Silicon Oxynitride Thin Films Research Articles

Trap assisted leakage current conduction in thin silicon oxynitride films grown by rapid thermal oxidation combined microwave excited plasma nitridation

Thin films of silicon oxynitride (SiON) were grown on Si substrates by nitriding rapid thermally grown SiO 2 layers in a microwave-excited nitrogen plasma and by subsequent re-oxidation. The enhanced leakage current in SiON at oxide fields 5–7 MV/cm is due to a trap assisted tunneling current. Trap assisted tunneling current analysis indicated a trap level of 1 eV below the conduction band edge, which is shallower than ∼2.5 eV level reported for nitrogen related traps in thermally nitrided SiO 2. This shallower trap level suggests that its origin could be oxygen vacancies in the rapid thermal oxide, generated in the plasma nitridation.

Structural investigation of Si-rich amorphous silicon oxynitride films

In this work we investigated the structural and chemical properties of amorphous silicon oxynitride thin films, with distinct composition, deposited by plasma enhanced chemical vapor deposition from nitrous oxide and silane gas precursors. The utilized characterization techniques were Rutherford backscattering spectroscopy, X-ray absorption spectroscopy at the Si K-edge, and Fourier transform infrared spectroscopy. The results show a silicon first coordination shell composed of silicon, oxygen and nitrogen atoms, in a proportion that fits their atomic content. The SiSi bonds are found only in samples having silicon content higher than ∼50 at.%. These films also present higher amount of SiH bonds. The film having the highest Si content, which shows evidences of Si clustering, was annealed in vacuum at 550, 750 and 1000 °C. The results demonstrated that the annealed film is chemically stable under heat treatments in vacuum up to 1000 °C. The hydrogen is totally released at 750 °C. The main effect of the annealing process is to increase the segregation of silicon clusters.

On the thermal re-oxidation of silicon oxynitride

We propose a two layer model to describe the growth of silicon oxide (SiO2) during the thermal re-oxidation (02) of silicon oxynitride (Si0,:N) thin films previously deposited on silicon. Based on this model, the activation energy for the diffusion coefficient of oxygen through the oxynitride layer was determined. The value observed (3.67 eV) is much higher than the activation energy for oxygen diffusion in Si02 due to the small concentration of nitrogen in the oxynitride film.

Effects of post annealing on removal of defect states in silicon oxynitride films grown by oxidation of silicon substrates nitrided in inductively coupled nitrogen plasma

Ultra thin (5 nm) silicon oxynitride (SiON) films were fabricated at a low temperature using nitrogen plasma generated by an inductively coupled plasma system. Effects of post-metalization annealing (PMA) of Al/SiON/Si MOS structure on the electrical properties of the SiON films were studied and correlations between the charge trapping states and the leakage current were established. Positive charge trapping by interface states generated by plasma damage was characterized by the hysteresis in high-frequency capacitance–voltage ( C– V) characteristics. Hysteresis was observed to be completely removed by PMA while interface state density at the Si mid band gap reduced from 2.2×10 13 to 3.7×10 11/eV/cm 2 and the oxide fixed charge density changed from 3.3×10 12 to −4×10 11/cm 2. The leakage current also decreased significantly, by more than two orders of magnitude, with PMA. The analysis of the leakage current using trap assisted tunneling (TAT) mechanism indicated that with PMA, the trap energy level in the SiON film becomes shallower from 1.3 to 0.7 eV. The positive trapped charges were observed to be annihilated by PMA and the trapping sites became neutral trap centers in the SiON film. This could lead to the reduction in the leakage current component given rise to by TAT.

The properties of nanocomposite aluminium–silicon based thin films deposited by filtered arc deposition

Thin films of aluminium silicon oxynitride have been deposited on conducting (100) silicon wafers by filtered arc deposition (FAD) under nitrogen and/or oxygen gas flow. The influence of the N 2/O 2 flow ratio on the crystal structure, optical and mechanical properties has been investigated. The results of X-ray diffraction showed that the film structure comprised of an AlN crystallite with amorphous Si 3N 4 and SiO x . The optical properties over the range of 350–800 nm were measured using spectroscopic ellipsometry and found to be strongly dependent on N 2/O 2 flow ratio. The refractive index values of the films were measured to be in the range of 2.2–1.64 at a wavelength of 670 nm for oxygen flow range of 0–100%. The hardness of the films was found to be strongly dependent on the oxygen content in the film. The hardness range of the films was between 10 and 22 GPa and for the stress between 0.3 and 1.2 GPa.

