Effect of si—h and n—h bonds on electrical properties of plasma deposited silicon nitride and oxynitride films

Strong correlations were observed between the improvement in the metal-insulator-semiconductor (MIS) (aluminum-nitride-semiconductor) electrical properties of plasma deposited silicon nitride and oxynitride films and their (Si—H/N—H) bonding ratios in the film bulk. Total hydrogen concentration and spin density of all deposited films decreased with post-deposition annealing. Films with more Si—H bonds and stable (Si—H/ N—H) ratios generally have lowerV _fb shift, less positive trap charge and higher breakdown dielectric strength. Silicon oxynitride films with refractive indices of 1.75-1.80, as-deposited and after annealing in forming gas (10% H₂ + 90% N₂) at various temperatures, were found to have stable (Si—H/N—H) bonding ratios, lower silicon dangling bond density, and better MIS electrical properties compared to other plasma deposited nitride and oxynitride films.     

Electrical characterization of hafnium oxide and hafnium-rich silicate films grown by atomic layer deposition

An electrical characterization comparative analysis between Al/HfO₂/n-Si and Al/Hf-Si-O/n-Si samples has been carried out. Hafnium-based dielectric films have been grown by means of atomic layer deposition (ALD). Interface quality have been determined by using capacitance–voltage (C–V), deep level transient spectroscopy (DLTS) and conductance transient (G-t) techniques. Our results show that silicate films exhibit less flat-band voltage shift and hysteresis effect, and so lower disordered induced gap states (DIGS) density than oxide films, but interfacial state density is greater in Hf–Si–O than in HfO₂. Moreover, a post-deposition annealing in vacuum under N₂ flow for 1 min, at temperatures between 600 and 730 °C diminishes interfacial state density of Hf–Si–O films to values measured in HfO₂ films, without degrade the interface quality in terms of DIGS.     

Hydrogen in MOSFETs – A primary agent of reliability issues

Hydrogen plays an important role in MOSFETS as it is intentionally introduced to passivate defects (primarily Si dangling bonds) at the Si–SiO₂ interface. At the same time, hydrogen has long been known to be involved in many degradation processes, with much attention being devoted recently to bias-temperature instability (BTI). Here, we give an overview of extensive theoretical results that provide a comprehensive picture of the role that hydrogen plays in several radiation-induced degradation modes and BTI. We identify a common origin for several degradation phenomena: H is released as H⁺ by holes either in the oxide or in Si and is driven to the interface by a positive or negative bias, respectively, where it depassivates dangling bonds via the formation of H₂ molecules. We close with a note about the role of hydrogen as a main agent for aging of microelectronics.     

Vibrational spectroscopy characterization of low-dielectric constant SiOC:H films prepared by PECVD technique

Low-dielectric constant SiOC:H films were prepared by plasma enhanced chemical vapour deposition (PECVD) from trimethyl-silane (H–Si–(CH₃)₃) and ozone (O₃) gas mixture. The samples were preliminarily annealed at 400 °C in N₂ atmosphere and then in N₂+He plasma. Afterwards, they were treated in vacuum at some fixed temperatures in the range between 400 and 900 °C. Structural investigations of the annealed films were carried out by means of vibrational spectroscopy techniques. FT-IR spectrum of a preliminarily treated sample shows absorption bands due to stretching modes of structural groups like Si–CH₃ at 1270 cm⁻¹, Si–O–Si at 1034 cm⁻¹ and C–H_x in the region between 2800 and 3000 cm⁻¹. No significant spectral change was observed in the absorption spectra of samples annealed up to 600 °C, indicating that the preliminarily treated film retains a substantial structural stability up to this temperature. Above 600 °C, absorption spectra show a strong quenching of H-related peaks while the band due to Si–O–Si anti-symmetric stretching mode shifts towards higher energy, approaching the value observed for thermally grown SiO₂. Raman spectra of samples treated at temperatures T500 °C exhibit both D and G bands typical of sp²-hybridised carbon, due to the formation of C–C bonds within the film which is accompanying the release of hydrogen. The intensity of D and G bands becomes more pronounced in samples annealed at higher temperatures, thus suggesting a progressive precipitation of carbon within the oxide matrix.     

