Ultrathin Silicon Nitride Films Research Articles

Application of Si-related Ultrathin (∼1 nm) Films to Crystalline Silicon Solar Cells

Ultrathin (∼1 nm) films have been widely used for high-efficiency crystalline silicon (c-Si) solar cells such as tunnel oxide passivated contact (TOPCon) solar cells. In this article, we present our recent results for the applications of ultrathin silicon oxide (SiOx) and silicon nitride (SiNx) films to c-Si solar cells. The following topics are reviewed. 1) Ultrathin SiNx can be utilized for passivating contacts instead of SiOx in the TOPCon structure. 2) The addition of SiOx between c-Si and thick catalytic-chemical-vapor-deposited (Cat-CVD) SiNx significantly improves the quality of surface passivation. 3) Ultrathin Al-doped SiOx films formed just by dipping in Al(NO3)3 solution on c-Si provide strong upward band bending due to negative fixed charges, which can be used for hole-selective contacts.

Surface kinetics and feature scale particle model of SixNy atomic layer deposition using Si2Cl6 precursor

One of the important steps in the fabrication of semiconductor memory devices is the deposition of ultrathin silicon nitride films with uniform film thickness and electrical properties. Such high-quality films have made atomic level control during deposition a necessity and can be achieved via atomic layer deposition (ALD) with excellent step coverage. While ALD has been studied experimentally by many authors, there exist significant gaps between their observations and the practical application of the ALD process in large-scale manufacturing. In this work, a computational model of thin film deposition for a silicon based ALD application was developed. The model includes a surface chemistry mechanism for the deposition of hexachlorodisilane (Si2Cl6) on a growing SixNy film. This mechanism quantifies the sticking probability of the Si2Cl6 precursor on the growth surface as well as an effective active reaction site density on these surfaces. This surface reaction chemistry was used in the context of a feature scale particle transport model to simulate ALD in 100 nm–1 μm critical dimension, ∼10–100 high aspect ratio holes. The model demonstrates the effects of hole size and aspect ratio dependence on the overall kinetics of the deposition process. An increase in the completion time for ALD processes with increasing hole aspect ratio and the increasing statistical nature of the deposition process with smaller critical dimension of the hole were predicted.

Preparation of Tunable Microchips to Visualize Native Protein Complexes for Single-Particle Electron Microscopy.

Recent advances in technology have enabled single-particle electron microscopy (EM) to rapidly progress as a preferred tool to study protein assemblies. Newly developed materials and methods present viable alternatives to traditional EM specimen preparation. Improved lipid monolayer purification reagents offer considerable flexibility, while ultrathin silicon nitride films provide superior imaging properties to the structural study of protein complexes. Here, we describe the steps for combining monolayer purification with silicon nitride microchips to create a tunable approach for the EM community.

Local Valence Electronic States and Valence-Band Maximum of Ultrathin Silicon Nitride Films on Si(111) Studied by Auger Photoelectron Coincidence Spectroscopy: Thickness and Interface Structure Dependence

The local valence electronic states of Si3N4 films grown on Si(111)-7 × 7 [Si3N4/Si(111)] have been investigated by coincidence spectroscopy. The Si L23VV Auger electron spectra (AES) measured in coincidence with the Sin+ 2p photoelectrons of β-Si3N4(0001)/Si(111)-8 × 8 indicate that the binding energy of the local valence electronic state at Sin+ increases as n increases. Si4+ L23VV AES measured as a function of the β-Si3N4(0001) thickness show that the binding energy at the valence-band maximum (BEVBM) of β-Si3N4(0001) decreases by 1.6 ± 0.5 eV as the Si3N4 thickness decreases from 3.6 to 0.7 A. The large decrease is attributed to the hybridization of the valence electronic state of Si3N4 with those of neighboring subnitrides and to the formation of β-Si3N4(0001) islands. The BEVBM value of the 3.6-A-Si3N4/Si(111)-quadruplet decreases by 0.7 ± 0.6 eV from that of 3.6-A-β-Si3N4(0001)/Si(111)-8 × 8. The decrease in BEVBM is attributed to the different interface structures.

Toward intelligent synthetic neural circuits: directing and accelerating neuron cell growth by self-rolled-up silicon nitride microtube array.

