Growth Of Silicon Nitride Films Research Articles

Reactions of NH3 on high-temperature silicon surface and structure evolution during silicon nitride film growth

Temperature and dosage-dependent reactions of NH3 on the Si(111)-(7 × 7) surface have been studied by low-temperature scanning tunneling microscopy. It was found that the surface reaction exhibited three different dissociative adsorption channels as the temperature increases at low exposure. Under the condition of high exposure, the amorphous structure of silicon nitride film gradually transformed into an ordered phase, with the increase of substrate temperature, and finally presented an 8/3 × 8/3 structure. This means that both exposure and temperature are critical for forming an ordered surface structure. Furthermore, many adsorbates were observed on the nitride region during the growth process, which is believed to be the intermediate reactants in the nitridation reaction and consumed in the subsequent annealing process to form an orderly and clean surface morphology.

Microscopic mechanisms of Si(111) surface nitridation and energetics of Si3N4/Si(111) interface

Nitridation of silicon surface is an important step in GaN or AlN nanostructures growth process which determines quality of fabricated devices. In this work modeling of gas-surface reaction of the Si(111) surface nitridation was performed using density functional theory calculations. We show that interface structure corresponding to first stoichiometric Si3N4 monolayer may be generated in a great number of different ways by means of vacancy-assisted mechanism. The nearly continuum distribution of total energies may be associated with such structures formed after exothermic reaction with considerable energy gain. Nevertheless founded global minimum corresponds to abrupt interface and crystalline-like Si3N4 monolayer structure. Suggested mechanism of silicon nitride film growth is based on the calculated energy barriers for diffusion of volatile species such as N, N2, SiN and SiN2 which are building blocks for the growth of Si3N4 film. At first stage atomic nitrogen diffusion from vacuum to substrate occurs. Then silicon vacancies in substrate and volatile SiN radicals are formed. The back diffusion of SiN from substrate to Si3N4-vacuum side is the main mechanism responsible for silicon nitride film growth.

A mathematical model and simulation results of plasma enhanced chemical vapor deposition of silicon nitride films

We developed a mathematical model of Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon nitride thin films from SiH4-NH3-N2-Ar mixture, an important application in modern materials science. Our multiphysics model describes gas dynamics, chemical physics, plasma physics and electrodynamics. The PECVD technology is inherently multiscale, from macroscale processes in the chemical reactor to atomic-scale surface chemistry. Our macroscale model is based on Navier-Stokes equations for a transient laminar flow of a compressible chemically reacting gas mixture, together with the mass transfer and energy balance equations, Poisson equation for electric potential, electrons and ions balance equations. The chemical kinetics model includes 24 species and 58 reactions: 37 in the gas phase and 21 on the surface. A deposition model consists of three stages: adsorption to the surface, diffusion along the surface and embedding of products into the substrate. A new model has been validated on experimental results obtained with the "Plasmalab System 100" reactor. We present the mathematical model and simulation results investigating the influence of flow rate and source gas proportion on silicon nitride film growth rate and chemical composition.

Parametrization of the Stillinger-Weber potential for Si/N/H system and its application to simulations of silicon nitride film deposition with SiH4/NH3

We determined the Stillinger-Weber interatomic potential parameters for Si/N/H system based on first principles density functional calculations. This new potential can be used to perform classical molecular dynamics simulation for silicon nitride deposition on Si substrate. During the first principles calculations, cluster models have been carefully and systematically chosen to make sampling of the interatomic potential supersurface more thoroughly. Global optimization method was used to fit the ab initio data into Stillinger-Weber form. We used a recursive method to perform the classical molecular dynamics simulations for silicon nitride (SiN) film growth on Si substrate with SiH4/NH3 gas mixtures. During the simulation, we could clearly observe the silicon nitride film growth progress. In this paper, we present the details of potential derivation and simulation results with different SiH4:NH3 ratios. It is demonstrated that this new potential is suitable to describe the surface reactions of the Si/N/H system and allows us to explore more complex SiN growing process such as plasma-enhanced chemical vapor deposition.

