Electron spin resonance study of defects in CVD-grown 3C-SiC irradiated with 2MeV protons

Electron spin resonance (ESR) was used to study defects induced by 2MeV-proton irradiation in cubic silicon carbide (3C-SiC) epitaxially grown on Si substrates by chemical vapor deposition. A new ESR signal labeled T5 was observed at temperatures lower than ≈100 K in Al doped, p-type 3C-SiC epilayers irradiated. The T5 signal has anisotropic g-values of g₁ = 2.0020 ± 0.0001, g₂ = 2.0007 ± 0.0001,and g₃ = 1.9951 ± 0.0001. The principal axes of the g-tensor were found to be along the 〈100〉 directions, indicating that the T5 center has D₂ symmetry. Isochronal annealing of the irradiated epilayers showed that the T5 center was annealed at temperatures around 150° C. A tentative model is discussed for the T5 center.     

Residual stress in silicon nitride films

The mechanical stress caused by Si₃N₄ films on (111) oriented Si wafers was studied as a function of the Si₃N₄ film thickness, deposition rate, deposition temperature and film composition. The Si₃N₄ films were prepared by the reaction of gaseous SiH₄ and NH₃ in the temperature range 700–1000°C. The curvature of the Si substrates caused by the Si₃N₄. films is related to the film stress; the substrate curvature was measured by an optical interference technique. The measured Si₃N₄. film stress was found to be highly tensile with a magnitude of about 10¹⁰ dynes/cm². For the thickness range of 2000–5000Å, there was no change in the measured stress. The total film stress was observed to decrease for decreasing deposition rate and increasing deposition temperature. A large change in film stress was observed for films containing excess Si; the stress decreased with increasing Si content. Based on published values for the thermal expansion coefficients for Si and Si₃N₄, a published value for Young’s Modulus for Si₃N₄, and the measured total stress values, a consistent argument is developed in which the total stress consists of a compressive component due to thermal expansion coefficient mismatch and a larger tensile intrinsic stress component. Both the thermal and intrinsic stress components vary with film deposition temperature in directions which decrease the total room temperature stress for higher deposition temperatures.     

Processing and characterisation of PECVD silicon nitride films

Amorphous Si-N films are synthesised from an NH₃/SiH₄ gas mixture by plasma-enhanced chemical vapour deposition (PECVD) at fixed radio frequency (13.56 MHz) and total gas pressure (34 ± 4 Torr). The variable process parameters and their ranges are: (i) substrate temperature, 200–400°C; (ii) RF power density, 0.08–0.35 W cm⁻²; (iii) NH₃/SiH₄ flow ratio, 40:400–40: 1200 ml min⁻¹. Fundamental properties of the Si-N films are characterised through elemental composition, chemical speciation, optical and electrical properties, all of which are dependent on the process parameters.     

Relaxation of a defect subsystem in silicon irradiated with high-energy heavy ions

The relaxation of a silicon defect subsystem modified by the implantation of high-energy heavy ions was studied by varying the electrical properties of irradiated Si crystal annealed at a temperature of 450°C. It is shown that quenched-in acceptors are introduced into Si crystals as a result of irradiation with comparatively low doses of Bi ions and subsequent relatively short annealing (no longer than 5 h); the distribution of these quenched-in acceptors has two peaks located at a depth of about 10 μm and at a depth corresponding approximately to the ions’ projected range (43.5 μm). The peaks in the distribution of quenched-in acceptors correspond to the regions enriched with vacancy-containing defects. As the heat-treatment duration increases, the acceptor centers are transformed into donor centers with the centers’ spatial distribution remaining intact. Simultaneously, an almost uniform introduction of quenched-in donors occurs in the entire crystal beyond the depth corresponding to the projected range of ions. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 565–569. Original Russian Text Copyright ? 2003 by Smagulova, Antonova, Neustroev, Skuratov.     

