Effects Of Vacuum Ultraviolet Radiation Research Articles

Comprehensive Review on the Impact of Chemical Composition, Plasma Treatment, and Vacuum Ultraviolet (VUV) Irradiation on the Electrical Properties of Organosilicate Films

Organosilicate glass (OSG) films are a critical component in modern electronic devices, with their electrical properties playing a crucial role in device performance. This comprehensive review systematically examines the influence of chemical composition, vacuum ultraviolet (VUV) irradiation, and plasma treatment on the electrical properties of these films. Through an extensive survey of literature and experimental findings, we elucidate the intricate interplay between these factors and the resulting alterations in electrical conductivity, dielectric constant, and breakdown strength of OSG films. Key focus areas include the impact of diverse organic moieties incorporated into the silica matrix, the effects of VUV irradiation on film properties, and the modifications induced by various plasma treatment techniques. Furthermore, the underlying mechanisms governing these phenomena are discussed, shedding light on the complex molecular interactions and structural rearrangements occurring within OSG films under different environmental conditions. It is shown that phonon-assisted electron tunneling between adjacent neutral traps provides a more accurate description of charge transport in OSG low-k materials compared to the previously reported Fowler–Nordheim mechanism. Additionally, the quality of low-k materials significantly influences the behavior of leakage currents. Materials retaining residual porogens or adsorbed water on pore walls show electrical conductivity directly correlated with pore surface area and porosity. Conversely, porogen-free materials, developed by Urbanowicz, exhibit leakage currents that are independent of porosity. This underscores the critical importance of considering internal defects such as oxygen-deficient centers (ODC) or similar entities in understanding the electrical properties of these materials.

UV-Induced Synthesis of Hybrid HMDSO/SiO2 Thin Films with Compositional Gradients for High-Performance Atomic Oxygen Resistance.

A flexible, dense, defect-free, highly adhesive, and highly dissociation energy-rich protective coating is essential to enhance the atomic oxygen (AO) resistance of polymeric materials in a low Earth orbit (LEO). In this work, a dense, defect-free hybrid HMDSO/SiO2 thin film coating with compositional gradients on the surface of polyimide was synthesized using vacuum-ultraviolet (VUV) irradiation. The effects of VUV irradiation on the morphology, optical transmittance, and chemical components of plasma-polymerized HMDSO (pp-HMDSO) thin-film coatings deposited on the polyimide surface were investigated in depth. There were no defects such as cracks and holes in the surface morphology of pp-HMDSO films after VUV irradiation, but the surface roughness increased slightly, and the corresponding optical transmittance decreased slightly. The chemical components of pp-HMDSO films were changed in the depth direction starting from the top of the surface, forming hybrid HMDSO/SiO2 thin films with compositional gradients. The component gradient HMDSO/SiO2 composite coating further enhanced the atomic oxygen resistance of the polyimide due to the surface layer of the UV-modified coating enriched with high dissociation energy SiOx material. Therefore, this work provides a facile UV-induced synthesis method to prepare dense, defect-free, and highly dissociation energy-rich protective gradient coatings, which are promising not only for excellent AO protection in LEO but also for potential application in water-oxygen barrier films.

Frontiers in the Interaction of Chemically Reactive Species From Gaseous Plasma With Hydrophobic Polymers

Surface functionalization of polymers by chemically reactive oxygen is a standard technique for increasing the surface energy of polymers. The technique, however, usually does not provide the desired surface finish of many polymers, including highly hydrophobic polymers like those rich in fluorine. The disappointing results are due to an incomplete understanding of the interaction between the plasma species and polymers on the atomic scale. The current state is presented, and recent advances in both theoretical and experimental descriptions of the surface mechanisms are illustrated. The scientific community faces challenges in both plasma characterization, separation of specific reactants, and detailed study of the interaction on the atomic scale. The effects of vacuum-ultraviolet radiation and its synergy with neutral reactive plasma particles are often neglected, but recent articles represent a pathway to the appropriate design of the experimental systems, which will enable systematic measurements of the evolution of surface functional groups versus the fluence of selected plasma species.