Characterization of silicon oxynitride gas barrier films

New transparent gas barrier materials made of thin silicon oxynitride films deposited on polyethylene terephthalate substrates via reactive sputtering in nitrogen plasma have been developed and characterized. The gas barrier properties of these materials have been evaluated and compared with silicon oxide thin films. The oxygen transmission rates of the silicon oxynitride (SiON) films were lower than those of the SiO x films. The SiON films are amorphous and contain no pinholes or cracks. The OTR decreases when relative nitrogen content in the SiON films increases. The increase in nitrogen content causes an increase in film density.

Local structure and bonds of amorphous silicon oxynitride thin films

This work reports on the local structure and bonds of amorphous silicon oxynitride thin films, deposited by plasma enhanced chemical vapor deposition. The dependence of the structural properties and chemical bonds with the film's composition was investigated. The used analytical techniques were X-ray absorption at the Si K-edge and Fourier transform infrared spectroscopies. The coordination numbers, interatomic distances and Debye–Waller disorder factors of the Si first shell and, the bond types and the concentration of hydrogen in the films were obtained. All the analyzed data support the formation of a material's homogeneous network with a random distribution of SiO and SiN bonds. The basic structural element of the network is a tetrahedron with a central Si atom connected to N and O, consistent with a random bonding model. As the nitrogen content in the solid phase decreases the SiON 3, SiO 2N 2 tetrahedral units gradually change to SiO 4, keeping the quantity of SiO 3N tetrahedrons almost unchanged, approximately 40%. The amount of SiO 4 units is 100% for films with high oxygen content. The nitrogen is preferentially bonded to silicon and hydrogen, while the hydrogen is mostly bonded to nitrogen.

Control of dielectric cap induced band-gap shift in 1.55 μm laser structures

Silicon oxynitride (SiOxNy) thin films, deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition, have been used to induce blueshifting of the emission wavelength of 1.55 μm partial three quantum well laser structures after an annealing treatment. The SiOxNy caps had thicknesses of about 1000 Å and refractive indices ranging from 1.45 to 1.85. Room temperature photoluminescence was used to measure the magnitude of the cap-induced blueshift. It was found that the maximum blueshift occurs for an index of refraction of 1.63. Rapid thermal annealing was applied after the deposition and the importance of accurate temperature control is discussed. Finally, the role of the microwave power is analyzed and its impact on the blueshift is discussed.

Reactive pulsed laser deposition of high-k silicon dioxide and silicon oxynitride thin films for gate-dielectric applications

We have successfully developed two reactive pulsed laser deposition (PLD) processes for the growth of high-k SiO2 and SiOxNy thin films. At a KrF laser intensity of 3×108 W/cm2, both SiO2 and SiOxNy films have been deposited by ablating a silicon target in a reactive gas atmosphere (O2 and O2/N2 mixture, respectively) on both Si (100) and Pt-coated Si substrates. Two key issues are presented here, namely (i) the effect of the deposition temperature (Td in the 20–450 °C range) and (ii) the effect of the N incorporation (in the 0.3–20 at. % concentration range) on the microstructure and electrical properties of PLD SiO2 and SiOxNy thin films, respectively. For the PLD-SiO2 films, 300 °C has been identified as the optimal deposition temperature that yields stoichiometric ([O]/[Si]≈1.9), hydrogen-free films with a low local disorder, a highly dense microstructure and a dielectric constant (k) higher than that quoted for thermally grown SiO2. On the other hand, the PLD SiOxNy films containing 20 at. % of N have exhibited a dielectric constant as high as ∼7. A rather good agreement is obtained between the k values deduced from the Poole–Frenkel emission (PFE) model and those obtained from direct impedance measurements, confirming thereby that the PFE remains the predominant conduction mechanism in the PLD SiOxNy films.

Oxidation of N + implanted silicon: optical and structural properties

The optical and structural properties of oxidized silicon wafers, previously implanted with N + ions at different doses, were investigated. A decrease in oxidation rate is observed as N + ion dose increases due to the effect of incorporated nitrogen. Higher refractive index of the grown layer, deduced from spectroscopic ellipsometry, indicates the formation of silicon oxynitride thin films. X-Ray photoelectron spectroscopy shows a small amount of nitrogen in the oxidized Si region, where the nitrogen atoms are mainly bonded to silicon. The SiO vibration band at 1096 cm −1, measured by FTIR, is at the same position as that at oxidation of unimplanted silicon. No bands connected to NH and SiH vibration bonds are observed indicating low content of hydrogen in the silicon oxynitride film.