Measuring stiffnesses and residual stresses of silicon nitride thin films

The mechanical deflection of circular membranes of SiN _x is presented as a technique for measuring the stiffness and residual stress of very thin, single-layer films. The dimensions of the membranes are controlled precisely using standard photolithography, dry etching and wet etching techniques. Thicknesses vary between 0.09 μm and 0.27 μm and average diameters range between 1100 μm and 4100 μm. A Nanoindenter is used to deflect the membranes with a point force at their centers, and to continuously record the applied forces and the resulting deflections. The analysis of the force-deflection data yields the values of Young’s moduli and residual stresses for the films.     

Analyses for stoichiometry and for Hydrogen and Oxygen in silicon nitride films

Optical, ion, and electron probe techniques can be effectively applied to analyze for H, O, and the Si/N ratio in thin films of silicon nitride. The films studied were formed by chemical-vapor deposition or plasma deposition for application as a gate dielectric in semiconductor memory devices and for circuit encapsulation. The H concentration is measured by the multiple internal reflection technique which detects NH and SiH vibrational modes. A decrease in SiH bonding with an increase in deposition temperature is shown for chemical-vapor-deposited silicon nitride, and a very high concentration of SiH bonds is observed in plasma-deposited silicon nitride. Ion back-scattering analysis is a direct method for measuring the Si/N ratio and a related nuclear reaction analysis technique is a direct method for measuring and profiling the O content. Backscattering analysis shows a significantly larger Si/N ratio for plasma than for chemical-vapor-deposited silicon nitride. The O profile obtained by reaction analysis for a nitride/oxide/Si structure is compared to that obtained by sputter Auger electron spectroscopy, and the results show that O concentrations down to ∼0.5 at % can be measured by either technique. Auger analysis gives better depth resolution than reaction analysis but it requires a calibration standard. Auger results also show N penetration of interfacial SiO2and accumulation of N at the Si-SiO2interface.     

Passivation of GaAs FET's with PECVD silicon nitride films ofdifferent stress states

The passivation of GaAs MESFETs with plasma-enhanced chemical-vapor-deposited (PECVD) silicon nitride films of both compressive and tensile stress is reported. Elastic stresses included in GaAs following nitride passivation can produce piezoelectric charge density, which results in a shift of MESFET characteristics. The shift of MESFET parameters due to passivation was found to be dependent on gate orientation. The experiments show that nitride of tensile stress is preferable for MESFETS with [011-bar] oriented gates. The shifts in V_TH,I_DSS, and G_M of the devices before and after nitride passivation are less than 5% if the nitride of appropriate stress states are used for passivation. The breakdown voltage of the MESFETs after nitride deposition was also studied. It is found that the process with higher hydrogen incorporation tends to reduce the surface oxide and increase the breakdown voltage after nitride deposition. In addition, the passivation of double-channel HEMTs is reported for the first time     

Nonempirical simulation of chemical deposition of silicon nitride films in CVD reactors

This work is devoted to the atomistic simulation of chemical vapor deposition (CVD) of thin silicon nitride films from the mixture of dichlorosilane (DCS) and ammonia in CVD reactors. The earlier developed chemical mechanism is substantially extended by including the reactions of catalytic decomposition of DCS, and a self-consistent atomistic model of a CVD process is developed. An extended chemical mechanism is constructed and analyzed that allows one to adequately describe kinetic processes in a gas phase within the ranges of temperature, pressure, and the DCS: NH₃ ratio of original reactants, that are characteristic of silicon nitride deposition. An effective kinetic model is developed that involves the calculation of the rate constants and the concentrations of the gas mixture components. A thermodynamic analysis of the surface coverage by various chemisorbed groups is carried out, and equilibrium surface concentrations are obtained for the main chemisorbed groups. Practically significant conclusions are made about the character of the deposition process and, in particular, about the role of the extended chemical mechanism.     

