Grown SiO2 Films Research Articles

Formation of SiO2 thin films through plasma- enhanced chemical vapor deposition using SiH4/Ar/N2O

SiO2 films and their formation technologies are critical for the fabrication of Si-based integrated circuits (ICs). SiO2 films fabricated using plasma-enhanced chemical vapor deposition (PECVD) have become increasingly important because of the increasing trend of three-dimensional (3D) architectures in ICs. SiO2 films formed by PECVD have been widely studied for over 40 years; however, owing to the complex plasma reactions and the differences in system conditions, the relationship between the experimental parameters and film characteristics are disputed. In this study, focusing on the two important characteristics (surface morphology and deposition rate) of SiO2 films for 3 D ICs manufacturing, SiO2 film growth was systematically investigated via SiH4/Ar/N2O in PECVD; a theoretical reaction process model (including gas-phase reaction, chemical adsorption, and surface reaction) bridging the experimental parameters (chamber pressure, gas ratio, radio frequency power, and substrate temperature) and characteristics (surface morphology and deposition rate) of SiO2 films was established. This study contributes to the precise formation of sub-100 nanometer SiO2 films using PECVD for manufacturing 3 D ICs.

Visible room-temperature emission and excitation photoluminescence in In+- and As+-co-implanted SiO2 films

The visible room-temperature emission and excitation photoluminescence spectra were studied as a function of the indium and arsenic profiles in the In+ and As+ ion-implanted thermally grown SiO2 films before and after the annealing at the temperature of 900 °C. As+ ions at the energy of 40 or 135 keV and In+ ions at the energy of 50 keV, providing a projective range ratio RpAs/RpIn of 1 or 3, respectively, were used. Four emission photoluminescence bands, peaked at ∼347 nm (3.57 eV), ∼440 nm (2.81 eV), ∼450 nm (2.75 eV) and ∼500 nm (2.48 eV), were obtained from the 40 keV As+ and 50 keV In+ ion-implanted samples under the excitation wavelength of 300 nm (4.13 eV), 350 nm (3.54 eV), 400 nm (3.10 eV) and 450 nm (2.75 eV), respectively. As the As+ energy increased to 135 keV, under the same excitation conditions, the emission bands peaked at 370 nm (3.35 eV), 420 nm (2.95 eV), 460 nm (2.69 eV) and 505 nm (2.45 eV) dominated in the photoluminescence spectra. The excitation spectra of the observed emission peaks were studied, too. We preliminarily interpret the observed photoluminescence peaks as a result of the T1 → S0 transition of molecular-like clusters associated with the oxygen deficiency provided by In or In–As in ion-implanted SiO2.

XPS Study of the Preparation of Single-Site Catalysts Based on Ir(I) and Rh(I) Complexes Immobilized on a SiO<sub>2</sub> Surface Using a P-Containing Linker

Samples of model single-site iridium and rhodium catalysts were synthesized by immobilization of complexes [Ir(COD)(IMes)Cl] and [Rh(COD)(IMes)Cl], where COD is cyclooctadiene-1,5 and IMes is 1,3‑bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, on the surface of silicon dioxide modified with a linker containing diphenylphosphine group (Ph2P). Silicon plates with a flat surface covered with a layer of natural oxide 1–3 nm thick, Si-SiO2(nat), or with a specially grown SiO2 film (∼300 nm), Si-SiO2(ox), were used as supports. The chemical compositions of the surface of the modified silicon plates and samples of model catalysts were characterized by XPS. Based on these XPS studies, a tentative conclusion was made about the coordination of immobilized complexes to the SiO2 surface. Catalyst samples were tested in the gas-phase hydrogenation of propene with parahydrogen.

Low-energy Ar+ ion-beam-induced chemical vapor deposition of silicon dioxide films using tetraethyl orthosilicate

This study was conducted to determine whether the simultaneous injections of Ar+ ions and tetraethyl orthosilicate (TEOS) to a substrate are able to fabricate a film on the substrate. The Ar+ ion energy was 100 eV. After the injections, we found a film deposited on the substrate. Following the analyses of the film with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, it was found that the deposited film was silicon dioxide (SiO2). We conclude that the low-energy Ar+ ion-beam-induced deposition method using TEOS is useful for the growth of SiO2 films.