In neural interface platforms, cultures are often carried out on a flat, open, rigid, and opaque substrate, posing challenges to reflecting the native microenvironment of the brain and precise engagement with neurons. Here we present a neuron cell culturing platform that consists of arrays of ordered microtubes (2.7–4.4 μm in diameter), formed by strain-induced self-rolled-up nanomembrane (s-RUM) technology using ultrathin (<40 nm) silicon nitride (SiNx) film on transparent substrates. These microtubes demonstrated robust physical confinement and unprecedented guidance effect toward outgrowth of primary cortical neurons, with a coaxially confined configuration resembling that of myelin sheaths. The dynamic neural growth inside the microtube, evaluated with continuous live-cell imaging, showed a marked increase (20×) of the growth rate inside the microtube compared to regions outside the microtubes. We attribute the dramatic accelerating effect and precise guiding of the microtube array to three-dimensional (3D) adhesion and electrostatic interaction with the SiNx microtubes, respectively. This work has clear implications toward building intelligent synthetic neural circuits by arranging the size, site, and patterns of the microtube array, for potential treatment of neurological disorders.

Improved growth of GaN layers on ultra thin silicon nitride/Si (111) by RF-MBE

High-quality GaN epilayers were grown on Si (1 1 1) substrates by molecular beam epitaxy using a new growth process sequence which involved a substrate nitridation at low temperatures, annealing at high temperatures, followed by nitridation at high temperatures, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. The material quality of the GaN films was also investigated as a function of nitridation time and temperature. Crystallinity and surface roughness of GaN was found to improve when the Si substrate was treated under the new growth process sequence. Micro-Raman and photoluminescence (PL) measurement results indicate that the GaN film grown by the new process sequence has less tensile stress and optically good. The surface and interface structures of an ultra thin silicon nitride film grown on the Si surface are investigated by core-level photoelectron spectroscopy and it clearly indicates that the quality of silicon nitride notably affects the properties of GaN growth.

Ultra thin silicon nitride films on Si(1 0 0) studied with core level photoemission

Ultra thin films of pure silicon nitride are grown on a Si(1 0 0) surface by exposing the surface to a microwave excited nitrogen plasma with a high content of N atoms at various substrate temperatures. These processes are monitored with synchrotron radiation induced core level photoemission spectroscopy. Below 500 °C the films grow uniformly with an amorphous character, but at higher growth temperatures, we find evidence showing that the growing nitride is microcrystalline as for Si(1 1 1), which we studied earlier. The interface between the substrate and the nitride film shows a different coordination for the Si(1 0 0) surface than for the Si(1 1 1) surface, at all temperatures. The growth of nitride in this process is self limiting with a final thickness, which increases with growth temperature. It is a clear indication from our studies that the Si(1 0 0)/nitride interface is less sharp and has a lower electrical quality than the Si(1 1 1)/nitride interface.

Plasma assisted growth of ultrathin nitrides on Si surfaces under ultrahigh vacuum conditions

Plasma assisted nitridation of Si is a very useful and easily controlled process for the direct in-situ deposition of pure silicon-nitride films on Si under ultrahigh vacuum conditions. The plasma used in the present work is formed by microwave dissociation of nitrogen gas. Under these circumstances an additional activation barrier to the formation of nitride exists which can be overcome by isothermal processing at temperatures from 300 °C and up. Room temperature growth of ultrathin silicon-nitride films on top of different substrates is also found to be possible through the use of dispersed atomic Si layers which react with the microwave excited nitrogen plasma at room temperature. Studies are undertaken with the Si(111) and Si(100) surfaces and the results for these two surfaces are compared. The conditions for the growth of amorphous versus microcrystalline films are established with a critical temperature around 500-600°C.

Angle-Resolved Photoelectron Spectroscopy Study on Ultrathin Gate Dielectrics

The paper reviews the non-destructive depth profiling of the composition and the chemical structure of ultrathin oxynitride films and ultrathin silicon nitride films using angle-resolved photoelectron spectroscopy. Depth profiles of nitrogen atoms in silicon oxynitride films were determined by applying the maximum entropy concept to angle-resolved photoelectron spectra. The layered structures of silicon nitride films formed using nitrogen-hydrogen radicals were determined by measuring soft X-ray excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels with the same probing depth.