Structure and photoluminescence properties of InN films grown on porous silicon by MOCVD

In this work, indium nitride (InN) films were successfully grown on porous silicon (PS) using metal oxide chemical vapor deposition (MOCVD) method. Room temperature photoluminescence (PL) and field emission scanning electron microscopy (FESEM) analyses are performed to investigate the optical, structural and morphological properties of the InN/PS nanocomposites. FESEM images show that the pore size of InN/PS nanocomposites is usually less than 4 μm in diameter, and the overall thickness is approximately 40 μm. The InN nanoparticles penetrate uniformly into PS layer and adhere to them very well. Nitrogen (N) and indium (In) can be detected by energy dispersive spectrometer (EDS). An important gradual decrease of the PL intensity for PS occurs with the increase of oxidation time, and the PL intensity of PS is quenched after 24 h oxidization. However, there is a strong PL intensity of InN/PS nanocomposites at 430 nm (2.88 eV), which means that PS substrate can influence the structural and optical properties of the InN, and the grown InN on PS substrate has good optical quality.     

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part II: effect of nitrogen plasma parameters on layer characteristics

In Part I we reported the results of an emission spectroscopic study of the plasma obtained in an SiH₄–N₂–Ar mixture. It was shown that argon in metastable electronic excited states provides a high concentration of atomic nitrogen. In this part we report the results of a study of the influence of argon dilution on the growth rate, composition and properties of silicon nitride films. The exact influence of nitrogen dilution with argon depends on the process parameters and on the method of coupling of the RF power, but it is found in general that a high concentration of atomic nitrogen leads to changes in the relative amounts of Si–H_j and N–H_i bonds and in the Si/N ratio of deposited films. In particular, it is shown that hydrogen incorporation can be reduced and improved stoichiometry can be obtained. © 1998 John Wiley & Sons, Ltd.     

Investigation of electrical properties of MOS structures with silicon nitride films doped with rare earth elements

One of the main problems of MOS devices in electronics is improving the stability of their characteristics. This problem is considered in this work. This solution is ensured by a decrease in the density of the surface states due to the use of silicon nitride films doped with rare earth elements as a tunneling and barrier layer and due to use of SiGe and Ge solid solutions as a storage medium of nanoclusters. CV-studies of the electrophysical parameters of MOS structures of Me-Si₃N₄ (rare earth elements)-Ge(SiGe)-Si₃N₄ (rare earth elements)-nSi nanoclusters, where rare earth elements with a different atomic radius are used as alloying components, are performed. The regularity of the influence of the atomic radius of rare earth elements on the electrical characteristics of MOS structures is revealed.     

Remote plasma-enhanced CVD of silicon nitride films: effects of diluting nitrogen with argon. Part I: effect on nitrogen plasma parameters studied by emission spectroscopy

In a series of two papers we describe the effect of argon dilution of the nitrogen passed through the RF discharge region on the plasma composition, growth rate and some characteristics of silicon nitride films deposited by remove PECVD. In this part we report the results of an emission spectroscopic study of the plasma obtained in an SiH₄–N₂–Ar mixture. It is shown that argon in metastable electronic excited states plays an important role during the RPECVD of silicon nitride films by providing a high concentration of atomic nitrogen which is necessary for the promotion of film growth. In Part II the influence of argon dilution on the growth rate, composition and some properties of silicon nitride films deposited by capacitively and inductively coupled remote PECVD is discussed. © 1998 John Wiley & Sons, Ltd.     

Transient photocurrent and photoluminescence in porous silicon

Transient photocurrent in porous silicon samples subjected to prolonged storage in air has been studied using the time-of-flight technique at temperatures in the range 300–350 K and electric field strengths of 10⁴–10⁵ V/cm. Photoluminescence has been studied in the same samples at T=300 K using time-resolved spectroscopy. A conclusion is made on the basis of comparison of the data obtained that localized states play important part in both the processes at characteristic times of these processes falling within the microsecond range.     

Photoemission spectroscopy of heterojunctions of amorphoushydrogenated silicon with silicon oxide and nitride

A study of the growth and electronic structure of a-Si:H/a-SiN_x:H and a-Si:H/a-SiO_x:H heterojunctions by photoemission spectroscopy is discussed. The interfaces in a-Si:H/a-SiO_x are atomically abrupt, except for the SiO_x on the Si interface which is graded over ~3 Å due to plasma oxidation. The offset energies between the a-Si:H valence band and those of a-SiN_x:H and a-SiO_x:H are 1.2 and 4.0 eV, respectively. Extra H(~2×10¹⁵) is incorporated in the Si on the SiN_x interface region. The hole wave functions in a-Si:H are localized on a scale of 1-2 interatomic distances     