Reactions between SiCl4 and H2O on rutile TiO2 surfaces in atomic layer deposition of SiO2 by first-principles calculations

Atomic layer deposition of SiO2 using SiCl4 and H2O is a classical process, which was initially developed for applications in the field of microelectronics. Recently, it has been demonstrated as an effective surface engineering of nanomaterials in many other applications, including catalysis, pharmaceuticals, and energetic materials. However, fundamental mechanisms of SiO2 film growth at the atomic scale have not been fully understood. In this work, DFT calculations were performed to understand the atomic mechanisms of SiO2 film growth from SiCl4 and H2O precursors on the bare and hydroxylated TiO2 surfaces. Climbing image−nudged elastic band (CI-NEB) method was used to find saddle points and the activation energies for the chemical reactions of several possible mechanisms. The recombination of the by-product HCl with the surfaces and the removal of surface chlorine were also calculated. The results show that SiCl4 can be continuously dissociated on the surface or react with H2O after the first dissociation/ligand exchange reaction. The activation energies from CI-NEB results point out the benefit of the surface hydroxylation in facilitating the initial reaction of SiCl4 on the surface and reducing the production of the adsorbed atomic chlorine as gaseous HCl is released as a by-product. The recombination of the HCl by-product with the surface by either molecular dissociation or ligand exchange reaction with –OH groups can further create atomic chlorine. The removal of the adsorbed chlorine is unlikely, accounting for a certain amount of Cl impurity found by experiments. The calculation results provide an atomic level prediction for designing experimental conditions to achieve desired film quality.

High quality low thermal budget low cost SiO2 film fabricated by O2 plasma immersion ion implantation

O2 plasma immersion ion implantation technique has been developed to form high quality low thermal budget low cost SiO2 films with unique feature of selective oxidation for three-dimensional or nonplanar structures of ultra-large-scale integration applications. The formed SiO2 material was extensively characterized and investigated. The SiO2 films have demonstrated good chemical stoichiometric composition, and good electrical properties including higher bulk resistivity ρ, higher breakdown charge QBD, comparable dielectric constant k and interface state density Dit. The formed SiO2 material has demonstrated better qualities than those of tetraethyl orthosilicate SiO2 film and comparable to those of thermal grown SiO2 film.

Inhibitor-free area-selective atomic layer deposition of SiO2 through chemoselective adsorption of an aminodisilane precursor on oxide versus nitride substrates

Area-selective atomic layer deposition (AS-ALD) offers complementary bottom-up patterning with atomic-level accuracy on pre-defined areas in conjunction with conventional top-down patterning, so it has attracted tremendous interest for enablement of multi-dimensional nanostructures toward sub-10 nm scale technology. In this work, we report a methodology for achieving inherently selective deposition of high-quality oxide thin films through chemoselective adsorption of an aminodisilane precursor, 1,2-bis(diisopropylamino)disilane (BDIPADS), on oxide versus nitride substrates. Density functional theory (DFT) calculations show higher reactivity for adsorption of BDIPADS on OH-terminated SiO2 compared with NH2-terminated SiN surfaces, indicating selective growth of SiO2 films in the SiO2 area. Applying BDIPADS precursor to both SiO2 and SiN substrates results in inherent deposition selectivity of ∼ 1 nm even without the use of inhibitory molecules such as self-assembled monolayers. Using this inherent selectivity as a starting point, we further enhance deposition selectivity using combined ALD-etching supercycle strategies in which HF-wet etching step is periodically inserted after 20 cycles of ALD SiO2, leading to an enlarged deposition selectivity of approximately 5 nm after repeated ALD-etching supercycles. This approach can be envisaged to provide a practically applicable strategy toward highly selective deposition using inherent AS-ALD that can be incorporated into upcoming 3D bottom-up nanofabrication.

Influence of Hydrogen-Nitrogen Hybrid Passivation on the Gate Oxide Film of n-Type 4H-SiC MOS Capacitors

Hydrogen-nitrogen hybrid passivation treatment for growing high-property gate oxide films by high-temperature wet oxidation, with short-time NO POA, is proposed and demonstrated. Secondary ion mass spectroscopy (SIMS) measurements show that the proposed method causes hydrogen and appropriate nitrogen atoms to accumulate in Gaussian-like distributions near the SiO2/SiC interface. Moreover, the hydrogen atoms are also incorporated into the grown SiO2 layer, with a concentration of approximately 1 × 1019 cm−3. The conductance characteristics indicate that the induced hydrogen and nitrogen passivation atoms near the interface can effectively reduce the density of interface traps and near-interface traps. The current-voltage (I-V), X-ray photoelectron spectroscopy (XPS), and time-dependent bias stress (TDBS) with ultraviolet light (UVL) irradiation results demonstrate that the grown SiO2 film with the incorporated hydrogen passivation atoms can effectively reduce the density of oxide electron traps, leading to the barrier height being improved and the leakage current being reduced.

