Vacuum Ultraviolet Treatment Research Articles

Influence of porosity on electrical properties of low-k dielectrics irradiated with vacuum-ultraviolet radiation

During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation emitted from the plasma. The porous structure of these materials makes them more sensitive to modification because of their low density and consequently deep penetration of active species into the film. Here, we investigate the changes to electrical properties of porous low-k dielectrics as a function of porosity after VUV irradiation. Organosilicate low-k films of porosities between 30% and 50% were exposed to synchrotron VUV radiation at 8 eV with a fluence of approximately 5 × 1014 photons/cm2. Capacitance-voltage measurements showed an increase in the dielectric constant along with a flat-band voltage shift. FTIR results show methyl depletion as well as water uptake after VUV treatment. These show that deterioration of the electrical properties after VUV exposure and the degree of damage are found to be higher for the more porous films.

Nanoimprint-induced orientation of localized wrinkles with SU-8

With thermal processing of multilayer systems' prevention of wrinkling is challenging, but when wrinkling results in well-controlled patterns, this self-forming process is interesting for a lot of applications, in particular, when mechanically stable and transparent materials are involved. The authors use the widely used negative tone photoresist SU-8; the hard top layer is realized by vacuum ultraviolet-treatment. Applicability of the established wrinkling theories to this SU-8 system is verified. The control of wrinkling is provided by masked lithography and nanoimprint. In combination, these two techniques allow controlling the wrinkling area and, moreover, are capable of inducing anisotropy to the wrinkling pattern. An analytical calculation of the anisotropy is presented and compared to experimental results. The calculation is based on the bending stiffness of two orthogonal directions. Two types of imprinted line-structures are investigated, normal and inverted V-grooves. Wrinkling amplitudes and anisotropies found are in good accordance with theoretical results.

Permanent hydrophilic modification of polypropylene and poly(vinyl alcohol) films by vacuum ultraviolet radiation

Polypropylene (PP) and Poly(vinyl alcohol) (PVA) both synthetics polymers but one of them biodegradable, were surface modified by vacuum ultraviolet (VUV) irradiation. After VUV irradiation in an inert nitrogen atmosphere, the films were exposed to oxygen gas. The treated films were characterized by water contact angle measurements (WCA), optical profilometry, FTIR-ATR, XPS, UPS and NEXAFS techniques. PP and PVA VUV-treated films reached superhydrophilic conditions (WCAs <10°) in about 30min of irradiation under our experimental conditions. It was observed that when the WCAs reached about 35–40° the hydrophilicity was permanent in both polymers. These results contrasted with typical plasma treatments were a rapid hydrophobic recovery with aging time is usually observed. UPS and XPS data showed the presence of new functionalities on the PP and PVA surfaces that were assigned to COO, CO, CO and CC functional groups. Finally, grafting of styrene (ST) as a typical monomer was tested on PP films. It was confirmed that only in the VUV irradiated region an efficient grafting of ST or polymerized ST was found. Outside the irradiated regions no ST grafted was observed. Our results showed the potential use of VUV treatment for surface modification and processing of polymers which lack chromophores in the UV region.

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.

Solid‐state bonding of silicone elastomer to glass by vacuum oxygen plasma, atmospheric plasma, and vacuum ultraviolet light treatment

We experimentally demonstrated that treating a silicone elastomer by a vacuum oxygen plasma, an atmospheric pressure plasma, and vacuum ultraviolet (VUV) radiation resulted in different surface modifications that gave different contact angles, contact angle aging, and bond strengths. The aim of this study was to assess whether high‐throughput surface modification techniques of atmospheric pressure plasma and VUV radiation have the potential to replace conventional oxygen plasma modification. Four silicone elastomers with different hardnesses were used as specimens. The surfaces of all four silicone elastomers were successfully modified from hydrophobic to hydrophilic and they were also bonded to glass surfaces by the three surface modification techniques, although considerable variations were observed in the surface hydrophobicity and the bonding properties. The results clearly reveal that atmospheric pressure plasma and VUV treatment have the potential to replace conventional oxygen plasma treatment. In particular, VUV irradiation produced the most hydrophilic surface that was preserved for a long time. Thus, VUV irradiation is the most promising technique for realizing high‐throughput surface modification and bonding of silicone elastomers. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Effects of Vacuum Ultraviolet Surface Treatment on the Bonding Interconnections for Flip Chip and 3-D Integration

