Vacuum Ultraviolet Exposure Research Articles

Modification of Porous Ultralow-k Film by Vacuum Ultraviolet Emission

Modification of spin-on-deposited porous PMO (periodic mesoporous organosilica) ultralow-k (ULK) SiCOH films (k = 2.33) containing both methyl terminal and methylene bridging groups by vacuum ultraviolet (VUV) emission from Xe plasma is studied. The temporal evolution of chemical composition, internal defects, and morphological properties (pore structure transformation) is studied by using Fourier transform infrared spectroscopy, in situ laser ellipsometry, spectroscopic ellipsometry, ellipsometric porosimetry (EP), positron-annihilation lifetime spectroscopy (PALS), and Doppler broadening positron-annihilation spectroscopy. Application of the different advanced diagnostics allows making conclusions on the dynamics of the chemical composition and pore structure. The time frame of the VUV exposure in the current investigation can be divided into two phases. During the first short phase, film loses almost all of its surface methyl and matrix bridging groups. An increase of material porosity due to removal of methyl groups with simultaneous matrix shrinkage is found by in situ ellipsometry. The removal of bridging bonds leads to an increase of matrix intrinsic porosity. Nevertheless, when the treated material is exposed to the ambient air, the sizes of micro- and mesopores and pores interconnectivity decrease with the VUV exposure time according to PAS and EP data. The last is the result of the additional film shrinkage caused by atmosphere exposure. During the second phase the increase of mesopore size is detected by both EP and PAS. The increase of mesopore size goes all the time as it is expected from in situ ellipsometry, but it is masked by the air exposure.

Effects of Oxygen Partial Pressure on Wood-Based Activated Carbon Treated with Vacuum Ultraviolet Light

This study uses vacuum ultraviolet (VUV) light with a wavelength of 172 nm as a surface treatment to enhance the adsorption capacity of wood-based activated carbon (AC). The AC surface treatment is performed under three O2 partial pressure conditions—5.0 × 104 Pa, where ozone (O3) effects dominate; 6.3 × 10−6 Pa, where VUV effects dominate; and 1.9 × 103 Pa for a balanced condition. For the O3-dominant condition, only graphene edge defects are etched (no aromatic carbon bonds are etched), resulting in increased surface roughness. When the VUV effects dominate, aromatic carbon bonds are cleaved, which then reacted with O2 or water adsorbed inside the pores. This increased both the number and size of the mesopores. Under the balanced conditions, the water adsorption capacity was enhanced by 45.5%, which is higher than that obtained before VUV exposure or with VUV under other conditions. This is because the surface roughness increased, as well as the pore sizes and numbers under the balanced condition. These results indicate that we can control VUV-based AC surface treatments via O2 partial pressure.

Vacuum-UV and Low-Energy Electron-Induced DNA Strand Breaks - Influence of the DNA Sequence and Substrate.

DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7-2.3×10-16 cm2 . The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies <3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold.

A Novel Photo Cross-Linkable Polymer Insulator for Printed OTFTs with Surface Selective Deposition By Vacuum-Ultraviolet Irradiation