Growth of silicon nitride films by bombarding amorphous silicon with N+ ions: MD simulation

In this study, the molecular dynamics simulation method was employed to investigate the growth of silicon nitride films by using N+ ions, with energies of 50, 100, 150 and 200eV, to bombard an amorphous silicon surface at 300K. After an initial period of N+ bombardment, saturation of the number of N atoms deposited on the surface is observed, which is in agreement with experiments. During subsequent steady state deposition, a balance between uptake of N by the surface and sputtering of previously deposited N is established. The Si(Nx) (x=1–4) and N(Siy) (y=1–3) bond configurations in the grown films are analyzed.

Plasma diagnostic study of silicon nitride film growth in a remote Ar–H2–N2–SiH4 plasma: Role of N and SiHn radicals

A remote expanding thermal plasma operated on an Ar–H2–N2–SiH4 mixture has been studied by several plasma diagnostics to obtain insight into the plasma processes and the hydrogenated amorphous silicon nitride (a-SiNx:H) growth mechanism from the N2–SiH4 reactant mixture. From Langmuir probe measurements, ion mass spectrometry, and threshold ionization mass spectrometry, it is revealed that the Ar–H2–N2 operated plasma source leads mainly to N and H radicals in the downstream region. The H radicals react with the SiH4 admixed downstream creating a high SiH3 density as revealed by cavity ringdown spectroscopy. By cavity ringdown measurements, it is also shown that Si and SiH have a much lower density in the downstream plasma and that these radicals are of minor importance for the a-SiNx:H growth process. The ground-state N radicals from the plasma source do not react with the SiH4 injected downstream leading to a high N density under the a-SiNx:H deposition conditions as revealed by threshold ionization mass spectrometry. From these results, it is concluded that N and SiH3 radicals dominate the a-SiNx:H growth process and the earlier proposed growth mechanism of a-SiNx:H from the N2–SiH4 mixture [D. L. Smith et al., J. Vac. Sci. Technol. B 8, 551 (1990)] can be refined: During deposition, an a-Si:H-like surface layer is created by the SiH3 radicals and at the same time this a-Si:H-like surface layer is nitridated by the N radicals leading to a-SiNx:H formation. This growth mechanism is further supported by the correlation between the SiH3 and N plasma density and the incorporation flux of Si and N atoms into the a-SiNx:H films as deposited under various conditions.

Ab initiostudy of the initial growth mechanism of silicon nitride onSi(100)−(2×1)usingNH3

Density functional theory (DFT) is used to examine the reaction mechanisms of nitridation of the $\mathrm{Si}(100)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}1)$ surface by ${\mathrm{NH}}_{3}.$ The surface is modeled using the cluster approximation. A detailed reaction mechanism that includes ammonia adsorption and decomposition, insertion of nitrogen into Si-Si bonds, hydrogen diffusion on the surface and ${\mathrm{H}}_{2}$ desorption is investigated. We find that nitrogen-containing species prefers to be on the surface, bonded to the two surface Si atoms. The energy barriers are also calculated. We find that the activation barrier of the nitridation rate-limiting step is 0.43 eV higher than the activation barrier for ${\mathrm{NH}}_{3}$ desorption. This confirms the experimental observation that a large fraction of ${\mathrm{NH}}_{3}$ that dissociates upon adsorption recombines and desorbs. We also find the hydrogen desorption barrier from the nitrided silicon surface to be 3.34 eV. As the surface hydrogen concentration decreases, we find that the activation barriers of the nitridation reactions become smaller. Our calculations show that the dissociation barrier decreases from 2.65 to 1.95 eV when two surface hydrogen atoms are removed from the reactive silicon dimer. This result agrees with the experimental findings that further nitride growth does not occur until hydrogen desorption takes place. Therefore, we conclude that the rate-limiting step for the nitridation reaction is the hydrogen desorption. Further dissociation reactions leading to stable species such as bridge-bonded $\mathrm{NH}(b)$ and $\mathrm{N}(b)$ species are also studied. Vibrational frequencies of the surface species are calculated and found to agree with experiments. This confirms our prediction of the nature of the surface species and the reaction mechanisms leading to the initial growth of silicon nitride films on $\mathrm{Si}(100)\ensuremath{-}(2\ifmmode\times\else\texttimes\fi{}1).$