Ultraviolet Spectroscopy and Photochemistry of SO2/H2O Ices

The presence of sulfur dioxide on the trailing hemisphere of Europa’s surface is well-established, and both its presence and its chemistry are influenced by sulfur ion implantation. Particle irradiation is known to be a significant radiolysis source, particularly on the trailing surface, which is subject to particles in Jupiter’s plasma torus. Photochemistry driven by solar ultraviolet (UV) photons is also significant. To date, most studies have investigated the effects of vacuum UV radiation, while photochemistry at longer wavelengths is less well-studied. This work investigates chemical changes in thin, cryogenic films of SO2/H2O at temperatures and pressures relevant to Europa’s surface when subjected to temperature changes and UV radiation at 147, 206, 254, and 284 nm. Spectra were collected in both the mid-infrared range and the UV range, which elucidates electronic transitions that are less diagnostic but perhaps more applicable to reflectance spectra of solar system bodies. These experiments show irreversible red shifting of the B̃ ← X̃ absorption peak upon heating likely as a result of crystallization and/or thermal chemical reactions. Further, photons with wavelengths up to 284 nm are shown to induce significant chemistry in SO2/H2O mixtures. This in conjunction with the increased solar flux compared to more energetic wavelengths and the strong C̃ ← X̃ and B̃ ← X̃ absorption bands in SO2 suggests that far-UV radiation plays a significant role in the sulfur cycle on Europa.

Fast Atom Beam- and Vacuum-Ultraviolet-Activated Sites for Low-Temperature Hybrid Integration.

The evolution of surface chemical structures of polyimide induced by Ar fast atom beam (Ar-FAB) bombardment and vacuum ultraviolet (VUV) irradiation was investigated using X-ray photoelectron spectroscopy (XPS) to clarify the activated sites for low-temperature hybrid bonding. These sites in molecular chains are considered corresponding to the bonding sites. They affect interfacial properties. Therefore, such analyses are necessary to optimize the processing parameters in different surface-modification methods. The XPS results demonstrated that Ar-FAB physical bombardment transformed the polyimide surface into benzene-dominant structures, whereas the effect of VUV irradiation was located at side chain groups such as ether and carbonyl, resulting in much longer molecular fragments (i.e., less matrix damage). Moreover, the calculated thickness of the VUV-induced modification layer grew to around 0.6 nm at its maximum.

Vacuum ultraviolet radiation effects on two-dimensional MoS2 field-effect transistors

Atomically thin MoS2 has generated intense interest for emerging electronics applications. Its two-dimensional nature and potential for low-power electronics are particularly appealing for space-bound electronics, motivating the need for a fundamental understanding of MoS2 electronic device response to the space radiation environment. In this letter, we quantify the response of MoS2 field-effect transistors (FETs) to vacuum ultraviolet (VUV) total ionizing dose radiation. Single-layer (SL) and multilayer (ML) MoS2 FETs are compared to identify differences that arise from thickness and band structure variations. The measured evolution of the FET transport properties is leveraged to identify the nature of VUV-induced trapped charge, isolating the effects of the interface and bulk oxide dielectric. In both the SL and ML cases, oxide trapped holes compete with interface trapped electrons, exhibiting an overall shift toward negative gate bias. Raman spectroscopy shows no variation in the MoS2 signatures as a result of VUV exposure, eliminating significant crystalline damage or oxidation as possible radiation degradation mechanisms. Overall, this work presents avenues for achieving radiation-hard MoS2 devices through dielectric engineering that reduces oxide and interface trapped charge.

The effect of vacuum ultraviolet irradiation on the time-dependent dielectric breakdown of organosilicate dielectrics

In this work, the effect of vacuum ultraviolet (VUV) exposure on the time-dependent dielectric breakdown (TDDB) properties of porous low-k films was investigated. Synchrotron irradiation was used to simulate the VUV photon irradiation from processing plasmas without any particle flux. The synchrotron flux varies with the wavelength, so the irradiation time was chosen to produce the same fluence at various photon energies. The deterioration of TDDB and generation of negative mobile charge were observed in the film after exposure to the VUV photons with 9 eV or higher energy. These effects were not observed in the films exposed with 7-eV photon energies or less. The creation of paramagnetic defects was observed with the ESR measurement and believed to be the reason for TDDB degradation. Depletion of carbon and breakage and rearrangement of the Si-O-Si structure were observed and believed to be the reason for mobile charge generation and the change in TDDB, chemical, and mechanical properties.

