T. Inokuma

Optical properties of Si clusters and Si nanocrystallites in high-temperature annealed SiOx films

Structure, optical absorption and photoluminescence (PL) properties of SiOx films subjected to thermal annealing at 750–1100 °C are investigated. Si crystallites with a few nanometers in size are observed in the SiO1.3 and SiO1.65 films annealed at 1100 °C. Threshold energies in optical absorption of the Si nanocrystallites are higher than that for bulk Si, suggesting a contribution from quantum confinement effects. The PL spectrum shows a remarkable increase in intensity after annealing at temperatures above 1000 °C. This PL behavior is closely related to the formation of Si nanocrystallites by the annealing. The PL peak energy of the annealed films shifts to higher energy with decreasing crystallite size but does not follow the blueshift for the absorption threshold energy. These results suggest that a localized state contributes to the PL mechanism. The SiO1.8 film annealed at 1100 °C, which contains no Si crystallites, exhibits an intense PL similar to the annealed SiO1.3 and SiO1.65 films. It is impl...

Vibrational properties of SiO and SiH in amorphous SiOx:H films (0 ≤ x ≤ 2.0) prepared by plasma-enhanced chemical vapor deposition

The stretching and bending absorptions arising from SiO and SiH bonds in amorphous SiOx:H films, prepared by rf glow discharge decomposition of a SiH4O2 mixture at 300°C, have been investigated by infrared absorption measurements as a function of the O content, x. Changes in the profiles of the SiH stretching absorption as a function of x were examined on the basis of a random-bonding model. A charge-transfer model is employed to derive the oscillator strength of the SiH stretching absorption and the peak frequencies of the SiH and SiO stretching absorption, for the Si(Si4−nOn)(n = 1−4) and HSi(Si3−nOn)(n = 0−3) bonding configurations. The absorption over the range 500–900 cm−1, related to the SiH and SiO bending motions, can be decomposed into five components around 650, 780, 800, 840 and 880 cm−1. It is found that the intensities of the 780, 840 and 880 cm−1 bands are closely correlated with those of the SiH stretching absorptions at 2115, 2200 and 2260 cm−1, respectively. The origins of these absorption bands along with the 650 and 800 cm−1 bands are discussed.

Optical properties of silicon nanocrystallites in polycrystalline silicon films prepared at low temperature by plasma-enhanced chemical vapor deposition

Abstract Silicon crystallites produced by low-temperature plasma-enhanced chemical vapor deposition technique have been shown to have size-dependent photoluminescent and second harmonic generation responses. The crystalline volume fraction was estimated by Raman spectra and the grain sizes of crystallites were measured by X-ray diffraction. The structural chemical properties of poly-Si films were studied by means of Fourier-transform infrared spectroscopy and transmission spectrophotometry. The size- and shape-dependent second-harmonic generation (SHG) of poly-Si films is also studied. The resonant SHG spectra show the fine structure with peak position at approximately 3.26 eV which is attributed to the response from Si–SiO 2 interface (for aged films). The second resonant peak can be explained as the size-dependent SHG response from the bulk of nanocrystallites.

Structure and grain boundary defects of recrystallized silicon films prepared from amorphus silicon deposited using disilane

The structure of polycrystalline Si (poly‐Si) films, prepared by annealing amorphous Si (a‐Si) films deposited using Si2H6, has been investigated by x‐ray diffraction (XRD), Raman scattering, transmission electron microscopy (TEM), and electron spin resonance, as functions of deposition conditions, such as deposition temperature Td (450–580 °C) of the a‐Si and annealing time under a fixed temperature of 600 °C. A dominant texture of the poly‐Si films changed from a 〈100〉 texture for Td below 530 °C to a 〈111〉 for Td above 530 °C, independent of the deposition rate of the a‐Si films and of the film thickness. Although the XRD grain size was independent of Td, the TEM grain size increased from 1.0 to 2.5 μm with decreasing Td. It is suggested that the increase in this TEM size is caused by enhanced lateral growth of 〈100〉 grains due to the presence of strain. The spin density Ns and the factor g were found to first increase with the annealing time, and rapidly decreased after the films were crystallized. It...

EFFECTS OF DEPOSITION TEMPERATURE ON POLYCRYSTALLINE SILICON FILMS USING PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION

The 200-nm-thick polycrystalline Si films were deposited by changing the deposition temperature (Td=150–750 °C) using plasma-enhanced chemical vapor deposition of monosilane–hydrogen mixtures. The structural and bonding properties were examined using techniques of Raman scattering, x-ray diffraction, infrared (IR) absorption, and electron spin resonance. Except for Td at 150 and 650 °C, crystallization of the films was observed, and the occurrence of two IR absorption bands around 850 and 1000 cm−1 and an increase in the density of Si dangling bonds were observed in the range of Td higher than 500 °C. These origins were discussed in connection with the mechanisms of disappearance of crystalline phases from the film at Td=650 °C.