The Element Depth Profiles in Ultrathin Silicon Oxynitride Films

ABSTRACTDistribution of nitrogen in the thin silicon oxynitride films (less than 5 nm) obtained by plasma nitridation of SiO2 has been studied by non-destructive angular dependent XPS. For obtaining information about the element distribution in-depth the regularization technique has been applied. It is shown that the depth of nitrogen penetration increases with decreasing the SiO2 film thickness. In this case the maximum of the nitrogen distribution is enhanced and shifted to the Si-SiO2 interface. The results are compared with depth-profiling obtained by sputtering and wet chemical etching. The dependence of the binding energies on the film thickness has been studied. The influence of different factors on the chemical shift in the ultrathin films has been analyzed.

Chemical and morphological properties of amorphous silicon oxynitride films deposited by plasma enhanced chemical vapor deposition

The deposition of amorphous hydrogenated silicon oxynitride thin films, varying the nitrogen and oxygen content in the solid phase, is reported. The films were deposited by plasma enhanced chemical vapor deposition at different nitrous oxide/silane flow ratios, keeping constant the silane flow and the deposition temperature at 320°C. The composition of the thin films was determined by Rutherford backscattering spectroscopy (RBS) and the morphological properties were investigated by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The composition data showed that the oxygen content increases and the nitrogen content decreases, inside the films, as the ratio between the nitrous oxide flow and silane flow goes toward larger values. The oxygen ( x) plus nitrogen ( y) content in the chemical formula (a-SiO x N y ) is always close to two, suggesting that these atoms share the same atomic positions around the silicon atoms in a local structure similar to SiO 2. The SAXS results revealed the presence of scatterers with an average radius 〈 R〉 that varies from small values, like 10 Å, up to 100 Å. The TEM results showed the formation of particles with a circular cross-section, composed of Si, N and O spread in a matrix with the same elemental composition. These particles have a radius larger than 50 Å.

Investigation on optical properties of CVD films used in MOEMS applications

Low-pressure chemical vapour deposition (LPCVD) amorphous silicon oxynitride (a-SiOxNy) thin films of various compositions as well as the atmospheric pressure chemical vapour deposition (APCVD) borophosphosilicate glass (BPSG) thin films with varying phosphorus and boron contents were investigated. The dependence of the optical properties of the films on the deposition temperature and the gas flow ratio was studied by spectroellipsometry (SE) and infrared spectroscopy (IR).

Effect of nitrogen plasma conditions on electrical properties of silicon oxynitrided thin films for flash memory applications

Thin silicon oxynitride films were deposited on Si(100) substrates using nitrogen plasma at various exposure times, followed by thermal oxidation in dry O 2 without the use of toxic or global warming gases. Secondary ion mass spectroscopy measurements confirmed that nitrogen is confined to the immediate vicinity of the surface. The damage induced in the thin silicon oxynitride film after exposure to nitrogen plasma for between 10 and 60 s was estimated from an analysis of capacitance–voltage and current–voltage measurements. Generation of different densities of positive oxide charge was observed. Correlation between the local bonding structures in the oxynitride films and the electrically active defective states at the oxynitride/Si interface are also discussed. It is proposed that improved electrical characteristics such as positive charge trapping, interface state density, leakage current, and stress immunity of thin silicon oxynitride films, can be obtained by using an optimal plasma exposure time of approximately 30 s. The preliminary results obtained in this study indicate that these oxynitride films can be considered as potential candidates for ultra-thin gate oxide flash memory applications.

Mechanical properties of plasma-deposited SiOxNy coatings on polymer substrates using low load carrying capacity techniques

Amorphous hydrogenated silicon oxynitride thin films were deposited on polycarbonate by plasma-enhanced chemical vapour deposition (PECVD) using a dual mode microwave/radio frequency (MW/RF) plasma system. The film composition was adjusted by varying the nature of the silicon gas precursor (silane or hexamethyl–disiloxane), and the flow rate ratio of nitrous oxide (N2O) and ammonia (NH3). The mechanical properties of the film (residual stress, hardness and scratch resistance) were determined by means of curvature method and by low load techniques (0.1–10 mN), such as depth sensing indentation and cantilever microscratch testing. Adequate contact conditions were evaluated using a simple analytical model of stress field distribution. Coating-specific properties were determined by using a low contact load (1 mN) and a sharp indenter (2 μm tip radius). The highest scratch resistance is obtained for hard coatings possessing low internal stress.