The effects of vacuum-ultraviolet radiation on defects in low-k organosilicate glass (SiCOH) as measured with electron-spin resonance

Defect concentrations in SiCOH low-k dielectrics deposited on high-resistivity silicon substrates were measured with Electron Spin Resonance (ESR). CP4 and HF treatments were used in order to eliminate dangling bonds from the backside of the silicon substrate as well as the sample edges. Two kinds of defects with characteristic g=2.0054–2.0050 and g=2.0018–2.0020 were detected in pristine samples and quantified using Lorentzian fitting. The defect with the g factor of 2.0054–2.0050 is likely to be from the silicon-dangling bonds. The defect with the g factor of 2.0018–2.0020 is most likely from carbon-related centers. Upon exposure to VUV synchrotron radiation (hν=12eV), the concentration of the silicon-dangling bonds is found to increase significantly.

Effects of vacuum ultraviolet irradiation on trapped charges and leakage currents of low-k organosilicate dielectrics

Vacuum ultraviolet (VUV) photoemission spectroscopy is utilized to investigate the distribution of trapped charges within the bandgap of low dielectric constant (low-k) organosilicate (SiCOH) materials. It was found that trapped charges are continuously distributed within the bandgap of porous SiCOH and the center of the trapped states is 1.3 eV above the valence band of the tested sample. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies between 7.6 and 8.9 eV was found to deplete trapped charge while UV exposure with photon energies less than 6.0 eV induces more trapped charges in tested samples. Current-Voltage (IV) characteristics results show that the reliability of dielectrics is improved after VUV irradiation with photon energies between 7.6 and 8.9 eV, while UV exposure results in an increased level of leakage current and a decreased breakdown voltage, both of which are harmful to the reliability of the dielectric. This work shows that VUV irradiation holds the potential to substitute for UV curing in microelectronic processing to improve the reliability of low-k dielectrics by mitigating the leakage currents and trapped charges induced by UV irradiation.

Effects of vacuum-ultraviolet irradiation on copper penetration into low-k dielectrics under bias-temperature stress

The effects of vacuum-ultraviolet (VUV) irradiation on copper penetration into non-porous low-k dielectrics under bias-temperature stress (BTS) were investigated. By employing x-ray photoelectron spectroscopy depth-profile measurements on both as-deposited and VUV-irradiated SiCOH/Cu stacks, it was found that under the same BTS conditions, the diffusion depth of Cu into the VUV-irradiated SiCOH is higher than that of as-deposited SiCOH. On the other hand, under the same temperature-annealing stress (TS) without electric bias, the Cu distribution profiles in the VUV-irradiated SiCOH were same with that for the as-deposited SiCOH. The experiments suggest that in as-deposited SiCOH, the diffused Cu exists primarily in the atomic state, while in VUV-irradiated SiCOH, the diffused Cu is oxidized by the hydroxyl ions (OH−) generated from VUV irradiation and exists in the ionic state. The mechanisms for metal diffusion and ion injection in VUV irradiated low-k dielectrics are discussed.

Decomposition of 1,4-dioxane by vacuum ultraviolet irradiation: Study of economic feasibility and by-product formation

We report the first use of vacuum ultraviolet (VUV) treatment to decompose 1,4-dioxane, a persistent organic contaminant that is difficult to remove by conventional drinking water treatment processes. The efficiency of VUV treatment was compared to that of VUV- and UV-based advanced oxidation processes (AOPs) (VUV/TiO2, VUV/H2O2, UV/TiO2, and UV/H2O2), and by-product formation was investigated. VUV treatment decomposed 1,4-dioxane more rapidly than did UV and UV/TiO2 treatments. The decomposition rate was enhanced when VUV irradiation was combined with TiO2 or H2O2. VUV/H2O2 decomposed 1,4-dioxane more rapidly than UV/H2O2 at a low H2O2 dose (1mg/L), but the rate difference became small at a high H2O2 dose (5mg/L). Electrical energy per order analysis revealed that VUV treatment, and the VUV- and UV-based AOPs, were economically feasible for 1,4-dioxane decomposition. Using raw water samples, we investigated by-product formation during VUV treatment and the effect of VUV irradiation on chlorinated disinfection by-product formation potential. Although the samples contained high concentrations of bromide, no bromate was produced by VUV treatment. VUV treatment slightly decreased trihalomethane formation potential (THMFP), whereas haloacetic acid formation potential (HAAFP) was unchanged, and total aldehyde concentration increased. The trend in HAAFP agreed with that had been reported for the VUV irradiation with much higher dose (Buchanan et al., 2006), whereas the trend in THMFP was different from that with much higher dose. THMFP, HAAFP, and aldehyde concentration were reduced by subsequent treatment with granular activated carbon (GAC) or biological activated carbon (BAC). Nitrite was produced by VUV treatment but disappeared after subsequent BAC treatment. These results suggest that VUV treatment should be combined with GAC or BAC treatment to suppress by-product formation.

