Yoshitoki Iijima

Prevention of the Reduction of CuO during X‐ray Photoelectron Spectroscopy Analysis

A method to prevent the reduction of CuO formed on Cu metal during x-ray photoelectron spectroscopy analysis is presented. When a bias voltage of -250 V was applied to the sample surface in the case of non-monochromatic Mg Kα 1.2 irradiation, the reduction of CuO to the lower oxide (Cu 2+ →Cu + ) was suppressed by 80-90% as compared with ordinary non-monochromatic x-ray irradiation. The degree of CuO reduction is the same as in the case of monochromatic Al Kα x-ray irradiation. It was found that slow electrons generated from the x-ray window and photoelectrons emitted from the surface by x-ray irradiation cause the reduction. As the reduction can be minimized by applying a bias voltage to the surface, the bias voltage method is very effective for preventing CuO reduction.

Surface characterization of polymethylmetacrylate bombarded by charged water droplets

The electrospray droplet impact (EDI), in which the charged electrospray water droplets are introduced in vacuum, accelerated, and allowed to impact the sample, is applied to polymethylmetacrylate (PMMA). The secondary ions generated were measured by an orthogonal time-of-flight mass spectrometer. In EDI mass spectra for PMMA, fragment ions originating from PMMA could not be detected. This is due to the fact that the proton affinities of fragments formed from PMMA are smaller than those from acetic acid contained in the charged droplet. The x-ray photoelectron spectroscopy spectra of PMMA irradiated by water droplets did not change with prolonged cluster irradiation, i.e., EDI is capable of shallow surface etching for PMMA with a little damage of the sample underneath the surface.

Surface analysis of polyimide bombarded by charged water droplets

500 eV Ar+ ion impact and the electrospray droplet impact (EDI), in which the charged electrospray water droplets are introduced in vacuum, accelerated and allowed to impact the sample, are applied for etching of polyimide (PI). After the bombardment, x-ray photoelectron spectroscopy (XPS) was applied to the surface analysis. Although oxygen and nitrogen are selectively etched by Ar+ ion impact, the XPS spectra did not change with prolonged charged water droplets irradiation, i.e., EDI is capable of shallow surface etching for PI with little damage of the sample after irradiation.

X-ray photoelectron spectroscopy analysis of organic materials etched by charged water droplet impact

Electrospray droplet impact (EDI) has been developed for matrix-free secondary ion mass spectrometry for surface analysis. When a target is etched by EDI, the physical etching on the target is suppressed to minimal, i.e., the occurrence of shallow surface etching. A novel approach to shallow surface etching of polystyrene (PS) by EDI was investigated. The charged water droplets were irradiated to a bulk and a spin coated PS. After irradiation, these samples were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. It was found that XPS spectra for PS were independent on the irradiation time by EDI. This indicates that EDI is a unique technique for the surface etching of the organic materials without leaving any damage on the etched surface.

Hardening Process and Surface Structure of Lacquer Films Studied byX‐ray Photoelectron Spectroscopy

The changes of the composition ratios and chemical binding states of the component elements in the surfaces of four varieties of lacquer films during the hardening process were studied by x-ray photoelectron spectroscopy (XPS). Additionally, the relationship between the surface structure and hardening process of lacquer films was studied by the pencil hardness testing method. The relative oxygen contents and the existence ratios among the COO, C=O, C-O-C, C-OH, C-N and N=O functional groups in the surfaces of the lacquer films increased significantly with the progress of hardening. In addition, it was revealed that a lacquer film with a faster hardening rate showed a higher relative oxygen content and a larger existence ratio among these functional groups in the surface. The increases support the progress of the following three phenomena in the surface of lacquer film during the hardening process, i.e. the concentration of gummy substances and nitrogen-containing compounds, laccase-catalysed oxidative polymerization and autoxidative polymerization.

Recent advances in the application of total reflection X-ray photoelectron spectroscopy in the semiconductor industry

A review of the applications of total reflection x-ray photoelectron spectroscopy (TRXPS) to the semiconductor surface are described. When the grazing angle of incident x-rays is below the critical angle of x-ray total reflection, the penetration depth of the x-rays into the material is strongly attenuated. Thus the surface sensitivity is enhanced, resulting in an increase in the XPS yield. This technique is particularly well suited to the study of surfaces in the thickness range 1–5 nm using soft x-rays with an energy of 1.4 keV. We have applied the TRXPS technique to the surface analysis of Si wafers. This paper is a review of data taken in our laboratories which illustrate its application to the surface analysis of Si wafers. Copyright

Analysis of Polyethyleneterephthalate Film Surface Sputtered with Ar Neutral and Ar Ion Beams

Polyethyleneterephthalate (PET) film surfaces sputtered with Ar neutral and Ar ion beams were investigated with scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). It was observed that the surface sputtered with the Ar neutral beam was flatter than that with the ion beam. AFM observation showed that the morphology size on the surface sputtered with Ar neutral beam was larger than that made by ion beam sputtering. XPS analysis showed that the decomposition of chemical bonding was reduced and the formation of amorphous carbon on the surface was suppressed when the surface was sputtered with the Ar neutral beam. The flattening mechanism could be clarified by AFM observation and XPS analysis. The sputtering process differs between the neutral beam and the ion beam with the same energy and dose.

Segregation of As on GaAs(100) Surface during Abrasion Process Studied by X-Ray Photoelectron Spectroscopy and Auger Electron Spectroscopy

When a GaAs(100) surface was mechanically scribed by a diamond tip in an ultrahigh vacuum (UHV), surface segregation of As was observed using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The same phenomenon was also seen when the surface was abraded in air using emery paper. In the latter case, angle-resolved XPS analysis of As3d and Ga3d spectra showed the formation of As-As bonds on the abraded surface. Ga-Ga bonds existed beneath the layer of As-As bonds isolated from Ga-As bonds. The mechanism of the surface segregation of As is discussed.

Hydrogen plasma etching method for depth analysis by x‐ray photoelectron spectroscopy

An etching device using a hydrogen plasma has been developed for x-ray photoelectron spectroscopy (XPS) depth profile analysis of organic compounds. The effect of the hydrogen plasma discharge was investigated using a photoresist film containing benzene rings, C– O bonds and C– F bonds formed on an Si(100) wafer. The condenser-type discharge tube employed is composed of electrodes, an etch tunnel (shield tube) and a quartz glass tube. Both the electrodes and etch tunnel have many holes. Experimental results show that the etching rate of the photoresist film is 26.7 nm min−1 at an r.f. power of 200 W, a gas flow rate of 6.0 cc min−1 and a hydrogen gas pressure of 26.6 Pa. This rate is higher than that achieved by the use of a conventional high-speed etching ion gun. It is observed that the etched surface is flatter than that obtained by parallel plate electrodes and an Ar ion beam. The amounts of C, O and F after hydrogen plasma etching were not remarkably different from those before etching, and the shape of the C 1s spectrum did not show any change, indicating no change in chemical bonding. The results show that hydrogen plasma etching is very effective for depth profile analysis of organic polymers by XPS. Copyright