SiO2 Films Research Articles

In English

The aim of this work is a comparative analysis of the biocidal efficiency of Ag nanoparticles (NPs) in the colloidal state, in the structure of films and dispersions of SiO2 and in the composition of textile fabrics, dependent on the method of synthesis, based on literature data and on own researches. Chemical reduction of silver (with borohydrides, hydrogen, hydrazine, etc.) allows one to adjust and control the size and shape of NPs. The shape of the NPs is mostly spherical, what is confirmed by the presence of a band of surface plasmon resonance in absorption spectra and by electron microscopy measurements. To prevent aggregation of NPs obtained by the method of chemical reduction in solution, the optimal ratio of two stabilizers based on surfactants and polymer at their minimum concentration was found, namely NaBH4 as a reductant and polyvinylpyrrolidone + sodium dodecyl sulfate as binary stabilizer of Ag NPs, with bactericidal activity of 99 % and stability for more than 3 years. Chemical reduction of silver ions was carried out also by the amino acid tryptophan (Trp) which has a dual function – a biocompatible reducing agent and stabilizer of silver NPs while maintaining their shape, size and stability for long-term use. Effective methods of photochemical synthesis of Ag NPs have been developed in different ways: by UV irradiation of Ag+ ions in solution in the presence of solid-state photosensitizer SiO2 with adsorbed benzophenone (SiO2/BPh); by UV irradiation of Ag+ ions in solution in the presence of the amino acid tryptophan (Trp); on silica surface when Ag/SiO2 sol-gel films production via irradiation of adsorbed Ag+ ions on SiO2 film (Ag+/SiO2) in the BPh solution. It is shown that when Ag NPs are adsorbed on the surface of highly dispersed SiO2, the logarithm of the reduction of microorganisms reduces and the time of their deactivation increases. A cheap and convenient way to modify of cotton textiles with Ag NPs by soft heat treatment of Ag+/cotton samples with high (90–95 %) efficiency of destruction of bacteria E. coli, K. pneumoniae, E. aerogenes, P. vulgaris, S. aureus, C. albicans, etc., with saving of biocidal activity after 5 cycles of washing has been developed. The dynamics of silver ions release from the surface of NPs in the structure of textile upon their contact with water for 72 hours and the number of irreversibly bound particles have been studied. The electrical resistance of the tissue is proportional to the quantity of NPs. That is NPs in the structure are in different degrees of binding, a certain part of them is retained (adsorbed) irreversibly, saving bactericidal properties after repeated contacts with water. On the basis of literature analysis it is shown that ecologically safe “green synthesis” is a promising way to silver NPs produce with pronounced bactericidal efficiency, which is becoming more common due to the large resource of cheap plant raw materials.

Simultaneous film thickness and refractive index measurement using a constrained fitting method in a white light spectral interferometer.

Film is widely used in optoelectronic and semiconductor industries. The accurate measurement of the film thickness and refractive index, as well as the surface topography of the top and bottom surfaces are necessary to ensure its processing quality. Multiple measurement methods were developed; however, they are limited by the requirements of a known dispersion model and initial values of thickness and refractive index. Further, their systems are rarely compatible with surface topography measurement methods. We propose a constrained nonlinear fitting method to simultaneously measure the thickness and refractive index of film in a simple white-light spectral interferometer. The nonlinear phase extracted by the spectral phase-shifting is fitted with the theoretical nonlinear phase obtained by multiple reflection model. The constraints of nonlinear fitting are obtained by the interferometric signal of vertical scanning, reconstructed by the integration of the white-light spectral signal to avoid local minima. The proposed method does not require a priori knowledge of the dispersion model and initial values of thickness and refractive index, and its system is compatible with the vertical scanning interferometry (VSI) method to reconstruct the surface topography of the top and bottom surfaces of film. Three SiO2 films with different thicknesses are measured, and the results show that the measured refractive index is within the theoretical value range of wavelength bandwidth and the measured thicknesses are closely aligned with the values provided by the commercial instrument. The measurement repeatability of refractive index reaches 10-3. Measurements on a polymer film demonstrate that this method is feasible for measuring the film without a priori information.

