P. Vitanov

Influence of stoichiometry of direct plasma-enhanced chemical vapor deposited SiNx films and silicon substrate surface roughness on surface passivation

In this article, we report on the use of direct plasma-enhanced chemical vapor deposited silicon nitride (SiNx) films deposited at low excitation frequency (440 kHz) on low-resistivity (1.5 Ω cm) p-type Czochralski silicon substrate surfaces with different textures, to elucidate the influence of microroughness of the substrate surface on the surface-passivating properties of thin SiNx films. Whereas flat surfaces get the best passivation from Si-rich SiNx films, the optimum passivation shifts towards stoichiometric nitride as the microroughness increases, which points to the increasing relative importance of a charge-induced field effect. When short high-temperature (firing) treatments are applied upon passivation layer deposition, the process window to yield good surface passivation broadens, although very Si-rich films tend to suffer from blistering.

XPS characterization of thin (Al2O3)x(TiO2)1-x films deposited on silicon

The study deals with thin films of a pseudobinary alloy (Al2O3)X(TiO2)1-X (PBA), deposited on silicon substrates using the chemical solution deposition (CSD) method. The thin films were obtained by spin coating followed by thermal treatment at 750°C. Both compositional and chemical bonding data were obtained by X-ray photoelectron spectroscopy (XPS). The depth analysis reveals that the stoichiometric (Al2O3) and (TiO2) ingredients detected at the surface are preserved up to the interfacial transition region with Si wafer. The analysis shows the presence of carbon impurities on the film surface only. The Si penetration and the interface PBA dielectric/Si is investigated and discussed. The interface with the Si substrate is studied with the purpose of explaining the electrical properties of the (Al2O3)X(TiO2)1-X/Si structure.

Deposition and dielectric properties of (Al2O3)x(TiO2)1−x thin films

The motivation for this study was to obtain an alloy system (Al2O3)x(TiO2)1−x, that is thermodynamically stable, in direct contact with Si and possessing a high dielectric constant. In the present study, (Al2O3)x(TiO)1−x films were investigated. They were prepared by spin coating from a sol solution, with additional thermal annealing. The chemical composition and stoichiometry of the films was studied by X-ray photoelectron spectroscopy. For the electrical characteristics, MIS capacitors were fabricated. The determined relative dielectric constants were larger than the reported values for pure Al2O3, due to the presence of TiO2.

Formation of porous silicon: Electron microscope investigation

Porous silicon structure was investigated by scanning electron microscope images of secondary electrons as well as by transmission electron microscope images of diffraction and phase contrasts. Different structure types in each one of the dissolution zones are found: crystalline structure of primary silicon, changed crystalline structure as a result of a partial dissolution process, and amorphous structure in the porous zone. A hypothesis about the type of the changed structure in the intermediate dissolution zone is put forward and an atomic model of this structure is presented. A theory of the mechanism of the dissolution process based on structure peculiarities, observed in the images, was formulated: the dissolution proceeds along the most favorable atomic planes of types (110) and (111). The dissolution front advances mainly in the direction [010]—it is zigzag shaped and parallel to the dissolution surface. Images of phase and diffraction contrasts have been simulated on the basis of models accountin...

Structural and dielectric properties of TiO2 thin films deposited by the sol-gel method on Si substrates

Titanium dioxide thin films with good dielectric properties were obtained on Si substrates using the sol-gel method. The metal oxide films were deposited by spin coating from sol solution and additionally annealed at 600 °C and 850 °C. XRD analysis, FTIR and Raman spectroscopy were used for revealing the film structure, the crystal phases and the formation of a polycrystalline material. The electrical measurements on metal-insulator-silicon (MIS) structures showed good dielectric properties. An optimal regime for high temperature annealing (850°C/15 min) was found, for which no effects related to the thermal instability of TiO2 film on Si were observed. The leakage current density of a 38-nm thick TiO2 film annealed at 850°C/15 min/O2 was approximately 1.95×10−9 A/cm2 at 1.6×10−6 V/cm.

Study of ZrO2/Al2O3/ZrO2 and Al2O3/ZrO2/Al2O3 stack structures deposited by sol-gel method on Si

Based on our previous experience with pseudobinary alloys of (Al2O3)x(ZrO2)1−x as high-k materials and passivating coatings for solar cells, stack systems of ZrO2/Al2O3/ZrO2and Al2O3/ZrO2/Al2O3, deposited by simple and low cost sol-gel technology have been studied. The thin films of ZrO2 and Al2O3 were sequentially obtained on Si substrates including spin coating deposition from stable solutions. High resolution scanning electron microscopy (HRSEM) was used to compare the morphology of the nanolaminates. The layers were optically characterized by UV-VIS spectrophotometry. The electrical measurements were carried out on metal-insulator-semiconductor (MIS) structures. Their leakage current and relative permittivity were determined.

Electrical properties of (Al2O3)x(TiO2)1-x films deposited on a silicon substrate

Direct current conductance in Al/(Al2O3)X(TiO2)1-X/silicon structure was studied, the dielectric layers being deposited by the chemical solution deposition method. The measurements were carried out at room temperature and 320, 340 and 360 K. The results correspond to bulk-limited conduction of the Poole-Frenkel type. High voltages and temperature lead to an additional current rise, explained by thermal excitation and tunneling of electrons through the lowered Poole-Frenkel barrier.

Application of impedance spectroscopy for the investigation of MIS structures with barium strontium titanate

Complex impedance spectroscopy was used for the investigation of MIS gate-stack structures with barium strontium titanate. Using a spectroscopic plot of the imaginary part of the impedance versus frequency, the different capacitive components of the MIS structure were evaluated. The BSTO relative dielectric constant εr was determined from the capacitive components.

Si nanoparticles embedded in pseudo binaries alloys with AI2O3

The present paper reports the incorporation of Si nanoparticles (NPs) in (Al2O3)x (B2O3)1-x films. A new approach for involving Si NPs (20 nm) p+ doped into sol solution was used. After spin coating deposition and additional annealing at 850°C, (Al2O3)x (B2O3)1-x films with Si NPs have been obtained with thickness of 75 and 120 nm. The (Al2O3)x (B2O3)1-x films were deposited on p-type and n-type Si wafers. The optical study reveals that Si NPs embedded in (Al2O3)x(B2O3)1-x leads to higher absorption in the visible spectral range compared to dielectric layer without nanoparticles. AFM studies show that the incorporated Si nanoparticles into the dielectric layer have probably a uniform distribution on film surface. This conclusion is confirmed by SEM observation. The current - voltage (I-V) characteristics of a structure (Al2O3)x(B2O3)1-x layer with Si NPs on p- type Si shows an ohmic type of conductivity. The sheet resistance is 480 Ohm/sq respectively, when the same layer is deposited on quartz substrate. This work presents a new technological approach for integration of Si NPs in dielectric matrix of (Al2O3)x (B2O3)1-x. The results can find applications for formation of ultra thin emitter for photodiodes and Si solar cells.