Silicon oxynitride integrated waveguide for on-chip optical interconnects applications

This work explores the microfabrication technology for realizing miniature waveguide structure for on-chip optical interconnects applications. Thick oxynitride films were prepared by plasma enhanced chemical vapor deposition (PECVD) with N₂O, NH₃ and SiH₄ precursors. The composition and the bonding structure of the oxynitride films were investigated with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy. Results showed that the silicon oxynitride deposited with gas flow rates of NH₃/N₂O/SiH₄ = 10/400/10 (sccm) has favorable properties for integrated waveguide applications. The refractive index of this layer is about 1.5 and the layer has comparative low densities of O–H and N–H bonds. The hydrogen bonds can be further eliminated with high temperature annealing of the as-deposited film in nitrogen ambient and the propagation loss can be reduced significantly with thermal annealing. An integrated miniature waveguide with cross-section of 2 μm × 3 μm was realized with the proposed technology. The waveguide is able to transmit signal in either TE or TM mode with propagation loss <0.6 dB/cm (at 1550 nm) and bending radius of about 6 μm.     

The influence of vacuum annealing temperature on the fundamental absorption edge and structural relaxation of <Emphasis Type="Italic">a</Emphasis>-SiC:H films

The effect of vacuum annealing temperature on the characteristics of the fundamental absorption edge and short-range order reconstruction in amorphous hydrogenated silicon carbide (a-SiC:H) films obtained by magnetron sputtering of silicon in an Ar/CH₄ mixture is experimentally investigated. It is shown that redistribution of chemically bound hydrogen occurs at low annealing temperatures (450°C). This redistribution is determined by (i) breakage of silicon-hydrogen bonds and (ii) trapping of atomic hydrogen by carbon dangling bonds. These processes lead to an enhancement of visible photoluminescence. Breakage of carbon-hydrogen bonds and clusterization of amorphous carbon occur at higher annealing temperatures. The proposition that the main nonradiative recombination centers in a-SiC:H films are electronic states related to the carbon dangling bonds is justified.     

Applications of DCIV method to NBTI characterization

The DCIV method was applied to investigate negative bias temperature instability (NBTI) in SiO₂ gate oxides. The DCIV technique, which measures the interface defect density independently from bulk oxide charges, delineates the contribution of the interface defect generation to the overall NBTI measured by the threshold voltage shift, ΔV_TH. The DCIV results obtained during both stress and relaxation phases are generally consistent with the main features of the reaction–diffusion (R–D) model, which suggests positive charge generation/annealing at the Si/SiO₂ interface due to breaking/re-passivation of the Si–H bonds. These results are in agreement with the spin-dependent recombination (SDR) experiments, which reflect the density of the Si dangling bonds at the Si/SiO₂ interface (P_b centers) and its vicinity (E′ centers). Comparison of degradation kinetics as measured by DCIV, charge-pumping, and I_D − V_G (ΔV_TH) techniques, however, suggests that ΔV_TH includes additional contributions, most likely from the oxide bulk charges. For comparison, an NBTI study was also performed on the high-k HfO₂/SiO₂ gate stacks. After adjusting for the high-k related contribution, similar kinetics of the long-term stress interface trap generation was observed in SiO₂ and high-k gate stacks suggesting a common mechanism of the interface degradation.     

Correlation between infrared transmission spectra and the interface trap density of SiO2 films

