lower sensitivity to bias stress. Using a device-quality nitride (x = 0.64) the properties of the TFTs were varied in two ways: 1) doping of the a-Si:H film with phosphine or diborane and 2) exposure of the nitride film to an oxygen plasma. The variation of the areal density of defect states, Nd, with Ec-EF suggests that the effective density of interface states, Ni, and the characteristic of undoped TFTs are determined by interface defects of the a-Si:H film. The plasma treatment introduces oxygen into a thin superficial layer of the nitride. By varying the exposure time te it is possible to change the properties of the TFTs continuously from nitride like to oxide like.

The accelerated degradation phenomena in amorphous silicon thin film transistors due to both electrical stress and visible light illumination under the elevated temperature have been investigated systematically as a function of gate bias, light intensity, and stress time. It has been found that, in case of electrical stress, the threshold voltage shifts of a-Si TFT's may be attributed to the defect creation process at the early stage, while the charge trapping phenomena may be dominant when the illumination periods exceed about 2 hours. It has been also observed that the degradation in the device characteristics of a-Si TFT's is accelerated due to multiple stress effects, where the defect creation mechanism may be more responsible for the degradation rather than the charge trapping mechanism.

We have studied the preparation and device application of a-Si by atmospheric pressure CVD using disilane. The deposition rate of a-Si increases with the partial pressure of disilane and with the total pressure. The deposition rate of APCVD a-Si is, therefore, very high compared with LPCVD. The photosensitivity of APCVD a-Si is 104 at 100mW/cm2. We have made an inverse staggered type a-Si TFT using SiO2 as a gate insulator. The on/off current ratio and field effect mobility are 105 and 0.19cm2/Vs, respectively.