Hironobu Umemoto

Radical Species Formed by the Catalytic Decomposition of NH3 on Heated W Surfaces

The catalytic decomposition processes of NH3 on heated W surfaces were examined by employing laser spectroscopic techniques. H atoms and NH2 radicals were identified as primary decomposition products on the catalyzer surfaces. The effective enthalpies for the production of these species were both determined to be 150 kJ/mol. NH radicals were also identified, but the production of this species is ascribed to secondary processes. N atoms are minor products in both the primary and secondary processes. The absolute density measurements show that the decomposition efficiency of NH3 is comparable to that of H2. The steady-state densities of NH3 and the stable products, H2 and N2, were also measured by mass spectrometry. When the catalyzer temperature is over 2000 K, the H2 density is comparable to that of residual NH3. H atoms are produced not only by the direct decomposition of NH3 but also by the decomposition of H2.

Ionizing and nonionizing decays of superexcited acetylene molecules in the extreme-ultraviolet region

Absolute measurements of the photoionization and photodissociation cross sections of C2H2 have been made using continuum monochromatized synchrotron radiation in the 53–93 nm region. The absolute photoabsorption cross section and photoionization quantum yield of C2H2 have also been measured. The excitation spectra of C2(d 3Πg→a 3Πu), C2(C 1Πg→A 1Πu), CH(A 2Δ→X 2Π), and H(Lyman‐α) fluorescence have also been obtained. The obtained results have been compared with theoretical calculations. An unresolved problem of the spectral interpretation concentrated on the σ * and π* shape resonances has been clarified by the straightforward demonstration of the photoionization quantum yield. The ionizing and nonionizing decay processes of the superexcited C2H2 molecules have been discussed in view of the strong competition of autoionization and neutral dissociation. An overlapping nature of Rydberg states with the shape resonance is found to be important.

Reactions of N(2 2D) and N(2 2P) with H2 and D2

Rate constants for the reactions N(2 2D)+ H2(D2) and N(2 2P)+ H2(D2) have been measured by employing a pulse radiolysis–resonance absorption technique at temperatures between 213 and 300 K. The rate constants were expressed by the following Arrhenius equations: kN(2D)+H2= 4.6 × 10–11 exp(–8.8 × 102/T), kN(2D)+D2= 3.9 × 10–11 exp(–9.7 × 102/T), kN(2P)+H2= 3.5 × 10–13 exp(–9.6 × 102/T) and kN(2P)+D2= 1.9 × 10–13 exp(–9.2 × 102/T), in units of cm3 s–1. The results for N(2P) suggest that the main exit channels are not chemical reactions to produce NH (ND) radicals. The Arrhenius parameters for N(2D)+ H2(D2) are compared with the results of transition-state theoretical calculations as well as those of quasiclassical trajectory calculations on the basis of extended LEPS potential-energy surfaces.

Substrate Temperature Dependence of the Photoresist Removal Rate Using Atomic Hydrogen Generated by a Hot-Wire Tungsten Catalyst

Instead of photoresist removal methods using chemicals, we investigated an environmentally friendly removal method using atomic hydrogen generated by decomposing hydrogen molecules by contact with a hot-wire tungsten catalyst. We set the distance between the catalyst and the photoresist substrate (DCS) at 20, 60, 100 and 120 mm and evaluated the apparent activation energy (EAP) for the reaction between photoresist and atomic hydrogen at each DCS. The EAP was determined from Arrhenius plots of the photoresist removal rate against the average substrate temperature. When DCS was 20 and 60 mm, EAP decreased with increasing catalyst temperature (WT=2040–2420 °C) and was not constant. However, when DCS was 100 and 120 mm, EAP was nearly constant at 19 ±1 kJ/mol without depending on WT. We might obtain the activation energy of about 19 kJ/mol in the reaction of photoresist with atomic hydrogen.

Quantification of Gas-Phase H-Atom Number Density by Tungsten Phosphate Glass

It is shown that H-atom densities in the gas phase can be evaluated by simply measuring the change in optical transmittance of tungsten phosphate glass plates. Tungsten oxide (WO3) doped in phosphate glass plates can be reduced by exposure to H atoms and the degree of reduction can be evaluated from the change in their optical transmittance. The difference in the logarithms of the transmittances before and after the reduction showed a linear dependence on the H-atom density evaluated by a vacuum-ultraviolet laser absorption technique. No change in the transmittance was observed in the absence of H atoms, showing that reduction of WO3 by H2 molecules can be ignored.