This paper focuses on the effects of a vacuum ultraviolet (VUV) surface treatment process on the interconnections for flip chip and 3-D integration. Organic contaminants that hinder reliable bonding are broken down and eliminated from the bumps and pad surfaces by irradiation with UV light at a wavelength of 172 nm at room temperature. There is no charge buildup, no temperature increase, and no ion bombardment damage during the process. Two different VUV cleaning conditions, with N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas in the vacuum chamber, were compared and evaluated. Samples of flip chip with Cu/Sn bumps and Au surface substrate were examined by measurement of contact angle, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) before and after VUV surface treatment. Cleaning times and ambient conditions have dramatic effects on the surface contact angles. The photoelectron spectra of C 1s were obtained by XPS analysis for information on the chemical species and the XPS results showed a reduction in surface carbon for both Au and Cu/Sn after the cleaning. The evidence indicates cleavage of the carbon-carbon bonds in the organic molecules occurs during the cleaning process. From the shear test results, it appears that VUV treatment improves the Cu/Sn-bump bonding strength, making it two times larger than for untreated samples. No delamination or obvious voids were detected on the bonding interface by Scanning acoustic microscopy (SAM) and cross-sectional SEM analysis. The experiments show that the VUV cleaning can effectively remove the organic contaminants on the surface of the bonding pads and improve the bonding strength.

Effects of Excimer Irradiation Treatment on Thermocompression Au–Au Bonding

We studied the feasibility of using vacuum ultraviolet (VUV) treatment as a surface improvement technique with Au–Au flip-chip bonding. For fine-pitch electrical interconnections in three-dimensional (3D) stack applications, robust and reliable bonding is desirable; in this case, surface modification treatment is needed before the bonding process. A VUV surface treatment was used to remove organic contaminants. Samples of electroplated Au pads were examined by X-ray photoelectron spectroscopy (XPS) to evaluate the chemical composition of the Au surfaces. The XPS results revealed that the carbon-based contaminants on the surface were removed by the VUV treatment. The shear strength of the bonded sample was also improved. The average shear strength of a bump with VUV treatment is 1.6 times larger than that of a bump without VUV treatment. Cross-sectional scanning electron microscopy (SEM) images of the bonded samples confirmed the absence of voids and cracks. The results show that VUV treatment has clear effects on Au–Au flip-chip bonding.

Vacuum ultraviolet smoothing of nanometer-scale asperities of Poly(methyl methacrylate) surface

Smoothing of the nanometerscale asperities of a poly(methyl methacrylate) (PMMA) film using vacuum ultraviolet (VUV) with the wavelength λ = 123.6 nm was studied. The exposure time and the residual air pressure in a working chamber were varied during the process of VUV treatment. A nanostructured sur� face of PMMA film is used as a sample to be exposed. The nanostructured surface of the PMMA film was obtained by treating the initially smooth spincoated film in oxygen radiofrequency plasma. The degree of VUV exposure is estimated using changes in the morphology and roughness of the nanostructured surface, which were determined by atomicforce microscopy (AFM). Recognition of morphological surface features on the AFMimages and determination of main geometri cal characteristics of these features are performed by using virtual featureoriented scanning method. It is discovered by morphology and Fourier spectra that the nanostructured surface of the PMMA film is partially ordered. The developed VUV smoothing procedure can be used to treat the electronb eam, UV, and Xray sensitive PMMA resists, PMMA elements of micro� electromechanical systems, biomedical PMMA implants, as well as to certify nanotechnological equipment incorporating UV radiation sources. DOI: 10.1134/S1027451010010015

Vacuum ultraviolet-induced surface modification of cyclo-olefin polymer substrates for photochemical activation bonding

The surface of cyclo-olefin polymer (COP) was treated with vacuum ultraviolet (VUV) light at 172nm wavelength to improve the wettability and adhesion properties. Through VUV treatment in air, the terminal groups of the COP surface were oxidized into oxygen functional groups, containing CO, CO, and COO components, making the COP surface hydrophilic. The extent of oxygenation was evaluated by XPS and FTIR-ATR spectra, and it was shown that the surface properties, hydrophilicity, and functionalization were dependent on both VUV irradiation distance and irradiation time, which have an effect on the concentration of oxygen functional groups. VUV-light treatment with a short irradiation distance was more effective in introducing oxygen functional groups.