Highly selective and vertical etch of silicon dioxide using ruthenium films as an etch mask

Highly selective and vertical profile etching of thermally grown SiO2 films using thin metallic Ru mask films was investigated in a commercial inductively coupled plasma etcher. The effects of varying chamber pressure, substrate bias, and gas composition on etch performance were all investigated. Selectivities (measured as the SiO2 etch rate divided by the Ru etch rate) ranging from 50 to as high as 370 were measured under various process conditions without compromising the etch profile quality. It was found that fluorocarbon gas mixtures (CF4/CHF3 and CF4/C4F8) gave the best results. The addition of SF6 to the gas mixture dramatically reduced selectivity, resulting in significant Ru mask faceting and necking in the etched pillars and is not recommended for use in a standard Ru/SiO2 etch process.

Atomic Structure and Optical Properties of Plasma Enhanced Chemical Vapor Deposited SiCOH Low-k Dielectric Film-=SUP=-*-=/SUP=-

The SiCOH low-k dielectric film was grown on Si substrate using plasma enhanced chemical vapor deposition method. Atomic structure and optical properties of the film were studied with the use of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) absorption spectroscopy, Raman spectroscopy and ellipsometry. Analysis of XPS data showed that the low-k dielectric film consists of Si-O4 bonds (83%) and Si-SiO3 bonds (17%). In FTIR spectra some red-shift of Si-O-Si valence (stretching) vibration mode frequency was observed in the low-k dielectric film compared with the frequency of this mode in thermally grown SiO2 film. The peaks related to absorbance by C-H bonds were observed in FTIR spectrum. According to Raman spectroscopy data, the film contained local Si-Si bonds and also C-C bonds in the s-p3 and s-p2 hybridized forms. Scanning laser ellipsometry data show that the film is quite homogeneous, homogeneity of thickness is ~ 2.5%, and homogeneity of refractive index is ~ 2%. According to analysis of spectral ellipsometry data, the film is porous (porosity is about 24%) and contains clusters of amorphous carbon (~ 7%).

HfO2/SiO2 anti-reflection films for UV lasers via plasma-enhanced atomic layer deposition

The laser-induced damage threshold (LIDT) of HfO2/SiO2 anti-reflection (AR) films for ultraviolet (UV) lasers was improved via low-temperature plasma-enhanced atomic layer deposition (PEALD). Focused on the chemical composition, optical absorption, surface scattering, and laser-resistance, the impact of precursor exposure time on PEALD SiO2 film properties and growth temperature on PEALD SiO2 and HfO2 film properties were investigated respectively. When irradiated by UV laser, PEALD SiO2 film exhibits a higher LIDT than the PEALD HfO2 film, which is consistent with their less impurity content and lower absorption. A bilayer structure HfO2/SiO2 AR film for 355 nm laser was designed and experimentally demonstrated via PEALD growth at a temperature of 150 °C. The prepared PEALD AR film shows a reflectance <0.2% at 355 nm as designed and better laser-damage resistance with a LIDT of 24.4 J/cm2 (355 nm, 7.8 ns) than the conventional e-beam deposition method.

Effect of post-deposition annealing on atomic layer deposited SiO2 film for silicon surface passivation

We have investigated the passivation performance of atomic layer deposited silicon dioxide (ALD-SiO2) films on crystalline silicon surface with various post-annealing temperatures. A maximum effective lifetime of 2157 μs can be achieved at the optimized annealing temperature of 650 °C on 3 Ω cm n-type silicon wafers. The improved passivation quality can be attributed to the low interface defect density and extremely high positive fixed charge density. Especially, the high positive fixed charge density of over 4 × 1012 cm-2 can be observed after annealing at high temperature. Therefore, it is inferred that the passivation mechanism for ALD-SiO2 films is based on not only chemical passivation but also field-effect passivation, which is more similar with the ALD-Al2O3 films rather than the thermally grown SiO2 films. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy and thermal effusion measurement revealed the variation of elements content and distribution of silicon, oxygen, hydrogen and carbon during the post-deposition thermal treatment process, indicating that the rearrangement and release of these elements create more oxygen vacancies and result in the improvement of interface quality and positive fixed charge density of ALD-SiO2 films.