Photoresist Removal Using Atomic Hydrogen Generated by Hot-Wire Catalyzer and Effects on Si-Wafer Surface

We investigated an environmentally friendly method using atomic hydrogen generated by contact catalysis on a tungsten hot-wire catalyzer to remove photoresist instead of using chemicals and its effects on a Si-wafer surface. We eventually obtained a photoresist removal rate of 2.5 µm/min attributable to a reaction of atomic hydrogen with a positive-tone novolak photoresist, without thermal shrinkage of the photoresist film during atomic hydrogen irradiation because the photoresist shrank only under the influence of substrate heating by the catalyzer. The effects of atomic hydrogen irradiation on the substrate surfaces cannot be confirmed.

Production and detection of reducing and oxidizing radicals in the catalytic decomposition of H2/O2 mixtures on heated tungsten surfaces

H atoms, O atoms, and OH radicals were identified in the catalytic decomposition of H2∕O2 mixtures on heated polycrystalline tungsten surfaces. In order to suppress the oxidization of the tungsten catalyzer surfaces, the H2∕O2 pressure ratio was kept more than 83, while the catalyzer temperature was kept below 2000K. The absolute density of H atoms was determined by a vacuum-ultraviolet laser absorption technique, while one-photon and two-photon laser-induced fluorescence techniques were employed to extend the dynamic range. Since the O-atom density was much smaller, only a vacuum-ultraviolet laser-induced fluorescence technique could be used for the detection. The absolute density could be estimated by comparing the induced fluorescence intensity with that for H atoms. OH radicals could be identified by a laser-induced fluorescence technique in the ultraviolet region. The absolute density was determined by comparing the induced fluorescence intensity with that of Rayleigh scattering caused by Ar. The H-a...

Production yields of H(D) atoms in the reactions of N2(AΣu+3) with C2H2, C2H4, and their deuterated variants

The production yields of H(D) atoms in the reactions of N2(AΣu+3) with C2H2, C2H4, and their deuterated variants were determined. N2(AΣu+3) was produced by excitation transfer between Xe(6s[3∕2]1) and ground-state N2 followed by collisional relaxation. Xe(6s[3∕2]1) was produced by two-photon laser excitation of Xe(6p[1∕2]0) followed by concomitant amplified spontaneous emission. H(D) atoms were detected by using vacuum-ultraviolet laser-induced fluorescence (LIF). The H(D)-atom yields were evaluated from the LIF intensities and the overall rate constants for the quenching, which were determined from the temporal profiles of the NO tracer emission. The absolute yields were evaluated by assuming that the yield for NH3(ND3) is 0.9. Although no H∕D isotope effects were observed in the overall rate constants, there were isotope effects in the H(D)-atom yields. The H-atom yields for C2H2 and C2H4 were 0.52 and 0.30, respectively, while the D-atom yields for C2D2 and C2D4 were 0.33 and 0.13, respectively. The pr...

Order of Reaction between Photoresist and Atomic Hydrogen Generated by a Tungsten Hot-Wire Catalyst

This paper clarifies the reaction order of photoresist removal using atomic hydrogen by investigating the relationship between atomic hydrogen density (nH) and photoresist removal rate (vrmv). Atomic hydrogen was generated by decomposing hydrogen molecules with a tungsten hot-wire catalyst. In the reaction between atomic hydrogen and photoresist, we found that vrmv increases in direct proportion to nH and revealed that the reaction exhibited a first-order kinetics with respect to nH.

The photodissociation dynamics of dichloroethenes at 214 and 220 nm

The nascent rotational distributions of HCl (v=0, 1, and 2) generated in the photodissociation of three isomers of dichloroethenes (DCE) at 214 and 220 nm were measured under molecular beam conditions. HCl molecules were probed by a (2+1) resonantly enhanced multiphoton ionization technique combined with time‐of‐flight mass spectrometry. The rotational distributions of vibrationally excited HCl (v=1 and 2) molecules were Boltzmann‐type, while those of HCl (v=0) could not be represented by a Boltzmann distribution and consisted of two components. These results suggest that there are more than two processes in the photodissociation of DCE. Cl(2P3/2) and Cl*(2P1/2) could also be detected when DCE were photodissociated. The branching ratios of Cl*(2P1/2) to Cl(2P3/2) obtained in the present work were much larger than those obtained at 193 nm.