Effect of Additional Oxygen on Formation of Silicon Oxynitride Using Nitrogen Plasma Generated near Atmospheric Pressure

We report that ultrathin silicon nitride films can be fabricated using N2 plasma near atmospheric pressure. In this paper, we describe the effect of additional oxygen on the formation of oxynitride films. Silicon oxynitride films were formed at an oxygen flow rate as low as 2.5 mL/min with a nitrogen flow rate of 10 L/min, in which the introduction of such a small amount of additional oxygen into the nitrogen plasma generated near atmospheric pressure enhances the oxidation reaction. X-ray photoemission spectroscopy analysis revealed that with increasing oxygen flow rate, the composition of the oxynitride films changed from Si3N3.5O0.7 to Si3N0.8O4.6. Optical emission spectroscopy showed emission peaks attributed to NO-γ transition as well as to the N2 second-positive system in the plasma discharge space. Emissions from the NO-γ transition show the dissociation of additional oxygen molecules, and active species such as oxygen atoms as well as NO and N2O molecules were generated by collisions between the N2(A3Σu+) and the O2(X3Σg-) states, resulting in the enhancement of Si oxidation near atmospheric pressure. Leakage current density decreases with increasing in the oxygen concentration. The 2.1-nm-thick silicon oxynitride film composed of Si3N0.8O4.6 showed a leakage current density as low as 3.5×10-4 A/cm2 at 5 MV/cm.

Valence band studies of the formation of ultrathin pure silicon nitride films on Si(1 0 0)

The growth of ultrathin films of Si 3N 4 directly on Si surfaces is studied with valence band photoemission. The information from these studies about the growth mechanism and the changes of the electronic structure is enhanced by the use of various photon energies with synchrotron radiation. The silicon nitride films are grown isothermally on the Si(1 0 0) and Si(1 1 1) surfaces by reactions with atomic N. The atomic nitrogen is produced by using a remote, microwave excited nitrogen plasma. The growth under these conditions was earlier shown to be self limiting. The details in the valence band spectra are identified and resolved with numerical methods, and followed systematically during the growth. Thus the identification of Si surface states, Si-nitride interface states and bulk nitride states becomes possible. The previously obtained separation between amorphous and crystalline growth occurring around 500 °C is further supported in the present studies.

Interfacial interactions at Au/Si3N4/Si(111) and Ni/Si3N4/Si(111) structures with ultrathin nitride films

Synchrotron photoemission spectromicroscopy has been used to study the interfacial interactions, metal diffusivity, and electronic barriers of Au and Ni contacts on ultrathin silicon nitride films. The Au/Si3N4 interface was found to be nonreactive, and only in the case of a very thin nitride film and elevated temperatures, Si can segregate from the Si(111) substrate and interact with Au. In the case of Ni/Si3N4/Si(111) structures, Ni diffusion and degradation of the Si3N4 lattice are evidenced even at room temperature and strongly enhanced at elevated temperatures, leading to formation of a Ni silicide interlayer.

Surface and interface structures of epitaxial silicon nitride on Si(111)

Surface and interface structures of an ultrathin silicon nitride film grown epitaxially on the Si(111) surface are investigated by core-level and valence-band photoelectron spectroscopy using synchrotron radiation. The Si $2p$ photoelectron spectra reveal a characteristic series of components for the Si species not only in stoichiometric ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ $({\mathrm{Si}}^{4+})$ but also in the intermediate nitridation states with one $({\mathrm{Si}}^{+})$ or three $({\mathrm{Si}}^{3+})$ nitrogen nearest neighbors. The Si $2p$ core-level shifts for the ${\mathrm{Si}}^{+},$ ${\mathrm{Si}}^{3+},$ and ${\mathrm{Si}}^{4+}$ components are determined to be 0.64, 2.21, and 2.74 eV, respectively. In sharp contrast to the well-known ${\mathrm{SiO}}_{2}/\mathrm{Si}(111)$ case, no trace of the ${\mathrm{Si}}^{2+}$ species is observed, indicating an atomically abrupt and defect-free interface in accordance with a recent interface model of $\ensuremath{\beta}\ensuremath{-}{\mathrm{Si}}_{3}{\mathrm{N}}_{4}/\mathrm{Si}(111).$ In addition, the origin of the characteristic N $1s$ spectra and a strong surface-state emission observed in the valence-band spectra are discussed.

Effect of Oxygen in Deposited Ultrathin Silicon Nitride Film on Electrical Properties

The role of oxygen inside deposited films has been investigated. We successfully controlled the oxygen concentration inside the bulk SiON and thickness of layer at interface independently. In the case in which the capacitance-voltage measurement is used, it is found that the defect density inside the SiON film containing 30% oxygen with the interlayer thickness of 1 nm is as little as that inside a film at the equivalent oxide thickness ranging from 4.2 to 4.5 nm. Moreover, we confirmed by X-ray photoelectron spectroscopy analysis that the bonding states of N and O atom inside the bulk region were mainly and The above results and the fact that 500°C as-deposited film composition obeys the alloy model indicate that the stacked structure of can achieve the minimum defect density. These results suggest that the addition of O atom releases strained energy in the bulk and the interface regions. © 2002 The Electrochemical Society. All rights reserved.