Effect of vacuum-ultraviolet irradiation on the dielectric constant of low-k organosilicate dielectrics

Vacuum ultraviolet (VUV) irradiation is generated during plasma processing in semiconductor fabrications, while the effect of VUV irradiation on the dielectric constant (k value) of low-k materials is still an open question. To clarify this problem, VUV photons with a range of energies were exposed on low-k organosilicate dielectrics (SiCOH) samples at room temperature. Photon energies equal to or larger than 6.0 eV were found to decrease the k value of SiCOH films. VUV photons with lower energies do not have this effect. This shows the need for thermal heating in traditional ultraviolet (UV) curing since UV light sources do not have sufficient energy to change the dielectric constant of SiCOH and additional energy is required from thermal heating. In addition, 6.2 eV photon irradiation was found to be the most effective in decreasing the dielectric constant of low-k organosilicate films. Fourier Transform Infra-red Spectroscopy shows that these 6.2 eV VUV exposures removed organic porogens. This contributes to the decrease of the dielectric constant. This information provides the range of VUV photon energies that could decrease the dielectric constant of low-k materials most effectively.

Effect of vacuum ultraviolet on the surface properties of high-filled polymer composites

The effect of vacuum ultraviolet radiation (λ = 90–115 nm) on the surface structure and optical properties of high-filled polymer composites based on high-impact polystyrene and organosiloxane filler is investigated. It is ascertained that VUV exposure leads to the surface smoothing and solar radiation absorption coefficient increasing by ∼15%.

The effects of vacuum ultraviolet radiation on low-k dielectric films

Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VUV induced charge generation, (2) dielectric-substrate interface, and (3) porosity of dielectrics, can be used to reduce trapped-charge accumulation during processing of low-κ SiCOH dielectrics. Photons from the plasma are responsible for trapped-charge accumulation within the dielectric, while ions stick primarily to the surface of the dielectrics. In addition, as the dielectric constant was decreased by adding porosity, the defect concentrations increased.

The effect of VUV radiation from Ar/O2 plasmas on low-k SiOCH films

The degradation of porous low-k materials, like SiOCH, under plasma processing continues to be a problem in the next generation of integrated-circuit fabrication. Due to the exposure of the film to many species during plasma treatment, such as photons, ions, radicals, etc, it is difficult to identify the mechanisms responsible for plasma-induced damage. Using a vacuum beam apparatus with a calibrated Xe vacuum ultraviolet (VUV) lamp, we show that 147 nm VUV photons and molecular O2 alone can damage these low-k materials. Using Fourier-transform infrared (FTIR) spectroscopy, we show that VUV/O2 exposure causes a loss of methylated species, resulting in a hydrophilic, SiOx-like layer that is susceptible to H2O absorption, leading to an increased dielectric constant. The effect of VUV radiation on chemical modification of porous SiOCH films in the vacuum beam apparatus and in Ar and O2 plasma exposure was found to be a significant contributor to dielectric damage. Measurements of dielectric constant change using a mercury probe are consistent with chemical modification inferred from FTIR analysis. Furthermore, the extent of chemical modification appears to be limited by the penetration depth of the VUV photons, which is dependent on wavelength of radiation. The creation of a SiOx-like layer near the surface of the material, which grows deeper as more methyl is extracted, introduces a dynamic change of VUV absorption throughout the material over time. As a result, the rate of methyl loss is continuously changing during the exposure. We present a model that attempts to capture this dynamic behaviour and compare the model predictions to experimental data through a fitting parameter that represents the effective photo-induced methyl removal. While this model accurately simulates the methyl loss through VUV exposure by the Xe lamp and Ar plasma, the methyl loss from VUV photons in O2 plasma are only accurately depicted at longer exposure times. We conclude that other species, such as oxygen radicals or ions, may play a major role in chemical modification at short times near the surface of the material, while VUV photons contribute to the majority of the damage in the bulk.