To realize printed manufacturing of electronic devices, including flexible displays, sensors, and integrated circuits that incorporate organic thin-film transistors (OTFT), developing and improving the materials and technologies used in this process is required. Solution processable organic semiconductors, insulating materials, and high-resolution patterning techniques of printed electrodes are all critical components of these electronic devices. The surface properties of insulators are particularly important because they contribute significantly to carrier transport at the interface of the organic semiconductors and affect the patterning of the printed electrode. Insulating materials that are solution-processable typically require high temperatures (∼150 °C) and long curing times during fabrication, which is undesirable because these conditions can cause significant distortion of common flexible substrates, such as polyethylene naphthalate. Thermal deformation of a flexible substrate prevents high-resolution patterning and the accurate alignment of the different layers within a device, and these problems become more significant as the size of the substrate increases. To overcome some of these challenges, we have recently developed a novel styrene-based polymer (PC200) for use as an insulating material that can be cured quickly via photo cross-linking. This material can be produced under atmospheric conditions, does not require heat treatment, is highly electrically insulating and has a low dielectric constant. Additionally, the surface of the PC200 insulating film can be transformed into a hydrophilic, wettable surface by selective irradiation using vacuum ultraviolet (VUV) radiation via a photomask. This allows the formation very fine printed electrodes using a metal nanoparticle ink. VUV exposure in air generates oxygen radicals and ozone molecules, which cause chemical bond dissociation on the polymer surface and render the region hydrophilic, resulting in patterned surfaces that are wettable. Compared with perfluoropolymers or parylene insulating films that have been reported recently, surface modification of the PC200 insulating film is relatively simple and requires less VUV irradiation. In this work, we have examined the electrical insulating properties of the PC200 insulator film and incorporated it into a short-channel OTFT with the recently developed soluble semiconductor (dithieno[2,3-d:2’,3’- d’]benzo[1,2-b:4,5-b’]dithiophene, DTBDT). The PC200 film was formed by spin-coating and subsequent UV exposure without heat treatment. The insulator film exhibited low surface roughness (RMS 0.5 nm), high electrical insulation (>3 MV/cm) and a low dielectric constant (εr=2.7). Additionally, we were able to form fine patterned electrodes on the polymer insulator with a minimum channel length of 5 μm using a VUV patterning technique. Importantly, these fine patterns (<10 μm) were formed without requiring a photoresist and wet-etching techniques, unlike conventional methods, such as photolithography. We fabricated short-channel OTFTs using the PC200 film as the patterning layer for printed Ag electrodes and DTBDT as the active layer. The OTFTs exhibited pronounced saturation curves with a steep onset and a sub-threshold swing of 0.3 V/dec, a low threshold voltage of −0.8 V, negligible hysteresis, a hole mobility of 0.5 cm2/Vs and a very large I on/I off ratio above 107. These results demonstrated that the PC200 insulator shows great promise for realizing a variety of flexible and printable electrical circuits for use in displays and sensors.

Effect of VUV Lamp on Wafer Charging by Single-Wafer Wet Clean

Wafer charging becomes an increasingly important issue, thus being a key parameter in 10 nm and sub-10 nm technology nodes. Single-wafer cleaning equipment has various advantages over batch-type processes, and adoption has been widespread in both BEOL and FEOL manufacturing. Since the process module is constructed primarily of plastic for chemical compatibility, there are significant challenges in managing charge build-up to an acceptable level. Amongst known charging failure modes, an arcing event is the most destructive toward device yield. Hagimoto, Matz, and Halladay discovered that cleaning chemistries with different conductivity and film stacks generate different types of punch-through defects on the wafer surface. Dielectric layers such as SiO2 and Si3N4 are where these charges accumulate. Typically these charges could be dissipated by Ionized CO2 Water (DI-CO2) [4, 5, 6]. However, 10 nm BEOL processes have a very tight specification on Cu film loss, limiting the use of DI-CO2. Hayashi et al. reported that dilute NH4OH has lower Cu etch rate than does DI-CO2and also has high discharge capability [7]. In this study, a different approach is investigated. A vacuum ultraviolet (VUV) lamp is used to dissipate charge generated in a de-ionized water (DIW) single-wafer clean process. Experimental A VUV lamp (wavelength ~200-nm) is used on wafer discharging. 1,000 Å thermal oxide wafers were processed with DIW-only at 200 rpm, 60s, and 1 lpm flow with center dispense. Charging profiles were measured on a Qcept metrology tool. Results Figure 1 shows the effect of VUV discharging. The solid lines represent typical wafer charging by a DIW process. The thermal oxide wafer is negatively charged at the center. This is because of DIW tribo-electric charging effects from the DIW dispense at the center of the wafer. At the wafer edge, the process generates positive charge. The mechanism is correlated with the center-negative charging. When Si-OH at the center is negatively charged, H+ ions are generated; these spin out from the wafer center and accumulate at the wafer edge. In Figure 1a, the VUV lamp is located at the wafer center, and the post-VUV exposure charging profile is changed from -10V to 0V (broken lines). In Figure 1b, the VUV lamp is located at the wafer edge, and it also shows from +4V to 0V discharging. Two sets of data suggest that VUV can neutralize both positive and negative charges. In order to understand if there is any negative impact of VUV exposure, k-value shift of the dielectric film is measured. In Table 1, k-values are compared for different wafer locations – center, middle, and edge. The VUV nozzle is scanned from center to edge. The results are normalized to reference data with no VUV exposure. The center area showed a severe k-value shift with prolonged exposure time. This means that optimized exposure is needed to minimize damage due to VUV. Additional damage studies and optimized VUV scan profile will be introduced in the conference. <align="left">(a) (b) Fig. 1: VUV discharge effects: (a) wafer center-negative charges are dissipated, (b) wafer edge-positive charges are dissipated. Table 1: Low-k film k-value shift after VUV exposure. By zone VUV 10s (normalized) VUV 120s (normalized) VUV 600s (normalized) Center 1.19 1.35 1.91 Middle 1.03 1.06 1.08 Edge 1.02 1.03 1.01 References [1] D. S. L. Mui, E. H. Lenz, C. Cyterski, K. Venkataraman and M. Kawaguchi, IEEE Transactions on Semiconductor Manufacturing., 24, Issue 4 (2011), 552. [2] Y. Hagimoto, H. Iwamoto, Y. Honobe, T. Fukunaga and H. Abe. Solid State Phenomena, 145-146, (2009), 112. [3] M. Wada, T. Sueto, H. Takahashi, N. Hayashi and A. Eitoku, Solid State Phenomena, 134, (2008), 263. [4] T. Guo, T. Tsai, C. Chien, M. Chan, C. Yang and J. Wu, Solid State Phenomena, 187, (2012), 63. [5] J. Halladay, B. Teeter, R. Newcomb, W. Usry, J. Yoo, K. Lam, J. Lansford and B. Brennan, Proceedings of SPCC08, Austin, TX, April (2008). [6] P Matz, T. Hurd, K. Cunningham et al., Proceedingsof the 212th ECS meeting, 7-10 October, (2007). [7] Y. Hayashi, M. Kawakami, D. Yano and K. Yamanaka, ECS Transactions, 69 (8), (2015), 37. Figure 1