Early stages of silicon nitride film growth studied by molecular dynamics simulations

The molecular dynamics method is used to simulate silicon nitride film growth through atomic deposition on an amorphous silicon surface, which is modeled by the stochastic classical trajectory-ghost theory. For the first time, realistic semi-empirical interatomic potential including both two-body and three-body interactions is employed to calculate the forces among deposited atoms. By the simulation we studied growth kinetics and the effects of substrate temperature and kinetic energy of vaporized atoms on the film growth. It is found that the film growth follows power law mechanism but with two different growth exponents in different growth stages, and changes of the substrate temperature and atomic kinetic energy lead to various film morphologies. This provides a possibility to precisely control the film properties, especially cluster size and compactness, by choosing suitable deposition parameters.

Ion-assisted deposition of silicon nitride films using electron cyclotron resonance plasma

Ion-assisted deposition (IAD) is one of the most widely used techniques for the deposition of thin films. Electron cyclotron resonance (ECR) ion sources are ideal for ion-assisted deposition due to high ionization efficiency even at low pressures. Silicon nitride films have been deposited by rf reactive sputtering with ion assistance from an ECR plasma. The ECR power was varied from 0 to 250 W. The effect of ECR plasma on the growth of silicon nitride films has been shown to be systematic and is characterized by using Fourier-transform infrared spectroscopy and atomic force microscopy. The surface roughness for the films deposited without ECR plasma was about 2 nm and decreased to about 0.7 nm for those deposited with 250 W of ECR power. The optical band gap changed from 2.2 to 4.9 eV as the ECR power was increased, indicating higher reactivity in the presence of ECR plasma. Good quality silicon nitride films with a band gap of 4.9 eV, a refractive index of 1.92, and an extinction coefficient of 4×10−4 have been obtained with an ECR power of 100 W (corresponding ion density of 1.5×1010 cm−3) and the surface roughness was less than 0.7 nm. The compositional analysis carried out using Auger electron spectroscopy showed a Si/N ratio of 0.73 for the films deposited under optimum deposition conditions.

Suppressing the surface roughness and columnar growth of silicon nitride films

The growth and structure evolution of silicon nitride films prepared by radio frequency magnetron sputtering at low pressure were investigated for thickness changes. Grazing-incidence X-ray reflectivity, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy were used to study the structure, surface roughness and composition, respectively, of the films. It was found that with an increase in thickness from 5 to 830 nm, the silicon nitride films have a similar surface structure and their surface roughness only slightly increases. The surface roughness of all the silicon nitride films is only a little more than 0.2 nm, much less than previously reported results. AFM measurement of the fractured film surface indicated that thin silicon nitride films with a thickness below approximately 300 nm have a dense, smooth and uniform structure, and columnar structures gradually appear only in thick films. These results are mainly attributed to the special design of the sputtering system and the energetic particle bombardment of the growing surface, by which the surface roughness and columnar growth were suppressed.

Layer-by-layer growth of silicon nitride films by NH3 and SiH4

Layer-by-layer growth of silicon nitride by NH 3 and SiH 4 was investigated using an ultraclean low-pressure CVD system with a Xe flash lamp. Thermal nitridation on Si(100) in an NH 3 environment with and without the flash lamp light irradiation is explained assuming Langmuir-type physical adsorption of NH 3 and reaction of the adsorbed NH 3 . The reaction can be enhanced by Xe flash lamp light irradiation, and the N atom concentration tends to saturate to ∼2.7×10 15 cm -2 . In Si deposition on the ultrathin silicon nitride, it is found that N desorption from the Si nitride films hardly occurs, and the deposited Si atom concentration increases up to about the single atomic layer concentration (6.8×10 14 cm -2 ), and then the Si deposition rate drastically increases. From FTIR/ATR and RHEED measurements, the structures of the Si film on Si and the Si nitride are found to be different. Layer-by-layer growth control of Si nitride is proposed by combining atomic-layer nitridation on Si and atomic-layer growth of Si on the Si nitride.