This work is an attempt to estimate the electrical properties of SiO₂ thin films by recording and analyzing their infrared transmission spectra. In order to study a big variety of films having different infrared and electrical properties, we studied SiO₂ films prepared by low pressure chemical vapor deposition (LPCVD) from SiH₄ + O₂ mixtures at 425 °C and annealed at 750 °C and 950 °C for 30 min. In addition thermally grown gate quality SiO₂ films of similar thickness were studied in order to compare their infrared and electrical properties with the LPCVD oxides. It was found that all studied SiO₂ films have two groups of Si–O–Si bridges. The first group corresponds to bridges located in the bulk of the film and far away from the interfaces, the grain boundaries and defects and the second group corresponds to all other bridges located near the interfaces, the grain boundaries and defects. The relative population of the bulk over the boundary bridges was found equal to 0.60 for the LPCVD film after deposition and increased to 4.0 for the LPCVD films after annealing at 950 °C. Thermally grown SiO₂ films at 950 °C were found to have a relative population of Si–O–Si bridges equal to 3.9. The interface trap density of the LPCVD film after deposition was found equal to 5.47 × 10¹² eV⁻¹ cm⁻² and decreases to 6.50 × 10¹⁰ eV⁻¹ cm⁻² after annealing at 950 °C for 30 min. The interface trap density of the thermally grown film was found equal to 1.27 × 10¹¹ eV⁻¹ cm⁻² showing that films with similar Si–O–Si bridge populations calculated from the FTIR analysis have similar interface trap densities.     

A comprehensive electron paramagnetic resonance study of influence of annealing on defect center in phosphorus ion-implanted C60 films

Electron paramagnetic resonance (EPR) measurements have been performed to investigate the effect of annealing on paramagnetic defect center in P⁺-implanted C₆₀ films, in order to control and improve the electronic properties of the implanted films towards photovoltaic applications. We have found a reduction in the dangling bond density upon annealing by approximately a one order of magnitude, in the temperature range between 100°C and 700°C, regardless of the annealing media whether vacuum or forming gas (N₂/H₂). The reduction in spin defect density was ascribed to the decrease in disordered dangling bond as a consequence of the reconstruction of the less stable defect sites. Indeed the modification in the spin density is accompanied with an improvement in the electrical conductivity and band structure of the films. Also, in the annealed carbon films, a correlation was observed among linewidth, relaxation times, and optical gap. In addition, we report about the temperature dependence of the linewidth, signal intensity and the susceptibility of annealed films. The susceptibility follows the Curie-law at sufficiently low temperature, while above 180 K a deviation was observed. The prime novelty of this study is that it is the first EPR study of effects of annealing on defect center in P⁺- implanted C₆₀ films.     

The influence of hydrogen and nitrogen on the formation of Si nanoclusters embedded in sub-stoichiometric silicon oxide layers

This work reports the study concerning the influence of the preparation conditions on the structure of silicon rich oxide (SRO) deposited by PECVD method by which the structural properties of the film are strictly related. In particular we investigated the role of reactant gases N₂O and SiH₄ on the total Si concentration, Si excess concentration, Si clustered concentration and size of nanoclusters formed by high annealing temperature. We payed particular attention on the role of the hydrogen and nitrogen during the Si agglomeration.The presence of hydrogen atoms on the as-deposited specimen, confirmed by the Si–H bonds peak on the FTIR analysis, has been directly correlated to the silicon excess concentration in the layer. The silicon, oxygen and nitrogen atomic density has been calculated from RBS analysis. These information were coupled to the ones obtained using methodology based on electron energy loss spectroscopy combined with energy filtered images, which allowed us to quantify the clustered silicon concentration in annealed sub-stoichiometric silicon oxide layers (SiO_x). We have verified that the nitrogen dissolved in the layer inhibits the Si excess clustering so that the efficiency of silicon agglomeration process decreases as the nitrogen content increases.     

Optical dispersion analysis within the IR range of thermally grown and TEOS deposited SiO2 films

SiO₂ thin films, with thickness ranging between approximately 13 and 95 nm, have been thermally grown at 950°C in dry oxygen and chemically vapor deposited at low pressures (0.3 Torr) by decomposition of tetraethylorthosilicate (TEOS) at 710°C, on Si (100) substrates. Dispersion analysis was performed on Fourier transform infrared (FTIR) transmission spectra of these films within the range 900–1400 cm⁻¹. It was found that the spectra were best described within this range, by four Lorentz oscillators located near 1060, 1089, 1165 and 1220 cm⁻¹ almost independent of film thickness. The polarization of the oscillators (proportional to their strength) was found to increase slightly, and their widths to decrease, with film thickness. From the study of the FTIR spectra obtained at room temperature, it was suggested that at this temperature, a considerable number of Si–O–Si angles in these SiO₂ films are distributed in a way expected at higher temperatures and that the distribution of the Si–O–Si angles depends on the thermal history of the film and the method of growth.     

