Noboru Akao

Structural and Electronic Properties of a Mn Oxide Diffusion Barrier Layer Formed by Chemical Vapor Deposition

A diffusion barrier layer of a few nanometers in thickness is required for a Cu/SiO2 interconnect structure for advanced integrated circuits (ICs). This paper reports a new barrier material and process by chemical vapor deposition (CVD) of a Mn oxide layer using a bis(ethylcyclopentadienyl)manganese precursor. A good adhesion was obtained when the MnOx layer was deposited below 300°C because of the small amount of carbon inclusion within the layer. The metal-oxide-semiconductor samples of Cu/MnOx/SiO2/p-Si showed a very low leakage current of less than 10-7 A/cm2 at 4 MV/cm and a negligible shift of the flat-band voltage after thermal annealing and bias temperature annealing. The obtained results indicated that the CVD-deposited MnOx is an excellent diffusion barrier layer for advanced ICs.

In Situ Ellipsometry Analysis on Formation Process of Al2O3-Ta2O5 Films in Ion Beam Sputter Deposition

Al 2 O 3 -Ta 2 O 5 thin films are known as highly corrosion-resistant materials for coatings. Here the formation process of Al 2 O 3 -Ta 2 O 5 films was analyzed by in situ ellipsometry during deposition by ion beam sputtering. Composite targets composed of Al 2 O 3 and Ta 2 O 5 plates were used for sputter deposition. During deposition, the formation process of thin films was monitored by a single-wavelength rotating analyzer ellipsometer attached to the sputtering system. The composition, the chemical binding states of constituent elements, and the depth profile of the elements of the films were analyzed by inductively coupled plasma-atomic emission spectroscopy, X-ray photoelectron spectroscopy (XPS), and auger-electron spectroscopy (AES), respectively. Ellipso-metric analysis showed that the thickness of the film increased linearly with time after short induction periods. The refractive index of the films increases with increasing tantalum cationic fraction. The extinction coefficient of the films was larger than those of single Al 2 O 3 and Ta 2 O 5 films. The XPS analysis showed that the preferential deposition of the Ta 2 O 5 component occurred in the induction period and the codeposition of Ta 2 O 5 and Al 2 O 3 in the linear growth stage. The AES analysis showed that the content of constituent elements was homogeneous from the top to the bottom of the films in the linear growth stage.

Corrosion and Electrochemical Properties of Sn-8% Zn Alloy-Coated Steel in Methanol Containing H 2 O , NaCl, and HCOOH

Corrosion and electrochemical properties of Sn-8% Zn alloy-coated steel prepared by a melt-dipping method have been investigated in methanol containing H 2 O, NaCl, and HCOOH, which are known as contaminants in methanol fuel. The coated steel showed high corrosion resistance in methanol containing 0.1-30% H 2 O and 0.1-30% H 2 O + 0.1% NaCI. However, the coated steel showed slight corrosion in methanol containing 0.1-30% H 2 O + 0.1% HCOOH. Polarization curves measured in methanol containing 0.1-30% H 2 O + 0.1% NaCl showed that the corrosion potential of the coated steel was close to that of Zn, while the pitting potential of the coated steel was close to that of Sn. Polarization curves of the coated steel measured in methanol containing 0.1-30% H 2 O + 0.1% HCOOH showed that both anodic and cathodic currents monotonously increased from corrosion potentials. This behavior was very similar to that of Zn. According to Auger electron spectroscopy and X-ray photoelectron spectroscopy analyses, the surface film of the coated steel after an immersion corrosion test in methanol containing 0.1% H 2 O + 0.1% NaCI was composed of a large amount of oxide and hydroxide of Zn and a small amount of those of Sn. It was presumed that the corrosion of the coated steel in methanol containing H 2 O, NaCI, and HCOOH proceeded through the selective dissolution of the Zn component in the coating layer.