Silicon nitride film growth for advanced gate dielectric at low temperature employing high-density and low-energy ion bombardment

Direct nitridation of silicon surface can be realized at a temperature as low as 430 °C by using high-density plasma above 1012 cm−3 featuring low ion bombardment energy below 7 eV. This study shows that stoichiometric silicon nitride can be obtained for the first time at a temperature of 400 °C by precise control of the nitrogen partial pressure to generate N2+ in the plasma. Moreover, hysteresis in the capacitance–voltage data that has been attributed to charge traps in silicon nitride film can be reduced dramatically by adding hydrogen to Ar/N2 plasma for terminating dangling bonds with hydrogen. The dielectric strength of silicon nitride films is nearly equivalent to those of thermally grown silicon nitride and silicon oxide. The leakage current of silicon nitride film is dramatically reduced compared to that of thermally grown silicon oxide even if their equivalent thicknesses are equal. The silicon nitride films have almost no stress-induced leakage current and very little trap generation even in high-field stress.

Silicon nitride film growth by remote plasma CVD using Tris(dimethylamino)silane

Silicon nitride (SiN x) films were prepared using an organosilicon monomer, Trisdimethyl-aminosilane ((Me 2N) 3SiH: TDMAS) by a remote plasma CVD. Plasma was generated by a mixture of hydrogen and nitrogen gases while the monomer was introduced into the downstream. Deposition of SiN x films were initiated by hydrogen radicals since no film deposition was observed in the absence of hydrogen radicals. The deposited films were contaminated with a small amount of carbon atoms for the substrate temperature over 400°C. It is proposed that at the initial step, Si–N or N–C bonds of the monomer are broken by hydrogen radicals. Furthermore, N atoms in the films are assumed to be originated from the plasma.

Theoretical Investigation on Silicon-Nitride Film Growth: Statistical Approach

The dependence of SiNx film growth on the initial energy was investigated theoretically using a statistical model based on nonempirical molecular orbital results. Our theoretical calculations successfully explain the experimental finding that it is easier to control the ratio of Si–N and Si–Si bond yields when a mixture of SiH2Cl2 and NH3 rather than that of SiH4 and NH3 is used as the source gas.

Isotopic tracing of Si during thermal growth of Si 3N 4 ultrathin films

We investigated the mobility of Si atoms during the thermal growth of silicon nitride films in ammonia using Si isotopic labeling, together with nuclear resonant reaction analysis for depth profiling. A thin 29Si-enriched layer of silicon with nominal thickness of 1.4 nm was deposited on a Si(001) wafer with natural isotopic composition (92.2% 28Si, 4.7% 29Si). After epitaxial recrystallisation of the enriched layer, a Si 3N 4 film with nominal thickness of 2.86 nm was thermally grown in ammonia atmosphere. Excitation curves of the narrow resonance in the 29Si(p,γ) 30P nuclear reaction at E R = 324 keV were measured using a high efficiency γ-ray detection system (solid angle around 4π). The very close similarity between the excitation curves obtained for two pieces of the same sample, one without and one with thermal nitridation led us to conclude that the Si atoms are not mobile during thermal growth.

Spectroscopic study of the vacuum ultraviolet windowless photodissociation of silicon hydrides for silicon-based film deposition

Optical emission characteristics of vacuum ultraviolet (VUV) light from large area (≊50 cm2) electrical gas discharges were investigated in order to develop a windowless photochemical vapor deposition (photo-CVD) reactor and to prepare silicon-based thin films at low temperature (≊300 °C). The electrodes configuration is such that the ions impact upon the substrate is strongly minimized. Among the four investigated gases (He, Ar, H2, and N2), argon is the best candidate because it provides the more monochromatic VUV light (121.5 nm) which corresponds well to the maximum of the silane and disilane photoabsorption curves. Emission spectra of the photo-CVD induced in argon–silane mixtures clearly give evidence of the formation of molecular hydrogen and of Si* excited atoms and, indirectly, the part played by low hydrogen content radicals (namely, SiH). The deposition rate of hydrogenated amorphous silicon films obtained by windowless photo-CVD using this strong emission band at 121.5 nm is proportional to the SiH4 and Si2H6 contents in argon up to 20% and 6%, respectively. The deposited films present a low average hydrogen concentration value of less than 10% and smooth surfaces (<20 Å) for silicon hydride gas partial pressures lower than 15%. Over this value, the deposits become very rough (≳500 Å), due to SiHn clusters formation in the gas phase. Finally, low temperature growth of silicon nitride films by the VUV dissociation of silane and/or disilane–nitrogen mixtures is demonstrated.