Atomic layer etching of SiO2 with self-limiting behavior on the surface modification step using sequential exposure of HF and NH3

Thermal atomic layer etching (ALE) for SiO2 films with self-limiting behavior on the surface modification step was developed using sequential exposure to HF and NH3 gases followed by infrared (IR) annealing. X-ray photoelectron spectroscopy analysis showed that an (NH4)2SiF6-based surface-modified layer was formed on the SiO2 surface after gas exposures and that this layer was removed using IR annealing. The etch per cycle (EPC) of the ALE process saturated at 0.9 nm/cycle as the gas exposure times increased. With this self-limiting behavior, SiO2 was etched with high selectivity to poly-Si and Si3N4. The dependence of the EPC on the partial pressures of HF and NH3 was found to be in good agreement with the Langmuir adsorption model. This indicated that the HF and NH­3 molecules were in equilibrium between adsorption and desorption during the exposure, which resulted in the self-limiting formation of the modified layer. In addition to the process with an HF gas flow, it was demonstrated that an H2/SF6 plasma can replace the HF gas exposure step to supply the SiO2 surfaces with HF molecules. The EPC saturated at 2.7 nm/cycle, while no measurable thickness change was observed for poly-Si and Si3N4 films.

Development of a novel wet cleaning solution for Post-CMP SiO2 and Si3N4 films

After CMP, the removal of ceria nanoparticle residues is difficult due to the formation of Ce–O–Si chemical bonds on the SiO2 film surface. After STI CMP, several post-CMP cleaning processes are performed, including the application of PVA brushing and megasonic technologies using conventional cleaning solutions such as SC1, SC2, and SPM. However, more effective post-CMP cleaning technologies are still needed for the fabrication of advanced integrated circuit devices. In this study, we developed a novel post-CMP cleaning solution consisting of tetramethylammonium hydroxide (TMAH), ethylenediaminetetraacetic acid (EDTA), and Disponil to replace existing cleaning solutions. In its non-diluted form, this cleaning solution removed 99.5% of residual particles and 98.3% of ceria residue on an SiO2 film surface, as well as 98.5% of residual particles and 98.1% of ceria residue on an Si3N4 film surface, respectively. At 5 × dilution, it removed 97.8% of residual particles and 97.0% of ceria residue on the SiO2 film surface, as well as 97.8% of residual particles and 96.3% of ceria residue on the Si3N4 film surface, respectively. The effectiveness of this cleaning solution for residual ceria nanoparticles is highly comparable to SC1 and SPM conventional cleaning solutions, even though it is used at a relatively low temperature with less etching. Additionally, AFM of the surface topography showed fewer particles and better surface roughness compared with SC1 and SPM cleaning. Thus, this approach can be used to remove ceria nanoparticles from polished SiO2 and Si3N4 films through increased wettability, slight dissolving of the film, and extremely enhanced repulsive force.

Controlled photocatalytic activity of TiO2 inverse opal structures with atomic layer deposited (ALD) metal oxide thin films

Atomic layer deposited (ALD) thin films of Al2O3, SiO2, and TiO2 with thicknesses ranging from 0.25 nm to 10 nm were studied on TiO2 inverse opal (IO) structures for their effect on photocatalytic activity under ultraviolet A (UVA) excitation. 1 nm coating of Al2O3 suppressed the photocatalytic activity significantly by more than 90% removing all water molecules from the surface. On the contrary, 0.25 nm SiO2 layer enhanced the photocatalytic activity by 112% by increasing the number of water molecules on the surface whereas 3 nm SiO2 layer reduced the activity by 87% as the thicker layer prevented electron and hole diffusion onto the surface. The highest photocatalytic activity enhancement up to 226% was observed with 10 nm ALD TiO2 layer.