Surface Chemical Conversion of Organosilane Self-Assembled Monolayers with Active Oxygen Species Generated by Vacuum Ultraviolet Irradiation of Atmospheric Oxygen Molecules

The chemical conversion of the top surface of n-octadecyltrimethoxy silane self-assembled monolayers (ODS-SAMs) on oxide-covered Si substrates using active oxygen species generated from atmospheric oxygen molecules irradiated with vacuum ultraviolet (VUV) light at 172 nm in wavelength has been studied on the basis of water contact angle measurements, ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. An ODS-SAM whose water contact angle was 104° on average was prepared using chemical vapor deposition with substrate and vapor temperatures of 150 °C. The VUV treatment of an ODS-SAM sample was carried out by placing the sample in air and then irradiating the sample surface with a Xe-excimer lamp. The distance between the lamp and the sample was regulated so that the VUV light emitted from the lamp was almost entirely absorbed by atmospheric oxygen molecules to generate active oxygen species, such as ozone and atomic oxygen before reaching the sample surface. Hence, the surface chemical conversion of the ODS-SAM was primarily promoted through chemical reactions with the active oxygen species. Photochemical changes in the ODS-SAM were found to be the generation of polar functional groups, such as –COOH, –CHO, and –OH, on the surface and the subsequent etching of the monolayer. Irradiation parameters, such as irradiation time, were optimized to achieve a better functionalization of the SAM top surface while minimizing the etching depth of the ODS-SAM. The ability to graft another SAM onto the modified ODS-SAM bearing polar functional groups was demonstrated by the formation of alkylsilane bilayers.

Preparation and characterization of TiO 2 thin films using vacuum ultraviolet light in a sol–gel process

In the current work, we prepared TiO 2 thin films using vacuum ultraviolet (VUV) irradiation of several different intensities before firing. We then investigated effects of VUV intensity and alkoxide mixtures on the microstructural evolution of the films. The microstructure of the film without VUV treatment comprises uniform anatase grains. Grains in films with VUV irradiation gradually form a domain-like microstructure with increasing VUV intensity. The heterogeneous hydrolysis rate in the mixed alkoxide will trigger formation of the domain-like microstructure.

Vacuum ultraviolet–induced photochemical nitriding of polyolefin surfaces

AbstractFilm samples of two very pure polyolefins, low‐density polyethylene (LDPE) and biaxially oriented polypropylene (BOPP), were surface‐modified by vacuum ultraviolet (VUV) photochemistry in low‐pressure ammonia. The influence of experimental conditions such as wavelength and intensity (photon flux) of the VUV radiation, ammonia pressure, and treatment duration, as well as the mechanisms involved in the surface modification were discussed. Changes in the surface energy and chemistry were investigated using suitable techniques like contact angle goniometry (surface energy) measurements, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance infrared spectroscopy, and time‐of‐flight secondary ion mass spectroscopy. We show that chemically bonded nitrogen concentrations [N], up to 25%, can be achieved on the polymer surfaces by VUV photochemistry, and that N is predominantly bonded as amine groups, thus leading to an important increase in the surface energy of treated samples. Finally, XPS, surface energy measurements, and atomic force microscopy were used to characterize possible degradation of the polymer surfaces during the VUV treatments. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3886–3898, 2004

Formation of Silica Coatings from Perhydropolysilazane Using Vacuum Ultraviolet Excimer Lamp

Silica coatings have been prepared by the spin-coating technique with the 172 nm vacuum ultraviolet (VUV) irradiation using a Xe2∗ excimer lamp. Perhydropolysilazane was used as a precursor. The chemical states, composition and optical transmittance of VUV-irradiated films were investigated by Fourier transform infrared, X-ray photoelectron, UV-visible absorption spectroscopies. The results showed that VUV irradiation was effective to remove hydrogen and nitrogen from the coating film and to incorporate oxygen to the film, so that the film transforms into silica. The effects of VUV treatment on the film were found to be dependent on oxygen concentration in surrounding gas. It was suggested that the effect of oxidation reaction due to active oxygen species and/or ozone is larger than that of the cleavage of a chemical bonding by photon energy.

Surface Modification of Vinyl Polymers by Vacuum Ultraviolet Light Irradiation

The photophysicochemical changes of vinyl polymers (polyethylene, polystyrene and poly(vinyl alcohol)) under 172nm vacuum ultraviolet (VUV) light irradiation from Xe2 excimer lamps were investigated by means of contact angle measurements, X-ray photoelectron spectroscopy and infrared absorption spectroscopy. The bond scission and oxygen incorporation to the polymer structure cause the formation of new functional groups (C=C, C-O, C=O, etc.), leading to the change in surface wettability. The effect of the VUV treatment on polymers depends on the surrounding gas (dry air or N2) during the irradiation.