Effect of VUV Lamp on Wafer Charging by Single-Wafer Wet Clean

Vacuum ultraviolet (VUV) is investigated for removing single-wafer clean-related charging. Very short exposure time, within 10 s, successfully removed both positive and negative charging created by the single-wafer wet clean process. Comparing to results from other wavelength and past studies, an electron-hole pair excitement mechanism is proposed to explain the VUV charging removal of embedded charging in SiO2 films. The proposed mechanism raised a concern for film damage. Oxide capacitance/voltage (CV) curves and MOS capacitor oxide leakage currents are measured. CV curves showed a negative impact from VUV, but MOS capacitors can tolerate short VUV exposure times. The positive and negative impacts from VUV exposure are discussed.

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.

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.

Measurements of Schottky barrier at the low-k SiOC:H/Cu interface using vacuum ultraviolet photoemission spectroscopy

The band alignment between copper interconnects and their low-k interlayer dielectrics is critical to understanding the fundamental mechanisms involved in electrical leakage in low-k/Cu interconnects. In this work, vacuum-ultraviolet (VUV) photoemission spectroscopy is utilized to determine the potential of the Schottky barrier present at low-k a-SiOC:H/Cu interfaces. By examining the photoemission spectra before and after VUV exposure of a low-k a-SiOC:H (k = 3.3) thin film fabricated by plasma-enhanced chemical-vapor deposition on a polished Cu substrate, it was found that photons with energies of 4.9 eV or greater can deplete accumulated charge in a-SiOC:H films, while VUV photons with energies of 4.7 eV or less, did not have this effect. These critical values were identified to relate the electric potential of the interface barrier between the a-SiOC:H and the Cu layers. Using this method, the Schottky barrier at the low-k a-SiOC:H (k = 3.3)/Cu interface was determined to be 4.8 ± 0.1 eV.