Low-energy O+ ion beam induced chemical vapor deposition using tetraethyl orthosilicate for silicon dioxide film formation

This paper presents an experimental methodology for forming silicon dioxide (SiO2) films with an ion beam induced chemical vapor deposition method using tetraethyl orthosilicate (TEOS). In this methodology, both O+ ion beam and TEOS were simultaneously injected onto substrates. The substrate temperature was set at room temperature. The energy of the O+ ion beam was 100 eV. At the completion of the experiments, films were found to be deposited on the substrates. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy of the deposited films showed that SiO2 films were formed on the substrates.

Porous SiO2 coated dielectric metasurface with consistent performance independent of environmental conditions

With the rapid advances of functional dielectric metasurfaces and their integration on on-chip nanophotonic devices, the necessity of metasurfaces working in different environments, especially in biological applications, arose. However, the metasurfaces’ performance is tied to the unit cell’s efficiency and ultimately the surrounding environment it was designed for, thus reducing its applicability if exposed to altering refractive index media. Here, we report a method to increase a metasurface’s versatility by covering the high-index metasurface with a low index porous SiO2 film, protecting the metasurface from environmental changes while keeping the working efficiency unchanged. We show, that a covered metasurface retains its functionality even when exposed to fluidic environments.

Fabrication of AlGaN High Frequency Bulk Acoustic Resonator by Reactive RF Magnetron Co-sputtering System.

In this study, aluminum gallium nitride (AlGaN) thin films are used as the piezoelectric layers to fabricate solidly mounted resonators (SMR) for high frequency acoustic wave devices. AlGaN film is deposited on a Bragg reflector, composed of three pairs of Mo and SiO2 films, through a reactive radio frequency (RF) magnetron co-sputtering system at room temperature. The optimized deposition parameters of AlGaN film have a sputtering power of 175 W for Al target, sputtering power of 25 W for GaN target, N2 flow ratio (N2/Ar + N2) of 60%, and sputtering pressure of 10 mTorr. The obtained AlGaN film has a smooth surface, uniform crystal grains, and strong c-axis orientation. The contents of Al and Ga in the AlGaN film, analyzed by energy dispersive X-ray spectroscopy (EDS) are 81% and 19%, respectively. Finally, the frequency response s11 of the obtained SMR device shows that the center frequency is 3.60 GHz, the return loss is about −8.62 dB, the electromechanical coupling coefficient (kt2) is 2.33%, the quality factor (Q) value is 96.93 and the figure of merit (FoM) value is 2.26.

Low-energy O+ ion beam induced chemical vapor deposition using hexamethyldisilane or hexamethyldisilazane for silicon dioxide film formation

A methodology for silicon dioxide (SiO2) film formation by an ion beam induced chemical vapor deposition (IBICVD) method using hexamethyldisilane (HMDS) or hexamethyldisilazane (HMDSN) is presented in this paper. In this method, an O+ ion beam was injected onto a substrate in conjunction with the source material (HMDS or HMDSN). The substrate temperature was set at room temperature. The O+ ion energy was 100 eV. After the experiment, a film was found to be deposited on the substrate and the film thickness was about 50 nm in both HMDS and HMDSN cases. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy of the deposited films showed that SiO2 films were formed on the substrates. XPS data of the film which was prepared by the injection of both O+ ions and HMDS to the substrate showed that no obvious peak was observed in the C1s region. On the contrary, a small amount of carbon was included in the film when the film was prepared by the injection of O+ ions in conjunction with HMDSN. These results suggest that HMDS is more suitable than HMDSN as the source material for SiO2 film formation when using the IBICVD method.

Various evolution trends of sample thickness in fluorocarbon film deposition on SiO2

Recently, fluorocarbon (FC) film deposition on a SiO2 surface has become one of the most important processes in semiconductor manufacturing because the formation of a passivation layer on SiO2 during the deposition process plays a crucial role in atomic layer etching and high aspect ratio contact (HARC) etching, areas that are attracting intense interest in the semiconductor industry. In this work, various trends of sample thickness change, namely, decreasing, increasing, and anomalously increasing trends with time, were observed during FC film deposition on a SiO2 surface. The total thickness including both SiO2 and FC film was found to change during the deposition process in various ways depending on the plasma conditions. This can be successfully explained by considering the mechanism of SiO2 etching with FC plasma, taking into account the dependence of the SiO2 etch rate on FC film thickness. This result is expected to be utilized in semiconductor processes such as HARC etching where a precise control of film thickness is needed.