Photoluminescence properties and chemical bond variations of SiN x :H films with silicon quantum dots

Hydrogenated silicon nitride(SiNx :H) thin films are deposited on p-type silicon substrates by plasma enhanced chemical vapor deposition(PECVD) using a gas mixture of ammonia and silane at 230 °C.The chemical compositions and optical properties of these films,which are dealt at different annealing temperatures,are investigated by Fourier transform infrared(FTIR) absorption spectroscopy and photoluminescence(PL) spectroscopy,respectively.It is shown that the FTIR presents an asymmetric Si-N stretching mode,whose magnitude is enhanced and position is shifted towards higher frequencies gradually with the increase of the annealing temperature.Meanwhile,it is found that the PL peak shows red shift with its magnitude decreasing,and disappears at 1100 °C.The FTIR and PL spectra characteristics suggest that the light emission is attributed to the quantum confinement effect of the carriers inside silicon quantum dots embedded in SiNx : H thin films.     

Characterization of interface defects related to negative-bias temperature instability in ultrathin plasma-nitrided SiON/Si1 0 0 systems

Interface defects related to negative-bias temperature instability (NBTI) in an ultrathin plasma-nitrided SiON/Si1 0 0 system were characterized by using conductance–frequency measurements, electron-spin resonance measurements, and synchrotron radiation X-ray photoelectron spectroscopy. It was confirmed that NBTI is reduced by using D₂-annealing instead of the usual H₂-annealing. Interfacial Si dangling bonds (P_b1 and P_b0 centers) were detected in a sample subjected to negative-bias temperature stress (NBTS). Although we suggest that NBTS also generates non-P_b defects, it does not seem to generate nitrogen dangling bonds. These results show that NBTI of the plasma-nitrided SiON/Si system is predominantly due to P_b depassivation. Plasma nitridation was also found to increase the P_b1/P_b0 density ratio, modify the P_b1 defect structure, and increase the latent interface trap density by generating Si suboxides at the interface. These changes are likely to be the causes of NBTI in ultrathin plasma-nitrided SiON/Si systems.     

Effect of annealing in an atomic-hydrogen atmosphere on the properties of amorphous hydrated silicon films and the parameters of p-i-n structures based on them

The decrease in the density of dangling silicon-silicon bonds in a-Si:H films as a result of annealing in an atomic-hydrogen atmosphere is determined by their density in the initial (nonannealed) film. The change in the total hydrogen density in a-Si:H films, annealed in an atomic-hydrogen atmosphere, is determined by the type of silicon-hydrogen bonds and the impurity content: The hydrogen content can decrease to 1 at. % in the presence of monohydride bonds (2020 cm⁻¹) and no change is observed in the hydrogen content in the presence of oxygen (≲0.1 at. %). A decrease in the defect density as a result of annealing in an atomic-hydrogen atmosphere is observed for all films. The Staebler-Wronski effect — AM-1 irradiation for 10 h — is observed for all films irrespective of the total hydrogen density, the type of silicon-hydrogen bonds, and the presence of oxygen. Fiz. Tekh. Poluprovodn. 32, 620–626 (May 1998)     

Spectroscopic ellipsometry characterization of ZrO2 thin films by nitrogen-assisted reactive magnetron sputtering

Spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of high-k ZrO₂ thin films on Si(1 0 0) substrates prepared by nitrogen-assisted, direct current reactive magnetron sputtering. The Tauc–Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films as a function of annealing temperature. Excellent agreement has been found between the SE fitting results and X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) results, indicating that our model adequately described the measured SE data. Optical band gaps (E_g) were also obtained based on the extracted absorption edge. Our results suggest that nitrogen-assisted process can effectively limit the interfacial layer growth in high-k oxides.     

