Synchrotron Radiation Irradiation Research Articles

Direct Photo-Etching and Surface Modification of Polytetrafluoroethylene by Synchrotron Radiation

Micromachining of various polytetrafluoroethylene (sintered PTFE, non-sintered PTFE and expand PTFE) using synchrotron radiation (SR) direct photo-etching has been carried out, and also the etched surface was studied by various analyses. The thin sintered (10μm) and expand (80μm) PTFE films were piled up, and the layered PTFE and non-sintered PTFE (1.2mm) irradiated by SR below the melting temperature, in order to clarify the degree of chemical and physical changes according to the depth from the etched surface. SR irradiated films were examined by 19F solid-state magic-angle spinning (MAS) NMR spectroscopy and differential scanning calorimetric (DSC) analysis. The results showed that the modification by SR irradiation depended on the depth from the surface: within about 60μm from the surface, the network structure formation would be induced even in its solid state; in deeper regions, the chain scission would be dominant. Furthermore, SR was irradiated for non-sintered PTFE with different molecular conformation, compared with usual PTFE. It was found that non-sintered PTFE was also crosslinked in the surface region. Moreover, the sintered and non-sintered PTFE could be etched well. In the case of non-sintered PTFE, the distance of the non-etched remaining structures shrank by heat-treatment at 360°C. The shrinking was about 20%.

Synchrotron-radiation-stimulated etching of SiO2thin films with a tungsten nano-pillar mask

A nano-pattern of SiO(2) on a Si (100) surface has been demonstrated by synchrotron-radiation-stimulated etching with a tungsten nano-pillar mask. The reaction gas was a mixture of SF(6) and O(2). The mask was fabricated using a focused ion beam with W(CO)(6) as the source gas. The width and height of the tungsten nano-pillar were approximately 80 nm and 160 nm, respectively. Synchrotron radiation irradiation with flowing SF(6) and O(2) effectively etches the silicon dioxide, and the etching process followed the surface photochemical reaction. The etched surface was very flat, and no undercutting occurred during the etching process.

Synchrotron radiation stimulated etching of SiO2 thin films

The synchrotron radiation (SR) stimulated etching of SiO2 thin film surface was investigated with a contact cobalt mask, and the etched pattern of SiO2 thin films on silicon was made. The SiO2 thin film was grown on silicon surface by thermal oxidation. The contact cobalt mask was fabricated on SiO2 thin film by combining the techniques of photolithography and RF-magnetron sputtering. In the experiment, the anisotropic etching of SiO2 was effectively achieved by SR radiation with SF6 as the reaction gas. The etching rate increased with increasing gas pressure of SF6 in a certain range, and with decreasing the substrate temperature. Under SR irradiation with flowing SF6 and O2 did not etch the silicon crystal and the etching stopped completely at the SiO2/Si interface. Furthermore, the Co provided high resistance against the SR etching, indicating that Co is an ideal mask material for the synchrotron radiation stimulated etching.

Temperature effect on the chemical composition of a polytetrafluoroethylene surface under the irradiation of synchrotron radiation by means of the X-ray photoelectron spectroscopy

The chemical composition and components of a polytetrafluoroethylene (PTFE) surface was investigated as a function of the temperature under the irradiation of synchrotron radiation (SR) by the X-ray photoelectron spectroscopy (XPS). When the temperature of PTFE under the SR irradiation was less than 100 °C, the C-rich surface appeared. With increasing the temperature more than 150 °C, the relative intensity of the F 1 s peak to the C 1 s peak increased markedly. At the temperatures of 150–180 °C, the C–C component became small and the CF 2 component was dominant. With further increasing the temperature more than 200 °C, CF 3, CF and C–CF components grew in addition to CF 2 component. Based on these XPS results, the temperature effect on the chemical composition and components is discussed.

Photoexcitation Process Leading to Modification on Poly(tetrafluoroethylene) Surface by Irradiation of Synchrotron Radiation in Soft X-ray Region

Photoexcitation process leading to a variation in the wettability of a poly(tetrafluoroethylene) (PTFE) surface induced by synchrotron radiation (SR) exposure in the soft X-ray region was investigated. It was found that two types of photoexcitation, that is, the formations of a hydrophobic surface and a hydrophilic surface, proceed on the PTFE surface with the exposure to SR. The formation rate of the hydrophobic surface strongly depended on substrate temperature.