Formation of high moisture and dopant diffusion resistivity silicon nitride films by catalytic-CVD method

High resistivity for moisture and dopant diffusion silicon nitride films are prepared by catalytic-CVD method. In this method, SiH 4 and NH 3 gases are decomposed by the catalytic-cracking reactions with a heated tungsten catalyzer placed near substrates, and so that silicon nitride films are formed without any help from plasma nor photochemical excitation at the temperature as high as 300°C. The properties of catalytic-CVD silicon nitride films are investigated. It is found that, 1) stoichiometric silicon nitride film whose refractive index is 2.0 shows high moisture resistance, 2) ultrathin silicon nitride film (equivalent oxide thickness: 3.5nm) blocks B diffusion even 1000°C annealing.

Effect of ions and radicals on formation of silicon nitride gate dielectric films using plasma chemical vapor deposition

We have clarified effects of ions and radicals on the film property of ultrathin silicon nitride (SiNx) films of 5 nm in thickness formed on Si substrates at 300 °C in electron cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD) employing ammonia and silane (NH3/SiH4), and nitrogen and silane (N2/SiH4) gases. In situ Fourier transform infrared reflection absorption spectroscopy and in situ x-ray photoelectron spectroscopy confirmed that in N2/SiH4 plasma, Si-N bonds in the film were increased by eliminating charged species, and thus, radicals promoted the formation of the SiNx film of high Si-N bond density. On the other hand, Si-N bonds in the film were decreased by eliminating charged species, and eventually, ions played an important role in forming the film of high Si-N bond density in NH3/SiH4 plasma. The excellent hysteresis of 0.04 V was successfully achieved with the NH3/SiH4 plasma. Furthermore, the quadrupole mass spectroscopy suggests that NH4+ charged species make a significant contribution to the formation of ultrathin SiNx films with high quality. These results provide insights into important species to be controlled in the PECVD for low temperature formation of the SiNx gate dielectric films in ultralarge scale integrated circuits.

Reaction-diffusion model for thermal growth of silicon nitride films on Si

Thermal growth of ultrathin silicon nitride films on Si in ${\mathrm{NH}}_{3}$ is modeled as a dynamic system governed by reaction-diffusion equations. Solution of the model yields profiles of the involved species consistent with experimental observations of a stoichiometric silicon nitride layer in the near-surface region and a subnitride layer of comparable thickness in the near-interface region. Self-limited growth kinetics are also obtained from the model equations in good agreement with experimental results, owing to a diffusion barrier layer to the nitridant species formed in the near-surface region by stoichiometric silicon nitride.

Ultrathin silicon nitride gate dielectrics prepared by catalytic chemical vapor deposition at low temperatures

The feasibility of using ultrathin silicon nitride (SiNx) films, prepared by catalytic chemical vapor deposition (Cat-CVD) method, as an ultrathin gate dielectric is reported. The effects of postdeposition treatments carried out using hydrogen (H2)-decomposed species or NH3-decomposed species formed by catalytic cracking of H2 and NH3 are also studied. A small hysteresis loop is seen in the C–V curve of as-deposited Cat-CVD SiNx films. The leakage current in the case of these films with equivalent oxide thickness (EOT) of 3 nm is slightly larger than that in the conventional thermal SiO2 films of similar EOT. However, it is found that the properties of Cat-CVD SiNx films are markedly improved by the postdeposition H2 or NH3 treatments, that is, the hysteresis loop disappears and the leakage current decreases by three orders of magnitude.

Highly robust ultrathin silicon nitride films grown at low-temperature by microwave-excitation high-density plasma for giga scale integration

This paper focuses attention on electrical properties of ultra-thin silicon nitride films grown by radial line slot antenna high-density plasma system at a temperature of 400/spl deg/C as an advanced gate dielectric film. The results show low density of interface trap and bulk charge, lower leakage current than jet vapor deposition silicon nitride and thermally grown silicon oxide with same equivalent oxide thickness. Furthermore, they represent high breakdown field intensity, almost no stress-induced leakage current, very little trap generation even in high-field stress, and excellent resistance to boron penetration and oxidation.

Control tribological and mechanical properties of MEMS surfaces. Part 2: nanomechanical behavior of self-lubricating ultrathin films

Results of nanomechanical studies of ultrathin silicon dioxide and silicon nitride films are discussed. Films applicable to MEMS technology were manufactured on single-crystal silicon wafer’s at atmospheric perssure by the glow discharge technique.