Vacuum ultraviolet annealing of thin films grown by pulsed laser deposition

The effect of a post-deposition annealing treatment in 1 bar of oxygen at moderate temperatures (<450°C) under illumination by vacuum ultraviolet (VUV) radiation emitted by an excimer lamp upon thin ZrO 2 and hydroxyapatite (HAp) films grown by the pulsed laser deposition (PLD) technique was investigated. The optical and structural properties of the films were improved by this treatment, the lower the deposition temperature and, accordingly, the poorer the initial characteristics, the more significant the improvements. The combination of these two techniques allowed us to obtain at temperatures below 350°C highly textured (020) ZrO 2 films, exhibiting optical absorption coefficients lower than 5×10 2 cm −1 and high refractive index values of around 2.25 in the visible region of the spectrum. The VUV treatment was also beneficial for the partially crystalline HAp layers containing tetracalcium phosphate and calcium oxide phases grown by the PLD technique under a low pressure oxidising atmosphere of only 10 −5 torr without any water vapours. After the VUV-assisted anneal, the crystalline structure and the stoichiometry greatly improved while the percentage of the other crystalline phases initially present was many times reduced.

Photolysis of a fluorinated polymer film by vacuum ultraviolet radiation

We studied the photolysis of a fluoroethylene–fluoropropylene copolymer (FEP) film by vacuum ultraviolet (VUV) radiation from a resonance Xe lamp at a wavelength of 147 nm and air pressures of 0.05 and 2.5 Torr. The chemical changes in the FEP surface layer were investigated by Fourier-transform infrared spectroscopy with attenuated total reflection attachment and X-ray photoelectron spectroscopy. Double bonds were found to be the main product in the case of VUV treatment at 0.05 Torr, while photo-oxidation of FEP occurred predominantly by VUV treatment at 2.5 Torr under formation of the —CF2C(O)F group. This oxygen-containing group was more effectively formed in the FEP surface layer by VUV photo-oxidation than by conventional surface oxidation techniques such as treatments by plasma and corona discharge and ozone. Storage of the VUV-treated polymers in air at 50% relative humidity resulted in hydrolysis of —CF2C(O)F to the —CF2COOH group. Substantial improvement of the film wettability was noticed after VUV photo-oxidation. These findings suggest that VUV irradiation provides a high potential for surface modification of fluorinated polymers which are known to be particularly resistant against functionalization by conventional surface modification techniques such as plasma treatment. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2215–2222, 1998

Improvement of the micro-wear resistance of silicone by vacuum ultraviolet irradiation

The change in micro-wear of polymers, especially a silicone rubber after vacuum ultraviolet(VUV) irradiation at the wavelength of 147 nm, was studied by means of AFM in scratching mode. It was found that the effect of VUV irradiation on polymer surface micro-wear was related to the extent of crosslinking, strongly depending on the chemical structure of polymers and irradiation conditions. The VUV treatment both in the presence of air and in vacuum resulted in a significant decrease in the micro-wear of silicone. In addition, VUV irradiation made the siloxane smoother, characterized by about a three-fold decrease in the average roughness. ESCA spectra revealed that the improvement in the micro-wear of silicone by VUV irradiation in vacuum (0.05 torr) and VUV photooxidation in air (2.5 torr) was associated with the formation of two different types of crosslinks via CH2 groups and O atoms, respectively.

Quantitative Comparison Between Vacuum-Ultraviolet Irradiation and Remote Hydrogen Plasma Treatment of Hydrocarbon Polymers

The photon flux of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation of a hydrogen plasma with and without a MgF2window was recorded by fluorescence measurements of sodium salicylate layers. After the compensation of the MgF2absorption by increasing the input power into the plasma source, a comparison between afterglow hydrogen plasma and VUV treatments was made. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were treated either with VUV radiation or with remote hydrogen plasma and mass loss and CH absorption loss were measured by a quartz crystal microbalance and by infrared reflection absorption spectroscopy, respectively. In the case of PE the effects of both treatments were found to be very similar white for PP slight differences were observed. For the actual set of experimental conditions, the radiation component is largely responsible for the efficiency of the plasma treatment. VUV and remote hydrogen plasma treatments of PS showed only a negligible loss of mass and CH absorption.

Experimental Evidence for the Dominance of vuv Photons in Remote Hydrogen Plasma Treatments

AbstractThe flux of vacuum ultraviolet (VUV) and ultraviolet (UV) photons from a hydrogen plasma was detected by fluorescence measurements of sodium salicylate sheets with and without a MgF2 window. In order to expose the samples to the same photon flux in all experiments, the power input to the microwave plasma source was adjusted. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were treated with VUV radiation or with a remote hydrogen plasma. The mass loss and the CH-absorption loss were recorded by in situ quartz crystal micro balance and by in situ IR reflection absorption spectroscopy, respectively. The VUV irradiation and plasma treatment caused similar effects in the case of PE, PP showed an increased polymer ablation in plasma treatments, and for PS a negligible loss in mass and CH absorption was detected in plasma and VUV treatments.