Atomistic Simulations of Plasma-Enhanced Atomic Layer Deposition.

Plasma-enhanced atomic layer deposition (PEALD) is a widely used, powerful layer-by-layer coating technology. Here, we present an atomistic simulation scheme for PEALD processes, combining the Monte Carlo deposition algorithm and structure relaxation using molecular dynamics. In contrast to previous implementations, our approach employs a real, atomistic model of the precursor. This allows us to account for steric hindrance and overlap restrictions at the surface corresponding to the real precursor deposition step. In addition, our scheme takes various process parameters into account, employing predefined probabilities for precursor products at each Monte Carlo deposition step. The new simulation protocol was applied to investigate PEALD synthesis of SiO2 thin films using the bis-diethylaminosilane precursor. It revealed that increasing the probability for precursor binding to one surface oxygen atom favors amorphous layer growth, a large number of –OH impurities, and the formation of voids. In contrast, a higher probability for precursor binding to two surface oxygen atoms leads to dense SiO2 film growth and a reduction of –OH impurities. Increasing the probability for the formation of doubly bonded precursor sites is therefore the key factor for the formation of dense SiO2 PEALD thin films with reduced amounts of voids and –OH impurities.

Diffusion and Interaction of In and As Implanted into SiO2 Films

By means of Rutherford backscattering spectrometry, electron microscopy, and energy-dispersive X-ray spectroscopy, the distribution and interaction of In and As atoms implanted into thermally grown SiO2 films to concentrations of about 1.5 at % are studied in relation to the temperature of subsequent annealing in nitrogen vapors in the range of T = 800–1100°C. It is found that annealing at T = 800–900°C results in the segregation of As atoms at a depth corresponding to the As+-ion range and in the formation of As nanoclusters that serve as sinks for In atoms. An increase in the annealing temperature to 1100°C yields the segregation of In atoms at the surface of SiO2 with the simultaneous enhanced diffusion of As atoms. The corresponding diffusion coefficient is DAs = 3.2 × 10–14 cm2 s–1.

Impact of encapsulation method on the adsorbate induced electrical instability of monolayer graphene

Monolayer graphene transferred onto a set of silicon carbide (SiC) substrates was encapsulated with a thin SiO2 film in order to prevent its interaction with atmospheric adsorbates. The encapsulation of graphene samples was realized by using two different thin film growth methods such as thermal evaporation (TE) and state-of-the-art pulsed electron deposition (PED). The encapsulation efficiency of these two techniques on the structural and electrical characteristics of graphene was compared with each other. Scanning electron microscopy (SEM) analysis showed that unlike the SiO2 thin film grown with PED, structural defects like cracks were readily formed on TE grown films due to the lack of surface wettability. The electronic transport measurements revealed that the electrical resistivity of graphene has been increased by two orders of magnitude, and the carrier mobility has been subsequently decreased upon the encapsulation process with the PED method. However, in-vacuum transient photocurrent spectroscopy (TPS) measurements conducted for short periods and a few cycles showed that the graphene layer encapsulated with the PED grown SiO2 film is electrically far more stable than the one encapsulated with TE grown SiO2 film. The results of TPS measurements were related to the SEM images to unravel the mechanism behind the improved electrical stability of graphene samples encapsulated with the PED grown SiO2 film.

Computational study on silicon oxide plasma enhanced chemical vapor deposition (PECVD) process using tetraethoxysilane/oxygen/argon/ helium

Plasma enhanced chemical vapor deposition (PECVD) of silicon oxide (SiO2) using tetraethoxysilane (TEOS) was investigated theoretically by developing an unprecedented plasma chemistry model in TEOS/O2/Ar/He gas mixture. In the gas phase reactions, a TEOS molecule is decomposed by the electron impact reaction and/or chemically oxidative reaction, forming intermediate TEOS fragments, i.e., silicon complexes. In this study, we assume that SiO is the main precursor that contributes to SiO2 film growth under a particular process or simulation condition. The surface reaction was also investigated using quantum mechanical simulations with density functional theory. Based on the gas and surface reaction models, we constructed a computational plasma model for SiO2 film deposition in a PECVD process. The simulation results using CHEMKIN pro and CFD-ACE + have shown that the neutral atomic O and SiO as well as the charged O2+ are the dominant species to obtain a high deposition rate and uniformity. The spatial distributions of various species in the TEOS/O2/Ar/He gas mixture plasma were shown in the study. The uniformity of deposited film due to the change in the plasma bulk property was also discussed.