Review on the thickness measurement of ultrathin oxide films by mutual calibration method

Mutual calibration was suggested as a method to determine the absolute thickness of ultrathin oxide films. It was motivated from the large offset values in the reported thicknesses in the Consultative Committee for Amount of Substance (CCQM) pilot study P‐38 for the thickness measurement of SiO2 films on Si(100) and Si(111) substrates in 2004. Large offset values from 0.5 to 1.0 nm were reported in the thicknesses by ellipsometry, X‐ray reflectometry (XRR), medium‐energy ion scattering spectrometry (MEIS), Rutherford backscattering spectroscopy (RBS), nuclear reaction analysis (NRA), and transmission electron microscopy (TEM). However, the offset value for the thicknesses by X‐ray photoelectron spectroscopy (XPS) was close to zero (−0.013 nm). From these results, the mutual calibration method was reported for the thickness measurement of SiO2 films on Si(100) by combination of TEM and XPS. The mutual calibration method has been applied for the thickness measurements of hetero oxide films such as Al2O3 and HfO2. Recently, the effect of surface contamination was reported to be critical to the thickness measurement of HfO2 films by XPS. On the other hand, MEIS was proved to be a powerful zero offset method which is not affected by the surface contamination. As a result, the reference thicknesses in the CCQM pilot study P‐190 for the thickness measurement of HfO2 films on Si(100) substrate were determined by mutual calibration method from the average XRR data and MEIS analysis. Conclusively, the thicknesses of ultrathin oxide films can be traceably certified by mutual calibration method and most thickness measurement methods can be calibrated from the certified thicknesses.

Anisotropy of 3D Columnar Coatings in Mid-Infrared Spectral Range.

Polarisation analysis in the mid-infrared fingerprint region was carried out on thin (∼1 m) Si and SiO2 films evaporated via glancing angle deposition (GLAD) method at to the normal. Synchrotron-based infrared microspectroscopic measurements were carried out on the Infrared Microspectroscopy (IRM) beamline at Australian Synchrotron. Specific absorption bands, particularly Si-O-Si stretching vibration, was found to follow the angular dependence of ∼, consistent with the absorption anisotropy. This unexpected anisotropy stems from the enhanced absorption in nano-crevices, which have orientation following the angular dependence as revealed by Fourier transforming the image of the surface of 3D columnar films and numerical modeling of light field enhancement by sub-wavelength nano-crevices.

Mechanic properties modification of SiO2 thin films by femtosecond laser

SiO2 films were deposited on fused silica substrates by ALD technology. The properties of ALD SiO2 films irradiated by femtosecond laser were investigated. Raman spectra confirms the molecular structure of SiO2 films is identical to that of fused silica. The relative content of the three- and four-membered ring of films irradiated is increased. Photoluminescence (PL) spectra shows that the defects of the films irradiated by laser of 10% power ratio are reduced. Indentation tests show that both hardness and elastic modulus are decreased by 1.8%, their standard deviations are decreased by 73.8% and 46.8% respectively. Scratch experiments exhibit that femtosecond irradiation improves the bonding performance of the films, and the critical load is increased by 10.8%. Meanwhile, the standard deviations of the lateral load and penetration depth are decreased on average from 0.0636 to 0.0336, from 8.3478 to 1.6747, individually. The plastic deformation ratio of the films are increased from 19.80% to 28.89%. The morphology and cross section of the scratches observed by optical microscopy and confocal laser microscopy suggest that the damage form of the films irradiated by laser is changed from the brittle fracture removal form to the mixed removal form of brittle fracture and plastic.

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.