Surface modification of PTFE by synchrotron radiation under the O 2 gas atmosphere

Synchrotron radiation (SR) process for the production of hydrophilic surface on PTFE sheet was examined by the SR irradiation using the gas cell filled with O 2 gas. High hydrophilic surface was obtained by the SR irradiation under the O 2 gas atmosphere. O atoms existing hydrophilic surface were considered to couple dominantly to PTFE surface during the SR exposure.

Cleaning of extreme ultraviolet lithography optics and masks using 13.5nm and 172nm radiation

Under extreme ultraviolet (EUV) exposure, the surfaces of the imaging optics and mask, which are coated with a Mo∕Si multilayer, become contaminated with organic compounds. Thus, an efficient method of removing carbon contamination from masks and the imaging optics is required. Then, we propose two methods as a removal method of contamination: one is in situ cleaning method without heating a sample by synchrotron radiation irradiation that is mainly targeted at the imaging optics, and another is cleaning method without heating a sample using by 172nm light irradiation that is targeted at an EUV lithography finished mask. For in situ cleaning so called online cleaning, the contamination removal rate is 0.24nm∕min in the condition of O2-rich-vacuum environment at a pressure of 5.0×10−2Pa and an electron beam current of 130mA of 1.0GeV electron storage ring. For offline cleaning using 172nm light, the contamination removal rate is 2nm∕min in the O2-rich-vacuum environment at the pressure of 2×10−3Pa. Both two methods restore the reflectivity of a Mo∕Si multilayer to its original level without causing any surface damage. The effectiveness of both in situ and offline contamination removal are confirmed.

Synchrotron radiation stimulated etching SiO 2 thin films with a contact cobalt mask

Patterning SiO 2 thin film on the Si (1 0 0) surface was demonstrated by synchrotron radiation (SR) stimulated etching with a contact cobalt mask. The reaction gas was a mixture of SF 6 and O 2. The contact cobalt mask was fabricated by sputtering cobalt films on a photolithography resist pattern and lift-off technique. The thickness of the mask was about 145 nm. The SR irradiation with flowing SF 6 and O 2 could effectively etch the silicon dioxide and the etching process stopped at the SiO 2/Si interface. The etching rate at room temperature was about 2.7 nm per 100 mA min. The etched pattern was evaluated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profile meter. Area-selective and anisotropy etching were achieved and the roughness ( R a) with a line profile on the etched surface was about 0.05 nm.

Synchrotron Radiation Effect in the Soft X-ray Region on the Surface Properties of Pyromellitic Dianhydride-Oxydianline Polyimide

The surface modification of a polyimide (PI) sheet using synchrotron radiation (SR) was carried out. The PI sheet was irradiated to white radiation ranging between 50–1000 eV in a vacuum chamber. The contact angle of the PI surface with a water droplet was found to decrease from 75° to 58° by the SR irradiation. The variation of chemical components of the PI surface was studied using X-ray photoelectron spectroscopy (XPS). The ratio of peak intensity from the O1s orbital to that from the C1s orbital increased remarkably by SR irradiation. The increase of wettability on the PI surface was ascribable to the production of an O-rich surface by SR irradiation in the soft X-ray region.

Shrinking of Spin-On-Glass Films Induced by Synchrotron Radiation and Its Application to Three-Dimensional Microfabrications

Photoinduced etching of siloxane-type spin-on-glass (SOG) by synchrotron radiation (SR) using a SF6/O2 etching gas and a Co contact mask has been investigated. The SOG film was etched by direct SR irradiation similarly to the case of thermally oxidized SiO2. We found that the indirect exposure to SR caused shrinkage of SOG under the Co mask. The shrinkage depth of SOG was attenuated by the thickness of the Co mask, but not eliminated even by a Co mask 350 nm thick, due to the high-energy photons (≥230 eV) being transmitted through the mask. The shrinkage phenomenon was successfully applied in the fabrication of a three-dimensional structure of the SOG thin film on Si(100). Atomic force microscopy observations showed that the surfaces were very smooth both on the completely etched Si area and on the shrunken SOG area. We investigated the mechanism of the shrinkage of SOG by Fourier-transform infrared spectroscopy.