Nanostructure of the Surface and Interface and Mechanisms of Thermal Growth of Ultrathin Films of Si3N4 on Si(001)

AbstractThe chemical situation of the Si atoms at the surface of Si3N4 ultrathin films thermally grown onto Si(001) substrates 2 × 1 reconstructed in a NH3 atmosphere has been recently studied in detail by core‐level spectroscopy using synchrotron radiation, as well as the chemical situation of the Si atoms at the film/substrate interface. The Si atoms at the surface are assigned to be either bonded to N atoms that are located in the layer just below the surface and having one dangling bond, or terminated by NH2. The Si atoms at the interface present intermediate oxidation states. Also recently high resolution isotopic tracing studies of N and H showed that nitrogeneous species (most probably NHx radicals, x < 3) are mobile during thermal growth of silicon nitride films, while isotopic tracing of Si showed that this species appears to be immobile during growth. This newly built experimental scenario for the nanostructure of the surface and interface, and for the atomic transport processes taking place during nitride growth, led us to develop a model for the mechanism of thermal growth of Si3N4 ultra‐thin films on Si(100), that is capable to explain the self‐limited character which makes them extremely attractive for applications in the VLSI and ULSI technologies for microfabrication of silicon devices.

Atomic transport during thermal growth of silicon nitride

By means of isotopic tracing of nitrogen and hydrogen we studied the atomic transport mechanisms during the thermal growth of silicon nitride films in ammonia ( 14NH 3, 15NH 3 and 14ND 3). The total amounts and the depth profiles of the different isotopes were determined by nuclear reaction analyses and step-by-step chemical etching of the nitride films. A pronounced exchange between hydrogen atoms in the silicon nitride films and those in the nitriding gas was observed, as well as an exchange between the nitrogen atoms on a smaller scale. The results of the present investigation indicate that the atomic transport through the growing nitride film occurs via nitrogenous species that include hydrogen. Silicon atoms or ions can also take part in the growth process but they cannot be the only mobile species.

Mechanisms of Thermal Nitridation of Silicon

We studied the mechanisms of thermal growth of silicon nitride films in ammonia using a resistance heated conventional furnace and a halogen lamp heated rapid thermal furnace. The methods are based on isotopic tracing of nitrogen and hydrogen using different kinds of isotopically enriched ammonia for the thermal growth, , , and . The total amounts of the different isotopes were measured by nuclear reaction analyses. The nitrogen and hydrogen profiles were measured by either nuclear resonance depth profiling or nuclear reaction analyses associated with step‐by‐step chemical etching. A pronounced exchange between the hydrogen atoms on the silicon nitride films and those in the nitriding gas was observed, as well as an exchange of nitrogen atoms on a smaller scale. The results of the present investigation indicate that the atomic transport through the growing nitride film occurs via nitrogenous species that include hydrogen. The transport of silicon atoms or ions can also participate in the growth process, but they cannot be the only mobile species.

Silicon nitride films grown by hydrogen radical enhanced chemical vapor deposition utilizing trisdimethylaminosilane

The growth of silicon nitride films using trisdimethylaminosilane (TDMAS) as a source material is described. TDMAS was decomposed by hydrogen radicals generated with a microwave plasma. Methyl groups included in the TDMAS were extracted from the film growing surface by hydrogen radicals. Composition, optical and electrical properties of SiN films have been examined with the aid of infrared absorption spectroscopy, electron-probe microanalysis, ultraviolet and visible light transmission spectra and voltage-current measurements. Transparent and insulating SiN films were obtained at low temperature.