Properties of silicious film on polycarbonate substrate prepared by vacuum ultraviolet irradiation: Effect of intermediate silane layer

We studied the effect of vacuum ultraviolet irradiation (VUV) on siliceous coatings of polycarbonate substrates derived by the sol–gel method, with the aim of improving the abrasion resistance of the substrate surface. The experimental conditions to insert an intermediate silane layer between siliceous film and polycarbonate substrate were examined in order to enhance the abrasion resistance and adhesion strength, using four kinds of silane coupling reagents, i.e., 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilne, phenyltriethoxysilne and ethyltriethoxysilane. After the formation of intermediate silane layer on the PC substrate, siliceous film was further prepared on it by VUV irradiation of the spin-coated sol solution containing methyltriethoxysilane and colloidal silica. Among the silanes examined in this research, 3-aminopropyltrimethoxysilne notably played a role as an appropriate intermediate layer for the enhanced abrasion resistance of siliceous-coated polycarbonate substrate. The average transmittance was kept as high as 70% even after abraded 140 turns.

Effects of vacuum ultraviolet radiation on deposited and ultraviolet-cured low-k porous organosilicate glass

The authors compare the effects of vacuum ultraviolet (VUV) irradiation on pristine and UV-cured low-k porous organosilicate glass (SiCOH). The authors find that during VUV irradiation, more trapped charges are generated in UV-cured SiCOH as compared to pristine SiCOH. VUV is also used as a tool to investigate effects of UV curing. From comparison of VUV spectroscopy and photoinjection current of the two samples, the authors find that UV curing reduces the number of defect states in SiCOH. The authors also find that UV-cured SiCOH has higher photoconductivity and intrinsic conductivity from VUV spectroscopy and trapped-charge decay rate, respectively.

低温等离子体表面改性提高材料的亲水性 of materials by Low Temperature Plasma Surface Treatment

为了提高材料表面的亲水性，应用低温等离子体技术对材料进行表面改性而提高其润湿性；初步探讨了真空紫外辐射对表面改性的影响；改性后疏水性材料表面的润湿性得到了明显改善，该技术与设备具有一定工业应用推广价值。 In order to improve the hydrophilic ability, the materials were treated by low temperature plasma to achieve its surface modification and improve its wettability. The effect of vacuum ultraviolet radiation to surface modification was initially described. The better wettability of hydrophobic material can be achieved, and the technique and the equipment have the promotional value for industrial application.

Radiation-induced decomposition of the metal-organic molecule Bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II)

The effects of vacuum ultraviolet radiation on the adsorbed copper center molecule bis(4-cyano-2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) (or Cu(CNdpm)2), (C24H36N2O4Cu, Cu(II)) was studied by photoemission spectroscopy. Changes in the ultraviolet photoemission spectra (UPS) of Cu(CNdpm)2, adsorbed on Co(111), indicate that the ultraviolet radiation leads to decomposition of Cu(CNdpm)2 and this decomposition is initially dominated by loss of peripheral hydrogen.

Synergistic effects of vacuum ultraviolet radiation, ion bombardment, and heating in 193nm photoresist roughening and degradation

The roles of ultraviolet/vacuum ultraviolet (UV/VUV) photons, Ar+ ion bombardment and heating in the roughening of 193nm photoresist have been investigated. Atomic force microscopy measurements show minimal surface roughness after UV/VUV-only or ion-only exposures at any temperature. Simultaneous UV/VUV, ion bombardment, and heating to surface temperatures of 60–100°C result in increased surface roughness, and is comparable to argon plasma-exposed samples. Ion bombardment creates a modified near-surface layer while UV/VUV radiation results in loss of carbon-oxygen bonds up to a depth of ∼100nm. Enhanced roughness is only observed in the presence of all three effects.