Structure of defects in silicon oxynitride films

Amorphous silicon oxynitride (a-SiNxOy) films were deposited at 300 °C using a plasma-enhanced chemical vapor deposition technique, which was carried out with variation in the nitrogen-flow-rate ratio (RN) and the oxygen-flow-rate ratio (RO) to control the nitrogen and oxygen contents, x and y, respectively. Changes in the structural properties and the characteristics of defects in the films were examined based on the electron spin resonance as well as infrared and optical absorption measurements. An increase in either RN or RO was found to decrease the deposition rate, the density of charged or neutral defects, and the randomness of the bonding network. Thus the incorporation of O or N atoms into Si nitride or Si oxide films, respectively, acts to improve the qualities of the insulating films. Furthermore, the nearest N and O atom neighboring to a Si site would be randomly bonded to the Si atom. Our results also showed that N-related dangling bonds, other than so-called K centers, are favorably created a...

Relationship between the stress and bonding properties of amorphous SiNx:H films

Amorphous SiNx:H (a‐SiNx:H) films were deposited at 300 °C on single‐crystal Si and fused quartz substrates using SiH4‐NH3 mixtures. The stress and vibrational absorption were investigated as a function of the N content x. Increased tensile stress subsequent to a reduction in the compressive stress with increasing x was observed. From the values of stress determined for films on two different substrates, values of Y/(1−ν) for a‐SiNx:H films were estimated, where Y is Young’s modulus and ν the Poisson ratio. The values of Y/(1−ν) rapidly decreased with an increase in x, from 4.2×1012 dyn/cm2 for a‐Si:H films to about 2.5×1011 dyn/cm2 for a‐SiNx:H films having x above 1.0. It was found that the measured tensile stress in a‐SiNx:H films for high x above 1.0 was caused by the intrinsic stress, and that incorporated NH bonds act to relax the intrinsic stress. These results were discussed in terms of the change in the bonding configuration as a function of x, based on a modified random bonding model.

Analysis of SiH vibrational absorption in amorphous SiOx:H (0≤x≤2.0) alloys in terms of a charge-transfer model

Amorphous SiOx:H films were deposited at 300 °C by rf glow discharge of SiH4‐O2 mixtures, and the SiH stretching vibrational absorption was investigated as a function of the oxygen content x. The absorption profiles were examined on the basis of the random‐bonding model (RBM). The length dSiH of SiH bonds in four H‐Si (Si3−nOn) bonding units was examined in terms of a charge‐transfer model, using the Sanderson’s electronegativity. Using these dSiH values, the peak wave numbers for the four components were found to be 2000, 2108, 2195, and 2260 cm−1, in agreement with the experimental ones determined on the basis of the RBM.

Influence of Organic Contamination on Silicon Dioxide Integrity

The influence of organic contamination before oxidation on 8-nm-thick silicon dioxide integrity was studied. Contamination results from the intentional adsorption of dioctyl phthalate (DOP) on silicon wafers. Metal-oxide semiconductor (MOS) capacitors were fabricated on the wafers to measure the electrical characteristics of the oxide. A reduction in the dielectric breakdown field strength of the oxide was found to occur after DOP adsorption of more than 1×1013 mol/cm2. The flat-band voltage shift (ΔVfb) and interface trap charge density (Dit) increased with an increase in the amount of DOP below 1×1013 mol/cm2. Positive charges arose from DOP in the oxide during oxidation, which was determined from a negative ΔVfb. Furthermore, with an increase in the DOP level from 1×1013 to 1×1015 mol/cm2, Dit hardly increased whereas ΔVfb gradually increased. This suggests that positive charges at the silicon-oxide interface are fixed. It is thought that an increase in the amount of positive charge in the oxide reduces the dielectric breakdown voltage. From infrared (IR) adsorption measurement, we found that even after DOP decomposition due to oxidation, positive charges within DOP remained, and they degrade oxide integrity.

Cathodoluminescence properties of silicon nanocrystallites embedded in silicon oxide thin films

Cathodoluminescence (CL) spectra for the Si nanocrystallites embedded in a matrix of silicon oxide films are measured at room temperature. The CL spectra consist of two principal bands whose peak energies are in a near-infrared (NIR) region ( < 1.6 eV) and in a blue region ( 2.6 eV), respectively. The spectral feature of the NIR CL band is similar to the corresponding PL spectra. The strong correlation between the presence of Si nanocrystallites and the formation of the NIR CL band are found as well as the PL spectrum. The peak energy of the blue CL band is slightly lower than that of the luminescence band originating from oxygen vacancies ( ≡Si Si ≡ ) in SiO 2 . Therefore, the blue CL band is considered to come from Si n clusters with n ≥ 3 in the oxide matrix. Under irradiation of electron beams, degradation of the intensity is observed for both the CL bands but the decay characteristics are different.