Sayumi Hirose

Photon-stimulated desorption of excited-state alkali atoms from alkali halides irradiated with synchrotron radiation

Photon-stimulated desorption of excited-state alkali atoms from sodium and potassium halides has been investigated by using a strong quasi-monochromatic undulator-radiation from an electron storage-ring as a light source. The atomic emission (Na D-line) due to the transition from desorbed excited-state sodium atoms is stronger in NaF than in NaCl, and is too weak to be observed in NaBr and NaI, while the intensity of the atomic emission line from excited-state potassium atoms is larger in the order of KI, KBr and KCl. This result corresponds well with the recent models of the defect formation and the intrinsic luminescence, and is interpreted in terms of the lattice instability due to the electronic excitation in the surface layer.

Performance of a compact beamline with high brightness for x-ray lithography

We have developed a short beamline with high brightness for x-ray lithography. The beamline contains a single, a scanning toroidal mirror and a vacuum-protection system with an acoustic delay line. The practical exposure intensity on a wafer was approximately 50 mW/cm2 at stored electron current of 500 mA. Dose uniformity of ±2.8% was achieved in a 26 mm×26 mm exposure area by optimizing the scan speed. Minimum resolution of 80 nm was obtained with a 15 μm gap. The optimum dose for TDUR-N908 (Tokyo Ohka) was 1300 mA s, which corresponds to exposure time of 2.6 s when the stored electron current is 500 mA. Since the sensitivity of TDUR-N908 is 110 mJ/cm2, the beam intensity in our beamline is estimated to be 43 mW/cm2. By reducing the exposure field, a beam intensity of more than 50 mW/cm2 can be achieved.

Time Response of Photon-Stimulated Desorption of Excited-State Potassium Atoms from KCl and KBr

The time response of excited-state potassium desorption from KCl and KBr was investigated with undulator radiation pulses. It was found that the decay curve of the optical emission from desorbed excited-state potassium atoms consists of two components, and that the fast component is several orders of magnitude faster than the existing results of time response for ground-state alkali atoms. It is suggested that the fast desorption of excited-state alkali atoms may be interpreted in terms of lattice instability due to electronic excitation in the surface layer, while a slow one originates from the thermal instability of surface defects.

Molecular Luminescence from Electron-Bombarded YBa2Cu3O7-x

Luminescence from electron-bombarded YBa2Cu3O7-x was investigated. It has been found that the luminescence is similar in shape and energy position to the vibronic luminescence due to the CN- molecule, indicating that the luminescence is attributed to the CN- adsorbed on the YBa2Cu3O7-x surface but not to the luminescence of intrinsic origin.

Compact synchrotron radiation lithography system for 70 nm device manufacturing

We report on the performance and reliability of our synchrotron radiation (SR) based x-ray lithography (XRL) system installed in Tanashi Works of Sumitomo Heavy Industries, Ltd. Our XRL facilities include a compact racetrack-type SR light source “AURORA-2S” (A2S), the injector microtron, a 3-m-long beamline, and the second version x-ray aligner. In 2000, A2S proved the beam lifetime of 16 h in regular operation at the designed beam current 500 mA. The XRL beamline offers a high-dose exposure rate of over 43 mW/cm2 on a wafer at beam current 500 mA. The x-ray aligner achieved an overlay accuracy better than 16 nm (3σ) using a video-based scattered-light alignment (SLA) system. In the SLA, edge scattering on matrix array patterns provides multispot video images for mask to wafer alignment. A 70 nm line and space (L/S) pattern was replicated with a gap of 15 μm. In resolution enhancement exposure, we replicated a 100 nm L/S and 1 100 nm hole pattern using a 200 nm L/S and a 200 nm hole pattern of x-ray mask,...

Photon-Stimulated Desorption of Excited-State Sodium Atom from NaF and NaCl under Valence-Band and Core-Level Excitations

The excitation energy dependence of excited-state Na desorption from NaF and NaCl has been investigated in the energy range of 20–47 eV with synchrotron radiation. The excited-state Na desorption from NaF was observed with valence-band excitation as well as core-level excitation. The excitation spectra of excited-state Na desorption from NaF and NaCl showed a peak corresponding to the Na L 2,3 core-exciton band. Contributions of core-level and valence-band excitations to the Na desorption at the Na L 2,3 core-exciton band were estimated by using the absorption and excitation spectra. The present results indicate that the Knotek-Feibelman mechanism based on core-level excitation is not valid to explain the excited-state alkali desorption. The desorption with valence-band and core-level excitations showed the similar time response having two components, indicating the two PSD models which correspond to the instability induced by electronic excitations in the surface layer and the thermal instability of surf...

Dynamics of Photon-Stimulated Desorption of Excited-State Alkali Atoms from Alkali Halides

The time response of photon-stimulated desorption (PSD) of excited-state alkali atoms from alkali halides has been investigated with synchrotron radiation pulses. It was found that the substance having a larger Rabin-Klick parameter shows a larger efficiency of the fast desorption. It was also found that there is a delay for the fast PSD, indicating the existence of the precursor state. It is proposed that the fast desorption may be produced by electronic transition in the surface layer, while the slow desorption may be due to the thermal instability of surface defects.

Nanosecond desorption of alkali fluorides excited by synchrotron radiation pulses

Abstract Desorption of the excited-state alkali atoms has been investigated on alkali fluoride crystals in the photon energy region of 20–75 eV, which includes the excitation energy for Li 1s-core excitons, Na 2p-core excitons, and valence excitations. The quantum yield of the excited-state alkali desorption was found to be comparable between valence and core-level excitations. Time response of desorption from LiF and NaF was also observed by using synchrotron radiation pulses. It was found that the time response consists of a nanosecond component and slower one, indicating that the fast desorption is due to the lattice instability induced by electronic transition and the slow one is due to the thermal instability of surface defects.

Laser-induced fluorescence study of fast desorption of ground-state K atoms from potassium halides excited by synchrotron radiation

Abstract The nanosecond desorption of ground-state K atoms from potassium halides was investigated for the first time using a laser-induced fluorescence method with synchrotron radiation and laser pulses. It was found that the desorption consists of a nanosecond component and a slow one of > 180 ns response time. The fast desorption is several orders of magnitude faster than existing results for the time response of ground-state alkali desorption. Therefore, the fast desorption of ground-state alkali atoms cannot be interpreted in terms of the existing mechanisms based on thermal processes and requires a new desorption model. We suggest that the lattice instability due to electronic excitation in the surface layer may play an important role in the fast desorption of ground-state alkali atoms.

Photon-energy dependence of excited-state Na desorption from Na halides by synchrotron radiation

Abstract Photon-energy dependence of excited-state Na desorption from NaF and NaCl has been investigated in the energy range covering the Na-2p level excitation. The excited-state alkali desorption from NaF is observed below the threshold of the core-level excitation. The excitation spectra of excited-state Na desorption show the peak corresponding to the Na L 2,3 core-exciton band, and indicate that contributions of the core-level and of the valence-band excitations to the desorption are almost the same. Therefore, the Knotek-Feibelman mechanism based on the Auger process is not valid for the desorption of excited-state alkali atoms even in the core-level excitation.