Electrochemical and Corrosion Properties of Fe2O3­Cr2O3­MoO2 Artificial Passivation Films in HCl Solutions

A series of Fe 2 O 3 -Cr 2 O 3 -MoO 2 artificial passivation films that analogize with passive films on Fe-Cr-Mo alloys were prepared on Pt substrates hy ion beam sputter deposition. Thinning rates of the films were measured in I M HCl by in situ ellipsometry under potentiostatic polarization. The addition of MoO 2 to Fe 2 O 3 -Cr 2 O 3 films suppressed the reductive dissolution of the Fe 2 O 3 component of the films under cathodic polarization, but accelerated the oxidation dissolution of the film due to the transpassive dissolution of MoO 2 . The transpassive dissolution of MoO 2 was suppressed by increasing Cr 2 O 3 content of the film. An Fe 2 O 3 -Cr 2 O 3 -MoO 2 film with the same cationic fractions as those of passive film on an Fe-18Cr-10Mo alloy hardly dissolved in the potential range of -0.3 to 1.0 V. This potential range covers the stable passivity region of Fe-18Cr-10Mo alloy in the same solution. Pitting potentials of Fe-Cr-Mo alloys containing Cr and/or Mo less than the Fe-18Cr-10Mo alloy exist in the reduction dissolution region of the Fe 2 O 3 component of Fe 2 O 3 -Cr 2 O 3 -MoO 2 films. This suggests that the reductive dissolution of the Fe 2 O 3 component in the passive films on the alloys may participate in pitting on the alloys.

Comparison of corrosion resistances between Fe{sub 2}O{sub 3}-TiO{sub 2} artificial passivation film and passivation film on Fe-Ti alloy

Fe{sub 2}O{sub 3}-TiO{sub 2} double-oxide films were formed on Pt substrates by low-pressure metallorganic chemical vapor deposition using iron acetylacetonate and tetraisopropoxytitanium as precursors and O{sub 2} as a reaction gas. Fe-Ti alloys were fabricated by an ion-beam sputter and an arc-melting process. The corrosion resistances of the Fe{sub 2}O{sub 3}-TiO{sub 2} films and the Fe-Ti alloys were examined in acid solutions. The thinning rate of the Fe{sub 2}O{sub 3}-TiO{sub 2} films in 5 M HCl decreased with an increase in the formation temperature. Likewise, the dissolution rate decreased with increasing titanium cationic fraction in the films. The films hardly dissolved at anodic potentials, while significant dissolution occurred at cathodic potentials in 1 M H{sub 2}SO{sub 4} owing to the selective reduction of iron oxide components in the films. Sputter-deposited Fe-Ti alloy films containing more than 39 atom % Ti and arc-melted Fe-Ti alloys containing more than 57 atom % Ti showed high corrosion resistance when passivated anodically in 5 M HCl. The dissolution rates of the Fe{sub 2}O{sub 3}-TiO{sub 2} films in 5 M HCl appear to be significantly smaller than those of the passive films on the Fe-Ti alloy films and the Fe-Ti alloys in the same solution.

Self-healing Corrosion Protection Ability of Composition-Gradient Al2 O 3 ⋅ Nb Nanocomposite Thin Films

Al 2 O 3 .Nb nanocomposite thin films have been known as films having self-healing corrosion protection ability. To attain high self-healing ability and low pinhole defect density, the optimization of composition and structure of the films has been examined. The films were prepared on an Fe thin film substrate on a glass slide using ion beam sputter deposition technique. The self-healing ability of the films was evaluated by the repassivation behavior of potential and current of specimens coupled with an Au auxiliary electrode just after scratching by a knife edge in 0.1 M NaCl. Microscopic observation showed that the pinhole defect density increased with increasing Nb content. Therefore, to use the films as corrosion-protection coatings, decreasing Nb content would be needed for decreasing pinhole defect density but increasing Nb content for increasing self-healing ability. To solve this contradiction, composition-gradient Al 2 O 3 .Nb films were introduced. The composition-gradient film with increasing Nb content from the film surface to the substrate interface showed low pinhole defect density and high self-healing ability. A three-layer film of Al 2 O 3 (outer)/composition-gradient Al 2 O 3 .Nb (middle)/Nb (inner) gave the best result.