Ultra-low stress high reflective film by dual-ion-beam sputtering deposition

The correlation between the process parameters of auxiliary ion source and the SiO2 film stress was systematically studied using dual-ion-sputtering deposition. Spectrophotometer and ellipsometer were used to measure the SiO2 film’s transmittance spectrum and reflection ellipsometry. The refractive index and thickness of SiO2 film were obtained by total spectrum inversion calculation. The laser interferometer measures the substrate surface shape to obtain film stress. The experimental result shows that film stress is related to sputtering energy during deposition, high-energy oxygen ion assisted deposition can significantly reduce it and the assisted ion beam voltage plays an important role in controlling it by data normalization analysis. Ultra-low stress high reflective film was prepared by dual-ion-beam sputtering deposition, where stress was 70% lower than traditional film. At the same time, this film can ensure sufficiently high optical quality to keep it reliable and stable in high-precision laser systems.

Infrared optical properties of SiO2 films on silicon substrate under different temperatures

SiO2 is a very important low refractive index film material that can operate in the UV to mid-IR regions. The SiO2 films used were deposited on Si substrates by different deposition techniques. We designed and manufactured a high-temperature infrared spectrum measuring equipment connected with a Fourier transform infrared (FTIR) spectrometer; the measuring temperature could range from room-temperature to 600°C. The FTIR transmission spectra of SiO2 films under different working temperatures were measured in the wavenumber region from 4000 to 400 cm − 1. From the measured spectra, it can be seen that IBS-SiO2 and IAD-SiO2 films are more stable and operating temperature can reach 400°C. EB-SiO2 film is worse and operating temperature is only 300°C. Complex dielectric functions of SiO2 films under different temperature conditions were calculated from FTIR transmittance spectra, and the best fitted method was obtained for calculating optical constants of dielectric materials in the high temperature condition. The results show that the structure of the Si-O-Si network in IBS-SiO2 films was the most stable structure. The experimental results were of great significance to practical application.

High Performance Predictable Quantum Efficient Detector Based on Induced-Junction Photodiodes Passivated with SiO2/SiNx.

We performed a systematic study involving simulation and experimental techniques to develop induced-junction silicon photodetectors passivated with thermally grown SiO2 and plasma-enhanced chemical vapor deposited (PECVD) SiNx thin films that show a record high quantum efficiency. We investigated PECVD SiNx passivation and optimized the film deposition conditions to minimize the recombination losses at the silicon–dielectric interface as well as optical losses. Depositions with varied process parameters were carried out on test samples, followed by measurements of minority carrier lifetime, fixed charge density, and optical absorbance and reflectance. Subsequently, the surface recombination velocity, which is the limiting factor for internal quantum deficiency (IQD), was obtained for different film depositions via 2D simulations where the measured effective lifetime, fixed charge density, and substrate parameters were used as input. The quantum deficiency of induced-junction photodiodes that would be fabricated with a surface passivation of given characteristics was then estimated using improved 3D simulation models. A batch of induced-junction photodiodes was fabricated based on the passivation optimizations performed on test samples and predictions of simulations. Photodiodes passivated with PECVD SiNx film as well as with a stack of thermally grown SiO2 and PECVD SiNx films were fabricated. The photodiodes were assembled as light-trap detector with 7-reflections and their efficiency was tested with respect to a reference Predictable Quantum Efficient Detector (PQED) of known external quantum deficiency. The preliminary measurement results show that PQEDs based on our improved photodiodes passivated with stack of SiO2/SiNx have negligible quantum deficiencies with IQDs down to 1 ppm within 30 ppm measurement uncertainty.