Monoisotopic silicon 28Si in spin resonance spectroscopy of electrons localized at donors

The fine structure of the spectra of a shallow-level Li donor center and a Fe⁰ deep donor (S = 1), which occupy tetrahedral interstices in a silicon lattice, is studied in monoisotopic silicon ²⁸Si due to considerable narrowing of the lines of ESR spectra. In the case of the Li donor center, experimental data are found to confirm the role of internal strains in the crystal when observing the ESR spectra of the ground state 1s T ₂ and state E at T = 3.8–10 K with g < 2.000. The anisotropy in the distribution of strains, which turned out to have a tetragonal type, is investigated using the angular dependences of the line width of the spin resonance corresponding to the triplet state T _2z of Li. Similar anisotropy is found in the case of the introduction of Fe⁰ ions into the initial crystals based on the theory of angular dependences of the width of ESR lines caused by the transitions ?1 → 0 and 0 → +1 (ΔM _s = 1) in comparison with the transition ?1 → +1 (ΔM _s = 2).     

Heteroepitaxial silicon-carbide nitride films with different carbon sources on silicon substrates prepared by rapid-thermal chemical-vapor deposition

Cubic crystalline silicon-carbon nitride (Si_1−x−yC_xN_y) films have been grown successfully using various carbon sources by rapid-thermal chemical-vapor deposition (RTCVD). The characteristics of the Si_1−x−yC_xN_y films grown with SiH₃CH₃, C₂H₄, and C₃H₈ are examined and compared by x-ray photoelectron spectroscopy (XPS) spectra, scanning electron microscopy (SEM) images, and transmission electron microscopy (TEM) patterns. The XPS spectra show that the differences of chemical composition and chemical-bonding state are co-related to the C bonding type of the different carbon source. The SEM images and TEM analysis indicate that the better Si_1−x−yC_xN_y film can be obtained using C₃H₈ gas as the carbon source. In addition, correlations between the growing stages to the microstructure of the cubic-crystalline Si_1−x−yC_xN_y films have been illustrated in detail.     

Mechanism of the subband excitation of photoluminescence from erbium ions in silicon under high-intensity optical pumping

The photoluminescence (PL) excitation spectra of erbium and band-to-band silicon in Si:Er/Si epitaxial structures under high-intensity pulsed optical excitation are studied. It is shown that the nonmonotonic dependence of the PL intensity on the excitation wavelength ??_ex near the absorption edge of silicon is due to inhomogeneity in the optical excitation of the Si:Er active layer. The sharp rise in the erbium PL intensity in the spectral range ??_ex = 980?1030 nm is due to an increase in the excited part of the Si:Er emitting layer on passing to subband light pumping (??_ex > 980 nm) with a low absorption coefficient in silicon because of the effective propagation of the excitation light in the bulk of the structures under study. It is shown that, under the subband optical pumping of Si:Er/Si structures, as also in the case of interband pumping, the exciton mechanism of erbium ion excitation is operative. Excitons are generated under the specified conditions as a result of a two-stage absorption process involving impurity states in the band gap of silicon.     

Effects of nitrogen and argon as carrier gases and annealing ambients on the physical properties of PECVD silicon nitride

Deposition of memory quality plasma-enhanced chemically vapor deposited silicon nitride and post-deposition modification by annealing using argon and nitrogen for carrier gases and annealing ambients have been studied. Although similar memory performance can be achieved, the deposition power and NH₃/SiH₄ ratio required to do so are functions of the carrier gas used since nitrogen actively participates in the deposition process. Fourier transform infrared, ultraviolet and Auger data reveal that materials deposited with the two gases have similar physical properties although argon films are less dense and lose hydrogen at a higher rate when subjected to annealing. Post-deposition annealing can be used to enhance memory properties of the material provided that the anneal is accomplished at 475°C for 30 minutes. However, enhancement of memory performance by annealling occurs only if the nitride has been deposited using optimum deposition parameters. When annealing is performed in nitrogen. Auger data suggest that nitrogen can be supplied to, or removed from, the material depending on the anneal temperature.