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 plasma and vacuum-ultraviolet exposure on the mechanical properties of low-k porous organosilicate glass

The effects of plasma exposure and vacuum-ultraviolet (VUV) irradiation on the mechanical properties of low-k porous organosilicate glass (SiCOH) dielectric films were investigated. Nanoindentation measurements were made on SiCOH films before and after exposure to an electron-cyclotron-resonance plasma or a monochromatic synchrotron VUV beam, to determine the changes of film hardness, elastic modulus, and crack threshold due to these exposures. This permits the effects of ion bombardment and photon bombardment to be analyzed separately. The role of energetic ions was examined with a variety of inert plasma-exposure conditions. The role of VUV photons was analyzed as a function of synchrotron photon energy. It was found that both energetic ions and VUV photons with energies larger than the bond energy of the Si-O bond cause a significant increase in film hardness along with a smaller increase in elastic modulus and crack threshold. Differential Fourier transform infrared spectra and x-ray photoemission spectroscopy results show that the energetic ions affect the SiCOH properties mainly through physical bombardment, during which the ions transfer their momentum to the Si-O-Si backbone and transform them into more energetically stable Si-O-Si network structures. This results in the Si-O-Si network structures becoming densified. VUV photons assist reaction that increase the number of bridging O3≡Si-O-Si≡O3 bonds and deplete nonbridging O3≡Si-O and C-Si≡O3 bonds. This increased degree of cross linking in porous organosilicate dielectrics can substantially enhance their hardness and elastic modulus while showing no significant film shrinkage or densification.

Bandgap measurements of low-k porous organosilicate dielectrics using vacuum ultraviolet irradiation

Vacuum ultraviolet (VUV) photoemission spectroscopy is used to investigate the effect of VUV radiation on porous organosilicate (SiCOH) dielectrics during plasma processing. By comparing photoemission spectroscopic results before and after VUV exposure, VUV irradiation with photon energies less than 9.0 eV was found to be beneficial in depleting accumulated charge in SiCOH films while VUV photons with higher energies did not have this effect. Moreover, VUV irradiation with 8.9 eV photons depletes the most charge. From this result, it can be concluded that 8.9 eV is the bandgap plus the electron affinity energy of SiCOH dielectrics.

The effects of plasma exposure and vacuum ultraviolet irradiation on photopatternable low-k dielectric materials

The effects of plasma exposure and vacuum-ultraviolet (VUV) irradiation on photopatternable low-k (PPLK) dielectric materials are investigated. In order to examine these effects, current-voltage measurements were made on PPLK materials before and after exposure to a variety of inert plasma-exposure conditions. In order to examine the effects of photon irradiation alone, PPLK samples were also exposed to monochromatic synchrotron radiation with 10 eV photon energy. It was found that plasma exposure causes significant degradation in electrical characteristics, resulting in increased leakage-currents and decreased breakdown voltage. X-ray photoelectron spectroscopy measurements also show appreciable carbon loss near the sample surface after plasma exposure. Conversely, VUV exposure was found to increase breakdown voltage and reduce leakage-current magnitudes.

Ion and Vacuum Ultraviolet Photon Beam Effects in 193 nm Photoresist Surface Roughening: The Role of the Adamantyl Pendant Group

AbstractPrevious studies have identified a synergistic effect of ion bombardment, vacuum ultraviolet (VUV) radiation, and moderate substrate heating in 193 nm photoresist (PR) surface roughening. The degree of surface roughness is comparable to that obtained from typical plasma etch processes. Ion bombardment results in a carbon‐rich surface layer with a thickness of a few nanometers, and VUV radiation causes bulk modification to a depth of about 100 nm. The probable difference in mechanical properties between the carbon‐rich surface layer and the softened underlayer is proposed to be the main cause of PR surface roughening. In the same vacuum beam apparatus, we further characterize the roughening of associated homopolymers: poly‐(2‐methyl‐2‐adamantyl methacrylate) (p‐MAMA) and poly‐(R‐functionalized adamantyl methacrylate) (p‐RAMA). MAMA is the leaving group, and RAMA is the polar group in 193 nm PR, respectively. Monitored by ex situ transmission FTIR and in situ mass spectrometry, p‐MAMA undergoes temperature‐dependent bulk degradation during VUV exposure while p‐RAMA is relatively insensitive to VUV. We identify the adamantyl leaving group as one of the main photolysis products from p‐MAMA. Higher substrate temperatures increase the vapor pressure and facilitate desorption of the detached adamantyl leaving group. The adamantane loss/detachment shows strong correlation to PR surface roughening. A bi‐layer wrinkling mechanism is proposed to qualitatively explain the observed surface roughening. The present results demonstrate that PR leaving group content and structure can couple to plasma etching processes and strongly alter post‐etch surface morphology. magnified image

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.