Growth and characterization of nitrogen-phosphorus hybrid passivated gate oxide film on N-type 4H-SiC epilayer

A novel nitrogen-phosphorus (N&P) hybrid passivation technique by NO-containing dry oxidation of phosphorus-implanted 4H-SiC epilayer has been proposed to grow high-property gate oxide film. For demonstration and contrast, n-type 4H-SiC MOS capacitors with N&P hybrid and only N passivation have been fabricated and tested. The results from Secondary Ion Mass Spectroscopy (SIMS) reveal that about 60% of the implanted phosphorus atoms remain in the SiO2 film after sacrificial oxidation of the implantation layer. And the distribution of phosphorus is approximately uniform throughout the grown SiO2 film with a concentration about 4 × 1019 cm−3, avoiding the SiO2 film converting to phosphosilicate glass (PSG). I-V and X-ray Photoelectron Spectroscopy (XPS) data show that the grown SiO2 film with the appropriate phosphorus passivation can effectively improve the quality of oxide film, leading the gate oxide bandgap and integrity improved and reducing the leakage current above two orders of magnitude. The bias stress measurements with ultraviolet light (UVL) irradiation also show that the N&P hybrid passivation treatment can completely restrain the near-interface electron traps (NIETs) in 4H-SiC MOS devices, indicating that incorporation an appropriate amount of phosphorus atoms in the grown SiO2 film also can make the electron trap density reduced effectively.

Time-dependent dielectric breakdown of atomic-layer-deposited Al2O3 films on GaN

Atomic-layer-deposited (ALD) Al2O3 films are the most promising surface passivation and gate insulation layers in non-Si semiconductor devices. Here, we carried out an extensive study on the time-dependent dielectric breakdown characteristics of ALD-Al2O3 films formed on homo-epitaxial GaN substrates using two different oxidants at two different ALD temperatures. The breakdown times were approximated by Weibull distributions with average shape parameters of 8 or larger. These values are reasonably consistent with percolation theory predictions and are sufficiently large to neglect the wear-out lifetime distribution in assessing the long-term reliability of the Al2O3 films. The 63% lifetime of the Al2O3 films increases exponentially with a decreasing field, as observed in thermally grown SiO2 films at low fields. This exponential relationship disproves the correlation between the lifetime and the leakage current. Additionally, the lifetime decreases with measurement temperature with the most remarkable reduction observed in high-temperature (450 °C) O3-grown films. This result agrees with that from a previous study, thereby ruling out high-temperature O3 ALD as a gate insulation process. When compared at 200 °C under an equivalent SiO2 field of 4 MV/cm, which is a design guideline for thermal SiO2 on Si, high-temperature H2O-grown Al2O3 films have the longest lifetimes, uniquely achieving the reliability target of 20 years. However, this target is accomplished by a relatively narrow margin and, therefore, improvements in the lifetime are expected to be made, along with efforts to decrease the density of extrinsic Al2O3 defects, if any, to promote the practical use of ALD Al2O3 films.

Sequential plasma activation methods for hydrophilic direct bonding at sub-200 °C

We present our newly developed sequential plasma activation methods for hydrophilic direct bonding of silica glasses and thermally grown SiO2 films. N2 plasma was employed to introduce a metastable oxynitride layer on wafer surfaces for the improvement of bond energy. By using either O2-plasma/N2-plasma/N-radical or N2-plasma/N-radical sequential activation, the quartz–quartz bond energy was increased from 2.7 J/m2 to close to the quartz bulk fracture energy that was estimated to be around 9.0 J/m2 after post-bonding annealing at 200 °C. The silicon bulklike bond energy between thermal SiO2 films was also obtained. We suggest that the improvement is attributable to surface modification such as N-related defect formation and asperity softening by the N2 plasma surface treatment.

The Validity of the Results of High-Performance Modeling of SiO2 Film Growth

This work is devoted to checking of the validity of the results of high-performance modeling of SiO2 film growth. Modeling of the high-energy deposition process shows that the refractive indices of deposited SiO2 films exceed the refractive index of a fused silica substrate. This is entirely supported by the analysis of spectrophotometric data obtained for practical thin films deposited using the respective deposition technique.