On the mechanism of carrier recombination in downsized blue micro-LEDs

The mechanism of carrier recombination in downsized μ-LED chips from 100 × 100 to 10 × 10 μm2 on emission performance was systemically investigated. All photolithography processes for defining the μ-LED pattern were achieved by using a laser direct writing technique. This maskless technology achieved the glass-mask-free process, which not only can improve the exposure accuracy but also save the development time. The multi-functional SiO2 film as a passivation layer successfully reduced the leakage current density of μ-LED chips compared with the μ-LED chips without passivation layer. As decreasing the chip size to 10 × 10 μm2, the smallest chip size exhibited the highest ideality factor, which indicated the main carrier recombination at the high-defect-density zone in μ-LED chip leading to the decreased emission performance. The blue-shift phenomenon in the electroluminescence spectrum with decreasing the μ-LED chip size was due to the carrier screening effect and the band filling effect. The 10 × 10 μm2 μ-LED chip exhibited high EQE values in the high current density region with a less efficiency droop, and the max-EQE value was 18.8%. The luminance of 96 × 48 μ-LED array with the chip size of 20 × 20 μm2 exhibited a high value of 516 nits at the voltage of 3 V.

Thermal Characterization of Metal-Oxide Interfaces Using Time-Domain Thermoreflectance with Nanograting Transducers.

Metal-oxide thermal boundary conductance (TBC) strongly influences the temperature rise in nanostructured systems, such as dense interconnects, when its value is comparable to the thermal conductance of the amorphous dielectric oxide. However, the thermal characterization of metal-amorphous oxide TBC is often hampered by the measurement insensitivity of techniques such as time-domain thermoreflectance (TDTR). Here, we use metal nanograting structures as opto-thermal transducers in TDTR to measure the TBC of metal-oxide interfaces. Combined with an ultrafast pump-probe laser measurement approach, the nanopatterned structures amplify the contribution of the thermal boundary resistance (TBR), the inverse of TBC, over the thermal resistance of the adjacent material, thereby enhancing measurement sensitivity. For demonstration purposes, we report the TBC between Al and SiO2 films. We then compare the impact of Al grating dimensions on the measured TBC values, sensitivities, and uncertainties. The grating periods L used in this study range from 150 to 300 nm, and the bridge widths w range from 72 to 205 nm. With the narrowest grating transducers (72 nm), the TBC of Al-SiO2 interfaces is measured to be 159-48+61 MW m-2 K-1, with the experimental sensitivity being 5× higher than that of a blanket Al film. This improvement is attributed to the reduced contribution of the SiO2 film thermal resistance to the temperature signal from TDTR response. The nanograting measurement approach described here is promising for the thermal characterization of a variety of nanostructured metal-amorphous passivation systems and interfaces common in semiconductor technology.

Atmospheric-Pressure Plasma-Enhanced Spatial ALD of SiO2 Studied by Gas-Phase Infrared and Optical Emission Spectroscopy.

An atmospheric-pressure plasma-enhanced spatial atomic layer deposition (PE-s-ALD) process for SiO2 using bisdiethylaminosilane (BDEAS, SiH2[NEt2]2) and O2 plasma is reported along with an investigation of its underlying growth mechanism. Within the temperature range of 100–250 °C, the process demonstrates self-limiting growth with a growth per cycle (GPC) between 0.12 and 0.14 nm and SiO2 films exhibiting material properties on par with those reported for low-pressure PEALD. Gas-phase infrared spectroscopy on the reactant exhaust gases and optical emission spectroscopy (OES) on the plasma region are used to identify the species that are involved in the ALD process. Based on the identified species, we propose a reaction mechanism where BDEAS molecules adsorb on −OH surface sites through the exchange of one of the amine ligands upon desorption of diethylamine (DEA). The remaining amine ligand is removed through combustion reactions activated by the O2 plasma species leading to the release of H2O, CO2, and CO in addition to products such as N2O, NO2, and CH-containing species. These volatile species can undergo further gas-phase reactions in the plasma as indicated by the observation of OH*, CN*, and NH* excited fragments in OES. Furthermore, the infrared analysis of the precursor exhaust gas indicated the release of CO2 during precursor adsorption. Moreover, this analysis has allowed the quantification of the precursor depletion yielding values between 10 and 50% depending on the processing parameters. Besides providing insights into the chemistry of atmospheric-pressure PE-s-ALD of SiO2, our results demonstrate that infrared spectroscopy performed on exhaust gases is a valuable approach to quantify relevant process parameters, which can ultimately help evaluate and improve process performance.