Tantalum film for x-ray lithography mask deposited by electron cyclotron resonance plasma source coupled with divided microwaves

An advanced electron cyclotron resonance (ECR) plasma source coupled with divided microwaves has been applied to Ta film formation. The feasibility of the Ta film as an x-ray mask absorber is investigated. The stress in an x-ray absorber material must be low, uniform, and stable. According to the results of an investigation on the stress-depth distribution in Ta film, the stress can be described as the sum of interfacial stress (that retained near the film–substrate interface) and bulk stress (that retained in the film bulk). It is found that these individual stresses can be independently controlled. The interfacial stress depends on the substrate temperature, working-gas pressure, and deposition rate. The bulk stress becomes compressive by adding Ar to the sputtering gas (Xe). A low stress film of 23 MPa (400 nm thick film) with no stress-depth distribution is obtained using optimized deposition parameters of 3.3×10−2 Pa of Xe, 1.75 sccm of Ar, and 280 °C substrate temperature. The ECR Ta film showed excellent stability against stress with a change in stress of less than 5 MPa after the x-ray mask fabrication process and synchrotron radiation irradiation. A highly accurate x-ray mask is fabricated by a wafer process using an ECR-deposited Ta film. The maximum image placement (IP) error of the x-ray mask is less than 60 nm, which includes the IP error induced by membrane shrinkage during back etching.

Quality of the YB 66 crystal of BL15XU at SPring-8

The quality of the YB 66 crystal was investigated by rocking curve measurements using a conventional X-ray source and the synchrotron radiation of BL15XU at SPring-8 before and after the irradiation with synchrotron radiation. It is confirmed by evaluating the full-width at half-maximum of rocking curve and by the Lang topographic method that the YB 66 crystal has a nonuniform quality and distribution of energy resolution, and that density of dislocations and subgrain boundary structures depended on the position of the crystal, as reported previously. A significant change in the quality of the YB 66 crystal was not observed between before and after irradiation of synchrotron radiation. The qualities of single YB 66 crystals are sufficiently good to maintain a high resolution for dispersing synchrotron radiation at power density and power of not more than 1.7 W/mm 2 and 0.13 W, respectively, for about 1000 h at the third-generation light source SPring-8. Furthermore, reactivity of YB 66 crystal with GaIn was studied by SEM, EDX in the laboratory and by a transmission function of synchrotron radiation dispersed by a YB 66 (4 0 0) double-crystal monochromator in the beam study of BL15XU. From these experiments, it is concluded that the reaction of YB 66 crystal with GaIn does not occur. Thus, GaIn as an interface material between a YB 66 crystal and a Cu holder coated with Ni is available for an indirect cooling system of BL15XU at SPring-8.

X-Ray Photoelectron Spectroscopy Study of Synchrotron Radiation Irradiation of a Polytetrafluoroethylene Surface

The effect of synchrotron radiation (SR) irradiation of a polytetrafluoroethylene (PTFE) surface was investigated using X-ray photoelectron spectroscopy (XPS). After the SR irradiation, the relative intensity of the F 1s peak to the C 1s peak decreased markedly. The chemical composition ratio of the F atoms to C atoms was estimated to be 0.29. From the curve fitting analysis of C 1s and F 1s XPS spectra, the chemical components and their intensity ratio were determined. The reason for the chemical composition change by the SR irradiation was discussed.

Irradiation effect of synchrotron radiation on crystallization of thin amorphous WO 3 film

In order to elucidate the effect of synchrotron radiation (SR) irradiation on crystal growth, crystallization of WO 3 films has been performed in vacuum under SR irradiation. The main results were compared with the results of heat treatment of the same film. Upon SR irradiation for 80 s using a toroidal mirror, a catastrophic change occurred, i.e. W 3O crystals (A-15 type) with a size of less than 30 nm appeared. Decomposition of the WO 3 film started at above 750 °C during vacuum heating. W, WO 2 and incommensurate WO 3 crystals appeared. W 3O crystal produced neither intense electron beam irradiation nor vacuum heating. These results will be discussed in terms of the differences caused by excitation with a SR beam, i.e. strong inner shell excitation and ionization of W and O may have taken place.