Study on 172‐nm vacuum ultraviolet light surface modifications of polydimethylsiloxane for micro/nanofluidic applications

AbstractIn this study, we developed a technique for modifying the surface of the silicone elastomer Poly(dimethylsiloxane) (PDMS) by 172‐nm wavelength vacuum ultraviolet (VUV) light exposure. Such materials have high potential for application to micro/nanofluidic devices if their surface properties can be adequately controlled. The hydrophilicity, zeta potential and bonding strength of the VUV‐exposed surfaces were investigated and compared to surfaces exposed to conventional vacuum oxygen plasma. It was found that the proposed technique was effective at modifying the surface conditions from hydrophobic to hydrophilic, increasing the zeta potential, and allowing good bonding to glass. The time required to produce the maximum bonding strength was found to be similar to that for vacuum oxygen plasma exposure. However, since VUV exposure does not require the creation of a vacuum, it offers a faster turnaround, making it suitable for mass production. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Interfacial Chemistry of Poly(methyl methacrylate) Arising from Exposure to Vacuum-Ultraviolet Light and Atomic Oxygen

We herein report on the chemical and physical changes that occur in thin films of poly(methyl methacrylate), PMMA, induced by exposure to high-energy vacuum ultraviolet radiation and a supersonic beam of neutral, ground electronic state O((3)P) atomic oxygen. A combination of in situ quartz crystal microbalance and in situ Fourier-transform infrared reflection-absorption spectroscopy were used to determine the photochemical reaction kinetics and mechanisms during irradiation. The surface morphological changes were measured with atomic force microscopy. The results showed there was no enhancement in the mass loss rate during simultaneous exposure of vacuum ultraviolet (VUV) radiation and atomic oxygen. Rather, the rate of mass loss was impeded when the polymer film was exposed to both reagents. This study elucidates the kinetics of photochemical and oxidative reaction for PMMA, and shows that the synergistic effect involving VUV irradiation and exposure to ground state atomic oxygen depends substantially on the relative fluxes of these reagents.

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

Spin-on silicon-nitride Films for Photo-lithography by RT Cure of Polysilazane

Perhydropolysilazane (PHPS) is widely used as high cure temperature pre-ceramic polymer. In this paper, we report the conversion of PHPS films into solvent insoluble amorphous-silicon-nitride at room temperature in an inert atmosphere by vacuum ultra-violet (VUV) exposure. The films were deposited using spin-coating and pre-baked at 80°C for 3 mins before VUV exposure. The FT-IR spectra show an increase in Si-N bonds, a large reduction in Si-H content and complete elimination of N-H on VUV exposure. The refractive index (RI) ∼2.1 and extinction coefficient (k) ∼0.45 at 193nm were calculated using Cauchy fitting of spectroscopic ellipsometry (SE) measurements. The extinction coefficient exhibits a linearly dependence on VUV exposure time, suggestive VUV exposure time can be used a parameter to control the optical parameters of the films. These films could be used as inorganic-BARC (bottom anti-reflection coating) for ArF photolithography and the results are in accordance with the ProLith simulations showing that film of thickness ∼22nm corresponding to the 1st minima of the swing curve is sufficient for pattern generation.

Absolute vacuum ultraviolet flux in inductively coupled plasmas and chemical modifications of 193 nm photoresist

Vacuum ultraviolet (VUV) photons in plasma processing systems are known to alter surface chemistry and may damage gate dielectrics and photoresist. We characterize absolute VUV fluxes to surfaces exposed in an inductively coupled argon plasma, 1–50 mTorr, 25–400 W, using a calibrated VUV spectrometer. We also demonstrate an alternative method to estimate VUV fluence in an inductively coupled plasma (ICP) reactor using a chemical dosimeter-type monitor. We illustrate the technique with argon ICP and xenon lamp exposure experiments, comparing direct VUV measurements with measured chemical changes in 193 nm photoresist-covered Si wafers following VUV exposure.