Mechanical stress in PECVD a-SiC:H: aging and plasma treatments effects

Hydrogenated amorphous silicon carbide (a-SiC:H) deposited by PECVD is one of the most promising dielectric diffusion barrier available in Cu—Ultra low k interconnections due to its low dielectric constant and good barrier ability. In this work, the mechanical stress evolution with time of a-SiC:H film exposed to room atmosphere is studied and compared with the behavior observed on other PECVD dielectrics (SiN, SiO₂, SiCN). For as-deposited a-SiC:H samples, a strong stress evolution with time toward compression is observed and the results are interpreted mainly in terms of surface reactivity and silanol buildup. Infrared spectroscopy analysis allows to confirm that the mechanical stress evolution and the OH content are linked. An oxidation of the hydrogenated amorphous silicon carbide film with time is also observed. Different plasma treatments (He, O₂ or H₂) are tested on a-SiC:H films to limit the stress drift with time. Each plasma treatments are able to limit the stress evolution of a-SiC:H films but the mechanisms are different in each case: densification of the film with He plasma treatment, formation of a dense oxide at the surface with O₂ plasma treatment and passivation of dangling bonds with H₂ plasma treatment.     

Phase Formation during the Surface-Diffusion Growth of Ti–Co–Si–N and Ti–Co–N Thin Films on Si and SiO2

The kinetics of phase formation in Ti–Co–Si–N and Ti–Co–N thin films on Si and SiO₂is investigated experimentally. With the deposition on Si, rapid thermal annealing (T 900°C) is shown to cause phase separation that ends in a TiN/CoSi₂/Si structure. If SiO₂is used, the alloy reacts with the substrate to produce compounds that are difficult to remove with selective etchants. This limits the potential uses of this process in the fabrication of contact systems for CMOS devices. It is shown that structure- and phase-dissimilar films can be formed on Si and SiO₂by means of the surface-diffusion reactions between a Ti–Co–Si–N or Ti–Co–N alloy and the substrate at 650–700°C. The effect of a TiN, Ti, or CoSi₂thin layer at the alloy–substrate interface on the phase separation is investigated.     

Thermal stability of high-k Er-silicate gate dielectric formed by interfacial reaction between Er and SiO2 films

We fabricated a high-k Er-silicate gate dielectric using interfacial reaction between Er and SiO₂ films and investigated its thermal stability. The reduced capacitance with increasing annealing temperature is associated with the chemical bonding change of Er-silicate from Er-rich to Si-rich, induced by a reaction between Er-silicate and Si during thermal treatment. Further an increase in the annealing temperature (>500 °C) causes the formation of Si dangling bonds, which is responsible for an increased interface trap density.     

Density functional theory applied to the calculation of dielectric constant of low-k materials

The interest of low-k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits is well known in the semiconductor industry. The use of these materials (especially hydrogen silsesquioxane (HSQ) and methyl silsesquioxane (MSQ): intermetal dielectric applications in the back end of line fabrication) leads to a reduction of the dielectric constant from k4 in a traditional intermetal dielectric material of silicon dioxide to a value of 2.5–3. The physical difference between HSQ or MSQ and a-SiO₂ is the presence of Si–H bonds (for HSQ) or Si–CH₃ bonds (for MSQ) and the density of the material. A theoretical calculation of bond polarizability (Si–H or Si–CH₃) associated to experimental values of electric dipole densities can lead, using the Clausius-Mossotti relationship, to the calculation of the dielectric constant. After validation of the calculation methods both on simulation and experimental values, it is shown that for a constant density, the difference between the materials could be due to the bond polarizability and furthermore that this difference accounts, in part, for the value of dielectric constant. Consequently, even if densification remains the main parameter explaining low-k values, the polarizability of building units of these materials is not negligible.     

Bond strain and defects at interfaces in high-k gate stacks

The performance and reliability of aggressively-scaled field effect transistors are determined in large part by electronically-active defects and defect precursors at the Si–SiO₂, and internal SiO₂–high-k dielectric interfaces. A crucial aspect of reducing interfacial defects and defect precursors is associated with bond strain-driven bonding interfacial self-organizations that take place during high temperature annealing in inert ambients. The interfacial self-organizations, and intrinsic interface defects are addressed through an extension of bond constraint theory from bulk glasses to interfaces between non-crystalline SiO₂, and (i) crystalline Si, and (ii) non-crystalline and crystalline alternative gate dielectric materials.