Effects of SR irradiation on tin-doped indium oxide thin film prepared by rf magnetron sputtering

The effects of synchrotron radiation (SR) irradiation on the electrical properties of tin-doped In2O3 (ITO) thin films prepared by rf magnetron sputtering have been studied. A white SR beam focused by a cylindrical mirror was used to irradiate ITO thin films at doses of 0.35, 1.98, 3.50, and 6.64 mA h. We have achieved resistivity of 2×10−4 Ω cm on ITO thin film at an irradiation dose of 3.5 mA h without extra heating. The mobility of the ITO films did not decrease after SR irradiation. The electrical properties in connection with the structural change due to SR are discussed.

Measurement of Temperature Rise of Quartz Plate during Synchrotron Radiation Irradiation Using Infrared Camera

The temperature rise of an attenuator under synchrotron radiation irradiation was measured with an infrared (IR) camera containing an InSb detection device. Since the measured value changes with the emissivity of the measured sample, in measurement by thermography, calibration is required. In order to determine the actual temperature rise, calibration of the IR camera was performed using a hot plate as a heat source under the same geometrical arrangement as the double quartz plates with a sapphire window. The calibrated temperature rise is three times higher than the temperature rise observed with the IR camera. The calibrated temperature rise is in agreement with temperature rise predicted by simulation. As a result, it is predicted that the temperature rise of the attenuator is 119°C at a beam current of 500 mA.

On the mechanism of polytetrafluoroethylene ablation using a synchrotron radiation-induced photochemical process

To clarify the ablation mechanism of polytetrafluoroethylene (PTFE) by synchrotron radiation (SR), the effect of the photon energy distribution of an SR beam on the ablation rate was examined. Carbon (C) and a carbon/magnesium fluoride/carbon (C/MgF x /C) membranes were used as filters to modify the photon energy distribution of incident SR beam. The fragments resulting from the decomposition of PTFE by SR irradiation were measured with in situ quadruple mass spectroscopy (QMS). The ablation mechanism of PTFE is due to absorption of the SR by fluorine. In addition, SR ablation was applied to form patterns in metal fluoride films for the first time.

Microfabrication of crosslinked polytetrafluoroethylene using synchrotron radiation direct photo-etching

High aspect-ratio (more than 10) microfabrication of crosslinked polytetrafluoroethylene (PTFE) has been carried out using synchrotron radiation (SR) direct photo-etching. The etching rates of crosslinked PTFE samples with various crosslinked densities were studied by changing photon fluence of SR at different sample temperatures. The etching rate of the sample with higher crosslinking density resulted in a higher etching rate. This rate was about two times higher than that of normal PTFE. The temperature dependence of the etching rates indicated that molecular motion of α-relaxation of samples and structures of smaller fragments (i.e., etched products) produced by irradiation of SR with high dose rate play an important role for SR direct photo-etching. Moreover, we have found that surface modification of PTFE had been proceeding during irradiation of SR to the PTFE at 140 °C. The results of differential scanning calorimeter measurements for the modified layers showed that the layers might have crosslinking character.

Film Density Dependence of Polymethylmethacrylate Ablation under Synchrotron Radiation Irradiation

Variations in the etch depth and refractive index of polymethylmethacrylate (PMMA) films of different molecular weights after synchrotron radiation (SR) irradiation are investigated. Reduction of the PMMA film molecular weight, density and thickness are observed after SR irradiation. The amount of film thickness loss depends on not only initial molecular weight but also film density. The PMMA density difference at the start of SR exposure affects the etch depth after SR ablation.

Operation of the PF ring vacuum system without an in situ bake-out

The vacuum system of the PF ring was commissioned without an in situ bake-out after its upgrading reconstruction in which a great number of vacuum beam ducts were replaced by new or improved ones. The degassing of the ring was decreased sufficiently by synchrotron-radiation irradiation as expected from previous experiments. The system was successfully commissioned and the required pressure was achieved within a reasonable short period.