Quantitative analysis of silicon-oxynitride films by EPMA

Thin films of silicon oxynitride with diverse compositions were prepared by de-magnetron sputtering of silicon, utilising oxygen and nitrogen gas flows and the sputtering power to vary the composition. In order to investigate the composition of these films, a method of analysis by electron probe micro analysis with energy dispersive detection was developed and the figures of merit were compared to the wavelength dispersive method used by other authors. The precision and repeatability of the results are evaluated and the accuracy is checked by comparison with Rutherford backscattering and nuclear reaction analysis. Energy dispersive X-ray spectrometry was proven to be applicable to analyse silicon oxynitride films of any composition yielding quantitative results for nitrogen and oxygen as well as silicon. Besides the good analytical performance, electron probe micro analysis with energy dispersive X-ray spectrometry has turned out to be a non-destructive, quick, easy to use and cost effective tool for the routine analysis of light elements in thin films.

Electrical characterisation of thin silicon oxynitride films deposited by low pressure chemical vapour deposition

Dielectric properties of various silicon oxynitride thin films (∼30 nm), deposited by low pressure chemical vapour deposition (LPCVD) technique, are studied by capacitance-voltage ( C– V), current-voltage ( I– V) and ageing under constant current injection ( V– t). It is found that the nitrogen-rich oxynitride layers have lower mid-gap interface trap sheet densities, lower fixed charge sheet densities and higher breakdown fields in comparison to oxygen-rich oxynitride layers. The experimental data for the dielectric constant are compared to the Bruggeman theory applied to the mix of silicon dioxide SiO 2 and silicon nitride Si 3N 4. A good agreement is obtained except for the oxygen-rich silicon oxynitride films where the SiO x N y porous structure and leakage current are responsible for errors. A Poole–Frenkel thermal-emission is shown to be the dominant conduction mechanism in the silicon oxynitride films while the leakage-current increases with increasing O/Si ratio.

Characterization of silicon oxynitride thin films by x-ray photoelectron spectroscopy

There has been a considerable effort in the past decade to incorporate nitrogen into SiO2 in order to improve the electrical properties of ultrathin (2–10 nm) gate oxides. Process conditions affect the nitrogen concentration, coordination, and depth distribution which, in turn, affect the electrical properties. X-ray photoelectron spectroscopy (XPS) is particularly well suited to obtaining the nitrogen coordination and, to a lesser extent, the nitrogen concentration in thin oxynitride films. To date, at least four different nitrogen coordinations have been reported in the XPS literature, all having the general formula: N(–SixOyHz), where x+y+z=3 and x⩽3, y⩽1, z⩽2. In this article we review the XPS literature and report on a fifth nitrogen coordination, (O)2=N–Si, with a nitrogen 1s binding energy of 402.8±0.1 eV. Next nearest neighbor oxygen atoms shifted the N(–Si)3 peak roughly 0.1 eV per oxygen atom. We also discuss results from a novel approach of determining the nitrogen areal density by XPS, the accuracy of which is dependent on the depth distribution of nitrogen. Secondary ion mass spectrometry is used to determine the depth N distribution, while nuclear reaction analysis is used to check the N concentration measured by XPS.

44.3: Inhomogeneous Thin‐Film Optical Coatings for Flat‐Panel‐Display Applications

AbstractOptical reflection filters for red, green, and blue colors for information display application could be easily fabricated by using inhomogeneous silicon oxynitride(SiON) thin films. Plasma‐enhanced chemical vapor deposition (PECVD) was used to deposit SiON thin film, A band rejection filter with its rejection peak at 490nm was designed and fabricated by the computer‐controlled PECVD.

Mechanical properties of silicon oxynitride thin films prepared by low energy ion beam assisted deposition

Silicon oxynitride (SiO x N y ) films (0.1–0.7 μm) were produced on Si (1 0 0), glass and 316L stainless steel substrates by ion beam assisted deposition (IBAD) using Si evaporation and the concurrent bombardment with a mixture of 200 eV N 2 and Ar, or O 2 and Ar ions. Adhesion was evaluated by pull-off tests. Film hardness was measured by a nanoindentation system with AFM. The measurement of internal stress in the films was carried out by the Stoney method. The film structure was examined by GXRD. XPS was employed to measure the composition of films and to analyze the chemical bonds. The dependence of mechanical properties on the film thickness and the processing temperature during deposition was studied. Finally, the relations between the mechanical properties of the films and the correlation with corrosion–protection ability of films are discussed and summarized.