Al2O3 ‐ Ta2O5 ‐ ZrO2 Thin Films Having High Corrosion Resistance to Strong Acid and Alkali Solutions

In order to develop an insulator film for an electrolyte-insulator-semiconductor capacitor pH sensor which can be used in a wide pH range, the corrosion resistance of Al 2 O 3 -Ta 2 O 5 -ZrO 2 films formed by metallorganic chemical vapor deposition has been investigated. Dissolution rates of the films deposited on a Pt substrate were measured by ellipsometry in 6 M HCI and 1 M NaOH solutions. The films with the cationic mole fraction of Al, X A l , smaller than 0.4, the cationic mole fraction of Ta, X T a , larger than 0.3, and the cationic mole fraction of Zr, X Z r , larger than 0.3 showed high corrosion resistance against both solutions.

Deposition Condition and Pinhole Defect Density of CrN x ( 1 ≧ x ≧ 0 ) Thin Films Formed by Ion-Beam-Enhanced Deposition

In order to produce a CrN x (1 ≥ x ≥ 0) thin film with a low pinhole defect density using an ion-beam-enhanced deposition method, the effect of deposition conditions, such as the N 2 gas flow rate, the beam current, the accelerator voltage, and the beam voltage of enhancement source, on the pinhole defect density was examined. CrN x thin films were deposited on type 304 stainless steel substrates, and then anodic polarization curves of CrN x -coated steels were measured in a deaerated 0.05 M H 2 SO 4 + 0.005 M KSCN solution. Pinhole defect density was evaluated by the ratio of the critical passivation current density of CrN x -coated steel to that of noncoated steel. It was found that the pinhole defect density was decreased with increasing the beam voltage of the enhancement source. The lowest pinhole defect density. 0.005 area %. was obtained by the following conditions: N 2 flow rate 5 seem. Ar flow rate 3 sccm, beam current 20 mA. beam voltage 200 V, accelerator voltage 600 V, and film thickness 65 nm.

Corrosion and Its Mechanism of Al-10% Si Alloy-Coated Steel in Methanol Containing H 2 O , NaCl, and HCOOH

Corrosion behavior and mechanism of Al-10% Si alloy-coated steel produced by a melt-dipping method have been investigated in methanol containing H 2 O, NaCl, and HCOOH as contaminants. Immersion corrosion tests were performed in deaerated or aerated methanol with and without 0.1-30% H 2 O, 0.1% NaCl, and 0.1% HCOOH, and ex situ surface analysis and observation were made using an electron probe microanalyzer, X-ray photoelectron spectroscopy, optical microscopy, and scanning electron microscopy. The corrosion rate of the coated steel was negligibly small in methanol containing 0.1-30% H 2 O. However, in methanol containing 0.1-30% H 2 O with 0.1% NaCI or 0.1% HCOOH, the corrosion rate increased sharply at 0.1% H 2 O. From the surface analysis and observation after the tests, the corrosion in methanol containing 0.1% H 2 O with 0.1% NaCI proceeds on Al components in dendrites and eutectic structures of the coating layer. Al components corrode forming methoxide while the Si components in eutectic structures remain as metallic Si. In methanol containing 1-30% H 2 O, the surface of the coating layer was covered by oxide films composed of SiO 2 -Al 2 O 3 -Al(OH) 3 , which prevents corrosion.

Pinhole Defect Density of CrN x Thin Films Formed by Ion-Beam-Enhanced Deposition on Stainless Steel Substrates

To improve the corrosion protection performance of CrN x films, the relationship between the pinhole defect density of the films and the surface condition of stainless steel substrates was studied. A commercial, heated type 304 stainless steel (ss) and a high purity heated type 316L ss substrate were used. The surface of substrates was finished with wet SiC paper polishing, diamond paste polishing, or electropolishing. CrN x films 41 nm thick were formed by ion-beam-enhanced deposition. The pinhole defect density was evaluated by the critical passivation current density method. The surface roughness was examined by atomic force microscopy. The pinhole defect density of CrN x films on a commercial 304 ss substrate decreased with decreasing surface roughness of the substrate in cases of diamond paste polishing and wet SiC paper polishing. Pits were caused by electropolishing on the surface of 304 ss substrate owing to the dissolution of manganese oxysulfide inclusions, which resulted in an increase in the pinhole defect density of CrN x film. However, no pits were caused by electropolishing on a high purity 316L ss substrate and an extremely low pinhole defect density of 4.1 X 10 -4 area % was obtained for CrN x film on this substrate.